PTFE Pricing Again – is there another price hike in the offing?

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The adage “Only the paranoid survive” has held very true in the PTFE industry these past 20 odd months. You see, while it is difficult to imagine worst case scenarios and constantly plan along their likelihood, it is usually the only way to make sure that one is not blind-sided by bad news when it does arrive. And since bad news has been arriving thick and fast, being mentally and commercially prepared for the price hikes in PTFE resins are what have allowed many PTFE processors to survive this period of turbulence.

So we choose to re-look at pricing again because despite the fact that PTFE prices have been stable since July 2011, the last thing we can afford to do is assume all will be well from now on and be rudely shocked if and when another price hike does come around.

But rather than subject ourselves to speculation, we have been looking at trends, hearing out rumors and gleaning information from various sources to gauge what might actually be the future of PTFE pricing in the near term. As always, there are various factors at play, but together they do suggest that another price hike is unlikely and that there may even be some easing out of prices in the offing.

1. Rate contracts

Our sources in Europe tell us that there is an increasing push by PTFE resin suppliers to enter into rate contracts for the coming quarter. In an environment where the suppliers have enjoyed increasing prices month-on-month, rate contracts suggest that the scenario may be changing and that an easing out of prices is expected.

Furthermore, many companies are rejecting the rate contracts, since there is a general feeling that prices will reduce in the near term.

2. China and Russia back in the game

In an earlier article we mentioned how both Chinese and Russian resin suppliers were experiencing capacity constraints due to a number of reasons ranging from Fluorspar reallocation to maintenance shutdowns and internal restructuring of capacities.

Now our sources tell us that China and Russia are once again making supplies into Europe and that the pricing is highly competitive in comparison to other suppliers.

Even locally, the marketing push by Chinese companies to try and sell resins into India has accelerated. We receive more mails every day from China and have even been approached by some sourcing agents, asking if we would be interested in entering an agreement to buy resins.

It was always our belief that prices may never come down, since the value growth due to pricing has more than compensated the volume reduction. However, we also know that China has always preferred higher volumes rather than higher margins (a strange strategy, but one that has allowed them to aggressively expand and build scale). So it is unlikely that they will join the rest of the world’s resin suppliers in keeping prices stable and highly probable that they will induce a price war of some sort – forcing prices to reduce.

A quick look at the global price benchmarks we have obtained show that while the rest of the world (India, USA, Europe) had stabilized around a price of US$25-27 per Kg, this rate was sustainable only as long as China and Russia were not supplying globally.

3. Anti-dumping duty no longer effective

When the anti-dumping duty on Chinese and Russian resins was first imposed in India, it effectively increased PTFE resin prices by US$3.3 per Kg. Given the local price of PTFE resins was US$7-8 per Kg at the time, this acted as a serious deterrent for processors buying from China and Russia. At US$20-25 per Kg, the US$3.3 duty ceases to be effective, as the landed cost of the resin would still be below the local rates being availed in India.

It does remain to be seen whether local resin manufacturers are able to bring about a further increase in the duty amount, but even this will take time, so it is likely China and Russia will re-enter India and put pressure on prices.

4. Re-opening of Fluorspar mines

An obvious trend – looking at the past year, may be that China is only able to supply PTFE resins now because there would be an easing out of domestic demand for R22 in refrigeration. We had in an earlier article suggested that in the medium term, as winter approached, there would be an increase in R22 available for PTFE resins and this would ease out prices. However, there is no guarantee that the same pattern would not repeat next year – with supply constraints forcing prices up again.

In the mean time, there are reports that mines in Mexico and South Africa have been re-opened, although it would take at least another 12-18 months for them to be operational. This suggests that prices may again increase during summer 2012 – although if processors stock up on raw materials prior to this, it would not allow the prices to escalate in the same manner as they did in 2011.

Up until last week, the local buzz was that PTFE resin prices were being hiked by up to 30% in January 2012. This has coincided with other news that points to the contrary – rate contracts, China and Russia, capacity expansion. It could be that we have missed out some key information and as a result, our own analysis is wrong. It remains to be seen whether there will be a price hike, but for now we’re staying paranoid – because it seems the safer option currently.

PTFE Membranes – Variants and Typical Uses

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Membranes involving PTFE have gained prominence over the past decade.  When we are approached for this product, however, it usually involves a lot of discussion and deliberation, as OEM clients are aware that they require PTFE membranes, but are not fully sure which type of membrane they require.

In our own experience, there are four variants of PTFE membranes. There may be many more – but these are the variants we most frequently encounter and together they encompass most of the properties that a membrane would need.

Before we delve into the variants, we need to first understand that both pure PTFE and expanded PTFE are used in membranes. We have earlier posted a piece on expanded PTFE, but for the sake of brevity, we will say that it involves a processing technique which effectively pushes air into PTFE, making it softer and lighter than pure PTFE and giving it a spongy texture.

We also need to understand that with membranes, 2 properties define the product itself and need to be looked at during product development and manufacture.

1. Pore size: this is the size (or range of sizes) of the individual pores or holes within the material. As we will see, controlling for pore size is an integral part of the process of making a membrane
2. Porosity: this is the overall extent to which the PTFE is permeated by the pores. Typically, this is easy to control and calculate, as the final weight of the membrane compared with the weight for pure PTFE of the same volume will tell us to what extent the membrane is porous

Variant 1: Pure PTFE Membrane

In truth, this should be called a “filter” rather than a membrane, but it is referred to as both. This is the simplest form of membrane, comprising a PTFE sheet of 0.5mm – 5mm thickness (maybe more) into which holes are drilled/ punched.  The process for making the sheet is the same as for any PTFE sheet: ie: skiving or moulding. The size and quantity of the holes can be altered based on the client requirement.

Typical uses of this membrane would be in separating large particles/ lumps from a liquid suspension. It finds uses in biotech, chemicals and even food processing – where the food grade and inert nature of PTFE makes it a suitable material to come in contact with chemicals/ food products and not react/ affect the materials passing through it.

Both porosity and pore size are easily controlled and measure here – as it is a machined item and the pore size is defined by the holes being drilled/ punched and the porosity is defined by the number of holes.

Variant 2: Porous PTFE membrane

Porous PTFE is made in the same way as pure PTFE ie: the material is molded or skived. The difference is that the resin is compounded with a substance, which would sublimate (move directly from solid to gas) at the temperatures at which PTFE is sintered. Thus, the material – which is molded along with the PTFE, is evacuated during sintering, leaving behind voids in the PTFE. The material would also make fissures within the PTFE as the sublimated gas charts a path through the PTFE during its exit

Porous PTFE is the most inexact of the membranes as it involves a foreign substance whose behavior cannot be predicted entirely. For one, the compounding process is unlikely to be 100% uniform – so you may have some amount of agglomeration of the substance implying that the porosity (and pore size) in one section of the PTFE, may be more than in another. Secondly, while pore size can be somewhat controlled by ensuring that the particles of the foreign substance are all within a fixed range (say 1-2 microns) – the fissures themselves are not possible to control, so 2 fissures may joint at some point to create a larger pore size than required. Overall porosity is controlled by limiting the ratio of PTFE to the substance – but as mentioned before, there will be some variance in porosity within the membrane due to the non-uniformity of compounding.Porous PTFE membranes do not have a huge demand in comparison to the other variants. Its typical uses are in automotives and chemical plants, where the particle sizes are in the range of 30-100 microns.

Variant 3: Plain expanded PTFE membrane

Expanded PTFE is used in cases where a much finer filtration is required. Pore sizes here can be as low as 0.1 micron – since the pores are formed by effectively incorporating air into PTFE and can thus be controlled by limiting the force and volume of air being used. Similarly, limiting the ratio of air to PTFE during the process also easily controls porosity.

The key feature of an expanded PTFE membrane is the property of “breathability”. This means that it is possible to control the pore size to an extent where air is able to pass through the membrane, but liquid vapors are not.

Such membranes find uses in medical equipments and also apparels – where many applications require the material to only allow the passage of air and not other substances.

Variant 4: Laminated expanded PTFE membrane

This is the most popular variant as per our experience. The drawback of plain EPTFE membranes is that due to its spongy texture, it does have a tendency to absorb some amount of moisture over time. Furthermore, EPTFE is very soft and light and thin membranes tend to cling to themselves, making handling difficult.

The lamination of the membranes is usually done with polypropylene or polyethylene. The benefit is that the membrane is easier to handle and also limits the long-term seepage of moisture. The limitation is that the laminate would not be nearly as effective as PTFE in withstanding harsh chemicals (although this is easily remedied by ensuring that the side facing the chemicals is the pure PTFE side). Furthermore, the membrane will not be able to withstand high temperatures.

We see a lot of applications of this membrane in filters for medical devices. There is also some use in the automotive segment – where the membrane acts as a filter to evacuate air from oil. The breathability ensures that only air is sucked through the filter and not oil.

In summary, one must point out that PTFE membranes are expensive due to the lengthy process involved in making them and the cost of the material itself. Hence they are sparingly used only in applications where only PTFE will suffice. Nonetheless, the range of options they offer – inertness, food grade, temperature resistance and breathability – make them unmatched by any other material in the area of membranes.

The Effect of Low Temperatures on PTFE Component Dimensions

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One of the most challenging elements of machining PTFE components for export markets is factoring the effects of temperature on the material when it moves into colder climates.

Since we do all our machining in Bangalore, India, where the room temperature varies between 22-32 Degrees Celsius (on average), we need to be constantly mindful of the dimensional shrinkage that would happen when machined parts are shipped to colder countries.

In many cases, this problem is not a huge one – since the tolerance on the part may be high enough that even after shrinkage it would still fall within the acceptable band for that dimension. A tolerance of +/-0.25mm, for example, could be machined with a plus side bias of 0.15-0.2mm – which is easily maintained on a CNC machine. After shrinkage, even if the dimension reduces by 0.2-0.3mm (not unheard of as we will later demonstrate), the part would still be acceptable when inspected at the client’s works prior to assembly.

The real challenge lies in accommodating much closer tolerances. In our own experience, we encourage customers to design the part keeping in mind a tolerance of +/-0.05mm at most. Often, as the customer may have dealt mainly with metal parts, they expect that PTFE would also conform to the same dimensional yardsticks as metal (which can be machined to tolerances as fine as 1 micron). In reality – PTFE is a much softer material, which undergoes the following changes during machining, affecting it’s ability to be attain very close tolerances:

• Stress build up in material due to tool hardness
• Deformation of material due to heat from machining
• Burrs forming on part which may need to be manually removed, affecting tolerance

The closest tolerance we have managed to maintain on PTFE has been +/-0.012mm – which was done on a component made from PTFE+15% glass fiber, having an outer diameter of 19.04mm.  We did this by experimenting with different combinations of tools, RPM, feed rates and programs, until the dimension was consistently within the tolerance range. However, when the part was shipped to the client in Canada, the trial lots failed due to being undersize. Eventually, through trial and error, it was found that a dimension of 19.08-19.10 was needed in India, in order for the part to be within tolerance in Canada.

While this worked out well eventually, in many cases, customers are not willing to experiment with trial lots – especially if their requirement is urgent. This has led us to seriously consider the practical implications of shrinkage and how we can make an educated guess on dimensions so as to avoid rejection/ rework and/or minimize trials.

The study

Virgin PTFE theoretically experiences a 1.3% variation in dimension between 0 and 100 Degrees Celsius. Plotting this as a linear progression around the dimension of 19.04 would give us a chart like this:

In other words, given the room temperature in Canada being ~10-15 degrees cooler than in India, a shrinkage of 0.03mm could be expected when the parts reached Canada. We expected that for glass filled PTFE, this may not be quite as high – as glass itself may not be as susceptible to dimensional deviation based on temperature.

In order to check this, we machined identical components from different grades of PTFE, having the outer diameter of 19.07mm at room temperature and cooled them down to well below 0 degrees Celsius. We measured this dimension when the pieces were taken out of the sub-zero environment and then allowed them to sit at room temperature, measuring the outer diameters and temperatures at regular intervals to plot a curve of dimension versus temperature.

The grades we used were the following:

• Virgin PTFE
• PTFE+15% Glass
• PTFE+40% Bronze

For each grade – 5 identical parts were machined and their dimensions were measured along the same point. The dimension considered was 19.07 +/- 0.02mm. The parts were first measured at room temperature (about 25 degrees Celsius) and then put into a sub-zero environment for 4-5 hours. Each part was then taken out individually and measured again at fixed intervals of 10 minutes. The aim was two –fold: (1) to observe the extent of shrinkage due to the cold and assess the rate of expansion as the part warmed up at room temperature (2) To gauge whether the part, when left at room temperature overnight, regained it’s original dimension. 

The charts below show the results for each grade:

It was observed that the virgin material experienced the highest shrinkage (0.9% over a temperature range of 40 degrees Celsius). Both Glass and Bronze filled PTFE experienced lower shrinkage (0.5% over a temperature range of 30-32 degrees Celsius). It is also interesting to note that virgin PTFE reached a much lower minimum temperature. While the filled grades were recorded as having temperatures of  -4 to -5.3 degrees at their lowest, the virgin material was recorded with a minimum of -11 degrees - despite being subjected to the same sub-zero environment prior to measurement.

Additionally, all three grades reverted to within 0.01mm of their original dimensions when left overnight to warm under room temperature. This suggests that the dimensional change is linked purely to the ambient temperature and that there is no observable stress build-up in the material due to the cold which causes it's original dimension to alter permanently (at least, not in the range of -15 to +30 degrees Celsius).

All three materials lend themselves to a high R-squared straight-line graph. While we accept that this is a fairly simplistic relation to assume, the R-squared changes only marginally when we try to introduce more complex equations. Furthermore, while the relation between the dimension and the temperature may not be a strictly linear one – for the purpose of practicality, we believe that it serves quite well. In other words, assuming a 0.2% shrinkage for every 10 degrees in temperature (for virgin PTFE) would imply that a 20mm dimension would need to accommodate a plus side tolerance of 0.4mm. This is in line with our own trial and error conclusions thus far, when exporting to colder countries.

Finally – it could be pointed out that the same experiment could be carried out at higher temperatures to gauge whether PTFE continues to expand the same way in the other direction. However, as the bulk of our export destinations are in fact colder countries, we have not looked at this right now. Perhaps the same could be taken up in a separate post.

Mapping the PTFE Price Increase

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While much has been said about the causes and implications of the PTFE price escalation, we felt it necessary to go through our archives and chart out the exact extent to which the prices have changed.

The chart below shows the price per Kg in US$ for three standard grades – Virgin PTFE, Glass Filled PTFE (15%) and Bronze Filled PTFE (40%). In addition, we have included a table showing the total and monthly growth in prices.

Needless to day, the growth has been unprecedented. In Virgin PTFE, a nearly 8% increase in prices every month has put the industry in a state where there is no breathing time between processors getting new pricing information and passing on that information to the customers.

Most processors are well aware of the effect this has had on their businesses. The main issue has been convincing customers regarding the price increase and furthermore making them aware that the trend may be expected to continue. In addition to this, there is the impact on repeat business, as clients withhold contracts which would have otherwise spanned their requirements over a full year - since processors are unable to commit to prices for more than a one month horizon.

PTFE pricing revisited – inevitabilities in long term supply and demand

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When we started this blog, our aim was two-fold:

1. To inform and educate readers about PTFE, it’s applications and derived products
2. To serve as a platform for clients and other end-users to understand PTFE better and make informed decisions regarding their applications

However, it seems to have been the articles on pricing which have brought most of our traffic as regardless of how important the applications of PTFE are, it is – understandably – on pricing that most questions currently centre.

We therefore want to look at pricing again, just to see if any new information gleaned over the past couple of months helps us understand the situation any better than we did earlier.

Since our last blog on the impact of Fluorspar on PTFE prices, we have – like all other processors – been praying for stability. We haven’t been praying for a reduction in prices – that would be optimism to the point of pure irrationality. However, if prices could simply stabilize – even for a few months, it would give us some time to re-group, re-assess and possibly resume normal operations.

However, the pricing fluctuations have been coupled with lesser-known events in the background and together, these effects are causing the stabilization process to take much longer than earlier assumed.

We would like to take a look at some of the news floating in the market at present. We can vouch that since these are from rather reliable sources, we are inclined to believe them and therefore base our outlook on their implications:

1) Fluorspar shortage is no longer an issue

A supplier who regularly sources semi-finished PTFE from a Chinese manufacturer told us this anecdote: The supplier approached the manufacturer with the offer to supply R22. The proposed arrangement was that the PTFE manufacturer could then supply the resin manufacturer with R22 (assumed to be in very short supply) and in return procure resin at a discounted price. The supplier was shocked to hear that the resin manufacturer declined – saying that they had ample R22 to meet their production needs. This does lead us to believe that although the Fluorspar story may have started the PTFE price frenzy, it is now not playing as significant a part.

2) European resin manufacturers have re-allocated resources away from PTFE

This was partly confirmed by a representative from DuPont, who stated that their company was slowly coming out of PTFE resin manufacture, as long-term competition against Chinese suppliers was not feasible for them. The resulting effect, we hear, was that most of the European resin manufacturers have sub-contracted their PTFE business to Chinese resin suppliers. Since the realization for PTFE resins in Europe is much higher – the European price has become the new acting price across the global market.

This impact does throw some light on why the PTFE prices have increased so drastically all over the world. On the one hand, we have a supply constraint, as European manufacturers no longer compete in the market. At the same time, you have a huge supply-demand mismatch as European demand for resins stays the same and this drives up prices.

3) Russian suppliers are in a state of flux

From what we have heard, Russia has two main companies who manufacture PTFE resins, one of which acquired the other. The combined company is said to be undergoing some transition issues and management is also contemplating moving away from PTFE and into ETFE. The result has again been to constrain supply, impacting prices in the process.

4) Pricing set to stabilize within the next 2-3 months

Obviously, many are hoping that things will settle down sooner than this, but considering the extent of changes occurring across the market, one might expect that it would take no less than a few months to stabilise.

Our own local the supplier – who increased prices by another 30% in the month of July 2011, assured us that this would be the last-but-one, if not the last, price revision from their side. The current price we are getting is US$26.5 per Kilo for virgin PTFE resin. From what information we have from our European counterparts, it appears that local rates there are around the same price – so it does look like some sort of balance has been reached.

For those thinking about the long term implications of all this, we can infer the following from what data we have already collected:

1. High prices are here to stay. If there is one thing that all this has shown us, it is that the demand has stayed strong enough despite the price escalation. This has justified the price hike for resin manufacturers from a business standpoint
2. Long term, quality will improve. Although it looks like Chinese companies will be doing most of the manufacturing of PTFE resins, if they are supplying through companies like DuPont and 3M, the quality controls will most probably be more stringent.
3. Volumes in PTFE will shrink. Although we have not seen a significant amount of substitution away from PTFE, there are murmurs of new materials and possible replacement materials in some areas. For the most part, we continue to believe that as a material, the extensive spectrum of properties offered by PTFE makes it a difficult material to shift out from. However, we do expect that at least 15-20% of the volumes in PTFE would slowly shift to other polymers such as PA66 and UHMWPE. Nonetheless, we can take comfort in the fact that a 15-20% fall in volumes when combined with a 100-200% increase in prices still implies an overall growth in the industry in value terms.
4. Repro is here to stay. Not that anyone though that reprocessed PTFE would go away, but we do believe that the acceptance of recycled material in many applications (due to the price implications) would bring about some regularization in the market, with manufactures offering transparency on the extent to which reprocessed PTFE is used and possibly on the properties it could be expected to exhibit. Again - this would be a good thing from a quality standpoint, as buyers of semi-finished PTFE would at least know exactly what they were getting.

To conclude – we have, like most other processors, been trying to make the best out of a situation that has been completely out of our hands. We have faced a rather torrid 15-18 months, so if the end were 2-3 months away, we would look forward to that. In the mean time we would recommend planning one day at a time, because there is no telling what might happen during the next week or month.

Cantilever Load Considerations for PTFE Sliding Bearings

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As a manufacturer of sliding bearings in India, one of the challenges we face is that there does not exist an official book of guidelines specifically for this type of bearing. The closest we have is the IRC:83 – which is the code book for POT-PTFE bearings, and which details the specifications of the materials to be used and also the testing parameters for POT bearings. As such the IRC:83 does provide some guidelines – but does not address the finer design requirements for sliding bearings. Consequently, during design and testing of the bearings, customers rely on the Quality Assurance Plan (QAP) we provide them, with the option to question, refute and even modify the requirements as they see fit.

Although the BS:5400 and AASHTO standards do make specific recommendations for PTFE sliding bearings, customers are not always willing to accept their parameters as they may sometimes vary from those specified in the IRC – in places where the codes overlap. This can result in technical stand-offs, between the customer and manufacturer, as each tries to convince the other regarding a certain process or parameter, without any official rule book, to back up their view point.

Among the more interesting technical debates we have had recently has been regarding the thickness of the top plate (upper sole plate) in bearings with high movement requirements.

Given a specified vertical load, a PTFE sliding bearing will be required to have a PTFE pad with side determined by the compressive strength of PTFE (usually taken at 100-200 Kgs per sq. cm). This side in turn determines the side of the lower sole plate. Give these two dimensions, the movement of the bearing (specified usually by the client/ contractor) will give us the side of the Stainless Steel sliding element, which in turn will give us the side of the upper sole plate.

Our designing of PTFE sliding bearings began with taking standard designs for specified loads and movements (such as C&P) and recommending them to clients. As we became better versed with PTFE sliding bearings, we started designing from scratch – using the parameters of movement, load and rotation to design customized PTFE bearings for specific project requirements. As many of the original standard drawings recommended sole plates of 12-15mm thickness for bearings up to loads of 50-65 Tonnes, we too continued with this recommendation. After all, the constraint of a bearing in taking a vertical load depends purely on the PTFE – as when compared with steel, PTFE has a much lower compressive strength (100-200 Kg per sq. cm versus steel’s 14000-15000).

It came as a surprise to us therefore when a client expressed concern over the top plate thickness – citing that the bending moment caused by the vertical load would be in excess of what the top plate could accommodate, given the overhang of the top plate over the bottom. This led us to revisit a lot of the standard designs – only to find that for similar load-movement parameters, other bearing designs did not recommend a thicker sole plate that our customer was insisting on.

We therefore went back to theory to gauge exactly how much of a bending moment would be caused by our given load and assess whether there was a case for changing our top plate design.

The formula for calculating the bending moment is as follows:

M= (P x L²)/2

Where:

P = Pressure (Kg/cm2)
L = Length of overhang (cm)
M = Maximum Bending Moment (Kg)

Once we know M, we divide by the Maximum Allowable Bending Stress (S) of the material (1650Kg/cm for steel) – to derive the thickness of the steel plate required.

In the example in question, the value of M obtained was 3941 Kgs, which when divided by S gave a thickness of 3.78cm – or 38mm.

This was a shocking revelation, as our recommendation was for 15mm – clearly insufficient for the load in question. Nonetheless, we wanted to dig deeper to find out how most standard bearing designs only called for a 12-15mm thickness – when the theory clearly showed that this was inadequate.

In most of our discussions with consultants and industry experts, the value of 38mm was ratified and we were told that this was in fact the thickness needed. They were unable to explain, however, why the standard designs did not tally with the theoretical calculations. Our question was finally answered when we spoke with a contractor who studied the drawings and design details and confirmed that while a thickness of 38mm was indeed required, the thickness of the insert plate also needed to be taken in to account.

The insert plate is installed at site and is simply a 25-30mm thick steel plate grouted/ cast along with the concrete substructure and/or superstructure. The bearing is welded or bolted to this plate and the load on the bearing is transferred through the plate as well. Thus, a bending moment will act through the layers of both the upper sole plates and the insert plates – meaning that even with a sole plate thickness of 15mm, the total thickness through which the load acts is 40mm – which is more than sufficient in our example.

We went back to our client with this, but were informed that they were not using an insert plate in this particular project and that the sole plate thickness needed to be at least 40mm as per our calculations.

The exercise was an eye-opener, because we had never before been questioned on the bending moment for sliding bearings, nor had we come across any design calculations for this in the various codebooks. However it is a critical point in the design of a PTFE sliding bearing – as there is always an overhang of top plate over the bottom. As a rule, one needs to verify that an insert plate is being used and of what thickness it is. Adding this thickness to the sole plate thickness, the designer needs to verify whether the bending moment is being accommodated. If not, the thickness of the upper sole plate must be re-worked.

The wonder that is Lubring (Turcite®)

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It is only rarely that a marketing push succeeds so thoroughly that the brand name becomes synonymous with the product itself. When Turcite B ® was first introduced, PTFE itself had been around for quite a while. Yet, so effective was the branding of this variant of PTFE that everything from the properties, to the composition to the colour merged under a single umbrella and became known simply as “Turcite ®”. The material itself has become a mainstay in the industrial goods market with machine tool builders, re-conditioners and bearing manufacturers demanding it for their applications.

As the market expanded, new manufacturers developed their own variants under different brand names (ours being Lubring), which all succeeded in their own way. However, to this day, clients will initially demand “Turcite ®” – following which there will be a brief discussion about the fact that our material is equivalent to Turcite ®, but that we brand it under a different name. Usually the client is happy as long as the properties match and that the colour of the material matches the turquoise-green shade developed specifically for Turcite ®.

We want to take a closer look at this material, because despite it’s widespread usage, there are always questions from clients regarding the application and installation of this material. We will look at the following aspects:

1. What is Turcite ® (Lubring)
2. Where can it be used? What are the possibilities and limitations?
3. How must it be installed?

What is Turcite ® (Lubring)?

Quite simply – Turcite ® is PTFE impregnated with fillers and additives that serve to enhance the wear properties of the material. It is used, most often in a sheet form, in thicknesses ranging from 0.5mm (0.02”) to 4mm (0.16”), although in some applications, it is also used as a bush and in more rare applications it is used as a thick plate.

Being based on PTFE, the material cannot be extruded like a normal plastic sheet and instead needs to be “skived” – the process most commonly used to make thin PTFE sheets (See: PTFE – Myths Busted!). Also, the material will not easily adhere to other surfaces – another feature resulting from its PTFE base. Therefore a chemical etching is required on one surface of the material, so the sheet can be bonded to other articles.

In a broad sense, Turcite ® (Lubring) offers the following key advantages:

• Very low friction for reduced power loss
• No stick-slip for positional accuracy / control
• Good specific bearing loads
• Low wear for long life
• Excellent chemical resistance / fluid compatibility
• Unlimited shelf life
• High temperature resistance
• Absorbs vibration during machining

Applications of Turcite ® (Lubring)

Most commonly, Turcite ® (Lubring) has been used in the machine tool industry where it serves to either replace or reinforce standard phosphor-bronze LM guideways. The material was earlier used primarily to recondition old machines in which the guideways had worn out. However, increasingly it is incorporated in new machines as well – owing to the higher life and lower maintenance required in comparison to metal guideways.

As mentioned above, Turcite ® is also used as a bush – which needs to be specially moulded and machined as per the customer’s requirements. These bushes are usually replacements for metal bushes – especially in areas where the lubrication of the metallic bush is as issue. Turcite ® – and in fact all PTFE grades – has self lubricating properties which means it can function deep within a sub-assembly taking enormous wear loads and does not need to be lubricated constantly to avoid damage.

However, the material is not an out-and-out replacement for metal. Being PTFE based, the material has a compressive strength limited to 150 Kgs per square cm (2,200 psi). This means that a single square foot of Turcite ® can accommodate a load of up to 150 Tonnes – which is more than sufficient for most applications. However, it is also a soft material (Shore D Hardness: 50-60) – meaning that point loads and excessive squeezing of the material can cause deformation.

Another limitation is with regards to insulation. Although the material has excellent temperature resistance (up to 260 Degrees Celsius/ 500 Fahrenheit), it does not have any electrical insulation.

In all, the industries for which we have supplied Turcite ® (Lubring) include:

• Automotive
• Machine tool
• Infrastructure
• Nuclear power
• Casting and forging
• Textiles
• Pumps and valves
• Pipe liners

Installation guidelines for Turcite ® (Lubring)

Preparation: The metal surface to be mounted with Lubring can be prepared by the normal machining methods such as, grinding, milling, shaping, and planning. The surface roughness of all forms of preparation should be preferably between Ra = 1.6 µm and Ra = 3µm and not more than Ra = 6µm. Once roughened the surfaces can be cleaned with Trichloroethylene, Perchloroethylene or Acetone.

Bonding: For bonding of Lubring the following resin adhesive can be used: Ciba Geigy's Araldite - Hardener - HV 953U; Araldite AW106. The Araldite should be applied both to metal and Slideway and be spread as uniformly as possible by means of a serrated spatula. To obtain the best dispersion of the adhesive, when spreading on the surface brush in the longitudinal direction; when spreading on the metal, brush in the transverse direction. The total quantity of bonding should be approximately 200gm per sq. mt.

Hardening: After mounting the Slideway a clamping pressure of between 30-35 Kg/cm2 is recommended. It is important to keep the pressure constant during the hardening process. Due to the differences in the thermal expansion coefficient of the materials, maximum curing temperature should not exceed 40°C. The hardening time for various temperatures is: 20°C min 15 hours; 25°C min 12 hours; 40°C min 5 hours.

Finishing: After curing of the adhesive, the PTFE can be machined by conventional means – if required. The choice depends on the machinery available viz.: grinding; grindstone.

Grinding: For grinding of Lubring use the same speed as grinding cast iron, taking care that sufficient cooling is used with an ‘open ’stone. The grindstone should be preferably silicon carbide based with rubber or polyurethane binding; grain size 80-30. Alternatively aluminum oxide with rubber bonding may also be used for soft, fine grinding action, pre-polishing and pre-mating treatment.

Oil Grooves: Lubring pads can be machined with oil grooves using the same methods and cutting data as used for cast iron. The form and depth of the oil grooves are optional. However, the oil grooves should never pierce through the Lubring Slideway. Oil grooves should be away from the edges by 6mm.

Metal Mating Surface: The metallic mating surface running against the PTFE pad should be preferably Stainless Steel (SS) 304 with a grade #8 mirror finish. Against this material, Lubring will have a coefficient of friction of between 0.1-0.12.

Conclusion

The recent surge in PTFE prices has obviously had a substantial impact on the price of Turcite ® (Lubring). However, owing to the ambiguity surrounding the material’s composition (many clients know it simply as “Turcite ®” and are unaware that it is PTFE based), there has been genuine confusion as to why the price has increased recently. While it take times and patience to convince clients that the price of Turcite ® is governed by the price of PTFE, it does serve as yet another reminder of how an effective branding campaign can truly give a product it’s own identity.

Turcite® is the registered trademark of Trelleborg Sealing Solutions

PTFE Wear Plates: Misconceptions and Applications for Heavy Equipments

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Although PTFE is used extensively for its wear resistant properties in a range of different products, its application as a wear resistant plate remains restricted and not widely known in certain areas where it would be ideal.

In most cases, the preferred composition for PTFE wear resistant material is PTFE with bronze (along with some friction reducing additives). As discussed in our earlier article (see: PTFE Compounds and their effects), this composition improves the PV value and wear rate for the material and although the coefficient of friction does increase, over-all it performs superbly as a replacement to metal bearing parts that require frequent lubrication.

Currently, some of the main applications for PTFE as a wear resistant material for which we supply include:

1. Slideway bearings: Commonly referred to by the brand name “Turcite” (Poly Fluoro brand name: Lubring), PTFE slideway bearings are used widely in the machine tool industry, where they serve to either replace or reinforce standard phosphor-bronze LM guideways. The material was earlier used primarily to recondition old machines in which the guideways had worn out. However, increasingly it is incorporated in new machines as well – owing to the higher life and lower maintenance required in comparison to metal guideways
2. Wear strips: PTFE wear strips are used either in running lengths or punched into flat components, which are used in sub-assemblies, like shock absorber struts and pistons. Usually the tolerance on thickness for such wear strips is very low – implying the requirement of a high precision skiving machine. In most case, where we supply these items, a tolerance of +/-0.02mm is maintained on thickness.
3. Piston rings: Here, thin bands of PTFE wear material are machined and fitted on the piston shaft to absorb the wear resulting from a constant back-forth movement. As this process is wasteful (and therefore expensive) due to the machining involved, sometimes customers prefer to buy wear strips and bond them around the shaft. However, bonding PTFE is usually only recommended when there is minimal shear force being applied on the item – so this method is usually unsuccessful.
4. Bushings: PTFE can either be machined into a solid bush, or be used as a layer on a metallic bushing (commonly called DU bushings). Again – the idea here is to create a self-lubricating bush, which can be installed within a sub-assembly and allowed to run without the constant need for lubricants.
5. Wear plates: Used in more heavy duty applications, wear plates are usually employed in thicknesses exceeding 10mm and often require milling on the surface to create oil-grooves and holes for bolting. In most cases, their function is similar to that of a slideway bearing, however we have noticed that many OEMs remain apprehensive to employ PTFE wear plates into their equipments. In an attempt to clarify certain points regarding PTFE wear plates, we are going to be looking at 2 aspects of their usage:

1) The common pitfalls clients experience when using these bearings and misinformation regarding the same

2) Our own experience in the Die Casting Industry, where the success of these plates has led us to aggressively recommend it to OEMs

Issues hindering the adoption of PTFE wear plates

1. Installation: We find that most people adopting PTFE wear plates do so because they have some prior experience with installing slideway bearings. Consequently, they assume the installation methods would also be the same. However, as slideway bearings are much thinner (going up to no more than 5-6mm) and because following installation, they remain subjected to very little shear loads, they can be bonded to the metal bed and this bond is likely to survive over a long period of time.
   
   In the case of wear plates, bonding is not an option as it is likely that there is some shear load which will get applied which, when coupled with the thickness of the plate would weaken the bonding and cause the plate to come loose in the medium to long term.
   
   The correct method of installation is bolting – although valid apprehensions exist with regards to this. For one: the plate needs to be milled with a stepped hole to allow the bolt to rest within the piece. Care needs to be taken to ensure that the bolt head does not rest above the surface of the PTFE plate. As an added measure, PTFE discs can be bonded to the head of the bolt to ensure that in the event that any extra pressure squeezes the PTFE plate, the contact between the bolt and the moving plate is not damaging. Furthermore, tightening the bolt too much can cause the PTFE plate to get crushed (a common reason cited by OEMs for not using a soft material like PTFE). Hence the correct method would be to use a metal bush to ensure the bolt is not tightened beyond a point (see below).
   
   The purpose of the bolt is to ensure the PTFE wear plate does not slide away during operation. As long as this is ensured, the plate will perform properly.
2. Load bearing
   
   A common misconception relating to the load bearing capacity of PTFE leads many machine tool builders to write-off PTFE as a wear pad material. The assumption is that phosphor-bronze, being a metallic material, is the only option strong enough to take the load of heavy moving parts.
   
   In truth – PTFE has a compressive strength of at least 135-140Kg per square cm. This implies that a 100mm x 100mm plate would be able to withstand 13.5-14 Tonnes of vertical load. In most heavy-duty equipments, maximum loads of 5-6 Tonnes are present, meaning that the load bearing is not an issue at all. Furthermore, the coefficient of friction of PTFE against another surface only reduces with the application of pressure – implying that apart from taking the load, the effectiveness of the wear plate in ensuring a smooth functioning of parts is greatly enhances.
3. Machining
   
   Clients who are looking to convert to PTFE wear pads frequently express two concerns pertaining to machining.
   
   The first is on tolerance: as the thickness on phosphor-bronze wear pads can be grond to within a few microns. In the case of PTFE – a maximum tolerance of 50 micros is possible – which we have found is acceptable in most industries.
   
   The other concern is around specific grooves and the exact positioning of holes. As PTFE can be milled (we use a CNC vertical milling centre) – any groove pattern and hole dimensions can be machined on to the surface of the wear plate.
4. Environment
   
   Finally – we have heard concerns over the conditions in which the equipment is used and whether PTFE will be able to withstand the same in the long term.
   
   Firstly – PTFE has the ability to withstand temperatures of up to 250 Degrees Celsius. In most industries we know, the actual heat generation never causes the surrounding temperature to go about 80 Degrees, so clearly there is no issue in using PTFE.
   
   The other concern is on the build up of dirt and whether grit and other hard particles will damage the surface of the PTFE plate. While the recommended option here would be to make a seal around the PTFE to ensure that dirt does not get accumulated between the PTFE and the other moving plate, it should also be noted that in case a particle does get lodged between the plates, PTFE has the unique ability to absorb the same so that it does not hinder the movement of the assembly.

Case Study: PTFE wear plates in the Die-casting industry

A client who was consulting on technical metrics with various companies engaged in aluminum die-casting approached us, a while back. The problem they were facing was that the wear plates that had been installed on as bearings between the platens was wearing out every 2-3 months, with the result that there was significant down time on the machines every time these plates needed to be replaced.

The plates being used were a fiber enforced resin plates and it was easy to see that a few months of usage had significantly worn out the plates leading to deformation and even cracks.

We offered them PTFE wear plates and these were installed on a few machines as a trial. The machines were run normally for a period of 3 months and the PTFE plates were analyzed with the following results:

1. Wear out was minimal: In fact, the PTFE wear plates were much the same dimension as when they were installed. The customer felt that the load of 2.5 Tonnes being applied on the plate would compress the plate and lead to a deformation on thickness – but this was not the case.
2. Lubricity was greatly enhanced overall: The plates had become completely smooth due to the constant sliding across its surface and this smoothness translated into the more efficient operation of the equipment. The customer also reported that while earlier there was some amount of “jerkiness” in the motion of the platens was no longer an issue.
3. Improved cycle time: Apart from the fact that the down-time of the machine was no longer an issue as the plates were not worn out, the overall cycle time of the machine during production was also improved. This was mainly because there was no longer a need to continuously monitor the level of lubrication on the wear plate.

Following the successful trial of the PTFE wear plates, the material was adopted in all machines of the client and we are now working with a number of clients in the die-casting industry to replace their resin plates with PTFE plates.

The various forms of Sliding Bearings

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The application of PTFE in load bearings is not new. Amongst its many other attributes, PTFE also has an excellent compressive strength, allowing it to absorb pressures of up to 200 Kgf/cm2 (2900 psi). This is approximately double the compressive strength of neoprene (the material used in most elastomeric bearings) meaning that PTFE bearing pads can be much smaller and manage the same load.

In addition to the load bearing capacity, PTFE also exhibits a low coefficient of friction (the lowest of any known solid) – which only goes lower with the addition of more pressure and is exceptionally low when PTFE slides against polished stainless steel (the lowest between any two known solids).

This combination of load bearing strength and low-friction makes PTFE the preferred material for sliding bearings – where both load bearing and sliding movement are required to create an effective bearing assembly.

The use of sliding bearings is fairly widespread. Some of the areas we have supplied to are:

1. Oil and gas pipelines
2. Waterways and water pipelines
3. Conveyor systems (both indoors and outdoors)
4. Boiler plants
5. Minor bridges
6. Power plants

The compact size and overall effectiveness of the bearing makes it an ideal choice in lower load applications (under 100 Tonnes). Furthermore, the simplicity of slide bearing design ensures that as long as the basic design specifications are adhered to, there exists a lot of latitude as to the exact dimensions and form of the bearing. This is useful for clients, who would prefer to design their structures independently and have the bearing modified to suit their overall design.

It must be pointed out that in India, there is no official rulebook for the design of sliding bearings. For the most part one refers to standards such as BS:5400 and AASHTO – taking care to cross check against the IRC:83 (the Indian code book for POT-PTFE bearings) to ensure that the material specifications match.

As a manufacturer of these bearings, this does add a lot of flavour to the task of design. Very rarely do two separate projects look for the same bearing design – there are always nuances and specific constraints against which the bearing must be altered to accommodate the client’s requirements. And although the constraints may be somewhat common – the method of accommodating them can vary significantly.

Movement

In many cases, the bearing requires a sliding movement in only one direction. This results in the requirement of guides. Our experience with guides is that as long as there is negligible horizontal load on the bearing (under 2 tonnes), any of the two following guiding elements can be used.

- Bracketed guides – these are normally two guide plates welded/ bolted to the side of the top or bottom plate

- Dowel guides – guide pins can be used either at the center of the plate or on the sides

In case the load is higher than 5 Tonnes, a centre dowel guide is always preferable. Some designs may also specify a guide that is monolithic with the top plate. While this is the definitely better from a load bearing stand point – it is often expensive, as the plate needs to be either cast or machined out of a much thicker plate.

In any case, as the horizontal load increases beyond 10-15 Tonnes, it becomes viable – both technically and commercially – to look at POT-PTFE bearings.

Rotation (lateral)

Rotation along the horizontal axis (perpendicular to the direction of the vertical load) is not a common requirement.

It is most easily achieved by employing a circular dowel pin at the centre of the bearing around which the top plate can rotate.

In case the load is high, you could also look at a hybrid POT bearing – where a PTFE disc is used in place of the elastomer and a polished stainless steel sheet is affixed on the piston to allow for rotational sliding movement.

Rotation (vertical)

Vertical rotation (around the direction of the vertical load) is most easily achieved by employing an elastomeric pad along with PTFE. In most design specifications, there is a stainless steel sheet required in between the PTFE and the elastomer.

In more heavy-duty applications, a fully reinforced elastomeric bearing may be employed. The bearing is affixed (either by bonding or during vulcanizing) to the base plate housing the PTFE.

However – as discussed earlier – the lower compressive strength of elastomeric bearing material (such as neoprene) would require the size of the PTFE bearing to be defined by the size of the elastomeric bearing required. In some cases, where space is a constraint, designers opt for spherical bearings to accommodate the vertical rotation.

The benefit of a spherical bearing is that it can be compact and that the radius can be changed to match the extent of the rotation required. In contrast, to accommodate higher rotation in an elastomeric bearing, the thickness of the bearing would need to be increased – making it more expensive and bulky.

On the other hand, the smoothness of the rotation provided by an elastomeric bearing (which is effectively using it’s elasticity to accommodate the rotation) is compromised in a spherical bearing. Although in most spherical bearings a PTFE-SS match is created to allow for smooth rotation – it will perform slightly less effectively than an elastomeric bearing. Ultimately, this is a trade-off that the designer will need to assess depending on the requirement of the project.

Arc bearing

Arc bearings are normally used in pipelines, as the bearing needs to take the curved shape of the pipe. The most common arc type bearings we have come across employ two sets of PTFE-Neoprene pads, which have been heated and bent to form the required radius needed to match the pipe. One set of PTFE-Neoprene is bonded with the pipe, such that the PTFE layer faces downwards. The second set is bonded to the concrete base, such that the PTFE surface faces upwards. When the pipe is lowered on to the concrete base, the PTFE layers mate, such that there is sliding along the length of the pipe. Also, due to the neoprene layers – there is rotation allowable.

This bearing can also be made using stainless steel to replace one of the PTFE layers. However, bending the stainless steel to match the radius of the pipe is more expensive than bending PTFE (which can be done using heat and a cheap metal die). Furthermore, it is likely that there would be slight variations on-site in the radii of the pipe and the concrete support. In this case, the stainless steel may develop kinks/ irregularities on the surface once the load is applied whereas PTFE, being much more pliable, will accommodate the same quite easily.

Two-way bearing

Our experience with this type of bearing has been mainly in the erection of conveyor systems. Often, along with the vertical load exerted on the bearing, there is some amount of horizontal load (along with restricted horizontal sliding movement in one direction) and some upward load. Usually, these loads are very small – within 2 Tonnes – so a complex or heavy-duty solution becomes wasteful

The concept of a low-cost, but effective bearing has let us to consider 2 alternate designs as shown below.

The simple design would employ side guides to form a bracket around the lower plate – allowing sliding movement in one direction and ensuring any uplift is contained. However, as the guides are welded, their strength is limited to within 2 Tonnes at most.

In case the uplift load is higher than 2-3 Tonnes, one would need to look at the second design – where a bolting arrangement allows the total load to go much higher. The second arrangement is altogether more elegant and compact – but comes at a much higher cost, owing to the extensive fabrication required and the extra thickness on the top plate needed to accommodate the guide-cum-anchor pin.

Rocker bearing

Although rocker bearings are usually stand-alone metal bearings, we have seen them used along with a PTFE sliding arrangement to give a rocking-cum-sliding arrangement.

The base plate housing the PTFE is usually the top plate of the rocker bearing.

Conclusion

We have described here only some of the bearing types and features that can be designed, based on the requirement of a specific project. Considering that projects take many forms and the constraints they may present could be very unpredictable, the above list could only be a fraction of the complete set of sliding bearings that can be envisaged. However, our experience in this field suggests that these are the primary features which are required of a given bearing and that ultimately, most bearings would be a combination of the above design forms.

PTFE and the “Repro” Conundrum

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In recent times, the landscape of the PTFE industry has been significantly altered by the ascent of PTFE recycling. The combining of recycled PTFE (known technically as “Reprocessed” or “Repro” PTFE) with pure PTFE has become so widespread and unchecked that more often than not the material that customers are buying does not even remotely adhere to the quality standards required – due the abnormally high levels of repro being mixed in an attempt to keep costs low for the processor.

More alarming – processors and dealers alike are choosing not to offer the transparency to most clients on the proportion of recycled material being used (or that it is being used at all). This misleads the client into assuming he is receiving a material which is superior in performance – but which will most likely fail in any long run application. Additionally – processors who supply pure PTFE are forced to compete on price with a material that is not truly a substitute.

We would like to look at the issue of Reprocessed PTFE – both from the technical standpoint as well as a commercial standpoint. We believe the issue is critical to the understanding of the PTFE industry and as a technical tool for those looking to incorporate PTFE in their applications.

Pricing irregularity in PTFE

By 2010, the price for PTFE resins globally had reached some level of stability. Those in the industry will know that this was short-lived as one year on, we continue to work in oblivion to what price fluctuations may occur in the next week or month. However, it would be fair to say that even historically – the prices availed during the first half of 2010 may be the lowest that PTFE prices have ever sunk. Nonetheless, the competitiveness of pure PTFE processors was still not great.

In the few years leading up to 2010 (just before the current price escalation began) we began observing an obvious disconnect in India between the price of PTFE resins and the price of semi-finished articles (rods and sheets) being imported from China by traders.

The price for virgin PTFE resin was about 8-9 US$ per Kg (3.6-4.1 US$ per pound), whereas the price for Chinese semi finished articles was 10-11 US$ per Kg (4.5-5 US$ per pound).

Given that the processing cost for PTFE is about 4-5 US$ per Kg (1.8-2.3 US$ per pound) – it seemed there was no way that manufacturers in India could compete with traders on price. Obviously, clients were equally surprised, as they should have been; you would expect manufacturers to be far more competitive than dealers, but this was not the case.

It seemed impossible that the price could be so low, considering it would need to include the price of resin in China plus the cost of shipping, plus the customs duties on Indian imports, plus the trader’s overheads and finally the trader’s margin.

To study this pricing abnormality, we placed a large enquiry to Chinese resin suppliers to gauge the local price in China and were offered a rate of 5.5 US$ per Kg (ex-works). If we used this as our base price (as we assume a large Chinese processor would avail such a price) and assumed the same costs of processing (not unlikely as India and China have similar wage structures and power costs), the cost structure for semi-finished PTFE could be built up as follows:

It turned out that the key difference between the prices was that Chinese suppliers are selling reprocessed PTFE – which allows the prices to be maintained at a much lower rate than if they used pure PTFE.

As you can see – the difference between the Implied Price and the Actual Price could be as high as 30%: the effect of using recycled material for processing semi-finished articles.

Of course, the figures above may not be fully accurate (customs could be as low as 11% if the trader is allowed to pass on excise duties), but it still points to a 12-15% gap, which can only be explained by the use of repro material.

Our trader contacts corroborated this – giving us figures ranging from 15% to 30% for the percentage of reprocessed PTFE used in making semi-finished articles. The estimations we came across for the price of repro were in the range of ~2.5-3 US$ per Kg – which could lower the raw material price by up to 15% - tying in with the overall price gap we estimated.

What is repro?

There are possibly a number of ways in which PTFE can be recycled for being used back into moulding. The most common way is to grind PTFE scrap (otherwise useless and therefore very cheap) into a fine powder and blend this powder with pure PTFE to be used either in compression moulding or ram extrusion.

Before grinding, the scrap is usually first heated to above its melting point to remove any organic contaminants. Once ground, it is treated with acid to dissolve inorganics after which it is washed and re-heated – to vapourise any volatiles.

However, since ground scrap is effectively sintered PTFE – during processing it will not form bonds with surrounding PTFE material the same way that un-sintered PTFE does (much the same way you cannot weld two PTFE articles to one another using heat alone). Therefore, it is essential to maintain a proportion of reprocessed PTFE that allows enough bonding of pure PTFE molecules during sintering to ensure the overall stability of the sintered product.

The right proportion to be used is as such not documented (there exists very little technical data on reprocessed PTFE as it is relatively “unorganized” in its application) – but one might like to think of one grain of repro PTFE needing at least 4 grains of pure PTFE surrounding it to ensure the bond strength is sufficient. So a ratio of 1:4 or 20% as an upper limit may not be off by much.

However, as the price of PTFE continues to increase, this rule of thumb has been stretched considerably. Recent reports suggest up to 45-50% of reprocessed PTFE being used in an attempt to keep the semi-finished price from escalating. The move has not been altogether successful as (1) the price of PTFE scrap has increased as well – making repro more expensive (though still cheaper than pure PTFE), and (2) the rejection rate has increased – which has increased costs and impacted price.

Aside from the commercial impact however, most end users remain unaware of the technical issues.

Issues with using reprocessed PTFE

Like any other material – recycling erodes the properties that the material originally had. In the case of PTFE, many of the core properties are so good, that reducing them by a small amount to keep costs low can be a feasible trade-off. So from the point of view of application, a 5-10% repro ratio would still allow the material to pass off as pure PTFE for most applications (although it would still be ethical to inform the client of the composition). As the ratio is increased, the degradation in core properties would continue to the point where the material is totally unsuitable for any regular application.

The table below illustrates how key properties we have observed change as the percentage of reprocessed PTFE increases.

One of the main issues with reprocessed PTFE is that it introduces porosity into the material, which then causes issues with water absorption and dielectric strength. Furthermore, weaker bonds between the molecules adversely impacts tensile strength and invariably causes crack lines within the material, which may not be visible, but will become apparent during machining and/or result in a failure of the component during long term usage. Although the chemical inertness remains good (as it is still 100% PTFE), the higher water absorption makes the material suspect for applications where the weather-ability and hydrophobic properties make pure PTFE such a sought after material.

Finally – there is the visual impact. In a given article, the percentage of black inclusions (normally due to foreign matter being mixed with the repro PTFE during the grinding process) could be as high as 40%. Usually, these are within the material – so it only becomes apparent after machining – which is doubly wasteful as the time spent machining is not recovered. In addition to this, too much repro will adversely impact the finish of the product to the point where the finish is rough to the touch and a white powdery discharge is seen on the surface of the machined part. Needless to say – these are all unacceptable for most clients.

To tie in the commercial and technical points we can say this: before it became apparent that the price gap was driven by the use of reprocessed PTFE, this gap was easily exploited by clients, who would compare our prices with the prices of traders and use it as a bargaining tool. However, as the use of repro has escalated, many clients have come back citing quality issues and inconsistency of properties (as would be expected). Even clients who had tested the repro material knowingly and found it to be in line with their requirements have found that in the long term, many of the initial properties have eroded. As a result, manufacturers are slowing gaining back favour – provided they are supplying pure PTFE and can support it with the appropriate test methods.

To conclude – reprocessed PTFE will always have inferior properties to PTFE and cannot be as consistent over time. The exact extent of this deviation in specifications is not easy to document. Therefore, it is always better to go in knowing what to expect and in case the core properties can be compromised on, it is better to experiment with reprocessed PTFE in your particular application to gauge the level with which you are comfortable.

We continue to get requests from clients who state in their enquiry that they are comfortable with recycled PTFE. This is because they are confident that their application does not require such high properties and that the trade off with better costing is worth their while. However, there comes a point where the material simply cannot be called PTFE anymore – and we have yet to come across a client that sees the feasibility in this!