Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

PTFE (Teflon) Tubing - Cost and Quality Concerns of Weaker Substitutes

It is not uncommon in an industry catering to high-performance polymers to frequently come up against the issue of pricing. Polymers such as PTFE, PEEK, PVDF and PPS command prices that are sometimes up to 20X the cost of cheaper plastics such as polypropylene or polyethylene. This results in suppliers sometimes passing off a low-grade polymer as the high-performance variant, with the client being none-the-wiser. There is also the very real and commercial issue that in many cases, it is the purchase department who procure the material, and their KRAs are tied closely with the cost of the product, rather than the authenticity. In addition to this, supplying a test certificate that claims the polymer is genuine is simple enough and so the material is passed without much ado.

It is only when the material fails, or when the client’s engineering teams takes the initiative to have the material tested in a lab that the true nature of the polymer becomes apparent. We have had clients come to us with material procured from local vendors that has failed miserably. The client – now concerned with quality – seeks clarification on the root cause of the failure. When we inform them that the material is not what they think it is, we are usually met with shock.

A similar pattern tends to follow specifically around PTFE tubing. For the most part, PTFE (Teflon) tubes look and feel like any other polymer. The colour of the tube ranges from milky white to translucent to nearly transparent (more on this later). This is not much different that the shades seen in tubes of nylon, polypropylene or polyurethane, to name just a few. In all these cases, the price of PTFE (Teflon) tubing is likely to be anywhere from 5X to 10X more expensive. Hence, many times the client will inform us that we need to check our costing, since their current procurement rates are far below what we have quoted.

In this article, we focus on both the cost benchmarks and quality metrics of PTFE (Teflon) tubes. We hope that with this information, a client would be able to better distinguish genuine PTFE (Teflon) tubes, from the cheaper variants that the market sometimes tries to push.

PTFE (Teflon) Tubes – Pricing Benchmarks

When we set out to install our PTFE paste extruder for making PTFE (Teflon) tubes, our first concern was competing with China. We had already witnessed the market for PTFE stock shapes (rods and sheets) become flooded with cheap – albeit low quality – Chinese material and did not want our product to suffer the same fate. Since nearly all PTFE tube is imported into India (we remain one of the very few with the technology to manufacture PTFE tubes in India), we procured import data from the preceding 2 years to analyse the landed cost of the imported material.

The table below shows the average price per Kg for PTFE (Teflon) Tubes from China, the US and Europe. Although as an engineering company, we rarely ever quote a client by weight, it is useful to compare the same to understand the costing.

 

China

Europe/US

Ex-works Price per Kg (US$)

31.0

45.1

Add: Freight @ US$1 Per Kg

1

1

Add: Customs Duties @ 15%

4.8

6.9

Landed Cost per Kg (US$)

36.8

53.0

Unsurprisingly, Chinese tubes are cheaper by over 30% when compare with Europe/US. This clearly does not consider any of the quality variations between the two sources or indeed between Chinese tubes and our own tubes. But having the China price – and the hard data to support this – has allowed us to refute the claims of clients who say they are buying PTFE (Teflon) tubes are US$10-15 per Kg.

We also found that our own tubes could be made for as low as 10% below the China price. Obviously, this depends highly on the grade od raw materials used. Since some grades – such as Daikin, DuPont and 3M need to be imported, our pricing is also impacted accordingly.

Therefore, our standard response when a client claims to be getting a lower price is to first quote the China price – which everyone agrees is about as low as the price can get – and then request the client for a sample of tube so we can verify whether it is PTFE or some other polymer. Our experience here has been fruitful. Genuine OEMs are not keen to use material that is inferior. They will usually respond positively to such an exercise and appreciate our efforts to supply authentic PTFE material. Traders and price players would rather ignore our data – which is an immediate warning signal for us to stay as far away from them as possible!

PTFE (Teflon) Tube – Variants and Substitutes

We mentioned above that tubes made from nylon, polypropylene and polyurethane are sometimes passed off as PTFE (Teflon) tubes. Notably, there is a vast difference in the basic properties of these materials (which is the reason PTFE is opted for in the first place). Most notably is the temperature capability. Quite simply, PTFE can withstand a temperature of 260°C without suffering any deformation or loss in properties. Since most of the cheaper polymers would melt at anywhere above 150°C, popping a small length of tube into an oven would be the easiest way to check the authenticity.

It should also be noted that PTFE (Teflon) tubes are rarely fully transparent. We will elaborate on this below but as a client, if someone is offering you low-cost PTFE (Teflon) tubes that have a glass-like transparency, you are most likely being sold a variant of polycarbonate or acrylic tubes.

In addition to substitute polymers, there exist variants within PTFE (Teflon) tubes that should also be investigated. The range of PTFE (Teflon) tubes described above gives us some clue as to the composition and quality of the tubes.

  1. Milky white tubes – good quality PTFE (Teflon) tubes should never appear milky white and opaque. This is a property of low-quality tubes – usually from China – and is a result of adding Titanium di Oxide to the PTFE. This both reduces the cost of the material and allows any dark spots or blemishes within the material to be masked. Property-wise, the additive diminishes the tensile strength of the material, leading to a lower burst pressure.

    Many traders will sometimes insist that milky-white tubes are genuine. They are sadly mistaken and have most likely been convinced of the same by a manufacturer wishing to squeeze out a lightly higher margin.

  2. Translucent tubes – most PTFE tubes made with good quality resins will appear translucent. With higher quality resins, there results in a bluish tinge in the tube. Suffice to say that if you observe these properties in your PTFE tubes, the quality is probably good.

  3. Transparent tubes – as mentioned above, this is a rare variant within PTFE (Teflon) Tubes. Transparency can only be attained if the resin is a ‘modified grade’. Companies such as Daikin, DuPont (Chemours) and even GFL have variants of extrusion grade resins which have been modified. This modified resin allows for the final tube to exhibit transparency. However, even with an extremely high grade of resin (we are told that the modified grade of Asahi Glass offers the highest clarity), the transparency would never be glass-like.

We hope that the above information gives a clear picture of the pitfalls when ordering PTFE (Teflon) tubes. It should be emphasized that PTFE (Teflon) tubes offer a set of properties unlike any other polymer. In addition to this, the techniques involved in processing the tube are both expensive and proprietary. All these factors contribute to the end-result that PTFE (Teflon) tubing is a high-end product and that getting it at a price comparable with a regular polymer should be viewed with caution.

Solar Tracker Bearings - Considerations for Design and Manufacture

With renewable energy showing no signs of slowing down, it has become of paramount importance to understand and adapt to the growing needs of this industry. The increase in outlay, combined with the aggressive targets that these projects set make it essential to have quick, ready solutions that are both scalable and replicable across projects.

Solar power plants – as we covered in an earlier article – are still on a path towards maximising efficiency. While it is true that some plants can now boast costs per unit below that of traditional power plants, this does not hold true across the industry. Furthermore, it is well known that without subsidies, many of these plants would not have been able to sustain themselves up to the point where they were no longer losing money operationally.

As one might imagine, solar plants are highly dependent on the extent to which they can maximise the exposure of their panels to the sun. It is not alone enough to have an ample quantum of sunlight. Without the panels at the right angles, the ‘harvest’ from the sun’s energy will remain low and the plant may not achieve the efficiencies needed to justify its operational viability.

We covered Solar Tracker Bearings in an earlier article, where we looked mainly at the composition of the material used. Since then, we have had the chance to explore both the design elements and manufacturing challenges that arise in this product. In addition to this, experience is showing us that the global industry is focussed on a few key sizes and developing these are the key to having a ready solution.

Load and stress considerations

The fundamental purpose of the solar tracker bearing is to bear the load of the square pipe on which the panels are fixed. This pipe is rotated by the solar tracker mechanism itself and the bearing also facilitates this rotation. The pipes are usually found in 90mm, 100mm, 120mm and 150mm sizes and these appear to be a standard across the industry.

Loads experienced by the bearing are typically vertical loads – the weight of the pipe – and radial loads as the bearings rotate while in contact with the clamps around them. It is therefore required to have bearings that can absorb this vertical load while having a low enough coefficient of friction to allow for smooth rotation.

Vertical loads could be in the range of 10-15KN (1-1.5 Tonnes). While this is a relatively low load, it is still vital to check that the bearing can accommodate it, before committing to the client.

We used 3D simulations of the assembly on our design of the bearing to check the stress points and displacements on the bearing. This is a part that would need to work over many years outdoors, so we needed to be sure it would not buckle under the loads. Our stress checks confirmed that given the loads we had defined, the part would experience a deflection of within 60 microns, which is well within the acceptable limits.

Part design considerations

As we covered before – one of the main criteria for the bearing is that it needs to be light-weight. The bearing weight feeds back into the efficiency of the solar plant. Heavier bearings imply a higher load on the solar tracker when it rotates the pipe. This in turns means a higher power consumption and a net energy loss to the system.

Keeping the bearings light-weight mean that the parts benefit from being injection moulded, not machined. Although we do have projects where we have supplied machined bearings, these are usually for trials and fitment. Once the bearings are needed in bulk, injection moulding not only allows for higher volumes, but also allows for designs such as the one we have shown above, ensuring a 60-70% weight (and therefore cost) saving over a machined part.

The mould for a given bearing would have a life of nearly 200-300K sets. Considering a single project requires anywhere between 20K and 30K sets, it is possible to develop a mould and use it over many projects.

In our experience, if the volume requirement exceeds 5K sets, it is more cost effective to develop a mould, rather than opt for the parts to be machined.

Material design considerations

We covered material composition in our earlier article. However, it is important to reiterate that the materials to be used must have the following properties:

  1. Light weight

  2. Low moisture absorption

  3. UV resistant

  4. High strength

  5. Low coefficient of friction

  6. Wear resistant

  7. Injection mouldable

Special formulations exist that offer the above properties. Being in control of the formulation allows the recipes to be tweaked based on a client’s requirements.

There is still much to learn about the solar tracker field, but with each project, our understanding and familiarity improves.

PEEK - Robust Enough for Nuclear Applications

Among the most rigours manmade environments ever created, the inside of a nuclear reactor would probably rate high on the list. The process that allows the reactor to generate the kind of energy we need is not only complex in theory but poses huge practical hurdles when it comes to containment and durability.

Apart from the energy release, nuclear reactions also give off radiation – most notably gamma radiation – which most standard materials are unable to withstand. Gamma radiation causes other materials to get ionised, which in turn makes them hazardous for human exposure. It also accelerates the degradation of materials, causing brittleness and fractures that can increase the likelihood of leaks and failures.

PEEK has long been known as a polymer with unparalleled strength. We have compared earlier the tensile strengths, tensile modulus, heat resistance and chemical resistance of PEEK. In addition to this, the material can reach strengths comparable with metals, when used with the right kinds of fillers. Adding to this list is the capability of PEEK to dwell within high-radiation environments without suffering any significant losses in properties.

Studies have shown that when exposed to the harsh environments seen within the nuclear reactor chamber, PEEK is able to survive over an extended period, where other materials would easily fail. Most notably, the effect of gamma radiation on PEEK is low, meaning that PEEK becomes the material of choice for a host of applications within the nuclear reactor.

  1. PEEK Seals
    The performance of seals to contain liquids that flow within the reactor is of utmost importance. Most materials would suffer from brittleness and deformation when subjected to radiation and heat from this system. PEEK seals have been shown to hold their shape over time and tests show that the hardness and crystallinity of the material is not severely affected by the conditions.

  2. PEEK linings
    Vats and chambers within the nuclear reactor have relied traditionally on using linings made from heavy metals such as lead and titanium. This is both expensive and makes the process of holding and disposing of nuclear waster very cumbersome. PEEK linings have been shown to be very effective in containing radiation. It is possible to make thinner walled tanks and have them lined or coated with a thin layer of PEEK.

  3. PEEK Valves, Plates and Nozzles
    Given the quantum of fluids within the reactor, PEEK is now replacing many of the standard valves, plates and nozzles to ensure that key components within the system do not fail. PEEK is both highly machinable and injection mouldable. Further, PEEK can be 3D printed to create specialised shapes that fit perfectly within an existing system. This versatility lends itself both to precision components needed within the system during construction of the nuclear reactor as well as specialised parts that may be required for maintenance, reinforcement and/or damage control once the reactor is already operational.

As the field expands, new applications of PEEK within the nuclear space are constantly being discovered. Given we know that PEEK is able to survive within the environment without suffering adversely, it remains to be see where else this polymer will find uses.