Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

Case Study - Cross Directional Expanded PTFE Gasket Tape

The challenges thrown by PTFE as a material are myriad. As we have already illustrated in various articles, the processing techniques needed for PTFE differ from those of other polymers so dramatically, that nearly every end-product requires a special-purpose machine that can be used for no other plastic. The main reason for this is that PTFE is not melt-processable. As a result, heating the polymer into a liquid state to then either mould or extrude it is not possible. Hence, we end up with processes such as paste extrusion (PTFE Tubes), skiving (PTFE tapes), and isostatic moulding (moulded PTFE parts).

Even within the space of PTFE, expanded PTFE (ePTFE) remains an anomaly in terms of processing complexity. We have covered in earlier articles that ePTFE depends on a minimum of nine different parameters, including the grade of material, the nature of the lubricant, the extrusion process, and the stretching process – to name only a few. Each of these parameters needs to be kept in range, with any deviations only revealed once the final product is out – at which point it is too late to make any changes.

While we have mastered the process of making mono-axial ePTFE gasket tapes – the standard ePTFE tape used in industrial applications – cross-directional tapes are another issue altogether. In this article, we look at the development of the same and what advantages it affords.

Difference between mono-axial and cross-directional gasket tape

The main issue with mono-axial ePTFE gasket tapes is that due to the orientation of the fibrils being in only one direction, the material is susceptible to tearing/splitting when tension is applied in the transverse direction. On the other hand, the material exhibits immense compressibility, allowing it to form a perfect seal with minimal pressure and retain its form over a range of temperatures. As such, the tape works brilliantly in applications such as flange-to-flange connections, where the assembly is not intended to be dismantled frequently, once installed.

However, in applications where the frequent opening of the system occurs, the mono-axial tapes fail over the medium-long term. For example, using mono-axial tape along the rim of a vessel that is opened multiple times a day would not work, since the constant application and relaxation of pressure would cause the fibrils to come loose and the tape to slowly disintegrate. Furthermore, with very poor recovery – mono-axial tape is soft but lacks elasticity – the seal becomes less effective each time the lid is closed and opened again.

To remedy this, we set out to create a cross-directional tape that would allow for strength in the transverse direction and be ideal in applications where recovery was needed. Within the industry, there are already ePTFE sheets that are made using multi-directional ePTFE layers. However, these sheets are prohibitively expensive, come in standard sizes of only 1.5mt x 1.5mt, and do not incorporate any fillers. The aim was to:

  1. Develop a low-cost tape to match the properties of multi-directional ePTFE sheets

  2. Create a highly customisable process in-house so that key properties such as compressibility, density, and thickness can be matched to suit the exact OEM requirement

  3. Incorporate fillers such as silica and barium sulphate to reduce creep and add stability to the material
     

 

Mono-axial ePTFE Tape

Cross-directional ePTFE Tape

Units

Standard

Specific Gravity

0.35-0.85

1.5-1.9

-

AMS 3255A

Tensile Strength

10-15

20-30

Mpa

AMS 3255A

Compressibility

60%

10-15

%

ASTM F 36

Recovery

-

40

%

ASTM F 36

The result

As the table above shows, the results were rather impressive. While the exact process remains proprietary, the use of special mixing techniques along with calendaring, drying, layering, and curing resulted in an enhancement of properties. The tensile strength was high in both lateral and longitudinal directions. Compressibility was understandably reduced, but the improvement in recovery meant that the material could be used in areas where pressures were erratic. Most importantly, with strength in both directions, there is no chance of any disintegration in the longer term.

By modifying the process slightly, we can influence the compressibility, thickness, and density. Further, the addition of fillers greatly arrests the cold flow of the material, meaning that long term application is more stable, as there is no risk of excess deformation slowly affecting the sealing effectiveness of a gasket.


Read More

1. Case Study - Development of a 4-axis PEEK Valve

2. Over-moulding PTFE on to Stainless Steel

Can Indian Manufacturing Survive COVID?

To say that the last 12 months have been very tricky to navigate would be a gross understatement. The combined impacts of COVID, the resulting lockdown, the migrant worker crisis, and the highly mercurial post-lockdown business climate have made each passing month a challenge to work through. And yet, most clients and vendors we have spoken with will agree that post-June 2020, things did somehow settle down on the business front. Demand picked up, companies slowly returned to a new kind of normalcy, and work started to get done.

Throughout history, India’s numbers have always been staggering. We swelled with pride as our population numbers were in no way reflected in the caseloads we saw post-September 2020. We beat our chests at the news that we were now supplying the rest of the world with vaccines.

The idea that within 6 short weeks, India went from a COVID success story to staring down the abyss of a potential apocalypse is stunning. The blame game aside – we all know the levers that helped nudge the numbers up so that there was enough critical mass to begin the avalanche of cases – the fact remains that as the developed world starts leaning towards a post-COVID environment, India is still mired in the depths of a crisis that does not seem to be letting up in any way. 

Most manufacturers have been terrified of a second lockdown. It was tough enough to make it through the first one, but companies somehow survived. A second shutdown would be devastating, possibly beyond recovery, mainly because this time, things are very different.

Last year, the world was united in its fight against COVID. Companies in every country came to a standstill and those of us lucky enough to have cooperative clients learnt that orders were not being cancelled – only pushed out by a month or so. Even those in industries where existing orders would not roll over and accumulate over the following months were relieved to know that India’s total lockdown was seen somewhat favourably by the rest of the world and demand resumed once doors reopened. At the same time, China was reeling under a lot of ill-sentiment thanks to COVID, so the tendency for export clients to shun Indian suppliers in favour of their Chinese counterparts was limited. Indeed, India’s problems with China in mid-2020 brought a lot of local demand back to local suppliers as the rush of patriotism temporarily eclipsed the lure of better margins.

It is not an exaggeration to say that none of these factors are very much at play anymore. For one, India-China relations, while still somewhat icy, are not strained enough to push Indian buyers away from China’s deliciously low prices. Even global sentiment towards China is somewhat muddled between still blaming them for COVID, holding them accountable for human rights abuses, and an inability to fully detach themselves economically. China continues to be the world’s factory and its supposedly excellent handling of the COVID crisis locally has allowed it to project a ‘back to business’ image while India still struggles with record-breaking caseloads each day.

Finally, the fact remains that the US and Europe – with a huge ramp-up in vaccinations – have started returning to normal and expect their businesses to function as such. It would not be feasible for a company to rest easy knowing that part of its supply chain depended on an Indian manufacturer. This year was supposed to be the time for everyone to get back on their feet and India’s inability to keep pace with the rest of the world has severely hurt both our image as well as the stability of our contracts with clients in other countries. Even the most generous of customers cannot be expected to indulge an Indian supplier marred by COVID cases and lockdowns when the client’s own business is being jeopardised by the resulting delivery delays.

It is possibly due to this reason that lockdowns, when imposed, have given leeway to manufacturers to stay open. However, manufacturers themselves need to juggle workload with the very real possibility that their employees remain at risk if the proper precautions are not taken. It is a very fine balance and Indian manufacturers need to tread it carefully for the next 3-4 months at least until the crisis is brought under some kind of control.

In this regard, there are certain things manufacturers can do to manage the situation:

  1. Plan ahead: considering we are consistently exceeding our expectations of worst-case scenarios, this is not always easy. However, where possible we need to stock inventories of raw materials, so we are not exposed to supply-side shocks ourselves. With a disruption in everything from logistics to production schedules to worker movement, the risks remain high that just-in-time manufacturing will not work in the present climate

  2. Prioritise: with resources scarce – especially around the workforce – we need to focus on clients and orders where timelines cannot be compromised. Indian clients may be more willing to understand delays, as many of them would similarly be dealing with demand and supply shocks. Export clients whose lines are depending on materials being delivered on time would need to take priority to ensure business relationships are not eroded.

  3. Communicate: a client may have ordered 15 different parts but might suffer a potential line stoppage only for 3-4 parts. Open communication with the client would help their work to continue smoothly while allowing the manufacturer the leeway to push some parts forward. Our experience with Indian vendors has been that they tend to stay quiet when things don’t go as planned. Most clients can adjust their schedules, provided they are given some advance warning. Avoiding last-minute surprises would help ensure the client retains confidence in the supplier.

  4. Train: Especially for a small enterprise, a key component of survival is building skills among its employees. Staggered working and the inevitable quarantine period of an employee with COVID means that work can come to a standstill if a key staff member is not present. Encouraging staff to gain a basic understanding of cross functions would be critical in making sure that work gets done even without full strength.

  5. Motivate: This is a time when many tend to feel hopeless. The toll that COVID has placed on us all is starting to wear individuals down and the fact that there is no end in sight can be demoralising. Keeping staff motivated is critical in a time like this. Employees need to know that they are working towards keeping the business alive and that their efforts will ensure that there is still a business around once the pandemic eases off!

As we said in the beginning – this has been a very tricky time to steer a business forward. The necessity for a manufacturing plant to operate in person has only made that tougher since not everyone has the privilege to work from home. At the same time, without manufacturing, the economy, in general, starts to stumble and could collapse in a manner that causes long-lasting damage. Only by carefully navigating through the current climate can businesses plot a course for sustainability beyond the pandemic.


Read More

1. The Challenge of Injection Moulded High-Performance Plastics

2. Polymer Prices Go to the Moon

3. PEEK - The Impact of Carbon Fibre Fillers on HPV Bearing Grades

The Challenge of Injection Moulded High-Performance Plastics

The polymer space is a wide spectrum of different products, each with properties, characteristics, and processing nuances that could take a lifetime to fully learn. On the one hand, melt-processible plastics – such as Polypropylene, Polyethylene, ABS, and Nylons – form the mainstay in terms of volumes, since these are commonly used in consumer goods and are both cheap and relatively easy to handle. In contrast, non-melt processable polymers – such as PTFE (Teflon) and UHMWPE – are relatively niche in their application and can only be machined into a final component using a ‘stock shape’, such as a rod, sheet, or tube.

Somewhere in between these two extremes are a collection of polymer grades that, while being melt-processable, are still mainly machined, due to certain challenges that not everyone can surmount in the moulding process.

Our journey through the polymer space has seen us delve deep into two such plastics: PEEK and PPS. While both PEEK and PPS are certainly injection mouldable (that is to say, they have a decent enough ‘melt flow’ that would allow them to be injected into a mould to give a final shape), there remain some complications with regards to the processing.

  1. Temperature – both PEEK and PPS melt at temperatures well above 300°C. This implies that any heating equipment designed for low-temperature plastics, such as Polypropylene (which melts at ~160°C) may struggle to maintain such high temperatures

  2. Equipment – while higher temperatures can be attained using additional or higher kilowatt heaters, the equipment itself often needs to be modified to handle PEEK. Our own experience with compression moulding told us that PEEK reacts to metals in a way that makes handling it in its liquid state very difficult. The screw and barrel of a normal injection moulding press would be unlikely to survive more than a few months with PEEK flowing inside it

Similarly, the mould itself would need to be specially constructed to maintain consistency over the long term

  1. Cost – one of the nice things about low-cost polymers is that trials are not expensive. The mould is usually the bulk of the development cost, after which throwing raw materials into the mix until all the kinks are ironed out does not burn any holes in one’s pocket. Polypropylene, for example, is presently selling for ~US$2 per Kg (after a recent spike of over 75%!). In contrast, PEEK sells for ~US$100 per Kg, while PPS is a slightly more sedate ~US$25-30 per Kg. In other words, we’re looking at a cost multiplier of 12-50X, meaning each trial becomes expensive to conduct and the financial risk of not getting a part right can be significant.

  2. Properties – compounding the cost issue is the fact that PEEK and PPS are temperamental materials. PPS, for one, tends to crack easily unless we use exactly the right combinations of temperature, pressure, and other fillers, such as glass. PEEK, which is a little better behaved, can still exhibit excessive shrinkage in some areas (leading to tool modifications and more trials), and also prone to internal stresses unless annealed properly.

With so many hurdles to getting it right, there is little doubt that even medium to high volume project requirements prefer to machine these polymers from stock shapes rather than mould them. The risks involved in moulding mean that the upfront development charges do not only include the cost of making the mould but also need to factor in high trial costs, which push the economics back in favour of machining.

However, there will always be parts that cannot be machined; where the dimensional complexities entail that moulding is the only way forward. One of the reasons that both PEEK and PPS are so sought after in fields such aerospace, automotive, and chemicals is that there exist few other materials that have both the physical strength, are lightweight, and have the chemical resistance needed to hold their own in any environment. Therefore, when PEEK and PPS are needed, there are no alternatives for an OEM other than to invest in the development of these components. In such a situation, processors that understand the material, invest in the right equipment and are willing to take a chance to develop and learn the behaviour of these polymers stand the best chance to thrive in an industry where injection moulding has devolved into a very commoditised space.

At Poly Fluoro, we have always stayed one step ahead in terms of our understanding and our willingness to explore new polymers. We did this when we put up India’s first paste-extrusion plant for PTFE tubes. We did it again with expanded PTFE, where we remain India’s only manufacturers and where we are even presently developing new variants of ePTFE tapes, tubes, and membranes for specialised applications. The same boldness allows us to expand into PEEK and PPS injection moulding, while our success with our other ventures fills us with the confidence that here too, we will succeed.


Read More

1. Case Study - Development of a 4-axis PEEK Valve

2. Polyphenylene Sulfide (PPS) - A robust polymer with multiple applications

3. The Effectiveness of PEEK Compressor Valve Plates