At Poly Fluoro Ltd, we have always tried to abide by the rule: Build capability, not just capacity.

In a world where manufacturers are constantly looking to scale up operations as quickly as possible, this may sound rather counterintuitive. Scale allows for many benefits, such as lower input costs and allowing fixed expenses to be spread more thinly.

However, when it comes to niche polymers, scale is never guaranteed. In most cases, the demand for complex machined polymer components only runs into the thousands. With limited scale, the challenge becomes one of achieving higher realisations for the same time spent. In this endeavour, adding capabilities helps a company move up the value chain and scale up on value, even while volumes may remain small.

A while back, we engaged in the development of a very complex valve made from PEEK. By the analysis done by our engineering, we knew the part required a 5-axis milling machine and even though we really wanted to add the part to our portfolio, our milling machines only had 3-axis functions. We therefore needed to build this capability.

We initially stepped out to see whether a vendor could take the PEEK valve part up for us. However, every vendor we spoke with either gave up upon seeing the drawing (the part is very complex!) or said that they did not have capacity to take up the job. We were intrigued. Not only was the part truly a challenge – which is something we love – but the lack of capacity in the market meant that acquiring our own equipment was probably a good idea in the long run.

However, given that a 5-axis milling machine can be rather expensive, we were hesitant to jump into something requiring such a large investment, when the value of the order in question was small in comparison. We then came across a new equipment vendor offering 5-axis machines at a fraction of the cost that was being asked by the larger manufacturers. We gave them the part to develop, assuring them that if successful, we would pay the advance on a new machine immediately.

Sadly, the PEEK valve development  was tougher than they anticipated (I did say it was complex) and after struggling for a few weeks, they abandoned the project with nothing to show. We were back to square one.

We sat down to review the part and – in what would surely be a major loss of face – decide how we were going to inform the client that we had failed and that we could not take the development further. During our review, it was commented that in truth, we only needed a 4th axis to give us the extra dimension needed to machine the part. This caused us to stop and think. We already had 3-axis machines; what would it cost to add only one more axis? Was such an extension even possible?

After speaking with our existing machine’s vendor, we were excited to learn that they had a 4th axis attachment suited to our equipment. What’s more, it would cost a third of what we would have paid to the supplier to whom we had given our part for development. 

Within two weeks the new attachment was in place, although the part’s development still took a few weeks more (did I mention the part is very complex?).

Our obsession with making the part led us down a path of discovery that culminated in a successful outcome. However, in pushing for this outcome, we managed to add a 4-axis capability to our machining repertoire, giving us the option to take on new parts that we may have otherwise had to regret. It is this determination to constantly push what seems infeasible that leads us into newer, more interesting avenues of our operations.

And if we do come across a part more complex than what we can handle? Well, there’s always that elusive 5th axis we still need to get!

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Read More

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

2. PEEK - Robust Enough for Nuclear Applications

3. The Effectiveness of PEEK Compressor Valve Plates

As a standalone material with no filler reinforcements, PEEK (PolyEtherEtherKetone) comfortably holds its own as one of the most robust polymers around. With the exception of Polyimide (aka Kapton), PEEK has no viable rivals on pure strength and high-temperature capabilities. A specific gravity of only 1.3 makes it a darling of the aerospace industry, while a chemical inertness that nearly matches that of PTFE makes it highly sought after in nuclear applications and refineries.

That said, there is always room for improvement. The same fillers that give materials such as PTFE or PPS enhanced properties also work well on PEEK. As such, with the aim being to maximise strength and durability, carbon is a key filler for PEEK.

Carbon (Coke) Powder vs Carbon Fibre

Before we proceed, a distinction must first be made between powdered carbon – which is effectively finely ground coal, and carbon fibre – which is a result of milling more complex carbon materials to yield miniscule, high-strength strands that go on to reinforce the polymer into which they are blended. While carbon fibre is far more expensive than conventional carbon powder, its impact too exceeds that of its poorer cousin by a significant margin.

Thus, when we refer to carbon filled PEEK, it should be understood here that we are speaking specifically about carbon fibre.

PEEK, PEEK+Carbon, and HPV PEEK

In this article, we will primarily be comparing three different grades.

Unfilled PEEK is the polymer in its virgin form. As stated above, even in this form – where the PEEK takes an even tan colour – the material is robust and capable of withstanding high loads and temperature.

PEEK+Carbon or Carbon-filled-PEEK is usually a blend of PEEK and either 15% or 30% carbon. For the purpose of this comparison, we will be looking at PEEK+30% carbon (CF30), as we have accurate data for the same.

PEEK HPV material is a special blend of PEEK popularised by the brand Ketron (Quadrant). HPV PEEK was designed to have a composition of 70% PEEK, 10% carbon, 10% graphite, and 10% PTFE. This unique blend offers a large boost to the strength of the base material – thanks to the carbon reinforcement – while also bringing better wear and friction properties due to the graphite and PTFE. HPV PEEK – also referred to as bearing grade PEEK – is both difficult to blend and prohibitively expensive in comparison to regular PEEK. However, given its fantastic properties, most OEMs are happy to pay the price.

Comparing Properties

As you can see from the table below, the addition of carbon and other fillers has an appreciable impact on the properties of the material. 

Apart from an increase in tensile strength of ~35%-207% for HPV and CF30 respectively, there are increases of anywhere from over 300% to over 500% on other metrics such as Young’s Modulus, Flexural Modulus, and Flexural Strength.

In addition to pure strength, what can also be observed are lower coefficients of thermal expansion and higher deflection temperatures under load – both indicative of a more dimensionally stable material in high-temperature applications.

HPV – which has a lower coefficient of friction and can go as low as 0.05 under lubricated conditions – is ideal for wear applications and dry-running applications.

	Unfilled PEEK	PEEK+30% Carbon	PEEK HPV	Unit	Test
Tensile Strength	97	201	133	Mpa	ASTM D638
Young's Modulus	3650	19700	11000	Mpa	ASTM D638
Flexural Modulus	3860	17500	10500	Mpa	ASTM D790
Flexural Strength	152	317	221	Mpa	ASTM D790
Coefficient of Linear Thermal Expansion	4.3 x 10-5	5.2 x 10-6	2.2 x 10-5	cm/cm/°C	ASTM E831
Deflection Temperature Under Load	162	315	291	°C	ASTM D648
Coefficient of Friction	0.35	-	0.25		ASTM D3702

Machining properties

As manufactures of high-precision machined components, a lot of our experience ultimately ends with understanding how well the part adheres to close dimensional tolerances.

Both bearing grade PEEK and Carbon reinforced PEEK are highly stable both during and post-machining. While special tools are needed to handle the material, tolerances of as low as 10 microns can be achieved on the machined parts. Further, the low coefficients of expansion allow for parts that are machined in one part of the world to travel elsewhere with no loss of dimensional integrity due to changing climates and environments.

Conclusion

While Carbon filled PEEK (CF30) is clearly the winner on pure strength, bearing grade PEEK (HPV) forms a decent middle ground between PEEK and CF30 and is an excellent choice for bearing applications. While it has traditionally been an expensive grade, in-house blending techniques have allowed for significant cost optimisations, allowing the price to rest only slightly above that of unfilled PEEK.

Whatever the requirement, it is evident that any application where strength is a key criteria would benefit from the reinforcement of PEEK with carbon.

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Read More

1. PEEK Components and Bearings - Durable, lightweight, and dependable

2. PEEK Seals - Numerous Applications, Many Choices

3. PTFE vs PEEK - A Comparison of Properties

With new developments being constantly introduced in the high-performance polymer space, exciting new products are always entering the market. However, as the scale remains low, most new plastics remain prohibitively expensive but for the niche applications for which they may have been created. Through all this, the erstwhile stalwarts - PTFE and PEEK - have retained much of their effectiveness as increased scale and breadth of application has allowed them to become more cost-effective and compete with existing medium-performance polymers on high-volume parts.

Apart from PTFE and PEEK, it is also important to look at FEP and PFA. Both these high performance polymer variants were an offshoot of PTFE. Indeed, few realise that the trade name “Teflon”, which is used so interchangeably with PTFE does in fact cover PFA and FEP as well.

The reason for developing PFA and FEP was quite simple: PTFE has a very low melt flow and hence cannot be injection moulded. This limitation makes PTFE a material that can only be machined, which in turn makes complex parts and high-volume parts a difficult prospect when using PTFE. FEP and PFA both have lower melting points and have melt flows which allow for injection moulding. However, it is important to note that in this trade-off, both polymers surrender various properties, making PTFE the superior material in terms of absolute performance and versatility.

The below table offers some key comparisons between these four polymers, in order to offer an understanding of each one’s advantages, disadvantages, and applications.