Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

The Impact of Carbon Fibre Fillers on HPV Bearing Grades

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.


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




Tensile Strength






Young's Modulus






Flexural Modulus






Flexural Strength






Coefficient of Linear Thermal Expansion

4.3 x 10-5

5.2 x 10-6

2.2 x 10-5



Deflection Temperature Under Load






Coefficient of Friction





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.


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.

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

A Comparison of High-Performance Polymers

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.


Trade name/ Typical name   PEEK PTFE PTFE 25 % GF PFA PFA 20 % GF FEP FEP20 % GF
Type of the Polymer   Thermoplastic Thermoplastic-Thermoset Thermoplastic Thermoplastic Thermoplastic Thermoplastic Thermoplastic
Advantages   PEEK is a high performance thermoplastic with the characteristics common to this group - strong, stiff, hard, high temperature resistance, good chemical resistance , inherently low flammability and smoke emission. It is pale amber in colour and usually semi-crystalline and opaque, except thin films are usually amorphous and transparent. It also has very good resistance to wear, dynamic fatigue and radiation Outstanding chemical resistance. Low coefficient of friction. High continuous use temp. 180 Cº . Very high Oxygen index. Higher modulus and surface hardness than PTFE. Improved creep resistance, dimensional stability and wear compared with PTFE. Melt processable, has similar chemical resistance to PTFE combined with the highest temperature resistance of melt processable fluoro plastics. Self-extinguishing. Retains room temperature stiffness and strength at elevated temperatures better than FEP. Excellent toughness. Significant increase in HDT and moderate increase in tensile strength compared with unmodified grades of PFA. Very high impact strength. Excellent high frequency electrical properties. Melt processable. Good weathering resistance. Significantly increased tensile strength, HDT and flexural modulus compared with unmodified grades of FEP. The mechanical properties of moulded components can be anisotropic.
Disadvantages   It is difficult to process and very expensive. Low strength and stiffness. Cannot be melt processed. Poor radiation resistance. Lower impact strength, lower tensile strength and more expensive than unmodified PTFE. Stiffness and strength similar to those of PTFE at room temperature. More expensive than PTFE. Decreased elongation at break and notched izod impact strength compared with unmodified grades of PFA. Very expensive, with the lowest strength and stiffness of all the fluoro plastics. Low HDT at c 50°C ( 120°F ) accompanied by poor wear resistance. Elongation at break and notched izod impact strength are reduced compared with unmodified FEP. The mechanical properties of moulded components can be anisotropic.
Applications   Applications include flexible printed circuit boards (film), fibres and monofilaments, injection moulded engineering components and items used in aerospace and radiation environments. Filled grades, including ones designed for bearing-type applications, are also used. Bearings, Chemical vessels linings, pipe and valve linings, gaskets, diapharms, piston rings, high temp. electrical insulation. As a coating of non stick applications. Wear pads, piston rings, and microwave oven rotating platforms. Heater cables, chemically resistant linings for pumps and pipes etc. that require a higher temperature resistance. Chemical plants. Coatings, protective linings, chemical apparatus, wire coverings, glazing film for solar panels. Valves, electrical components and equipment for chemical plants.
PROPERTIES UNIT              
Density g/cm³ 1.26 - 1.32 2.15 2.25 1.6 2.2400000000000002 2.1 2.2000000000000002
Surface Hardness RR M 99 [Rockwell] SD 63 SD72 SD60 SD 68 RR45 RR65
Tensile Strength Mpa 70-100 25 17 29 33 14 40
Flexural Modulus Gpa   0.7 1 0.7 0.7 0.6 5.5
Notched Izod Imapact strength kJ/m 0.85 0.16 0.12 A.06+ 0.7 1.06+ 0.2
Linear Expansion /Cº x 10?5   15 12 21 13.5 5 5
Elongation at Break % 50 400 250 300 4 150 2.5
Strain at Yield %   70 N/Y 85 N/Y 6 N/A
Max. Operating Temp. 250 180 180 170 170 150 150
Water Absorption % 0.1 - 0.3 0.01 0.01 0.03 0.04 0.01 0.01
Oxygen Index % 35 95 95 95 95 95 95
Flammability UL94 V 0 @ 1.5 mm V0 V0 V0 V0 V0 V0
Volume Resistivity log ohm.cm 10¹5-10¹7 18 15 18 18 18 14
Dielectric Strength MV/m 19 @ 50 ?m 45 40 45 40 50 13
Dissipation Factor 1kHz 2.9999999999999997E-4 1E-4 3.0000000000000001E-3 2.0000000000000001E-4 1E-3 2.0000000000000001E-4 5.0000000000000001E-4
Dielectric Constant 1kHz 3.2-3.3 @ 50Hz-10Khz 2.1 2.8 2.1 2.9 2.1 2.5
HDT @ 0.45 Mpa › 260 121 125 74 160 70 260
HDT @ 1.80 Mpa 160 54 110 30 150 50 158
Material Drying hours @ Cº 4-6 HOURS @ 200° NA NA NI NA NA NA
Melting Temp. Range 360-420 NA NA 360-420 360-420 340-360 350-380
Mould Shrinkage % 0.8 - 1.5 NA NA 4 0.8 2.5 0.4
Mould Temp. Range 175 - 200 NA NA 50-250 50-250 50-200 50-200

Self-lubrication Solutions for Critical Applications - Polymer Bearings

About Polymer Bearings

In an already crowded bearing space, polymer bearings have made their mark for a host of different reasons. As a result, an area that was once dominated by steel and phosphor bronze is increasingly giving way to high performance polymers such as PTFE, PEEK, POM, and Nylons, where the sheer breadth of grades and fillers allows for a whole range of properties tailored to match the end-application and offer a solution that far exceeds what metal bearings were able to hitherto provide.

The advantages and disadvantages of polymer bearings against metals can be shown on the chart below:

Polymer Bearing




Limited load capability

Fully customisable

Can be expensive


Limiter temperature range

Easy to replace



As shown above, metallic bearings are typically preferred where the loads and possibly the temperatures are much higher. Here too, however, certain polymers such as PEEK and Polyimide (Kapton), can bear enormous loads and remain functional in temperatures of 300°C+. However, such polymers come at a price and are therefore limited in applications such as aerospace and medical, where cost may not be a key criterion.

However, for many applications, polymer bearings find that their advantages are highly sought after. Key among this is the ability to self-lubricate. Self-lubricating polymers such as PTFE, POM, and UHMWPE - to name just a few – offer dry-running capabilities which greatly reduce the need for external lubrication. This is especially valuable in consumer goods, where the structure of the device or appliance is such that the user will not have access to the moving parts. Similarly, in certain industrial applications, self-lubrication ensures minimal down time and greatly reduces the wear and load due to the build-up of friction.

Types of Polymer Bearings

Polymer bearings come in various shapes and sizes and can be either machined from a drawing or reverse-engineered from an existing part. Some of the typical bearings offered by Poly Fluoro Ltd. include:

1. Flange bearings
Flange bearings are designed to handle both axial and radial loads. In some designs the flange is also used as a locating mechanism to hold the sleeve in place.

Flange bearings can be machined either from stock rods or moulded. Polymer grades used would include PTFE (usually with a glass or bronze filling), PEEK (virgin or carbon filled), PPS (usually with a glass filling), and POM.

Flange bearings require a little more machining to the housing but can solve the unique load conditions of a shaft and some type of thrust surface.

2. Mounted bearings
Mounted bearings are machined with a double flange in order to sit within a pillow block. These bearings can be fabricated using several different plastic bearing materials to improve wear and reduce or eliminate lubrication.

3. Thrust bearings
Put simply, thrust bearings are washers made from any number of materials such as PTFE, PEEK, PPS, POM, Nylons, or Polyimides. They are generally thin, easy to install and prevent metal on metal contact in any thrust load conditions. They are easy to use and do not require lubrication of any kind in most conditions.

Although the design is simple, there is a need to machine the part so that the surfaces are perfectly parallel. This is where Poly Fluoro excels.

4. Sleeve bearings
These are the most common bearings, with a simple ID, OD, and length. However, as with the washers, care needs to be taken to ensure the tolerances are tight. Where most manufacturers would only offer a 100 Micron tolerance on linear dimensions, Poly Fluoro is able to go down to as low as 10 Microns in some cases.

The bearings are designed to carry linear, oscillating, or rotating shafts. The key to successfully designing a plastic sleeve bearing is paying attention to temperature, P, V and PV ratings for the material and match it with your application.

5. Spherical bearings
Spherical bearings are designed to allow for shaft misalignment, as they can rotate in two directions. Spherical bearings typically support a rotating shaft in the bore that calls for both rotational and angular movement.

Using self-lubricating polymers with very low static coefficients of friction, Poly Fluoro is able to ensure that even minor variations in alignment are immediately accommodated by the bearing to allow for non-stop performance.

While the above bearings are most common, application engineers are constantly finding new areas in which to apply the bearing properties of polymers. Ultimately, any application with repeated motion will benefit from a polymer bearing as it offers an unmatched ability to reduce wear and friction over a very long period of running time.

Related Posts

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2. Cantilever Load Considerations for PTFE Sliding Bearings

3. Oil Free Polymer Bearings - Fluoropolymer Formulations for Applications Needing Self-lubrication