Ceetak: Ultra-High Molecular Weight Polyethylene (UHMWPE)

Is this an overlooked material?

What is UHMWPE? 

Ultra-High Molecular Weight Polyethylene (UHMWPE) is a thermoplastic polyethylene with extremely long molecular chains. Also known as high-modulus polyethylene (HMPE), it’s produced as a rod, sheet, or in fibre form and best performs independently due to its incompatibility with other polymers.

Ordinarily, long chains between molecules would weaken a material, however UHMWPE has multiple overlaps in these chains which strengthens it, creating a high number of molecular bonds. The result is a very tough material that has the highest impact strength of any thermoplastic.

What are its qualities?

First produced commercially in the 1950’s, this odourless thermoplastic has unique properties making it an ideal choice for seals and other components in valves.

UHMWPE can withstand high shear forces between its molecules giving it very high abrasion resistance. It also has self-lubricating properties, and a friction coefficient lower than many alternatives.

Why use UHMWPE?

Possessing abrasive wear resistance 5-10 times higher than many filled grades of PTFE, UHMWPE is a great option for seals that involve the flow of aggressive or non-lubricating media. This can include pastes or slurries, or in gruelling conditions prone to contamination either in the fluid being transmitted, or from the outside environment.

Compared to some elastomers, UHMWPE is not affected by accelerated wear or damage to the seal after dynamic operation, in either dry or poorly lubricated conditions for extended periods of time (or after extended periods of inactivity). It is therefore an ideal seal material for pneumatic applications.

UHMWPE has a high chemical resistance to both acids and bases, as well as numerous organic solvents and corrosive chemicals. Although caution is needed with certain acids and hydrocarbons, it’s generally stable in all hydraulic fluids. Due to its very low water absorption rates, it’s also suitable for water-based hydraulics, and often outperforms PTFE seals in such applications.

High pressure environments

The tough nature of the material, with good extrusion and creep resistance, makes it suitable for applications at high pressures, or where large extrusion gaps are unavoidable. 

Remaining flexible at a very low temperature (into the cryogenic range) with a minimum recommended limit of

-200°C, UHMWPE is a little more limited at the higher end. The recommendation is to operate at a maximum of 80°C (but for short periods, up to 120°C can be sustained without significant loss of material properties). 

With the development of premium grades, the upper temperature limit can increase to 135°C for prolonged periods under the correct operating conditions. This provides more opportunity to use UHMWPE in a broader range of applications. 

Time to break away from the norm?

Sometimes regarded as a niche material, compared to the near-universal chemical compatibility of PTFE, serious consideration should be given to UHMPWE for seals, wear rings or seat components in valve applications. With its economical price point, high-performing properties, exceptional chemical resistance, and extended material service life, it may be the right material to consider for your application. 

How Ceetak can help you choose the right material for your application.

We understand the challenges, technical demands and the need for long service life and minimal maintenance needed for valve application sealing.  Our extensive expertise means we can quickly identify and specify the optimal material selection.

For more information about how Ceetak’s products and services can benefit your organisation, visit www.ceetak.com or to speak to one of our expert team, phone +44 (0)1234 832200.

Telephone:    +44 (0)1234 832200

Email:           enquiries@ceetak.com 

Website:        www.ceetak.com

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Published: 28th June 2023