Why use PEEK plastic as a material for the backup ring

What is back up ring

Back up ring plays a very important role in the seals. You can tell its function from the name: it back up the O-ring. Usually, the backup rings are just structural support that keeps the O-ring away from the extrusion gap in hardware. Actually what seals is the O-ring and the O-ring is usually made of rubber. If the pressure acts on the O-ring sealing surface, it may cause O-ring deformation resulting in permanent seal failure. Especially in some high-pressure working applications, such as coal mining or oil drilling, so the backup ring is essential. 

What material can be used in this application

Generally, the material of backup rings usually uses polymer. Also, the material chosen should be based on the working condition, pressure, temperature, and other factors. And the commonly used materials are acetal, nylon, PEEK, and PTFE according to different applications, but among these plastics, PEEK and PTFE are most used. 

What are the PEEK’s excellent properties?

Excellent mechanical strength

Compared to other common plastics, PEEK has higher mechanical strength. We can see in the table below that the modulus of PEEK natural is 4200mpa, tensile strength and flexural strength are all above 100mpa. These values mean PEEK natural could be functioning normally under very high pressure and temperature. 

While in some certain extremely high temperature and high-pressure conditions, PEEK GF30 is a better choice. This material has an even higher modulus. Because the glass fiber is reinforced, it performed better than PEEK natural under high temperature and high pressure working conditions. 

Besides the great mechanical strength, PEEK also has a very high long-term service temperature which is up to 260℃. 

Combining the excellent mechanical capacity and high continuous operating temperature, the PEEK backup ring could keep the rubber O-ring functioning well under high temperature and high-pressure working conditions. A very typical example is the PEEK backup ring used in the oil downhole tool which the working temperature is up to 175℃ and the pressure is 140mpa at the same time.

What needs illustration is that the backup ring design is also vital. Only combining the right material and good design structure could achieve the best results.

Great dimensional stability and easy to machine

When you design a backup ring, you want all the designed dimensions to keep in the tolerance. But unfortunately, after machining or other molding methods, due to the variation of stress and other factors, all the plastic may be deformed. However, compared to other plastic, PEEK always keeps dimensional stability due to its molecular structure and low water absorption. Meanwhile, PEEK does not need a very special machining process.

What are the potential issues in using PEEK backup ring

May cause assemble inconveniently

As mentioned before, PEEK has good mechanical strength, high modulus, and good dimensional stability. This means PEEK is very hard plastic. If the backup ring is slightly larger than the hardware, the soft material like PTFE may be able to deform to fit in the hardware, like squished into the place. However for PEEK, even very slightly oversized, see 0.001, may cause the assemble problem. 

May cause higher costs

As we all know, PEEK is an advanced plastic. The raw material, molding difficulty cause the high price. Nevertheless, our company could provide you with a wide range of size extrusion PEEK natural tubes and compression molding PEEK or PEEK modified rings. For compression molding, the super large size and customized size are also available. This could help you to reduce the cost.