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J-Flex – as industrial rubber specialists we have the answers to your questions

Over the years we’ve been asked a lot of questions – and have always been pleased to share our knowledge with others.

Here is a list of the more commonly asked questions, as well as some of the more quirky or interesting ones we’ve come across – and of course, the answers.


Which type of rubber is best for my application?

There are a range of natural and synthetic rubbers with different properties, making some more suitable than others for particular applications – the key of course is choosing the most appropriate one! For quick reference you can use the table ‘Industrial Rubber Types Guide at a Glance’. For specific requirements, please ask our rubber products specialists for guidance.

What are the coefficient ratios I need to be aware of?

The two key ratios are Coefficient of Friction and Coefficient of Thermal Expansion. The first (friction) indicates the force needed to move an elastomer over a given surface versus the total forces pressing on the elastomers and surface. The latter (thermal expansion) shows the ratio of the original length versus the change in length as a result of temperature variation.

What does 'hystersis' mean?

This is the term used to describe the build up of heat in an elastomer sample caused by rapid deformation.

How exactly is 'rebound resilience' measured?

Quite simply, a metal ball of a particular size and weight is dropped from a given height onto an elastomer sample. The rebound resilience figure is an indication of how much the ball actually bounced.

What is the correct way to store rubber sheeting?

Rolls of Rubber Sheeting should be stored in accordance with the “Guidelines for storage – Rubber products” as detailed in the Specification BS ISO 2230-2002. This International Standard gives guidelines for the inspection; recording procedures; packaging and storage of products, assemblies and components made from vulcanised or thermoplastic rubber prior to being put into circulation.

It is applicable to both solid and cellular rubber products made from natural and synthetic materials. This is a most useful standard and we would recommend its use to all customers who store rubber based products.

How can thickness tolerance be maintained?

At J-Flex we have invested in automated laser sensing equipment that performs in line measurements of the specified thickness for calendered sheet rubber products. As a result we confidently provide thin and tight tolerance products to our clients worldwide. For specific requirements please ask our rubber products specialists for guidance.

What is a Fluoroelastomer?

Fluoroelastomers are fluorinated synthetic polymers designed for harsh environments including aggressive chemical and temperature applications. These materials are sometimes referred to as Viton™, which is a registered trademark of DuPont Performance Elastomers.

J-Flex is an official Chemours Viton™ licensee. Other suppliers of Fluoroelastomer polymer are Dyneon; Solvay and Daikin.

Fluoroelastomer compounds are based on polymer that takes advantage of the high strength of the fluorine to carbon bond and the high ratio of fluorine to hydrogen. This unique chemistry and proper compounding means that some fluoroelastomer materials can perform continuously in temperatures of 204°C and 300°C intermittently.

The ASTM D2000 designation for fluoroelastomers is HK meaning the highest heat resistance and the lowest swell available of rubber type elastomers.

So what's the difference between FPM and FKM?

FPM is the international designation according to ISO, whereas FKM is the ASTM abbreviation. Both of these designations stand for the same base material: fluoro rubber.

Which grade of fluoroelastomer is best for my application?

There are a number of different families and types of Viton™ Fluoroelastomer for example. Each grade or family has been specifically designed over the years to provide a particular solution to an operating application or problem. Here at J-Flex we would be pleased to try and help with your specific requirements.

What products made from Fluoroelastomer do J-Flex offer?

J-Flex boast one of the largest stocks worldwide of sheet products made from Viton™ – ‘A’ & ‘B’ grades + White FDA + Nomex Reinforced + Sponges that are all available for immediate despatch to you. Specials like Colours; Thin Gauge; GF & ETP etc, all made to order.

Is it possible to identify a rubber type when sending in a sample?

There is a crude but useful method that can be used for identifying different polymers simply by burning on a direct flame. We would urge caution with this method and ensure that all tests are carried out in a well ventilated area away from hazardous goods.

Our tests and observations were conducted by taking samples of sheet and extruded products and results are shown in a table Polymer Identification by Flame Test. which is taken from our popular Ask the Experts Technical Guide.

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Why buy from J-Flex?

If you are looking for a friendly and helpful industrial rubber products supplier, with great product knowledge and excellent customer service, then you’re in the right place. We supply a vast range of quality items including rubber sheet and an array of fabrications made from premium grade elastomers including silicone and Viton™ - many of which are available for next day delivery. With over 35 years operating experience, J‑Flex is the preferred supplier of industrial rubber products - providing engineered rubber components and specialist rubber sheetings you can trust. Whether you are looking for silicone sheets, rubber mouldings, gaskets, sleeves, extrusions, bellows, fabrications, rubber sealants or adhesives -including Viton™ sheets and sealants, J‑Flex can help. You'll find our Accreditations, Approvals, Certifications and Compliance​ information here.