Rubber Extrusions Guide

Looking to use an extruded rubber profile?  Make sure you understand what you are buying, and the options available to you.  Ascertaining your ultimate requirements early on in the process may save you time and money.  This guide is designed to help engineers and designers at the initial design and prototype stage, and to assist buyers who are looking for either a new product or a replacement/alternative to an existing item.

What is rubber extrusion, and what does it do?

Rubber extrusions are continuous profiles, used often in sealing applications such as doors and windows, weatherstrip, draught excluders or more robust applications such as D-fenders on ships.  Extrusions can range from simple geometric shapes through to complex seal designs using dual materials. The name relates directly to the manufacture method, and although this of course is not the only way of producing a length of rubber, it is the most effective way of creating consistent, continuous lengths of profiled rubber.

How is an extrusion manufactured?

Rubber extrusions are produced using a die; a metal disk with a machined opening in the shape of the profile required.  Behind the die sits the extruder, a rotating screw inside a heated cylinder, into which the raw compound, pigments, curing agents and other specialist ingredients are fed.  The screw forces the uncured material out through the die cavity under considerable shear and heat.  On exiting the die, the material must be cured; this can happen using a variety of processes including ovens, microwaves, and water, and is often part of a continuous process.  The final production step will be finishing – adding coatings, cutting to lengths, etc.

Can I buy an ‘off the shelf’ option?

There are a range of dies already manufactured and available for use; the more popular extrusion profiles are kept in stock and you can order these as required, by the metre, in which case they are available within 2-3 days.  The remaining collection of dies will be available but will have to be scheduled for production; as such this will result in a longer delivery time, and may also incur a minimum order quantity (MOQ) in order to account for the set-up and material required.

If an extrusion is required to a profile not currently in existence, a die can be manufactured specific to your requirements; this will incur a cost but will result in a bespoke product to cater for your precise needs.

What factors should I take into consideration when designing a bespoke profile?   

When a die is machined to produce a particular profile, it will be manufactured specific to the material it is designed to run – this is because rubber, upon curing, will shrink; each type of rubber shrinks by a different percentage, thus creating a variable between materials.  This means that if you see a profile displayed as available in EPDM, it does not necessarily follow that the same die can be used to manufacture the extrusion in silicone.   For more information on materials and their benefits/compatibility, please see our Materials Guide. A dimensioned 2D drawing will be required in order to produce a die for you; we will adjust the sizing of the die to account for shrinkages and other relevant factors, so please draw the finished product that you wish to receive.   If you are looking for a replacement extrusion and have a sample available, we can match to this sample but please be aware that if it is used or worn, the effects of this will be replicated in the final product.  

When using an extruded profile as a face seal, it is important to consider a number of factors in the detail of the design; the mechanical clamping forces available, the surface condition of the mating face for the seal to rest on, and the fluid pressure that must be resisted, amongst others. High pressure extruded seals may be energised simply by virtue of the pressure involved in the application, but low pressure seals may require thin lip features which in turn might need mechanical energisation, or careful design of the material and profile to provide sufficient natural elasticity to effect a good seal. Our experienced staff are on hand to offer advice on specific applications.

How do I select and order a standard profile?

If you wish to purchase direct from our catalogue, please browse for the closest profile to that which you require, and contact us for a quotation with details including the quantity (metres) that you are looking for.

The catalogue is designed on the basis that the images are a 1:1 representation of size, however if you are viewing it on a screen it is recommended that you contact a representative of Martin’s Rubber to clarify the overall size in case of differences in screen set-up.  The catalogue is currently being re-designed to include dimensional drawings for clarity, and the most popular profiles will soon be available to purchase on line.

The majority of the standard profiles are manufactured using EPDM and the items will show a material code if this differs.

Can extrusions be cut and joined into a finished assembly?

Yes, this is possible by preparing the cut surfaces and vulcanising them with a shot of uncured rubber in a specially designed mould to form a corner; we offer this process in-house and for further details you can read about shot joining on our extrusion expertise page.

Can you supply a sample?

If the selected profile is a stocked item, you can purchase a metre to trial.  Any profile that requires manufacture will have an associated MOQ and therefore a sample will not be available. 

If you have opted for a bespoke die to be manufactured, we may be able to run a short sample prior to the full run but this must be requested at quote stage; assuming the part has been manufactured to drawing, alterations can be made but will be chargeable.

What are the benefits of rubber extrusion?

Extruding a profile in this way will mean a consistent, repeatable product, which can be cut to length to suit the application in question. Rubber mouldings, by comparison, are restricted by the size of the press in which the product is manufactured, and therefore the maximum straight length achievable would usually be around 1m.  Rubber sheet can be stripped to produce square or rectangular profiles but it is restricted both in terms of tolerances, and size/shape – an extruded product may hold tighter tolerances and much smaller shapes/thinner sections, and more intricate geometries.  Due to the method of manufacture, for some applications extruding will be a more cost-effective solution, particularly if large quantities are required; the tooling is generally less expensive than a moulding tool, whilst maintaining greater accuracy than a stripped product.  Whilst hardness may be a restricting factor in extruding (very soft grades can be difficult to extrude), there are a wider range of materials available for use, and if aesthetic finish is a concern, colour matching in materials such as silicone can be undertaken.

Conclusion

To browse our full catalogue, please view our brochure page in pdf and take note of the introduction regarding materials and stocked items; these do vary so please contact us for confirmation of availability. If you wish to view our extrusions currently in stock and available for purchase online, please follow this link: .

If you are unable to find a profile which matches your requirements, please send a drawing of the extrusion to sales@martins-rubber.co.uk or send an actual sample to us at our factory in Southampton, using the details on our Contacts page.