Archives: DP Blog

DP Seals’ blogs

Natural vs Synthetic Rubber

Examples of DP Seals custom rubber seals, gaskets and mouldings

Natural vs synthetic rubber – They both have their place

In the natural vs synthetic rubber debate, Statista state that there were 15.2 thousand metric tons of synthetic rubber and 13.2 thousand metric tons of natural rubber consumed globally in 2018. Indeed, although synthetic rubbers can provide a myriad of property improvements both have their place in respect to relative performance characteristics and cost.

Natural rubber

Natural rubber can only grow in tropical climates and doesn’t age well. Most natural rubber is produced from the softwood Hevea brasiliensis tree, which is native to Brazil. However there are several other species of trees and shrubs from which natural rubber is sourced.

It has a high tensile strength, higher tear resistance, low odour, and is resistant to fatigue from wear such as chipping, cutting or tearing. It also has tack, which means it can adhere to itself as well as other materials. This is particularly the case for steel cord which makes it an excellent material for use in tires. Natural rubbers are also a very popular choice in the Subsea, Oil & Gas field particularly.

On the down side natural rubber has only moderate resistance to damage from exposure to heat, light and ozone. It also contains natural proteins which may cause allergic reactions when placed in contact with human skin for prolonged periods.

Synthetic Rubber

Synthetic rubber is artificially produced from polymers in different varieties to mimic the properties of natural rubber. So, for many countries, it is easier to use.

In general, synthetic rubber offers better resistance to abrasion than natural rubber, as well as superior resistance to chemicals, fluids, ozone, electrical heat and the effects of aging. Many types of synthetic rubber are flame-resistant, so it can be used as insulation for electrical devices. It also remains flexible at low temperatures and is resistant to grease and oil. Because of this synthetics offer excellent results for applications in extreme temperatures and corrosive environments.

For more detailed information about specific compounds see our data sheets and chemical compatibility database or call our material technologists.

Rubber Chemical Compatibility

CCD App on Android

 

These top tips are based on speaking with design engineer customers and our experience and expertise of custom rubber seals,  gaskets and mouldings  chemical compatibility gained in over 40 years.

Tip1: Use look up tables.

This can really help design engineers with initial investigations. DP Seals have had a Chemical Compatibility Database on our website for some time!

Tip 2: Get in touch with your manufacturer as early as possible.

Once you’ve done your initial investigations we’d suggest getting straight in touch with the manufacturer. They’ll be able to provide further advice about chemical compatibility at different temperature ranges and under different conditions such as vapour, gas, flowing or static liquid. They’ll also be able to outline any negative consequences of material selection.

Tip 3: Don’t discount materials just because of cost until you’ve spoken with your manufacturer

Cost is obviously a key consideration.  FFKM or Perfluoroelastomers are some of the most incredible rubber materials but they do come at a very high cost. However at DP Seals, due to our expertise and experience, we can often utilise these materials to create a much more effective solution that offers significant savings. Ultimately good advice can sometimes mean we pick alternative lower cost materials as well.

Tip 4:  Ensure the manufacturer can ensure consistency batch to batch for your current project and years into the future

This is, of course, critical to maintain performance. At DP Seals we achieve this through having a recorded preparation compound reference number that is tied in against the customer’s part. Once the part is approved for production, that reference number is locked down and used every time for all future production. This ensures stable and repeatable performance for every component.

Tip 5: Think about all the environments the rubber moulding will be in, not just when it is performing.

It is not only important that the moulding remains chemically inert within its typical product environment, but also to think of all the environments the rubber moulding will be in. For example, any detergents or chemicals used for cleaning. Overlooking this could result in contaminated wash systems and product de-gradation.

Summary

In this article we’ve touched on some of the key things engineers should consider in respect to chemical compatibility when designing custom rubber, seals, gaskets or mouldings.

  1. Using look up Chemical Compatibility Tables to save time
  2. Getting in touch early with the manufacturer to consider issues, operating conditions, negative consequences and product lifespan
  3. Not discounting materials too early, because of cost, without speaking to the manufacturer
  4. Ensuring batch consistency and
  5. Considering all environments the rubber part will be in. Not just when it’s performing

If you have any questions about this post or would like to discuss your own rubber chemical compatibility application please get in touch.

Rubber Hardness Considerations

Medical Moulding

Five top tips on rubber hardness considerations for engineers

These top tips on rubber hardness considerations are based on speaking with design engineer customers and DP Seals 40 years experience and expertise in the custom rubber seals, gaskets and mouldings business.

Tip 1: Think about how dynamic or static your application will be.

The rubber hardness selected really does depend on the planned application and, in particular, how dynamic or static the moulding will be. We must remember that the material is still a solid and although a lower hardness will flex and move more freely it will not behave as a sponge or foam like material. It must have space in which to displace.

Tip 2: Think about how material hardness might impact on mechanical arrangement.

The profile of the part, its mechanical and human use, calculating compression, there’s a lot to think about. Of course working with a manufacturer that has technical expertise will help immensely as they will have the experience and knowledge of specifying material to match performance requirements. At DP Seals we work closely with all our customers and will do all we can to help with technical input. This will always include hardness as a key element in the manufacturing process.

Tip 3: Depending on material type a given mould can be used to produce samples in numerous hardness grades.

Within limits, and depending on material type, a given mould can be used to produce samples in numerous hardness grades. Through fine tuning it can then be pin pointed to what reacts well and serves the application best. We can actually start at quite different ends of the scale and then close in on what is working best for the customer after initial testing.

Once we have reached a final conclusion the rubber compound formulation can be locked down with a specific preparation number to ensure future reproducibility and consistency.

A seal manufacturer who has a tool room and makes their own moulds will have a much better understanding of how the mould should be built in order to produce the component to the best quality and, of course, the lowest possible cost.

Tip 4: Ensure you can achieve consistent and repeatable performance

How can engineers be confident that the rubber mouldings will do their job over the lifetime of the product? Engineers should be confident in their manufacturer. This includes quality standards, testing conducted (both dynamic and static) and reliability of the compounder used. At DP Seals we’ve formed long-standing partnerships with industry leaders who have processes in place to guarantee repeated consistency. In addition we have our own documented database detailing material and each process stage through to the finished item – and that’s for every component we produce.

Tip 5: Communicate early

Material hardness is just one consideration and shouldn’t be seen in isolation. Every part is different with its own unique features. We’ve covered some of the key ones in this article relating to hardness but there are others. So our final tip is to talk to your manufacturing partner as early as possible in the process. Communication really is key and can save a lot of time and money in the long-run.

Summary

We’ve touched on some of the key things engineers should consider in respect to rubber hardness when manufacturing custom rubber, seals, gaskets or mouldings. We’ve mentioned thinking about hardness relative to:

  1. How dynamic or static the application will be, including thinking about displacement.
  2. The overall mechanical configuration of the product.
  3. The re-use of moulds.
  4. Repeatable and consistent performance.
  5. Communicating early with your manufacturer.

We hope this short read has proved useful but if you have any questions or thoughts you would like to discuss please get in touch.

Watch the video.

Rubber Moulding Process Comparisons

Compression Moulding Diagram

Rubber moulding process

There are various rubber moulding processes available.  At DP Seals we believe that in most cases there is no need to go to full injection mould tooling and its typically high process control costs. Let’s take a closer look at each rubber moulding process in turn.

Compression moulding

The rubber material is placed in an open, heated mould cavity. The mould is closed and pressure applied to force the material into contact with the mould area. Heat and pressure are maintained until the moulding material has cured. This is shown on the diagram below.

Compression Moulding Diagram

The compression moulding process is useful for small to medium volume, straightforward and precision components, particularly where metal parts are required. It is also great for expensive materials like FFKM / perfluoroelastomers as there is very little wastage and it is the lowest cost tooling option.

 

Transfer moulding

The amount of moulding material is measured and inserted to the transfer moulding in, what is called, a transfer chamber. Once the raw material is in the chamber it is forced through runners and into the mould cavity or cavities. The mould remains closed until curing has taken place.

Transfer Moulding Diagram

The transfer moulding process is a great technique for high quality, precision and intricate part designs in larger volumes. It is also particularly useful where less flash is required.

 

Injection Moulding

Components are produced by injecting raw material into a mould. Material for the part is fed into a heated barrel, then mixed and forced into a mould cavity.

A diagram of the injection moulding process

This extremely versatile process is useful for varied sizes of components. However there are higher set up and tooling costs compared to transfer or compression moulding so it is ideal for high volume production of the same part where the per-unit cost can be reduced.

 

In summary

The combination of specialised compression and transfer moulding we offer allows us to cater for both high and low volume custom solutions achieving the excellent precision and quality for which we are known.

As outlined previously injection moulding is not something we offer but we’ll happily recommend a supplier should this be the best process for your particular requirements.

Rubber Moulding Quality Tips

Interfacial seals

Rubber moulding quality considerations are a significant area to be aware of when designing custom rubber seals, gaskets or mouldings so here are some top tips for your consideration. They are based on speaking with engineer customers and DP Seals 40 plus years experience and expertise in the custom rubber seals, gaskets and mouldings business.

TIP 1: Think about and prioritise the different aspects of quality before talking with your manufacturer

Prioritisation is key and one of the best tips I can give design engineers is to really think about what they mean by quality before discussing this with their manufacturer. Quality could mean less flash, split line, integrity, surface finish, appearance or even rubber mix. Prioritising your requirements will really help in discussions about material selection and technical considerations.

TIP 2: Understand where you do need extra quality as well as where you don’t!

Following on from the previous tip I think it’s important to review the overall technical elements of the part like fit and function. Review elements such as hardness, material choice, tolerance criteria, surface finishes and feed point positions to build a strong picture of where you do and don’t require extra quality.

Tip 3: Closely consider the capability and credentials of your manufacturing partner.

A custom made rubber moulding can sometimes really push the boundaries with, for example, the need for tiny holes, radius or lip features. All of these details are very often critical to how the component functions in application and this may necessitate the requirement for no ‘flash’, ‘feed’ points or ‘split’ lines in these areas.

Thoroughly consider the toolmaking, moulding, prototyping, manufacturing, quality and certification standards of your manufacturer.  At DP Seals, for example, it is our patented ‘transfer’ moulding system and first class approach to quality that makes many of the demanding requirements we’ve described possible.

TIP 4: Get your manufacturing partner involved in the process as early as possible

The most important thing for a manufacturer is to have the opportunity to be involved early in the process. At DP Seals, as a team with over 40 years experience we can add real value at this stage through our expert knowledge in material selection, technical experience, prototyping and helping with all the points we’ve made in this article.

Summary

In this article we’ve touched on some of the key things engineers should consider in respect to quality when designing custom rubber, seals, gaskets or mouldings. We’ve mentioned:

  • the importance of prioritisation
  • thinking about different quality requirements for different aspects of the part
  • sharing what you don’t need as much as what you do need
  • choosing a manufacturer with the required credentials and capabilities
  • involving your manufacturer early in the process

Of course we’ve largely written about quality in respect to finish of the part in this article but we like to consider quality throughout the whole process. From initial discussions through to your manufacturing partner checking that you’re happy with the solution after receipt of the parts. Quality should run throughout.

It’s also important to remember that quality is just one consideration and shouldn’t be seen in isolation. Every part is different with its own unique features.

Get in touch with us now to discuss your requirements further.

Rubber Friction

Fluorinated piston seals

Rubber Friction and Slip

Design engineers often come across the challenge of having to reduce rubber friction, or increase the slip, of a rubber moulding. 

Applications

Typically some of the reasons for reducing rubber friction include: 

  • Stopping pieces sticking together 
  • Helping stop compressed rubber sticking in grooves and maintaining the longevity of rubber parts in airtight seal applications
  • Reducing activation force 
  • Reducing wear 
  • Helping a component easily slip in place

Processes

Reducing friction and increasing slip can be achieved in a number of ways in synthetic rubbers :

Coatings and additives 

Soap, graphite, PTFE and castor oil are well known lubricants that help reduce the surface friction of rubbers. Dry PTFE powders are very effective as an additive in many different rubbers and fluoroelastomers. When used as an additive or coating PTFE has the benefit of helping increase the life of rubber mouldings by reducing surface wear and improving surface properties.

Another example of this approach is self-lubricating silicone. The silicone is pre-mixed with a lubricant which, after vulcanisation, migrates out to the surface of the rubber. The silicone and amount of lubricant can be adapted to suit requirements. The surface friction of silicone can also be lowered by applying a micron thick, solvent based, curable coating. When cured, the coating is completely dry and non-migrating.

Fluorination and Chlorination

It is also possible to change the surface friction of cured moulded rubber by the process of Fluorination or Chlorination. Both processes can be carried out on any size or shape of parts that fit the treatment chamber and rely on a chemical reaction to change the rubber surface properties rather than coating the rubber itself. 

Using the Fluorination process products are exposed to a mixture of Fluorine gas and Oxygen which causes the highly reactive fluorinated gas to swap a portion of the hydrogen atoms on the rubber surface with fluorine atoms. The amount of surface change is controlled by increased pressure and time in the chamber and the mixture of Fluorine and Oxygen gas. Whilst the properties and dimensions of the rubber remain completely unchanged it is the surface energy and polarity that are influenced by the fluorine, and these effects are permanent.  

Chlorination is a similar process whereby rubber is exposed to a Chlorine solution for varying lengths of time, causing the chlorine gas to swap a portion of the hydrogen atoms on the surface with Chlorine atoms. This has the effect of reducing surface friction, improving appearance and can also  lower tensile strength and extensibility, more so on synthetic than natural rubbers.

Below you can see the friction coefficient for untreated and fluorinated EPDM parts compared with PTFE.

EPDM Fluorination Chart

Summary

Elastomer parts can benefit enormously from these types of treatments to increase surface energy, polarity and enhance adhesive receptivity and wettability. The greatly reduced friction coefficient of rubber can reduce drag and make part assembly much easier.

The processes can be ideal for small or complex rubber components and can deliver consistent and repeatable improvements to the surface properties across all edges, angles, openings and holes.  DP Seals have vast experience in reducing rubber surface friction and increasing slip so if you have an application which might benefit from these processes why not give us a call.