These top tips on rubber moulding tolerances are based on speaking with design engineer customers and DP Seals 40 plus years experience in the custom rubber seals, gaskets and mouldings business.
Tip 1: Consider the use of a custom rubber seal, gasket or moulding where you need to build in more dynamic functionality or hold precise tolerances.
Using a standard part in a custom design or bespoke application can often restrict the products ability to work at its very best. Understanding the demands, size of the component and space that the seal, gasket or moulding needs to work in all becomes very important.
Tip 2:Don’t bias tolerance on drawings towards metallic, machined or turned parts. Rubber is quite different!
Custom design offers some real advantages over standard components but what we often find is that there is a default tolerance on drawings that can be biased toward metallic, machined or turned parts. Rubber is quite different and due to its nature as a material this must be taken into account. For example – shrinkage from the mould tool cavity.
Tip 3: Use a manufacturer with in house tooling and moulding
At DP Seals we fundamentally use a closed cavity system of moulding. This allows us to control material very well and therefore maintain tight tolerances of up to two thousandths of an inch or 50 microns.
Tip 4: Only specify tight tolerances where you actually need them.
Specifying tight tolerances for all parts of the design can create more cost and complexity when it might not be required.Only specify tight tolerances where you really need it.
Summary
We’ve touched on some of the key things design engineers should consider in respect to tolerances when designing rubber, seals, gaskets or mouldings. We’ve mentioned:
Considering custom designs where you need to build in more dynamic functionality or hold precise tolerances
Considering things like shrinkage from the mould tool cavity in your drawings when using rubber
Using a manufacturer with in-house tooling and moulding to save time and improve communication
Only specifying tight tolerances where you actually need them.
If you have any questions about this post please get in touch with our rubber technologists.
At DP Seals we are experts in the rubber to metal bonding process and have vast experience in this area. Let’s take a look at our process in a little more detail.
5 step rubber to metal bonding process
Part composition and geometry
Preparation of the part
Application of the bonding agent
Moulding
Testing
Let’s take a look at each of these in turn.
1. Part composition and geometry
The choice of metal depends on the strength and durability requirements for the part being produced. Steel is commonly used, but due to weight factors, aluminium is increasingly common. Almost any metal can be bonded – so please speak with your manufacturer early in the process for advice.
These rubber to metal bonded seals manufactured for Hope Technology are a vital component in their high performance braking systems for sports bikes.
Once you have specified the geometry of the metal component, along with the grade and type of metal, engineers will evaluate the approach. It is at this point that they will also make recommendations on the rubber compound to be used.
Considerations will include the cure characteristic of the rubber to ensure it satisfies application dynamics like fatigue, creep and maintenance and also the bonding environment within the cure cycle. As the rubber filling the mould has very low viscosity, the geometry of the part can present challenges. The mould must enable a positive shut-off or clamp-off on the metal component to reduce the amount of flash.
Stamped or punched metal components may also present problems, as the process does not always hold tight tolerances reliably. The component can only be procured once all parties agree on the optimum material.
2. Preparing the part
Preparing the part for maximum bond strength is a key consideration. It is here that the complex chemistry of metal and rubber interaction and the effects of the moulding process itself must be addressed. Metals may be treated by mechanical or chemical means and preparation includes a combination of the following steps:
Cleaning the component with a solvent to eliminate any remnants of machine oil or grease
Aqueous degreasing to meet stringent environmental standards
Treating the surface through grit blasting and other physical abrasion to allow more bonding surface area
Treating the surface with chemical agents such as zinc phosphate or ammonium persulphate
Drying
3. Application of the primer and bonding agent
Miniature plunger, rubber to metal bonded for sampling and analysing sea water samples on mini-sub drone.
Oxidation of metal means there may only be a small window to apply the primer. Most bonding agents are diluted with a reagent grade of solvent which makes it easier to spray or dip. It is critical that the correct mixing ratio of bonding agent to solvent is developed to ensure that bonding agent thickness and percent solids are sufficient to provide a strong bond.
If the blend is too viscous, it can result in the bonding agent not properly setting up correctly. Too low viscosity and it can be swept off the component due to the high-pressure rubber flowing into the cavity.
Application of the bonding agent includes a combination of the following steps:
Masking a section of the component to cover everything except the specific area where rubber is to bond
Applying heat-activated primer and bonding systems through dipping, spraying or by brush
Baking the primed component to ensure it is dry and set up for moulding
Depending on the rubber material being used either one or two coats of primer/bonding agent will be applied
4. The moulding process
This rubber to metal bonded seal plays a vital role within the mechanism of an in-flight refuelling system
This is the most important part in the process and there are various moulding techniques available. At DP Seals, we believe that in most cases there is no need to go to full injection mould tooling and its attendant high process control costs.
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 levels of precision and quality for which we are known.
We have also been granted a UK patent for our unique tooling and moulding system which results in drastically reducing and even removing any potential for flashing. This enables us to produce small, close tolerance, flashless mouldings that no-one else can match.
5. Test with prototypes or finished parts
We conduct testing to see how the parts react when stressed through compression, tension, shear or torsion. The only testing methods for determining bond strength involve destroying the part and tests such as hand peeling or stripping are common for visual performance results. Machines such as tensile testers are more scientific and will measure the amount of force required to break the bond.
Summary
Cutaway, showing the details of this rubber to metal bonded gasket for the motoring industry.
Every step of the rubber to metal bonding process must be expertly conducted to develop a bonded component that is stronger than the sum of its parts. DP Seals has over 40 years’ experience and is a specialist in the field so we are ideally placed to help you. From in-flight refuelling systems to a 3mm rubber to metal bonded plunger seal used to sample ocean water, we have the adaptability and innovative approach to help achieve your goals.
For further details including ‘Why use rubber to metal bonding?’, ‘Typical applications’, ‘The importance of early communication’ and some ‘Top tips’ download your free Rubber to metal bonding guide right now.
Get in touch
If you’d like to discuss your project feel free to get in touch and see how we can help you reduce cost and improve quality through the combination of the following value-added services:
When it comes to comparing rubber vs metal seals for any joint solutions some of the benefits that rubber can provide are as follows:
Improved resistance and longer cycle life. Rubber joints can exceed 50,000 cycles vs. 2,000 cycles of metallic
No vibration fatigue. Rubber joints act as a dampener.
This dampening can also help to reduce noise.
No danger from stress corrosion. Metallic joints are subject to irregular cracks from stress and corrosion.
Resistance to external damage.
No corrosive electrolytic action. Metallic requires costly gaskets.
Shock resistance. Rubber absorbs shock well.
More flexibility in less space.
Simultaneous axial and lateral deflection.
No internal sleeves required.
Lightweight. Rubber has obvious advantages here.
Very low movement forces required.
High resistance to abrasion and erosion.
Compound stability where extreme hot or cold temperatures are experienced.
Get an unbiased view – we promise!
When making these decisions about your requirements DP Seals Technical Team are always on hand to help advise if rubber is better suited, or not, to your specific application. Simply get in touch via our Contact page or email info@dpseals.com with the details of your specific application and one of our team members will be happy to help you.
The versatile properties of silicone enable it to be used in a wide range of industries including medical, aerospace, automotive, electronics, energy, subsea, food and more.
Here are some of the characteristics that make it such an excellent material.
Thermal stability and insulation
Silicone can operate effectively in both extremely high and low temperatures retaining its flexibility in the latter. This makes it suitable for many aerospace and subsea applications.It is also flame retardant and offers excellent electrical insulation making it a good choice for instrumentation and electronics.At DP Seals we can also make silicone conductivewith the use of carbon nanotube technology,silver loaded particles and other additives.
Resistant, naturally inert, and non-toxic
In addition to excellent temperature resistance silicone can be formulated so that it is also resistant to many other materials including bases, acids, chemicals, oil and fungus. Its chemical and biological inertness make it an excellent choice of material, particularly in the medical industry where it remains non-reactive to chemicals and human tissue. It is also ideal for many other industries where rubber mouldings are required to operate in hazardous environments.
Non-porous
Porosity is obviously of major concern for the medical industry. Porous rubber materials that trap bacteria, fluids or other microorganisms can cause infection or irregularities in the surface of devices which impact on performance. A major benefit in this respect is that medical grade silicone is non-porous.
Silicone sterilisation
Compatible with FDA regulations, silicone can withstand electron beam, gamma radiation, ethylene oxide, steam autoclaving and dry heat sterilisation methods.
Silicone properties moulding versatility
Silicone can be manufactured as translucent or can be colour matched to a particular pantone or RAL code, or even glow in the dark. It is easy to mould and customise, making it a great material for innovative designs and custom rubber seals, gaskets and mouldings.
Dynamic
Silicone is also an extremely dynamic material with mechanical properties for excellent reliability and durability.
To find out more about the properties of silicone and its common applications visit our silicone page.
Common silicone materials
Here are a couple of other useful links to common silicone materials we use:
At DP Seals we are material specialists. We produce custom rubber compounds enabling us to supply materials to your exact requirements. Please get in touch with our materials technologists so we can discuss your needs.
In the metal to rubber bonding process almost any substrate can be used provided that it can withstand the heat and pressures of the rubber moulding process. However, each metal has a different chemical composition that can react to the type of rubber being used.
Expert advice on metal to rubber bonding
An important step is to determine the best metal type and grade as well as the optimal type of rubber to specify for the application. DP Seals can advise on the best rubber material and develop custom compounds with additives to aid metal bonding.
Brassed off
One problematic material is brass, which contains lead that chemically counteracts rubber bonding. The softer, free-cutting brass materials have higher lead content and can be difficult to bond. Better bond strength can be achieved with the lowest possible level of lead content. Substrate preparation is absolutely key along with timely application of two coat bonding agent systems.
Custom seals offer some fantastic advantages but for many general applications standard rubber seals, gaskets and mouldings are fine. There may also be times when the up-front cost of a standard rubber part make it seem like the sensible option.
However if you’re unsure which route to take here are nine reasons for choosing custom seals as a better alternative.
1. Intricate applications
A standard product just won’t do. For example, when the moulding is a major part of the end product, such as the rubber boot for the sub-sea cable connector pictured above.
2. Greater sealing surface
Custom seals can be designed with multiple point contact offering greater seal protection.
3. Lower friction
Design custom rubber parts with less ‘squeeze’ to maintain a more effective seal and resulting in reduced friction. This can also be combined with fluorination techniques to reduce flash.
4. Longer life
Customised materials and design can result in seals lasting longer.
5. Reduced maintenance and operational costs
This resulting longer seal life can lead to lower maintenance and operational costs.
6. Quality of finish
Tooling is designed to ensure finish and the ability to hold tolerances as required, including flash removal techniques.
7. Environmental
Criteria like temperature, pressure, liquids, contaminants, exposure to processes, light, out-gassing and just plain old water may necessitate a custom solution.
8. Regulations
Occasionally, the introduction of new regulations will extend the role of the seal. For example, a seal originally designed to prevent ingress of dirt and fluids into a ruggedised electronics unit can be enhanced to shield against EMI.
9. When you’re not even sure what rubber part you want!
Sometimes the requirement for a seal, gasket or moulding is only recognised late in the process or perhaps you know you need a seal or moulding but aren’t exactly sure how it could work.
Whatever your situation reach out and get in touch. We can help.
These videos provide useful tips, advice and information about the rubber moulding process and DP Seals.
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