Bonding Rubber to Metal
What is rubber-to-metal bonding?
Rubber-to-metal bonding is exactly as the name suggests, mechanically bonding rubber to a metal component. This happens during the moulding process. The material is “bonded” to another part when it is chemically prepared, attached or encapsulated as a part of the vulcanisation process, to another item. This is very useful when designing components where both the properties of the metal and the rubber are required in a single component.
Which metals and rubbers can be bonded?
Today, it is possible to bond almost any elastomer to any substrate, providing it can withstand the heat and pressure of the rubber moulding process. Each material has a different chemical composition which should be taken into consideration when selecting the bonding agent and process employed.
The most important job is to determine the best metal type and grade for the application, as well as the optimal type of rubber to specify for the application.
Metals that can be bonded to rubber are:
Rubbers that can be bonded to metal are:
The Rubber-To-Metal Bonding Process
Bonding metal to rubber is a very popular practice as the metal and rubber combined create an even stronger, more durable and versatile material. This new and improved material can be used to withstand the harshest of conditions.
Preparing the Part
Preparing the metal part correctly is vital for achieving maximum bond strength. 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 for more bonding surface area.
- Treating the surface with chemical agents such as zinc phosphate or ammonium persulphate.
- Drying the component.
Application of the Primer and Bonding Agent
There may only be a small window to apply the primer due to the oxidation of the metal. 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. This is to ensure that the bonding agent thickness and percent solids are sufficient in providing a strong bond. If the blend is too viscous, it can result in the bonding agent not properly setting up correctly. If the viscosity is too low, 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 appropriate to the design:
- 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 we will either apply one or two coats of primer/bonding agent.
The Moulding Process
Now that the metal part has been cleaned, prepared and the primer and bonding agent applied, the rubber can now be moulded onto the metal part. This can be applied by any of the injection, compression, or transfer moulding methods. The only difference here is that the metal part is placed in the mould before the moulding methods is carried out. Check out our article on rubber moulds to gain a better understanding of the different moulding methods.
What Are the Typical Applications for Metal-To-Rubber Bonding?
Metal-to-rubber bonding is suitable for many applications, including:
- The adhesion of rubber to metal plates within industrial processes.
- For automotive applications, including the attachment of rubber to metal engine mounts.
- Within hydraulic and pneumatic applications.
- To coat medical devices, such as instrument handles, to ensure cleanliness and comfort.
- In the manufacture of electrical appliances and other industries, including bulkhead seals, rollers, connectors, hoses, valves, and insulators.
Why Use Rubber-To-Metal Bonding?
Manufacturers in several industries rely on rubber-to-metal bonding for some of the components they manufacture. There are a wide variety of reasons for this, including:
- In the production of parts that require the flexibility of rubber and the stability of metal.
- To combine several parts into a single assembly part.
- To ensure the longevity of critical functions with stronger adhesions than a traditional adhesive connection.
- To enhance soundproofing and vibration control in an industrial environment.
- To seal and protect against solvents, seawater, boiling water, and other abrasive environments.