The Rubber-to-Metal Bonding Process
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 more bonding surface area.
- Treating the surface with chemical agents such as zinc phosphate or ammonium persulphate.
Application of the Primer and Bonding Agent
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 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 done 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.