Rubber to Metal Bonding

Bonding metal to rubber is usually done in one of two ways. Either through the application of an adhesive (glue) or vulcanization (bonding).

Gluing metal to rubber is a secondary, manual process for joining rubber to a metal insert. It is a good solution in specific situations where bonding is not possible either for cost or practical considerations.

Vulcanized bonding is the term used to cover the process of chemically bonding an elastomer to a metal surface that has been pre-coated. It is used for applications that require the flexibility of rubber and the strength of the metal. Popular types of metal for this process include aluminum, steel, iron or aluminum castings.

The Process

1. Glue

This is done by applying an adhesive to a molded elastomer part and securing it to a metal item.  This process is effective for specific applications, but not all.  The bond strength is determined by the adhesive and is not as good as a molded solution. This method is also fairly labor intensive as it is done as a secondary process and requires multiple touches by production personnel.

There are some instances where gluing rubber to metal as a secondary process is a better solution. In instances where the metal is a casting that has not been precision machined, the tolerances are not tight enough to place the inset into a mold and clamp it under pressure. Additionally, if the end-product will not be exposed o harsh weather, submerged in water or exposed to chemicals, gluing rubber to metal may be the most efficient solution, as well as being a cost-effective option.

The technique can also be used when the metal inserts included welded components. If precision welding is not a workable option from a cost perspective, the variations may mean that the metal insert does not fit correctly into the rubber mold. This would lead to damage of the mold or the metal inserts.

2. Bonding

Rubber to metal bonding is a means by which the rubber is mechanically bonded to a metal insert during the molding process.

This process is accomplished by first preparing the insert/metal item.  The metal must undergo a degreasing or chemical or grit blast cleaning system to rid the parts of any contaminants.  Once this is complete, a heat activated bonding agent is applied either by spraying, dipping or by hand. There are strict protocols in place to ensure that the thickness of the bonding agent is controlled throughout the process.

Once prepared, the metal inserts are placed into each cavity of the mold, and the molding process is performed. The bond vulcanization happens at the same time as the cure of the elastomer as bonding agents have been specifically designed to work optimally with the rubber processing. This allows the rubber to bond directly to the metal. The strength of the bond is maximized under pressure in transfer, injection or compression molds.

Rubber to Metal Bonding: Glue vs. Bonding

Vulcanized rubber to metal bonding is typically the stronger, more effective solution. Especially in environments that expose the bond to stress such as extreme temperatures or chemicals.

There are specific instances where gluing rubber to metal is the better option, this occurs in cases where the size and shape of the metal insert is not uniformly consistent, and the variations could cause damage to the mold or the inserts themselves.

Applications

Gluing rubber to metal is an effective solution in a number of instances particularly where the end product will not be regularly exposed to harsh weather elements or chemicals.

Vulcanized bonding is used in a number of applications that require the added stability of metal as well as the flexibility of rubber. In the automotive industry, the technology is used for components such as small mounts for motors and large suspension parts. It is also used for industrial applications such as adhering rubber to metal plates, door seals, hoses, valves, and insulators. Specialized solutions enhance sound-proofing and vibration control.

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