Achieving plastic/rubber bonding without adhesives

Evonik Industries

German machinery company LWB Steinl and chemical firm Evonik Industries say they are combining their experience to manufacture a rotation-symmetrical plastic/rubber composite part. Evonik supplies its polyamide 612 Vestamid DX9325 for adhesive-free bonding with EPDM, and LWB Steinl supplies its expertise in two-component injection moulding.

Wherever rubber parts must be permanently fixed or mounted, composite parts made of a hard component and an elastomer have proven their worth. For the purposes of weight reduction, the hard component that has traditionally been made of metal has been replaced in recent times by suitable plastics. These offer two further advantages: they do not corrode, and in an injection moulding process, can be efficiently formed into complex moulded parts. This gives the designer greater flexibility when designing complex components.

The bonding between hard and soft component—the decisive criterion for the long-term functioning of composite parts, especially those subject to dynamic stress—is usually achieved using adhesive agents, which are applied in additional processing steps. Protective measures are required against emissions from the solution used and the solution must also be disposed of in an environmentally friendly manner.

Evonik says it has developed various plastic-compounds, which have rendered adhesive agents superfluous. Components made of these compounds form tight and permanent bonds with suitable rubber compounds without the need for pretreatment or the application of adhesives or bonding agents. Its DX9325 grade is an approx. 40% glass-fibre-reinforced polyamide 612 compound, which has been developed specifically for plastic rubber-compound technology. It can also be co-vulcanised with EPDM rubber. As a semi-crystalline material, DX9325 features chemical resistance, for example, to fuels, oils and fats.

The composite part with EPDM can be manufactured in a single step, mostly automated procedure, similar to two component injection moulding in a single tool. There is no need for multiple handling of the components, most sources of error are avoided, and the reject rate falls.

Depending on the plant-specific conditions, therefore, cost savings of up to 30% can be achieved, say the companies.


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