Failure rubber/cement

RC - Rubber/Cement failure failure at the rubber to cement (adhesive) interface. 

Rubber/cement (RC) failures indicate that the weakest point in the bonded part is at the interface between the rubber and adhesive. These failures are characterised by a relatively glossy and hard bonded surface with little or no rubber present. Common causes of RC failure are the incorrect choice of adhesive, insufficient dry film thickness of adhesive, failure to properly agitate the adhesive to achieve a uniform dispersion prior to application, pre-cure of adhesive caused by excessive dwell time in the mould cavity before introducing rubber, low mould pressure, undercure of the part, migration of plasticisers and other ingredients from the body of the rubber to the rubber/adhesive interface or contamination of the surface of the adhesive coated part. 

In many cases, combinations of the above failure modes appear on the same part. For instance, a failed part may show some R failure, as well as RC and CM failure. Steps must be taken to increase the proportion of R failure while reducing the other, unwanted failure modes. Bond failures are usually given in terms of the percent of the bonded area that contains a certain failure mode. For example, a failed part with the designation 65R, 15RC, 20CM means that in the bonded area, 65% of the bond surface shows failure in the rubber, 15% shows rubber/cement failure, and 20% shows cement/metal failure. 

RC = failure at the interface between the rubber and the cover cement. 

Cement/primer (CP) failures are characterised by the appearance of the primer on the bonded surface. Usually the adhesive and primer are different colours to allow for easier identification of both layers. CP failure is usually caused by contamination of the primer surface before application of adhesive, migration of plasticiser from the rubber into the adhesive/primer interface, insufficient drying of the primer film before application of the adhesive or by incompatibility between primer and adhesive. 

The 1" X 5" bonded samples were peeled at 180° on a Scott Tester or similar machine at 2 Vininute. The peel value was recorded and the type of failure was noted [e.g., 80% R, 15 RC, 5 CF is failure within the stock (80%), some failure between the rubber and the cement (15%), and a slight amount of failure (5%) between the cement and fabric]. 

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