Heavyweight Phosphating of Rubber-to-Metal Bonded Products

Abstract

The initial objective set for this project was to identify a range of anti-corrosion finishes for rubber-to-metal bonded products, that would withstand the periods of exposure to the salt spray test required by the sponsoring manufacturer's customers. Preliminary research showed that the range of finishes used were capable of meeting the customers requirements but the phosphate and sealant finishes used for over 45% (volume) of production were failing to meet the requirements imposed on them. Having determined that the phosphate and sealant finishes could not easily be replaced the objective became to ensure that these finishes achieved their potential resistance to the salt spray test. A literature survey is presented, covering the salt spray test and the heavyweight phosphating of mild steel. The work then concentrates on three areas, the preparation of the metal surfaces for phosphating, the phosphating solution used and the phosphating plant used. Preparation of the metal surfaces for phosphating was found to be inadequate. The work of identifying and installing a machine capable of the required cleaning action is described. Organic materials leached from the rubber sections of the products were detected in the phosphating solution. It is suggested that these materials interfered with the phosphating reactions. The work of identifying and introducing a more suitable phosphating solution is described. These changes resulted in the phosphate and sealant finishes meeting the customers salt spray resistance requirements, and the performance of the finishes in an atmospheric corrosion test also show a corresponding improvement. To ensure the consistent production of the required quality of phosphate and sealant finishes the purchase ofa fully automatic phosphating plant is recommended. The sponsors attitude to anti-corrosion finishing is discussed with reference to the business environment in which the company operates.