Full definition
Rubber-to-metal bonding is a critical process in industrial applications that involves the permanent adhesion of pre-vulcanized rubber to metal substrates. This multi-step adhesive system is essential for situations where co-vulcanization, or bonding during the molding process, is not feasible. The process begins with meticulous metal preparation, where thorough degreasing is performed using solvent wipes or vapor degreasing methods. Following this, grit blasting is executed to achieve a surface profile of SA 2.5 / NACE 2, utilizing 16-30 mesh alumina or steel grit. This step is vital, as the quality of the surface profile directly influences the bond strength between the rubber and metal components.
Once the metal surface is adequately prepared, the next step involves the application of a primer within four hours of blasting to prevent re-oxidation. This primer chemically interacts with the metal oxide layer, enhancing the adhesion capabilities of the subsequent adhesive layer. The adhesive, often referred to as the cover coat, is then applied and must bond effectively to both the primer and the freshly buffed rubber surface, which exposes reactive rubber for optimal bonding. The assembly phase involves pressing the rubber onto the metal with consistent and firm pressure to ensure a uniform bond.
The curing phase can either take place at room temperature over a span of 24 to 72 hours or be accelerated through elevated temperature curing methods. It is crucial that the bond strength achieved during this process exceeds the rubber's tear strength, indicating that failure will occur in the rubber material rather than at the bond line. Leading adhesive systems used in this process include those from LORD Corporation, such as the Chemlok and Chemosil products, Henkel’s Loctite and Bonderite, and Rema Tip Top solutions. Testing for bond strength is conducted in accordance with ASTM D429 standards, ensuring reliability and performance in various applications such as rubber lining of pipes and vessels, repair of anti-vibration mounts, roller re-covering, and conveyor drum lagging.