Copper Strip Corrosion in Lubricants

Description

Evaluates the corrosivity of oil and its sulfur-containing extreme pressure additives towards parts made of copper and its alloys (bronze, brass).

Modern extreme pressure (EP) additives, rich in active sulfur, perfectly protect steel gears from welding. But this same «active sulfur» can be ruthless to non-ferrous metals: it literally eats away bronze worm gear crowns and brass synchronizers in manual gearboxes. The copper corrosion laboratory analysis (ASTM D130) from RENA is a mandatory safety test for any gear or industrial oil. This analysis guarantees that your chosen lubricant will be chemically neutral to soft metals, protecting expensive parts from blackening and crumbling. The test is an accelerated simulation of a chemical reaction at the operating temperatures of the assembly. A reference strip of pure electrolytic copper (> 99.9% purity) is used for the test. The strip undergoes a strict mechanical preparation procedure: it is polished with special silicon carbide paper to a mirror shine without a single scratch, washed with a solvent, and dried. Immediately after this, the prepared strip is completely immersed in a test tube with the tested petroleum product. The test tube is hermetically sealed and placed in a liquid thermostatic bath. The standard temperature regime is 100 °C (or 121 °C for gear oils) for exactly 3 hours. During this time, any aggressive sulfur compounds or acids in the oil react with the copper surface, forming sulfides. At the end of the time, the strip is extracted, washed, and compared against a standardized lithographic scale (ASTM Copper Strip Corrosion Standard), which consists of 13 color plaques from light orange to coal-black.