Copper Corrosion by Lubricating Grease

Description

Evaluates the corrosivity of lubricating greases toward copper and its alloys, preventing the destruction of bronze and brass parts in bearings.

Even the best extreme-pressure grease can become poison for your equipment if it corrodes non-ferrous metals. Bearing cages, bronze bushings, and guides often suffer from the aggressive action of active sulfur additives that manufacturers add to protect steel. Copper corrosion analysis for greases according to the ASTM D4048 standard at the RENA laboratory is a mandatory safety test guaranteeing that your chosen product is chemically neutral and will not lead to the crumbling of bronze mechanism parts. The test is an adaptation of the classic «fluid» test for thick greases. A reference strip of pure electrolytic copper is carefully polished to a mirror shine, washed, and completely immersed in a beaker tightly packed with the lubricating grease under test (to avoid the formation of air pockets). The beaker is placed in a thermostat and held at a strictly set temperature (usually 100 °C) for 24 hours. Under heating conditions, aggressive compounds from the grease enter into a chemical reaction with the copper. After the test is completed, the grease is carefully washed off the strip with a solvent. The lab technician visually compares the color change of the copper strip with the standardized lithographic scale (ASTM Copper Strip Corrosion Standard), which ranges from a slight tarnish to a black sulfide deposit.