The Tru Temp low-temperature black oxide process from Birchwood Casey uses no EPA-regulated chemicals to produce a black finish without the drawbacks of high-temperature black oxide. The system operates at 200°F and produces a durable, satin black magnetite coating, 20 millionths thick (0.5 micron), with no effect on material hardness or tensile strength, the company says. The finish can withstand as much as 100 to 200 hours of neutral salt spray (ASTM B 117) or several hundred hours of humidity (ASTM D 1748). It is Mil Spec compliant and offers corrosion protection for both part storage and shipment in corrosive atmospheres, including ocean shipment.
A two-stage oxidation process enables the use of milder chemicals and lower temperatures than common black oxide. Conventional 290°F hot oxide tends to splatter and boil over, making it dangerous to operate, and other phosphate processes can cause hydrogen embrittlement and etching of the metal surfaces. This system uses mild alkaline chemistry that does not embrittle metal or create salt bloom in and around part-recessed areas, the company says.
Other advantages of the system include decreased processing time and operating cost. Small parts can be processed in bulk loads or larger parts finished on racks. Most existing tank lines can be retrofitted for the system, and new process lines are available. Solutions contain no EPA-regulated chemicals, and waste treatment equipment usually is not required. In most areas, rinse waters are sewerable as non-hazardous discharge.