Synchronous belt wheel black metal heat treatment is a commonly used method, the principle is to make the metal surface to produce a layer of oxide film, to cut off the air, the purpose of rust. The surface of the steel parts black finish, also called blue. Bluing is a kind of chemical surface treatment, its main function is formed in the surface layer of dense oxide film, prevent the workpiece on the corrosion rust, improve the wear resistance, it is a kind of surface treatment, not for any impact on the internal organization, it is not heat treatment, quenching and a fundamental difference between the two. Black steel synchronous belt wheel processing technology, mainly completed by the following process steps: cleaning: skim: workpiece must be completely immersed in the degreaser; Degreasing fluid concentration of 12 - ph 10-14, processing time Every 3 to 30 min 5 minutes shaking up and down several times, solution concentration below ph12 supplement to take off the powder. Water for pickling: ph 2 - acid liquid concentration 4, 5 - processing time Black: 10 minutes pool fluid concentration ph 2. 5 - 3. 5, 10 - processing time 12 minutes, finally is dry and oiling the steps. Synchronous belt wheel black when the required temperature tolerance is larger, probably between 135 and 155 ℃ can get a good surface, just needed some length of time. In practice, it is important to note the quality of the workpiece cleaning and degreasing before dark, and the passivation oiled after dark. Black quality often change because of these processes.