tailieunhanh - Handbook of Lubrication Episode 2 Part 1

Tham khảo tài liệu 'handbook of lubrication episode 2 part 1', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Volume II 349 calcium and ferrosilicon as deoxidizing materials. A resulting low-melting ternary inclusion then spreads over the tool face in high-speed machining and acts as a diffusion barrier. Coated Tools In the late 1960s crater formation was found to be retarded by the vapor phase deposition of a very thin in. 5 pm coating of TiC on a steel cutting grade carbide tool. It was later found that such coatings also tended to reduce the wear-land wear. The TiC coating provides a material in contact with the iron surface of the chip that is less likely to give up its carbon than WC. Use of such a coating avoids the tool-weakening effect associated with relatively large additions of TiC or TaC to the tool in bulk. Tools have also been coated with A12O3 and this material is thought to function as a diffusion barrier which is one of the mechanisms believed responsible for the success of the specially deoxidized steels. In addition to TiC other coating materials is use include TiN HfC and HfN. All of these appear to provide a more stable material relative to decomposition in the presence of hot iron and at the same time act as diffusion barriers. A TiN coating gives lower tool-face friction than TiC when cutting a low-alloy steel. Although TiC is more stable than WC there will be some decomposition of TiC. The carbon that is released will be absorbed by the low-carbon steel thus strengthening it and causing an increase in tool-face friction. TiN does not appear to be as good a diffusion barrier as TiC but when it decomposes the nitrogen released does not have as great a strengthening action on the steel as does carbon. This results in lower tool-face friction for a TiN coating than for a TiC Tools have also been coated with A12O3 which also acts as a diffusion barrier. The subject of tool coating is a rapidly developing and further important developments are expected. Cutting Fluids Cutting fluids have a dual role cooling and lubrication. In high-speed