Improving Atmosphere Homogeneity in Heat Treatment Furnace with High-Speed Gas Injectors

摘要

In Heat Treatment processes mechanical fans are commonly used to circulate the atmosphere gases and to maintain furnace atmosphere and temperature homogeneity. The fans are inefficient and need an inner liner and special lid which takes up valuable loading space. Inside the furnace, the gas velocities frequently are too low or non-uniform leading to, e.g., an irregular carburizing case profile. Moreover, fans are prone to frequent failures and are expensive to maintain. The CARBOJET~R technology developed and patented by Linde, is a CFD optimized system, which uses the free energy available from nitrogen to stir the atmosphere and maintaining its uniformity. It has no moving parts. Available higher nitrogen pressure is utilized through specially designed gas injectors to circulate and maintain atmosphere inside the furnace. This results in improved circulation, atmosphere uniformity, and time savings in surface reactions like carburizing, carbunitriding, etc. The paper illustrates the effectiveness of the CARBOJET~R system with reference to a pit furnace used to carburize of C15 material (0.15% C) at 925°C. The modelling of the furnace both with a fan and with various high-speed gas injection options was an important step prior to practical trials. This modelling and the practical results showed significant savings can be made while improving quality. Simultaneously, it can increase loading capacity and reduce resources, energy cost and maintenance cost. Both temperature uniformity and carbon profile were improved using the high-speed gas injection system compared with the fan. The overall scatter in carbon content was reduced by a third by the use of high-speed injectors. The paper also presents results from a number of existing CARBOJET~R installations.