Development of Continuous, Direct Feedback Control Systems for Sintering of Metallic Components

Apelian, Diran ; Baum, Marc M.

Worcester Polytechnic Institute, MA 01609

关键词: Temperature Gradients Delubrication, Sintering, Fe Compact, Pyrolysis, Infra Red Spectra;    Feedback;    Process Control;    Delubrication, Sintering, Fe Compact, Pyrolysis, Infra Red Spectra;    Pyrolysis;   

DOI  :  10.2172/891507
RP-ID  :  DOEF241.3
RP-ID  :  FC36-03ID14464
RP-ID  :  891507

美国|英语

来源: UNT Digital Library

【 摘 要 】

N,N.-Ethylenebisstearimide (EBS) is one of the most commonlyused lubricants in the powder metallurgy (PM) industry in the sintering process. During sintering, the lubricated powder compacts are heat-treated to temperatures in excess of 1,200 °C thus fusing adjacent particles and yielding a part with improved mechanical strength. Delubrication commonly is achieved in the first zone of a sintering furnace by heating the part to temperatures in the 500-600 °C temperature range at a fixed rate and under controlled atmospheric conditions; this strategy minimizes defects, carbon contamination, and compact deformation. The de-lubricated part then enters the second zone (commonly in the 1200-1300 °C temperature range) for sintering. The third zone cools the sintered part at a desired rate to obtain the requisite micro-structural properties. Controlled delubrication is imperative towards achieving high quality parts for the following reasons: the elevated thermal gradient at the transition between the first and second zones can cause parts to expand rapidly and develop microscopic fissures (.blistering.); improper gas flows and belt speeds can lead to carbon deposition on the part and at the grain boundaries (sooting); delubrication products deposit throughout the furnace, even in the coolers, which are far removed from the preheating chamber, leading to significant maintenance costs; pollutants emitted in the exhaust stream of furnaces operating inefficiently are increasingly of environmental concern. In practice, lubricant removal is difficult to control, which often leads to reduced yields in PM manufacturing processes. Throughput is another important issue: process control ideally should lead to a delubrication cycle that yields defect-free parts in a minimum of furnace time, thereby increasing productivity and reducing the net energy consumption. Efficient process control requires rapid monitoring of suitable indicators, preferably gasphase products of delubrication. EBS thermolyzes relatively cleanly in a range of furnace atmospheres, but the mechanism governing the pyrolysis of EBS, compacted with iron powder, is not known and needs to be investigated to determine the parameters important for industrial control, as well as the optimal conditions of delubrication. In addition, a thorough understanding of the pre-sintering chemistry will enable the development of a process control sensor.