Views: 0 Author: Site Editor Publish Time: 2020-04-08 Origin: Site
This paper introduces the common processing methods of engine valves, explains the application characteristics and applicable scope of each processing technology.
The valve is a key basic part for sealing the intake and exhaust ports during the engine's working process. It is used to block the air flow channel and control the gas exchange of the engine. The valve working place is in a high-temperature oxidizing and corrosive atmosphere, bearing repeated impact loads, and also under the combined effects of thermal stress and gas pressure during combustion. Valve materials are made of martensitic or austenitic heat-resistant steel and high-temperature alloys.
Different valve manufacturers have their own valve processing technology, which is related to factors such as production equipment, production line layout, processing technology and processing experience of the same type of valve. This article will introduce the common processing technology of valves.
Typical valve structures are divided into integral martensitic valves, integral austenitic valves, and friction welded valves. The main difference between these three valve processes is the different stages of the valve blank. The machining process after the blank is basically the same.
The overall martensitic and austenitic valve blank process is relatively simple, specifically: blanking → flat two end surfaces → electric upsetting → heat treatment and straightening. The heat treatment of martensitic valve blanks is quenched and tempered, while the heat treatment of austenite valve blanks is solid solution aging or aging.
The mechanical processing technology after the blank is formed is quite different among valve manufacturers, but the processing methods used for each part of the valve are relatively consistent in the industry. The valve stem grinding machine mainly uses two machining methods, turning and grinding, and different manufacturers have different design ideas for valve machining. This article mainly describes several commonly used processing technology ideas.
(1) High frequency quenching after cutting the total length. Valve manufacturers' machining equipment is arranged according to the production line, and the high-frequency quenching, chrome plating and nitriding processes are not synchronized with the production cycle of machining equipment. The machining section and (semi-) finishing section machining processes make up as much as possible the process layout of the production line.
(2) After roughing is completed, induction hardening is performed. In the roughing section, the valve disk outer circle, disk end face and chamfering are finished to the finished product. The valve neck, stem and end face are processed for the first time, and then high frequency quenching is performed. After the valve is quenched, it enters the semi-finishing section.
(3) After finishing (semi) finishing, then chrome or nitriding. For some nitriding valves, it is required not to grind after nitriding, only the rod part needs to be polished after nitriding, and then the valve is nitriding after finishing. Some CNC valve cut off machine manufacturers' chrome plating process is outsourced, and chrome plating is often used after finishing. Valve flaw detection procedures are often placed in the semi-finished or fine-finished section.
(4) Some valves require hardening of the end face of the rod after nitriding or grinding the tapered surface of the rod end after nitriding, and then the valve is finished after nitriding. Some chrome-plated center-less valves require higher accuracy. To ensure valve accuracy, the valves are required to be finished after chrome-plating.
