How to carburize the valve seat to extend its service life？

The valve seat is a key wearing part of the diaphragm pump. It is subject to severe impact, erosion and wear during operation. Its inherent quality will directly affect the working efficiency and service life of the entire machine. The optimal service life of the valve seat is more than 1200h, but during the user's use, 40% of the workpieces cannot meet the requirements.

Valve seats have high requirements for heat treatment. In response to this phenomenon, we conducted a comprehensive analysis of the heat treatment (carburizing, quenching, and tempering) process of the valve seat and found the main reason in the heat treatment process. During the high-temperature heating process in the carburizing and quenching stages, there were problems with the fixtures and furnace installation methods for placing the valve seat, which caused the valve seat to deform during the heat treatment process, resulting in uneven hardness of the quenched layer after grinding the valve seat. , the service life is reduced and cannot meet the design requirements. It is necessary to redesign and improve the tooling fixtures and furnace loading methods of the valve seat during the carburizing and quenching stages, and add calibration tooling fixtures to ensure the uniformity of the depth and hardness of the valve seat's hardened layer, thereby increasing the service life of the valve seat.

1. Technical requirements for valve seat production

The technical requirements of the valve seat are: carburization, carburizing layer depth ≥ 2.3mm, hardness after quenching 55~60HRC. The processing route is: forging → rough turning → preliminary heat treatment → semi-finishing → carburizing → all finishing → quenching and tempering → grinding. There are three heat treatment processes in the entire processing route, which are key links to ensure the inherent quality of the valve seat and improve its service life.

2. Failure forms and causes of valve seats

The analysis of the failed valve seat was summarized in two points: one is surface peeling; the other is impact and erosion wear. The reason for the failure is that the working surface of the valve seat has uneven hardness. During the working process, it is washed by high pressure and hard slurry at high speed, causing the inner surface of the valve seat to quickly form washed grooves or peeling, causing the valve to become damaged. Premature seat failure. The hardness of the severely worn valve seat was tested and it was found that the hardness distribution around the valve seat was uneven. Metallographic analysis was performed and it was observed that the depth of the penetration layer was uneven.

The entire process of on-site production of the valve seat was tracked, and it was found that the key factor causing uneven hardness was the deformation of the valve seat during the heat treatment process, which caused uneven thickness of the penetration layer and quenching layer on the working surface of the valve seat after grinding, resulting in uneven use. Short life.

3. Design and improve tooling fixtures for valve seat heat treatment

(1) Tooling fixtures during carburizing


When the valve seat is installed in the furnace for carburizing, only two layers of workpieces are placed on each layer of partitions, which greatly reduces the deformation of the workpieces during high-temperature carburizing.

       (2) Design tooling fixtures for valve seat quenching


The valve seat undergoes a quenching process after finishing. In the past, the manual single pick quenching method was used. Due to the different strength of each operator and the different pick and quenching parts, deformation is inevitable, and the deformed parts are also different, and the amount of deformation And the quantity is also larger. In order to solve the problem of less and no deformation of the valve seat, it is necessary to redesign the special jig for valve seat quenching. Place 12-15 valve seats on the quenching jig at the same time, which not only reduces the deformation of the workpiece, but also reduces the labor intensity of the workers and improves production efficiency.

       (3) Add valve seat calibration tooling


In view of the deformation of individual valve seats after carburizing and quenching, a valve seat calibration tooling fixture is added. The deformed valve seat after quenching should be reheated and corrected (gas protection), and then re-quenched after sandblasting. According to the production practice of multiple batches, the calibration effect is very good, and no deformation beyond the machining allowance is achieved after heat treatment.

4. Conclusion

Improvements in carburizing fixtures and changes in furnace loading methods have reduced the deformation of the valve seat during high-temperature carburization.

The design and use of special quenching fixtures reduce the deformation of the valve seat during quenching, greatly reduce the labor intensity of workers, improve production efficiency, and ensure the inherent quality of heat treatment.

After adding the valve seat calibration tooling, the uniformity of the carburized layer and the uniformity of the hardened layer after quenching are ensured, which increases the service life of the valve seat.