The hardening issue of the mouth ring!

When the engine is idling, a rhythmic and distinct hissing sound can be heard at the oil filler cap; this sound disappears as the engine speed increases. This issue is usually caused by broken piston rings or ring lands, and further inspection can be carried out by turning off the fuel supply to each cylinder one by one. If the hissing sound disappears after a cylinder loses spark, it indicates that the piston ring in that cylinder is broken. If there is a hissing sound at idle speed, and rapid acceleration is performed several times, a distinct rhythmic \"thumping\" metal-like noise can be heard, along with pulsating smoke coming from the oil filler cap. During a spark cut test, the knocking sound in that cylinder disappears, but the hissing sound remains; the smoke from the oil filler cap also disappears or decreases. This situation is usually caused by issues such as excessive clearance between the piston rings, misalignment of the piston rings, poor sealing between the piston rings and the cylinder walls, or insufficient elasticity in the piston rings. If there is a distinct rhythmic \"clunking\" metallic noise at idle, which worsens as the engine speed increases, and if smoke emanates from the oil fill port along with pulsations, and that smoke contains oil, it is likely that the noise is caused by the piston rings sticking together

The poster is referring to the impeller ring of the centrifugal pump, right!

If so, it occurs more frequently in multi-stage centrifugal pumps. The main reasons are: 1. Excessive wear of the balance disc results in large axial movement, as well as friction between the moving and stationary parts ； 2. The pump often experiences cavitation or air locking, along with abnormal vibration ； 3. The pump shaft is bent.

The materials of the mouth rings should generally be one hard and the other slightly softer; otherwise, friction at the same hardness level can easily cause them to stick together. It’s also fine to increase the gap of the mouth ring slightly; generally, as long as it doesn’t exceed 1 mm, there is basically no impact. The key is to avoid vibration; once the vibration problem is resolved, the mouth ring will not experience wear or seizure

I would like to ask what are the different methods for hardening mouth rings! Specific applications

I would like to ask about the various methods for hardening the mouth ring of centrifugal pumps!

Hardening of mouth rings is essentially heat treatment. There are processes such as internal surface carburizing and nitriding, surface high-frequency treatment, full quenching (tempered to 35°), and quenching and tempering; different materials are selected depending on the process used.