FAILURE ANALYSIS OF MECHANICAL SEAL

Mechanical seal is one of the most widely used seal types in fluid machinery. It is widely used in pump machinery. It has many advantages, such as power saving, reliable seal and so on. Mechanical seal is very important. Once there is a problem, the consequences are serious. So it is very necessary for us to understand some of its common faults and solutions.

1. Common Failure Causes and Treatment of Mechanical Seal

(1) Corrosion Failure

There are many mechanical seal failures caused by corrosion. The common types of corrosion are as follows.

Surface Corrosion

Due to the corrosive effect, the mechanical seal will have surface corrosion. Even corrosion perforation will occur when it is serious. The spring parts are more obvious. The stainless steel material can reduce the surface corrosion.

Pitting Corrosion

The spring sleeve often has large area pitting or regional pitting, some of which lead to perforation. This kind of local corrosion will not cause very serious consequences to the use of the seal, but it should also be replaced during overhaul.

Intergranular Corrosion

The stainless steel ring seat of tungsten carbide ring is connected by copper brazing. In usage, the stainless steel seat is prone to intergranular corrosion.

4.Stress Corrosion Cracking

Under the joint action of stress and medium corrosion, metal welded bellows and spring often break. Because of the sudden break of spring, the seal fails. Generally, increase the wire diameter of spring to solve the problem.

Crevice Corrosion

Due to the difference of the concentration of the medium inside and outside the gap, the gap corrosion occurs between the inner hole of the moving ring and the surface of the shaft sleeve, between the screw and the screw hole, between the 0-ring and the shaft sleeve. In addition, the gap corrosion also occurs between the ceramic inlay ring and the metal ring seat. Generally, ceramic is sprayed on the surface of the shaft sleeve, and the surface of the inlay ring is coated with adhesive to reduce the gap corrosion.

Electrochemical Corrosion

Dissimilar metals often cause electrochemical corrosion in the medium, which makes the Inlay Ring loose and affects the sealing. In general, the inlay joint is coated with adhesive to overcome this problem.

(2) Heat Loss Failure

Hot Cracking

If the sealing surface is in dry friction and cooling, but suddenly interrupted, or impurities enter into the sealing surface, radial cracks will appear on the ring surface. It will cause sharp wear of the dual ring, and the leakage of the sealing surface will increase rapidly. Hot cracking of tungsten carbide ring is common.

Foaming and Carbonization

In usage, if the temperature of graphite ring exceeds the allowable temperature, the resin will be separated from the surface, and the resin near the friction surface will be carbonized. When there is adhesive, it will foam and soften, which will increase the leakage of sealing surface and cause sealing failure.

2. Precautions for Mechanical Seal Installation

(1) Pay Attention to the Installation Position

Before the installation of mechanical seal, the exact location of the mechanical seal should be consistent with the drawings and plans. At the same time, make sure the parts of the mechanical seal are complete.

(2) Choose the Right Model

There are many types of mechanical seal. Distinguish different types of mechanical seal according to the requirements, and choose the matching and the type of mechanical seal correctly.

(3) Select High Guality Materials

The selection of mechanical seal should choose high-quality materials, because it belongs to high-precision mechanical parts, so its material requirements are relatively high.

(4) Carry out Lubrication Operation

Lubrication operation on the shaft surface of mechanical seal is a way to reduce friction and wear. It also helps to improve the service life of mechanical seal and reduce costs.

Although the mechanical seal may be small enough to hold in hand and the concept is very simple, it is actually a very complex device, so it deserves our attention.

Ningbo Haijia Seal Industry Co., Ltd. is an enterprise specializing in the production of mechanical seal and sealing materials. Its products include silicon carbide seal ring, tungsten carbide seal ring, alumina ceramic seal ring, 0-type seal ring, packing, gasket, etc.