Analysis of the quality problems of the barrel flange cracking (1)

Analysis of the quality problems of the barrel flange cracking (1)

â–¡ Yang Wenliang

In the steel drum production process, the quality problems are various, but the biggest quality problem affecting the steel drum is the leakage problem of the steel drum. There are many reasons for the leakage problem, among which the barrel flange is one of the most common causes, which directly causes leakage of the crimping and seam welding triangle after the sealing. Although in recent years, domestic barrel factories are constantly carrying out equipment transformation and process improvement, but due to the relatively unfamiliar production of steel barrels by equipment manufacturers, there are many problems in process equipment, which are now widespread. The problem is analyzed, and it is hoped that it will lead the way.

First, the quality of raw materials

There are generally two methods for the steel barrel flanging process, one is rolling flange and the other is mold flanging. Although there are differences between the two processes, the requirements for raw materials are consistent. Due to the performance problems of raw materials, the quality of the flanging can be directly affected. An important factor in the flanging crack is the material problem.

1. The raw material steel plate should have good plasticity and surface quality.

For the flanging process, the raw materials are required to have good plasticity. In the part of the flanged deformation zone, the internal stress of the material is mainly tensile stress, and the deformation is mainly elongation and thickness thinning. When the main deformation site exceeds the forming limit, it will cause cracking. Therefore, the material is required to have good plasticity and plastic deformation stability. A good plastic material allows a wide range of forming limits, which reduces the problem of flanging cracks caused by poor material quality. The degree of extreme deformation when flanging can be analyzed by the flanging coefficient, and its value is

K=d0/d1

Where K is the flanging coefficient;

D0 - the diameter of the barrel before the flange;

D1 - the maximum diameter of the vertical edge obtained after the flange is turned.

Due to the elongation deformation of the metal under the tangential tensile stress in the deformation zone during the burring, the limit burring coefficient is mainly determined by the plasticity of the metal material. The value of the tangential elongation deformation of each point in the radial direction in the deformation zone when the flange is turned is that the maximum elongation deformation occurs at the edge of the flange, so the elongation deformation of the metal at the edge portion should be less than that when the flange is flanged. The limit values ​​allowed for the material. The maximum elongation at the edge of the deformation zone when the barrel is turned over is:

ε=(d1-d2)/d0=1/K-1≤δ

It can be seen from the above formula that the limit flanging coefficient of the steel barrel when it is turned over is inversely proportional to the elongation δ of the material. However, in practice, the value of the elongation δ used in the above formula is usually larger than the uniform elongation obtained in the simple tensile test, because the elongation and deformation of the points in the diameter direction of the flange deformation zone are different. : The elongation deformation on the edge is the largest, and the elongation deformation at each point rapidly decreases as the distance from the edge increases. So the most prone to cracking is the edge of the flange, which depends to a large extent on the elongation of the material.

The chemical properties, metallographic structure and mechanical properties that affect the plasticity of the material. In general, the increase of carbon, silicon, phosphorus and sulfur in steel will reduce the plasticity of the material, increase the brittleness, and the carbon content has the greatest influence on the plasticity of the material. It is generally considered that the carbon content does not exceed 0.05~0.15%. Carbon steel has good plasticity. Steels with a silicon content of less than 0.37% have little effect on plasticity, but greater than this value makes the steel plate hard and brittle even if the carbon content is small. When sulfur is combined with manganese or iron in steel, it appears in the form of sulfide, which seriously affects the hot rolling properties of steel materials. Sulfide promotes the formation of strips and also reduces plasticity. Therefore, steel barrel production materials should be made of high quality low carbon steel.

The sheet used to make the steel drum should have a good surface quality. If there are defects such as scratches, pitting, scratches, pores and shrinkage holes on the surface, or delamination on the cross section of the material, stress concentration will occur in the defective part during the burring process and cause cracking.

2, material heat treatment problem

For the material used for the barrel, the material should be subjected to the necessary heat treatment before the raw materials are shipped to improve the processing performance. If the material is not heat-treated, the material will have a large hardness, which will cause brittle fracture during processing. The low carbon steel used for the barrel is generally annealed at a low temperature, and the heating temperature is 600 to 650 ° C, and it is cooled in the air. If low-temperature annealing does not receive good results, high-temperature annealing can be used. The material is first heated to 700-780 ° C, and after 20 to 40 minutes of incubation, it is cooled in air.