Analysis of the quality of barrel flange cracking (1)

In the steel drum production process, the quality problems are various, but the greatest quality problem of the steel drum is the leakage problem of the steel drum. There are many causes of leakage problems. One of the most common causes is the cracking of the barrel. It directly results in the leakage of the crimped and seam welded triangle after the roll closure. Although in recent years, various domestic barrel factories are continuously carrying out equipment reforms and process improvements, due to the relative unfamiliarity of the production of steel barrels by equipment manufacturing plants and other reasons, many problems have arisen in the process equipment, which are currently prevalent. The problem is given analysis, hope can initiate.

First, the quality of raw materials

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

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

For the flanging process, raw materials are required to have good plasticity. In the region of the flanging deformation zone, the internal stress of the material is mainly tensile stress, and the deformation is mainly the elongation and the thickness becomes thinner. When the main deformation site exceeds the forming limit, it can cause cracking. Therefore, the material must have good plastic and plastic deformation stability. Plastic-friendly materials allow a wide range of forming limits, which reduces the problem of flanging due to poor material quality. The limit deformation degree at the time of flanging can be analyzed by the flanging coefficient. Its value is

K=d0/d1

In the formula K - flanging coefficient;

D0—the diameter of the barrel before the flange;

d1—The maximum diameter of the vertical edge obtained after burling.

Due to the elongation and deformation of the metal in the deformation zone under the tangential tensile stress during the flanging, the ultimate flanging coefficient is mainly determined by the plasticity of the metal material. The value of the tangential elongation at each point in the deformation zone in the deformation zone is different at the edge of the flange. The maximum elongation deformation occurs at the edge of the flange, so the elongation of the metal at the edge should be less than the elongation at the edge of the flange. The allowable limit of the material. The maximum elongation deformation produced on the edge of the deformed zone when the barrel is flanged is:

ε=(d1-d2)/d0=1/K-1≤δ

It can be seen from the above equation that the limit flanging coefficient of the steel drum flanging is inversely proportional to the elongation δ of the material. In fact, the value of the elongation δ used in the above formula is usually larger than the uniform elongation obtained in the simple tensile test, which is due to the different size of the elongation and deformation in the diametrical direction of the burring deformation region. : The elongation at the edge is the largest, and the elongation at each point is rapidly reduced as the distance from the edge increases. Therefore, the most vulnerable part is the edge of the flanging, which depends to a large extent on the elongation of the material.

Material plasticity, metallographic structure, and mechanical properties affect the plasticity of materials. In general, the increase of the content of carbon, silicon, phosphorus, and sulfur in steel will reduce the plasticity of the material and increase the brittleness. The carbon content has the greatest influence on the plasticity of the material. It is generally believed that the carbon content does not exceed 0.05 to 0.15%. Carbon steel has good plasticity. Steels containing 0.37% or less of silicon have little effect on plasticity, but larger values ​​than this will make steel hard and brittle. After sulfur is combined with manganese or iron in steel, it appears in the form of sulfides, which seriously affects the hot rolling properties of steel materials. Sulphide promotes the formation of strips and also reduces plasticity. Therefore, steel drum production materials should use high-quality low-carbon steel.

Plates used to make steel drums should have good surface quality. If there are defects such as scratches, pits, scratches, pores, and shrinkage holes on the surface, or if there is delamination on the cross-section of the material, stress will concentrate on the defective part and cause cracking during the flanging process.

2, material heat treatment

The materials used for making the barrels should be heat-treated before the raw materials are shipped to improve the processing performance. Material heat treatment is not good, will make the material has a greater hardness, resulting in its crisp cracking process. The low-carbon steel used for drummaking is generally low-temperature annealed at a heating temperature of 600-650°C and cooled in air. If the low-temperature annealing can not receive good results, you can use high-temperature annealing, the first heating material to 700 ~ 780 °C, 20 ~ 40 minutes after the insulation in the air cooling.