Analysis on the quality problem of the barrel flange crack
Text / 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 methods, the requirements for raw materials are correct. Due to the performance problems of the 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 part 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 ultimate deformation when flanging can be analyzed by the flanging coefficient, and its value is:
K=d0/d1
Where: K - the flanging coefficient;
D0——the diameter of the barrel before the flange:
D1 - the maximum diameter of the vertical edge obtained after the flange.
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 at 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 ensured when the flange is not smaller than the material. The allowed limit value. The maximum elongation at the edge of the deformation zone when the barrel is turned over is:
It can be seen from the above formula that the limit flanging coefficient when the steel drum is turned over is inversely proportional to the elongation S of the material. However, in practice, the value of the elongation S 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 at the edge is the largest, and the elongation at each point decreases rapidly as the distance from the edge increases. Therefore, the most prone to cracking is the edge of the cuff. This is very It 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; it 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 plates used to make steel drums should have good season season 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.
Second, the 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 to heat the material to 700-780 ° C first; after 20 to 40 minutes, it is cooled in air.
Second, the welding edge pretreatment problem
Before seam welding, the barrel welds are generally pretreated. The traditional edging process used in most barrel mills also uses milling and other processes. However, no matter what process is adopted, the purpose is to remove the corrosion of the steel sheet surface. Impurities such as dirt, in order to facilitate good electrical conductivity on the surface of the steel plate during welding, reduce welding and leakage welding, and enhance welding strength. However, in actual production, the treatment of the weld edge is often unsatisfactory. Sometimes the edging temperature is too high, causing the surface to burn black; sometimes the surface impurities still exist; some galvanized sheets still have some metal zinc remaining on the surface. The most serious is that sometimes the edge is too large, resulting in a corner at the corner, as shown in Figure 1. All of these shortcomings can result in poor strength during welding, especially in the absence of corners, which may result in lap joints at both ends of the barrel. Such a quality weld can of course not withstand the effect of the flanging force when flanging, and it is inevitable that the flanging crack will occur.
Therefore, to reduce the defects of the flange cracking, the quality of the weld edge pretreatment should be solved first in the production process.
Third, the quality of the seam welding process
The quality defects of the seam welding process itself are mainly due to insufficient welding strength, excessive indentation, and burn through. These defects are the main causes of flange cracking. The occurrence of these defects is mainly related to the unreasonable selection of welding process parameters. The main parameters affecting the welding quality are welding current, electrode pressure, welding time, rest time, welding speed and diameter of the welding wheel.
1, welding current
The heat required for seam welding to form a nugget is generated by the use of electric current through a computer in the weld zone. Under the conditions given by other conditions, the magnitude of the welding current determines the penetration and overlap of the nugget. In the seam welding of steel drums, the average penetration rate of the nugget is 30 to 70% of the thickness of the steel sheet, and 45 to 50% is optimal. In order to obtain a higher strength weld nugget overlap should be no less than 15 to 20%. When the welding current exceeds a certain value, continuing to increase the current can only increase the penetration rate and the amount of overlap of the nugget without increasing the joint strength, which is uneconomical. If the current is too small, defects such as excessive indentation and burn through of the weld may occur.
2, electrode pressure
The electrode pressure during seam welding has a large influence on the size of the nugget. Excessive electrode pressure can make the indentation too deep and accelerate the deformation and loss of the welding wheel. Insufficient pressure will result in shrinkage cavities, and the contact resistance will be too large to shorten the life of the welding wheel.
3, welding time and rest time
In seam welding, the industrial size of the nugget is mainly controlled by the welding time, and the overlap is controlled by the cooling time. At a lower welding speed, the ratio of the welding to the rest time is 1.25:1 to 2:1, and satisfactory results can be obtained. When the welding speed increases, the spacing of the solder joints increases. At this time, to obtain the welds with the same amount of overlap, the ratio must be increased. For this reason, at a higher welding speed, the ratio of welding to rest time should be 3:1. Or higher.
4, welding speed
The welding speed determines the contact area between the welding wheel and the steel plate, and the contact time between the welding wheel and the heating part, thus affecting the heating and heat dissipation of the weld. When the welding speed is increased, in order to obtain sufficient heat, the welding current must be increased. Excessive welding speeds can cause burns on the surface of the drum and adhesion of the welding wheel, so even with external water cooling, the welding speed is limited.
At present, according to the degree of automation of the welding machine, three schemes of high speed, medium speed and low speed can be adopted. When moving the barrel manually, in order to facilitate the alignment of the predetermined weld position, the medium speed is often used. In automatic welding, if the capacity of the welder is sufficient, high speed or higher speed can be used. If the welder has insufficient capacity and cannot guarantee a sufficiently large melt width and penetration without lowering the speed, only low speed can be used.
When seam welding of galvanized steel drums, care should be taken to prevent cracks. The reason for the crack is that the zinc remaining in the nugget and diffusing into the heat-affected zone causes the weld to be embrittled and caused by stress. The method to prevent cracks is to correctly select the process parameters. Practice has proved that the smaller the penetration rate (10 to 26%), the less crack defects. When the seam welding speed is high, the heat dissipation conditions are poor, the surface is overheated, and the penetration depth is large, and cracks are likely to occur. Generally, under the conditions of ensuring the diameter of the nugget and the strength of the joint, a small current, a low welding speed and a strong external water cooling should be used as much as possible.
Fourth, the quality of the flanging process
The last step affecting the quality of the flanging is the flanging process, which is also the most important process. At present, the steel drum manufacturing production line of the domestic barrel industry has two roughing processes: one is rolling flange and the other is mold flange. Although the two methods of flanging are different, the results are basically the same. For the material of the burring part, it is a deformation of thinning and stretching. In addition to other reasons for the above analysis, the main technical quality problem is the technical problem of the burring process. From the perspective of actual production, the flanging is related to the angle of the flanging, the arc degree, and the flanging speed.
Depending on the production line of each steel drum, some require the angle of the flange (the angle between the flange portion and the barrel) is 90° (such as 95° or 100°, etc.). In comparison, the larger the cuff angle, the smaller the diameter of the cuff edge, the smaller the relative deformation, and the less likely to be broken when the cuff is turned; the vertical cuff, the diameter of the cuff edge is most likely to be broken. As far as the steel drum manufacturing process is concerned, many crimping machines have to press the lid and the barrel body tightly before the sealing, so that the barrel can be tightened tightly with the lid, generally speaking It is unfavorable that the flange is too straight (90°), and the angle of the flange is relatively larger, which is more advantageous for the edge of the flange to be close to the lid.
The connecting part between the barrel and the turned part after the burring generally has a certain arc over-expansion, and the radius of the arc is sometimes the main factor leading to the hem. When the radius of the arc is larger, the deformation force is relieved, and the deformation time is relatively extended, which is favorable for the uniform transmission of the flanging force, and the crack is not easy to occur; if the radius of the arc is too small, the deformation is sudden, the deformation force is not urgently transmitted, and the deformation The time is too short and the rupture is easy to happen. In the production practice, the problem of flange cracking caused by this reason is more and must be paid attention to.
The time during which the flanging process takes place is also one of the factors that affect the flanging crack. Some manufacturers' equipment is stamping and burring of the mold, the process is faster, the deformation time is short, the deformation force is not urgently transmitted, and the rupture is more likely to occur; some equipments use hydraulically driven mold flanges, because the hydraulic speed is relatively slow, The force transmission is softer, so the possibility of rupture is much smaller: there are some equipment, especially some old equipment, which use rolling and flanging, and the burring process is the slowest in all kinds of burring methods. Although the production efficiency is low, since the flanging force is slowly transmitted, like the double-action press stretching, the possibility of cracking is very small. In the case of the same material and the previous process, rolling flanges cause the least cracking.
private label Body Care ,30 years experience guangzhou cosmetics factory supply ,OEM/ODM service is welcomed .
Guangzhou Athena Cosmetics Manufacturing Co.,Ltd is a subsidiary of YALAN international group which is located in Guangzhou,china.it is the production center of YALAN international group branding products,specialized in the development and production if cosmetics.ATHENA is qualified for import and export.
controls the quality in full accordance with GMP, ISO9001 quality system good manufacturing practice for cosmetics and key points of cosmetic production licence inspection.
Body Lotion,Deodorant &Perfume ,Body Wash,Body Scrub,Essential Oil
Athena(Guangzhou) Cosmetics Manufacturer Co., Ltd , https://www.ydgzathenaskincare.com