Kermit Share | Causes and Solutions of Aluminum Bubbles

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As one of the main varieties of aluminum processing materials, aluminum profiles have one-time extrusion molding and high physical properties, unique decoration, good processability, excellent sound insulation performance and recyclability,

1. foreword

aluminum profile as one of the main varieties of aluminum processing materials, with one extrusion molding and high physical properties, unique decoration, good processability, excellent sound insulation performance and recyclability, combined with the use of heat insulation strip heat insulation adhesive to make up for its high thermal conductivity caused by poor insulation defects, is currently the preferred material for domestic door and window production, with the rapid development of the real estate market in the past few years, the demand for doors and windows products is also increasing, and the production of aluminum profiles with quality and quantity has become increasingly important.

Aluminum Rod Extruding the substrate through the extrusion process is an important process in the production of aluminum profiles, and in the process of substrate extrusion, the profile often has the defect of bubbles, bubbles become the top three reasons for the substrate scrap, reducing the yield and increasing the production cost. Therefore, it is particularly important to analyze the causes of bubbles and find solutions to reduce bubbles in the extrusion process.

2. Bubble Cause Analysis and Corresponding Solutions The direct cause of

Bubble is that air is mixed into the aluminum flow during the extrusion stage, and then extruded together and appears on the profile. The key to solving the bubble problem is to find the cause of air entry and propose corresponding solutions. According to the research in the production process, there are three main ways for air to enter: extrusion cylinder, die and aluminum rod surface water and oil, and the reasons for each way to enter the air are various, and various reasons are involved with each other, resulting in the difficulty of bubble control. Therefore, the analysis of all the reasons for the formation of bubbles, and comprehensive measures for these reasons can be taken to improve the bubble problem in the production process of aluminum profiles.
1. Hot Shearing Machine Shearing Bar Unevenness
At present, most of the building materials and some industrial materials are produced by long bar hot shearing furnace shearing bar. This method has high production flexibility and low cost, and is currently the main method for processing aluminum bars in the production of building aluminum profiles. However, with the increase of the use time of the long rod hot shearing furnace, the matching of the hot shearing machine scissors will gradually deteriorate, the knife edge will wear out, the section of the short rod cut out cannot be flat and vertical, and the section of the aluminum rod cut out by some older hot shearing machines will be oval and chamfered, which will seriously cause the bending of the aluminum rod. If the end face of
aluminum rod is uneven, when the aluminum rod is extruded, there may be residual air on the end face of the aluminum rod and the mating surface of the die, and this part of the air will appear on the profile in the form of bubbles at the rod head. Therefore, in the daily equipment maintenance, the scissors mouth of the hot shearing machine should be maintained to make it cooperate well and reduce the bubble waste caused by the unqualified shearing rod.
2. The diameter of the unextruded aluminum rod is different from that of the extrusion cylinder due to the thick aluminum rod pier. The diameter of the aluminum rod is about 5% smaller than that of the extrusion cylinder (the thick pier coefficient is 1.05). Therefore, after the aluminum rod enters the extrusion cylinder, there is a process of gas discharge when the thick pier is formed. When the aluminum rod pier is thick, if the temperature before and after the aluminum rod is approximately equal, the pier thickness is generally bulging from the middle, and the gas is discharged to both sides. The gas in the back row can be smoothly discharged through the gap between the extrusion rod and the ingot holder, while the air at the front end needs to be discharged from the master cylinder. This is why the master cylinder needs to be discharged before reaching the breakthrough pressure after extrusion starts.
Generally, extruders are equipped with an automatic exhaust process with a fixed exhaust pressure. Most models can exhaust air once. However, some harder material alloys have greater deformation resistance and cannot exhaust air only by automatic exhaust. Some older equipment cannot exhaust air even if dynamic exhaust is performed.
To solve this type of foaming, the best method is gradient heating, so that the aluminum rod is thicker when the head is high and the tail is low, so that the deformation resistance of the head end with higher temperature is smaller, and the drum starts to be formed first, so that the aluminum rod is formed from the head end to the tail end in turn, and the gas will be discharged smoothly from the beginning to the end without residual air at the front end, thus effectively reducing the generation of the bubble. This method requires the use of power frequency furnace, so equipped with power frequency furnace machine, in the aluminum rod heating process, try to choose the head high tail low rod temperature, reach about 15 ℃ temperature gradient, can effectively reduce the generation of bubbles. The

extruder model also affects the exhaust process of the pier roughness to a certain extent. Since the aluminum rod is put into the extrusion cylinder before the extrusion rod enters the extrusion cylinder for pier thickening, the aluminum rod is not at the center of the extrusion cylinder, but at the lower point of the extrusion cylinder. When the pier is thick, the filling of the aluminum rod is uneven up and down, while the front loading long-range extruder is that the aluminum rod is fixed on the die and then the extrusion cylinder is sleeved forward on the aluminum rod, and the center of the aluminum rod is basically located on the extrusion cylinder, the rough exhaust of the pier will be more uniform, which also reduces the generation of bubbles to a certain extent.

3. The use of joint rods

The use of joint rods is also a major cause of bubbles. In daily production, the use of the joint rod is inevitable. Among the two small rods of the joint rod, the last aluminum rod of the previous long rod cannot be returned to the furnace because the rod is too long and short, so the temperature is relatively low. This aluminum rod with lower temperature generally enters the extrusion cylinder as the head end of the rod, which makes the overall rod temperature of the joint rod show a gradient of lower front and higher back, the exhaust direction is the most unsatisfactory state, and there is inevitably a gap between the two short rods, which is easy to retain air, which further aggravates the frequency of bubbles in the output profile of the joint rod.

Therefore, in daily production, the key to solving the joint rod lies in changing the sequence of the joint rod and increasing the number of manual exhaust. The last section of the last long rod is used as the rod tail of the short rod, so that the temperature gradient of the joint rod is high before and low after, the exhaust direction is changed, and the number of manual exhaust is increased, so that the bubble generation of the joint rod can be reduced to the greatest extent.

4. The residual process of shearing after the completion of extrusion

After the completion of extrusion, the extrusion rod retreat and the residual process of shearing are also a major way for air to mix in. When the short rod extrusion is completed and the main cylinder retreats, the extrusion pad is easy to adhere to the residual pressure, causing the residual aluminum in the mold to be taken out when the extrusion rod retreats, resulting in a gap between the residual aluminum in the mold and the mold, mixed with air, so that the air will appear on the rod head of the long rod in the form of bubbles during the next extrusion. Therefore, in the daily production process, it is necessary to supplement the separating agent to the extrusion rod in time according to the aluminum pulling situation after the extrusion rod is withdrawn. It should be noted here that many enterprises apply oil to the extrusion pad to separate the residual pressure from the extrusion rod. This method will pollute the inner wall of the extrusion cylinder and aggravate the shrinkage of the profile. When producing profiles with requirements for low-magnification organization, attention should be paid to the number of times of applying oil to the extrusion pad and the minimum amount of uniform application of oil.

As the service time of the equipment becomes longer, the pressure surplus scissors will also be worn and poorly matched. The gap between the scissors and the end face of the mold will become larger and the scissors will be worn. In this way, the scissors will give an outward pulling force to the aluminum in the mold during the cutting and pressing surplus, resulting in a gap between the residual aluminum in the mold and the mold and air entering, in this way, these gases appear in the form of bubbles at the head end of the profile when the rod is extruded. The best solution to this situation lies in timely maintenance of the scissors of the equipment, timely adjustment of the fit between the scissors and the end face of the die, so as to ensure that the residual aluminum in the die is not brought out during the shearing process and prevent gas from entering.

5. Mold design

Mold design is also a major cause of bubbles. In the design of the split die, if the split hole is too large or the angle of the inner wall of the split hole is too large, the residual aluminum in the split hole is easy to be taken out during shear pressure. Due to the cross-section of the flat die, a flow-guiding pit is generally designed to balance the flow rate of each part of the cross-section. The residual aluminum in the flow-guiding pit may be pulled out during shearing and pressing to mix with air. Even sometimes the shearing and pressing residue will pull off the metal in the flow-guiding pit and form pits on the end face of the die. In this way, many small bubbles will appear intermittently on the extruded whole profile, lead to the scrap of the whole long material. Therefore, in the mold design, the size of the shunt hole should be reasonably designed, the appropriate tilt of the shunt hole should be adopted, and the guide pit should be designed with a certain negative angle, so that the residual aluminum in the mold is not easy to be taken out when shearing and pressing the residual, so as to solve this type of bubble.

Three Conclusion

Aluminum profile bubbles seriously affect the appearance and organizational continuity of the profile, and the production process, equipment, operation and mold may cause bubbles. A variety of methods should be adopted to comprehensively solve the problem of air entry, such as reasonable mold design, regular maintenance of equipment scissors and other equipment that affect the flatness of the end face of the aluminum rod; Gradient heating of the aluminum rod, using appropriate separating agent to separate the residual pressure of the mold; Only by standardizing the use of joint rods can the generation of aluminum bubbles be truly contained at the source of production. The control of the bubble defect of the profile is more a test of the comprehensive management ability of the enterprise, which is the embodiment of the comprehensive management level of an enterprise.