Abstract: In actual production, it is found that the defects that are easily generated during the molding process of air-conditioning aluminum foil fins includes punching cracking, lamination, patterning and rewinding. From the aspect of aluminum foil material, the factors related to these defects are explained: the aluminum alloy brand and state of the foil, the shape, thickness, surface roughness, coating performance, etc. of the aluminum foil.
Aluminum foil for air conditioning fins (air conditioning foil for short) is divided into air conditioning element foil and hydrophilic foil. Air-conditioning foil is used to make the radiating fins of air-conditioning heat exchangers, and its air convection heat exchange effect. Air-conditioning heat exchangers and compressors are the key components of household air conditioners, and the air-conditioning fins are the main components of the heat exchangers. The quality of the molding and the shape and size after expansion will affect the heat exchange efficiency and manufacturing of the heat exchanger. Cost has a big impact. With the rapid development of air-conditioning industry production, air-conditioning foils are developing in the direction of thinning, high strength, high formability, high heat exchange and high corrosion resistance. As an air conditioning foil manufacturer, we must understand the key indicators in the air conditioning fin molding process and their correlation with the performance and quality of air conditioning foils in order to produce air conditioning foil products that meet various needs.
1 Features of air conditioner fins
The air-conditioning foil is processed into a heat exchanger through the main processes of punching, pipe threading, pipe expansion and drying.
1.1.1 Stamping process
Existing high-impact fin mold molding methods includes DOF (47mm), DT (9.52mm), ECO (9.52mm), CB (9.52mm), etc. These molding methods are all from the original stretching method and The extrusion method evolved. Typical molding methods of domestic air conditioner manufacturers:
- Twice stretching, punching, reaming and turning;
- Stretching four times, punching and flanging.
1.1.2 Air conditioning fin shape
At present, in order to improve the heat dissipation effect of air-conditioning fins, the shape of the fins is constantly updated, including flat fins, corrugated fins, bridge fins, double side slits of blinds, etc., and the spacing of the side slits is getting smaller and smaller.
1.1.3 Production cost of air conditioner fins
Air-conditioner manufacturers are constantly working to improve the heat exchange efficiency of air-conditioning heats exchangers, while also continuously reducing production costs, such as reducing the thickness of air-conditioning foils, increasing the height of flanging, etc.
2 Forming defects of air conditioner fins
2.1 Punching cracking
2.1.1 Definition of punching cracking
Punching cracking is the occurrence of flanging cracks, flanging gaps, flanging hole root cracks, rotten holes and other defects in the air conditioning foil during the stamping process, or the flanging cracks expand during the tube expansion process, which affects the heat exchange effect Of such defects. Generally, air conditioner manufacturers regard copper pipes not exposed after expansion as the criterion.
2.1.2 Factors affecting the cracking of punching
The thickness of the foil, surface roughness, plate shape, surface aluminum powders and the mechanical properties of the foil will all affect the punching cracking.
2.2 The fin is deformed when the tube is expanded
2.2.1 Lamination and flower
Laminated fins: The lower fin flanging mouth is embedded to the top and the fin flanging roots, resulting in a reduction in the gap between the fins, or even touching each other, which seriously obstructs air flows, reduces the overall heat exchange efficiency, increases noise, and destroys the overall appearance.
Flakes: The spacing between the fins is still maintained, but the roots of the fin flange is deformed, so that the outer edges of the fins and the upper (or lower) outer edges of the fins touch together, obstructing air flow, reducing heat exchange efficiency, and destroying Beautiful. It is not easy to distinguish the laminated sheet and the flower sheet from the appearance, in fact, there is a difference between the two.
Rewinding often refers to the fins at the inner arc surface, the layer-to-layer bending and the outer end (contacting the sliding plate) of the heat exchanger when the two-layer heats exchanger is assembled and bent on the bending machine. The inverted shape blocks the heat exchange air, reduces the heat exchange efficiency of the heat exchanger, and affects the appearance of the heat exchanger.
2.2.3 Reasons for fin deformation
The thickness, surface roughness and yield strength of the foil is all related to the deformation of the fin when the tube is expanded.
The inner wall of the fin flanging hole has high friction, and the sinking of the fin is hindered during expansion, and it is easy to produce laminations or patterns.
If the outer diameter of the fin flanging is not enough or the transition arc at the root of the fin hole wall is too large, lamination will be produced.
The fin hole wall is not round, the root is poorly formed, or the hole wall thinning rate is too large, all of which are prone to flaking or falling.
3 Aluminum foil for air conditioner fins
3.1 Alloy grades
At present, the main alloy grades of aluminum foil for air-conditioning fins on the market are 8011, 1030B, 3102, 1100, 8006, etc. The aluminum alloy states are mainly 0, H22 and H26.
3.2 Requirements for aluminum foil in stretch and extrusion punching
In stretch forming, the gap between the mold is greater than the thickness of the material, and the quality of the forming depends mainly on the plasticity of the foil. For this punching method, alloys with a certain strength and good plasticity are often used, such as 8011-H22.
In extrusion molding, the die gap is smaller than the material thickness, and the inner wall of the hole after molding is bright without obvious rolling lines. This is the intuitive difference between it and the stretch molding. For this kind of forming method, not only the foil must have a certain degree of plasticity, but also the r-value of the foil is very critical during the reaming and flanging forming. It reflects the fact that the foil is shaped by the same reaming or flanging. The thickness of the material itself is reduced. This kind of forming method mostly uses foil with higher yield strength, such as 1030B-H26 foil.
When we supply new air-conditioning foils customers, we can only determine the aluminum alloy and state of the foil that are most suitable for this forming process after determining the process of high-impact forming. To meet the needs of air-conditioning foil customers to the greatest extent, avoid batch punching defects.
3.3 Plate shape
The shape of the aluminum foil used for air-conditioning fins must be good, and many air-conditioning foils are aligned to ensure a good shape. The air conditioner foil with a good plate shape is smoother when punching and feeding; if the plate shape is not good, a crack will appear, and the crack is often broken at a certain position in the width direction; a bad plate shape will Affects the feed, resulting in defects such as rotten holes and plugging due to poor feed, affecting the punching process.
In the process of punching and forming the air conditioner fin, the thickness of the air conditioner foil is too thick, too thin, or the thickness difference is large, which will cause local deformation and cracking. And if the thickness is too thin, the flanging height cannot reach the set height, and cracks will occur.
3.5 Surface roughness
The surface roughness of the air-conditioning foil determines the friction between the mold and the aluminum foil during the punching process, and has a great influence on the quality of the molding. Moreover, if the surface roughness is too large, it is not conducive to the process of piercing and expanding the pipe.
3.6 Coating performance
Coating properties includes coating thickness, adhesion, hydrophilicity, corrosion resistance, heat resistance, low odor and so on. For coating performance, stable process control and high-quality coatings are essential.
Indoor heat exchangers basically use hydrophilic foils. Because as
If air-conditioning element foil is used, the air-conditioning fins are repeatedly exposed to dry and wet conditions and are prone to corrosion, causing “white powder” problems.
Among the coating properties, hydrophilicity is the most important performance. When the air conditioner is running, it reduces the ventilation resistance and improves the cooling efficiency. This not only reduces energy consumption but also greatly improves the efficiency of the air conditioner. In addition, low odor is becoming more and more important for manufacturers in recent days.
4 Judgment of punching cracking
In addition to some characteristics of the air-conditioning foil itself, the punching process is also related to the punch, the die, the punching process setting, the punching oil, and the feeding mechanism.
To determine the cause of the punching cracks, a complete sample must be taken from the punch, including samples for each step of the punching process. Then, we look at whether there is a periodicity in the cracking position and which step is in the punching step to determine whether it is related to the equipment. If it is the cause of the aluminum foil material, analyze and determine the possible material cause through the sample defects morphology
During the molding process of aluminum foil for air conditioning fins, the main molding defects are punching cracking, lamination, patterning, rewinding, etc. Sometimes there will be incorrect blanking, row cutting or leaf window burrs, row cutting or cross-cutting, in most cases The bottom has little to do with the aluminum foil material.
In addition, the performance of aluminum foil coating is an important indicator, which not only affects the heat exchange efficiency of the heat exchanger, but also affects the fin forming process to a certain extent.
In short, to understand what kind of punching defects is produced, you must understand the punching process flow, find out the specific location, distribution, morphology, etc. of the defects, carefully analyze and determine the specific reasons.
This article is very helpful for air conditioner manufacturers to understand the various problems that may occur when the air conditioner evaporator condenser and heat exchanger are punched with aluminum foil, and how to solve the problem. Welcome to share! If you are interested in our aluminum foil products, please contact Jack Han [email protected]