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Welding Process Analysis of Aluminum and Copper Pipes

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Pre-welding treatment: 
1. Joint design: The unilateral clearance of the joint should be controlled between 0.08 and 0.2 mm, and the length of the weld is generally not more than 30 mm.

2. Surface treatment: Use alkali or metal cleaning fluid to clean the oil stain and other contaminants on the welded joint, and then use a scraper (or coarse sandpaper, copper brush, wire brush) to scrape the insulation layer from the welded joint surface. 
Note: It can't be polished, because the solder is welded by capillary action, which is not conducive to welding after polishing.  

3. Pre-preparation: prepare aluminum welding rods and powders first, then mix aluminium welding powders with distilled water, reserved, start to weld aluminium pipes and aluminium pipes, first polish aluminium pipes and welding rods, then insert a stainless steel pipe into aluminium pipes, now start welding ignition with neutral flame, acetylene more oxygen less spot roasting aluminium pipes, and then use welding rods. The distance between the welding nozzle is about 15 millimeters and the angle of 45 degrees. When the welding piece melts, the welding rod keeps pace with the welding piece at any time. At this time, the welding rod and the welding piece melt into one. At this time, the welding rod and the welding torch are removed after welding.

Welding copper and aluminium pipes is said to be a difficult technical problem, requiring professional equipment and so on. In fact, as long as some key problems are mastered during welding, manual welding can be done well.

1. When heating, the copper pipe must be heated
Because the melting point of copper tube is much higher than that of aluminium tube, you can heat it as hard as you can, and you don't have to be afraid of the melting of copper tube. Of course, you should pay attention to the flame temperature. As for the temperature of the flame, see next note.

2. Selection of flame type.
If you add oxygen with liquefied gas, you can choose the heating flame as the oxidation flame, that is, the brightness of the middle flame core is about 1-1.5 cm, and the length of the flame ejection is about 7-10 times the length of the flame core. At this time, the proportion of oxygen is larger, and the flame emits more uniform sound.

3. Heating position
Heating the copper tube, and continuously moving the torch along the tube axis, moving the flame back and forth, using the position of slightly reddish flame edge as the main heating area, which is about 2 to 3 centimeters away from the flame head. 

4. Heating degree
In the process of heating the copper tube, the edge of the flame will be deformed, which will affect the aluminum tube and heat it. At this time, the position of the aluminum tube being heated is generally the edge of the aluminum tube. The brightness of the tube body is higher than that before heating. When the edge of the aluminum tube is chapped, it is the best time to add solder. 

5. Adding solder.
When the chapped edge of the aluminium tube appears and the melting phenomenon has not yet occurred, the copper-aluminium welding wire is firmly placed in the center of the flame and is strongly close to the joint of the copper tube and the aluminium tube.

6. Welding of solder. 
When the solder is put in, the solder melts in about 1 to 2 seconds. If the temperature and oxidation degree are well controlled, the solder will flow along the gap and fill the gap naturally. If the flame can rotate around the copper pipe and continuously add solder, the solder will fill the gap continuously.

7. Points for attention.
Flame type; the oxygen should be sufficient but not too large; the time to add solder; if not completed at one time, need to surround the tube, reheat again, and then add solder.

quality problems
Generally, there are two kinds of problems, one is insufficient heating. The phenomenon is that the added solder only melts on the copper tube, the aluminum tube itself is not contact with solder, and the solder appears as granular on the aluminum tube; the other is over heating, which will cause the collapse of the aluminum tube itself, or even the melting pit of the copper tube. At this time, the welding has basically failed and needs to restart.

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