The main process of welding PE Water Supply Pipe(hot-melt butt joint) is adjustment, heating, switching, seam pressurization and cooling. The materials in the viscous flow state at the interface flow and diffuse during the butt joint. Too much flow is not conducive to diffusion and entanglement. The flow must be restricted to a certain range to achieve "post-melting welding" in the limited flow. Therefore, the key to the docking process is to adjust the three parameters of temperature, time and pressure during the docking process. To consider the performance, stress status, geometric shape and environmental conditions of the connection interface material to achieve reliable fusion welding.
Process Requirements
Material preparation: The roundness of the pipe used for welding pipe fittings should be higher than the standard value. And a cutting allowance of 10-20mm should be left during blanking. When used for pipe connection, the two pipes to be welded should be placed on a flat ground. The clamping pipes should be replaced with the basic fixture according to the pipe fittings to be welded. And the appropriate slips should be selected. The welded pipe must be clamped before cutting.
- Cutting: Cutting the impurities and oxide layer on the end face of the welded pipe section to ensure that the two butt joint end faces are smooth and clean.
- The misalignment of the two pairs of welded pipe sections in the alignment should be as small as possible: If the misalignment is large, it will cause stress concentration. The misalignment should not exceed 10% of the wall thickness.
- Ensuring Enough Molten Material: Heating to ensure that there is enough molten material to prepare for the mutual diffusion of molecules during the melting and docking.
- The shorter the switching period the better: The period from the end of heating to the beginning of the fusion docking is the switching period. To ensure the quality of the fusion docking, the shorter the switching period the better.
- Melting butt joint is the key to welding: The process of fusion butt joint should always be carried out under melting pressure.
- The cooling of the weld must be carried out under a certain pressure: Due to the poor thermal conductivity of plastic materials, the cooling rate is correspondingly slow. The shrinkage of the weld material and the formation of the structure proceed at a slow speed over a long period of time. Therefore, the cooling of the weld must be carried out under a certain pressure.
The Working Steps and Precautions of Hot Melt Butt Welding
- Turn on the power of each part of the welding machine
It must use 220V, 50Hz alternating current, the voltage change is within 10%, the power supply should have a grounding wire. At the same time ensure that the surface of the heating plate is clean and free of scratches.
- Connect the pump station and the frame with hydraulic wires
Check and clean up the dirt at the joint before connecting to prevent dirt from entering the hydraulic system and damaging the hydraulic components. After the hydraulic wire is connected, the joint part should be locked to prevent the danger of the joint being opened during high-pressure work.
- Fixed pipes and pipe fittings
Clamp the pipes (pipe fittings) to be welded and fix them on the frame. When welding large-diameter pipes, it is best to use discarded pipe joints or special brackets to level up to protect the pipes and reduce friction during welding.
- Install milling cutter
Open the frame, put in the milling cutter and turn the locking knob to fix the milling cutter on the frame. When starting the pump station, it should be carried out when the direction control handle is in the neutral position.
- Start the milling cutter
Start the milling cutter and close the fixture. Cut the end face of the pipe (pipe fitting).
- Reduce the pressure & close the milling cutter
When a continuous cutting is formed, reduce the pressure, open the fixture and close the milling cutter. This process must be carried out in the order of first reducing the pressure, then opening the fixture, and finally closing the milling cutter.
- Check the gap between the two ends of the pipe
Remove the milling cutter, close the clamp. And then check the gap between the two ends of the pipe . The gap should not be greater than 0.3mm! When removing the milling cutter from the machine frame, avoid collision between the milling cutter and the end face. If the collision has occurred, it need to re-milling. Do not touch the milled end face or be contaminated by oil.
- Check the concentricity of the pipe
Check the concentricity of the pipe. Make sure the maximum amount of misalignment is 10% of the pipe wall thickness. If the gap between the two ends and the amount of misalignment cannot meet the requirements, it should be re-clamped and milled. The next step can be carried out after it passed the test.
- Check the temperature of the heating plate
The appropriate temperature of the heating plate is about 210℃±10℃. If the red indicator light of the heating plate is on or flashing, it explains the temperature is appropriate. After the first light on the heating plate is turned on, it is best to wait another 10 minutes to use it to make the temperature of the entire heating plate uniform.
10.Test the drag pressure P0 of the system and record it
The dragging pressure of each welding port needs to be measured. When the dragging pressure is too large, it can be solved by using short pads.
Problems and Solutions During The Fusion Butt Joint Process
| Quality Problem | Cause | Solution |
| Weld bead is narrow and high | High melting pressure, long heating time, high heating temperature | Reduce the melting butt pressure, shorten the heating time and lower the temperature of the heating plate |
| Weld bead is too low | The melting butt pressure is too low, the heating time is short, the heating temperature is low. | Increase the melting butt pressure and the temperature of the heating plate, and extend the heating time |
| Both sides of the weld bead are not the same height | ①The heating time and heating temperature of the two pipes being welded are different ②The materials of the two pipes are different, and the melting temperature is different, so that the melting degree of the end faces of the two pipes is different. ③The alignment of the two pipes is not good, and the deviation occurs, so that there will be errors before the two pipes are melted and connected. |
① Make the temperature on both sides of the heating plate the same ②Choose the same batch or the same grade of materials ③ Make the center lines of the two fixtures of the equipment coincide, and center the pipe after cutting |
| There is a deep groove in the middle of the weld bead | The temperature of the melt is too low and the switching time is too long during the melt butt joint | Check the temperature of the heating plate, increase the operating speed, and minimize the switching time. |
| Seriously misplaced interface | The alignment of the two pipes before the fusion butt joint is not good, and the misalignment is serious. | Strictly control the offset of the two pipes, and check the alignment before heating and docking the pipes. |
| Partially not curled or rolled outside or not rolled inside or rolled inside or outside | ①The milling blade is loose, causing the pipe end to be milled unevenly, and the local gap between the two pipes is too large after the two pipes are aligned. ②Insufficient heating time ③The surface of the heating plate is uneven, causing the pipe to not be heated locally. |
①The adjustment equipment is in good condition, and the local gaps should meet the requirements after the pipe is cut ②Appropriately extend the time of pressurizing and heating until the minimum curling height meets the requirements ③Adjust the heating plate to be flat and evenly heated |
| False welding | ①The melting butt pressure is too large, and the molten material between the two pipes is squeezed away ②High heating temperature or long heating time will cause the molten material to overheat and decompose |
①Reduce melting butt pressure ②Reduce the heating temperature and reduce the heating time |