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Connection Method of Heat-shrinkable Steel Strip Pipe (Strip)
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The heat shrinkable pipe (strip) connection of steel strip pipe manufacturer is a connection method which uses fiber reinforced polyethylene heat shrinkable belt as inner layer, heat shrinkable tube as outer layer, and hot melt glue coated on the inner surface of heat shrinkable tube. After heating, the heat shrinkable pipe (strip) is connected with the close hoop of the adjacent pipe end.
Heat-shrinkable pipe connections are generally used for steel band reinforced polyethylene spiral bellows with diameter less than 1200 mm (at present, only fiber reinforced polyethylene heat-shrinkable bands can be used to wrap two layers along the interface with two clamps). The connection must be operated according to the technological requirements of the heat-shrinkable pipe (belt). First, the outer wall of the pipe at the connecting part should be polished clean and the surface of the pipe should be treated. Then, the heat-shrinkable pipe should be sleeved at the two ends to be connected. Then, the inner wall of the heat-shrinkable pipe (belt) should be bonded with the outer wall of the pipe by heating. After cooling, a constant wrapping force should be formed to meet the requirements of the pipe connection. When using heat shrinkage connection for steel strip pipes, the ends of the pipes to be connected should be aligned and no gap should be left as far as possible. When heating the heat shrinkage sleeve, attention should be paid to the flame temperature, which can be gradually heated from the middle of the heat shrinkage sleeve to both sides, or from one end to the other. The gas between the heat shrinkage tube and the pipe should be removed to make it all fit with the pipe. At the same time, the hot melt adhesive should be separated from the heat shrinkage port.
The construction environment temperature of heat-shrinkable pipes (belts) should generally be - 20 - 60 C. If the environment temperature is lower than 0 C, insulation measures should be taken. The operation steps (heating from one end to the other end) of heat-shrinkable pipes (belts) must be operated in accordance with the technological requirements of heat-shrinkable pipes (belts) as follows:
1) Check whether the butt ends of the two connecting pipes are flat, and require the local clearance of the two ends to be closed to be less than mm. If it fails to meet the requirements, it needs to be repaired on site until the requirements are met.
2) Overhead two nozzle ends, so that they are at a certain distance from the ground or trench wall (in order to facilitate the operation of heating tools in the circumferential direction is appropriate).
3) Pull the heat-shrinkable pipe through one end of the two connecting pipes and pull it to a position larger than 500 mm away from the connecting end surface (at this time, the protective paper layer on the inner wall of the heat-shrinkable pipe can not be destroyed and must be complete to prevent dirt, dust and water from immersing into the inner wall of the heat-shrinkable pipe).
4) The cylindrical surface layer 120 mm long from the butt end surface of the two nozzles to be connected should be roughly polished by steel wire brush. At least three half-wave sections should be polished. The shape of the steel wire brush should be the same as that of the bellows (one steel wire brush for each specification).
5) Use a clean cloth to wipe off the polished end of the pipe.
6) Align and fix the ends of the two pairs of nozzles without dislocation.
7) Use PE electrodes fused with the connected tubes, heat the joints and electrodes with a small red flame or a small hot air beam of a small nozzle, and uniformly weld more than four places around the circumference (a longer weld is better) in order to fix the joints of the two tubes.
8) Preheat the circumference of the two pipe ends (three wave distances from the butt end) with red flame, so that the surface temperature can reach 40 50 C (the preheating temperature should be 15 lower than the softening point temperature of hot melt adhesive). Surface thermometer can be used for monitoring.
9) Wrap and bake the heat-shrinkable ribbon at the joint, requiring at least to circumvent the circumference and lap firmly.
10) Preheat both ends of the nozzle to the grinding line so that the surface temperature can reach 40 - 50 C.
11) Carefully move the heat-shrinkable tube to the polished surface at one end. The moving position is approximately 1/3 of the length of the heat-shrinkable tube from the initial heating point to the butt end (according to the actual experience, the length of each specification is finalized), and the protective paper layer in the heat-shrinkable tube is removed (be careful not to stick the paper scraps and other dirt on the preheated corrugated surface and the inner wall of the heat-shrinkable tube). The wedge-shaped insulation made of anti-sticking material supports the other end of the heat shrinkage sleeve, so that the heat shrinkage sleeve and the bellows are concentric, so as to ensure the uniform circumferential gap between the heat shrinkage tube and the bellows, and to improve the shrinkage uniformity and surface smoothness of the heat shrinkage tube.
12) Baking: First, start with a red flame (or a special annular baker) and move uniformly along the circumferential direction of the heat shrinkage tube (no flame moving along the long axis or staying in one place). After the one-week contraction of one end is completed, the heating is gradually extended (notice that it should also be heated uniformly once a week, but not in a straight line along the axis, otherwise the surface will rise. Wrinkle or crack. During the baking process, the contracted part should be pressed gently with a smooth drum (cylinder or rod with the shape and size of the trough) or wearing heat-proof gloves to make it close to the waveform and remove the residual air (be careful not to burn the bellows). When the heating shrinks to 5 cm away from the end surface, the flame can be turned to the hot melt glue on the inner wall of the heating contraction tube, and then to the outer wall. After the heat shrinkage tube is completed, the hot melt glue is heated uniformly by micro-fire (to melt the hot melt glue sufficiently) until the hot melt glue overflows at the end.
It should be emphasized that the flame heating temperature should not be too high to burn the outer wall of PE pipe, crack the end of the heat shrinkage pipe, and the temperature should not be too low to cause the hot melt adhesive not to melt sufficiently, not to adhere, and not to meet the requirements of peeling strength.
In order to do a good job of connection, we must have good operating tools. The above mentioned baking heat sources and leveling tools should be carefully prepared. Small liquefaction tanks for heat sources can be used for natural gas, methane, liquefied gas and spray lamps. However, a set of nozzles corresponding to the diameter of bellows must be provided. It is better to use a set of special process operating tools, such as special automatic baking machines, to improve the connection quality.