1. You must choose a hot-melt welding machine with qualified quality.
(1) The temperature control must be correct. PP-R hot melt welding temperature is: 253℃-274℃. If the temperature is lower than 253℃, the pipes and fittings are only a thin layer of surface melting. Once they are welded, the strength of the weld cannot be guaranteed. This is what we usually call the phenomenon of false welding; If the temperature is higher than 274℃, the surface molecules of the pipes and fittings will be destroyed by high temperature, making PP-R form a thin liquid, which will make the inner diameter of the pipe smaller after connection, and more importantly, brittle cracks will occur in the connecting part. Especially when the piping system is fully completed and pressurized with water, such problems often occur.
(2) The constant temperature time should be long. The length of the constant temperature time is one of the important signs of the performance of hot-melt welding equipment. There is still a problem of heat consumption for hot melt equipment after heating up to the set temperature. Especially in winter, the heat consumption of the tuyere, even in the non-operating gap, is also very large, and once it is in operation, its pipes and fittings All are consuming heat energy separately, which requires the equipment to have strong heat energy storage capacity and timely replenishment capacity.
2. A qualified and suitable welding sleeve must be selected.
Qualified welding sleeves are designed with full consideration of the transverse structure and welding depth of the pipe after welding, as well as surface non-stickiness and surface finish. At present, there are hundreds of domestic manufacturers who weld PP-R, PPC, PE and other water supply pipes by hot-melt method. Due to the different raw materials and additives used in the pipes produced by various manufacturers, different environmental conditions, and different equipment options, the sizes of pipes and pipe fittings produced by each manufacturer are also different. Therefore, each pipe manufacturer and user must choose a welding sleeve suitable for their pipe diameter. For the operator, the surface of the welding sleeve should be cleaned after the last welding to avoid impurities in the welding part.
When welding pipes with a diameter of more than 40mm, due to the large diameter, it is not possible to work with personal strength, and mechanical equipment must be used to ensure the depth and straightness of the pipe into the pipe. We found that five to six workers were used to weld a 110mm diameter interface on many construction sites. It took a lot of effort to ensure the straightness and insertion depth of the pipe. The entire pipeline was bent and bent, and it was difficult to imagine that it would be at a certain water temperature. And under pressure.
Third, the problems that are prone to occur in hot melt welding.
It should be said that the piping system, which is constructed strictly in accordance with the requirements of the welding process and welding technology, will not cause any problems when used under normal temperature and pressure. However, we often find that bursts or blisters occur at the joints of pipes and fittings during daily construction.
The main reasons are as follows:
⑴The temperature of the hot-melt welding machine is incorrect, too high or too low, which will change the properties of polypropylene;
⑵The surface of the welding sleeve is not properly treated, or the surface coating falls off, causing blisters in the contact part with the pipe;
⑶ The size of the welding sleeve is wrong, and the design is wrong, which makes the melting depth of the pipe and the welding structure inappropriate;
⑷The welding surface of the pipe is not cleaned before welding;
⑸ The welded pipe and pipe fittings are not kept concentric or straight.
4. Correct welding procedures.
(1) Preparation work before hot melt welding
① For pipes with an outer diameter of 25-110mm, a chamferer should chamfer the pipe port by 15° to half of the original pipe wall thickness;
② Use a cleaning machine (or alcohol) and a brush to clean the surface of the welded part of the pipe;
③When the pre-assembled parts are welded, mark the required position of the pipe and the fitting before connecting.
④For welding pipes with diameters above 40mm, flat and vertical pipe welding machines must be used;
⑤After each dissolution, clean the heating jacket and heating head with a dry cloth or dry paper. Do not use detergent.
(2) Hot melt and connection
①After inserting the pipe and the pipe fitting into the heating jacket and heating head respectively, do not rotate or move too fast (make the material have enough time to melt).
②After heating, remove the pipe and fittings from the heating element, do not rotate the heating part.
③Press the pipe and fittings together along the axis immediately after heating, do not rotate. Strictly observe the holding time and cooling time of the hot melt welding standard.
