With the construction of national key projects such as West-to-East Gas Pipeline, the application of polyethylene pipeline is increasingly extensive. At present, the product has been widely used in gas, natural gas, water supply and other fields.

PE pipeline has the characteristics of easy construction, high speed, corrosion resistance, no pollution and long service life. There are two main methods for PE pipeline connection: hot melt connection and electric melt connection. At present, the main pipeline is mainly connected by hot melt. The principle of hot-melt connection is that the mating surfaces of two PE pipes are tightly attached to a heating tool, and the flat end surfaces are heated until they are melted. After the heating tool is removed, the two melted end faces are closely attached together, and the joint is cooled under pressure to make it a whole.

First, welding preparation. Preparations for hot melt welding construction are as follows:

(1) Install the slips conforming to the pipeline specifications into the rack;

(2) Prepare enough supports to ensure that the pipeline to be welded can be at the same height as the center line of the frame and can be easily moved;

③ Set the temperature of the heating plate to 200 ~ 230℃ (this data is subject to the welding machine provided by Hangzhou Welding Magic Electromechanical Co., Ltd., and the specific temperature is subject to the data provided by the manufacturer);

(4) Turn on the power supply of the welding machine, turn on the switch of the heating plate, milling cutter and oil pump, and start the test run.

Second, welding. The welding process flow is as follows: check and clean the pipe end → fasten the pipe → mill the pipe end with a milling cutter → check the dislocation and gap of the pipe end → heat the pipe and observe the minimum curl height → weld the pipe and cool it to the specified time → take out the pipe. In the welding process, the operator should refer to the parameters of the welding process card and make appropriate adjustments according to the weather, ambient temperature and other changes when necessary:

(1) Check whether the specification and pressure grade of the pipeline to be welded are correct, and check whether there are bumps, scratches and scratches on its surface. If the scar depth exceeds 10% of the pipe wall thickness, it should be partially removed before use;

(2) Use soft paper or soft cloth dipped in alcohol to remove oil stains or foreign bodies at both pipe ends;

(3) Put the pipe to be welded into the slip of the frame, so that the lengths of both ends are equal (as short as possible without affecting milling and heating, which should be kept at 20~30mm), the outer part of the pipe rack is supported by a bracket, so that the axis of the pipe is at the same height as the center line of the frame, and then fastened with the slip;

(4) Mount the milling cutter, first turn on the power switch of the milling cutter, then close both ends of the pipe, and apply appropriate pressure until continuous chips appear at both ends (the chip thickness is 0.5 ~ 10 mm, and the chip thickness can be adjusted by adjusting the height of the milling cutter blade), then remove the pressure, wait for a moment, then return the movable frame and turn off the power supply of the milling cutter;

⑤ Take out the milling cutter, close the two pipe ends, and check the alignment at both ends (the misalignment at both ends of the pipe should not exceed 10% of the wall thickness, which can be improved by adjusting the straightness and elastic slips of the pipe; The clearance between the two ends of the pipe shall not exceed 0.3 mm (below DE 225mm), 0.5mm (between DE 225mm and 400mm) and1mm (above DE 400mm). If it doesn't meet the requirements, it will be milled here until it meets the requirements.

⑥ After the temperature of the heating plate reaches the set value, put it into the frame and apply the specified pressure until the minimum hems on both sides reach the specified height and the pressure drops to the specified value (both sides of the pipe end just keep in contact with the heating plate to absorb heat). When the time is up, loosen the movable frame, take out the heating plate quickly, and then close the two pipe ends, so that the switching time will be shortened as much as possible. After cooling to the specified time, release the pressure, loosen the slips and take out the connecting pipe.

Thirdly, welding process parameters are directly related to welding: temperature, time and pressure. The welding process diagram is expressed as the relationship between pressure and time during welding.

Welding process diagram (omitted)

Wall thickness e/mm, hemming height h/mm, heating temperature (t): (2 10 10)℃