What is Heat Staking?

Hot-melt is generally used as a hot-melt connection. The principle of hot-melt connection is that the mating surfaces of two PE pipes are pressed against a heating tool to heat the flat end surface until melting. After removing the heating tool, the two molten end faces are abutted. Together, they are kept under cooling by the pressure until the joints are cooled, allowing the two sections of pipe to be connected as a whole.

Hot Melt

Right!

Hot melt is generally used as a hot melt connection,

1. Welding preparation. Preparations for hot melt welding construction are as follows:

Put slips in line with the specifications of the pipe into the rack;

Prepare enough supports to ensure that the pipe to be welded can be at the same height as the centerline of the rack and can be easily moved;

Set the temperature of the heating plate 200 230 (The data is based on the welding machine supplied by Hangzhou Welding Electromechanical Co., Ltd., the specific temperature is based on the data provided by the manufacturer);

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

Second, welding. The welding process is as follows: Inspect the pipe and clean the pipe end Fasten the pipe Mill the mill end of the pipe Check the pipe end for misalignment and clearance Heat the pipe and observe the minimum crimp height The pipe is welded and cooled to the specified time Remove the pipe During the welding process, the operator should refer to the parameters of the welding process card, and if necessary, it should be adjusted appropriately according to changes in weather and ambient temperature:

Check whether the specifications and pressure level of the pipe to be welded are correct, and check whether the surface is scratched, bumped, or scratched. If the depth of the scar exceeds 10% of the thickness of the pipe, it should be partially removed before use;

Use a soft paper or cloth dipped in alcohol to remove oil or foreign matter from the ends of the two tubes;

Put the pipe to be welded in the rack slip so that the lengths of the two ends are equal (as short as possible without affecting milling and heating, it should be kept 20 ~ 30mm). Use the parts other than the pipe rack The support is held up so that the pipe axis is at the same height as the center line of the rack, and then fastened with slips;

Insert the milling cutter, first turn on the milling cutter power switch, and then close the two ends of the pipe, and apply appropriate pressure until continuous chips appear at both ends (chip thickness is 0.5 ~ 10mm, by adjusting the height of the milling blade Adjustable chip thickness), remove the pressure, wait for a while, then retract the movable rack, and turn off the milling cutter power;

Take out the milling cutter, close the ends of the two pipes, and check the alignment of the two ends (the amount of misalignment of the two ends of the pipe cannot exceed 10% of the wall thickness. It can be improved by adjusting the straightness of the pipe and the elastic slip; the gap between the two ends of the pipe cannot exceed 0.3mm (de225mm or less), 0.5mm (de225mm ~ 400mm), 1mm (de400mm or more), if it does not meet the requirements, it should be milled here until it meets the requirements.

After the temperature of the heating plate reaches the set value, put it into the rack and apply the specified pressure until the minimum curling on both sides reaches the specified height, and the pressure is reduced to the specified value (the two ends of the tube end and the heating plate just keep in contact with each other. After the time is reached, loosen the movable rack, quickly remove the heating plate, and then close the two tube ends. The switching time should be as short as possible. After cooling to the specified time, release the pressure, loosen the slip, and remove the completed pipe.

Third, welding process parameters The parameters directly related to welding are: temperature, time, pressure. The welding process curve is shown as the relationship between pressure and time during the welding process.

Welding process curve (omitted)

Wall thickness e / mm Hemming height h / mm during heating Temperature (T): (210 ± 10) Endothermic pressure Pa1: 0.15MPa Endothermic time ta2 / S ta2 = 10 × e Temperature (T): (210 ± 10) endothermic pressure Pa2: 0.02MPa Allowable maximum switching time tu / S Pressurization time tf1 / S Cooling time tf2 / min of the weld under pressure holding state Pf1 = Pf2 = 0.15MPa

<4.5 0.5 45 5 5 6

4.5 to 7 1.0 45 to 70 5 to 6 5 to 6 6 to 10

7 to 12 1.5 70 to 120 6 to 8 6 to 8 10 to 16

12 19 2.0 120 190 8 10 8 11 16 24

19 26 2.5 190 260 10 12 11 14 24 32

26 to 37 3.0 260 to 370 12 to 16 14 to 19 32 to 45

37 to 50 3.5 370 to 500 16 to 20 19 to 25 45 to 60

50 to 70 4.0 500 to 700 20 to 25 25 to 35 60 to 80

Pa1 heating pressure pa2 endothermic pressure pf1 welding pressure pf2 cooling pressure ta1 heating time Tu switching time (including heating plate withdrawal time) tf1 pressurization time tf2 cooling time

4. Welding inspection practice proves that the most easily damaged and leaked part of polyethylene gas pipelines is the pipeline interface. The key to the success and failure of the project is the quality of the pipeline connection. Therefore, strict interface quality acceptance is very important for underground gas pipeline projects. Destructive tests are required on polyethylene pipe joints to check internal quality.

(1) After the polyethylene pipes are connected, the construction self-inspection and third-party acceptance shall be strengthened, and a certain proportion of interfaces shall be appropriately selected for internal inspection.

(2) Check the welding data records of all welds

(3) The appearance quality inspection shall be carried out at 100%. The inspection and acceptance unit shall select a certain percentage of welds for visual inspection according to the construction quality, and the number shall not be less than 10% of the number of welds, and each welder shall have no less than 5 welds.

(4) Each project should be subjected to a destructive test of the interface. For the interface of the hot-melt connection, 3% welds should be taken. It is recommended that not less than one be used. In the destructive test, the weld can be cut into 4 pieces, and the internal fusion is checked. Incomplete fusion is regarded as unqualified. A tensile test can also be performed to see if the tensile strength meets the design and specifications. For unqualified interfaces, the welder's interface should be double-checked. If unqualified interfaces are found again, all the welder's interfaces will be reworked.

This entry is organized by ccj328