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) setting the temperature of the heating plate at 200-230 DEG C.
(This data is subject to the welding machine provided by Hangzhou Dong Lei Machinery Factory, 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.
Duckweed in autumn
Second, the welding process.
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.
Third, the welding points.
Welding inspection practice has proved that the most easily damaged and leaked part of polyethylene gas pipeline is the pipeline interface. The key to the success of the project is the quality of pipeline connection. Therefore, strict interface quality acceptance is very important for underground gas pipeline engineering. Destructive tests are needed to check the internal quality of polyethylene pipe joints.
(1) After the polyethylene pipes are connected, the construction self-inspection and third-party acceptance should be strengthened, and a certain proportion of interfaces should be cut for internal inspection.
(2) Check the welding data records of all welded joints.
(3) Appearance quality inspection shall be conducted according to 100%. Supervision and other acceptance units shall take a certain proportion of welds for visual inspection according to the construction quality, the number of which shall be no less than 10% of the number of welds, and the number of welds of each welder shall be no less than 5.
(4) Destructive interface test shall be conducted for each project, and 3% welded joints shall be selected for hot-melt connection, and it is recommended that there be no less than 1 joint. In destructive test, the weld can be cut into four pieces to check the internal fusion. Incomplete fusion can be regarded as unqualified, and tensile test can also be done to see whether the tensile strength meets the design and specification requirements. For unqualified interfaces, the welder's interfaces shall be sampled twice. If unqualified interfaces are found again, all interfaces constructed by welders should be reworked.
Common problems and prevention of hot melt welding of PE pipe
With the continuous development of gas and the continuous extension of PE pipeline, there is a shortage of welding technicians in each construction team. Common problems and preventive measures of PE pipe hot melt welding are introduced as follows:
1, pipeline butt joint: common fault, nozzle misalignment is greater than 10℅.
Note: The welder should be responsible for adjusting the mouth several times, and there is no obvious wrong edge outside the circumference by visual inspection, and there is no wrong edge by touching the handle.
2, nozzle milling: common problems, milling end face is uneven, there are convex and concave phenomena.
Precautions: When continuous shavings are generated in the milling process, the milling cutter should not stop before opening the end face, and observe whether there are bumps on the milling end face, and re-milling if necessary. Close the end faces of the two pipes and check whether the dislocation of the two pipe ends is within the allowable range. If it is unqualified, it must be adjusted and milled again until it is qualified.
3, welding pressure, heating heat absorption: common problems, welding pressure is too large or too small, heating time is too long or too short will lead to flanging too large or too small to form false welding. Especially the manual welding machine, the pressure is not easy to control.
Precautions: Before construction, calculate the pressure, temperature and heat absorption time of welded pipeline. General welding pressure is drag pressure plus specified pressure. Before welding, the drag pressure can be measured, and the specified pressure (Mpa) is equal to the cross-sectional area of the pipeline (mm2)×0. 15/ cylinder cross-sectional area mm2, and the heat absorption time depends on the pipe diameter.
Under normal circumstances, when the flanging amount reaches the height specified by visual inspection, it will be transferred to the heat absorption stage, and the pressure will be released to drag pressure in the heat absorption stage, and the heat absorption time is the wall thickness (mm) multiplied by 10 (second).
4. Cooling of welded joints: Common problems: insufficient cooling time (generally, in order to grab the construction period and progress, the cooling time is often greatly shortened, so that there is no problem with welded joints at that time, but it will bring hidden dangers to the future engineering quality).
Cooling time requirements: SDR 17.6 tubes 19 minutes, 250mm 160mm 13 minutes,10mm9 minutes. Pressure must be maintained during cooling. No external force is allowed.
Precautions for customers before construction:
Customers should determine the direction of water pipes according to the decoration design drawings and room structure. The direction of water pipes can be divided into suspended ceiling layout, wall slot layout, ground layout and exposed pipe installation. Choose which layout should be negotiated with the decoration team.
Positioning of water equipment: for example:
First, in the pipeline system, pre-filters, booster pumps or buried faucets should be placed before installing water pipes, otherwise the construction will be affected.
Second, the fuses produced by regular manufacturers generally have red and green indicator lights, with red light representing heating and green light representing constant temperature. You can't use it when you reach the green light for the first time, and you can only use it when you reach the green light for the second time. The temperature during fusing is 260℃-280℃. Below or above this temperature, the joint will not be completely fused, leaving a hidden danger of water seepage.
Three, before construction should check whether there is any damage on both ends of each pipe, in order to prevent damage to the pipe in the process of transportation. If there is any damage or uncertainty, the port of the pipeline should be reduced by 4-5cm during installation, and it is not allowed to hit the pipeline with a hammer or a heavy object to prevent the pipeline from bursting and improve its service life.
Four, cutting pipe must make the end face perpendicular to the pipe axis, pipe cutting should use special pipe shear.
5. When heating: guide the pipe end into the heating die sleeve without rotation, insert it to the marked depth, and push the pipe fitting onto the heating die head without rotation to reach the specified mark. The heating time shall be performed according to the following table.
Six, after reaching the heating time, immediately remove the pipe fittings from the heating mold at the same time, and insert them into the hot melt depth in a straight line without rotating, so as to form a uniform flange at the joint and control the rebound after insertion.
Seven, within the processing time specified in the above table, the newly welded joint can also be corrected, but it can be rotated slightly, but after the processing time, it is forbidden to forcibly correct it. Note: the connected pipes and fittings should not be inclined, but should be basically horizontal and vertical, so as to avoid the wrong angle when installing the faucet and the normal installation cannot be carried out.
Eight, in the cooling time specified in the above table, it is forbidden to let the newly processed joint bear external force.
Precautions for installation:
1. When using PP-R pipe fittings with metal threads, the white raw material belt must be tightly sealed to avoid thread leakage.
2. When the PP-R pipe fittings with metal threads are excessively tightened, the pipe fittings may crack and cause water leakage, so attention should be paid to moderate force.
3. Precautions for installing wall tops, wall troughs and ground pipes are as follows:
Install pipes on top of the wall.
1. The spacing between cold water pipe clamps is 50 5 cm, and the spacing between hot water pipe clamps is 35 5 cm. If the fixture is not in the proper position, the pipeline will shake and make noise.
2. The direction of the water pipe should be horizontal and vertical (on the premise that the slot is horizontal and vertical), so as to avoid pulling or twisting the water pipe hard, which will cause the water outlet to be not parallel to the wall surface and affect the appearance and the installation of the mixing faucet.
3. If two water pipes walk in parallel, the distance between the two water pipes should be 10 15 cm, otherwise the water pipes are too close, and condensed water will be produced in a closed condition. Causing mildew on the wall.
Installation of wall trench pipeline
1, the construction party (decoration company) should groove according to the standard, otherwise it will affect the correct positioning of the water outlet of the water pipe, which will make it difficult to install the faucet or triangle valve.
2, water pipe spacing 3-5cm.
Ground pipeline installation
1, the pipeline is horizontal and vertical, and the outlet is vertical to the wall.
2. After the pipeline installation, attention should be paid to the protection of finished products. Water pipes walking on the ground should be leveled with cement and yellow sand to avoid direct trampling or heavy pressure.
4. If pipes and fittings are directly exposed to direct sunlight or ultraviolet radiation without any protection, the molecular structure of propylene will be destroyed and the service life will be shortened. Therefore, it is necessary to put an anti-ultraviolet foam hose (insulation sleeve) on the outside of the pipeline.
Pipeline inspection and acceptance:
During the 1. pressure test, a pressure gauge with the measuring accuracy of 0. 1 Pa must be used, and the pressure gauge should be installed at the lowest point of the whole pipeline system as far as possible.
2. After the pipeline is filled with water, remove the air in the pipeline, and then close the main valve of the water meter to start the test.
3. The test pressure is 1.5 of the maximum possible working pressure (usually 8- 10 kg water pressure). If the pipes are connected by PVC joints, the pressure test can only be carried out after the PVC joints are connected for about 5 hours, and the maximum pressure shall not exceed 6 kg. The pressure measuring and pressure maintaining time of PP-R water pipe is generally 30 minutes. For example, if the whole system is blocked and there is no water leakage, it is normal for the pressure pointer to drop to 0.5 kg. The reason is the pressure expansion inside the pipeline, but for installation, the whole pipeline system must be checked again.
Note: it is forbidden to pressurize with electric pump.
If the piping system and welding points leak during use, there are the following reasons:
1, fuser temperature is too high or too low.
2. The die is seriously worn and aged, and the welding surface is not smooth.
3. During the welding process, water and oil stains stick to the welding point, which will lead to the failure to weld the contact surface.
4, technical personnel without formal training, improper operation.
5, the decoration team in the construction process of human factors, such as heavy objects hit the water pipe or nails break the water pipe.
6, pipes and fittings are not the same brand, different raw materials, can not be welded.