Common production control process of tubular heating elements

- Apr 27, 2020-

Common production control process
The elements of electric heat pipe are mainly composed of five parts: alloy heating wire, magnesia oxide, metal tube, drawing rod and silicon rubber. The quality of these parts directly affects the stability and safety of product quality. In the production process of electric heat pipe, its production control and inspection are closely connected.
The main processes of producing and manufacturing electric heat pipe are: alloy electric heating wire winding, metal inner and outer tube cutting, magnesia oxide demagnetization, magnesia oxide filling, metal tube shrinkage, metal tube annealing, metal tube bending, metal tube welding, electric tube port sealing, metal tube surface treatment, water pressure test, electric tube terminal test. The metal tube shrinkage is a special process.

Heating wire winding production control:
Alloy heating wire production process is an important link in the production of electric heating tube and spring is approximately the same manufacturing process, winding in the winding machine in the professional, some of the winding machine with the design calculation of the resistance wire length and number of turns, automatic counting, winding, wire forming, cutting function, for the integration of multi-function winding machine, direct input calculated value selection on equipment, through automatic winding type electric heating wire will automatically cut off. Then, according to the length of the electric heat pipe and the size of the outer tube, insert the lead rod and screw in the length of the electric heating wire 1-2cm to ensure good contact and fastening. The length of the screw in can be tested by resistance meter, and the electric heating wire can be stretched to the specified length. When checking, it is necessary to pay attention to whether the wire is evenly wound and whether the products are arranged in a neat way.
Cutting process control of metal pipe:
Straighten the metal tube to less than 3%. Measure the cut size with a long ruler and a tape measure. The difference between the outer diameter of each pipe and the thickness of the pipe wall shall not exceed 2mm. After cutting, the cutting surface shall remove the burrs caused by friction. Meanwhile, the surface of the metal tube shall be cleaned twice with a brush and steel wire ball.
Filling process control of metal electric heat pipe:
The magnesia filling machine to fit for the position of the pipe size, vibration frequency selected 100-150 times/min, the belt derivation of the heating wire rod screwing positioning sleeve, wear it again into the empty tube fixed anchor point after the vibration table, positioning hose up and down solid and tight to prevent deviation, put the casing in the electric heating tube, fixed tube start the electric vibration table, put the magnesium oxide into the pipe and location, uniform improve positioning tube, mention while filling magnesia oxide. Different equipment has different filling methods, but the process is the same. When filled with magnesia, seal the end of the rubber sleeve. The heating wire is now in the middle of the loaded magnesia oxide. Take off the electric heat pipe and put it into the test area. Use the voltage tester to test the electrical strength according to the different power and customer requirements with the voltage of 2 000-2 500 V. Pass is qualified
process control of metal tube shrinkage:
The electric heat pipe filled with magnesia oxide was put into the electric tube shrinking machine, and the tube shrinking machine was used to compress magnesia oxide for many times, and a small amount of residual air could be discharged at the same time. Generally, the tube was compacted for 5-9 times, and then the electric strength test of 2,000-2,500v voltage was carried out with the voltage resistance tester, and the aate was tested for four times170% a9
2. After mmo cutting, the cutting surface shall remove the burrs caused by friction. Meanwhile, the surface of the metal tube shall be cleaned twice with a brush and steel wire ball.
Filling process control of metal electric heat pipe:
The magnesia filling machine to fit for the position of the pipe size, vibration frequency selected 100-150 times/min, the belt derivation of the heating wire rod screwing positioning sleeve, wear it again into the empty tube fixed anchor point after the vibration table, positioning hose up and down solid and tight to prevent deviation, put the casing in the electric heating tube, fixed tube start the electric vibration table, put the magnesium oxide into the pipe and location, uniform improve positioning tube, mention while filling magnesia oxide. Different equipment has different filling methods, but the process is the same. When filled with magnesia, seal the end of the rubber sleeve. The heating wire is now in the middle of the loaded magnesia oxide. Take off the electric heat pipe and put it into the test area. Use the voltage tester to test the electrical strength according to the different power and customer requirements with the voltage of 2 000-2 500 V. Pass is qualified.
Process control of metal tube shrinkage:
Good filling of magnesia oxide into the electric machine, electric heating tube by the indentation machine multiple shrinkage tube have the effect of compaction magnesia oxide, can put a small amount of residual air discharge at the same time, generally after 5 to 9 times shrink tube compaction, reoccupy withstand voltage tester for 2 000-2 500 V voltage electric strength test, after the test pass again into the next procedure.
Heat treatment process control of metal pipes:
Heat treatment can eliminate the stress of the heat pipe, when the heat pipe is bent into a variety of shapes, it is not easy to crack, but also can remove part of the residual air moisture in magnesium oxide. The heat treatment temperature of copper pipe is determined according to the specific production variety, with oxygen welding flame annealing, annealing temperature of about 400 ℃, visual color is dark red; Can also be carried out in the oven, but the time is longer, need more than 4h to eliminate the stress. Carbon steel pipe to carry out local annealing at about 500 ℃, the color is red, can also be annealed in the oven at 600℃ for 5h, stainless steel pipe to be annealed at about 700℃, color micro white, can also be annealed at 800℃ on the special annealing furnace.

Process control of bending of metal pipe:
The metal pipe after heat treatment should be bent in a timely manner, to ensure that the bending pipe shape, bending radius is less than 3 times the diameter of the metal pipe, the appearance of good electric heat pipe should not appear obvious mechanical damage, local expansion, concave and convex, after the completion of bending check whether the appearance of crack phenomenon. The equipment commonly used in this process are mechanical automatic pipe bender and manual manual pipe bender. After the pipe bending is formed, the electrical strength test of 2,000-2,500v is carried out with the pressure-resistant tester. Failure to break down is considered as qualified
Surface treatment process control of metal tube:
Metal pipes with impurities should also be manually cleaned. Surface treatment with water containing 3% nitric acid for internal and external cleaning, remove the surface of grease, Corrosives, and some oxides, and then with water for a second manual cleaning, and then daily check the cleanliness of the metal tube. In addition to stainless steel, copper pipe these two kinds of materials, in order to prevent corrosion and oxidation of the surface, the surface of other electric heat pipe metal materials to carry out chromium plating, copper plating or galvanized treatment, after the treatment, check the finish, pass as qualified.
Sealing process control of insulating materials for metal pipe ends:
The commonly used sealing materials are 704 white rubber, silicone rubber, silica gel, silicone oil, epoxy resin, glass powder, alumina viscose and other insulation materials. A common method for secondary sealing is to prepare epoxy resin according to the temperature requirements of different electric heat pipes. Epoxy resin is made of two kinds of insulation materials with different proportions. The adhesive is strong. After the preparation, the sealing operation should be carried out on the electrical heat pipe mouth immediately. Silicone oil, silica gel is also a commonly used sealing material of the electric heat pipe, the use of phenyl oil more. Some electric heat pipe sealing is directly in the electric heating pipe nozzle injection of silicon oil, and then use 704 silica gel sealing, this way is often used for 200-500℃ electric heat pipe. Another kind of glass sealing adhesive has powder and liquid two kinds, its cohesive force is strong, the insulation property is strong, is suitable for the high temperature electric heat pipe sealing, commonly used as 800-1 700℃ between the electric heat pipe sealing material. After the sealing process is completed, the pressure resistance tester is used to test the electrical strength under 2,000-2,500v voltage. Passing is considered as qualified
Welding process control of metal pipe outlet terminal pins:

The Terminal pins of the electric heat pipe should be spot welded to ensure the tight connection of the wire and stable conductivity. Before welding, put a high temperature resistant gasket to cover the magnesium oxide at the end. The purpose is to ensure that impurities will not stay on the magnesia during welding, otherwise it will affect the electric gap and creepage distance of the electric heat pipe. After the welding is completed, the electrical strength shall be tested with the voltage of 2,000-2,500v by the voltage resistance tester, and the pass shall be deemed as qualified.
Water pressure and seal test:
Make the two ends of the metal pipe come out of the water, the other parts are immersed in the water, add 2% hydrochloric acid for 3h, apply 1.2mpa water pressure on the professional equipment, and then conduct the electrical strength and leakage current test according to the above standards. Compliance with the relevant standards and national standards is qualified.