Ordinary magnesium oxide powder absorbs moisture relatively quickly, and requires strict glass sealing technology to prevent external moisture from entering the electric heating tube to achieve better results.
(1) The structure of the seal
The compressive strength of the glass material is greater than the tensile humidity. Therefore, when the structure is designed, the glass is subjected to compressive stress. The typical sealing structure, the sealing of this structure, when the electric heating tube is cooled, the unsealed metal at the end of the tube can be Free contraction produces a bending moment at the interface of glass and metal. Because the two sides are symmetrical, the moments cancel each other out and the sealing is reliable.
(2) Sealing process
1. Handling before sealing
(1) Cut the magnesium oxide powder at both ends of the heating tube to a depth of about 8mm.
(2) Clean the inner surface of the tube and the lead rod without leaving MgO powder and dirt.
(3) Put the above-mentioned electric heating tube into an oven at 200℃ to remove moisture so that the insulation resistance is greater than 10kMΩ.
2. Put the above-mentioned electric heating nozzle quickly into an appropriate amount of glass sealing material, and then heat it to 800±20℃ to realize the sealing of the nozzle.
Heating method:
(1) Box-type eMule, 880°C, 4 minutes, with the furnace cooling at 300°C and out of the oven.
(2) Gas-protected electric furnace, with 50% oxygen content, and the method is the same as (1) Heating and cooling.
(3) Box-type electric furnace, cover the nozzle with quartz glass or high temperature resistant material before entering the furnace.
(4) For high-frequency electric furnace, put the output coil of the high-frequency electric furnace on the part that needs to be heated, and wait for it to be heated to 880℃, and then cool down after power off.
(5) Alcohol torch, heat the nozzle of the alcohol torch for about 40 minutes to reach 880℃～550℃.