| 摘要 |
PURPOSE:To improve perfectly hermetically sealing properties of sealed part and mechanical strength after sealing, by using a specific composition comprising MgO as a main component as a sealing agent for sealing the end of electrode removal side of a sheath type heater. CONSTITUTION:The heater wire 2 such as Ni-Cr wire, etc. is inserted into the stainless steel protecting tube 1, the electrically insulating powder 3 such as alumina, magnesia, silica, etc. is packed into the gaps of the protecting tube 1, the electrode rod 5 is inserted into the opening of the protecting tube 1 and brought into contact with the tip of the Ni-Cr wire 2. In the operation, the sealing agent 6 is packed into the gaps between the opening and the electrode 5. A composition consisting of 50-70pts.wt. MgO, 15-25pts.wt. low- melting glass containing 50-80wt% PbO, and 15-25pts.wt. beta-spodumene (LiO2, Al2O3, 4SiO2) is used as the sealing agent. In order to remove stress and strain of the protecting tube 1, the low-melting glass is melted during heating, permeated and diffused to the powdery MgO, and solidified, so that perfect sealing with improved mechanical strength is carried out.
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