Improvement of Vacuum Furnace Seal Structure

o Zhao Jinyi True Furnace Sealing Modification The vacuum furnace designed for vacuum sintering of carbide has a design temperature of 1600, a volume of 50L, and a power of 50 kW. The heating element is assembled from graphite rods and its working voltage is low (phase voltage 1000A). In order to ensure the working vacuum degree of the vacuum furnace and reduce the vacuum leakage, accessories such as the inlet electrode and the thermocouple outlet device installed on the furnace body are all designed with a sealing structure, but the sealing structure has certain problems in installation and use.

First, the improvement of the inlet electrode sealing structure The inlet electrode of the vacuum furnace (also called water-cooled electrode, copper electrode or copper electrode) is a conductive device that introduces electrical energy into the furnace heating element (in this case, a graphite rod). Water-cooled, made of copper. It is connected to the graphite heating element in the furnace chamber. Through the furnace shell (the vacuum furnace shell adopts a cylindrical double-layer water-cooled structure, not shown in the figure), a good vacuum seal must be ensured; at the same time, the electrode and furnace shell should be Has good insulation properties. Therefore, a seal structure is designed between the feed stage and the furnace shell.

The original vacuum sintering furnace enters the electrode sealing structure, there are two PTFE (or use electric bakelite) insulating sleeve between the electrode and the electrode hole of the furnace shell, and the sealing type 0 rubber ring is placed between the two insulating sleeves. . During installation, the position between the inlet electrode and the furnace shell is kept relatively fixed, and the nut outside the copper electrode is gradually tightened. The type 0 rubber seal expands under the compression of the two insulating sleeves, and finally forms the gap between the inlet electrode and the electrode hole. Completely sealed.

This kind of sealing structure seems simple, but when the nut is tightened during installation, the incoming electrode will go outwards with slight rotation, which will drive the graphite transition electrode in the furnace to rotate, and it is difficult to keep the position between the electrode and the furnace shell relatively fixed. The excessive displacement of the inlet electrode can easily damage the graphite transition electrode and the graphite heating element in the furnace.

The gap between the inlet electrode, the insulation sleeve and the electrode hole of the furnace shell is very small, there is no room for adjustment, and installation is difficult. In normal use, although there is cooling water in the inlet electrode, carbon felt is also used in the furnace to prevent heat radiation. A small part of the insulation sheath that projects into the furnace is used under the combined effect of conduction heat and the remaining radiant heat. It will soon be deformed, the compression force on the Type 0 rubber seal will decrease, and the final seal will be damaged, leading to a vacuum leak.

2. Improved electrode seal structure The improved electrode seal structure is shown. The nuts used for fastening are replaced with flanges. The 0-ring is moved outside the furnace shell. The flange 1 (welded on the furnace shell) is made of stainless steel (to prevent eddy current effect). From the perspective of insulation, the flange 2 should be used. Polytetrafluoroethylene material, which is connected with a small length of insulating sleeve into the furnace shell into the electrode hole. The gap between the flange 1 and the flange 2, the inlet electrode, and the gap between the flange 2 and the flange 3 are sealed with 0-rings. When this structure is fastened, it can ensure that there is no displacement of the inlet electrode.

The thinner insulating sleeve increases the clearance between the inlet electrode and the hole, and has a large adjustment during installation, so that the connection with the graphite transition electrode can be easily achieved. Even if the insulating sleeve is deformed, the flange sealing will not be damaged. After this improvement, it meets the requirements for installation and use and improves product quality.

Second, thermocouple sealing structure improvement Thermocouple as a temperature measurement and temperature control device temperature sensing device is an important test device for the vacuum furnace heating chamber. The working temperature of the cemented carbide vacuum sintering furnace is more than 1400, and at the same time, the precision of the temperature control is high. Therefore, the expensive B grade thermocouple is used for the temperature measurement in the furnace. Therefore, it is not only necessary to ensure that the lead of the thermocouple wire meets the requirements of the vacuum seal, but also that it is convenient to use and reduce costs.

The original thermocouple seal structure of the original thermocouple seal structure, vacuum rubber seal and PTFE sleeve drilled with two small holes, the electrode wire on the thermocouple (舛. 5mm) through the middle, tighten the outside Pressing the nut, the rubber gasket is sealed by the extrusion of the PTFE pad. Regardless of whether or not a protective sleeve is used in the furnace, the thermocouple wire is always exposed to a vacuum atmosphere, and is corroded by a carbon-containing atmosphere at a high temperature, and the service life is rapidly reduced. Practice shows that the sintering of 12 furnace products, thermocouple will be broken, which is neither from the thermocouple consumption or from the production point of view of the product is not economical.

Improved thermocouple seal structure Improved thermocouple seal structure As shown, the corundum protection sleeve (pl6mm) extends from the furnace to the outside of the furnace, and a 0-type rubber seal seals between the sleeve and the furnace shell for thermoelectricity. Even directly into the casing to measure temperature. At this time, the corundum casing isolates the vacuum in the furnace from the atmosphere outside the furnace, and the thermocouple is in the atmosphere, and long-term use will not be damaged. The disadvantage of this method is that although the corundum casing is resistant to helium temperature (above 1800T), the long-term thermal expansion and contraction will cause it to produce fine cracks. It is observed that the oxidation of the heating element near the casing should be promptly replaced.

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