JPS6057197B2 - Manufacturing method of sheathed heater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a sheathed heater used for heating.

Generally, in a sheathed heater, a heating wire with lead conductors connected to both ends is passed through the inside of a metal tube, and insulation is maintained by filling the gap between the heating wire and the metal tube with insulating powder such as magnesia.
They were manufactured by reducing the tube diameter and sealing both tube ends with heat-insulating material such as silicone rubber.

However, since magnesia powder is active, it has the property of absorbing moisture, and the sealing material such as the silicone rubber also cracks when heated repeatedly, causing water absorption through the gaps.

The absorbed magnesia may cause a decrease in insulation properties.
In order to prevent this deterioration of insulation properties, magnesia powder is manufactured by mixing heat-resistant insulating resin such as silicone resin in advance, and then the silicone resin is melted by heating with a heater and the silicone resin is applied to the surface of each fine particle of magnesia. In addition to forming a coating on magnesia, methods are being used to make magnesia inactive by bonding individual fine particles to prevent hot air from entering.

However, in this method, it is difficult to mix the amount of silicone resin, and it is difficult to obtain the desired product whether it is too much or too little. The present invention allows silicone oil to permeate through the tube end of a sheathed heater by capillary action, and by heating twice at different temperatures, the silicone oil is completely solidified and the oil diluent is introduced into the tube. The purpose is to inactivate magnesia and completely prevent air from entering, without leaving any residue, and the purpose is to obtain a sheathed heater that is easy to manufacture, has high insulation properties, and has little deterioration. .

The manufacturing method of the present invention will be explained below with reference to the drawings. 1 is a sheath tube made of a metal tube, both ends of which are open, and the tube wall is completely non-porous.

Inside this sheath tube, a spiral electric heating wire 3 having lead conductors 2, 2' attached to both ends by welding or the like is inserted and installed. A temporary stopper 4 is provided at one opening of the sheath tube, and magnesia powder is tied between the electric heating wire 4 and the inner wall of the sheath tube from the other opening. By this operation, the electric heating wire is insulated and supported with respect to the sheath tube. A temporary stopper 4' is also applied to the opening into which the magnesia powder was introduced. Next, the pressure is reduced by sequentially applying blows to the wall of the sheath tube from one end of the outer periphery. Due to the reduced pressure, the sheath pipe increases its length and reduces its diameter, becomes a predetermined length, and is molded into a shape according to the purpose of use. The molded product is thoroughly dried at a temperature of 200°C to 400°C. This drying time is approximately 2 hours or more. Remove the stopper 4,4'' from the dried product and immediately immerse it in a silicone oil bath.The faster the time between drying and immersion in the bath, the better.Magnesia has excellent absorption properties. If you take time during this time, there is a risk that it will suck out again.The immersion time in the silicone bath is about 4 to 5 hours.During this time, the magnesia powder in the sheath tube absorbs silicone oil from both ends due to capillary action. The product taken out of the bathtub is placed in a furnace and heated at 200°C for about 2 hours.During this time, most of the silicone oil is dried.When this drying is complete, the temperature of the furnace is raised to 340°C to 410°C and heated for about 2 hours. Then, the sheathed heater is completed.Alumina, zirconium oxide, beryllia, thorium oxide, etc. may be used in addition to the magnesia powder, and methyl or silicone polymer may be used as the silicone oil used in the bathtub.

Figure 2 shows a comparison of insulation resistance characteristics between the sheathed heater manufactured by the present invention and a conventional sheathed heater. C shows the product heated for 2 hours, and C shows the product sealed with conventional silicone rubber. The sheathed heater manufactured according to the present invention has achieved particularly good results. As described above, according to the present invention, silicone for inactivation is infiltrated into an insulating material such as magnesia of a sheathed heater from the end face of a sheath tube by capillary action, so silicone is mixed with the entire magnesia. Unlike other things, only a small amount is sufficient.

Moreover, since the intrusion of air is seen from the end face of the sheath tube, the purpose can be sufficiently achieved by inactivating only the end face. In addition, since the manufacturing method is simple, conventional manufacturing equipment can be used as is, and it can be used in sheathed heaters for high-temperature casting, and sheathed heaters that require welding of the base etc.

[Brief explanation of drawings]

The drawings show one embodiment of the sheathed heater manufactured by the present invention. Fig. 1 is a longitudinal cross-sectional side view of the sheathed heater showing one process during manufacturing, and Fig. 2 shows the sheathed heater of the present invention and the conventional sheathed heater when energized. FIG. 1...sheath pipe, 2,2''...outlet conductor, 3...
...Electric heating wire.

Claims (1)

[Claims] 1 Install an electric heating wire with lead conductors connected to both ends through the inside of the sheath tube, pack magnesia powder, etc. between the sheath tube wall and the electric heating wire, and reduce the diameter of the sheath tube to increase the density of the magnesia powder, etc. The product is heated and dried, then immersed in a silicone oil bath for about 4 to 5 hours, and the product taken out from the silicone oil bath is heated at a temperature of about 200°C for about 2 hours, and then heated to a temperature of about 340°C to 410°C. A method for manufacturing a sheathed heater characterized by heating for about 2 hours.