JPS6077305A - Electrically insulating filling material of superhigh temperature sheathed heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrically insulating filling material for sheathed heaters that has excellent insulation resistance and withstand voltage under ultrahigh temperatures.

It is well known that nickel has traditionally been used as part of the heating wire and metal pipe composition as a material for sheathed heaters, and the surface temperature of the metal pipe of the sheathed heater has been kept at high temperatures of 850'C or higher for long periods of time. While using
The biggest problem is that nickel vapor is generated from the above-mentioned seed material and deprives the magnesia powder of oxygen, and on the other hand, the diffusion of the exothermic wire progresses, eventually causing a disconnection phenomenon.

The present invention has been invented in view of the above-mentioned problems, and is intended to solve these problems.

The present inventor has already clarified the economic efficiency and quality stability of the electrofused magnesia powder used in the present invention in Japanese Patent Application No. 58-89746 on an industrial scale, and the gist of the present invention is based on this electric insulating filling material. By adding an additive effect, the operating temperature of the sheathed heater can be raised to a high temperature range (800℃~
850'C) to an ultra-high temperature range (900-950°C).

The configuration of the present invention will be described below.

That is, the gist of the present invention is to add a small amount (all one type) of nickel nitrate, carbonate, and hydroxide to electrofused magnesia powder whose chemical composition and particle size have been sufficiently adjusted in advance. By filling the gap between the heating wire and the metal pipe with the added material and subjecting it to low-temperature heat treatment, nickel oxide with a high oxygen content is generated, and at the same time, magnesium oxide (magnesium oxide) is uniformly dispersed throughout the rice. The electrical insulation material of the sheathed heater is suitable for use.

Next, the present invention will be explained in more detail.

N1 (NO3) 2 is added to the electrofused magnesia powder prepared in advance as an electrically insulating filling material for high-temperature sheathed heaters.
, N i CO3, N i (CO3)2 , N+
(OH)2.3Ni (OH)2, 214icO3, etc. is added to the gap between the heating wire and the metal pipe, which is a step in the production of sheathed heaters. ~300'C1 Low temperature heat treatment is preferably performed at 200 to 260°C for 10 minutes to 24 hours, preferably 30 minutes to 8 hours. As a result, various Nikel compounds gradually thermally decompose into fine Ni
Ni2O3 is generated via O2. Furthermore, Ni2O3, which has a lot of surplus oxygen, has strong oxidizing properties, and after being filled into the sheathed heater, as the internal temperature rises when electricity is applied, it releases surplus oxygen and changes into high-temperature stable NiO. do. However, strictly speaking, regarding the high-temperature stable NiO shown here, N1O
-Ni203-based solid solution, and the stable region of relatively pure NiO is assumed to be from about 800° C. to around the melting point where thermal dissociation begins. For this reason, NiO and surplus oxygen or Ni0
The magnesia filling material containing Ni203-based solid solution and excess oxygen suppresses the generation of nickel vapor from the sheath and at the same time prevents oxygen deficiency in the magnesia powder. This ultimately brings out the high insulating properties of magnesia. Furthermore, as a starting material for additives, nitrate of Kel,
The purpose of using carbonates and hydroxides is also expected to be effective in removing impurities or harmful gases remaining inside the heater after filling.

As is clear from the above explanation, the present invention is a groundbreaking method for electrically insulating filling of ultra-high temperature sheathed heaters by adding a relatively simple process without significantly changing the manufacturing process of conventional magnesia filling materials. It makes it possible to produce materials on an industrial scale.

Examples of the present invention will be described below.

Example 2.5% by weight of Ni(NO3)2 was added and mixed to electrofused magnesia powder, which had been adjusted in advance to a packing density of 2.37 (g/cJ) and a fluidity of 203 (see/100g), and this was subjected to p5 radiation. After filling the gap between the metal pipe and the metal pipe, the diameter is reduced by rolling to create an inner diameter of 6.5 mm and a total IK of 5.
We prototyped a sheathed heater for 00'am. Incoloy 800 was used for the metal pipe. Furthermore, after heat-treating the child sheathed heater in the atmosphere at 250° C. for 6 hours, both ends of the sheathed heater were completely sealed with lead glass. The heating wire is energized to generate heat and the surface temperature of the metal pipe reaches 930℃.
After reaching °C and being sufficiently stabilized, the insulation resistance was measured. Then, the withstand voltage was determined within 60 minutes after the surface temperature of the metal pipe completely returned to room temperature after the power was cut off. For comparison, measurements were also taken on a sheathed heater prototyped only from fused magnesia powder under the same conditions as the conventional example, so the results are not listed in the table below.

In addition, N shown in the example as a nickel compound to be added is shown in the table.
In addition to i(NO3)2, N1cc13, Ni (CO3)
2, Ni (OH)t, 3Ni (OH)2 ・2NI
Nickel compounds selected from CO3 gave equally good results.

Claims (1)

[Claims] Nickel nitrate, fused magnesia powder whose chemical composition and particle size have been carefully adjusted in advance
At least one type of carbonate or hydroxide is added to the mixture, which is filled in the gap between the heating wire and the metal pipe, and then subjected to low-temperature heat treatment to produce nickel oxide with a high oxygen content, and at the same time produce magnesium oxide powder. A filling material for electrical insulation of ultra-high temperature sheathed heaters, which is characterized by being uniformly dispersed in the material.