JPS6040152B2 - Insulating material for embedding heating wires - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulating material for embedding heating wires in embedded type heaters and sheathed heaters used in heating plates such as stoves, hot plates, coffee boilers, etc. The purpose is to prevent the occurrence of cracks, reduce the amount of expensive binder used, and improve insulation performance.

Generally, this type of embedded heater is made by forming a groove in a metal heating plate, and embedding a heating wire in the center of the groove with an insulating material. Conventionally, the insulating material used in the above-mentioned embedded heater has been a mixture of insulating powder of silica, talc, and magnesia to which water-soluble aluminum phosphate and silicone varnish have been added. Silica and magnesia are expensive, and this insulating powder has many types of mixtures, requiring measurement for each type, which increases man-hours.Also, it requires two types of binders: aluminum phosphate and silicone varnish, which are expensive. Since it was also necessary to mix water-soluble aluminum phosphate and water-insoluble silicone varnish, there was a drawback that the process required more complicated steps and was therefore more expensive overall. In addition, if a large amount of silicone varnish is used, the shrinkage due to the shrinkage peculiar to silicone resin during firing will be large, and the difference between the coefficient of thermal expansion of the heating plate will be large, causing cracks in the insulating powder, and the heating wire at the cracked part will be exposed to the atmosphere. Due to contact with the heating wire, oxidation of the heating wire progresses, causing wire breakage and a drop in insulation resistance. Another drawback of the insulating material is that cracks cause it to break into small pieces, making it more likely to peel off than a hot plate. The present invention eliminates the drawbacks of the insulating material for embedding heating wires in the conventional embedded heaters, etc., and embodiments of the present invention will be described below with reference to the accompanying drawings.

In FIGS. 1 and 2, reference numeral 1 denotes a heating plate made of die-cast aluminum or cast iron, and a groove 2 having a substantially U-shaped cross section is formed on one side surface. 3 is an insulating material, and a heating wire 4 is buried in the center of the groove 2.

After filling with the insulating material 3, it is pressed at a pressure of, for example, 100 k9', and is further fired for 380,005 hours. Experiments were conducted by limiting the materials to inexpensive talc (milk Mg0,4Si02, day 20), metal oxide (A203 or Mg○), and silicone varnish, and varying the blending ratio. First, considering that the particle size changes slightly during powder mixing and press molding, the weight percent of alumina 7 with a particle size of 100 French m in the molded and fired state and 30 weight percent of talc with a particle size of 30 French m. The amount of silicone varnish was varied with respect to the mixed insulating powder.

Note that the particle size shown here is the center particle size, and the actual particle size includes 95% by weight or more of particles with a particle size in the range of 10 cm for each soil. The granularity that appears in the following explanation is the same idea. In addition, the silicone varnish used later had a resin content in a fixed proportion. As a result, when the resin content of the silicone varnish is less than 3% by weight based on the insulating powder, the amount of silicone varnish is so small that it does not penetrate between all the insulating powder particles and does not act as a binder. Therefore, although it could be formed, when a durability test was conducted, the insulating material was missing and it could not be used. In addition, if the resin content of silicone varnish exceeds 15% by weight based on the insulating powder, the shrinkage due to the shrinkage peculiar to silicone resin will increase during the subsequent firing process, and the difference between the coefficient of thermal expansion of the hot plate and the insulating material will increase. A crack has occurred. From the results of the above experiments, it was found that the appropriate resin content of the silicone varnish was in the range of 5 to 15% by weight based on the insulating powder, and 9% by weight was optimal. Note that even if the particle size and blending ratio of talc and alumina were changed within the limits of the particle size and blending ratio that will be explained later, there was no need to change the amount of silicone varnish added. Next, the inventors examined various blending ratios of talc and alumina so that the resin content of the silicone varnish was 9% by weight based on the insulating powder. First, various weight percent of alumina 7 having a particle size of 100 m in the press-formed and fired state and 3 weight percent of alumina having various particle sizes shown in Table 1 below were mixed. Silicone varnish was added to the insulating powder so that the resin content was 9% by weight. This result is the first
Shown in the table. Table 1 As is clear from the results shown in Table 1, particle size 100
The particle size of the 3 weight % talc was required to be 40 mm or less, and preferably 30 mm, compared to the weight % of Alumina 7 of 3 mm.

Next, various weight % of talc 3 with a particle size of 30 rm in the molded and fired state and weight % of alumina 7 with various particle sizes shown in Table 2 below are mixed, and with respect to this mixed insulating powder,
The study was conducted by adding silicone varnish so that the resin content was 9% by weight. The results are shown in Table 2. Table 2 It should be noted that although there is no problem if the particle size of the alumina containing 7% by weight is 2,000 m or more, it is not practical because it would be difficult to bury the heating wire.

From the results in Table 2, the weight percent of talc 3 with a particle size of 30 m
The particle size of the alumina containing 7% by weight was required to be 80 French m, and 100 French m was optimal. In addition, 3
If the particle size of the talc in the weir cloud content is 40 mm or less, the particle size of the alumina in the 7% by weight is not limited to 100 mm, but may be 80 mm or more.

In addition, it was confirmed in another experiment that if the particle size of alumina containing 7% by weight is 80mm or more, the particle size of talc containing 3% by weight is not limited to 30mm and may be 40mm or less. Ta. Furthermore, the inventors investigated the blending ratio of powders with different particle sizes. The results are shown in Table 3. Note that silicone varnish was added to the powder so that the resin content was 9% by weight. Table 3 Note that contaminants include, for example, talc of 40 m or more, 80
40 even if it contains less than 5% by weight of metal oxides etc.
There was no effect on the performance if the talc with a diameter of m or less was 15% by weight or more, the metal oxide with a diameter of 801m or more was 1% by weight or more, and the total of both was 95% by weight or more.

From the results shown in Table 3, it is necessary that the amount of alumina with a particle size of 100mm is at least 1% by weight or more, and the amount of talc with a particle size of 30mm is at least 15% by weight, as well as coarse alumina particles and fine talc particles. The total amount of is 95% by weight.
It turned out that this was necessary. In addition, coarse particles are 80 to 10
It was confirmed that the same performance can be obtained with the same blending ratio even when the fine particles have a particle size in the range of 0.00 French m and 0.1 to 401 m. Note that outside this range, voids are formed between particles, and as the particle size increases, these voids expand and cracks occur. Further, the optimum case was that the amount of alumina with a particle size of 100 mm was 70% by weight, and the amount of talc with a particle size of 30 m was 3% by weight. Similar results were obtained by using magnesia instead of alumina, or by using materials with the same crystal structure, such as rouseite, mica, kaolinite, nacrite, defukite, and halloysite, instead of a tar with a scale-like structure. FIG. 6 also shows the insulation performance of each embedded heater using insulating material B, which is a mixture of silica, talc, and magnesia, and insulating material A of this example, at a temperature of 4,000 ℃ and humidity of 90%. This is a comparison. The embedded heater using the insulating material of this example uses a powder with a scaly crystal structure that allows particles to adhere easily, the particle size is mixed so that the gaps between particles are filled, and silicone varnish is mixed. Because there are
The silicone resin penetrates into the minute voids, improving insulation performance, resulting in an embedded heater with almost no insulation deterioration even in high temperatures. In addition, Figure 7 shows 30% by weight of talc with a particle size of loAm, % by weight of alumina 7 with a particle size of 100 fm, and silicone varnish added to these talc and alumina so that the resin content is 9% by weight. After filling the groove 2, it was pressed with a pressure of 100 kg' and heated at 380℃5.
This is an electron micrograph of a cross section of an insulating material that has been fired for a period of time.

As is clear from the above description, according to the present invention, at least 15% by weight of fine particles having a scale-like crystal structure with a particle size of 40 mm or less and at least 15% by weight or more of coarse particles of a metal oxide with a particle size of 80 mm or more are contained. 3 to 3 for mixed insulating powder with fine particles and coarse particles of 95% by weight or more by mixing 1% by weight or more.
By using an insulating material to which silicone varnish is added to have a resin content of 15% by weight, an embedded heater with good insulation performance and improved heating wire embedding can be achieved without missing or cracking of the insulating material. is obtained.

In addition, alumina is thermally stable, does not react with water, and is easy to mix in particle size.Furthermore, it is free from alumina, talc, etc., which is about 1/2 to 1/8 the cost of conventionally used magnesia, etc. In addition, there are only a few types of insulating powder, which eliminates the need for measuring and other man-hours, and since the powder has a scaly crystal structure and has good adhesion between particles, the binder can be silicone varnish, and the amount required is also small. Less is needed,
We can provide inexpensive products. It goes without saying that the insulating material of the present invention can also be used in a sheathed heater to achieve similar effects, such as preventing the occurrence of cracks.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embedded heater showing an embodiment of the present invention, FIG. 2 is an enlarged sectional view of the same essential part, FIG. 3 is a schematic diagram of an insulating material in an embodiment of the invention, 5 and 5 are schematic diagrams of insulating materials in other embodiments, FIG. 6 is a time characteristic diagram of insulation resistance of an embedded heater according to an embodiment of the present invention and a conventional embedded heater, and FIG. The figure is an electron micrograph of an insulating material showing one embodiment of the present invention. 3...Insulating material. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1. Fine particles having a scale-like crystal structure and a particle size of 40 μm or less account for 15% by weight or more, metal oxide coarse particles having a particle size of 80 μm or more account for 10% by weight or more, and the fine particles and the coarse particles contain 95% by weight or more. For insulating powder that is more than % by weight,
An insulating material for embedding heating wires containing 3 to 15% by weight of silicone resin.