JPH0787111B2 - Seesheater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sheathed heater widely used as a heating source for general household appliances and industrial electric furnaces, and more particularly to a sheathed heater used in a relatively low temperature range. It relates to the improvement of metal pipes.

2. Description of the Related Art Conventionally, a sheathed heater has been widely used as a heat source used at a relatively low temperature by performing aluminum die casting or aluminum casting on a rice cooker or iron.

This type of sheathed heater is generally a coil-shaped heating wire provided with electrical outlet terminals at both ends is inserted into the central portion of a metal pipe, and the metal pipe is filled with an electrically insulating powder made of electro-fused magnesia powder, Then, after the diameter reduction of the rolling, an annealing heat treatment was performed to bend it into a predetermined shape.

When water repellent treatment is applied to the electrically insulating powder, the water repellent agent, which is an organic component, is carbonized by the annealing heat treatment and the original insulating property cannot be obtained. (Japanese Patent Application Laid-Open No. 59-23432).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, the above-described metal pipe that requires annealing heat treatment after rolling reduction has many manufacturing processes and is a factor of high cost including heat treatment management. On the other hand, JP-A-59-
The low carbon metal pipe found in Japanese Patent No. 23432 is excellent in that it does not require annealing heat treatment after rolling reduction, but it is excellent in a non-oxidizing furnace so that the grain size is 4 to 5 and the hardness is 60 to 80 HV. It was necessary to anneal the metal pipe within a very narrow range of 770 to 790 ° C for 6 to 8 minutes. Furthermore, when processing into a sheathed heater, to reduce the rolling diameter,
There was an increase in hardness due to processing hardness, and there was a restriction on the bending radius in bending.

Regarding the rust generation in the atmosphere, the lower carbon has the better corrosion resistance, but it is still insufficient.

An object of the present invention is to provide a sheathed heater that solves such problems.

Means for Solving the Problems In order to solve the above problems, the present invention, as a metal pipe, C: 0.005% or less, Si: 0.05% or less, Mn: 0.50% or less,
P: 0.05% or less, S: 0.05% or less, Ti: 0.001 to 0.03%, Fe:
The sheath heater is processed by using a metal pipe composed of the rest.

First of all, the reasons for limiting the above chemical components are described below. As shown in JP-A-59-23432, C has a better characteristic as the content is lower. With current state-of-the-art technology, the limit is about 0.001%, and considering the cost, 0.0
It was less than 05%. The lower the content of Si, the better, but from the viewpoint of current technical capability and cost, it was set to 0.05% or less.

Mn is a component that brings about the tensile strength, but considering the increase in hardness, it was set to 0.50% or less. P is a harmful substance,
Due to technical difficulties, it was set to 0.05% or less. S is a harmful substance and was set to 0.05% or less. Ti is the most important additive component and is added so as to form a carbide and a nitride in order to form a strong {111} texture excellent in drawability and to make it completely non-aging. That is, a small amount of solid solution carbon and solid solution nitrogen are fixed as titanium carbide and titanium nitride by the addition of Ti. The addition of Ti is also effective in suppressing excessive grain growth during annealing and preventing rough skin. However, if the added amount is large, the solid solution or precipitation of Ti causes hardening. Therefore, the added amount must be the minimum necessary. Desirably, 4 times the amount of C to C + N amount is suitable, but in the present invention, 0.001 to 0.0
It was set to 3%. Fe is the basic component of this material.

As is clear from the above explanation, it is extremely low carbon and Ti
By adding an appropriate amount of, it is possible to suppress excessive grain growth due to annealing heat treatment, as a result, it becomes easy to adjust the grain size, temperature control during annealing heat treatment 750 ~ 8
It can be roughened at 20 ° C for 6-8 minutes. Also, since C is fixed as titanium carbide, the solid solution carbon in Fe is extremely reduced, and as a result, the work hardening during the processing of the sheathed heater is also reduced, the workability is greatly improved, and the bending radius is increased. Even if it is made small, cracks, pinholes and rough skin will not occur. In addition, since there is little work hardening, there is no need to perform annealing heat treatment even when working from a hoop material to a metal pipe, and it has the advantage that it can be used as it is. The generation of rust due to the heat treatment is extremely reduced.

Examples Hereinafter, specific examples of the present invention will be described. First, Table 1
Using the metal pipes of the three compositions shown in (3), the linear sheathed heater shown in the figure was prototyped. In the trial production, a heating wire 2 made of a coil-shaped nichrome wire having electrical outlet terminals 1 at both ends was prepared, and the heating wire 2 was prepared by using a metal pipe 3 having the composition shown in Table 1.
Was filled in with the electric insulating powder 4 made of electro-fused magnesia powder to which silicone resin powder was added, and the diameter was reduced by rolling from the outer diameter of 9.0 mm to 8.0 mm.

Table 2 shows the results of occurrence of rough skin and cracks when this sheath heater was used to bend into a U shape at an arbitrary bending radius.

In the conventional example of No. 1, 100% cracking occurred at R13.0mm. Also
In the conventional example of No.2, rough skin occurs from R11.0mm and R10.0mm
A crack started to occur. On the other hand, in the present invention No. 3, R8.0
Roughness started to occur at mm, but cracking did not occur.

As is clear from the above description, the effect was exhibited by using ultra-low carbon and adding an appropriate amount of Ti, and bending work was possible even with a small bending radius, and rough skin was less likely to occur.

Therefore, it becomes possible to design with a small bending radius, and as a result, the product shape can be made compact and a low-cost product can be supplied.

Further, Table 3 shows the mechanical performance of the metal pipe 3 and the change in hardness during processing.

From the characteristics shown in Table 3, it can be seen that the metal pipe used for the sheathed heater of the present invention has a small grain size, a large elongation, and little hardening by working.

This also supports the fact that there are few cracks and the like during processing, and since there is little work hardening, it is possible to omit the annealing heat treatment after processing on metal pipes, which greatly contributes to the reduction of product costs. It has been found.

On the other hand, Table 4 shows the results of examining the degree of rust generation in a high temperature and high humidity atmosphere at 40 ° C and a relative humidity of 95%.

As is clear from Table 4, the sheathed heater of the present invention hardly generated rust, and storage of the metal pipe and storage of the sheathed heater became almost unnecessary. This is Ti
This is because the solid solution carbon in Fe was extremely reduced by the addition of.

EFFECTS OF THE INVENTION As is clear from the description of the above embodiments, the sheathed heater of the present invention, as a metal pipe, has C: 0.05% or less and Si: 0.05%.
Below, Mn: 0.50% or less, P: 0.05% or less, S: 0.05% or less, T
Since i: 0.01 to 0.03%, Fe: balance is used for the metal pipe, it has excellent corrosion resistance, little work hardening, and can be bent easily to a small bending radius. The heat treatment can be omitted, and as a result, it is possible to provide a sheath heater which is compact, has excellent characteristics, and is inexpensive.

[Brief description of drawings]

FIG. 1 is a sectional view of a sheathed heater showing an embodiment of the present invention. 2 ... Heating wire, 3 ... Metal pipe, 4 ... Electrically insulating powder.

Claims (1)

[Claims] 1. A sheathed heater equipped with a heating wire in a metal pipe and filled with electrically insulating powder, wherein the metal pipe has C: 0.005% or less, Si: 0.05% or less,
Mn: 0.50% or less, P: 0.05% or less, S: 0.05% or less, Ti: 0.00
A sheathed heater characterized by using a metal pipe composed of 1 to 0.03% and Fe: balance.