Electric heating – Metal heating – For bonding with pressure
Reexamination Certificate
1999-01-08
2001-04-24
Ryan, Patrick (Department: 1725)
Electric heating
Metal heating
For bonding with pressure
C219S117100, C219S078010, C219S091200, C219S091230
Reexamination Certificate
active
06222152
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electric heating treatment method, an electric heating treatment apparatus, and an electrode for the electric heating treatment apparatus, and more particularly, to an electric heating treatment method and an electric heating treatment apparatus for treating the surfaces of works by electrically heating the works.
2. Description of the Related Art
In general, the surfaces of the inter-valve sections of a cylinder head formed of aluminum alloy casting in a diesel engine, for example, are provided with remelting treatment to make them resistant to high thermal stress. Conventionally, the remelting treatment is carried out by applying high-density energy using a TIG arc, plasma arc, laser beam, electron beam, etc. For instance, in the case of the remelting treatment using an arc, as schematically shown in the sectional view of
FIG. 35
, a high temperature arc
42
is radiated from a torch
41
placed away by a predetermined distance from the surface of a work
40
to melt the surface of the work
40
by the heat transmitted from the arc
42
. Then, the torch
41
is continuously moved along a portion requiring the remelting treatment. At this time, right beneath the arc
42
, a new crater
45
is created by the arc
42
, and the portion melted by the arc
42
flows to a portion that has been a crater
45
a
before the torch
41
was moved so as to fill the crater
45
a
; the portion is rapidly self-cooled due to the withdrawal of heat to a base material and it solidifies. As a result, the structure of the surface portion of the work
40
is turned into a continuous finer structure as the torch
41
is moved so as to produce a reinforced layer
46
. A shielding gas
43
of argon, helium, or other gas is simultaneously sprayed from the torch
41
at around the arc
42
to prevent the melted portion from being oxidized due to contact with air.
It has been proposed to evenly heat a whole cam shaft by abutting electrodes against both ends of the cam shaft to perform preheating prior to the remelting treatment of the cam shaft as disclosed in, for example, Japanese Patent Publication No. 5-156346.
As disclosed in, for example, Japanese Patent Publication No. 6-172846, it has been known that a metal strip moved in a continuous heat treatment furnace is electrically heated by carbon roll electrodes to anneal it.
Further, it has been proposed in, for example, Japanese Patent Publication No. 64-56817, to abut an electrode against a part of a work and to form a bypass electric path for detouring a hot portion or the abutted portion of the work. Thus, when the portion other than the hot portion of the work reaches approximately the same temperature as the hot portion, the bypass electric path is released to electrically heat the whole work.
Furthermore, it has been known to electrically heat a metal strip moved in a continuous heat treatment furnace by carbon roll electrodes to anneal it as disclosed in, for example, Japanese Patent Publication No. 6-172846.
SUMMARY OF THE INVENTION
The prior art described above, however, have the following shortcoming. When the remelting treatment is performed by the arc
42
, the crater
45
is produced by the arc
42
; therefore, in order to prevent the crater
45
from being left at the end of the treatment in the portion requiring the remelting treatment, it is necessary to continuously move the torch
41
even to a portion that does not require the treatment. For this reason, the prior art present such disadvantages as difficulties in successfully remelting just a particular spot only, much time required for the treatment, and possibilities of cracks attributable to undue thermal stress developed in the vicinity of a portion under the treatment. Further, a phenomenon known as a magnetic arc blow disturbs the arc, causing displacement from time to time. Furthermore, there is a danger of the treatment not being performed because of an ignition failure. The heat withdrawal to a base material causes directive solidification from the base material to the surface of a work to perform degassing; however, the heat is withdrawn also to the surface as the torch
41
is moved, undesirably resulting in insufficient directive solidification. Still another disadvantage is the need for the shielding gas
43
to prevent the surface from being oxidized.
Using the laser beams or the like to remelt a work formed of an aluminum constituent, which is highly reflective, presents a problem of poor efficiency. This makes it difficult to achieve deep remelting treatment of a portion requiring the treatment. Concentrating energy also causes craters as in the case of the treatment carried out by arcs.
As possible solutions, there have been available the surface treatment processes implemented by electric heating as in the prior art described above. However, in the cases of the treatments disclosed in Japanese Patent Publication No. 5-156346 and No. 64-56817, the high heat conductivity of the aluminum constituent makes it difficult to successfully achieve localized rapid heating although it makes it possible uniformly heat the whole work. In the case of the treatment described in Japanese Patent Publication No. 6-172846, since the metal strip is continuously moved with respective to the carbon roll electrodes, the heat is withdrawn also to the surface of the work. Thus, all of the prior art make it difficult to protect the work surfaces from oxidization or to permit satisfactory directive solidification in the remelting treatment.
Accordingly, the present invention has been made with a view toward solving the problems described above, and it is an object thereof to make it possible to achieve quality localized treatment by an easy method by improving the conventional electric heating treatment methods to perform surface treatment such as remelting on the surface of a work.
To this end, according to the present invention, there is provided a method and an apparatus for electric heating treatment for carrying out predetermined heating surface treatment on a surface portion of a work, wherein electric current is supplied between an energization electrode and a work while maintaining a distal end of the energization electrode nearly in close contact with the surface portion to effect localized heating by electric heating that makes use of the heat generation from the self resistance of the energization electrode itself and the heat generation from the contact resistance at the interface between the distal end of the energization electrode and the surface portion, thereby providing the surface portion with the predetermined surface treatment.
Thus, the heat generated from the self resistance of the electrode itself and from the contact resistance at the interface between the electrode and the work is concentrated only on the surface portion of the work in contact with the electrode. This allows the surface portion to be locally heated, permitting the surface treatment to be quickly completed before the heat is withdrawn to other portions. Hence, abutting the electrode only against a portion requiring the treatment enables localized treatment to be carried out easily. Since the electrode is held nearly in close contact with the surface portion, the portion is not exposed to air during the treatment; therefore, the surface can be protected against oxidization without the need for using a shielding gas or the like. Moreover, during the remelting treatment, the electrode maintains the heat insulation effect even after the supply of electric current is stopped, so that the heat is hardly withdrawn from the surface, thus enabling the directive solidification to be reliably fulfilled from the base material to the surface of the work. This permits quality surface treatment to be accomplished easily. It is to be understood that the predetermined treatment means the remelting treatment of a work or alloying a work and a material different from the constituent of the work. Thus, an optimum specific treatm
Nomura Seiji
Sugimoto Yukihiro
Elve M. Alexandra
Mazda Motor Corporation
Nixon & Peabody LLP
Ryan Patrick
Studebaker Donald R.
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