Static molds – Including means within surface to confine heat exchange medium – Mold part of particular material
Reexamination Certificate
1999-12-14
2002-12-31
Silbaugh, Jan H. (Department: 1722)
Static molds
Including means within surface to confine heat exchange medium
Mold part of particular material
C249S116000, C249S079000, C264S219000
Reexamination Certificate
active
06499715
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved resin mold or pattern used for making, for example, a vehicular panel or sheet.
2. Description of the Related Art
A known resin mold for making a vehicular panel or sheet by vacuum or press forming is disclosed in, for example, Japanese Patent Publication No. HEI-07-106576 entitled “RESIN MOLD”. The mold has an electrically conductive intermediate layer of a polymer formed on a thermosetting resin, and a metal plating layer formed on the surface of the intermediate layer by, for example, nickel plating. The metal plating layer is required to have a sufficiently large thickness ranging, for example, from 50 to 300 microns to ensure durability. The formation of such a thick layer, however, requires a lot of time which is undesirable from the standpoint of productivity in a job of mold manufacture. Moreover, the layer is not satisfactory in wear resistance, since it is formed simply by plating the surface of the intermediate layer with, for example, nickel, chromium, copper or zinc. It is likely to get worn relatively soon if the mold is used for vacuum or press forming vehicular panels or sheets repeatedly.
Therefore, there is also known a resin mold which does not have any such plating layer, but is satisfactory in wear resistance, and can be made in a relatively short time. The mold has a wall structure as fragmentarily shown in FIG.
14
. The mold
100
comprises a main body
105
and a surface layer
101
formed on its surface. The main body
105
is formed from a thermosetting epoxy resin
107
containing aluminum particles
106
. The surface layer
101
is formed from a thermosetting epoxy resin
103
containing aluminum flakes
102
. The surface layer
101
has a molding surface
108
having recesses
108
a
and protrusions
108
b
by which an uneven, or grained surface is formed on the surface
110
a
of a sheet
110
, as described below.
When the mold
100
is used for press forming the sheet
110
, it is cooled to 50° C., while the sheet
110
is heated to 180° C. Then, its surface layer
101
is pressed against the sheet
110
to form it into a desired shape. The heat of the sheet
110
is transferred to the surface layer
101
, and main body
105
of the mold
100
to raise its temperature to 120° C. Then, the mold
100
is opened, the sheet is removed therefrom, and after it is cooled to 50° C. again, the process as described above is repeated for another sheet. For raising the productivity of the press forming operation, therefore, it is important to cool the mold
100
from 120° C. to 50° C. quickly and shorten the time for which it has to wait to be cooled. The aluminum particles
106
in the main body
105
of the mold
100
are, however, not uniform in size, but include large and small particles. Therefore, the aluminum particles
106
are not joined together in a regular mold, and there are, for example, small particles
106
a
not contacting medium-sized or large particles
106
b
or
106
c
. The failure of those small particles
106
a
to contact medium-sized or large particles
106
b
or
106
c
makes it difficult for the main body
105
to have a high thermal conductivity. Thus, the mold
100
has to wait for so long a time to be cooled from 120° C. to 50° C. and become ready again that it is difficult to obtain a high productivity in any press forming operation. Moreover, the main body
105
is low in strength, since small aluminum particles
106
a
are not securely held by medium-sized or large ones
106
b
or
106
c.
The surface layer
101
contains a large amount of thermosetting resin
103
, since it fills the interstices between the aluminum flakes
102
densely. On the other hand, the main body
105
contains a small amount of thermosetting resin
107
, as compared with that of the resin
103
in the surface layer
101
, since it has a porous structure formed by the aluminum particles
106
not uniform in size, but creating open pores
109
which are required for the evacuation of the cavity of the mold. As the thermosetting resin
103
or
107
has a higher coefficient of linear expansion (hereinafter referred to as coefficient of thermal expansion) than aluminum, the surface layer
101
, or main body
105
has a coefficient of thermal expansion depending on the amount of the thermosetting resin
103
or
107
which it contains. As the surface layer
101
contains a larger amount of resin, it has a higher coefficient of thermal expansion, but its thermal expansion is restricted by the main body
105
. As a result, a high stress is produced in the surface layer
101
and this eventually causes it to crack.
SUMMARY OF THE INVENTION
It is, therefore, a first object of this invention to provide a resin mold which can be made in a short time and is excellent in wear resistance.
It is a second object of this invention to provide a resin mold which is improved in thermal conductivity and strength.
It is a third object of this invention to provide a resin mold having a sufficiently small difference in coefficient of thermal expansion between its layers to prevent any cracking of its surface layer.
According to a first aspect of this invention, there is provided a resin mold which comprises a main body formed from a thermosetting resin containing metal particles and having a molding surface, and a surface layer formed on the molding surface from a thermosetting resin and containing fine particles of silicon carbide.
This surface layer can be formed simply by thermosetting the resin. As it does not call for any plating, the mold can be made in a short time. The silicon carbide in the surface layer is high in hardness and wear resistance, and makes it resistant to wear.
The resin forming the surface layer preferably contains 50 to 80% by weight of silicon carbide. If the proportion of silicon carbide is less than 50% by weight, the surface layer may not be satisfactorily resistant to wear, as its entire surface may not be completely covered with silicon carbide. If its proportion exceeds 80% by weight, the surface layer is difficult to form, since the proportion of the resin is too small for its satisfactory fluidity.
The main body has a porous structure defined by open spaces formed between the adjoining metal particles and enabling the mold to be evacuated.
According to a second aspect of this invention, there is provided a resin mold which comprises a main body formed by metal particles held together with a thermosetting resin and having a molding surface, and a surface layer formed on its molding surface from a thermosetting resin, the metal particles being spherical and substantially equal in diameter, every adjoining three of those particles contacting each other.
The mold has a high thermal conductivity owing to the spherical metal particles having substantially the same diameter and therefore maintaining contact between every two adjoining ones. When the mold is used for shaping, for example, a sheet, the heat transferred from the sheet to the mold can be dissipated effectively, so that the mold can be cooled in a short time. Moreover, every two adjoining metal particles are held fast by each other and thereby contribute to improving the strength of the mold.
The spherical metal particles preferably have a diameter of 0.3 to 3.0 mm. If their diameter is smaller than 0.3 mm, the open spaces formed between every three adjoining particles are too small for evacuation purposes. If their diameter exceeds 3.0 mm, the open spaces are too large for the mold to maintain a high thermal conductivity.
According to a third aspect of this invention, there is provided a resin mold which comprises a main body formed from a thermosetting resin containing metal particles and having a molding surface, an intermediate layer formed on its molding surface from a thermosetting resin containing pieces of a nonwoven metal fabric, and a surface layer formed on the intermediate layer from a thermosetting resin, the intermediate layer having a coefficient of thermal expansion which is l
Chujo Kenichi
Furuya Tamio
Hashimoto Hiroe
Wakabayashi Kazushiro
Yamada Satoru
Honda Giken Kogyo Kabushiki Kaisha
Merchant & Gould P.C.
Nguyen Thu Khanh T.
Silbaugh Jan H.
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