U.S. patent number 3,802,591 [Application Number 05/217,681] was granted by the patent office on 1974-04-09 for a synthetic resin box with double wall structure.
This patent grant is currently assigned to Mitsubiski Rayon Company Ltd.. Invention is credited to Kyohei Mizushima, Yukio Yada.
United States Patent |
3,802,591 |
Mizushima , et al. |
April 9, 1974 |
A SYNTHETIC RESIN BOX WITH DOUBLE WALL STRUCTURE
Abstract
A synthetic resin-made box with double wall structure, adapted
for use as the box frame of a refrigerator or the like, includes a
double-walled box body of a synthetic resin with wall sections
constituting the inner wall of the box body formed integrally. The
wall sections constituting the outer wall of the box body are
formed separately and extend obliquely outwardly with one edge each
thereof connected to the respective inner wall sections. After
molding the outer wall sections are brought to normal positions
extending horizontally or vertically in adjacent relation to the
inner wall sections. The adjacent edges of the outer wall sections
are connected by means of coupling members. The the space defined
between the inner wall and outer wall is filled with a heat
insulating material. The open rear end of the box body is closed
with a closure plate.
Inventors: |
Mizushima; Kyohei (Tokyo,
JA), Yada; Yukio (Tokyo, JA) |
Assignee: |
Mitsubiski Rayon Company Ltd.
(Tokyo, JA)
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Family
ID: |
27564021 |
Appl.
No.: |
05/217,681 |
Filed: |
January 13, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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63677 |
Aug 14, 1970 |
3688384 |
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Foreign Application Priority Data
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Sep 9, 1969 [JA] |
|
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44-71003 |
Dec 19, 1969 [JA] |
|
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44-101694 |
Dec 19, 1969 [JA] |
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44-101695 |
Dec 29, 1969 [JA] |
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44-123951 |
Dec 29, 1969 [JA] |
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44-123952 |
Mar 24, 1970 [JA] |
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45-24091 |
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Current U.S.
Class: |
220/592.1;
220/685; 220/684; 220/902 |
Current CPC
Class: |
F25D
23/062 (20130101); F25D 23/064 (20130101); A47B
47/042 (20130101); A47B 55/00 (20130101); F25D
2500/02 (20130101); Y10S 220/902 (20130101) |
Current International
Class: |
A47B
47/00 (20060101); A47B 55/00 (20060101); A47B
47/04 (20060101); F25D 23/06 (20060101); B65d
025/18 () |
Field of
Search: |
;220/9F,80
;206/46FC,46FR ;229/14C,14H |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Lowrance; George E.
Assistant Examiner: Marcus; Stephen
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Parent Case Text
This is a division of application Ser. No. 63,677 filed Aug. 14,
1970, now U.S. Pat. No. 3,688,384.
Claims
What is claimed is:
1. A box having a double wall structure of injection molded
synthetic resin, said box comprising:
a box-shaped inner wall having a first end, a second end and a
plurality of wall sections formed integrally with said second end
and with each other, said wall sections expanding outwardly toward
said first end;
an outer wall having an open end and a plurality of wall sections,
each of said wall sections of said outer wall being integrally
formed with one of said wall sections of said inner wall at said
first end thereof, said wall sections of said outer wall being
separated at the adjacent side edges thereof, said wall sections of
said outer wall being molded to normally diverge outwardly toward
said open end of said outer wall;
said wall sections of said outer wall being deformed toward said
wall sections of said inner wall with said adjacent side edges of
said wall sections of said outer wall in contact to define a space
between said wall sections of said inner and outer walls;
a plurality of separate coupling members, each of said coupling
members securely connecting said adjacent side edges of said wall
sections of said outer wall; and
a heat insulating material filling said space.
2. A box as claimed in claim 1, wherein said second end of said
inner wall is closed.
3. A box as claimed in claim 1, wherein said second end of said
inner wall has an opening therein, and further comprising a plate
closing said opening.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method of producing synthetic
resin-made boxes with double wall structure which are primarily
used as the box frames of refrigerators, hot boxes, dish-washing
machines, etc.
With reference to a refrigerator, the inner and outer walls of the
box frame thereof are usually made from a steel plate having a
special rust-proof coating thereon. Therefore, it is possible that
the coating is separated from the steel plate due to collision
against other articles or during use of the refrigerator for an
extended period, thus degrading the appearance of the refrigerator.
Once such condition has occurred, the box frame rusts immediately
as a result of water contacting the exposed steel plate. This not
only further degrades the apperance of the box frame, but also
causes the box frame to be progressively structurally damaged from
the rusted portion. However, when the box frame is made of a
synthetic resin, particularly of ABS resin material having
excellent mechanical properties, such as shock resistant property,
hardness and tensile strength, the entire box frame can be
maintained with an attractive appearance over an extended period,
without being damaged by collision against other articles and being
rusted by contact with water or other liquids, and thus the
aforesaid disadvantage can be eliminated. In the production of such
a box frame, it is most advantageous to mold the box frame
integrally by means of an injection molding machine, from the
standpoint of the cost of metal mold and the working cycle.
However, by conventional methods, it is practically impossible to
mold the box frame integrally since the box frame is double-walled.
Further, when an injection molding machine is used, the metal molds
must have at least 1 degree of gradient to provide for separation
of the molds and, in molding a large sized box, such as a box frame
of a refrigerator, such a slight gradient will result in a large
dimensional difference between the top and bottom of the box, which
causes a wedge-shaped gap to be formed between the outer wall
surface of the refrigerator end the adjacent wall when the
refrigerator is placed, for instance, at the corner of a kitchen,
thus spoiling the appearance of the kitchen.
SUMMARY OF THE INVENTION
The present invention has been made with these points in mind, and
the principal object of the invention is to provide a novel
synthetic resin-made box with double wall structure in which the
inner and outer wall sections can be molded integrally and which
enables the influence of a slip gradient of the metal molds used to
be eliminated from the outer wall sections.
Another object of the invention is to provide a novel synthetic
resin-made box with double wall structure, of the character
described above, in which a section of the outer wall of the box is
provided separately after molding, so that a desired shape and
function may be imparted to one section of the box.
Still another object of the invention is to provide a novel
synthetic resin-made box with double wall structure, of the
character described above, having an optional pattern formed on the
outer wall sections.
Still another object of the invention is to provide a novel
synthetic resin-made box with double wall structure, of the
character described above, having shelf-supporting ribs formed on
the inner wall sections.
Still another object of the invention is to provide a novel
synthetic resin-made box with double wall structure, of the
character described above, in which the outer wall sections formed
have a uniform strength.
Still another object of the invention is to provide a novel
synthetic resin-made box with double wall structure, of the
character described above, in which the inner and outer wall
sections molded can be easily separated from the metal molds, and
having a back panel which can be easily connected.
Still another object of the invention is to provide a novel
synthetic resin-made box with double wall structure, of the
character described above, in which the box is molded with means
which facilitate mounting of fittings for a door panel.
In order to attain the objects of the invention set forth above,
according to the invention there is provided a synthetic resin-made
box with double wall structure, formed by molding a double-walled
box body of a synthetic resin in a metal mold by injection molding.
The inner wall sections of the box body are formed integrally and
the outer wall sections thereof are formed having one end each
connected thereof to the inner wall sections. The outer wall
sections are separated from each other and extend obliquely
outwardly from such one end thereof. After the box body is removed
from the mold the outer wall sections are brought into the normal
positions extending vertically or horizontally in adjacent relation
to the respective inner wall sections. The adjacent edges of the
outer wall sections are connected with each other.
As stated above, while the inner wall of the box body is formed
integrally in a progressively converged shape, the sections of the
outer wall of the box body are formed separately and distributed in
such a manner as to provide a slip gradient to the metal mold.
Therefore, in the formation of the outer wall sections both the use
of a metal mold having a slip gradient and the integral formation
of the outer wall sections become possible. Furthermore, since the
outer wall sections are formed separately, they can be formed in a
rectangular or square shape and, since the outer wall sections thus
formed are subsequently brought into the normal positions extending
vertically or horizontally and the adjacent edges thereof are
connected with each other, the outer wall of the box can be
assembled into the shape of a cube or a rectangular parallelepiped,
regardless of the slip gradient of the metal mold. Thus, according
to the invention the outer wall of the box can be formed
integrally, even by the use of an injection molding machine and a
metal mold having a slip gradient and moreover the outer wall thus
formed is in the shape of a cube or a rectangular parallelepiped.
Therefore, in accordance with the present invention there is formed
a large sized box, such as the box frame of a refrigerator, of a
synthetic resin in a desired shape highly efficiently and at a low
cost.
BRIEF DESCRIPTION OF THE INVENTION
Other objects, features and advantages of the present invention
will become apparent from the following description of preferred
embodiments of the invention when taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a vertical cross-sectional view exemplifying a metal mold
used in the formation of a synthetic resin box according to the
present invention;
FIG. 2 is a perspective view of an injection molding machine
incorporating the metal mold of FIG. 1, which is used for forming
the box of this invention;
FIG. 3 is a fragmentary perspective view showing portions of the
injection molding machine;
FIG. 4 is a perspective view a box body molded by the metal mold of
FIG. 1;
FIG. 5 is a plan view of the box body shown in FIG. 4;
FIG. 6 is a fragmentary perspective view showing, in transverse
cross-section, the adjacent outer wall sections coupled together by
means of a coupling member;
FIG. 7 is a fragmentary perspective view exemplifying means for
closing the back side of the box body;
FIG. 8 is a vertical cross-sectional view of a box with a double
wall structure obtained from the box body molded by the metal mold
of FIG. 1;
FIG. 9 is a perspective view of the box, with shelf-supporting
ribs, notches and a motor housing concurrently formed therewith and
with a separate panel attached to the top end thereof;
FIG. 10 is a perspective view of the box body, showing the back
side thereof;
FIG. 11 is a vertical cross-sectional view showing another form of
the metal mold;
FIG. 12 is a plan view of a box body molded by the metal mold of
FIG. 11;
FIG. 13 is a vertical cross-sectional view of a double-walled box
obtained from the box body molded by the metal mold of FIG. 11;
FIG. 14 is a vertical cross-sectional view of still another form of
the metal mold;
FIG. 15 is a vertical cross-sectional view of a box body molded by
a metal mold similar to that shown in FIG. 14; and
FIG. 16 is a vertical cross-sectional view of still another form of
the metal mold.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail hereinafter with
reference to an embodiment in which a box frame of a refrigerator
is produced. In the production of the box frame, use is made of a
metal mold unit consisting of a pair of cooperating metal molds,
such as metal molds A and B shown in FIG. 1, which are capable of
molding a double-walled box body in such a manner that the inner
wall sections or panels thereof are formed integrally into the
shape of a progressively inwardly converged box and the outer wall
sections or panels afe formed separately from each other, with one
edge each thereof connected to the free edges of the inner wall
sections, and extending obliquely outwardly from such one edge. The
box body is molded by metal molds A, B and an injection molding
machine C, shown in FIGS. 2 and 3, which is of the type known in
the art, in the usual manner.
Referring to FIGS. 2 and 3, the injection molding machine C
includes a hopper D for feeding a pelletized resin therethrough, a
screw conveyor E for melting the pelletized resin and conveying the
molten resin towards a nozzle F to extrude it therethrough, a mold
mount G being movable in the direction of the arrows with one of
the metal molds A mounted thereon, and another mold mount H with
the other metal mold B mounted thereon in opposed relation to metal
mold A. In operation, the mold mount G is advanced with the metal
mold A thereon, to bring the metal mold A into engagement with the
metal mold B in the state shown in FIG. 1, and then the molten
resin is injected into the clearance defined between the metal
molds A and B through the nozzle F. After the resin has been
solidified, the mold mount G is retracted with the metal mold A
thereon and then the resultant molding is removed from metal mold
A. In the present invention, since the metal molds A, B are
constructed as shown in FIG. 1, the resultant molding will take the
form as shown in FIGS. 4 and 5. Namely, in the embodiment
illustrated the molding, that is a double-walled box body, has an
outer wall consisting of outer wall sections 1, 2, 3, 4 which are
separated from each other and extend obliquely outwardly from one
edge 1a, 2a, 3a, 4a each thereof respectively, and an inner wall 5
which is formed integrally in the shape of a progressively inwardly
converged box. The outer wall sections 1 and 2, and 3 and 4, i.e.
the opposed outer wall sections are formed in the same shape and
size, and these outer wall sections 1, 2, 3, 4 are connected to the
inner wall 5 through connecting portions 6 which respectively
extend from edges 1a, 2a, 3a, 4a of the outer wall sections towards
the inner wall 5. Each of the outer wall sections 1, 2, 3, 4 is
concurrently formed at each side edge thereof with an enlarged
engaging portion 1b, 2b, 3b or 4b as best shown in FIG. 6. The
outer wall sections 1, 2, 3, 4 thus formed are brought into the
normal vertical positions in the directions of the arrows
respectively and the engaging portions 1b, 2b, 3b, 4b of the
adjacent outer wall sections are coupled together by means of a
coupling means 7 as shown in FIG. 6, which coupling means 7 serve
simultaneously as a decorative element. Thus, the outer wall
sections 1, 2, 3, 4 are assembled into an integral outer wall.
Now, the invention described above will be further illustrated by
way of practical example.
A box body of the type described above was molded of Diapet ABS
(the tradename of the ABS resin produced by Mitsubishi Rayon
Company, Ltd.), which box body has an inner wall of 700 .times. 370
.times. 400 mm in size, an outer wall of which one pair of opposed
wall sections were 850 .times. 453 mm in size and the other pair of
opposed wall sections were 450 .times. 453 mm in size, and a wall
thickness of 3 mm, the width of the connecting portions 6 being 40
mm. In this case, metal molds defining an angle of inclination (the
angle .alpha. in FIG. 1) of 9.degree.30' and having 12 gates open
at the connecting portins 6 were used. The resin was injected at a
temperature of 270.degree.C., using an injection molding machine
having a mold-tightening capacity of 2,200 tons, while maintaining
the metal molds at a temperature of 55.degree. - 65.degree.C. After
the box body thus molded was removed from the metal molds, the
outer wall sections were brought into the normal positions and
coupled together at their side edges by means of the metallic
coupling means 7 as shown in FIG. 6.
In the manner described, a synthetic resin box with double wall
structure is obtained, but in this state, a heat insulating
material has not been filled in the space between the inner and
outer walls of the box. Further, the back side of the box has not
been closed. However, the heat insulating material may be filled in
the space between the inner and outer walls after or at the same
time when the outer wall sections are coupled together. In the
latter case, the heat insulating material is inserted between the
outer wall and the inner wall, immediately before the outer wall
sections 1, 2, 3, 4 are coupled together, whereby the charging of
the heat insulating material and the coupling of the outer wall
sections 1, 2, 3, 4 can be accomplished concurrently and the
subsequent heat insulating material-charging operation can be
eliminated. For closing the back side of the box, a pair of the
opposed outer wall sections 1, 2 may be made longer than those
shown in FIGS. 4 and 5, and the extended portions of such outer
wall sections may be flexed in the directions of the arrows shown
in FIG. 7 and coupled together at their confronting edges by means
of suitable means, such as the coupling means 7 shown in FIG. 6, or
alternatively a back wall or panel, formed separately, may be
attached to the open back side of the box and secured thereto by
suitable means such as the coupling means 7 of FIG. 6. Thus, a
double-walled box is formed, with the space between the inner and
outer walls thereof being filled with the heat insulating material,
which can be used as the box frame of a refrigerator of the type
having an opening and closing door. Such a box is shown in FIG. 8,
in which reference numeral 8 designates the back panel and 9
designates the heat insulating material, such as foamed
polyurethane or foamed styrol. Besides the ABS resin, the box may
be molded of such resins as polypropylene, polyethylene, etc.
Other advantageous features of the present invention will be
described hereunder: As is well known, the surface of the top panel
4 of a refrigerator is used as dresser, etc. and, therefore, it
must be resistive to heat and wear. If the top panel is made of a
synthetic resin material, however, such properties cannot be
imparted to the top panel, so that the box is molded with no top
plate and a metallic top panel 10, prepared separately, is attached
to the top end of the box by means of the coupling members 7 of
FIG. 6, as shown in FIGS. 9 and 10. It may be necesary to use a top
panel of complicated configuration or to provide a condensing unit
(not shown) on the bottom plate 3, depending upon the type of
refrigerator, and in such a case, the outer section 3 or 4 of the
box body is not needed. In these cases, the desired shape may be
imparted or the desired provision may be made, in the same manner
as described above.
In forming the box illustrated in FIGS. 1, 4 and 5, the shaping
surfaces of the metal molds A and B are flat and hence the surfaces
of the outer wall sections 1, 2, 3, 4 of the molded box body become
flat and smooth. Where a pattern is desired to be formed on these
surfaces, an aventurine or engraved pattern is previously formed on
the shaping surfaces of the metal molds A, B, whereby a pattern as
shown in FIGS. 3, 9 and 10 can be obtained on the outer surfaces,
for example, of the wall sections 1 and 2, concurrently with the
molding of the box, and the subsequent pattern-forming operation
can be eliminated.
Further, in forming the box illustrated in FIG. 1, 4 and 5, since
the shaping surfaces of the metal molds A, B are flat as stated
above, the inner surface of the inner wall also becomes flat and
smooth. However, by forming recesses in the shaping surfaces prior
to the molding, the complementary ribs 15 (or projections) are
formed on the inner surface of the inner wall as exemplified in
FIGS. 9 and 10, which may be used as shelf-supporting ribs when the
box is used as the box frame of a refrigerator. Such practice is
advantageous in eliminating the operation of forming such ribs or
projections, otherwise required subsequently of the molding
operation.
Still further, in the method illustrated in FIGS. 1, 4 and 5, it is
possible to mold a double-walled box integrally and in a desired
shape, such as the shape of a rectangular parallelepiped, owing to
the fact that the outer wall of the box is not subjected to the
influence of the slip gradient of the metal molds, as stated
previously. On the other hand, however, the following problem
arises: Namely, in the operation described above the outer wall
sections 1, 2, 3, 4 are molded extending obliquely outwardly from
edges 1a, 2a, 3a, 4a thereof. Therefore, when the method is applied
to the molding of a large-sized box, such as that used as the box
frame of a refrigerator, and the gates of the metal molds are
located at the connecting portions 6 between the inner and outer
walls, the areas of projection will become so large, i.e. the
length l in FIG. 1 becomes so large, that an extremely large
molding machine must be used. For instance, in case of the box
frame of a refrigerator on the order of 105 .times. 530 mm in size,
the area of projection is about 900 cm.sup.2 and thus it becomes
necessary to use a molding machine which has a mold-tightening
capacity of 3,500 tons. However, the maximum mold-tightening
capacity of the presently available molding machines is about 2,500
tons. Thus, the production of a large box as mantioned above would
require a molding machine of large capaicty as mentioned above to
be newly designed, which of source is expensive. This is
economically disadvantageous. However, if the metal molds A, B ar
constructed such that a land B' formed on the metal mold B is
received in a depression A' formed in the metal mold A, at the time
of molding, as shown in FIG. 11, the area of projection of the
metal molds is decreased accordingly and it becomes unnecessary to
use a large capacity molding machine. The form of the box body
immediately after molding by such metal molds is shown in FIG. 12.
Namely, the molded double-walled box body has an outer wall
consisting of sections 1 to 4 formed separately and extending
obliquely outwardly, and an inwardly converged inner wall 5, the
outer wall sections 1 and 2 being rectangular in shape and of the
same size, the outer wall sections 3 and 4 being rectangular in
shape and of the same size, and outer wall sections 1, 2, 3, 4
being connected to inner wall 5 through connecting portions 6. An
opening 11 is formed in the bottom wall of the inner wall 5,
leaving a rim of a width 5a.sub.1 around the periphery thereof.
After molding the box body in the manner described, the outer wall
sections are brought into the normal positions extending vertically
as viewed in FIG. 4 and the side edges 1b to 4b of the adjacent
walls are coupled together by means of the coupling members 7 to
form an integral outer wall. The opening 11 is closed by a plate
member 12 as shown in FIG. 13, which is suitably formed, such as by
vacuum forming. For the sake of decreasing the areas of projection,
the opening 11 is preferably as large as possible, but in case of
the box frame of a refrigerator, the size and shape of the opening
11 should be suitably selected while considering various equipment,
such as a motor, to be provided at this portion. An embodiment
thereof is shown in FIGS. 9 and 10. In the embodiment of FIGS. 9
and 10, the opening 11 is seen at the center of the box frame, and
at the right lower portion of the opening is formed a box-shaped
motor compartment 13 which is open to the back side of the box
frame. In case of a box, such as the box frame of a refrigerator,
it is unnecessary to form all of the four outer wall sections as
stated previously and, in this embodiment, the outer wall section
corresponding to the bottom plate of the box frame is omitted. As
shown in FIG. 11, the metal molds A, B are respectively provided
with projections A" and bores B" for receiving projections A". The
interlocking engagement between these projections A" and bores B",
plus the interlocking engagement between the aforesaid land A' and
depression B', stabilizes the relative position of the metal molds
A and B, and enables a molding of high precision to be obtained.
However, the interlocking engagement between the projections A" and
the bores B" results in the formation of holes 13 in the molding,
as shown in FIGS. 12 and 13, and these holes 13 must be closed by
suitable means. Where the holes 13 are formed at suitable locations
and are rectangular in shape, these holes may be utilized for
mounting an instrument, such as a control panel. Likewise, the
opening 11 may also be utilized for mounting equipment although it
is finally closed with the closure plate 12 as stated above.
Namely, in a refrigerator or the like, a condenser is mounted on
the outside surface of the back panel of the box frame and an
evaporator is mounted in the upper portion of the box frame. When
the opening 11 is formed in the back panel of the box frame,
mounting of this equipment can be achieved only by previously
assembling the major portion of the refrigeration system and
inserting the evaporator into the box frame from the back side.
Thus, the mounting operation of the equipment can be extremely
simplified. The difference between the metal molds A, B of FIG. 1
and the metal molds A', B' of FIG. 11 brings about the following
difference in the injection molding machine used: Namely, in
molding a double-walled box body having an inner wall of 700
.times. 370 .times. 400 mm in size, an outer wall consisting of
front and back wall sections of 850 .times. 450 mm in size and side
wall sections of 450 .times. 450 mm in size, a connecting portion 6
of 40 mm in width and a wall thickness of 3 mm, using Diapet ABS
(the tradename of the ABS resin produced by Mitsubishi Rayon
Company, Ltd.), at an angle of inclination of the metal molds (the
angle .alpha. in FIG. 1) of 9.degree.30', by injecting the resin at
the connecting portion 6, when the opening 11 was not intended to
be formed in the inner wall, the area of projection was about 5,000
cm.sup.2 and a molding machine of 2,200 tons in mold tightening
capacity was required. Whereas, when the opening 11 of 650 .times.
320 mm in size was intended to be formed in the inner wall, the
area of projection was decreased to about 2,700 cm.sup.2 and a
molding machine of only 1,250 tons in mold tightening capacity was
required for molding the box body.
In forming the box in each of the embodiments described above, the
following problem will be encountered: Namely, when the box body to
be molded is large in size and used as the box frame of a
refrigerator or the like, the edges 1a, 2a, 3a, 4a of the box body
must be equal to or even larger in thickness than the other
portions, since a door is connected thereto, and in this case,
difficulty is encountered in bringing the outer wall sections back
to the normal positions after molding. For this reason, in the case
of a large box body, it would be considered that this portion be
formed with a thickness smaller than that of the other portions to
facilitate the movement of the outer wall sections. However, such
practice is unsatisfactory because, in case of the box frame of a
refrigerator or the like, the subject portion undergoes an external
force every time the door, connected thereto, is opened or closed,
and will undergo failure in a short period of time. However, if the
outer wall sections 1, 2, 3, 4 of the box body are molded in an
arcuate shape by the use of metal molds A, B of the type shown in
FIG. 14, it will be possible to mold the portions 1a, 2a, 3a, 4a of
the respective outer wall sections at a thickness equal to or
larger than that at the other portions and at right angles to the
connecting portions 6. Namely, since the outer wall sections 1, 2,
3, 4 are curved gently as a whole, they can be brought back to the
normal positions by deforming them little by little and it is
unnecessary to reduce the thickness at any portion thereof. In
addition, since a heat insulating material, such as foamed
polyurethane or foamed styrol, is placed in the space between the
inner wall and the outer wall sections when the outer wall sections
are brought back to the normal positions, as stated previously, the
heat insulating material aids in shaping each outer wall section
into a flat panel and consequently the appearance of the box body
is not impaired. In practice, however, it is desirable to form the
subject portions in the manner as indicated by numeral 14 in FIG.
15. In the metal molds of FIG. 14, the radius of curvature r is
selected within the range of m < r < 3m wherein m is the
length of the curved wall section.
In practicing the embodiments described above, there also arises
the following problem: Namely, in removing the molded box body from
the metal molds upon separating the metal molds from each other,
the box body tends to remain on the mold B, since the contacting
area of the box body is larger with the mold B than with the mold
A, and in this case the outer wall sections 1, 2, 3, 4 and the
inner wall 5 are held so deep in the mold B that the removal of the
box body is not easy and takes a considerably long time, making
quick molding impossible. If the box body is removed with an
unreasonable force, the outer surfaces of the outer wall sections
1, 2, 3, 4 will possibly be damaged. However, such a problem may be
solved by the following method: Namely, recesses A'" are formed in
the metal mold A on which the molded box body is desired to be
retained, as shown in FIG. 16, so as to form stoppers 1d, 2d, 3d,
4d (1d and 2d being not shown in the drawing) on the inside
surfaces adjacent the outer edge portions 1c, 2c, 3c, 4c (1c and 2c
being not shown in the drawing) of the outer wall sections. In this
case, it is necessary that the inward surfaces of the stoppers 1d,
2d, 3d, 4d be inclined by an angle .beta. (about .+-. 1.degree.
relative to a horizontal plane) inwardly relative to the inside
surfaces of the respective outer wall sections 1, 2, 3, 4 (see FIG.
16). By so doing, the molded box body is retained on the metal mold
A, when the metal molds A and B are separated from each other, due
to the engagement of the stoppers 1d, 2d, 3d, 4d with the
respective recesses A'". After the metal mold B has been relatively
moved away from the metal mold A, the molded box body is removed
from the metal mold A, by pulling the inner wall 5 in the direction
of the arrow Y upon releasing the outer wall sections 1, 2, 3, 4 by
pulling them in the directions of the arrows X shown in FIG. 16.
The stoppers 1d, 2d, 3d, 4d formed on the inside surface of the
other edge portions 1c, 2c, 3c, 4c of the outer wall sections can
advantageously be used for mounting the back panel 8.
Where the box body thus molded is used as the box frame of a
refrigerator, hinges for opening and closing the door and a magnet
for holding the door in its closed position under magnetic
attraction must be provided on the connecting portions 6. The
operation of attaching such elements to the box frame may be
eliminated if the hinges and the magnet are placed, prior to the
injection of a molten resin, in recesses formed in the metal mold A
at the portions corresponding to the connecting portions 6 of the
molded box body and then injecting the molten resin, whereby said
parts are embedded in the connecting portions concurrently with
molding. It is also advantageous, for achieving smooth injection of
the molten resin and thereby molding even a large sized box body
quickly, to progressively reduce the width of the gap, formed
between the metal molds A and B, at a location remote from the
resin injecting side (the connecting portions 6) and thereby
progressively reducing the thicknesses of the outer wall sections
1, 2, 3, 4 and the inner wall section 5 accordingly.
Although the present invention has been described and illustrated
herein in terms of specific embodiments thereof, it should be
understood that the invention is not restricted only to such
embodiments, but that many changes and modifications are possible
without deviating from the spirit and scope of the invention.
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