Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Starting material is nonhollow planar finite length preform...
Reexamination Certificate
1998-02-02
2001-02-13
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Starting material is nonhollow planar finite length preform...
C156S285000, C156S292000, C425S388000, C425S504000
Reexamination Certificate
active
06187252
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the art of household appliances and, more specifically, to a method and apparatus for thermoforming a plastic appliance door from two plastic sheets.
2. Discussion of the Prior Art
It is commonly known to produce a plastic appliance door, and in particular, a refrigerator door by independently manufacturing the various components that combine to make the door and then, in a separate manufacturing step, assembling the various components. For example, as represented in
FIG. 1
of this application, it is common to form an outer refrigerator door panel
5
from a single stamped sheet of metal which is folded in order to form sides
8
and inwardly turned flanges
10
. The inner liner
13
associated with such a refrigerator door is often thermoformed on a male mold member. In general, such an inner liner
13
is made on the male mold member because of the high draw ratios that would be involved with the use of a female mold member. Once the outer refrigerator door panel
5
and the inner refrigerator door liner
13
are formed, inner liner
13
is secured to door panel
5
along flanges
10
, along with an annular gasket
16
, by means of a plurality of connecting strips
18
and screws
20
. A separate handle
22
is then secured to outer refrigerator door panel
5
by means of screws
24
. Outer refrigerator door panel
5
is also generally formed with upper and lower aligned holes
27
which are adapted to receive pivot bushings
29
for mounting the assembled refrigerator door to a refrigerator cabinet. For insulation purposes, it is also known to inject foam between refrigerator door panel
5
and inner liner
13
after complete assembly of the refrigerator door.
The manufacturing procedure associated with constructing such a refrigerator door formed from various, individually produced components which are later assembled together, is inefficient. Such a process is extremely time consuming and requires various manufacturing stages wherein the individual components are made and assembled. In addition, since the outer refrigerator door panel
5
is made of metal, its outer surface must be painted for aesthetic purposes. The need for these multiple manufacturing stages obviously increases the overall costs associated with manufacturing such a refrigerator door.
It has also been proposed to manufacture a hollow refrigerator door formed entirely from plastic. Such an arrangement is generally shown in
FIGS. 2
,
3
a
and
3
b
and disclosed in U.S. Pat. No. 5,306,082. According to this method of making a refrigerator door, the first step in the manufacturing process involves independently making the individual components which combine to form the inner door members. As shown in
FIG. 2
, these inner components generally constitute opposing side members
35
,
37
and a plurality of shelf defining members
40
-
42
. In general, these interior components are separately blow molded by arranging two parallel sheets of plastic between first and second mold members (see
FIGS. 3
a
and
3
b
), closing the mold members so as to pinch the sheets about outer perimeters thereof and injecting air between the sheets so as to cause the sheets to expand against the mold members. Side members
35
,
37
and shelf members
40
-
42
are formed with tabs
45
which are adapted to extend within slots
48
formed in an outer door panel
50
that is constituted by a hollow plastic slab which is also blow molded. In a final stage of the blow molding of the outer door panel
50
, the tabs
45
provided on side members
35
,
37
and shelf members
40
-
42
are positioned within slots
48
such that slots
48
form about tabs
45
in order to secure side members
35
,
37
and shelf members
40
-
42
to outer door panel
50
. An annular gasket
52
is then secured by means of connecting strips
55
and screws
57
to an outer annular flange portion
59
of door panel
50
. In addition, a separate handle
62
is secured to door panel
50
by means of screws
64
.
The refrigerator door construction arrangement as represented by
FIGS. 2
,
3
a
and
3
b
has several advantages over the construction arrangement represented in FIG.
1
and discussed above. First, the entire refrigerator door of the
FIG. 2
arrangement is formed from plastic and therefore its desired shape can be readily varied. In addition, such a manufacturing operation does not require a subsequent painting stage for outer door panel
50
. Furthermore, making the outer door panel
50
from plastic can provide some additional heat efficiency benefits since the metal door panel of the
FIG. 1
arrangement will be a better conductor of heat into the refrigerator than the plastic door. Finally, the use of plastic presents the ability to integrally form the outer door panel with a handle as also proposed in the prior art and represented in FIG.
4
.
However, these previously proposed all-plastic refrigerator door arrangements suffer from various drawbacks. For example, the various components which make up each of the refrigerator doors are still separately manufactured and subsequently assembled. As indicated above, this is considered inefficient as it adds to the manufacturing time and cost associated with making such doors. Furthermore, the known all-plastic refrigerator door arrangements are generally not aesthetically appealing since the interconnection between the various components are often noticeably visible and there will be a pinch line where the mold halves close. Finally, although forming an outer door panel of plastic with an integrally formed handle reduces manufacturing costs associated with the outer door panel and is rather aesthetically appealing, the prior proposed system as represented in
FIG. 4
forms the handle, generally indicated in
68
, by creating a recess in the front surface
71
of the outer door panel
74
which inherently reduces the energy efficiency of the refrigerator door as a whole due to its reduced thickness.
Therefore, there exists a need in the art for a plastic refrigerator door which can be produced in a minimum number of manufacturing stages so as to reduce the manufacturing costs associated with the refrigerator door. In addition, there exists a need in the art for a all-plastic refrigerator door and method of making the same wherein the energy efficiency associated with the refrigerator door is maintained or increased. Finally, there exists a need in the art for an aesthetically appealing plastic refrigerator door.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved method and apparatus for thermoforming an all-plastic appliance door which minimizes the manufacturing stages and associated costs of producing such a door.
It is another object of the invention to provide an improved thermoforming apparatus wherein the male and female mold members for forming the inner and outer door panels are both located on a first movable platen.
It is a further object of the present invention to provide an improved method of thermoforming wherein an exterior plug assist is located within a shuttle box mounted on a second movable platen.
It is a still further object of the invention to provide an improved method of thermoforming wherein the shuttle box and exterior plug assist are mounted for shuttle movement between the male and female molds.
These and other objects of the present invention are achieved by a method and apparatus for thermoforming an appliance door including providing a male mold member shaped to the contour of an inner door liner being formed and providing a female mold member shaped to the contour of an outer door panel being formed. Also provided is a movable shuttle box including a first plug assist, the shuttle box and first plug assist being moveable into registry with either of the male and female mold members. Further to this method, a first plastic sheet is moved into position with respect to the male mold member and subsequently the shuttle box and first plug ass
Rhoades Randy R.
Tirrell Steven G.
Lee Edmund H.
Maytag Corporation
Orsund Allan P.
Silbaugh Jan H.
LandOfFree
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