US3826553A

US3826553A - Front loading dishwasher employing plastic tub construction

Info

Publication number: US3826553A
Application number: US00319203A
Authority: US
Inventors: D Cushing; T Jenkins
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1972-12-29
Filing date: 1972-12-29
Publication date: 1974-07-30
Anticipated expiration: 1991-07-30
Also published as: CA1007144A

Abstract

A unipartite plastic tub is employed in a front loading dishwasher in substitution for the usual solid, lined or coated metal tubs. The disclosure relates, broadly, to those problems arising as a function of the substitution and, more specifically, to the use of a supporting frame in combination therewith to rigidify the open front end of the tub, to provide a rigid anchor base for dishwasher load component mountings and to constitute a firewall separating the plastic tub from the electrically operated equipment.

Description

United States Patent [191 Cushing et al.

[111 3,826,553 [451 July 30, 1974 1 FRONT LOADING DISHWASHER EMPLOYING PLASTIC TUB CONSTRUCTION [75] Inventors: Donald S. Cushing; Thomas E.

Jenkins, both of Louisville, Ky.

[73] Assignee: General Electric Company,

Louisville, Ky.

[22] Filed: Dec. 29, 1972 [21] Appl. N0.: 319,203

[52] US. Cl 312/253, 248/19, 312/229,

312/311 [51] Int. Cl A47b 77/08 [58] Field of Search 312/213, 214, 228, 229,

[56] References Cited UNITED STATES PATENTS 3,044,842 7/1962 Abrcsch et a1 .1 312/348 3,094,363 6/1963 Fremstad et a1. 312/344 X 3,190,709 6/1965 Dutcher ct al 312/228 3,347,613 10/1967 Krzewina 312/348 X Primary Examiner-Bobby R. Gay Assistant ExaminerWilliam E. Lyddane Attorney, Agent, or Firm-Francis H. Boos [57] ABSTRACT A unipartite plastic tub is employed in a front loading dishwasher in substitution for the usual solid, lined or coated metal tubs. The disclosure relates, broadly, to those problems arising as a function of the substitution and, more specifically, to the use of a supporting frame in combination therewith to rigidify the open front end of the tub, to provide a rigid anchor base for dishwasher load component mountings and to constitute a firewall separating the plastic tub from the electrically operated equipment.

8 Claims, 5 Drawing Figures PATENIED sum 2 or 4 PATENTEU mama SHEET & 0F 4 FRONT LOADING DISHWASHER EMPLOYING PLASTIC TUB CONSTRUCTION BACKGROUND OF THE INVENTION The invention is directed to large capacity front loading dishwashers of the type normally comprising a permanent installation and employing upper and lower dish supporting racks as opposed to the smaller, low capacity, portable and/or top loading dishwashers. The reason for the distinction is that the ultimate objective of the invention is the employment of a unipartite plastic tub in large capacity, front loading dishwashers and while some of the problems presented by a proposed use of such a tub would be common to dishwashers of either type; the majority are distinct. Typical distinctions relate to increasing wall flexibility with increasing area, the absence of encompassing metal housings, greater tub shape complexity and additional interior tub mountings such as dual rack support structures. Accordingly, the ensuing background discussion relates primarily to front loading dishwashers of the type normally adapted for a permanent, under cabinet, installation.

The high temperature, corrosive environment to which automatic dishwasher chambers are subjected dictates that the surfaces of those internal components in contact with such environment be either highly resistant, or immune, to corrosion. Corrosion resistant metals such as stainless steel represent a substantial cost factor in this highly competitive appliance field and the long term industry trend has been toward the use of inert materials to resist the corrosive effects of the chamber environment which are magnified adjacent the usual metal tub seam welds. Insofar as the tub itself, representing the far greater internal surface area exposure, is concerned; the general trend in the United States has been toward the application of an adherent plastic coating to the tub interior while European manufacturers have gone more to the use of plastic tub liners. In either event, the basic structural and design parameters that have prevailed since the advent of the modern front loading automatic dishwasher remained valid. This for the reason that overall dishwasher design parameters, both as regards utility and structural integrity, are virtually unaffected by whether the conventional metal tub is coated, lined or exposed.

Conceptually, the use of a unipartite' plastic dishwasher tub, i.e., one not requiring a more rigid backing or outer support structure, represents a substantial advance in the art. Exemplary are the greatly decreased cost factors of a molded plastic tub vis-a-vis that of a metal tub requiring a further coating or lining operation; reduction in finishing labor requirements and particularly tub welding operations; longer tub life due to corrosion resistance which is independent of faulty coating procedures or chipping; decreased thermal and acoustical transmission thus minimizing need for separate insulation; and a lesser inventory requirement for separable components susceptible of integral molding with the tub.

The reduction to practice of such a concept, as applied to front loading dishwashers on an assembly line basis, however, presents a myriad of problems which arise as a requirement for different approaches to those engineering considerations which had previously been predicated upon the use of a metal tub. The distinctions are primarily those associated with material strength, the unusually high temperature environment to which the tub is subjected and considerations relating to plastic molding procedures. Thus, while the structural integrity of a metallic box beam shape defined by the conventional front loading tub is more than sufficient to resist excessive wall deformation as a function of normal loading forces as during installation, adjustment or use and temperature variations from room ambient to approximately 255F.; such normally applied loading forces would, in the absence of appropriate compensating structure, produce unacceptable wall deformation in a like configured plastic tub. The use of strand-like reinforcing fillers such as fiber glass would, seemingly, ameliorate the overall problem of wall deformation. In actuality, however, the presence of such reinforcing fibers not only effect tub discoloration, as discussed below, but their random distribution precludes an accurate prediction of thermal growth characteristics which is an essential parameter in the design of the necessary compensating structure herein discussed. Similarly, impact strength is normally of little moment in the design and installation of metallic tubs but is a matter of major concern in plastic tub design. Furthermore, various structural features appearing in a formed plastic tub as an incident of the forming operation create problems not previously associated with metal tub fabrication. Exemplary of the latter distinction are the presence, on the finished product, of mold lines and/or mold retention ribs creating localized areas of decreased impact resistance as well as the usual wall draft to permit removal of the product, or tub, from the forming mold. One primary disadvantage arising from this necessary wall draft concerns the mounting of the upper dishwasher rack supporting tracks in parallel.

ln addition to the foregoing considerations which relate primarily to mounting and/or assembly procedures for larger capacity front loading machines, the desirability of precluding tub discoloration and the desirability for firewall separation of the tub and those electrical components constituting a fire hazard are common to all automatic dishwashing appliances. As regards plastic tub discoloration, it is preferred to avoid the use of certain conventional strand type reinforcing fillers, such as chopped strand fiber glass, for the reason that their intersection with the interior plastic surface may provide a bleed path for food stains to permeate the tub structure.

The necessity for firewall separation is a safety requirement but one which may be used to dual advantage in connection with the construction herein disclosed, which is basically nothing more than a plastic tub equipped with a door and tub support frame, by utilizing the necessary firewall construction as a power equipment support.

The prior art suggestions relating to the use of small capacity plastic tubs of the top loading type, as in US. Pat. No. 2,591,986 and the use of separate plastic tub components, as in US. Pat. Nos. 2,877,788; 3,385,306 and 3,460,878 offer little in the way of guidelines as regards a practical reduction to practice of a large capacity front loading tub for the reason that most of the problems requiring solution are not present in smaller and/or top loading units and particularly those which employ an enveloping metal housing.

The present invention relates to the mounting and support of a front loading plastic tub, the various load component. mountings and associated power operated equipment whileother of the aforementioned matters are more fully described and claimed in the following, commonly owned, copending application Ser. Nos; Ser. No. 319,556, filed Dec. 29, 1972, for Double, Reversed Mounting Boss for Plastic Tub; 319,348, filed Dec. 29, 1972, for Unit-Handled Roller Assembly for Plastic Tubs; 319,201, filed Dec. 29, 1972, for Fill Funnel Construction for Plastic Tubs; 319,555, filed Dec. 29, 1972', for Thermal Growth Compensation and Mounting for Plastic Dishwasher Tubs; 319,202, filed Dec. 29, 1972, for Radiused Mold Walls for Plastic Tubs; 317,368, filed Dec. 22, 1972, for Angled Levelling Foot for Domestic Appliance; 319,200, filed Dec. 29, 1972, for Torsionally Reinforced, Skeletal Support Frame for Plastic Tubs; 319,557, filed Dec. 29, 1972, for Impact Protection for Plastic Tub Employing Mold Retention Ribs; 319,199, filed Dec. 29, 1972, for Plastic Tub Wall Alignment for Dishwasher Rack Mounting.

Elimination of the conventional front loading metal tub and the substitution therefor of a plastic tubnecessitates the presence of mounting and/or support structure to compensate for those inherent characteristics previously available in the use of a metal tub which include a nonflammable composition, a modulus of rigidity sufficient to preclude wall deformation and provide secure'anchor points for component mountings and whose box beam tub shape insures adequate resistance to external loading forces. It is apparent that if the advantages of the invention, asregards decreased cost and weight, are to be retained the necessary mounting and support structure must not, in effect, comprise a confining tub support housing. Rather, a purpose of the invention is to provide-an operative, front loading dishwasher unit having a plastic tub whose outer walls comprise the great majority of the outer dishwasher unit construction and would actually be exposed to view prior to installation of the dishwasher unit withinan outer decorative housing, which decorative housing may comprise a free standing, pore table unit or a permanent undercabinet installation.

SUMMARY OF THE INVENTION and a relatively narrow (as compared to the tub depth) metal collar upstanding from the base assembly and extending across the top and sidewalls of the tub immediately adjacent the open end thereof. The front, open end of the tub is then secured to the surrounding, composite box beam" collar and base assembly thus anchoring the open end of the tub to a relatively rigid metal shape. The savings in fabrication cost and weight involved in bending a narrow metal strap into an approximate U-shape to form a collar and then joining the same to a base assembly as compared with the utilization of a complex metal shape to either form the tub or envelope a tub liner are obvious.

In addition to an obvious. tub support role, the base assembly is designed to perform the dual function of supporting the power operated equipment andproviding a nonflammable firewall between the equipment and tub.

The tub itself is a unipartite, injection molded tub which is homogeneous throughout and thus exhibits no surface exposed, reinforcing fibers along which food stains could permeate the tub structure. More specifically, the tub is comprised of a homogeneous, unipartite, polypropylene based plastic.

' In front loading dishwashers of the type herein disclosed, upper rack loads of 40 pounds are common as is multiple daily usage over an expected dishwasher and tub lifetime in excess of 10 years.'lt is thus apparent that the tub walls, per se, having an exemplary wall thickness of less than 0.2 inches cannot be expected to support the upper rack mounting tracks both by reason of wall deformation under such loads and inherent cold flow characteristics. As regards the latter, reference is had to the presence of track and/or roller mounting bores which, if supported solely by the plastic sidewalls, would fish tail or enlarge under repeated loading and impact. The problems of mounting bore enlargement and wall deformation are accommodated, in the present invention, by positioning the anchored supports for the upper rack structure immediately adjacent the open end of the tub so that the supporting fasteners may be anchored in the encompassing metal collar rather than in the tub sidewalls.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a broken perspective view from the open front end of a front loading dishwasher employing a plastic tub;

FIG. 2 is a bottom perspective view of the dishwasher base assembly and equipment supported thereon;

FIG. 3 is a broken, front elevation of the dishwasher;

FIG. 4 is a broken side elevation thereof; and FIG. 5 is an exploded perspective of the plastic tub and support frame.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1, 3 and 4 is illustrated a frontloading dish- Washer 10 having the usual front closure 12, lower spray bar 14, heating unit 16, and upper and lower

dish supporting racks

18, 20.

As best shown in FIGS. 1 and 4, a unipartite plastic tub 22, as well as the remaining dishwasher load component mountings such as the closure, rack supports, etc., is mounted on a tub support frame 24 comprising a floor engaging base assembly 26 and a rigidly interconnected mounting collar 28 upstanding from the forward end of the support frame.

The electrically operated power equipment for dishwasher 10 including motor 30, pump 32 and blower 34 as well as the power connections therefor are mounted to the undersurface of tub backing plate 36 which is rigidly interconnected, at opposite sides thereof, with side support panels 38 intermediate upper and lower

panel side edges

40, 42 which backing plate and side support panels comprise base assembly 26. An anchor plate 44 for door conterbalance spring 46 is carried by lower panel side edge 42 as are the conventional screw operated levelling feet 48. Inasmuch as the base assembly is of metal construction, it provides firm anchorage for conventional mounting fasteners 50 by means of which the various power equipment and power connections therefor are mounted to the undersurface of the backing plate. Those service connections extending through all of the service openings such as

service openings

52, 54 and 56, 58 in backing plate 36 and the lower plastic tub wall 60, respectively, areof nonflammable construction and the otherwise imperforate backing plate provides anadditional firewall function between the plastic tub and that portion of the power operated equipment comprising a fire hazard.

The weight of tub 22 and its contents is primarily supported along the upper panel side edges 40 engaging horizontal ledge walls 62 molded integrally with tub 22 while the open end of tub 22 is rigidified by securing the same to the encompassing mounting collar 28 as by fasteners 64 extending through the tub walls and collar. Mounting collar 28 may be rigidly interconnected with base assembly 26 in any desired manner as by the use of sheet metal fasteners 66 extending through the lower collar ends and side panels. Similarly, fasteners 68 sup porting trunnions on which rollers 70 are journalled for the adjustable anti-friction support of upper rack supporting tracks 72 extend through the tub sidewalls 74, 76 and are anchored in metal collar 28. The width of mounting collar 28, as measured in the fore and aft direction of tub depth, represents only a minor fraction thereof and is calculated to be as narrow as consistent with its role of rigidifying the open end of the tub. One readily observable limiting parameter as to the required rigidity is the maintenance of the collar mounted door latch subassembly 78 in latching alignment with the handle operated mechanism 80 carried by the door or closure member 12. This for the reason that the position of the latch subassembly 78 at the central bight portion of the generally U-shaped mounting collar is effectively at the extreme end of any lever arm movement that would be reflected by flexure of the collar as during installation, adjustment or use. A second limiting parameter as regards the width of mounting collar 28 is that it be sufficiently wide to mount the upper rack, track supporting rollers in such spaced paired arrangement as to insure the cantilever support of the upper rack in the fully withdrawn position. The reason for the required mounting of these rollers 70 to the mounting collar will be more readily understood upon considering the applied torques which must be withstood by the lower front and upper rear rollers when a fully loaded rack is withdrawn to the access position.

While the background discussion of this specification is related primarily to front-loading dishwashers of the type normally adapted for a permanent undercounter installation as opposed to the type of dishwasher having a hinged top closure for top-loading, it should be emphasized that many such machines are commercially produced and purchased for indefinite use as a freestanding model adaptable at a later time by the owner to a built-in unit beneath a kitchen countertop to blend with the matching cabinet structure of the kitchen. Generally, the difference between the unit designed as a convertible and the unit to be immediately permanently installed is the inclusion of side, rear and top cabinet appearance panels to the basic unit structure as designed for permanent installation. Therefore, it should be understood that the present invention is specifically directed to the front-loading type of dishwasher structure whether of the generally lower-cost unit having no appearance cabinet enclosure or the more elaborate, temporarily portable unit designed for later modification for use in a fixed location.

We claim:

1. In a front loading dishwasher, the improvement comprising; a plastic tub having a generally rectangular cross-section and service opening means extending through the lower wall thereof; a tub support frame including a base assembly underlying and backing said lower tub wall and a tub mounting collar upstanding from the front end of said tub support frame embracing the top and sidewalls of the tub immediately adjacent the front open end thereof in backing relation thereto; and said tub support frame having a greater modulus of rigidity than said plastic tub.

2. The dishwasher of claim 1 wherein said base assembly includes leg means mounting a nonflammable tub backing plate in spaced relation to the lower floor engaging ends thereof; service opening means extending through said tub backing plate; nonflammable means including service connections extending through said last named service opening means; electrically operated power means secured to and supported by said base assembly in underlying relation to said backing plate whereby said backing plate functions as a firewall intermediate said plastic tub and electrically operated power means.

3. The dishwasher of claim 2 wherein said tub support frame comprises an integral metal frame; and said service connections interconnecting said power means with power operated means in the interior of said tub via the service opening means in said backing plate and tub.

4. The dishwasher of claim 1 wherein the rearwardmost extent of said tub mounting collar constitutes a minor fraction of the tub depth as measured rearwardly from the open end of said tub.

5. The dishwasher of claim 4 including securing means interlocking the open end of said tub with said tub support frame.

6. The dishwasher of claim 5 wherein said securing means comprise fastener means extending through said tub and tub frame.

7. The dishwasher of claim 6 including an upper dish supporting rack; and means including at least some of said fastener means supporting said rack from said tub support frame for movement into and outwardly of the open front end of said tub.

8. The dishwasher of claim 1 wherein said plastic tub is of homogeneous, unipartite construction.