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(11) | EP 0 385 675 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Improvements in and relating to tubular bodies |
| (57) This invention relates to a method of forming components including a generally tubular
(1) body such as a so-called cooker oven cavity. Briefly, the method according to
the invention comprises forming at least one groove (8) extending generally longitudinally
of a tubular body and opening into the interior of the body, wherein material from
which the body is made is outwardly deformed by fluid pressure against an outer former
defining a shape which corresponds at least to the shape of each groove, each groove
terminating at each end thereof within the longitudinal extent of the body so as to
leave a portion (12) of the body undeformed. |
[0001] This invention relates to forming components including a generally tubular body. Tubular bodies of various cross-sections, for example round or rectangular are required for many industrial and domestic applications and are made by a number of different processes such as moulding, vacuum forming, roll forming and mechanical pressing. Although particular reference will be made in this specification to the production of, what in the art is called a cooking oven cavity, the underlying concept may be used for producing tubular bodies for other uses, for example a drum for a laundry washing machine and a cavity for a dish washing machine. A cooking oven cavity in accordance with the present invention may be used for both domestic and commercial/industrial cookers heated by gas or electricity.
[0002] Cooker oven cavities are usually made from sheet metallic material and comprise a tubular body of rectangular cross-section having one end (the back) closed and an opposite end (the front) open, to afford access into the oven cavity via a hinged door. It is known to produce grooves in each opposite and vertical side wall with each groove in one wall disposed parallel to a corresponding groove in the other wall for receiving an oven shelf. In section, when viewed from the front, the grooves are usually, not necessarily triangular in cross-section with the base of the triangle constituting an oven shelf support. Thus, when viewed from the front, each side wall of the oven cavity will resemble a series of saw teeth with the cross-sectional shape of the grooves affording access from the front enabling insertion and removal of the oven shelves. Conventionally, such sheet metallic cooker ovens are produced using the following sequential steps:-
i) cut sheet to required size;
ii) deform sheet material in a mechanical press against a former and in an inward
direction considered relative to the internal cavity of a completed cooker. This results
in all cases in the width across the flat areas or faces of the vertical side walls
being greater than the distances between the inward facing extremities of the shelf
support grooves.
Deformation of the sheet to from the grooves causes unavoidable stress regions at
those edges of the sheet in the region of the ends of the grooves resulting in turn,
in buckling/ribbing due to material displacement during deformation. It is, therefore,
necessary to trim or otherwise remove the buckled and ribbed region prior to:
iii) folding the grooved sheet into a rectangular sectioned cavity;
iv) the folded sheet is then welded or roll jointed and a back wall welded or roll jointed to the side walls;
v) the so formed cavity is stove enamelled or otherwise treated with a self-cleaning composition and finally a frame hinge mounting units fitted for receiving a door.
[0003] It will be appreciated that trimming or removal of the buckled or ribbed region is not only time consuming but also wasteful of sheet material. It is an object of the present invention to reduce not only the extent of the deformed region caused by the buckling/ribbing but also the wastage of sheet material.
[0004] According to one aspect of the present invention there is provided a method of forming at least one groove extending generally longitudinally of a tubular body and opening into the interior of the body, wherein material from which the body is made is outwardly deformed by fluid pressure against an outer former defining a shape which corresponds at least to the shape of each groove, each groove terminating at least at one end thereof within the longitudinal extent of the body so as to leave a portion of the body undeformed. Preferably, the outer former is shaped to produce not only the shape of the required groove or grooves but also the finished cross- sectional and longitudinal shape of the body. Thus, where the method of the invention is used for producing an oven cavity, the cross-sectional shape of the finished body will be essentially rectangular and the ends of the tubular body will be open. The grooves formed by outward deformation of a sheet metal tubular body will, in the case of an oven cavity be disposed in, what in use, will constitute side walls of the oven cavity and serve as guides or supports for oven shelves. This allows flat regions of the side walls to be left at a width less than the width across inward facing extremities of the shelf support grooves. Thus features such as shelf stops (referred to hereinafter) can be readily integrated into the cavity side wall. The grooves may be of any desired cross-section such as, semi circular or resembling a right angled triangle. In the latter case, the base of the triangle will form a support for an oven shelf and the hypotenuse will extend upwardly to join the base of an adjacent triangular sectioned groove whereby the internal wall has a zig-zag or saw-toothed appearance.
[0005] According to a second aspect of the present invention, a method of producing a tubular body includes at least one groove extending generally longitudinally of the body with each groove opening into the interior of the body and terminating at each end thereof within the longitudinal extent of the body, the method comprising the steps of:
(a) forming a tubular body of required length and suitable cross-sectional shape from a deformable material;
(b) assembling the so-formed tubular body over an inner former including a plurality of passages with one or more inlets connectable to a source of pressure and having one or more openings which open into an external circumferential surface of the former and facing, when assembled, the interior of the tubular body;
(c) locating the so-assembled tubular body and inner former within an outer former having a shape corresponding to a final external shape of the tubular body and each groove;
(d) sealingly clamping the tubular body between the inner and outer formers, and
(e) applying a source of pressure to the said one or more inlets of the inner former so as to outwardly deform the material of the body into conformity with the outer former.
[0006] In order to reduce the possibility of oven shelves supporting hot food, dishes etc. being inadvertently removed from an oven, the grooves are conveniently formed with shelf stops. To this end, the grooves are preferably in two lengths spaced apart by an undeformed region for receiving a depending projection on the oven shelf. In such a construction, a user is required to displace the shelf slightly upwardly until the projection is disengaged from the undeformed region so as to permit removal of the shelf.
[0007] The existence of the undeformed region in a position along the length of the groove would, during normal pressing techniques, tend to produce not only regions of high stress but also a tendency to buckle or rib the surrounding area. Such tendencies are, however, considerably reduced using the method of the invention where the material of the tubular body is deformed outwardly, under pressure against the former. Preferably, deformation according to the present invention is performed using hydroforming techniques. Where indented, relieved, fielded or depressed regions are required in an oven cavity for housing heating elements, gas burners, fans, such regions can be formed simultaneously with the deformation of the grooves. In addition, those end regions to which a back panel and door frames are to be ultimately fitted and any additional reinforcement can also be formed simultaneously with the grooves.
[0008] The method of the present invention may be used for producing single oven cavities or two or more cavities in the end to end relationship from a single tubular body of any desired cross-sectional shape. Conveniently, the tubular body is of generally rectangular, circular or multi-sided cross-sectional shape prior to hydroforming. Where two or more cavities are formed from a single tubular body, all required deformation is carried in a single step and, therefore, the so formed cavity structure is divided as appropriate.
[0009] One form of cooker cavity in accordance with the present invention will now be described, by way of example, with reference to the accompanying drawings in which:-
Figure 1 is a perspective of an oven cavity showing one side and the top of the cavity;
Figure 2 is a perspective showing the cavity interior through that end which would, in a complete oven, be enclosed by an oven door;
Figure 3 is a perspective showing the exterior of the cavity from the rear and one side;
Figure 4 is a side view taken from the opposite side of the cavity shown in Figure 1;
Figure 5 is a rear view, and
Figure 6 is a plan view, and
Figure 7 and 8 show stages 1 and 2 in the hydroforming of the oven cavity of Figures 1 to 6.
[0010] Referring to the drawings, an oven cavity 1 made from sheet metal and of generally rectangular cross-section having a top wall 2, a bottom wall 3, two side walls 4 and 5, and a rear wall 6.
[0011] Each side wall 4 and 5 has a number of shelf supports 7 created by hydroforming the sheet metal into a series of panelled grooves or ribs 8. The ribs, see Figure 1 have a generally flat region 9 and an inclined region 10. The flat region 9 serves to support an oven shelf not shown. The ribs 8 are broken at 11, see Figures 1 to 4, dividing the flat region 9 into a short portion adjacent the front of the cavity and a longer portion extending towards the rear of the cavity. Cooker oven shelves frequently include a depending projection which is located in the break 11 to restrict fore and aft movement of the shelf within the oven. The break 11, constitutes a safety device to prevent removal of the shelf and hot food support therein unless a user raises the shelf to release the projection from the break.
[0012] It will be seen from the several Figures that the grooves or ribs 8 stop short of the cavity ends leaving a plain undeformed peripheral band 12. The plain undeformed peripheral band 12 serves to establish a surface against which the back 6 can be attached. The back 6 and the band 12 may be formed by roll forming or the back may be formed with a flange permitting the back to be slid into the cavity from the rear and, thereafter, seam welded to the band as shown in Figures 5 and 6.
[0013] Hinge mountings and/or door frame supports may also be formed in the peripheral band 12 surrounding the cavity opening. Following completion of hydroforming the cavity, the cavity is treated and finished using conventional stove enamelling and self cleaning coating techniques.
[0014] Although in this specification, particular reference has been made to hydroforming oven cavities, the same techniques may be used for forming cylindrical or multi-sided drums used in laundry, dishwashing and tumble drying machines. Preferably, in the latter case, the grooves are formed to follow a helical path thereby assisting in agitation of the clothes during washing and drying. Further, the method described herein may be used for forming any material capable of permanent plastic deformation, e.g. plastics material.
[0015] Figures 7 and 8 shows stages 1 and 2 in the hydroforming of the oven cavity 1. In Figure 7 a tubular body A of generally rectangular section is shown assembled over an inner former B. The inner former B includes a plurality of passages having an inlet B1 and outlets B2. An outer former 1 consisting of four parts of which two parts, namely, C1 and C2 are shown have, when assembled, a shape corresponding to the final external shape of the tubular body and each groove. In Figure 7 the two parts C1 and C2 are shown laterally displaced relative to the tubular body assembled over the inner former B. Each of the two parts C1 and C2 include a groove G1 which corresponds to the shape of the shelf support grooves 8 of the oven cavity and a further cut out G2 serves to produce the break 11 (Figure 1) which constitutes a shelf stop.
(a) forming a tubular body of required length and suitable cross-sectional shape from a deformable material;
(b) assembling the so-formed tubular body over an inner former including a plurality of passages with one or more inlets connectable to a source of pressure and having one or more openings which open into an external circumferential surface of the former and facing, when assembled, the interior of the tubular body;
(c) locating the so-assembled tubular body and inner former within an outer former having a shape corresponding to a final external shape of the tubular body and each groove;
(d) sealingly clamping the tubular body between the inner and outer formers, and
(e) applying a source of pressure to the said one or more inlets of the inner former so as to outwardly deform the material of the body into conformity with the outer former.