WO2011026871A2

WO2011026871A2 - Method and installation for manufacturing a shelf, particularly for refrigerated installations

Info

Publication number: WO2011026871A2
Application number: PCT/EP2010/062824
Authority: WO
Inventors: Jean-Gérard LECONTE; François VARDON
Original assignee: Saint-Gobain Glass France
Priority date: 2009-09-01
Filing date: 2010-09-01
Publication date: 2011-03-10
Also published as: WO2011026871A3; FR2949377B1; FR2949377A1

Abstract

This method of manufacturing a shelf (1), particularly for a refrigerator or the like, in which the shelf comprises a panel (2) and a frame (3) which surrounds at least part of the periphery of the panel, the frame (3) being made of a plastic capable of undergoing shrinkage as it cools from a temperature higher than ambient temperature to ambient temperature, comprises: manufacturing the frame (3) by moulding the plastic in a moulding device; - extracting the frame (3) from the moulding device; - in a heating device, maintaining the frame (3) at, or heating the frame (3) to, a temperature higher than or equal to a minimum insertion temperature for inserting the panel (2) into the frame, the minimum insertion temperature being the minimum temperature at which the dimensions (A, B) of the frame (3) in its main plane are strictly greater than the corresponding dimensions (C, D) of the panel (2); inserting the panel (2) into the frame (3) at an insertion temperature higher than or equal to the minimum insertion temperature; assembling the panel (2) and the frame (3) by cooling the frame, so as to cause the frame to shrink around the panel and cause at least part of the frame to come into contact with the panel.

Description

METHOD AND INSTALLATION FOR MANUFACTURING A SHELF, PARTICULARLY FOR REFRIGERATED INSTALLATIONS The present invention relates to a method of manufacturing a shelf which is intended to be mounted, advantageously removably, in the chassis of a piece of furniture. In particular, it relates to a method of manufacturing a shelf that can be used in refrigerated compartments, such as refrigerated cabinets, refrigerating units, refrigerators, for supporting items, particularly food items. The invention also relates to an installation for manufacturing a shelf and to a shelf.

Conventionally, a refrigerator shelf is in the form of a plastic or glass panel intended to support items, which is associated with a plastic frame or surround. The plastic frame is designed to prevent the risk of injury on the sharp edges of the panel and/or to reinforce the panel. The sides of the plastic frame may be straight and uniform or more complex in shape, possibly having in particular peripheral parts or extensions for functional or aesthetic purposes. The front side of the frame may, for example, form a handle for handling the shelf, and the lateral and rear sides of the frame may be designed to collaborate with the chassis of the item of furniture in which the shelf is intended to be fitted, which generally has shelf supports.

To manufacture such a shelf, there are various methods of assembling the plastic frame with the panel. In a method known as "encapsulation", the plastic of the frame is injected onto the periphery of the panel placed in a mould, such that the panel is held in a pincer grip by the plastic which constrains it around its edges and on each of its upper and lower faces. However, a method such as this requires a dedicated installation for each design of shelf produced, leading to a high cost of manufacture.

In other known methods, the plastic frame is formed independently of the panel and the frame is assembled with the panel by bonding or clipping or nestling the frame around the panel. In particular, US-A-6 679 573 describes a shelf of which the glass panel and the plastic frame are assembled by clip fastening. More specifically, the frame has elastically deformable panel retaining tabs which deflect upon insertion of the panel into the frame, then return to their initial rest position in such a way as to retain the panel. With such a method of assembly by clip fastening, there is a risk that the tabs of the frame will deform and release the glass panel when a heavy load is applied to the shelf in its configuration of use. This risk means that it becomes necessary to provide, in the chassis of the refrigerator, ribs which are intended to support the tabs of the frame in order to prevent them from deforming, as such deformation could cause the panel to become detached from the frame of the shelf.

It is this disadvantage that the invention more particularly seeks to remedy by proposing a method of manufacturing a shelf, particularly for a refrigerator or the like, that makes it possible to obtain reliable assembly between the panel and the frame of the shelf, particularly an assembly which is able to withstand a significant loading applied to the shelf in its configuration of use, without requiring the chassis of the item of furniture in which the shelf is intended to be mounted to have a special structure, this method of manufacturing further being able to be automated for the most part.

To this end, the subject of the invention is a method of manufacturing a shelf, particularly for a refrigerator or the like, this shelf comprising a panel and a frame which surrounds at least part of the periphery of the panel, the frame being made of a plastic capable of undergoing shrinkage as it cools from a temperature higher than ambient temperature to ambient temperature, characterized in that it comprises:

- manufacturing the frame by moulding the plastic in a moulding device;

- extracting the frame from the moulding device;

- in a heating device, maintaining the frame at, or heating the frame to, a temperature higher than or equal to a minimum insertion temperature for inserting the panel into the frame, where the minimum insertion temperature is the minimum temperature at which the dimensions of the frame in its main plane are strictly greater than the corresponding dimensions of the panel, the minimum insertion temperature being higher than ambient temperature;

- inserting the panel into the frame at an insertion temperature higher than or equal to the minimum insertion temperature; - assembling the panel and the frame by cooling the frame, so as to cause the frame to shrink around the panel and cause at least part of the frame to come into contact with the panel. Within the meaning of the invention, the term "frame" denotes either a frame surrounding all the edges of the panel or a partial frame surrounding just some or part of the edges of the panel. In addition, "ambient temperature" means a temperature lower than 30°C, generally of the order of 15 to 25°C.

In the method according to the invention, the panel is assembled with the frame of the shelf by the shrinkage of the plastic of the frame around the panel, making it possible to obtain not only a secure attachment and, where appropriate, a good seal between the panel and the frame, but also improved mechanical strength of the shelf, particularly under load. The step of heating the frame to a temperature higher than or equal to the minimum insertion temperature further makes it possible to guarantee that the panel will be able to be fitted easily into the frame, with no interference between the frame and the edges of the panel. Hence, the step of inserting the panel into the frame can readily be automated.

According to other advantageous features of the method according to the invention:

- the panel is inserted into the frame at an insertion temperature at which a limiting dimension of the frame in its main plane is strictly greater than a corresponding dimension of the panel, the difference between the limiting dimension of the frame and the corresponding dimension of the panel being at least of the order of 0.5 millimeters;

- prior to inserting the panel into the frame, an adhesive and/or a soft insulating gasket is deposited over at least part of the frame intended to come into contact with the panel;

- the frame is manufactured by injection moulding the plastic;

- the frame is maintained at, or heated to, a temperature higher than or equal to the minimum insertion temperature using a resistive and/or infrared heating device;

- after the panel has been inserted into the frame, a locking member for locking the panel relative to the frame is introduced into a hole made in a rib of the frame; - the locking member is introduced into the hole in the frame before the frame has completely shrunk around the panel;

- the material of which the locking member is made has a thermal expansion coefficient lower than the thermal expansion coefficient of the material of which the frame is made;

- the shrinkage of the frame is at least 0.25% with respect to the dimensions of the frame in its main plane, and preferably ranges between 0.5% and 2%, and more preferably is of the order of 1 .5%. Another subject of the invention is an installation for manufacturing a shelf, particularly for a refrigerator or the like, this shelf comprising a panel and a frame which surrounds at least part of the periphery of the panel, the frame being made of a plastic capable of undergoing shrinkage as it cools from a temperature higher than ambient temperature to ambient temperature, the installation comprising a moulding device for manufacturing the frame by moulding the plastic, wherein the installation further comprises a heating device for heating the frame, after its extraction from the moulding device, to a temperature higher than or equal to a minimum insertion temperature for inserting the panel into the frame, where the minimum insertion temperature is the minimum temperature at which the dimensions of the frame in its main plane are strictly greater than the corresponding dimensions of the panel, the minimum insertion temperature being higher than the ambient temperature. According to other advantageous features of the installation according to the invention, considered in isolation or in combination:

- the heating device is a resistive and/or infrared heating device;

- the installation comprises a conveyor for conveying the frame from the moulding device to the heating device, the heating device being designed to allow the frame to be heated while it is on the conveyor.

Finally, another subject of the invention is a shelf, particularly for a refrigerator or the like, comprising a panel and a frame which surrounds at least part of the periphery of the panel, this shelf being manufactured using the above method.

The features and advantages of the invention will become apparent from the description which will follow of one embodiment of a method and of an installation for manufacturing a shelf according to the invention, which description is given solely by way of example and made with reference to the attached drawings in which:

- Figure 1 is a view from underneath of a shelf according to the invention;

- Figure 2 is a perspective view of the shelf of Figure 1 during a first step of inserting the panel into the frame;

- Figure 3 is a schematic partial cross section on a larger scale on the plane III of Figure 2;

- Figure 4 is a view similar to Figure 2 during a second step of inserting the panel into the frame;

- Figure 5 is a perspective view on a larger scale of a single piece incorporating locking members for the shelf of Figure 1 ; and

- Figure 6 is a graph showing the change in the limiting dimension of the frame, after its extraction from the moulding device, as a function of frame temperature.

The shelf 1 depicted in Figure 1 is intended to be fitted in a refrigerator. Figure 1 is a view of the shelf 1 from underneath, that is to say a view of its underside, which is intended to face downwards when the shelf in its configuration of use mounted in the chassis of a refrigerator. Throughout this description, the terms "front", "rear", "right", "left", "lower", "upper" and equivalent expressions refer to the configuration of use of the shelf mounted in the chassis of a refrigerator.

The shelf 1 comprises a parallelepipedal panel 2, made of mineral or organic glass, and a relatively rigid plastic frame 3, for example based on polypropylene. The frame 3 is designed to allow the shelf 1 to be mounted in the chassis of a refrigerator, not depicted, that is to say comprises mounting means able to collaborate with complementary means provided in the chassis of the refrigerator.

The frame 3 comprises a peripheral vertical wall 4 which defines a rectangular outline more or less complementing the periphery of the panel 2 and which is intended to press against the edges, or edge faces, of the panel when the frame is in the configuration in which it is assembled with the panel. The wall 4 of the frame 3 has a height greater than the thickness of the panel 2 and surrounds the latter over its entire thickness in the configuration in which the frame is assembled with the panel.

In this assembled configuration, the distance between the wall 4 of the frame 3 and the edges of the panel 2 is small, particularly zero, at least in certain places, as a result of the method of manufacture according to the invention, which involves shrinking the frame 3 around the panel 2. This method of assembly by shrinkage makes it possible to ensure a secure connection and, if appropriate, a good seal between the frame and the panel.

On its upper face 3A and around its entire periphery, the frame 3 forms an inwardly directed rim 5, of small thickness, shown in dotted line in Figure 1 and intended to press against the upper face 2A of the glass panel 2. The lower face 3B of the frame 3 comprises, on its lateral sides 32 and 34, cavities 6 separated by ribs 7, allowing material to be saved in these regions while at the same time allowing the frame 3 to retain sufficient rigidity. These cavities 6 and ribs 7 may be obtained using the technique known as "air moulding".

The front side 31 of the frame 3, intended to face the front edge 21 of the panel 2, comprises a rigid rim 35 designed to press against the lower face 2B of the panel. The rim 35 has a width l₃₅, in a direction Y perpendicular to the front side 31 of the frame, greater than about 0.5 centimeters, preferably ranging between about 0.8 centimeters and about 1 centimeter.

The rim 35 delimits, with the wall 4 and the rim 5, a groove 37 that accommodates the front edge 21 of the panel 2. As depicted in Figure 1 , the rim 35 extends only over a portion of the length of the front side 31 . As a variant, the rim 35 could be longer and extend over the entire length of the front side 31 , until it attaches to the two lateral sides 32 and 34 of the frame 3. In this instance, the rigidity and loading strength of the shelf 1 are further improved.

The right 32 and left 34 lateral sides of the frame 3, which are intended respectively to face the right edge 22 and the left edge 24 of the panel 2, each comprise a rim 39 designed to press against the lower face 2B of the panel. Each of the rims 39 has a width l₃₉, in a direction X perpendicular to the lateral sides 32, 34 of the frame 3, of less than about 0.5 centimeters and preferably ranging between about 0.2 centimeters and about 0.3 centimeters.

Furthermore, the rear side 33 of the frame 3, intended to face the rear edge 23 of the panel 2, comprises a rib 7A which runs alongside the panel 2, being offset inwardly with respect to the external peripheral edging 8 of the frame 3. The rib 7A projects with respect to the lower face 2B of the panel when the frame is gripping the panel. The rib 7A defines part of the wall 4 of the frame, intended to come into contact with the rear edge 23 of the panel.

Two characteristic dimensions of the frame 3 in its main plane, which is a plane parallel to the plane of the panel 2 in the assembled configuration, are denoted A and B. As shown in Figure 1 , the dimension A is the minimum width of the frame 3, which is equal to the distance between the internal free edges of the two lateral rims 39, whereas the dimension B is the depth of the frame 3, which is equal to the distance between the part of the wall 4 that forms the closed end of the groove 37 and the part of the wall 4 defined by the rib 7A. Two characteristic dimensions of the panel 2 in its plane are also denoted C and D, these corresponding respectively to the dimensions A and B of the frame, C being the edge-to-edge width of the panel 2 and D being the edge-to-edge depth of the panel 2.

As is clearly visible in Figures 2 and 4, the rib 7A defines two holes 9 each able to accept a locking or retaining member 10 that locks or retains the panel 2 in the frame 3 at its underside 2B. More specifically, the shelf 1 comprises two locking members 10, connected together by a rod 1 1 so as to form a single piece 12. The single piece 12 is made of a rigid plastic that has good mechanical strength properties, particularly a plastic based on acrylonitrile-butadiene- styrene (ABS) or on high impact polystyrene (HIPS). The piece 12 is advantageously injection moulded as a single piece with the locking members 10 positioned with respect to one another in such a way that they can be housed simultaneously in the two holes 9 in the rib 7A. For preference, the plastic of which each locking member 10 is made has a thermal expansion coefficient lower than the thermal expansion coefficient of the plastic of which the frame 3 is made, which is indeed the case for a locking member 10 made of an ABS-based or HIPS-based plastic and a polypropylene-based plastic frame 3. Choosing a plastic with a low thermal expansion coefficient ensures that each locking member 10 will have good rigidity.

As shown in Figure 1 , in the configuration in which the locking members 10 are housed in the holes 9, the members 10 do not protrude from the external peripheral edging 8 of the frame 3, this being allowed through the arrangement of the rib 7A which is offset inwards with respect to the external edging 8. Thus, the locking members 10 do not impede the fitting of the shelf 1 into the chassis of a refrigerator.

As shown in Figure 5, each locking member 10 comprises, in succession, in the direction of a central longitudinal axis Xio of the member, a first part 13 and a second part 14 which are joined together at two lateral shoulders 15 of the member. The first part 13 of each locking member 10 comprises a bulge 19 formed on its upper face and intended, in the configuration in which the locking member 10 is in one of the holes 9, to press against the rib 7A by one of its faces 19a. The bulge 19 is equipped, in its opposite face 19b to the face 19a, with a recess 19c allowing a thrusting force tending to push the member into a hole 9 to be applied to the member 10.

In the mounted position, each of the two locking members 10 of the piece 12 is immobilized in position, in the direction of its axis Xio, in one direction by the shoulders 15, and in the other direction by the bulge 19 in abutment against the rib 7A. In particular, in the configuration in which the two locking members 10 of the piece 12 are housed in the two holes 9, the parts 13 and 14 of each member 10 are immobilized pressing, respectively, against the lower face 2B of the panel 2 and the rib 7A on one side of the hole 9 in the case of the part 13, and against the rib 7A on the other side of the hole

9 in the case of the part 14.

The first part 13 of each locking member 10, which is intended to press against the lower face 2B of the panel 2 in order to lock the latter, is rigid and has a width o, measured in the direction of the central axis Xio of the locking member, that is to say in a direction perpendicular to the rib 7A of the frame 3 in the configuration in which the locking member 10 is in the order of 0.8 centimeters.

The shelf 1 is obtained by forming the plastic frame 3 by hot moulding, the panel 2 then being assembled with the frame 3 in the hot state. Depending on the plastic used to form the frame 3, the frame shrinkage may be brought about by cooling from a temperature higher than ambient temperature T₀ down to ambient temperature To, possibly also by a change in state of the plastic, for example a transition to the semi-crystalline state with internal reorganization of the material. For preference, the level of shrinkage of the frame 3 does not exceed 2% of the dimensions of the frame in its main plane, in order to avoid visible deformation of the walls and a deterioration or an inaesthetic appearance of the whole. Advantageously, the overall shrinkage of the frame 3, from its leaving the mould at a temperature higher than ambient temperature T₀ until its assembled state assembled with the panel 2 at ambient temperature To, is substantially linear in all directions and of at least 0.25%. In a preferred embodiment, the frame shrinks linearly in all directions by a factor of between 0.5% and 2%, preferably of the order of 1 .5%, with respect to the width A and the depth B of the frame. Such a percentage shrinkage of the frame 3 may be obtained by using a suitable material of which to make the frame, for example a material based on polypropylene with a high fluidity coefficient, at least equal to 20 grams per 10 minutes.

A method of manufacturing the shelf 1 comprises steps as described hereinbelow.

First of all, the frame 3 is manufactured by moulding the plastic of which the frame is made, which is, for example, based on polypropylene as described hereinabove, possibly filled with talc in order to improve its mechanical strength. By way of example, the frame 3 is manufactured by injection moulding, injecting the plastic of which the frame is formed, previously heated and melted, into a moulding device such as a closed mould or a press.

Once moulded, the material cools and solidifies, firstly in the moulding device, from 160°C onwards in the form of a semi-crystalline product, in order to yield a semi-finished product that can be extracted from the moulding device without globally losing its shape, and then out of the moulding device. The frame shrinkage phenomenon occurs to a significant extent especially once it has been extracted from the moulding device. As the frame shrinks, the dimensions of the frame in its main plane reduce, but the shape of the frame remains appreciably the same.

The frame 3 in the hot state, as it leaves the moulding device at a temperature Ti , is then placed on a conveyor, for example in such a way that its face 3A, comprising the rim 5 and intended to be the upper face of the frame 3 in the position of use of the shelf 1 , is resting on the conveyor. The conveyor is designed to convey the frame 3 from the moulding device to a heating device. The heating device, which in particular may incorporate infrared emitters and/or electric resistive elements, is positioned in relation to the conveyor in such a way as to allow the frame, while it is on the conveyor, to be heated to a temperature higher than or equal to a minimum insertion temperature T₂ for inserting the panel 2 into the frame. By way of example, the heating device may be in the form of a heating bridge or tunnel, under or through which the conveyor passes. As a variant, the heating device may be a convection oven, which makes it possible to obtain a homogeneous temperature.

The use of a conveyor for conveying the frame 3 from the moulding device to the heating device is preferred, but not mandatory. As a variant, the frame 3 can be taken manually out of the moulding device and placed manually in the heating device.

The minimum insertion temperature T₂ is the minimum temperature of the frame 3 at which the dimensions of the frame in its main plane are strictly greater than the corresponding dimensions of the panel 2. Thus, when the frame 3 i s at an insertion temperature T, higher than or equal to the minimum insertion temperature T₂, it is possible for the panel 2 to be deposited between the sides of the frame with no interference between the frame and the edges of the panel 2. In practice, in the embodiment of the frame 3 depicted in the figures, it is the width A of the frame which is the limiting dimension for inserting the panel, that is to say the dimension which, if it is strictly greater than the corresponding dimension C of the panel 2, guarantees that all the other dimensions of the frame are strictly greater than the corresponding dimensions of the panel, in particular that the depth B of the frame is strictly greater than the depth D of the panel.

The insertion temperature T, of the frame 3 at the moment that the panel 2 is inserted into the frame may for example be defined as the frame temperature at which the difference between a limiting dimension of the frame and the corresponding dimension of the panel, that is to say in the embodiment depicted in the figures, the difference between the width A of the frame and the width C of the panel, is of the order of 0.5 millimeters. The value of this insertion temperature T, may be determined using a graph that expresses the change in the width A of the frame 3 as a function of temperature, as shown on Figure 6. Such a graph can be obtained by measuring, for a template frame, the change in the width A of the frame, after it has been extracted from the moulding device and as it cools down.

On Figure 6, the value C of the edge-to-edge width of the panel 2 and the minimum value A_min of the width of the frame 3 allowing an insertion of the panel into the frame with no interference between the lateral rims 39 of the frame 3 and the lateral edges 22 and 24 of the panel 2, which minimum value A_min is chosen equal to C + 0.5 millimeters, are shown on the ordinate axis. The graph of Figure 6 makes it possible to determine the value of the insertion temperature T,, which is the value of the frame temperature at which the width A of the frame is equal to A_min. While it is being conveyed on the conveyor between the moulding device and the heating device, the frame 3 may cool down to a temperature T₃ lower than the minimum insertion temperature T₂, the heating device then being used to reheat the frame 3 up to a temperature higher than or equal to the minimum insertion temperature T₂. If the cooling of the frame 3 on the conveyor between the moulding and heating devices does not lead to a frame temperature lower than the minimum insertion temperature T₂, it may nonetheless be necessary to reheat the frame 3 up to a temperature higher than the minimum insertion temperature T₂ or to maintain the frame 3 at a temperature higher than or equal to the minimum insertion temperature T₂, using the heating device.

As an option, once the frame 3 has been heated to a temperature higher than or equal to the minimum insertion temperature T₂ and before the panel is inserted into the frame, adhesive is deposited on at least part of the frame 3 intended to be in contact with the panel 2, so as further to improve the sealing and adhesion between the frame and the panel. This is preferably a viscoelastic adhesive, for example of the polyurethane type, making it possible to compensate for the respective expansions of the panel 2 and of the frame 3 resulting from changes in temperature, particularly when the shelf 1 is in use. The shelf 1 according to the invention may thus comprise, in addition to the panel 2 and the frame 3, an adhesive deposited preferably along the peripheral wall 4 of the frame, for example in the form of a flexible bead which is compressed as the panel is combined with the frame.

As an alternative or supplement to the adhesive, it is possible, before inserting the panel 2 into the frame 3 at the insertion temperature T, higher than or equal to the minimum insertion temperature T₂ and over at least part of the frame 3 intended to be in contact with the panel 2, to fit isolating gaskets, for example self-adhesive gaskets or gaskets in the form of a foam or of a "hot melt" adhesive inflated by air bubbles. Advantageously, the bead of adhesive and/or the gasket deposited is given a special shape, for example a conical shape, for improved contact when the adhesive and/or the gasket is mechanically compressed between the panel 2 and the frame 3.

The surface of the panel 2 may have been pretreated, for example sand blasted, in order to improve its adhesion with adhesive. In addition, prior to depositing the adhesive and/or the gasket, the frame 3 may have undergone a surface treatment on those of its parts that are intended to accept the bead of adhesive or the gasket, for example the formation of grooves or roughnesses, or a plasma treatment aimed at increasing the area of contact between the plastic of the frame and the adhesive or the gasket. The frame 3 may likewise be equipped with a groove to accept the adhesive and/or the gasket.

When operations have to be performed on the frame 3 after it has been heated and before it is assembled with the panel 2, such as a deposition of adhesive and/or gasket as described hereinabove, the temperature to which the frame is heated by means of the heating device needs to be higher than the minimum insertion temperature T₂ by a certain margin, so that the frame once these operations have been performed is at an insertion temperature T, which is still higher than or equal to the minimum insertion temperature T₂. The temperature to which it is necessary to aim to heat the frame in such an instance may, for example, be determined, knowing the duration of the operations to be performed on the frame as it leaves the heating device, using a graph that expresses the change in a limiting dimension of the frame 3, that is to say the width A in this embodiment, as a function of temperature, as shown on Figure 6, in conjunction with a graph that expresses the change in the limiting dimension or the temperature of the frame 3 as a function of time.

As a variant, during the optional depositing of adhesive and/or of soft insulating gasket, the frame 3 may be held at a temperature higher than or equal to the minimum insertion temperature T₂.

The panel 2 is then positioned between the sides 31 , 32, 33, 34 of the frame 3 at an insertion temperature T, higher than or equal to the minimum insertion temperature T₂, on the side of that face 3B of the frame that is intended to be its underside when the shelf is in the position of use.

To do this, the front edge 21 of the panel 2 is inserted under the rigid rim 35, in the groove 37 delimited by the front side 31 of the frame 3, as shown in Figure 3. The panel 2 is then tilted in the direction of the arrow Fi in Figure 2 in order to set the panel 2 down between the sides 32, 33 and 34 of the frame. The panel 2 is fitted into the frame 3 while the frame is at the insertion temperature T, higher than or equal to the minimum insertion temperature T₂, that is to say in a state that is sufficiently hot and expanded for there to be no interference between the lateral rims 39 of the frame 3 and the lateral edges 22 and 24 of the panel 2 or between the rib 7A of the frame 3 and the rear edge 23 of the panel 2.

Optionally, the panel 2 once in position between the sides of the frame 3 may be pushed toward the closed end of the groove 37, that is to say towards the wall 4, as illustrated by the arrow F₂ in Figure 4.

The frame 3 is then left to cool and shrink partially around the panel 2, until at least part of the frame comes into contact with the panel. This then secures the panel 2 and the frame 3 together, thanks to the wall 4 of the frame which is designed with a height greater than the thickness of the panel 2 and which grips the panel 2 over its entire thickness.

Once the frame 3 has shrunk partially, but preferably before it has completely shrunk, the assembly of the panel 2 and of the frame 3 is reinforced and locked, for safety reasons, by introducing the two locking members 10 of the single piece 12 into the two holes 9 of the rib 7A on the rear side 33 of the frame. This insertion is generally performed when the frame 3 has come into a position gripping the panel 2. Introduction of the two members 10 of the piece 12 into the two holes 9 is performed by exerting a thrusting force on each of the two recesses 19c of the piece 12, in the direction of the arrows F₃ of Figure 4.

In practice, this thrusting force may be applied by hand or in an automated way. When the assembly is in the locked configuration, the first part 13 of each locking member 10 presses against the lower face 2B of the panel 2 on a first side of the corresponding hole 9, whereas the second part 14 presses against the rib 7A on the other side of the hole 9. By virtue of the fact that each locking member 10 has been introduced into one of the holes 9 in the rib of the frame 3, preferably before the frame has completely finished shrinking, the frame continues to shrink around the locking member. This shrinkage of the frame around the locking members 10 improves their grip, making them very difficult to remove. This shrinkage also enhances the securing of the assembly of the frame 3 and of the panel 2 and further improves the seal between the one and the other. This is of great practical importance because the shelf 1 is intended to support foodstuffs which may spread out and slip into the plastic-glass regions of connection, detracting from good use of the refrigerator.

As becomes evident from the above description, a shelf 1 according to the invention possesses good rigidity. Specifically, the assembly between the panel 2 and the frame 3 of the shelf, obtained by shrinking the frame around the edge faces of the panel, is made all the more secure by means of locking the panel with respect to the frame, acting from the side of the lower face 2B of the panel. These locking means, which consist of the locking members 10 and of the rim 35, specifically comprise parts pressing against the lower face 2B of the panel which are rigid and wide enough to eliminate any risk of the panel becoming extracted from the frame. These parts bearing against the lower face 2B of the panel are designed not to be able to be bent without breaking, thus preventing any detachment of the panel from the frame through deformation of the bearing parts of the locking means, even when a substantial weight is applied to the shelf.

Advantageously, each locking member 10 is shaped in such a way that it can be introduced into a hole 9 from the inside of the rib of the frame with respect to the panel. What this means is that the part of the locking member used for grasping is sheltered behind the rib in the configuration of use of the shelf 1 according to the invention. Thus, the possibility of removing the locking member is limited in this configuration of use of the shelf, thus improving the secureness of the assembly between the panel and the frame. The aesthetic appearance of the shelf 1 is also preserved because only restricted parts of the locking members project on the outside of the rib with respect to the panel, and these parts do not extend beyond the peripheral external edging of the frame. In particular, no locking member interferes with any means there might be provided on the frame 3 for fitting the shelf 1 , thus avoiding any impediment to fitting the shelf in the chassis of a refrigerator.

Furthermore, the method of manufacturing a shelf 1 according to the invention is simple and readily automatable, for the most part thereof. In particular, the step of fitting the panel 2 into the frame 3 at a temperature higher than or equal to the minimum insertion temperature T₂ can be performed in an automated manner, by inserting one side of the panel 2 into a groove on one side of the frame 3, then tilting the panel between the other sides of the frame. The lateral rims 39 of the frame 3 do not touch the lateral edges 22 and 24 of the panel 2 as the latter is being set down in the frame 3 at a temperature higher than or equal to the minimum insertion temperature T₂ and therefore do not interfere with the edges of the panel. Thus, the lateral rims 39 allow the panel 2 to be fitted unimpeded into the frame 3. In addition, the lateral rims 39 contribute to stabilizing the panel 2 in the frame 3 once the frame has shrunk by forming, with the wall 4 and the rim 5 of the frame, lateral slides that accept the lateral edges 22 and 24 of the panel. Of course the exemplary embodiments described and depicted have been given by way of nonlimiting examples, and modifications may be made without thereby departing from the scope of the present inventing. The method and the installation both according to the invention may in particular be implemented for manufacturing a shelf different from the one described hereinabove.

In particular, the shelf may comprise a frame that has any structure, possibly without rims 5, 35, 39 and ribs. As already mentioned, the frame may also be either a full frame, designed to cover all the edge faces of the panel, or a partial frame covering only certain edge faces, or part of the edge faces of the panel. The shelf may also have no locking members, secure assembly between the frame and the panel in this case resulting from radial pressure applied by the frame to the edge faces of the panel, because of the assembly by shrinkage of the frame around the panel, possibly combined with an adhesive between the frame and the edge faces of the panel. In addition, when the shelf has locking members for locking the panel with respect to the frame, these members may be of any appropriate type other than that described hereinabove, and the number and distribution of such members may be different from those described hereinabove. The locking members may also not be connected together to form a single piece.

Finally, the method according to the invention may involve manufacturing the frame of the shelf by any suitable moulding technique, without being restricted to injection moulding. The step of the method according to the invention that consists in heating the frame to a temperature higher than or equal the minimum insertion temperature may likewise be carried out using any appropriate heating means, for example using an oven, the frame not necessarily having to be placed on a conveyor during this step. In addition, the heating device may be adapted so that it is able to heat only part of the frame, for example only the sides of the frame which need to be elongated in order to increase the limiting dimension of the frame, that is to say the sides 31 and 33 in figure 1 in order to increase the limiting dimension A. In this case, the heating device may for example comprise two rows of heating elements, each row being intended to face one of the sides 31 or 33. When it is desirable to improve the sealing and adhesion between the frame and the panel by means of an adhesive and/or a gasket as mentioned above, the adhesive and/or the gasket can also be deposited on the frame 3 before the frame is heated to a temperature higher than or equal to the minimum insertion temperature T₂, provided that the adhesive and/or gasket can withstand the heating.

Claims

1 . Method of manufacturing a shelf (1 ), particularly for a refrigerator or the like, this shelf comprising a panel (2) and a frame (3) which surrounds at least part of the periphery of the panel, the frame (3) being made of a plastic capable of undergoing shrinkage as it cools from a temperature (Ti, T₂) higher than ambient temperature (T₀) to ambient temperature (T₀), characterized in that it comprises:

- manufacturing the frame (3) by moulding the plastic in a moulding device;

- extracting the frame (3) from the moulding device;

- in a heating device, maintaining the frame (3) at, or heating the frame (3) to, a temperature higher than or equal to a minimum insertion temperature (T₂) for inserting the panel (2) into the frame, where the minimum insertion temperature (T₂) is the minimum temperature at which the dimensions (A, B) of the frame (3) in its main plane are strictly greater than the corresponding dimension (C, D) of the panel (2), the minimum insertion temperature (T₂) being higher than ambient temperature (T₀);

- inserting the panel (2) into the frame (3) at an insertion temperature (Ti) higher than or equal to the minimum insertion temperature (T₂);

- assembling the panel (2) and the frame (3) by cooling the frame, so as to cause the frame to shrink around the panel and cause at least part of the frame to come into contact with the panel.

2. Method according to Claim 1 , characterized in that the panel (2) is inserted into the frame (3) at an insertion temperature (T,) at which a limiting dimension (A) of the frame in its main plane is strictly greater than a corresponding dimension (C) of the panel, the difference between the limiting dimension (A) of the frame and the corresponding dimension (C) of the panel being at least of the order of 0.5 millimeters.

3. Method according to any one of the preceding claims, characterized in that, prior to inserting the panel (2) into the frame (3), an adhesive and/or an insulating gasket is deposited over at least part of the frame (3) intended to come into contact with the panel (2).

4. Method according to any one of the preceding claims, characterized in that the frame (3) is manufactured by injection moulding the plastic.

5. Method according to any one of the preceding claims, characterized in that the frame (3) is maintained at, or heated to, a temperature higher than or equal to the minimum insertion temperature (T₂) using a resistive and/or infrared heating device.

6. Method according to any one of the preceding claims, characterized in that, after the panel (2) has been inserted into the frame (3), a locking member (10) for locking the panel (2) relative to the frame (3) is introduced into a hole (9) made in a rib (7A) of the frame (3).

7. Method according to Claim 6, characterized in that the locking member (10) is introduced into the hole (9) in the frame (3) before the frame has completely shrunk around the panel (2).

8. Installation for manufacturing a shelf (1 ), particularly for a refrigerator or the like, this shelf comprising a panel (2) and a frame (3) which surrounds at least part of the periphery of the panel, the frame (3) being made of a plastic capable of undergoing shrinkage as it cools from a temperature (Ti , T₂) higher than ambient temperature (T₀) to ambient temperature (T₀), this installation comprising a moulding device for manufacturing the frame (3) by moulding the plastic, characterized in that it further comprises a heating device for heating the frame (3), after its extraction from the moulding device, to a temperature higher than or equal to a minimum insertion temperature (T₂) for inserting the panel into the frame, where the minimum insertion temperature (T₂) is the minimum temperature at which the dimensions (A, B) of the frame (3) in its main plane are strictly greater than the corresponding dimensions (C, D) of the panel (2), the minimum insertion temperature (T₂) being higher than ambient temperature (T₀).

9. Installation according to Claim 8, characterized in that the heating device is a resistive and/or infrared heating device.

10. Installation according to either one of claims 8 or 9, characterized in that it comprises a conveyor for conveying the frame (3) from the moulding device to the heating device, the heating device being designed to allow the frame to be heated while it is on the conveyor.

1 1 . Shelf (1 ), particularly for a refrigerator or the like, comprising a panel (2) and a frame (3) which surrounds at least part of the periphery of the panel, wherein the shelf is manufactured using the method of any one of claims 1 to 7.