PALLET AND METHOD FOR PRODUCING THE SAME

Abstract: A novel industrial pallet (10) for use in supporting and moving goods, engageable by conventional forklift trucks, comprises an upper platform (12), one or more lower planar reinforcements (16) and cylindrical spacers (14) therebetween, defining a space suitable for access of the forks of a forklift truck from all sides. Some or all of the components are made of thermoplastic-type materials, so that the structures can be economically and simply made by friction welding (e.g. spin/vibration welding). Alternatively, a thermoplastic material may be positioned between components, to act as a thermoplastic glue of respective parts on friction welding.

Description: PALLET AND METHOD FOR PRODUCING THE SAME This invention relates to industrial pallets, of the type used in indu for supporting goods so that they can be lifted by forklift trucks transported stored. The common industrial pallet is made of wood. It is provided similar top and bottom continuous or slatted surfaces, spaced apart by wooden blo elongated wooden spacers reinforcements and side walls to provide a gap appropriate size therebetween, to give access to the lifting forks of a forklift tr from two or four sides. Such pallets should be robust and rugged in construction, withstand the weight of goods stacked on them and lifted on top of them, and withstand the impacts of truck forks driven into them as a result of misalignm They are commonly made in a variety of different shapes and sizes. They may nailed, screwed or riveted together, using the particular design and choice of wo appropriate for their particular use and the loads they are intended to carry. Such wooden pallets, in particular those made of softwood, disposable, one-way items. They are sufficiently cheap in terms of raw materials a manufacturing costs, and also sufficiently heavy and bulky, that their retu transportation when empty is not economic. However, they are prone to damage use, and on exposure to weather. In addition, many manufacturing environmrats not tolerate wood dust or loose splinters, nails, rivets etc. Since in addition su pallets pose significant disposal problems, there are legislative moves to reduce eliminate their use. ET Reusable, returnable industrial pallets are also known. These normally made of thermoplastics or thermosetting materials, by processes of injecti molding or compression molding. These processes of manufacture require relative high investment in both tooling and machinery. Moreover, the high cost for t plastics raw materials contribute to the relatively high overall cost of such pallets. It is an object of the present invention to provide novel returnab industrial pallets. It is a further object to provide an economical process for producin such pallets and other similar industrial structures, so that the resulting products ar relatively cheap but at the same time strong and durable. The present invention provides a novel form of returnable industria pallet which is strong, durable and light weight, and which can be economicall manufactured. It is made at least in part from thermoplastic materials, or at any rate, from materials having thermoplastic characteristics rendering it suitable for friction welding. The parts can be pre-cut or pre-molded, and shipped in convenient, knocked down form to the site of use, and there assembled by a friction welding technique. Thus, from a first aspect, the present invention provides an industrial pallet for supporting and moving goods, comprising: an upper planar goods receiving platform; a lower planar reinforcement; cylindrical spacers disposed between the upper platform and the lo reinforcement, each spacer having a rigid connection at one end to a lower surfa of said upper platform, and a rigid connection at the other end to an upper surfa of the reinforcement; at least one of said rigid connections being comprised of thermoplastic weld; said cylindrical spacers each having a length suitable to space the upp platform from the lower reinforcement a distance of from about 1 - 9 inches. Preferably, the cylindrical spacers are hollow, so as to reduce th overall weight of the pallet, and to provide for ease of manufacture as describe below. The provision of cylindrical spacers allows for ready deflection of the ton of the forklift truck to one side or other should the tongs be introduced into the spac defined by the cylindrical spacers at a misalignment. This reduces the risk of damag caused by impact of the forks of the forklift truck. The materials of construction of the various components can be chose from a wide variety, depending upon the design and intended use of the resultan SUBSTITUTE SHEET pallet, with the proviso that the combination must be friction weldable togeth Thus, at least one of the components must have thermoplastic characteristics. Wh the platform and the spacers are both thermoplastic materials, and when the space and the reinforcement are both thermoplastic materials, they can be friction weld together. When neither of the adjoining parts to be secured together is thermoplasti it is necessary to place, at the junction site, a reservoir of thermoplastic material t form a thermoplastic glue to bond the components on friction welding. It is preferred to use thermoplastic materials for the cylindrical spacers in the embodiments of the invention. When the same thermoplastic material is chosen for the upper platfor and for the cylindrical spacer, e.g. polyethylene, they can be directly ftiction welde together, by spin and/or vibration welding, without the provision of special grooves, receptor slots or the like. The end of the cylinder will fictionally weld directly to the flat surface of the platform. The same of course applies to the cylindrical spacer and the lower reinforcement. When the adjacent components are of ώss-jmilar thermoplastic materials, e.g. polyethylene/polypropylene, polyethylene/ABS, polypropylene/ABS, etc., it is preferred to provided a positioning groove, slot, undercut or other formation on the undersurface of the platform and/or the top surface of the reinforcement, for effective positioning and ftiction welding of the cylinder end thereto. Where all of the components are made from materials which are unsuitable for ftiction welding, a receptor slot, groove or similar formation is provided on the undersurface of the platform and/or the top surface of the reinforcement, and a ring SU of suitable thermoplastic material, e.g. polyethylene, is positioned within formation. Then, spin or vibration welding of the cylindrical spacer within receptor slot is achieved by melting the thermoplastic ring as a result of the fric welding process, and causing the molten thermoplastic to act as a thermoplastic gl According to a further aspect of the invention, there is provide process of manufacturing an industrial panel having a platform, a pla reinforcement and a plurality of hollow cylindrical spacers disposed therebetween having their annular ends thermoplastically welded to a surface of the platform a surface of the reinforcement, said process comprising: placing a first end of at least one of said cylindrical spacers agains surface of the platform, at a predetermined location thereon; placing a second end of said cylindrical spacer against a surface of planar reinforcement, at a predetermined location thereon; and rotating the cylindrical spacer, under pressure, about longitudinal axis, to effect friction welding of the cylindrical spacer to the platfo and the reinforcement. Friction welding, e.g. spin welding, vibration welding etc., is technique which has previously been used, in one industrial area, to form permane connections between lengths of thermoplastic pipe, by rotating one or both ends SUBSTITUTE SHEET the pipes under pressure against each other It has also been used, in anoth industrial area, to weld the thermoplastic reinforcement of an automobile bumper in the thermoplastic front fascia by vibrating both surfaces under pressure against ea other. It relies upon the heat generated by friction in the relative movement of o surface relative to another, under conditions of pressure contact between t respective surfaces. As a result, the thermoplastic material of one or both of t surfaces melts, and on cooling, a union is formed with the thermoplastic material the other surface, to form a thermoplastic weld on cooling. In this aspect of the present invention, where the contacting surface are both made of the same thermoplastic material, such a union of the two surface is effected, to form a full ftiction thermoplastic weld. This also occurs when th respective materials are not exactly the same, but have a high degree of compatibilit with one another. When non-compatible thermoplastics are subjected to the same process, the resulting friction thermoplastic weld is not based on the formation of a union between the two surfaces, but rather on a mechanical anchoring of both surfaces to each other. In such cases, undercuts are preferably provided on the outside and/or inside surfaces of the cylindrical spacers, close their ends, or alternatively in the platform surface or in the reinforcement surface. The ftiction thermoplastic weld now achieved is derived not only from the melting of one or both of the materials, as they move relative to one another, but also on the softening of the end of the spacers and the deformation of them under pressure. If only one of the surfaces is SUBSTITUTE SHEET made from a thermoplastic material, this one surface melts under the heat genera by the friction, to act as a melt glue after cooling. The presence of underc improves the welding strength in such situations. When neither of the surfaces made of thermoplastic components, a thermoplastic material, suitable for fricti welding, is placed between the two relatively moving surfaces, and softened a melted in the same way. The soften/molten thermoplastic material deforms or flo under pressure, into surface perocities and undercuts provided in the adjoini formations, to anchor both pieces together after cooling. In this aspect of the present invention, friction welding is used to bo the end of a cylindrical spacer to the under surface of the planar platform, and als to bond the other end of the cylindrical spacers to the planar reinfbrceπien Accordingly, only the cylindrical spacers are rotated/vibrated under pressure to cau the melting of the thermoplastic material and effect the weld. For welding t cylindrical spacers to the lower reinforcements, apertures may be cut into th reinforcement at appropriate locations, of a size such that the end of the cylindric spacer overlies the aperture as it is pressed against the surface, so that tool access t the interior of the cylinder, for spin driving purposes, is provided. For this purpose, the cylindrical spacers may be hollow or semi hollow, and provided on their interior surfaces with appropriate configurations t allow positive engagement with a complementarily shaped mandrel or spinning tool After the tool has engaged the spacer, its movement is started and pressure is applie to the moving surfaces, from the opposing sides of the platform and or th SUBSTITUTE SHEET reinforcement, or both, if simultaneous welding of the two ends of the cylind spacer is being effected. Heat is thus generated on the touching surfaces, softening or melting of the thermoplastic materials occurs. After sufficient of material has been softened or melted, the movement of the tool is stopped, but pressure is kept applied to the hot surfaces for a few extra seconds. Then the t can be retracted and the finished pallet can be removed, achieving its full stren after approximately 2-3 minutes of cooling. The cylindrical spacers are preferably hollow or semi-hollow, not o to reduce the weight of the resulting pallet and to provide access to the inside of t spacers for the rotating mandrel, but also to improve the efficiency of the fricti welding process. Spinning or vibrating the hollow spacers concentrates the heat the relatively narrow top and bottom edges of the spacers which contact the respecti surfaces, and avoids dissipation of the heat over the continuous circular area of solid cylinder. Accordingly, less energy is required with hollow cylinders, to achiev the necessary weld. Spin welding machines are readily available, and are relativel inexpensive. Accordingly, pallets of the present invention can conveniently b assembled by spin welding at the site of their intended use. The individua components, namely the cylindrical spacers, the upper platforms and the lower stri members, may require manufacture by relatively expensive techniques such as injection molding and compression molding and this is conveniently conducted at a central location, where the components can be made in large numbers. Then the components can be shipped as parts ready for assembly by spin welding at the u location. Thus, according to a further aspect of the present invention, the provided a kit of parts adapted to be assembled into an industrial pallet as defi above, and comprising: a planar sheet-like upper platform; a plurality of thermoplastic cylindrical members, thermoplastically s weldable to the sheet-like platform; a planar reinforcement thermoplastically spin weldable to s cylindrical members. A specific preferred embodiment of the invention will now described, for illustrative purposes, with reference to the accompanying drawings, which: FIGURE 1 is a perspective view, of an assembled industrial pall according to the present invention; SUBSTITUTE SHEET FIGURE 2 is an exploded perspective of the pallet of Figure showing the individual components thereof, and which comprise a kit of pa according to the present invention; FIGURE 2A is a view similar to the that of Fig. 2, but iUustrating alternative embodiment; FIGURE 3 is a manu_acturing process flow diagram, illustrating th method of manufacture and assembly of the pallets from the components illustrate in Figure 2; FIGURE 4a is a cross-sectional view and FIGURE 4b is a plan vie illustrating diagrammatically an alternative step in the manufacture of a palle according to the present invention. FIGURE 5 is a diagrammatic cross sectional view, in exploded form, of an arrangement of parts having undercuts to improve the friction weld; FIGURE 6 is a similar view of an alternative embodiment employing a separate thermoplastic reservoir to achieve the thermoplastic weld. In the drawings, like reference numerals indicate like parts. SUB Figure 1 diagrammatically illustrates a pallet 10 having an upper like platform 12, a plurality of cylindrical spacers 14 and three mutually par lower reinforcements 16, spaced apart from one another and spaced equally fro platform by a distance corresponding to the length of the cylindrical spacers 14, distance being typically of the order of one to four inches. As shown in Figu the platform member 12 prior to assembly is a planar sheet, typically of thermopl material for example polypropylene. The cylindrical spacers 14, also suitabl polypropylene, are injection or compression molded, or constitute pieces of extr pipe, and are hollow. The lower reinforcements 16 each have three apertures 18 there through, or molded therein, of a size equal to or smaller than the size of interior aperture in the cylindrical spacer. The lower reinforcements are suitabl the same material as the platform 12, eg. polypropylene. The industrial pallet of invention in its simplest form is manufactured from sheet and pipe. reinforcements 16 are suitably prepared by trimming oversize sheets, leaving a portion to form the platform member 12 and severed strip portions to form reinforcements 16. Then they are appropriately cut or drilled to provide the apertu 18, appropriately of about 3.7 inches diameter. Next, a pipe with an outer diam of 4" and an inner diameter of 3.7", having a pair of inwardly projecting, radi opposed continuous ridges or ribs, with an equal width and a height of about 0. for engagement of a rotation tool, is cut into 4" long segments to form the spac 14. The process of manufacture of a pallet 10 from the component pa shown in Figure 2 is diagrammatically illustrated in Figure 3. The platform 12 SUBSTITUTE SHEET clamped in a face-down position by means of holders 20, and the required plura of cylindrical spacers 14 is placed thereon at predetermined locations, with an ai contact with the surface of the platform 12 and the other protruding upwardly. Th the reinforcements 16 are placed on the free ends of the cylindrical spacers 14, w the apertures 18 aligning with the inner diameter of the cylindrical spacers 14. Ne a rotation tool 24, with a length of 3.7" and with a cross section virtually identi to the inner shape of the pipe, is inserted through the apertures to a depth of 3.5" i the spacers 14. As shown in Figure 3A, these spacers 14 conveniently have a p of inwardly projecting, radially opposed ridges 22. Whilst holding the platform and the reinforcements 16 in fixed position, the rotation tool 24 starts slowly rotate, engaging the ridges 22 in the spacer 14 so as to rotate the spacer 14 the with. The speed is increased and once the spacer has reached its optimal rotatin speed, pressure "P" is increasingly applied to the assembly, from the exterior of t reinforcements 16, especially around the surface engaging portions of the spacers 1 The friction heat generated at the contacting surfaces causes first softening and the melting of the thermoplastic material in these areas. Once enough material is molte in these areas, the rotating tool and consequently the spacer 14 stop rotation, but th maximum pressure "P" is still applied for about 5 seconds after which the rotatin tool is retracted and finished pallet can be removed. After cooling of approximatel 2 - 3 minutes, the full strength of the welded areas is achieved. Conveniently, a multi-mandrel spinning/vibrating machine is used, with the mandrels 24 appropriately spaced so that one row of or all of the cylindrical SUBSTITUTE SHEET spacers 14 are engaged and rotated at one time, simultaneously to form the spin w to unite the parts and form the pallet 10 illustrated in Figure 1. Figures 4a and 4b illustrate an alternative process or manufactu pallets according to another embodiment of the present invention. In this case, the platform 12 and the reinforcements 16 are provided with integral gro formations 26, 28 respectively, facing each other and in registry with one anot The groove formations are circular, and the width of the groove opening is suffici to receive the walls of cylindrical spacer 14 in close engagement therewith and allow he melted thermoplastic material, generated during the spin welding, to fl between the inner and outer edge of the spacer 14 and the inside of the groove, t generating a shear joint. Friction belts 30, 32 are provided, to press against engage frictionally the outer surfaces of the cylindrical spacers 14, between platform 12 and reinforcements 16. These friction belts are moved at high speed opposite directions so as to cause rotation of the cylindrical spacers 14 relative to platform 12 and the reinforcements 16, and thereby effect the thermoplastic spin w under increasing pressure "P" at the upper and lower ends of the spacers 16. In t way, spin welds are formed simultaneously by rows of aligned cylindrical memb 14, to form the finished pallet 10. A large number of variations are possible within the scope of t present invention. Thus, grooves in the platform surface and in the low reinforcements surfaces can be of a wide variety of shapes, including undercuts as shown in the arrangement of Fig. 5. This particular arrangement provides improved anchoring of, for example, a thermoplastic spacer 14 in a non-thermopla platform 12 and reinforcement 16. The grooves, whatever their configuration, sho constitute surfaces of revolution, to receive the ends of the cylindrical spacers i loose close fit and permit relative rotation thereof to form the thermoplastic s welds. Similarly, the spacer 14, having a circular shape on both ends, can hav variety of internal shapes, including inner longitudinal transverse ribs with rectangu apertures therethrough, as shown at 36 in Figure 5, to allow a variety of differ rotation/vibration tools to engage mechanically. When vibration welding is used the joining method, the engagement of the rotation tool is in both rotation directions. "Vibration" as the term is used herein means circular motion about t longitudinal axis sequentially and rapidly in clockwise and anti-clockwise direction with sudden reversals of such direction. Rotation tools can have expandable grippi formations to engage against the inner surfaces of the cylindrical spacers 14, so th the provision of engaging formations such as ribs 22 on the interior of the cylinde is not necessary. Clearly, a wide variety of engaging formations can be adopted desired. Figure 6 diagrammatically illustrates an arrangement of spacer 14 reinforcement 16 and platform 12 for use in the case when none of these component are themselves thermoplastic. They could for example, be SMC-thermoset polyeste sheet molding compound. In this case, a welding aid 38, in the form of a ring o polyethylene, is placed in the bottom of circular grooves 34 of the non-thermoplastic platform and reinforcement. By rotating the spacers 14 under pressure "P" in the way described above, the welding aid 38 is heated by friction, melts and starts to flow under pressure "P" to fill the space between the spacer 14 and the groov providing after cooling a shear joint of high strength. By providing undercuts the outer rim of the spacer 14, or alternatively in the grooves 34, additional stre can be achieved. The pallets and other structures according to the invention ca made from and made of recycle material. SUBSTITUTE SHEET

Claims: THE EMBODIMENTS OF THE INVENTION, IN WHICH AN EXCLUS PRIVILEGE OR PROPERTY IS CLAIMED, ARE DEFINED AS FOLLOWS: 1. An industrial, pallet for supporting and moving goods, comprising: an upper, planar, goods receiving platform; at least one lower planar reinforcement; a plurality of cylindrical spacers disposed between the upp platform and the lower reinforcement, each spacer having rigid connection at one end to a lower surface of said upp platform and a rigid connection at the other end to an upp surface of the reinforcement; at least one of said rigid connections being comprised of thermoplastic weld; said cylindrical spacers each having a length suitable to spac the upper platform from the lower reinforcement a distance o from about 1-9 inches. 2. The pallet of claim 1 wherein the cylindrical spacers are hollow. 3. The pallet of claim 2 wherein the thermoplastic weld is a spin we a vibration weld. 4. The pallet of claim 3 including a plurality of lower pl reinforcements in strip form, arranged mutually parallel to another. 5. The pallet of claim 4 wherein the reinforcements are spaced apart one another, extending over an area substantially corresponding to of the upper platform. 6. The pallet of claim 5 wherein the cylindrical spacers are thermoplas 7. The pallet of claim 6 wherein the upper platform is thermoplastic thermoplastic-based chipboard, and the cylindrical spacers thermoplastically welded thereto. 8. The pallet of claim 6 wherein the cylindrical spacers thermoplastically spin welded to the upper platform. 9. The pallet of claim 5 wherein the cylindrical spacers are made of same thermoplastic material as the platform and the reinforcemen and are thermoplastically spin welded thereto. SUBSTITUTE SHEET 10. The pallet of claim 6 wherein the cylindrical spacers are of a diff material from that of the reinforcement, and are thermoplastically, welded into grooves formed in the upper surfaces of the reinforce 11. The pallet of claim 6 wherein the cylindrical spacers are of a diffe material from that of the platform and are thermoplastically welded into grooves formed in the lower surface of the platform. 12. The pallet of claim 9, claim 10 or claim 11 wherein the upper plat and the lower strip members are constructed of the same material. 13. The pallet of claim 10 or claim 11 wherein the grooves are underc 14. The pallet of claim 10 or claim 11 wherein the spin weld is form from a reservoir of thermoplastic material disposed in the groove. 15. A process of manufacturing an industrial panel having a platform, planar reinforcement and plurality of hollow cylindrical space disposed therebetween and having their annular ends thermoplastical welded to a surface of the platform and a surface of the reinforcemen said process comprising: SUBSTITUTE SHEET placing a first end of at least one of said cylindrical sp against a surface of the platform, at a predetermined loc thereon; placing a second end of said cylindrical spacer agains surface of the planar reinforcement, at a predeter location thereon; and rotating or vibrating the cylindrical spacer, under pres about its longitudinally axis, to effect friction welding o cylindrical spacer to the platform and the reinforcement 16. The process of claim 15 wherein the cylindrical spacers are grippe rotation or vibration by gripping means disposed within the cylind spacers. 17. The process of claim 16 wherein the gripping means protrude thro the apertures in the reinforcement into the interior of the cylind spacers. 18. The process of claim 15 wherein the cylindrical spacers are gripped rotation by gripping means disposed exteriorly thereof. SUBSTITUTE SHEET 19. The process of claim 15 including the initial steps of cutting strip a planar sheet of material having thermoplastic characteristics to the platform and the reinforcements, and cutting apertures through reinforcements of a size and shape substantially corresponding t the internal size and shape of the cylindrical spacers. 20. The process of claim 15 for the manufacture of an industrial palle defined in claim 1. 21. A kit of parts adapted to be assembled into an industrial pallet defined in claim 1, and comprising: a planar sheet-like platform; a plurality of cylindrical members thermoplastically sp weldable to the sheet-like platform; a planar reinforcement thermoplastically spin weldable to t sheet-like platform. 22. The kit of claim 21 wherein a surface of said sheet-like platfor carries indicia for positioning of said cylindrical members thereon. SUBSTITUTE SHEET 23. The kit of claim 21 wherein said reinforcement is provided apertures therethrough of a size and shape substantially corτespon to the internal size and shape of said cylindrical members. 24. The kit of claim 23 wherein at least one of the platform and reinforcement has grooves of a size and shape to receive the end said cylindrical members in a loose fit therewith. 25. The kit of claim 24 wherein at least one of the grooves include reservoir of thermoplastic material. 26. The kit of claim 23, claim 24 or claim 25 comprising a plurality apertured, planar strips to constitute the reinforcement. 27. The kit of claim 24 wherein said grooves are undercut. SUBSTITUTE SHEET AMENDED CLAIMS [received by the International Bureau on 04 August 1992 (04.08.92); original claims 1,12,17 and 33 amended; other claims unchanged (4 pages)] 1. An industrial pallet for supporting and moving goods, comprising: an upper, planar, goods receiving platform; at least one lower planar reinforcement; a plurality of cylindrical spacers disposed between the upper platform and the lower rein¬ forcement, each spacer having a rigid connection at one end to a lower surface of said upper platform and a rigid connection at the other end to an upper surface of the reinforcement; both of said rigid connections being comprised of a thermoplastic weld; said cylindrical spacers each having a length suitable to space the upper platform from the lower reinforcement a distance of from about 1-9 inches. 2. The pallet of claim 1 wherein the cylindrical spacers are hollow. 10. The pallet of claim 6 wherein the cylindrical spacers are of a different material from that of the reinforcement, and are thermoplastically, spin welded into grooves formed in the upper surfaces of the reinforcement. 11. The pallet of claim 6 wherein the cylindrical spacers are of a different material from that of the platform and are thermoplastically spin welded into grooves formed in the lower surface of the platform. 12. The pallet of claim 9, claim 10 or claim 11 wherein all the components are constructed of the same material. 13. The pallet of claim 10 or claim 11 wherein the grooves are undercut. 14. The pallet of claim 10 or claim 11 wherein the spin weld is formed from a reservoir of thermoplastic material disposed in the groove. 15. A process of manufacturing an industrial panel having a platform, a planar reinforcement and plurality of hollow cylindrical spacers disposed therebetween and having their annular ends ther¬ moplastically welded to a surface of the platform and a surface of the reinforcement, said process comprising: placing a first end of at least one of said cylindrical spacers against a surface of the platform, at a predetermined location thereon; placing a second end of said cylindrical spacer against the surface of the planar reinforcement, at a predetermined location thereon; and rotating or vibrating the cylindrical spacer, under pressure, about its longitudinally axis, to effect friction welding of the cylindrical spacer to the platform and the reinforcement. 16. The process of claim 15 wherein the cylindrical spacers are gripped for rotation or vibration by gripping means disposed within the cylindrical spacers. 17. The process of claim 16 wherein the gripping means protrude through apertures in the rein¬ forcement on the platform into the interior of the cylindrical spacers. 18. The process of claim 15 wherein the cylindrical spacers are gripped for rotation by gripping means disposed exteriorly thereof. 23. The kit of claim 21 wherein said reinforcement or platform is provided with apertures therethrough of a size and shape substantially corresponding to the internal size and shape of said cylindri¬ cal members. 24. The kit of claim 23 wherein at least one of the platform and the reinforcement has grooves of a size and shape to receive the ends of said cylin¬ drical members in a loose fit therewith. 25. The kit of claim 24 wherein at least one of the grooves includes a reservoir of thermoplastic material. 26. The kit of claim 23, claim 24 or claim 25 com¬ prising a plurality of apertured, planar strips to constitute the reinforcement. 27. The kit of claim 24 wherein said grooves are undercu .

Inventors: HOEDL HERBERT K, HOEDL, HERBERT, K.
Applicants: HOEDL HERBERT K, HOEDL, HERBERT, K.
Application year: 1992
Main classification: B65D19
IPC codes: B29C65, B65D19