US3709162A

US3709162A - Single sheet pallet

Info

Publication number: US3709162A
Application number: US00888569A
Authority: US
Inventors: R Roper
Original assignee: Wallace Expanding Machines Inc
Current assignee: Wallace Expanding Machines Inc
Priority date: 1969-12-29
Filing date: 1969-12-29
Publication date: 1973-01-09
Anticipated expiration: 1990-01-09

Abstract

A pallet including an annular leg concentrically formed in the pallet and a coiled edge extending around the entire periphery thereof. The pallet is formed out of sheet metal by repeated draw operations whereby the central portion of the pallet is first formed and then the central configuration is held by tightly gripping dies while the outer portions of the pallet are formed progressively. The outer edge portion of the pallet is coiled around the complete periphery thereof by a die arrangement which captures the coil in a closed container and retains it as it is being formed. The outer edge portion of the pallet is first formed in the shape of a flange extending perpendicularly of the central portion of the pallet. Recessed dies are then closed about the flange and a set of centrally located holding dies, which grip the pallet, are moved relative to the recessed dies causing one of the recessed dies to wipe one of the holding dies and causing the outer edge portion of the pallet to be coiled in the closed space between the recessed dies.

Description

United States Patent 1 Roper 51 Jan.9,1973

154] SINGLE SHEET PALLET [75] Inventor: Ralph E. Roper, Indianapolis, Ind.

[73] Assignee: Wallace Expanding Machines, lnc.,

Indianapolis, Ind.

[22] Filed: Dec. 29, 1969 [21] Appl. No.: 888,569

[52] U.S. Cl.. ..l08/5l, 108/58, 108/53 [51] Int. Cl. ..B65d 19/00 [58] Field of Search ..l08/5758; 72/347 [56] References Cited UNITED STATES PATENTS 2,101,686 12/1937 Offutt ..l08/46 H X 2,544,734 3/1951 Vrabeak ..l08/58 X 3,359,929 12/1967 Carlson ..lO8/58 3,424,110 l/l969 Toot ..l08/53 3,228,358 l/l966 Sepe et al.... ..l08/58 3,172,374 3/1965 Allen ..l08/58 X 2,463,214 3/1949 Stoner ..lO8/52 2,903,218 9/1959 Altenburg .....108/53 2,991,965 7/1961 Drieborg ..lO8/58 3,120,825 2/1964 Johnson ..l08/5l 3,140,672 7/l964 De Luca 1 ..l08/53 3,167,341 1/1965 Higgins ..108/58 x 3,433,184 3/1969 Addy ..l08/58 Primary ExaminerBobby R. Gay Assistant Examiner-Glenn O. Finch Attorney-Woodard, Weikart, Emhardt 8:. Naughton [57] ABSTRACT A pallet including an annular leg concentrically formed in the pallet and a coiled edge extending around the entire periphery thereof. The pallet is formed out of sheet metal by repeated draw operations whereby the central portion of the pallet is first formed and then the central configuration is held by tightly gripping dies while the outer portions of the pallet are formed progressively. The outer edge portion of the pallet is coiled around the complete periphery thereof by a die arrangement which captures the coil in a closed container and retains it as it is being formed. The outer edge portion of the pallet is first formed in the shape of a flange extending perpendicularly of the central portion of the pallet. Recessed dies are then closed about the flange and a set of centrally located holding dies, which grip the pallet, are moved relative to the recessed dies causing one of the recessed dies to wipe one of the holding dies and causing the outer edge portion of the pallet to be coiled in the closed space between the recessed dies.

3 Claims, 20 Drawing Figures PATENTEDJAN 9 I975 SHEET 1 [IF Fig.1

31 (32 /ll L L W W 17 Fig.2

INVENTOR.

RALPH E; ROPE/ BY W W/ m M l/m AT TORNEYS PATENTED JAN 9 I975 SHEET 2 [IF 4 I NVEN TOR. RALPH E. ROPEF? BY a/mmwmqz ma #Wu AT TOHNEYS PATENTED JAN 9 I973 SHEET 3 [1F 4 Www F ig.14

INVENTOR.

. RALPH 5. Papa? BY mm,wm,m M

AT TORNEYS PATENTED JAN 9 I975 SHEET [1F 4 A v M W.

INVENTOR.

' RALPH E. ROPER BY WWII/MM (5% AT TORNEYS SINGLE SHEET PALLET BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to pallets and to method and apparatus for making them.

Description of the Prior Art Examples of the pallets in the prior art are shown in the following U. S. Pat. Nos.: Strong 2,774,490; Martin 2,893,388, Sepe et al. 3,228,358 and Addy 3,433,184.

SUMMARY OF THE INVENTION One embodiment of the device of this invention might include a pallet formed of sheet material and comprising: (a) a generally rectangular panel formed of sheet material and having an upper load bearing surface; and (b) an annular leg formed in said panel and projecting downwardly for supporting said panel.

One embodiment of the method of this invention might involve a process for making a pallet which comprises drawing the central portion of a sheet of metal into a desired shape including one side of an annular leg while simultaneously yieldably resisting movement of the outer portion of the sheet toward the central portion of the sheet, holding the central portion of the sheet in its desired shape while drawing the outer portions of the sheet of metal into a desired shape includ ing the other side of the annular leg, and coiling the outer edge of said pallet.

One embodiment of the apparatus of this invention might be apparatus for making a pallet which comprises a convex first die formed to fit a pallet having a peripheral flange extending perpendicularly to the inner portion of said pallet, said first die having an outer wall against which said peripheral flange is received, a second ,die adapted to cooperate with said first die for gripping said pallet between said dies, a third die in contact with the outer wall of said first die and having a curved recess adapted to receive the lower end of said flange, a fourth die, means yieldably holding said fourth die in engagement with said third die, means for causing relative movement of said third die and said first die so that said third die wipes the wall of saidfirst die causing sald flange to be coiled by said third die recess, said fourth die cooperating with said flange and said third die to define in cross section a closed container retaining the flange as it is coiled.

Objects of this invention are to provide a nestable pallet; to provide a stronger pallet; to provide a pallet which is liftable by the tines of a lift truck being inserted from four directions; to provide a pallet which is rigid throughout and not loosely bendable; to provide an improved method for making a pallet; to provide improved apparatus for making a pallet; and to provide a method and apparatus for making a pallet which is strong, liftable by the tines of a lift truck being inserted from four directions, and rigid throughout and not loosely bendable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l'is a top plan view of a pallet embodying the present invention;

FIG. 2 is a section taken along the line 22 of FIG. 1 in the direction of the arrows;

FIG. 3 is a perspective view of a sheet of metal used in practicing the process of the present invention;

FIG. 4 is a vertical section through the center line of drawing apparatus used in practicing the present invention and showing the apparatus in a starting position;

FIG. 5 is a view similar to FIG. 4 showing the apparatus after the part has been drawn;

FIG. 6 is a perspective view showing the sheet metal after it has been drawn in the apparatus of FIGS. 4 and FIG. 7 is a vertical section through the center line of further apparatus used in practicing the process of the present invention;

FIG. 8 is a view similar to FIG. 7 showing the apparatus after the part has been drawn;

FIG. 9 is a perspective view of the part after it has been drawn in the apparatus of FIGS. 7 and 8;

FIG. 10 is a section taken through the center line of further apparatus in which the part of FIG. 9 is placed for further procedure in the practice of the process of the present invention;

FIG. 11 is a view similar to FIG. 10 showing the apparatus after the part has been drawn;

FIG. 12 is a perspective view showing the part after it has been drawn into the configuration of FIG. 11 by the apparatus of FIGS. 10 and 11;

FIG. 13 is a vertical section through the center line of apparatus for trimming the outer edge from the periphery of thepart of FIG. 12; 4

FIG. 14 is a view similar to FIG. 13 but showing the apparatus after the trimming has been accomplished;

FIG. 15 is a perspective view showing the part after having been carried through the process steps of FIGS. 13 and 14;

FIG. 16 is a vertical section through the center line of further apparatus used in forming a coiled peripheral edge on the pallet and showing the apparatus in starting position; e FIG. 17 is a view similar to FIG. 16 but showingthe pallet after the outer peripheral edge has been coiled thereon;

FIG. 18 is an enlarged section showing in detail portions of the structure illustrated in FIG. 16 in an intermediate position;

FIG. 19 is an enlarged section showing in detail portions of the structure illustrated in FIG. 17 in the same position as FIG. 17; and

FIG. 20 is a perspective view showing the pallet after it has been completely formed by carrying out of the process of this invention with the apparatus of this in vention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularly to the drawings, there is illustrated a pallet 10 which is formed of sheet metal and has a generally rectangular configuration with an upper load bearing surface 11. The pallet is provided with a single annular leg 12 which is located 3 concentrically in the pallet and projects downwardly for supporting the pallet. The pallet is formed from a single sheet or panel of metal and has a coiled edge portion 16 extending around the entire periphery of the panel. The coiled portion 16 of the pallet is one of the features which causes the pallet to be extremely rigid and resistent to loose bending.

Another feature of the pallet which provides great strength is a deeply drawn leg 12 which has a flat annular generally rectangular bottom 17 and has

sidewalls

18 and 19 which taper downwardly and inwardly from the upper load bearing surface 11. The panel also has annular rigidifying

embossments

21 and 22 formed therein, embossment 21 being located outwardly of the annular leg 12 and the embossment 22 being located inwardly thereof. Depending on the size of the pallet, additional ones of the embossments 21 can be provided. For example, in a 36 inch pallet only the single embossment 21 is provided whereas in a 42 inch pallet two such embossments are provided and in the 48 inch pallet three such embossments are provided. Such a triple embossment pallet is shown in FIGS. 10 through 20. In one embodiment of the invention the material used for the pallet is a sheet steel having a thickness of 0.048 inches.

Referring more particularly to the

embossments

21 and 22, it will be noted that each has a flat generally rectangular bottom 25 and 26, and also has sidewalls 27 and 30, 31 and 32 which taper downwardly and inwardly from the upper load bearing surface 11. The coiled edge 16 has its upper surface 35 flush with the upper load bearing surface 11 and forms a part of that upper load bearing surface 11. The leg 12 extends downwardly a substantially greater distance than the

embossments

21 and 22 and the coiled edge 16. It

should also be noted that the coiled edge 16 in cross section includes a portion which extends from the remainder of the pallet in a continuously decreasing radius which extends through at least 360 degrees. In the illustrated form of the invention the coiled edge extends through approximately 630 degrees or 1% circles.

Referring now more particularly to FIGS. 3 through 20, the process of the present invention is illustrated along with'the apparatus of the present invention. In FIG. 3 there is illustrated a flat sheet 40 of metal which has a generally rectangular shape with the comers 41 clipped therefrom. The flat sheet 40 is the initial shape of the panel 15. The sheet metal 40 is placed in a press which might be, for example, any hydraulic or mechanical press, such as a Warco Press manufactured by McKay Machine Tool Company of Youngstown, Ohio. This press has mounted therein the dies illustrated in FIGS. 4 and 5.'The press is capable of double action, that is it includes shafts or rods 42 which extend through the platen 45 so as to cause a different movement and exert a different force on the die 46 than is caused and exerted on the die 47. In the structure of FIGS. 4 and 5, there is also provided an upper die 50 tion of a different force and a different movement of the outer die 46 as compared to the inner die 47. When the press is operated, the upper platen forces the upper die 50 downwardly until the surface 51 of the upper die engages the sheet metal 40 and causes gripping of the sheet metal at its outer peripheral portion between the surface 51 and the outer die 46. The cylinders providing motive force to the shafts 42 are caused to bleed so that the loss of air from those cylinders permits downward movement of the shafts 42 toward the position illustrated in FIG. 5. The upper die surface of the die 47 has a projection 55 formed therein and a recess 56. The inner portion of the surface 57 of the die is flush with the projection 55.

As the upper die 50 travels downwardly with the sheet metal gripped between it and the outer annular die 46, the inner portion of the sheet metal is stretched over the upper surface of the inner die 47 .-As the upper die 50 and outer die 46 travel downwardly, the sheet metal tends'to slip inwardly from between the two dies, thus providing metal to the central portion of the pallet and permitting the one side 19 of the leg to be formed. The upper die 50 has a projection 60 formed thereon which cooperates and mates with the recess 56 in the inner die 47. When the upper die reaches the completion of its stroke, the projection 60 causes the embossment 22 to be formed. It will be noted that the

sidewalls

31 and 32 of the embossment 22, as well as the sidewall 19 of the leg, are formedby stretching between.

being represented at and the lower platen at 101.

Similarly to the above described press, the rods 102 permit a different movement of the lower outer die 105 as compared to the lower inner die 106-The upper outer die 107 is fixed to the upper platen 100 while the upper inner die 110 is yieldably mounted on the upper platen 100 by compression springv means 11 acting between the upper platen 100 and the upper inner die 110 and by suitable guide means and limit means such as those shown, for example, in FIG. 10..

The purpose of the inner dies 106 and 110 is to tightly grip the already formed inner portion of the pallet while a further portion of the leg 12 is drawn. In operation the apparatus of FIG. 7 first causes the

platens

101 and 100 to move toward one another to a position wherein the sheet metal 40'is tightly gripped between the die 106 and the die 110. The die 106 has an' upwardly extending projection 112 which has a rounded comer 115 which, together with the rounded corner 116, serves to shape and form the outer side 18 of the leg 12. After the inner dies 106 and 110 have tightly gripped the workpiece, the outer dies 105 and 107 grip the outer peripheral portion 117 of the sheet metal 40. Continued downward movement of the upper platen 100 causes the metal of the sheet 40 between the base 17 of the leg ,12 and the outer portion 117 of the sheet to be stretched. The gripping of the outer portion 117 of a sheet by the dies 105 and 107fis sufficiently light to permit slipping of that metal inwardly to provide sufficient metal to form the one side 18 of the leg 12 with the final position of the die being illustrated in FIG. 8. The strength of the springs 111 and the PSI or force exerted on the annular die 105 by the shafts 42 can be determined by experimentation. It has, however, been found that the proper and necessary strength and force is easily determined.

FIG. 9 shows the part after it has been operated on by the apparatus of FIGS. 7 and 8. The part is then taken to the apparatus illustrated in FIGS. 10 and 11. The part illustrated as being formed in FIGS. 10 and 11, as well as in the remainder of the present description, includes the three outer annular embossments mentioned above instead of the single outer annular embossment illustrated in FIGS. 1 and 2. It will be appreciated, however, that if the size'of the pallet is smaller, the pallet will be provided with only one or two outer annular embossments.

The purpose of the step illustrated in FIGS. 10 and 11 is to form a flange 200 on the work piece which flange extends generally axially all the way around the pallet. This flange 200 which is arranged perpendicularly to the main portion of the pallet is later used to form a tightly coiled strengthening element around the entire periphery of the pallet. As shown in FIGS. 10, 11 and 12, the portion 201 of the sheet metal outwardly located relative to the leg 12 extends in a flat condition radially outwardly. The function of the apparatus illustrated in FIGS. 10 and 11 is to grip the inner portion of the sheet metal including the leg 12 and the portions inwardly thereof so as to hold those portions in their already formed shape while the forming of the outer portion 201 of the sheet metal is being carried out. The upper platen 202 and the lower platen 205 of the press are the only force exerting structure needed and the

shafts

42 and 102 used in the previous steps are not needed. The inner die 206 has recesses 207 and 210 which receive, respectively, the leg 12 and the embossment 22. The inner upper die 211 incorporates a projection 212 which cooperates with the recess 207 to grip the leg 12. The inner upper die 211 is resiliently forced downwardly against the inner portion of the sheet metal by compression spring means 212. The inner upper die 211 is guided in vertical movement relative to the upper platen 202 by a plurality of guide members 215 which are fixed tov the upper inner die 211 and are slidably received in the upper platen 202. Such guide limit members may be used in all of the various illustrated die members where appropriate.

The die structure also includes an upper die 216 which is'also secured to the upper platen 202 for vertical relative movement and is yieldably biased away from the upper platen 202 by a compression spring 217 acting between the upper die 216 and upper platen 202. Also mounted within and vertically slidable within suitable vertically extending openings 220 in the die 216 are members 221 which operate to form the outer embossment 21 as well as the additional outer embossments 223. The members 221 have dies 224 attached to the lower ends thereof. The dies 224 are rounded and of reduced size relative to the size of members 221. The openings 220 are smaller at their lower portions than at their upper portions whereby the members 221 are retained and prevented from dropping out of the openings. There is also provided outer upper die 225 inner die 211 has been forced downwardly by the,

spring means 212 so as to engage the leg 12 and the inner portion of the pallet and to grip the inner portion of the between the die 211 and the die 206. Thus, the die 211 and the die 206 hold the shape of the leg 12 as the upper platen 202 continues downwardly. Further downward movement of the upper platen 202 causes the metal between leg 12 and the outer peripheral portion 230 to be stretched over the upper outer portion of the lower die 206. It will be noted that the upper outer corner 229 is rounded. The metal portion 230 isgripped between the dies 225 and 226 only to a sufficient extent as to hold the metal but to also permit it to slide between the dies 225 and 226 thus providing metal for forming of the flange 200. When the

platens

202 and 205 complete their stroke, the parts will be in the position as illustrated in FIG. 11. Just prior to reaching this final position the members 221 are forced downwardly by the platen 202 causing the dies 224 to project out of the dies 21.6 downwardly into recesses 232 in the die 206, thus forming the

embossments

21 and 223 in the pallet. The forming of the embossments in the pallet takes looseness out of the metal which would otherwise be present therein because of the forming of the flange 200. The thus formed part is illustrated in perspective in FIG. 12.

Referring to FIGS. 13 and 14, there is shown a further press operation, with a press such as the one mentioned above, which involves the trimming of the radially outwardly projecting periphery 235 from the pallet. This is accomplished by placing the pallet between the dies 236 and 237 which function to grip the pallet while the trimming is taking place. The upper die 236 is held resiliently downwardly by spring means 240 which acts between the upper platen 241 and the upper die 236. An outer annular cut-off member 242 cooperates with the lower die 237 to shear off the outwardly projecting periphery 235 of the platen. The thusly trimmed part is illustrated in FIG. 15.

FIGS. 16 and 17 illustrate the structure used to coil the outer edge of the pallet. A press such as the above described

press including platens

300 and 301 are used. A shaft 302'extends through the platen 301 and acts to exert force on the inner die 305. The die 305 cooperates with a die 306 to grip the outer portion 307 of the pallet. The lower die 305 includes a vertical wall 310 against which the flange 200 is received. A further outer die 311 is positioned outside of the inner die 305 and has an inner surface 312 which slides across the outer wall 310 and cooperates therewith. The outer lower die 311 has formed therein a recess 315 which in part is part-circular in cross section and which includes no undercut portions. The lower outer die 311 cooperates with an upper outer die 316. The upper outer die 316 is mounted for vertical movement about the upper inner die 306 and is normally held yieldably and resiliently downwardly by means of a compression spring 317 which acts between the platen 300 and the die 316. FIG. 16 shows the various dies in starting position. FIG. 18 shows a subsequent position of the apparatus after the upper platen 300 has been moved downwardly so that the die 306 and its projections 320 cooperate with the die 305 and its recesses 321 to grip the portion 307 of the pallet. In the position of FIG. 18, the upper outer die 316 is also in contact with the lower outer die 311. It will be noted that the upper outer die 316 has a slight recess 325 formed therein.

The forming of the tightly coiled outer peripheral portion 16 on the pallet which extends completely around the pallet is then accomplished by continued movement of the upper platen 300 toward the lower platen 301. The shaft 302 functions to permit measured relatively slow downward movement of the inner die 305 as air is bled from the cylinders holding the shafts 302 in position. The spring 317 simultaneously permits upward movement of the combined dies 316 and 311.

Because the dies 311 and 316 are held tightly together by the springs 317, a closed space 330 is provided which is made up of the recess 315 in the die 311 and the surface and recess 325 of the die 316. This closed space prevents'the coil 16 being formed on the outer periphery from going anywhere except into a more tightly coiled condition which finally results in the relatively tightly coiled condition illustrated in FIG. 19. The apparatus of FIGS. 16-49 is particularly useful at the corners of the work piece because it resists the tendency of the metal to resist proper tight coiling at those corners. It will be noted also that the apparatus illustrated in FIGS. 16 and 17 permits the part to be removed from the dies by merely moving

platens

301 and 300 apart until they again assume the position as illustrated in FIG. 16. The thus formed final part is illustrated in FIG. 20 as well as in FIGS. 1 and 2.

It can be appreciated from the above that this invention produces a pallet which is extremely strong and rigid yet is capable of stacking in a nested condition in a small space for storage.

While the invention has been disclosed and described in some detail in the drawings and foregoing description, theyare to be considered as illustrative and not restrictive in character, as other modifications may readily suggest themselves to persons skilled in this art.

The invention claimed is:

1. In a pallet formed of a single sheet of material, said sheet having a continuous annular leg depression constituting a pallet leg, said sheet having an upper load bearing surface and an edge portion extending circumferentially around the pallet, wherein theimprovement comprises:

said sheet has a horizontal center portion with a first top surface and a continuous shallowchannel coterminous with the periphery of said center por- I tion which has a constant cross sectional configuleg and has an inner side wall, a first flat annular bottom wall, and an outer wall, said inner and outer wall converge from said upper load bearing surf e to aid t annular ottom all w eh i parallel with sai irst top surface and i s posiiioneti closer to said first top surface than to the bottom of said leg, said sheet further includes an intermediate horizontal wall surrounding said channel with an inner portion coterminous with said outer side wall and an outer portion surrounding and coterminous with said leg, said sheet includes an outer horizontal wall coplanar with said intermediate wall and said horizontal center portion, said outer horizontal wall has an inner edge portion coterminous with said leg, said outer horizontal wall has an outer edge portion extending circumferentially around the periphery of said outer horizontal wall, said outer edge portion is configured as a closed coil which extends unbroken completely around the pallet;

2. The pallet of claim 1 wherein the improvement further comprises:

said sheet is of a generally rectangular shape with rounded comers, said closed coil configured edge portion extends continuously and smoothly through said corners and between said corners;

said closed coil in cross section includes a tightly coiled portion which extends from the remainder of said pallet in a continuously decreasing radius to at least 360 degrees; and,

said leg is hollow and includes a first leg side wall, a

second leg side wall, and a second'flat annular bottom wall, said first and second leg side wall converge from said upper load bearing surface to said second flat annular bottom wall which is parallel with said upper load bearing surface, said leg has a constant cross sectional configuration extending circumferentially around said intermediate horizontal wall.

3. The palletof claim 14 wherein:

said outer horizontal wall has a continuous generally rectangular groove of constant cross section extending circumferentially around said leg, said groove has a third bottom wall coplanar with said first flat annular bottom wall and a pair of side walls which converge from said upper load bearing surface to said third bottom wall, said closed coil is located below said upper load bearing surface, said pallet is supported only by said leg.

Claims

1. In a pallet formed of a single sheet of material, said sheet having a continuous annular leg depression constituting a pallet leg, said sheet having an upper load bearing surface and an edge portion extending circumferentially around the pallet, wherein the improvement comprises: said sheet has a horizontal center portion with a first top surface and a continuous shallow channel coterminous with the periphery of said center portion which has a constant cross sectional configuration extending circumferentially around said center portion, said channel is concentric with said leg and has an inner side wall, a first flat annular bottom wall, and an outer wall, said inner and outer wall converge from said upper load bearing surface to said flat annular bottom wall which is parallel with said first top surface and is positioned closer to said first top surface than to the bottom of said leg, said sheet further includes an intermediate horizontal wall surrounding said channel with an inner portion coterminous with said outer side wall and an outer portion surrounding and coterminous with said leg, said sheet includes an outer horizontal wall coplanar with said intermediate wall and said horizontal center portion, said outer horizontal wall has an inner edge portion coterminous with said leg, said outer horizontal wall has an outer edge portion extending circumferentially around the periphery of said outer horizontal wall, said outer edge portion is configured as a closed coil which extends unbroken completely around the pallet.

2. The pallet of claim 1 wherein the improvement further comprises: said sheet is of a generally rectangular shape with rounded corners, said closed coil configured edge portion extends continuously and smoothly through said corners and between said corners; said closed coil in cross section includes a tightly coiled portion which extends from the remainder of said pallet in a continuously decreasing radius to at least 360 degrees; and, said leg is hollow and includes a first leg side wall, a second leg side wall, and a second flat annular bottom wall, said first and second leg side wall converge from said upper load bearing surface to said second flat annular bottom wall which is parallel with said upper load bearing surface, said leg has a constant cross sectional configuration extending circumferentially around said intermediate horizontal wall.

3. The pallet of claim 14 wherein: said outer horizontal wall has a continuous generally rectangular groove of constant cross section extending circumferentially around said leg, said groove has a third bottom wall coplanar with said first flat annular bottom wall and a pair of side walls which converge from said upper load bearing surface to said third bottom wall, said closed coil is located below said upper load bearing surface, said pallet is supported only by said leg.