Inertial spin welding of thermoplastic and thermoplastic coated container parts

Abstract

A thermoplastic container bottom is inertially spin welded into the interior of a cylindrical container body of paperboard internally lined with a layer of thermoplastic material. A body supporting mandrel has an expansible body engaging portion which is inserted into the body and subsequently expanded to define a cylindrical surface of a diameter exactly equal to that of the specified internal diameter of the body. A seating member at the end of the body supporting mandrel establishes the depth to which the container bottom is inserted into the body and is provided with a low-friction projecting resilient member which contacts the rotating bottom.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application is a on housing 44 by means such as welding or as by screws 90 (FIG. 6). A recess 96 is formed on the lower side of seating member 88 and a resilient member 98, whose purpose will be described in greater detail below is fixedly mounted in and projects downwardly from the recess. Member 98 can be compressed to lie entirely within recess 96. In order to reduce friction, member 98 may be made from or coated with a low-friction material such as polytetrafluoroethylene (Teflon).

An ejector plate 100 having a circular opening 102 is mounted at the lower end of a plurality of support rods such as 104, support rods 104 being fixedly mounted in table 24.

Referring now to FIGS. 7-9, in those figures are shown cross-sectional views of a container body and bottom which are to be spin welded by the apparatus described above. Referring first to FIG. 7, a container body CB of cylindrical shape is shown in cross-section. The container body CB is formed by a cylindrical tube of paperboard 106 whose interior surface is lined with a moisture barrier liner or coat of a suitable thermoplastic material 108 such as polyethylene, polystyrene, or polypropylene. A container bottom B is formed of the same thermoplastic synthetic plastic material with a bottom 110 and an integral upwardly projecting peripheral flange 112. As best seen in the enlarged view of FIG. 8, flange 112, is formed with a downwardly and outwardly inclined surface at its upper end, because in order to perform the desired spin welding operation, there must be an interference fit between the inner surface of the thermoplastic layer 108 on container body CB and the outer surface 116 of flange 112. The inclined surface 114 enables the flange to be pushed axially inwardly into the container interior with a shoehorn-like action.

A second upwardly projecting flange 118 preferably is located upon the container bottom B to protect the lower edge of the paperboard portion of the container body, as best illustrated in FIG. 9, which shows the bottom and container body at the conclusion of the spin welding operation.

The container bottom B preferably is provided with a downwardly projecting flange 120 and a plurality of radially extending ribs 122 extend from the inner side of flange 120 to the bottom surface of bottom B to provide a rotary drive coupling between the bottom B and lugs formed on the upper surface of lower mandrel 30.

THE OPERATION

A general sequence of operation of the apparatus described above is illustrated schematically in FIGS. 10-1 through 10-7.

The initial step in the operation is shown in FIG. 10-1 in which upper mandrel 28 is raised to its maximum elevation and cam actuating rod 82 is likewise raised to its maximum elevation to position cam member 78 relative to body engaging members 62 in the position shown in FIG. 2. As previously described, vertical positioning of upper mandrel 28 and cam actuator 82 is controlled by rollers 38 and 40 respectively, these rollers riding in grooves in the stationary upper cam track 14 (FIG. 1) to raise and lower the respective rollers as the upper and lower mandrels are rotated about the axis of central post 12 of the machine frame. The broken lines 38C and 40C in FIGS. 10-1 through 10-7 approximately indicate the configuration of the cam tracks upon which rollers 38 and 40 ride. Similarly, the broken line 34C indicates the cam track upon which the lower mandrel positioning roller 34 moves.

With cam rod 82 and cam 78 in their maximum elevated position relative to body engaging segments 62, garter spring 72 has radially contracted the lower ends of segments 62 so that the cylindrical outer surfaces of segments 62 in FIG. 10-1 approximate a downwardly convergent frustoconical surface having an outside diameter at its lower end substantially less than the internal diameter of a container body CB.

In FIG. 10-1, a container body CB is located on a feed table FT-1 in underlying coaxial alignment with upper mandrel 28. A container bottom B has been fed from a second feed table FT-2 onto the upper end of lower mandrel 30.

In FIG. 10-2, upper mandrel 28 has been lowered to insert the container body engaging segments 62, fully into the interior of the container body CB. During this lowering movement of upper mandrel 28, cam actuating rod 82 is simultaneously lowered so that no relative vertical movement between actuating rod 82 and upper mandrel 28 occurs, and the body engaging segments 62, located in the interior of container body CB in FIG. 10-2 are thus still in the radially contracted position as in FIG. 10-1.

In FIG. 10-3, actuating rod 82 has been moved downwardly relative to upper mandrel 28. Referring briefly to FIG. 2, the lowering action of rod 82 illustrated in the transition from FIG. 10-2 to 10-3 causes cam member 78 to move downwardly from the position shown in FIG. 2, this downwardly movement of cam member 78 causing its inclined cam surfaced surfaces 80 to slide downwardly along the inclined surfaces 76 on body engaging members 62 to pivot the members 62 radially outwardly about their respective pivots 70 into full contact with the interior wall of container body CB.

As previously described above, the characteristics of container body CB and the process by which the container body is manufactured are such that at the time the container body is fed into the spin welding apparatus, the internal diameter of the body is normally somewhat smaller than its specified diameter. The container bottom B, on the other hand, is quite accurately formed to its specified diameter and maintains this diameter quite accurately after its formation. In order that the spin welding of the container body to its bottom may be efficiently performed, it is essential that the container body be at its specified internal diameter at the time the container bottom is inserted into the body so that the desired interference fit between these two parts, one of which is rotating relative to the other, will generate the desired amount of frictional heat to fuse the opposed thermoplastic surfaces to each other.

As described above, the outer surfaces of the body engaging members 62 of upper mandrel 28 are accurately machined to a diameter corresponding (with a slight negative tolerance) to the specified internal diameter of container body CB. The radial expansion of body engaging members 62, by actuation of cam rod 82 after the members have been inserted into the container body, is likewise accurately regulated so that at the conclusion of the cam actuated expansion of body engaging members 62, the outer surfaces of these members are conformed to a cylindrical surface of a diameter equal to the specified internal diameter of the container body (with a slight negative tolerance). Thus, in FIG. 10-3 in conclusion of the expansion of body engagning engaging members 62 by lowering of cam actuator 82, the interior of the container body has been accurately expanded to its specified diameter. The lower ends of body engaging members 62 are spaced upwardly slightly from the bottom of the container body to afford sufficient axial clearance for the insertion of flange 112 of the container bottom C.

In FIG. 10-4, lower mandrel 30 has been elevated to position the container bottom B closely beneath, but out of contact with, the lower end of the container body CB supported upon the upper mandrel. In this step of the process, the lower mandrel 30 is engaged with a drive belt DB which drives the lower mandrel in rotation about its axis. The drive belt DB operates along a portion of the circular path followed by the lower mandrel, see U.S. Pat. No. Re. 29,448 for details of this driving arrangement. The container bottom B is rotatively locked to lower mandrel 28 by the webs 122 and thus rotates with the lower mandrel.

The next step in the sequence of operation finds upper mandrel 28 being lowered slightly to seat the container bottom B within the bottom of the container body. Just prior to this lowering step, lower mandrel 30 passes out of engagement with drive belt DB, however, the rotary inertia of lower mandrel 30 maintains the lower mandrel in rotation as the bottom inserting step is performed. Because the container body CB carried by the upper mandrel 30 is held against rotation, the relative rotation between the engaged thermoplastic lined interior of container body CB and the rotating thermoplastic bottom B carried by the lower mandrel generates frictional heat melting the two engaged surfaces and at the same time exerts a braking action upon the rotating lower mandrel and container bottom. This braking action swiftly brings the freely rotating lower mandrel to a halt, the energy expended in the braking operation being converted to the heat which melts and, upon halting, fuses the container bottom to the container body.

In FIG. 10-6, the lower mandrel has been lowered to its original position, the now fused container body and bottom are carried above an outfeed table OF and cam actuating rod 82 has been elevated to permit the body engaging members 62 to be restored to their contracted position by garter spring 72.

In FIG. 10-7, upper mandrel 28 has been elevated to its original position to drop the container body CB onto the outfeed table, this separation of the container body from the upper mandrel having been assisted by stripper plate 100 (FIG. 2).

While one embodiment of the invention has been described in detail, it will be apparent to those skilled in the art that the invention may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.

Claims

1. Spin welding apparatus comprising upper and lower mandrel means mounted for vertical movement toward and away from each other along a common vertical axis, said upper mandrel means being adapted to releasably support an open ended cylindrical container body and said lower mandrel means being adapted to releasably support a container bottom of thermoplastic material having an axially upwardly projecting peripheral flange insertable into said container body with a press fit, first drive means for driving at least one of said mandrel means in rotation about said vertical axis relative to the other mandrel means, and second drive means for driving said mandrel means in movement along said vertical axis to seat said container bottom within said container body while said mandrel means are rotating relative to each other to insert and frictionally weld said container bottom in said container body; with radially expansible and contractable body engaging means mounted on the lower end of said upper mandrel means in symmetrically disposed relationship about said vertical axis, said engaging means being normally disposed in a contracted position wherein said engaging means may be axially inserted into a container body, expanding means for radially expanding said engaging means to an expanded position wherein the radially outer surfaces of said expanding means lie on a common cylindrical surface having a diameter equal to the specified internal diameter of said container body and further comprising a seating member mounted at the lower end of said upper mandrel means and engagable with said container bottom to establish the depth to which said container bottom is inserted within said container body by operation of said second drive means.

2. The invention defined in claim 1 wherein said body engaging means comprises a plurality of like body engaging members, each of said engaging members having an outer surface conformed to a circumferential segment of said common cylindrical surface.

3. The invention defined in claim 2 wherein said engaging members are circumferentially spaced from each other when said engaging members are in said expanded position.

4. The invention defined in claim 3 further comprising pivot means at the upper end of each of said engaging members mounting said members for pivotal movement on said upper mandrel means about respective axes lying in a common horizontal plane and tangent to a circle centered on said vertical axis.

5. The invention defined in claim 4 further comprising spring means adjacent the lower ends of said engaging members resiliently biasing said engaging members to their contracted position.

6. The invention defined in any of claims 2, 3, 4, or 5 wherein said expanding means comprises an actuating cam mounted for vertical reciprocation relative to said engaging members, said cam having a plurality of vertically inclined cam surfaces respectively slidably engaged with complementary inclined surfaces on each of said engaging members to force said engaging members radially outwardly upon vertical movement of said cam in a first direction relative to said engaging members.

7. Spin welding apparatus comprising lower mandrel means for supporting and rotating a thermoplastic container bottom having an upwardly projecting peripheral surface, upper mandrel means for supporting a cylindrical container body, drive means for inducing rotation of said lower mandrel about a vertical axis, and means for moving said mandrels relative to each other along said vertical axis to seat the peripheral surface of said bottom within the lower end of said body while said lower mandrel is rotating to frictionally weld said bottom to said body; wherein said upper mandrel comprises a plurality of body engaging members symmetrically disposed about said vertical axis, each of said body engaging members having an outer surface corresponding to an axially extending segment of a cylindrical surface of a diameter equal to the specified internal diameter of said cylindrical container body, mounting means mounting said body engaging means on said upper mandrel means for radial expanding and contracting movement relative to said vertical axis between an expanded position wherein the outer surfaces of said body engaging members cooperatively define the major portion of a cylindrical surface coaxial with said vertical axis and of a diameter equal to said specified internal diameter and a radially contracted position wherein said body engaging members may be axially inserted into the interior of a container body, and expanding means operable when body engaging members have been axially inserted into a container body for expanding said body engaging members to their expanded position to mount said body on said upper mandrel means and to size said body to said specified internal diameter and further comprising a low-friction bottom seating member mounted on the lower end of said upper mandrel means for establishing the depth at which said bottom is located within said container body while being frictionally welded thereto.

8. The invention in claim 7 wherein said mounting means comprises pivot means at the upper end of each member mounting the member for pivotal movement relative to said upper mandrel means about a horizontal axis, the horizontal axes of said pivot means being tangent to a common circle centered on said vertical axis, and spring means coupled to said members adjacent to the lower ends thereof resiliently biasing said members to said contracted position.

9. The invention defined in claim 8 wherein said expanding means comprises a cam member mounted in said upper mandrel means for vertical movement relative thereto, said cam member having a plurality of cam surfaces inclined relative to said vertical axis, and actuating surfaces on the interior of the respective members adjacent the lower ends thereof slidably engaged with the respective cam surfaces to cause expanding pivotal movement of said members upon vertical movement of said cam member in a first direction.

10. The invention defined in claim 7 further comprising means defining a recess in the bottom of said seating member, and a resilient low-friction pad member mounted in said recess and normally axially projecting below said seating member to engage said container bottom prior to the seating of said container bottom against said seating member, said resilient pad member being compressible into said recess upon seating of said container bottom against said seating member.

11. The invention defined in claim 10 wherein said pad member further comprises an external surface of polytetrafluoroethylene.

12. Spin welding apparatus comprising upper and lower mandrel means mounted for relative vertical movement along a vertical axis, said upper mandrel means being adapted to releasably support a container upper part having a thermoplastic peripheral surface and said lower mandrel means being adapted to releasably support a container lower part having a thermoplastic peripheral surface adaptable to axially mate with said surface on said upper part with an interference fit, first drive means for driving said mandrel means in relative movement along said vertical axis to telescope said upper and lower part surfaces in mating relation, and second drive means for driving at least one of said mandrel means in rotation about said vertical axis relative to the other mandrel means to frictionally weld said surfaces, radially expansible and contractable part engaging means mounted on an end of one of said mandrel means in symmetrically disposed relationship about said vertical axis, said engaging means being disposable in a contracted position wherein said engaging means may be axially inserted into one of said parts, and expanding means for radially expanding said engaging means to an expanded position wherein the radially outer surfaces of said expanding means lie on a common cylindrical surface having a diameter equal to the specified internal diameter of said container part into which it is inserted.