GB2217255A

GB2217255A - Spin welding components

Info

Publication number: GB2217255A
Application number: GB8908068A
Authority: GB
Inventors: Malcolm George Collins
Original assignee: MB Group PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1988-04-13
Filing date: 1989-04-11
Publication date: 1989-10-25
Anticipated expiration: 2009-04-11
Also published as: GB2217255B; GB8808752D0; GB8908068D0; GB2217254A

Abstract

The annular surfaces of two components 56, 57 bear axially against each other in order to be joined by spin welding upon relative rotation and define an inner flash trap zone surrounded by an annular weld zone and an outer flash trap zone surrounding the annular weld zone. The annular surfaces define a weld land 64 and void 66 flanked by complimentary annular projections 60 and troughs 62 to function as the inner and outer flash trap zones and so to seal the weld zone against melt leakage. The projections 60 may appear on one component while the troughs 62 on the other. Alternatively, each component has a projection and trough to cooperate with those on the other. Again the surface 68 of one component 57 may be plain while the other 56 includes troughs 62 which alone form the trap zones. The void 66 projects at an angle of 3 to 5 degrees. <IMAGE>

Description

SPIN WELDING COMPONENTS n f) 1 r7 - /- z_ 1 1 2 5 5 This invention relates

to spin welding and more particularly to spin welding a first component of plastics material to a second component of plastics material.

In the spin welding together of plastics components it is important that material melted at the weld zone is retained to form a strong weld rather than allowed to escape to form unsightly flash.

In a first aspect this invention provides first and second components having respective annular surfaces adapted to bear axially against each other and be joined by spin welding wherein the annular surface of said first component has annular surface features to define, when pressed against annular surface features of said second component, an inner flash trap zone surrounded by an annular weld zone, and an outer annular flash trap zone, said flash trap zones serving to contain melt arising at the annular weld zone during spin welding.

In a second aspect this invention provides a method of spin welding first and second components having respective annular surfaces adapted to bear axially against each other and be joined by spin welding said method comprising the steps of:

a) providing a first and second component having annular surface features to define, when pressed against each other an inner flash trap zone surrounded by an annular weld zone and an outer flash trap zone surrounding said annular weld zone b) applying pressure in an axial direction to force said annular surfaces of said first and second components into cooperating engagement to define the flash trap and weld zones c) rotating one of the components relative to the other component whilst continuing application of axial pressure to cause fusion of said flash trap zones so that wiping of a seal is developed to contain melt arising at the weld zone.

The embodiments of the invention along with apparatus for spin welding components in accordance with the invention are described below with reference to the accompanying drawings in which:- FIG. 1 is a perspective side view of spin welding tools and a pair of components cut away to show prior art devices for holding or driving one component relative to the other;

FIG. 2 is a perspective side view of spin welding tools and a pair of components each of which has a lateral flange extending between the tools and webs for holding or driving as is also known in the prior art;

11 1 FIG. 3 is a perspective view of a tool and a component located within the tool and cut away to show drive/holding spikes; FIG. 4 is a perspective sketch of the component of Fig. 3 united with a lid to make a container; FIG. 5 is a sectioned side view of first and second tools during spin welding of a pair of components; FIG. 6 is a graph of motor torque and associated motor speed v time; FIG. 7 is a sectioned side view of one of the spikes FIG. 8 is a sectioned side view of spin welding apparatus in which the centring surface of one of the tools is a plug; and FIG.S 9-12 are fragmentary sections through components according to the invention.

In Fig. 1 a container comprises a body 1 connected to a collar 2 by an annular weld 'W' created by spin welding.

The body 1 has a side wall 3 closed at one end by a bottom wall 4 which has two hollow ramp-like structures 5 which accommodate holding blocks 6 of a lower tool 7. The lower tool 7 is held stationary by its shank 8.

The collar 2 has a cylindrical plug wall 9 which enters the top of the side wall 3 until external flange 10 abuts the top of the side wall. The plug wall 9 extends, in an axial direction, beyond the radial flange 10 to define castellations 11 which receive drive dogs 12 of upper tool 13 which is rotated by means of its shank 14 by a drive system (not shown) to cause frictional heating of the interfacial weld zones of collar 2 and side wall 3 as the collar rotates upon the side wall 3 of the body. it will be readily understood that engagement of the drive dogs 12 with the castellations 11 of the collar, and engagement of the holding blocks 6 with the hollow ramp-like structures 5 is sudden and potentially desctructive. Furthermore the appearance of the welded container may be spoiled by the castellations and ramp-like structures, particularly if they are damaged.

In Fig. 2 another container has a body 15 and a collar 16. The body 15 comprises a side wall 17 terminating at an upper end in an outwardly directed flange 18 and at the other in a bottom wall 19. The flange 18 is supported by a plurality of buttress webs 20 rooted in the side wall 17. The collar 16 further comprises an annular end wall 24 having an internal flange 25 to define the mouth of the container. A plurality of buttress shaped webs 26 extend from the collar flange 22 to the cylindrical wall 21 of the collar.

In Fig. 2 recesses 27 in a driven top tool 28 receives the webs 26 of the collar for the purpose of delivering rotational drive while recesses 29 in a stationary bottom tool receive webs of the body to hold the body 15 stationary during spin welding. once again, the appearance of the welded body is at risk of being spoiled if the webs 20, 26 become damaged, and more seriously damaged webs may fail to deliver the necessary torque to achieve a sound weld. Damage to webs or castellations may be reduced to a minimum by control of application of axial pressure during a period of slow spin rotation while the drive and holding tools engage with driving and holding webs or castellations but at a cost of machine time.

Fig. 3 shows a tool for holding or driving one of a pair of components to be united by spin welding. The tool comprises a centring surface 31 in which the side wall 17 of a component fits snugly to be held centrally on a rotational axis. An annular thrust surface 32 of the tool fits against the underside of a flange 18 of the component to support the flange 18 in correct shape. In Fig. 3 the flange is cut away to reveal four of the twelve equispaced spikes 33, rooted in the thrust surface, which protrude to penetrate the underside of the flange of the component. A benefit from this type of tool is that the flange is held flat so that the weld zone on the opposite - 6 surface of the flange is in good shape to frictionally engage a complimentary weld zone.

The tool of Fig. 3 may be used to make the container shown in Fig. 4. The container has a body and a collar as discussed with reference to Fig. 2 so like parts are denoted by the same reference numbers as used in Fig. 2, namely, a body 15 has a side wall 17 terminating in an outwardly directed flange 18 and the collar 16 also terminates in an outwardly directed flange 22. The peripheral skirt 23 of the collar flange 22 (shown in Fig. 5) is not essential and is omitted from Fig. 4 so that the weld is visible. However it will be noticed that the container of Fig. 4 has no visible driving webs, castellations or the like.

The apparatus shown in Fig. 5 comprises a top tool 34 and a bottom tool 35, the bottom tool being fixed by studs 36 to a base plate 37 so that it remains stationary. As the bottom tool 35 and the component drawn therein are identical to the tool and component shown in Fig. 3 the same part numbers are used to denote like parts.

The top tool 34 comprises a cylindrical wall 38, the interior surface of which acts as a first centring means and an annular end surface 39 which acts as a thrust surface from which protrude a plurality of spikes one of which is denoted 40. We have found that steel gramophone needles are suitable for use as spikes because they have a 7 - suitable point to penetrate plastics materials on a shank long enough for firm rooting in the cylindrical wall 38. An end wall 41 spans the cylindrical wall and a shank 42 centrally placed on the end wall extends upwardly to permit fixing to rotational drive means (not shown). A hollow plug 43 extends from the end wall into the space defined by the cylindrical wall 38 to act as a second centring means by entering the mouth of a collar defined by the flange 25. If desired, the plug may be made long enough to centre the collar before the pins penetrate the flange 22 of the plastics collar. In any case the plug, end wall and interior surface of the cylindrical wall all serve to keep the collar in correct shape before the torsion forces of spin welding are applied.

The method of using the tools of Fig. 5 comprises the steps of spacing the tools of Fig. 5, placing the plastics body component in the bottom tool so its side wall 17 is centred by the internal centring surface 31 and its flange 18 rests on the spikes 33 upstanding from thrust surface 32.

A plastics collar moulding is placed in the top tool 34 so that a side wall of the collar is centred in the cylindrical wall and the spikes upstanding from the thrust surface.

8 - The top tool 34 is then moved in an axial direction towards the bottom tool 35 so that the flanges 22, 18 are brought into frictional engagement; the spikes 40 penetrate flange 22 and the spikes 33 penetrate the body flange 18 so that the body is held stationary by lower tool 35 and the collar is spiked on the top tool ready for rotation.

The top tool 34 is then rotated so that frictional forces at the interface of flanges 22, 18 generate heat to spin weld the collar to the body. Thereafter rotation of the top tool is promptly stopped and the tools are moved apart to release the welded container.

EXAMPLE:-

A collar moulded from polypropylene to have a peripheral flange 2.5 mm wide and overall diarteter 100 mm was welded to a flange 2.5 mm wide and overall diameter 100 mm. of a hollow body. The collar flange had a peripheral skirt 23 (as shown in Fig. 5) which served to contain melt arising during spin welding and prevent unsightly flash emerging to spoil the appearance of the finished weld.

The driven tool was rotated at 4000 rpm using a low power servo motor capable of delivering only 24 Nm torque. A fully fused weld was made in a total time of 0.37 sec. using an axial (thrust) load of about 150N.

The actual speed and torque traces are shown in Fig. 6 where it can be seen that the motor required about 0.14 sec. to accelerate the tooling and driven component up to 4000 rpm where it remained for a further 0.15 sec. before being braked to a standstill in about 0.08 sec.

Themaximum motor torque was exerted during the acceleration phase but thereafter a lower torque of 16 Nm was exerted on the component simply to maintain the welding speed. A reverse torque of only 9.5 Nm was required to effect the rapid braking required because of the assistance afforded by the visco-elastic drag of the molten polymer of the weld zone.

These torques were amply transmitted to the upper component and resisted by the lower component by means of twelve equispaced spiked steel projections on each of the two respective pieces of tooling. The axial length of each conical projection was 0.8 mm and the diameter of each at its root about 0.53 mm as shown in Fig. 7.

The same tooling was successfully used to weld these components using axial loads as slow as 1ON although naturally the weld time had to be considerably increased to create sufficient melt to achieve integral welds. In other words, although high axial loads are beneficial insofar as they are more likely to encourage the positive engagement of spikes with components, as well as facilitate short Yeld time, modest axial loads can also be successfully used if required.

In all cases the witness marks left by the penetrating spikes are extremely difficult to detect visually so that the finished appearance of the welded container is pleasing to the eye and suitable for most commercial applications where such thermoplastic components are required to be spin-welded together.

Fig. 7 shows one of the spikes 33,40 used in the example described. The included angle of the point of the spike was 30 0 and the extent of protrusion beyond the thrust surface 32 was 0.8 mm. A shank length of about 15 mm was rooted in the support surface, the shank diameter being 0. 53 mm. It was surprising that only twelve of these small spikes on each tool were so effective in holding/driving the components and left impressions which were hardly visible.

In Fig. 8, a container comprising a moulded plastics body 44 and a plug fit ring 45 is shown to be held between a bottom tool 46 which holds the body stationary while a top tool 47 rotates the collar to spin weld the ring to the body.

The container body 44 is typically moulded in polypropylene to have a side wall 48 and a bottom wall 49. The bottom wall 49 is centred on the spin welding - il - axis by seating in a recess in the bottom tool 46. An array of spikes 50 protrude from the bottom surface of the recess to arrest rotation of the body in the recess by penetrating the bottom of the body.

The ring 45 has a cylindrical plug wall 51 which is a push fit into the side wall of the body. A peripheral flange 52 prevents the plug wall entering too far into the side wall 48 of the body. A frustoconical wall 53 extends radially inwards and axially downwards from the flange to terminate in an annulus 54 which defines the mouth of the ring. The top tool 47 has an end surface 56 which fits upon the flange 52 and frustoconical wall 53 of the ring to act not only as a centring means but also as a thrust surface to impose an axial load (or top pressure). A plurality of spikes 55 protrude from the end surface 56 of the top tool to penetrate the frustoconical wall 53 to deliver a torsional drive as the top tool is rotated to effect a spin weld between the plug wall 51 of the ring and side wall 48.

If however, it is desired to only weld the flange to the end of the side wall of the body the spikes could usefully protrude into the flange of the ring instead of the frustoconical surface.

The flanged welding area, such as shown in Figs. 2,3 and 5 are of simplified design and indicate one flat surface being pressed against the other during welding.

In practice this does not work well since molten polymer produced at the interface tends to be readily displaced to form both internal and external "flash" to leave an essentially "dry" interface. Mechanical. means for preventing this loss of melt can sometimes be effective but in the case of an annular flange where flash is unsightly an attractive integral weld can be achieved using moulded features both to retain the melt within defined limits and encourage interfacial fusion.

Examples of how this can be achieved using moulded components are shown in Figs. 9-12 where components 56 and 57 have cooperating features. In Fig. 9, component 56 has annular projections 60 which fit within the annular troughs 62 of component 57 when the two components touch at the melt-generating "land area", 64. Component 56 is profiled such that a wedge-shaped annular separation 66, of width "t" exists between the two components when assembled prior to welding and during the spin welding operation, melt-generated at the land area flows into this wedge angle denoted 9 0 and fuses the two components together.

The outermost projection 60 and trough 62 prevent the melt from emerging at the periphery and the innermost projection 60 and trough 62 likewi se prevent melt from flowing beyond the inner boundary walls of the mating components.

k 1 1 These projections and troughs not only act to limit the radial flow of melt in the aesthetic sense but actually effect a physical barrier against the loss of melt which would otherwise occur to the catastrophic detriment of weld integrity. This is particularly true of semicrystalline polymers such as polypropylene which has a very low melt viscosity, but equally applies to polyethylenes and nylons for example.

The angle 0 0 of the annular wedge portion, is preferably in the order of 3 0 to 5 0 and the width "t" of the separation zone is about equal to "L", the width of the contact land.

The projections and troughs are dimensioned such that prior to spin welding, the projections reach substantially to the bottoms of the troughs and during spin welding the projections wipe the bottoms of the troughs so that a seal is developed to contain melt arising at the weld zone.

As indicated in Figs. 10 and 11 the various features defining the weld zones and flash traps may be provided on one or other of the components. Fig. 12 shows an embodiment where the projections are omitted and the surface 68 of component 57 is plain; troughs on the other component alone forming the flash traps.

In order to avoid the generation of melt and the radially inner and outer edges of the flanges of the components 56, 57 it is preferable if a slight gap 70 is formed at these points prior to spin welding. During spin welding these gaps will close to form a neat joint.

Whilst the invention has been described with reference to components having peripheral flanges the invention is not limited thereto. For instance a pair of hemispherical components of sufficient thickness could be welded edge to edge to make a ball for a ball valve.

Z 1 -

Claims

Claims:

1. First and second components having respective annular surfaces adapted to bear axially against each other and be joined by spin welding wherein the annular surface of said first component has annular surface features to define, when pressed against annular surface features of said second component, an inner flash trap zone surrounded by an annular weld zone, and an outer annular flash trap zone, said flash trap zones serving to contain melt arising at the annular weld zone during spin welding.

2. First and second components according to claim 1 wherein each of the inner and outer annular flash trap zones is provided by an annular projection on one of the components and an annular trough on the other of the components; the projections entering into and extending substantially to the bottom of the troughs when the components are brought together for welding.

3. First and second components according to claim 1, wherein the first component has an annular surface comprising a first inner annular projection, a flat annular land extending in a radial direction from the root - 16 of the inner annular projection, an annular surface extending at an acute angle from the flat land to a second annular projection concentric with the first annular projection; and the second component has an annular surface comprising a first inner annular trough, a flat annulus extending radially from the trough to a second annular trough concentric with the first trough; such that when the annular surfaces are assembled together the land of the first component contacts the flat annulus of the second component and the annular projections of the fiist component enter into and reach the bottoms of the respective troughs on the second component.

4. A pair of components according to claim 2 or claim 3, wherein the projections are narrower than the trough widths.

5. A pair of components according to any preceding claim wherein the annular surface of each component is the underside of a flange extending outwardly from a hollow body having a round side wall surrounded by the flange and an end wall closing one end of the side wall.

1 17 - 1

6. A method of spin welding first and second components having respective annular surfaces adapted to bear axially against each other and be joined by spin welding said method comprising the steps of: a) providing a first and second component having annular surface features to define, when pressed against each other an inner flash trap zone surrounded by an annular weld zone and an outer flash trap zone surrounding said annular weld.zone b) applying pressure in an axial direction to force said annular surfaces of said first and second components into cooperating engagement to define the flash trap and weld zones c) rotating one of the components relative to the other component whilst continuing application of axial pressure to cause fusion of said flash trap zones so that wiping of a seal is developed to contain melt arising at the weld zone.

7. A method according to claim 6, wherein in step (a) the weld zone is defined by a first component having an annular surface having an annular flat land portion surrounded by a frustoconical surface and a second component having a flat annular surface portion so that in step (c) the rotation and continued axial pressure melts the flat land and progressively melts the frustoconical surface material, melt arising being contained by the flash trap zones.

8. A method according to claim 6 or claim 7, wherein in step (a) at least one of the flash trap zones is defined by an annular bead upstanding from the annular surface of one component entering a wider annular trough in the other component to create a radial clearance between the bead and trough in which melt is arrested.

9. A method according to claim 8, wherein each component is provided with a peripheral flange extending laterally of a side wall portion closed at one end so that the side wall portions of both components are held in axial alignment by a cavity in a respective tool and the annular surfaces of the flanges are pressed together by cooperation of the end walls of each tool.

10. A method according to claim 9, wherein axial pressure is applied to the flanges by an end wall of a tool having an array of spikes upstanding from said end wall of each tool so that one tool holds a component while the other tool rotates the other component.

1 19 - 1

11. First and second components substantially as described herein with reference to the accompanying drawings.

12. A method of spin welding substantially as hereinbefore described with reference to the accompanying drawings.

publishadl 159at ifttent)MOe- te HOu68, 86"71 High Holborn.LondonWUR4TP. Further copies maybe obtained from The p&tentomoe. Was Branch, at Mary Cray, Orpington, Kent BFZ 3RD. Printed by Multiplex techniques ltd, St MB37 Cray, Kent, Con. 1/87