CA1043060A - Moulding apparatus - Google Patents

Abstract

A B S T R A C T
Container closures are given the customary sealing gasket of plastics material by a two stage deformation of a pellet of the plastics material. In a first stage the material is partly deformed and is heated by direct conduction from a heated deforming member, and in the second stage a relatively cool final moulding die effects further deformation to impart the desired finished configuration to the gasket. The pressure member, and possibly also a workpiece support on which the upturned closure rests, is heated by means of a radiant heat source directing radiant heat onto a blackened roughened surface of the pressure member, and the work-piece support where applicable. The pressure member has a low-adhesion surface of polytetrafluoroethylene.

Description

~L043060 The present in~ention relates to a method o~ and app~ratus for moulding thermoplastic co~positions. In a preferred form, the invention relates to the moulding of liners or gaskets in con-tainer closures.
Hitherto it has been known for example when forming a liner for a container closure to pre-heat the thermoplastic material and to mould the heated and thus softened material using a mould die which is not itself heated and may even be positively cooled so that in either case it presents a relatively cool moulaing surface. ~owever, the above described moulding process involves a considerable dwell time of the thermoplastic material in an oven, through which closures carrying metered quantities of the plastics material, are passed along a tortuous conveyor path. Such a system is for example, disclosed in our United States Patent 3,963,396,Keith Shotbolt, June 15, 1976 in which the heat is imparted to the thermoplastic material by radiation within the oven.
~his has the disadvantage that, i~ for any reason the movement of the closure-carrying conveyor through the oven stops, the closures in the oven rapidly become overheated and "scorched" with the result that they are unsuitable for use.
In accordance with the present invention there is provided in a method of moulding a thermoplastic material into a gasket for a con-tainer closure comprising the steps of heating a quantity of the material and deforming said material into a desired finished configuration, the improvement wherein the material in the form of a pellet is placed into the closure and is subjected to two consecutive deformation operations, the first operation being carried out with a heated pressure member which both heats the thermoplastic material and deforms it into a partially moulded configuration, and the second operation being carried out using a positivel~ cooled moulding member, shaped to impart the desired ~inished configuration to the thermoplastic material, which is maintained at a .
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temperature lower than that of the heated and partially defo~med thermo-plastic material.
The present invention provides a method of moulding thermoplastic ~aterial comprising the steps of heating a quantity of the material by contact with a heated pressure member which both heats the thermoplastic material and deforms the naterial into a partiall~ moulded configuration and subsequently deforming the material into a desired finished configura-tion, using a moulding member shaped to impart the desired finished con-~iguration to the thermoplastic material but maintained at a temperature less than that of the heated - la -,~ 's ~\

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and partially de~ormed thermoplastic material, m e die is ~hus de~irably not heated at all or is positively cooled.
In order ~o en~ure that the thermoplas~ic material does not ~tick to the heating member that ~urface ~ the pressure m~mber which in ~e contacts the ~hermQplastic material may be coated with a medium imparting low~adhe~ion ch2racter-istics~ Preferably the coating may oomprise polytetra~luoro-ethylene (P,TtF,E~)~ Mbre pre~exably, ~he particular P,T.F~E~
coating employed may be in accordance wi~h the "ARM~URCOTE"
syst~m in which the sur~açe o~ the pressure member i~ first o~ all yiven a sintered sta~nless steel layer, onto which the su~se~uently applied PoT,F,E~ can more securely ba keyed~
~y exerting pressure on the pellet or spot while heating it, ~he thickness of the thermoplastic material i3 redu ed and the area i5 increaqed~ mus the ra~e of transfer o~ heat is increased markedly~ ~or example, if the diam~r o~ a pellet is doubled the heat trans~er is increased by 16 times, ~e invention also provides apparatus ~or applying a moulded surface coveri.ny of a thermoplastic m~terial to a work-pieca comprising means for ~up~orting the w~rkpiece, means ~or placin~ a thenmopla~tic material into contact with the work-piece, a heated pressure member for par~ially de~orming the thermoplastlc material and ~mpart~ng heat there~o, a moulding die driveable towards and away ~rom the workpiece *or further de~orming said partially de~ormed thermop~astic material7 ~nd temperature control mean~ ~or maintaining the t~mperatures o*
said moulding die and said pre~sure member at separate ~alues with the m~ulding die cooler than the pre3sure m~mber.
The invention ~ur~har provides a con~ainsr do~uxe ~ ~r~

~ ~ 3~ ~ ~
having a sealing gasket moulded ~herein ~y the above method or use of the above ~pparatus.
Preferably, the presisure member is given a low-a~he.~ion ~u~face such as P,T~F,E, Desirably the appaxa~us may include a rotary burret incorporating a pluxality o w~r~piece support~
an~ a pluxalit~ o~ separate pressure membersy all associated with a comm~n radiant hea~ source and arranged on a circular arcuate path around the ~ds of ro$ation of the tuxret~ The workpiece can be supported on a respective one of the workpiece supports and the associated pressure m~mbers will be driven down into ~ontact with thenmoplaRtic material on the wvrkpiece to lmpart heat thereto while causing initial deformation o~
the thermopla3tic material, Advantageously, means ma~ be provided ~or heating the workpiece supportA, SG ~hat the w~rkpieces ~hemselve~
are heat~d thereby, Conveniently the means ~or heating the praqsure m~mber an~or the workpiece support may comprisa a source of radiant heat located adjacent the pre~sure member, Ad~antageou~lyD the pres~ure m~mber includes a blackened surface di3posed directly opposite the radiant heat ~ource which, in a preferred ~orm, may be an infra-red electrical heating el~ment which can be caused tQ glow when energised~
Other ~lternative forms o~ hea~ing ths pressure membe~ and/or the workpiece suppoxt~ may be employed~ Fbr example the heat m~y be imparted by direct conduction from electrical cartridge heater~, or by playing a ga~ ~lame on the heaking memb~r and/or the ~uppoxt, _ 3 -- .

1~3~66) A stripper me~ber may be locate~l aboYe ~he workpiece path to hold down the ~rorkpiece as the pressure member is withdrawn after hot pressing the plastics material. ~here the ~orkpieces are container closures the stripper member is a plate with a slot extending peripherally of the turret to receive the pressure member, in this case a plunger which may have flats formed to enter the slot ~hile the hot pressing operation is carried out by a moulding head below the stripper plate ~hich may or may not have similar flats, as desired.
The heating turret may include separate temperature sensors for detecting the temperatures of the workpiece supports and the temper-atures of the pressure members and a separate control system may desirably be provided ~or controlling the temperature of the supports and the pressure members to maintain optimum heat transfer conditions.
This heating turret may be fed from an insertion device, such as a further turret of the form disclosed in our United States Patent 3,963,396, Keith Shotbolt, June 15, 1976, and the heating turret may be arranged to deliver the workpiece with partly deformed plastics material directly to a further moulding turret.
The workpieces may suitably be preheated before insertion of the plastics material by means of a rotary preheating turret in which the workpieces rest on hot supports. The hot supports may be heated by electrical cartridge heaters, gas flames or the like, Advantageously the supports may be heated by means of conduction from a hot receptor arranged to receive heat from a stationary .

1~)43~6~) r~diant source such as ~n infra~red heating el~mept.
By avoiding the conventional convective or direct radiation heating of the plastics material, it i9 pos~ible to impart to the plastics material the desired softnes~
together with an advantageous pre shaping in a time which9 when moulding l1ners or ga~ket~ in container clo~ure~, can be reduced from the order of 25-40 æecond~ down to the order o~ 2.5 seconds. In the event of ~hut dow~ of the machine while the heating turret is loaded~ very few if any clo~ures will be rendered unu~able 7 because they are not ~ubjected to intense heat.
SLmilarly the use of direct conduction ~or preheating ~he empty workpieces means that heat can be transferred quickly into the workpiece from a large capacity heat-tran~mit ing conductor member without the need for fierce radiatioD directly onto ~he wor]~piece sur~ace since this radiation tends to mar some lacquers used on container closures:.
~he main heating turret u~ed in the preferred em~odiment o~ apparatus according to the invention i8 ~ar more compact than the previously used ovens.

In order that the pre~ent invention may more readily be under~tood the following description i~ given, merely by way of exampleg reference ~eing made to the accompanying drawings in which:-~igure 1 i9 a ~chematic top plan view of apparatus for lining container closures in accordance with the present invention;
Fi~uxe 2 i~ a vertical sectional view through one o~ the positions on the heatin~/pressing turret;

~0~3C~ 0 ~ igure 3 is a horizontal sectio~ on t~e line III-III of Figure 2; and Figure 4 is a vie~ similar to ~igure 2 but showing an alter-native form of heating/pressing turret;
Figure 5 is a plan view of the stripping plate shown in Figure 4, Figure 6a and 6b are a side elevational, partly sectional and an end elevati~nal view, respectively, of the plunger bottom pad shown in Figure 4.
Re~erring now to Figure l, the closures to be lined are advanced along a schematically illustrated chute conveyor generally designated l, to a feed star wheel 2 from which the stream of empty closures is fed to a preheating turret 3 to be preheated by direct con-duction of heat ~rom a closure support. The closures passing around the turret 3 are heated to a temperature sufficient to cause subsequently inserted pellets o~ thermoplastic material to adhere securely to the inner ~ace o~ the closure for subsequent operations.
From the preheater turret 3 the closures pass around a first trans~er star wheel 4 and are fed to a pellet insertion turret 5, prefer-ably o~ the form dieclosed in our United States Patent 3,963,396, Keith Shotbolt, June 15, 1976.
The star wheel 4 has a plurality o~ pockets which advance the closures while the disc-like end walls o~ the closures ride on a smooth guide rail which has a small contact area with the closures so as to minimiæe heat loss from the already preheated closures and to avoid scratch1ng the decorative lacquer which will already have been applied to the ou-ter surface of the closure.

1~43~i0 Individual pellets of ~herm~plastic material are introduced ~o respective ones of the preheated closures by turret 5 }:efore the closures are trans~erred by means o:E a similax secondary trans~er star wheel 6 onto a turret 7 to be heated and initially deformed~ as will be described in more detail b~low. ~rom the heating turret 7 ~he clo~ures which now have a soft flattened pla~3tic3 disc thereir~9 are transferred, ~ a third cimilar type o~ trans~ex star wheel 89 to a moulding turret 9 where mould dies considerably lQ cooler than both the thexmoplas~ic ma~erial and the heaked de:orming members of turret 7 impart the final desired ~h~pe to the thermoplastic m~terial, hefore the clo~3ures then advance to an ins~ection station along the ~une or a di~ erent conveyor as shown at 10 ~
Fi~ure 2 shows one station 11 on the heater turret 7 comprising a vertically movable pressure men~er or h~3ating plurlger :L2 having an upper part l~a o~ an asbestos impr~
A nated phenolic re~in kno~ by the Trada ~ame Ferobestos, At the top end oi~ the upper part 12a is the cam follower roller 25 mounted in a bi:~urcated carrier 26 which is spring urged upwardly by a helical compression spxing 27 into contact with a circumferential cam 16~ A heat-absorption member 13 on the plun~er 12 ha~ an arcuate ~urface 1~ arranged on a circular arc about the c~tre o~ a thermostatically controlled heating element 1~ which itsel~ extends around the circum-~erence o~ the main turret.
t~he circum~erential cam 16 a~ the ~op o~ the machine provides th means for causing periodic raising and lowering o~ each plunger 12 relative to a container closure resting on a support member 17, so that a removable bottom ~r~ rK

~913~
pad 18 of the plunge~ e~ters the closure to co~press the pellet o~ a thermoplastic material, in this case a composi~ion consisting o~ poly-ethylene and but~l rubber as disclosed in British Patents ~os. 1112023, 1112024 and 1112025. Amongst man~ other suitable materials is polyvinyl chloride. Also suitable are the mixtures of polyethylene and styrene butadiene as disclosed in British Patents Nos. 1196125 and 1196127.
mis action imparts heat to the pellet allowing it to soften and at the same time to spread due to the downward compression of the plunger. By the end of the heating and compression operation the entire body of the plastics material is soft and read~ for a subsequent moulding operation using a relatively cold mould at the moulding turret 9.
The arcuate surface 14 of the heat receiving member 13 is both blackened and roughened so as to improve its heat-absorption characteristics with respect to radiant heat, and a reflector 19, extending around the circumference of the turret, throws back radiant heat against the surface 14. The heat picked up by the surface 14 is then conducted through the heat absorption member 13 to the plunger 12 so as to maintain the bottom surface 18 at a temperature of approximately 200C to impart the necessary heat to the plastics material.
The closure-supporting member 17 is provided with a similar heat-absorbing member 20 mounted close to a second separately thermostatical-ly~ controlled heating element 21 and a second reflector 22 so that the underside of the closure is also heated to assist in transferring heat to the pellet.

The entire turret is driven for rotation in synchronism ~ith the remainder of the apparatus.
As sho~n in the top plan view o~ Figure 3, the various heat absorbing members for the closure support members and the plungers are angularl~ spaced from one another to avoid any problems of circumferential expansion in the range of temperature encountered between room temperature and the operating temperature of around 200C.
Compressing the pellet as it is heated ensures thattthere is improved contact area between the plastics material and the heated surface of the plunger and the surface 18 is coated with the "*Armourcote" technique using sintered stainless steel as a keying surface for P.T.F.E. The portion of the plunger 12 carr~ing the P.T.F.E. may be detachable, so that it can be xeplaced should the P.T.F.E. become worn, The heating system of the preheater turret 3 is similar to that of the main heating/pressing turret 7 in that the closure supports are heated from below by radiation from a thermostatically controlled heating element with a reflector to throw back the radiant heat towards a blackened heat-receiving surface of the closure support.
A stripping plate (not shown) is provided Just above the work-piece path around the turret 7 at the position where the plungers arewithdrawn from the closures, this stripping plate having an arcuate slot through which the plunger extends slidably. As the plungers are withdxawn upwardly the rims o~ the closure skirts will strike the underside of the stripper plate to hold the closures down to effect separation of -the plungers from the heated plastics material Figure 4 sho~s a vertical sectional view similar to *Trade Mark _ g _ ~09~3~
that of Figure 2, but de~icts a modified form of the he~ting plunger construction for use on the main heating~pressing tur~et 7.
Since many of the components of the turret of Figure 4 are identical to those o~ Figure 2, the same re~erence numerals have, ln many cases been employed. Where the reference numerals in Figure ~ have been primed, they denote modified elements which may be analogous to the corres-ponding elements of Figure 2.
The plunger 12' in this embodiment of the turret co-operates with a slotted stripping plate 28 which extends horizontally above the path of the closure support members 20 at the part of the heating/pressing turret where the plunger 12' is to rise away from the partially moulded plastics composition in the container closure 30.
The stripping plate 28 acts in the same manner as the non-illustrated stripper plate of Figure 2 to hola down the closure 30 since the rim 31 of the s~irt of the closure will rise to strike the underside of the stripping plate 28 as the plunger is withdrawn and further withdrawal of the plunger 12' will raise the bottom pad 18' away from the heated and partially ~ormed plastics composition in the bottom of the closure since the adhesion of the plastics composition to the bottom of -the closure is stronger than it: adhesion to the bottom pad 18', by virtue of the coating of polytetrafluoroethylene on the underside of the paZ 18'.
In order to allow this co-operation between the stripper plate 28 and the plunger~l2', the plunger and the bottom pad both have flats 29 formed in their lateral surfaces and these flats leave the plunger 12', 18' with a 301~0 transverse dimension which is considerably less ~ha~ the diameter parallel to the flats. These ~lats allow the plunger to be withdrawn up~ardly into the slot of the stripper plate 50 as -to release the closure for radially outward removal from the press~heating turret 7 at the third transfer star wheel 8ifor advancing to the moulding ~urret 9.
After this stripping action has been completed, the plunger 12' will continue its travel around the turret 7 and will rise out of the end of the slot 43-in the stripper plate 28 after the closure 30 has been separated from the heating pad 18'.
m is flatted circular form of pad 18' is particularly advantageous where, as illus-trated in Figure 4, the closures 30 are of the deep drawn type without a beaded rim to the skirt, since the transverse dimension of the stripper plate slot will be as small as possible so that the delicate closure rim bears against the stripper plate over as great as possible a pa~t of its periphery thereby distributing the end loading on the skirt rim more evenly.
As illustrated in Figures 6a and 6b, the mounting system for the bottom pad 18' involves a stud 32 of unthreaded form on the pad, but having at some point along its length a peripheral groove 33 whose lower wall is defined by a radially extending planar face and whose upper wall is of upwardly divergent conical form when in situ. A grub screw 34 extends radially inwardly of the plunger 12', as shown in Figure 4, and a similar screw extends inwardly from a diametrically opposite position so that these two screws both abut the upwardly divergent conical wall of the groove to pull the stem 32 upwardly as the two grub screws 34 are tightened. In this ~ a secure cla~ping action c~n be exerted on the bottom plate 18~ independently of -the particular orientation o~ the pad 18' about the ~ertical axis.
Although not shown in detail in Figure 2, the bottom pad 18 is circular and has a threaded stem which is screwed into a threaded socket in the bottom end of the pluneer 12. Such an arrangement requires a widening at the downstream end of the stripper plate slot to accommodate the circular plunger. The initial separating action o~ the plunger and closure occurs at a narrower upstream portion o~ the slot where flats in the plunger body allow the plunger body to pass along the slot even though the bottom pad 18 is wider than this part of the slot and is still disposed in the closure below the narrow slot portion. The arrangement in Figure 4 is preferable where flatted bottom pads lô' are to be used.
The side elevational, partly sectional, view of Figure 6a illustrates the profile of one form of pad where the end face is slightly concavely dished.
Temperature control for the heating elements 15 and 21 is effected by means of a thermocouple 35 which picks up radiant heat from the heat-collecting member 13 for the plunger 12', and a further thermo-couple 36 for sensing the temperature of the closure support bosses 17.The thermocouple 35 is effective to control the power supply to heating element 15 for maintaining accurate temperature stability of the plunger 12' and the thermocouple 36 is effective to control the power supply to the lower heating element 21 for ensuring temperature stability of the closure support 17.

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~ he temperature monitoring station is disposed at a part of the turret pcriphery p~st which all the closure ~uppoxt members 17 and heating members 1~' move while the plunger~ 12' are down in their heating and de~orming 5 positions, and is effective to vary the power ~upply to the heaters in response to the mean temperature7 around the turret, Oæ these respective sets of elements.
A ~ur~her di~erence between the turret of Figure 2 and that of Figure 4 is that the peripheral edge cam is replaced by the plate cam 16' of Figure ~ having a cam slot ~ormed in one edge to receive the cam follower roller 25~
which i~ Figure ~ is mounted on the side of the plunger body at the top end of the plunger~ Ihis disp~nses with the need for a spring return action since the slo~ can now both drive ~he plunger downwardly and lift th~ plunger up again tha~ks to the side mounted cam follower roller configuration~
Furthermore, whereas in Figur~ 2 the upper plunger portion 12a was formed of the asbestos-impregnated phenolic ~ resin m~terial known by the trade n~me Ferobestos~ chosen for its temperature stability chaxacteristic3, it has been ~ound convenient to adopt a dif~erent arrangement in the embodiment of Figure 4. ~ere the plunger 12 has a ~tainless ~teel main body portion 37 with an integral threaded upper ~haft portion 38 at the upper end o~ this portion 37~ The threaded sha~t extends as a clear~nce fit through the carrier 39 on which the cam follower roller 25' i~ secured in a sid~-mounted configura~ion, me heat-receiving member 13 is clamped to the bottom end o~ the stainless ~teel body portion 37 by mean~ o~ a cap f~e /YI~

--. 13 1043~
$crew 44 which bears against a heat-insulating bush 45 o~ the thermal insulating material known by the trade nar4e Sindanyo, This bush 45 is received in a bore 46 of the heat-receiving member 13, and a further heat insulating bush 47 is placed between the stainless steel main body portion 37 of the plunger and the upper side of the heat-receiving member 13.
Total thermal insulation of the plunger body 37 from the heat-receiving member is completed by an air gap 48 between the screw 44 and the heat-receiving member.
Above and below the carrier 39 are nuts 40 and 41 which can be adjusted in their position up and down the threaded shaft 38 so as to set precisely the ver-tical distance between the upper face o~ the cam groove in cam 16' and the lower extremity of the bottom plunger pad 18' at the lobe of the cam. mis is clearly an important dimension in the machine since even the smallest inaccuracy in the spacing between the top face of the closure support 17 and the flat underneath face of the pad 18' will provide a considerable variation in the degree o~ pressing to which the plastics material 49 is subJected during the heating operation.
The extent of this squashing action is particularly important in view of the fact that the heat exchange contact area between the botto~ pad 18' and the plastics material 49 varies as the square of the radius of the squashed plastics mass. The carrier 39 may be formed of any suitable material. For example it may be formed of *Ferobestos or may be injection moulded from a plastics material.
Thus, once the turret has been assembled it is rotated step by step between successive ad~ustment stages in which, as each plunger 12' is brought into line with the *Trade Mark ~43~160 lobe of the cam 16~, the clearance between the flat bottom face of the pad 18' and the ~lat upper face o~ the closure support 17 is checked and i~ necessary ad~usted by moving the shaft 38 upwardly or downwardly relative to the carrier 39 by virtue o~ the ad~usting nuts 40 and 41.
Apart from the cam operated fully automatic turrets illustrated in Figures 2 and 4, it has also proved ad~antageous to construct a labor-atory test rig in which a pellet of plastics material is placed manually in an upturned closure using a hand-held insertion tool operated in a similar manner to the inserter disclosed in our United States Patent 3,963,396, Keith Shotbolt, June 15, 1976, and for this pellet of plastics material to be moved into register with a press/heating plunger similar to the plunger 12 of Figure 2, or the plunger 12' of Figure 4, and then for the closure with its partially pressed plastics composition to be moved to a moulding station where a relatively cold final moulding tool is brought down manually with the assistance of lever action to compress the plastics material into its ~inal moulded configuration. Suitable means fF pre-heating the closure be~ore insertion of the plastics material will, of course be employed even if not incorporated ~n the actual laboratory rig.
In this way it is possible for the various parameters of the moulding process, ~or example the composition o~ the plastics material, the pre-heating temperature, the configuration or temperature o~ the press/
heating mould, the configuration of -the moulding face of the cold mould tool and many other variables to be changed relatively easily so as to ascertain the optimum ~43~
conditions for any particular type of closure. ~n this way the develop~
ment work can be carried out on a single station machine and the lessons from this development work can subsequently be incorporated in a multi-station machine similar to the turrets illustrated in Figure 2 and Figure 4.
The advantages of the direct conduction form of heating for the plastics composition as proposed by the present invention include the fact that the heat is now applied directl~ to the top face of the plastics composition by conduction, and the rate of supply of heat increases during the pressing operation because of the progressive increase in the contact area between the squashed plastics composition and the bottom pad 18, or lo' of the plunger 12 or 12'.
This improvement of deforming while heating the plastics composi-tion assists in ensuring a more easily mouldable state for the plastics material which, on arrival at the final cold moulding station, has approximately the desired finished diameter. The cold mould now only has to carry out the final shaping operation so a much thinner centre panel can be provided in the finished gasket.
Furthermore, with the press/heating step of the presen-t invention there is no incidence of a '7shad~w" of the top surface of the initial pellet in the finished gasket. This phenomenon was apparently due to the fact that the cold mould initially contacts the top face of the so~t but undeformed pellet to "freeze" it so that during a subsequent moulding operation the material which was initially at the top o~ the pellet is never adequately deformed. With the present invention the cross-section of the pellet grows during heating and thus when the cold moulding tool impinges on the 1~4~Q
pre-pressed pellet or disc L~9 the ~hole of the top surface o~ the disc starts at a uniform temperature and finishes up at a uni~orm temperature immediately after moulding.
Furthermore, whereas in the past the final cold moulding tool configuration was contoured to give the finished gasket a central portion contoured in the form of a plurality of concentric circular ribs and grooves in order to disguise the unpleasant appearance of the "shadow", the fact that this shadow no longer appears makes it possible ror the gasket thickness to be considerably reduced in that these ribs and grooves may be eliminated if desired. m is in turn provides greater economy of plastics material, an important saving having regard to the spiralling cost of plastics materials generally. However grooves or ribs may be included to give the centre panel of the gasket a more pleasing shape if desired.
The above described process is particularly suitable for use with bottle caps, such as crown caps or other caps and is especially suitable for deep drawn caps or the very deep drawn caps known by the trade name *Stel Caps.
In order that the heated workpiece support member 17 shoul;d present the smoothest possible surface to the delicate lacquer on the closures, the member 17 preferably has a highly polished chromium plated upper surface.

~Trade Mark

Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a method of moulding a thermoplastic material into a gasket for a container closure comprising the steps of heating a quantity of the material and deforming said material into a desired finished con-figuration, the improvement wherein the material in the form of a pellet is placed into the closure and is subjected to two consecutive deformation operations, the first operation being carried out with a heated pressure member which both heats the thermoplastic material and deforms it into a partially moulded configuration, and the second operation being carried out using a positively cooled moulding member, shaped to impart the desired finished configuration to the thermoplastic material, which is maintained at a temperature lower than that of the heated and partially deformed thermo-plastic material.

2. The improvement of claim 1 wherein the finished article is a sealing gasket in a bottle closure and the said moulding member has a con-figuration which imparts to the gasket a cross-sectional form which conforms sealingly with the container to be closed.

3. The improvement of claim 2 wherein the bottle closure rests on a heated support during the first deformation operation.