Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~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
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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
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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,
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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
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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;
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~ 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.
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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
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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
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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
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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
0
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
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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
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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.
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