IE39995L - Producing hollow articles by injection and blow moulding. - Google Patents

Abstract

1480647 Injection-blow-moulding; temperature control UNILEVER Ltd 30 July. 1974 [1 Aug 1973] 33554/74 Heading B5A In an injection-blow-moulding process, the preform is formed by injection-moulding in the thermoplastic temperature range, cooled to the thermoelastic temperature range, expanded in an intermediate blow-mould where the desired temperature profile in the preform is obtained by locally differential heat exchange between the expanded preform and the mould walls, blow-moulded with that temperature profile in a final blow-mould and cooled to set. A plurality of intermediate blow-moulds may be used to effect heat exchange in a number of successive steps and the pressure in the preform may be released between each step. As shown in Fig. 1, a turret 1 carries four radially disposed mandrels 2-5 and is indexed between stations where the cores are engaged with injection mould 6, first and second intermediate blowmoulds 9, 10 and a final blow-mould 11. In the embodiment of Fig. 2 (not shown), mandrels (23) are mounted on both faces of and parallel to the axis of the rotary turret (21) for co-operation with moulds (e.g. 17, 18) on platens (16). Different zones of the intermediate blow-moulds are maintained at different temperatures by means of materials of different thermal coefficients, heating elements of different numbers, density or temperatures, ducts for fluids at different temperatures or induction heating of different zones. The moulding material may be p.v.c. [GB1480647A]

Description

U 9 9 9 5 This invention relates to a process lor the production of hollow articles, particularly pressure-resistant bottles suitable for carbonated drinks, in which hollow pro forms ore produced by injection moulding thermoplastic material through an Injection nozzle into a preliminary mould having n rnro fortaed'.hy a mandrel, creating a temperature profile i in the preform and subsequently blow mould int.' the preforms to tin* final shape.

Preforms, particularly of thermoplastic material such as PVC, are further processed in various ways to produce end products. The preforms can be produced separately from Ihe further processing or the further processing can lie effected almost immediately after production of the preforms, ie with only any noocssary preparatory steps then' between ms ;i re required to prepare Lhc preform for (lie blow mmi I d i ny oper.-ition. This latter method generally takes place in a single appropriately designed machine in which a preliminary mould with an injection no/.v.lc can be connected willi n conventional injection moulding apparatus, a mandrel ho inn i ii I roduccd into the preliminary mould in order to /rive the preform n hollow shape. After the preform is produced it. is taken to one or more intermediate work stations of I lie apparatus, where preparatory steps are taken to brin/r the Iemperature of the preform to that required lor the blow moulding step.

A number of factors such as the temperature of the material when injected into the preliminary mould ami the ambient conditions around the machine in the production plant lead to a certain temperature profile beinp produced ill I lie preform before the blow mould1n/r takes place. 3999 3 Nevertheless, in series production this temperature profile can be subject to wide variations which give rise to rejects in the manufacturing process. As a result of the injection moulding of the preform and the subsequent 5 preparatory steps the temperature of the preform is not identical in all parts. This temperature pattern is referred to herein as the temperature profile. Dependent upon the shape and size of the preform and the blow moulded article to be produced it will be understood that certain lO optimum temperatures are required in different parts of the preform before blowing. When the temperatures in all parts of the preform are at the optimum temperatures the preform has the optimum temperature profile.

It is an object of the present invention to provide l"i a process in which in series production an optimum temperature profile is produced in successive preforms.

According to the present invention there is provided a process for the production of hollow articles of thermoplastic material comprising forming a hollow preform by 2() injection moulding the material in the thermoplastic temperature range, cooling the preform to thermoelastic temperature range, introducing the preform into an intermediate blow mould havinq an interior size larger than the preform and smaller than the article to be produced, expanding the preform 25 by internal pressure into contact with the walls of the intermediate blow mould, effecting locally different heat exchange between the walls of the mould and the expanded preform to produce the optimum temperature profile in the preform, and subsequently blow moulding the preform with 30 that temperature profile to the finished shape in a final blow mould and cooling the article to set. - 3 - 39995 The process according to l.h<> invention produces n I cmperaturc profile closer f.«» Ihe optimum I. cinpcrn In it-pro rile const si ent ly ovit siicci'mn i vi» preforms. Ki i .si l\ Mi** preform In not allowed to cnol down In room temperature arter it has boon manu factured anil hp fori* its temperature is adjusted to the blowing temperature. This ensures that the condition of tl^e preforms as they arrive at tin* intermediate blow mould Is more consistent than If they were reheated to the thermoclastic temperature from room temperature. Secondly the adjustment of the temperature profile is carried out within the confines »l' l.he inter-mediate blow mould the temperature of which can be very closely regulated and the time that the preforms reside (.herein ran lie closely controlled. Thirdly hecause Mir preform is confined within the intermediate blow mould during the temperature adjust i up steps l.he influence of variations in ambient temperature on l.he temperature profile of the pre fr-nis is minimi sed. furthermore, hecause the preform is expanded undi-r pressure into contact with the inside walls of the inteimediale blow mould there is a good and consistent contact between the preform anil the heat exchanging walls of the mould. Also l.he fact that the preform is expanded reduces the wall thickness of the preform. The degree of expansion is not large enough to lead to any undue thinning of the preform which would cause hlow outs or rejects at the final blow nouldinq step hut the reduction in wall thickness which does occur facilitates the more rapid temperature adjustment of the preform throughout the material thickness. Sol only is the time required for adjusting the temperature to the I 39995 ■ Irs i red temperature pro file shortened ImiI. also the temp i-inliifr d i f tVii'iiri- between tin- preform mill (In- mould r;ni In- less than il' |.h<* preform were not i>\|innili'il wliilsl. sl.il I effecting tlx- snrac overall amount of lira I exchange.

Tims I.Ik- danger of overheat i up or ovrrcool inp particular parts ol' the pro form, particularly the outer wall ol' the l>it-lorn in contact with the mould, is minimised.

When llic preform is introduced into the intermediate blow nioulil II11- tempera In its at «) i r To rout points ol' l.li<- preform |ii are wil-liin the thermoe lasti«? tempi*rfttu re range ImiI depend i up upon the optimum profile to lie achieved i I. may lie neeessnry for certain areas to lie heated and lor other ;ire;is to lie coo I eil. Similarly it may lie necessary lo have a Inciter rate of heat transfer a I. some pails of Ihe I r, preform than at other parts which necessitates ililfcicul I emperat ii res of Llic walls of the intermediate blow mould at ilil'fcrcnt parts of the mould.

Ill large scale series production if is desirable I ha I Ihe cycle time of the process, l.e.the time rei|iiir<-il l.o jii itt.'i tin far in re a sinplc article, is as short as possible. liven in a mil I i i station proccss it will he realisi-il tlial the cycle lime is /■overiled hy the longest time i <-i| n i reil a I any stall no for that. pa r t i cu l;i r step of tin- process I ■> lie carried out. ;>!"> According to another aspect of the present i 11 venI i on .

I In- temperature profile o.r the preform can lie adjusted in more I ban one step by expanding the preform successi\ely into contact with Ihe wnlls of the more I ban • >ne i n i e rmed i a I e blow mould. lu Since the lime rei|iiired for repti I a I. i up I lie I empera I u re ol I In- pre In rm is /•••noin I I y nuiny I. i mi- s I li.-i I required fin i ii.ji-«-|. i up Ihi- preform, or Mia). ri-i|ii i ml I'm blow iihhi I il i nr ami cooliup to si-1 the liiiishi-il article, rppn I a I i iii> the I tMiiprrnl.ii re of flu* pro form in n numhrr of successive slcps allows Mii> eye-1e limp to bp rpdiippd to thr minimum.

II. is possible for each of IIip 111 tprmodinto blow moulds In Ikivp ill rrpipnt boat pxchangp rapacities. l-'or example il is possible for Ihp dil'fprpncp in tompprature lirtwppn Hie prprorm ami the mould to bp high in Ihp first intermediate blow mould. In this way the temperature of the wall area o I" the preform away 1'rom the intermediate wall, ie the inside wall ol' the preform the temperature ad.jusIment of which has to bp el'frctpd through tin- thickness of Ihe preform, mid hence takes longor than the wall of the preform in contact with the mould, can bp more quickly re>Mi lateil. This hiph tempprature diffprencp may result in l.he wall of the preform in contact with l.he mould wall lieiiie lie.nl eil nr cooled too much but Lhis can he correct.nl 111 ••il li si'i| u en t I eiupe ra til re ail.jusf i a/; steps in siihsei|ijc 111, inI.-rmediate blow moulds. Clearly to obtain the optimum I empe ra t u re throughout the thickness of the material in I lie shortest time it is desirablp initially to adjust the temperature of the preform farthest away from tlio mould wall and arrange that subsequent tempprature adjusting steps have little or no pffpot on tlip temperature of I he inside wall of the preform.

TIip expansion of the preform can In- greater in each successive temperature adjusting step. This makes il possible to lir inp the [ire form step by step closer In t lull na I shape and size of the finished hollow articli-. Thus 3 9 9 5) 5 not only is the temperature profile adjusted but also the shape the preform assumes during each temperature step. In the first temperature adjusting step the temperature profile of the preform deviates a relatively large amount 5 from the optimum temperature profile but since the degree of expansion of the preform is small, no particular overstretching can occur. As the temperature profile approaches the optimum temperature profile the degree of stretching can be increased without damaging the preform. In the brief lO moments between the individual temperature adjusting steps the internal pressure in the preform can be released thereby allowing the preform to contact towards its original injected shape.

The invention will now be more particularly described lr> with reference to the accompanying diagrammatic drawinqs. l-'lyiiro I is a sectional elevation showing schematically one example of an apparatus for carrying out the invention; Figure 2 is a side elevation of an alternative 20 apparatus; Figure 3 is a longitudinal sectional elevation of an intermediate blow mould of the apparatus of Figure 2; Figure 4 is a longitudinal sectional elevation of an 25 alternative intermediate blow mould; and Figure 5 is a diagram illustrating the method of the present invention.

Referring now to Figure 1 there is shown a turret type carrierlwhich carries four mandrels 2,3, 4 and 5 extending 30 radially from the carrier. The carrier is adapted to be indexed in the direction of arrow A. - 7 - 39995 in jo As shown in Fig. t the mandrel 2 is at an injection moulding station, the mandrel 2 being .surrounded hy an injection mould 6 which Is shown in engagement with the nozzle of nil injection moulding device 7 having n feed strew fl which forces the plasticised material into the injection mould.

The mandrel :i is shown at a Tirst temperature adjusting station at which the mandrel is enclosed in a first intermediate blow mould 9 whilst the mandrel 4 is at a second temperature adjusting station at which it is enclosed in a second intermediate blow mould lO. The interior sizes of ench of the intermediate blow moulds 9 and 10 are liipircr Minn the size o I" the preform and the second intermediate blow mould is larqer than the first but not as lortre as the final blow mould. Means, not shown, are provic.ed for lien ting or cooling the mandrels as is already known in the art, and Tor maintaining the desired temperatures in the walls or the intermediate blow mould.

The mandrel f» is nt the blow moulding station where it Is enclosed in a final blow mould 11 having an internal shape corresponding to the desired shape of the finished article.

In operation the mandrel carrier is indexed to tiring ench mandrel in turn successively to each of the stations so that alter injection moulding a preform in the injection mould R the preform is taken to each of the intermediate blow moulds before heing finally blow moulded in the final blow mould. It will be appreciated that each of the moulds , |<> and 11 are in two halves and can lie opened lo ,ill«.u i he mandrels to lie indexed round with the carrier. s - 39995 M each ol' I In- tnIcinedI a Ie Mow mouM:i .uul nt. the* llit.il liliw nion lit (i siii tattle vnlvo mechanism.

A I t.or having injection moulded tho preform, which operation is carried out in tho thermoplastic temperature riiiipe oT the material, tho preform begins to cool. Vhon the outer surface is cool enough tho preform is removed l«> front the injection mould and transferred to tho first inter mediate blow mould. Tho temperature profile of tho pre form at this stage is other than tho optimum profile required for final blow moulding but tho proform can nevertheless lie expanded without difficulty to contact the l-~» inside walls of tho intermediate blow mould. The wall temperatures at different points of tho intermediate blow mould an- maintained so as to bring the temperature profile of llif prrlurm nearer to the optimum, the thicker areas of tin- |iifloim requiring the greatest, amount of lieat rxcliniifr 2d liecausc of the greater amount of heat contained therein in relation l.o the thinner areas.

Alter having first released the air pressure within the preform it. is transferred to tho second intermediate blow mould. AI. this station the temperature profile is nearer jr> I ti«- optimum profile and the proform can bo safely expanded under nir pressure to a greater extent without risk of dauin;'c to the preform. Thus the proform is expanded again t.o contact, the inside walls of the second i nto rmed j a !.<• blow mould. The walls of the second intermed!ate blow mould are •'!<> ma i n La i tied at the desired temperature t.his l.imc selected - «> - 39995 so that the optimum temperature profile in produccil in tho preform. Because the temperature profile has already been partially adjusted in the first intermediate blow molild the amount of heat exchange required to be effected in this 5 second adjusting station can be less than at the first station. Thus the differences In temperature between the walls of the mould and the actual optimum temperature profile required in the preform for final blow moulding can be small so that any variations In the time that different 10 preforms are contained within the Intermediate blow mould has little or no influence on the actual temperature profile of successive preforms as they are finally blow moulded. Successful blow moulding is therefore less dependent on the attainment of rigidly fixed cycle times. Furthermore 1.1 the same temperatures can be achieved throughout the thickness of the material at any given point of the preform. The expansion of the preforms in the Intermediate blow moulds substantially assists both the achievement of the optimum profile I>y virtue of the greater area of proform which is 20 contacted by the intermediate blow mould walls, and also the achievement of the same temperatures throughout the thickness of the material at any given point by virtue of the thinning of the wall thickness when the preform is expended. 25 The preform is then transferred to the final blow mould where it Is blown to the final shape and cooled to set before being removed from the final blow mould.

Kig. 5 shows a typical time/temperature curve of the method of the present invention when producing hollow .10 articles from PVC. The thermoelastlc temperature range - 10 - 39995 is shown at E and above this is the thermoplastic range indicated by the arrow P. The preform is injectiou moulded at time tft in the tbcrmoplasticsterappraturo range after which it immediately begins to cool. At time t^ the prefona is introduced into the temperature adjusting intermediate blow mould by which time some parts of the preform nre above and some parts below the optimum temperature required at those parts of the preform for final blow moulding.

Thus in the temperature adjustment period between time t( anil t0 the temperature of certain parts of the preform is raised whilst other parts are lowered. The shaded area in Pig. 5 shows the temperature variationsin the preforms which nre adjusted during the time t. to t_ to achieve 1 u the desired profile.

Referring to Fig. 2 there is shown an alternative apparatus for carrying out the present invention. The apparatus comprises a bed l.'l which is substantially "H" sliapeil as seen in Fig. 2 and has fixed guideways H on both the right and left hand parts. Each of the guideways M carry a movable member 15 movable back and forth on Ihe guideways in the direction of arrow B by a hydraulic cylinder 15a fed by a hydraulic line 15b. Mounted on the movable members are mould carrier plates 16 which each carry at least one injection mould 17, intermediate blow mould 1R and final blow mould (not shown). For each injection mould 17 there i s an associated injection device if) comprising a conventional plasticising and Injection unit having a feed funnel 20.

In tho valley of the "U" shaped bed between the guideways 14 a rotatable mandrel wheel 21 is mounted to 39995 rotate about its axis 22. The mandrel wheel 21 carries a number of mandrels 23 which extend parallel to the axis of rotation 22 of the wheel.

As shown In Fig. 2 tho mandrels 23 nre not enclosed 5 hy the moulds mounted on tho carrier plate 16 In which position the mandrel wheel can be Indexed round to bring the mandrels into position for the next step of an operating cycle. The mandrel is indexed round by an indexing motor 21a having a driving shaft drivably engaging in with a toothed periphery 21b of the mandrel wheel 21.

Provision is made for feeding in a medium to regulate the temperatures of the mandrels 23, the medium bein£ led l»y a hose line 24 to a fixed member 25 of a distributor, the distributor having a second member 26 which is mounted 15 to rotate with the mandrel wheel. The medium passes from the second member 26 of the distributor via a hose line 27 to each of the mandrels.

A temperature regulating medium for the intermediate blow moulds is fed by a hose line 28 to the back of the mould ^i) carrier plate and through passages in the plate to the intermediate blow moulds.

Provision is also made in a similar manner for the return flow of the temperature regulating mediums.

A further hose line 29 is connected to the back of 25 the mould carrier plate to convey air to the mandrels 2.1 for the expansion of the preforms in the intermediate blow moulds and final blow moulds. A hose line 29 connects with no//.les .10 mounted on the mould carrier and which ent?.*u'e with valves .11 when the moulds are brought into position Hi around the mandrels. From the valves 31 air passes - 12 - 39995 through further hose lines 32, or passageways in tho out ml r i'I wheel, to the mandrels.

As mentioned above, at least one injertion mouJil, intermediate blow mould and final blow mould is mounted on the mould r, carriers. Depending upon the size, shape and material etc. of the articles to he produced, further moulds can l»e Mounted on the carrier to either provide further (••uipcrulure regulatitip. stations or to provide lor the M.-IMU far lure or more than one article simultaneously on lo caili side of the mandrel wheel, or both. It will he apparent that the number of moulds, mandrels, injection moulding stations and blow moulding stations together with I lie indexing of the mandrel wheel can be varied to suit the articles to be produced. 1.1 Referring now to Fig. 3 there is shown a longitudinal cross-section through part of the apparatus of Fig. 2 showiup Llic mandrel wheel 21 which is rotatablc about the nxis :!J nud carrying a mandrel 23. The mandrel 23 is enclosed in a temperature regulating intermediate blow mould 18 mountedcn :>o the carrier 16. The mould IB is divided into individual •/.ones I. 11, III, IV, V and VI which each consist of different materials having different thermal co-efficients. A preform :i:i is shown on the mandrel 23. The preform is expanded hy air pressure into contact with the intermediate ,r-( blow mould walls which by virtue of the different materials cllcct varying amounts of henting or cooling of the preform in the different zones 1 to VI by heat transfer. - This heat transfer can also be varied by the sin-rare smoothness of the interior walls of the different mntorin I s of the mould and is of course also dependent 1 :i - 9995 upon the temperature. The mould can be heated or cooled in any known manner.

Fig. 4 shows an alternative Intermediate blow mould ■ construction in which the mould is qgaln divided into 1 mlividual zones VII. VIII, IX, X, XI and XII. These /oiios arc however made of the same materials but they differ rrom one another in that they are heated to different temperatures. The different zones are heated by heating coils 34 of different numbers and density in each zone. Alternatively the heating means can be channels for a heating medium, the temperature of the medium in different •/.ones being the same or different in order to build up or maintain the different temperatures on the different zones. Yet a further alternative is to provide induction heating of the mould in the different zones. ft is of course also possible to combine the structure of l-'ig. 3 with that of Fig. 4.

Whilst the different Intermediate blow mould constructions have been described with reference to the apparatus of Kip. 2 it will be apparent that the mould constructions arc also applicable to the apparatus illustrated in Fig. 1. 39995

Claims (5)

1. A process for the production of hollow articles from theraoplastic material comprising forming a hollow preform by injection moulding the material in the thermoplastic temperature range, cooling the preform to the thermoclastic temperature range, introducing the preform into an intermediate mould, partially expanding the preform by internal pressure into contact with the walls of the Intermediate mould, effecting locally differont direct heat exchange between the walls of the mould and the expanded preform to produce tho optimum temperature profile in the preform, and subsequently blow moulding the preform with that temperature profile to the r inished shape in a blow mould and cooling the article to set.

2. A process according to Claim 1 in which tho tomperatu profile of the preform is adjusted in more than one stop by expanding the prefrom successively into contact with the walls of more than one intermediate mould

3. A process according to Claim 2 in which the expansion of the preform is greater in each successive temperature adjusting step.

4. A process according to Claim 2 in which the internal pressure in the preform is released between each tomperatu adjusting step. 39995

5. A process for the production of hollow articles substantially as hereinbefore described with reference to the accompanying diagrammatic drawings. F. R. KELLY & CO. AGENTS FOR THE APPLICANTS. - 16 -