AU613156B2

AU613156B2 - Process and device for producing pressings from thermoplastic material

Info

Publication number: AU613156B2
Application number: AU30524/89A
Authority: AU
Inventors: Andreas Iseli; Gerhard Keller
Original assignee: Automation Industrielle SA
Current assignee: Automation Industrielle SA
Priority date: 1988-02-12
Filing date: 1989-02-09
Publication date: 1991-07-25
Anticipated expiration: 2009-02-09
Also published as: AU3052489A

Description

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i ii I ii I OPI DATE 06/09/89 AOJP DATE 05/10/89

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(51) Internationale Patentklassifikation 4 B29C 33/00, 31/06, B29D 23/20 B29C 43/36, 43/34 APPLN- ID 30524 89 PT NMBe PCT/E9/0 119 P al rBgER DIE NS (PCT) 11) In ernationale erftentlichungsnummer: WO 89/ 07516 Al (43) Internationales Veroffentlichungsdatunm: 24, August 1989 (24.08.89) (21) Internationales Aktenzeichen: PCT/EP89/00119 (22) Internationales Anmeldedatum: 9. Fbruar 1989 (09,02.89) (81) Bestimmungsstaaten: AU, BG, BR, HU, JP, KR, SU.

Veroffentlicht Mit internatianlem Recherchenbericht.

(31) Prioritiitsaktenzeichen: (32) Prioritiitsdatum: (33) Prioritlit!,and: P 38 04 44,.1 12, Februar 1988 (12.02.88)

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(71) Anmelder: AISA AUTOMATION INDUSTRIELLE S.A. [CH/CH]; Route de Savoie, CH-1896 VDouvry

(CH).

(72) Erfinder: KELLER, Gerhard Chemin du Maconnex, CH-1805 Jongny ISELI, Andreas Rue de la Tour, CH-1867 Ollon (CH).

(74) Anwalt: ZELLENTIN, Zellentin Partner, ZweibrickenstraBe 15, D-8000 Mifnchen 2 (DE), (54) Title: PROCESS AND DEVICE FOR PRODUCING PRESSINGS FROM THERMOPLASTIC MATERIAL (54)Bezeichnung: VERFAHREN UND VORRICHTUNG ZUR HERSTELLUNG VON PRESSKORPERN AUS THERMOPLASTISCHEM KUNSTSTOFFMATERIAL (57) Abstract The above process involves heating the thermoplastic, forming a blank by means of a possibly annular nozzle and separation thereof by possible use of a heated gas stream surrounding the nozzle and oriented towards the point of separation, introduction of the blank into a pressing mould, closure of the latter, forming of the pressing by application of a pressure and cooling of the pressing at least partly under pressure, The entire heated thermoplatic material required for a blank is deposited on the surface forming one part of the pressing mould of an intermediate carrier extended under the nozzle and is separated from the nozzle, whereby the Intermediate carrier is lowered on closing of the pressing mould. Also described is a device for performing the process with an extruder for heating thermoplastic material with a possibly annular, closable nozzle suitable for delivering portions of material, said nozzle being possibly surrounded by an annular nozzle for supplying a possibly heated gas flow directed against the separating point of the material portions of the nozzle with at least one closable pressing mould composed of a mould die and a mould punch whereby the mould die can be arranged on the one hand under the nozzle and on the other hand coaxially to the mould punch and whereby a pressure can be applied and/or maintained on the mould punch (13) and/or mould die The mould die contains an extendable intermediate carrier the free surface (11) of which forms, in the retracted position, a part of the mould surface of the mould die which returns the pressing.

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DESCRIPTION

The invention relates to a process for the manufacture of compression-molded articl~es from thermioplastic compound, by heating of the thermoplastic compound, molding of a blank by means of a die, the l.atter being annular, if need be, and separation, uasing a heated stream of gas, the latter surrounding such die and being directed at the point of separation; introduction of the blank, in a compression-molding mnold; closing of the mold; molding of the compressed article to a device for carrying out the process of the invention, with an extruder for heating thermoplastic compound with a closable die suitable for dispensing portions of the molding compound, such die being annular, if need be, and surrounded, if necessary, by an annular die for discharging a heated, if need be, stream of gas directed at the point of separation of the compound portions; with at least one closable compressionmolding mold consisting of a molding matrix and a molding mandrel; whereby the molding matrix can be arranged beneath the die, on the one hand, and coaxially with the molding mandrel on the other hand; and whereby a molding pressure is applicable to and maintainable on the molding mandrel and/or the molding matrix.

Such. a process is known from US-2S 3,313,875. In said process, the thermoplastic compound is dispensed by an annular die and applied to a projection of the die, whereby the connection with the gap of the die is maintained and the molding compound adheres to the projection of the die, from where it is later stripped when the mold is closed.In this i i the blank is cooled even before it is passed into the mold, on the one hand, and problems are encountered, on the other hand, with the stripping of the compound due to the adhesion and sticking of the thermoplastic compound to the projection of the die, such problems interfering with the function of the stripper.

A similar process is described in German patent DE-PS 30 23 415, in which the blanks, which are separated from the die by the closing of the latter, are admitted into the hollow space of the molding press by freely falling into such. space. In this way, the separated portions of the molding compound do not come into contact with the cooled surfaces of the mold as such portions drop down.

However, the blanks dwell in the cooled mold for a longer period of time amounting to multipe times the dropping time, until the mold is removed from the die and brought into the axial position with the molding plunger, whereby the blanks have relatively large areas of contact with the cooled mold, so that the plastic material starts to cool off in such areas of contact, which adversely affects the compressibility of the plastic material and the quality of the manufactured molded articles. If the die and/or its m>~

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-4closing elements are not finished with the highest degree of precision, or if such elements are not clean and have foreign matter sticking to them, the blank is not exactly separated at the same time along the entire circumference, so that it does not drop into the hollow space of the mold with exact alignment, which by itself or in combination with parts of the plastic compound that have prematurely cooled on the cooled walls of the mi-,d, leads to uneven molded articles, to waste, or rejects. The same negative effect can be produced if the annular stream of gas, if any, directed at the point at which the blank is separated from the die, acts uneven on such blank, which, on the one hand, effects an uneven detachment of the blank, and, on the other hand, accelerates such blank in a non-axial direction, so that such blank cannot pass into the hollow space of the mold with a centered alignment.

Devices are known from US-PS 3,313,875, DE-PS 30 23 415, and also from DE-PS 28 42 515, for carrying out the processes afflicted with the above-mentioned problems.

The problem of the present invention is to enhance the process and the device specified above in such a way that the contact between the blank and the cooled mold is kept limited to a minimum.

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This problem is resolved by the features contained in claim 1.

By depositing the thermoplastic, heated molding compound exiting from the molding die on the surface of an intermediate support, such support being a part of the compression-molding f mold and extended under the die, an aligned and thus centered dispensing is accomplished due to the short distance, on the one hand, so that any uneven separation of the blank or contamination along the circumference cannot exert any influence on the position of~ the blank. The same applies to th.e effect of an annular stream of gas, if usea'. '!e blank rests on only one part of the mold, so that any cooling of the blank on such part has practically no inafluence on the gulity of the molded article. Bly maina,,. ng the in~termediate support in the extended position, the blank is exposed to hot ambient air on all sides except for the side on whicbi it rests, so that the blank comes into contact with the major part of the cooled mold only once 4-he actual compression molding starts.

Due to the fact that the blank is subjected to minor coolin-g from the moment it is produced until it is compressed, and during that period practically only at points whi"ch no longer have to be moved in the final shaping of the blank, r the temperature of the heated plastic material can be lower than in the known processes, which, on the one hand, saves melting energy, and, on the other band, accelerates the solidification of the material, as it does not have to cooled for a long time. Hence the invention significantly contributes to energy savings and acceleration of the manufacturing process.

According to a beneficial feature of the process of the invention, the blank is deposited on the surface of the inermediate support in a way such that it overlaps such. support along the circumference. In this way, the area of contact between the blank and the intermediate support is reduced further, so that even less cooling is required.

The problem of the invention is resolved also by the device with the features according to claim 3. Other beneficial features of the device are disclosed in claims 4 and As the surface of the intermediate support is part of the mold delimiting the final shape of the molded article, minor cooling of the blank that may occur in the contact zone is not disadvantageous because the plastic compound LI -L.r 1(.~LU .v I; _i -7needs not to be removed from this central zone during the actual compression process.

The invention is explained in greater detail in the following by reference to an embodiment of a device for the manufacture of the head pieces of tubes, whereby the body of the tube can be simultaneously joined with the head part to be manufactured. Such an embodiment is shown schematically in the sectional drawing, in which: Fig. 1 shows an open molding die for dispensing or metering thermoplastic molding compound, and an intermediate part, the latter being a component of a molding matrix of a compression mold; Fig. 2 shows the same as Fig, 1; however, the molding die is shown in its closed position; Fig. 3 shows the molding matrix according to Figs. I and 2, and a molding mandrel associated therewith; and Fig. 4 shows the molding matrix and the molding mandrel in their compressing positions.

Figs. 1 and 2 show a molding die I for metering and dispensing thermoplastic molding compound from an extruder not shown in the drawing, by which the thermoplastic compound is .iJ. LK'I

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I I -8heated. The molding die 1 has a closing element 2, by which of which a desired quantity of a plastic molding compound can be dispensed in the form of an annular blank 3.

The outlet of the die 1 is surrounded by an annular nozzle 4.

Hot air may be admitted into the latter for the purpose of facilitating the separation of the blank 3 as the closing element 2 of the nozzle or die 1 is being closed, and also for corculating hot air around the blank 3 in the position it is supported, in order to prevent cooling of the blank.

A molding matrix 5 is arranged axially with the die 1, such matrix being a part of a mold for the manufacture of a tube head 6 (Fig. The interior of the molding ,matrix 5 is d.signed in such a way that it reproduces the external shape of the tube head 6 to be manufactured, Customarily the molding matrix 5 has a structure composed of several parts, and with a part 7 for the threaded neck of the tube head 6. An intermediate support 8 is centrally arranged and axially displaceable between the top and bottom stops 9, 10. In the final top position, which, is limited by the stop 9, the intermediate support a arranged with a spacing from the die 1 such that the molding compound exiting from the die 1 is directly deposited on the surface 11 of the intermediate support 8. The spacing between the surface 11 and the die 1 can be selected in such a way that the required quantity of molding compound can be exactly accommodated. However, it is possible also to arrange the surface 11 of the intermediate support 8 directly beneath the die 1, and to continuously lower the intermediate support 8 as required by the quantity being dispensed.

An extendable rod 12 is arranged centrally within and coaxially with the intermediate support 8. This rod .12 protrudes beyond the surface 11J o the intermediate support 8 and, on the one hand, serves for centering the flow of molding compound exiting from the die I with an anrialar ,clross sectlon, such stream of plastic forming the blank 3, and, on the other hand, keeps the outlet opening of the tube head 6 free as the latter is being compression-molded.

The intermediate support 8 and, the rod 12 may be extended and retracted by any desired, kown drive (not shown) for example by spring force, hydraulically or pneumatically.

The surface 11 may be designed plane or it may be adapted to the requirements of the shape oi thie tube head. Preferably, the 5urface 11 of the intermediate support 8 may be concave cr dish-shaped, or it may be designed, with an elevated edge of the intermediate support 8 forms (see Fig. 4) the part of th odn arx5saigteexternal surface surouningtheopeingof he ubehead 6.

Fig. 3 shows the bottom end of a molding mandrel 13.

Ti-,e latter has a sleeve 15 supporting a tube body 147 a molding plunger 16 reproducing the inner shape of the tube head 6 is axially movable in the sleeve 15 and movable therein relative to sucb, sleeve.

The process is carried out in said device as follows: A molding matrix 5 is arranged beneath the die I. of the extruder not shown in the drawing, On opening of the closing element 2 of the die 1, a stream of heated thermoplastic molding compound with an annular cross section flows from the orifice of the die and supports itself on the surface 11 of the intermediate sup-port 8, with the die 1.

in the open position. Tge latter remains open until the required quantity of mrolding compound has been dispensed, whereby the la~tter preferably freely overlaps the edges of the surface 11 of the. Intermediate support 8. When the die I. is open, the rod 12 in the intermediate support a is in contact with the closing element 2 of the die It, which guides and ocntor8 the flow of plastlic molding compound the latter exitinq in I1 the form of a tube in the interior. By closing the closing 'i element 2, if necessary with the support of a heated stream of gas exiting from the annular nozzle 4, the feed of further plastic compound is cut off and a tubular blank 3 with overlapping edges is separated, as shown in Fig. 2.

The latter shows that there is only little contact between the blank 3 and the intermediate support 8 or rod 12 based on the total mass of the blank, in particular due to the fact that unlike the molding matrix 5, neither the rod 12 nor the intermediate support 8 is cooled directly Cthe molding matrix is cooled customarily in order to assure faster cooling by means not shown in the drawing). Minor cooling is not only acceptable, but even positive because the points of contact must practically not be moved or moved only slightly during the actual compressing process, so that no high mobility of the plastic molding compound is needed there.

By isolating the cooled molding matrix 5 with air, the latter practically cannot transmit any cooling effect to the blank 3. IX heated air exits from the annular nozzle 4t such air circulates around the blank 3 and the latter may be kept at the desired temperature by controlling the air t:emperatures AiY~ k- f j -12the blank may be heated too, if necessary. '.dt blank 3 is kept in the upper position until the molding matrix has been coaxially aligned with the molding mandrel 13.

As the molding matrices are cuistomarily arranged in a rotary table, such alignment may be carried out in one cycle or several steps without risking significant cooling of the blank 3, as it would necessarily be the case if a blank 3 were deposited from the die directly on a cooled molding matrixz When the molding mandrel 13 is dri'ven into its working position (cf. Fig. when the plunger 16 of such mandrel comes into contact with the '-op end of the rod 12, and the molding mandrel 13 is then lowered further, the intermediate support 8 with the rod 12 is lowere& too until reaching the bottom stop 10. The sleeve -15 with the tube body 14, too, is shifted into the intended position within the molding matrix 5, whereupon exclusively the molding plunger 16 is lowered further in the molding matrix S, applying a compressing pressure, whereby the rod 12, too, is disiplaced relative to the intermediate supporL 8 into the position shown in Fig, 4, whereby the the tube head receives its final shape and it is joined with the body of the tube, Tn this position, the molding plunger 16 is maintained under pressure until the required cooling time has elapsed.

Of course, it is possible, too, to move or displace only the ,.Pe j/wj -13molding matrix against a stationary molding mandrel, or vice versa; furthermore, it is possible, too, to displace both the mandrel and the matrix against each other.

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Claims

1. A process for the manufacture of compression molded artlcl~s from thermoplastic compound comprising the steps: compression molding of a blank on an intermediate support by means of a die; separation of the blank; introducing the blank into a mold through lowering of the intermediate support; compression molding the blank into an article; wherein the intermediate support may be moved between a position where it may receive a blank from the die and a position where it is part of the mold.

2. A process as claimed in cl-aim 1, wherein the die is annular.

3. A process as claimed In any one of the previous claims, wherein the blank is separated from the die by means of a stream of heated gas,

4. A process as claimed in any one of the previous claims, wherein the blank Is deposited on the surface of the intermediate support in such a way that it overlaps the surface of the Intermediate supporc along the circumference of the intermediate support.

A device for manufacturing a molded article from thermoplastic compound comprising: a die; a mold; and an intermediate support movable between a position whore the intermediate support is below the die and a position where the intermediate support forms part of the mold; wherein the mold Is adapted to compression mold an article.

6. A device as cla~imed in claim 5 wherein tha, die is adapted to extrude an annular blank.

7. A device as claimed in, either claim 5 or 6, wherein jet means are provided, said jet means providing a stream of hot gas to assist In the separation of the blank from the die,

8. A device as claimed in any one of claims 5 to 7, wherein a co-axially arranged, axially extendible iod Is provided as a part of the intermediate support, STA/l 559w 15

9. A device as claimed in any one of claims 5 to 8, wherein the surface of the intermediate support has an elevation depending on the circumference.

A method for the manufacture of compression molded articles substantially as hereinbefore described with reference to the accompanying drawings.

11. A device for the manufacture of compression molding articles substantially as hereinbefore described with reference to the accompanying drawings. DATED this SEVENTH day of MAY 1991 o* S. AISA Automation Industrielle S.A. *to S* Patent Attorneys for the Applicant SPRUSON FERGUSON S Sr0 0 S STA/1559w