GB2093396A - Injection-blow moulding - Google Patents

Abstract

An injection-blow-moulding machine is described in which parisons of plastic material are injection moulded at (27) on cores carried by a first rotatable platen (21), are cooled after injection during rotation of the platen (21), are discharged into conditioning moulds (33)-(36) carried by a second rotatable platen (32), and the desired parison temperature conditions are attained in the parison walls during rotation of the second rotatable platen (32). The parisons are transferred from the conditioning moulds to a blow mould (37) and these blown and optionally stretched. The first platen (21) is provided with four core- carrying mould sets (27)-(30), the number of cores in each set being the same as the number of conditioning mould cavities in each of the conditioning moulds (33)-(36). The number of blow mould cavities in the blow mould (37) is half the number of cores and conditioning cavities in the sets (27)-(30) and (33)-(36) respectively, so that during each injection moulding cycle (at (27)) there are two successive blow moulding cycles at (37). <IMAGE>

Description

SPECIFICATION Plastic moulding machine This invention relates to a machine for injection-blow-moulding plastics material. The invention has been developed for the manufacture of containers such, for example, as plastic bottles to contain carbonated soft drinks.

Injection-blow-moulding is a well known art. It has been proposed to manufacture containers by forming parisons of plastics material on cores by injection moulding, transferring the parisons from the cores to conditioning moulds or cavities in which the desired temperature conditions in the parison is attained, and transferring the parisons from the conditioning moulds to blow moulds where they are blown to form the desired finished articles and are then ejected. It is also known mechanically to stretch the parisons either just prior to or simultaneously with the blow moulding.

In order for an article or container so made to have the required strength it requires to be biaxially oriented and this is obtained by the blow moulding, or stretch-blow-moulding, in which the parison is elongated and also has its radial dimensions increased so that it is stretched both circumferentially and axially.

For orientation to occur, however, the temperature conditions of the parison have to be closely controlled. If the parison is too hot when it is blow moulded no orientation will occur and if the parison is too cold it will shatter or blow moulding will be impossible. There is a very small range of temperature for most plastics materials at which blow-moulding to produce a bi-axially oriented structure is possible.

For the injection-blow-moulding process to be applied economically to small containers it is necessary that a machine for producing them has a low cycle time. By way of example, in a particular machine it may take five seconds to mould parisons on cores and the cores will have to stay in the mould cavities for at least ten seconds in total to ensure that the parisons are sufficiently cool to remain on the cores when the mould is opened. To blow the parisons takes only three seconds but to bring the parisons from the temperature at which they leave the injection mould to the required temperature conditions at which they can be blown with bi-axial orientation would require, in this instance, twenty-four seconds.

If, therefore, one has a machine in which one set of parisons is being formed by injection while another set of parisons is being conditioned and brought to the correct temperature while another set of parisons is being blown, the cycle time of the machine will be governed by the time taken to bring the parisons to the blowing temperature conditions. In the above example, the conditioning time is approximately twice the injection cycle and therefore this will prevent the injection part of the machine operating at its optimum speed.

It is an object of the present invention to provide a machine whose output can be optimised irrespective, within limits, of the relation between the injection cycle time and the conditioning cycle time.

According to one aspect of the invention, therefore, we provide an injection-blow-moulding machine comprising: a fixed platen; a first mould part on the fixed platen and having cavities therein; a first rotatable platen arranged above the fixed platen to rotate about a first vertical axis and carrying at least two second mould parts complementary to the first mould part and having cores to enter the cavities in the first mould part; means to index said platen about said axis so that each of second mould parts is brought in turn into alignment with the first mould part; clamping means to clamp together the first mould part and that second mould part which is in alignment with the first mould part; means to conduct molten plastics material into the cavities in the clamped together first and second mould parts to form a parison on each core of the second mould part; a second rotatable platen rotatable about a second vertical axis spaced from the first axis and carrying two or more sets of conditioning moulds; means to index the second rotatable platen about said second axis to bring each set of conditioning moulds in turn into juxtaposition with a second mould part when the latter is not in alignment with the first mould part; means for transferring parisons from the cores of the second mould part which is in juxtaposition with a set of conditioning moulds.into the moulds of said set of conditioning moulds as the aligned first and second mould parts are clamped together; a blow mould assembly; the indexing means for the second rotatable platen bringing the sets of conditioning moulds in turn to a delivery position juxtaposed the blow mould assembly; means for transferring parisons from the juxtaposed conditioning moulds to the blow mould assembly; means for blowing the parisons in the blow mould assembly to make finished articles; and means for ejecting the finished articles from the blow mould assembly.

The operation of the machine will be described in detail below but, in essence, the parisons which are formed on the cores of the second mould parts are cooled as the first platen is indexed to bring the cores carrying the parisons from the first mould part to the conditioning mould sets. When the parisons are in the conditioning mould sets the latter are indexed on the second rotatable platen from the position in which they receive the parisons to a position juxtaposed the blow mould assembly. During this indexing there is sufficient time for the desired temperature conditions in the parison walls to be attained. When the parisons are transferred to the blow mould assembly, therefore, they are appropriately temperature conditioned for being blown to produce a container having bi-axial orientation.

The invention will now be described in detail by way of example with reference to the accompanying drawings in which:~ FIGURE 1 is a side elevation of an injectionblow-moulding machine showing the injection unit in an operative position; and FIGURE 2 is a plan view of the machine shown in Figure 1 but with the injection unit in a retracted position.

Referring now to the drawings the machine has three main parts, i.e. a conventional plasticiser and injection unit 10, a three-tie-bar clamping unit 11 and a conditioning and blow moulding unit 12.

The unit 10, is substantially conventional and will not be described in detail but it comprises an injection head 13 which is movable between a retracted position as shown in Figure 2 and an extended position as shown in Figure 1 in which it is adjacent to the clamping unit 11 and molten plastics material can be delivered through the nozzle 4 into a first mould part 15 on the clamping unit.

Turning now to the clamping unit it comprises a fixed platen 16 on which the first mould part 15 is received. The fixed platen is connected to an upper frame member 17 by three tie-bars 1 8, 19 and 20.

Rotatable about the tie-bar 18 is a first rotatable platen 21. The platen 21 is carried by a frame member 22 slidable on the tie-rods and controlled by a fluid pressure cylinder 23 secured to the upper frame member 17 and operable so as to reciprocate the frame member 22 on the tie-rods and capable of clamping together a second mould part carried by the platen and the first mould part 15 during injection of material into the mould thus produced.

The slidable frame member 22 carries an indexing motor 24 which is capable of indexing the platen 21 via an indexing mechanism 25 so that the platen 21 rotates about the vertical axis 26 of the tie-bar 18.

The platen 21 carries four second mould parts 27,28,29 and 30. Each of the mould parts carries a plurality of water-cooled cores, those on the mould part 27 being indicated at 31. The cores are arranged to enter cavities (not shown) in the first mould part 15 so that when the platen 21 is lowered from the position shown in Figure 1 the mould parts 15 and 27 cooperate with the cores 31 in the cavities in the mould part 15. The mould parts are clamped together by the fluid pressure cylinder 23 while molten plastics material is injected into the clamped together mould parts from the nozzle 14. As a result of this injection, parisons are formed about the cores 31.After the parisons have cooled sufficiently to become selfsupporting the sliding frame member 22 is lifted by the fluid pressure cylinder 23 to the position shown in Figure 1 and the mould part 27 carries, on its cores 31, parisons. The platen 21 is now indexed so as to bring the second mould part 30 into alignment with the first mould part 15 and the second mould part 27 moves to the position which was previously occupied by the mould part 28. A further cycle is then carried out so that parisons are formed on the cores of the second mould part 30, the platen is then indexed again to bring the mould part 29 into alignment with the mould part 15 and so on.It follows that for each cycle of the unit 11 the cores of one of the mould parts 27, 28, 29 and 30 will be furnished with parisons and these parisons will be cooled in air and by the water cooling in the cores 31 as the platen 22 is indexed. The parisons on the cores 31 of the mould part 27 will continue to cool as the mould part 27 is indexed until it comes to occupy the position shown for the mould part 30 in Figure 2 so that the parisons can be transferred to the unit 12 which will now be described.

Turning now to the unit 12, this comprises a second rotatable platen 32 which is rotatable about a vertical axis 49 which is spaced from the axis 26. On its upper surface the platen 32 carries four sets of conditioning moulds 33, 34, 35 and 36, only the set of conditioning moulds 36 is shown in Figure 1. Each set of conditioning moulds has twenty four cavities arranged in four rows of six cavities each and these are spaced and arranged on the same centres as the cores 31 on the second mould parts 27-30 and as the cavities in the first mould part 15. The conditioning moulds are arranged to receive from the cores the parisons thereon and to bring the parisons to the desired temperature conditions for orientation during blow-moulding.

While moulding is taking place in the mould constituted by, for example, the mould parts 27 and 15, the parisons on the mould part 30 are being transferred into the cavities in the set of conditioning moulds 33. The platens 21 and 32 rotate in synchronism, the platen 21 rotating in an anticlockwise direction and the platen 32 rotating in a clockwise direction as viewed in Figure 2. It will be appreciated from the description thus far that at each cycle of the machine one set of parisons is moulded in the mould part 15 while another set of parisons which has already been moulded is transferred into a set of conditioning moulds in a position shown for the set 33 in Figure 2.During each injection cycle the platen 32 indexes so that after three indexing movements the conditioning moulds which were at the position shown at 33 in Figure 2 arrive at the position shown for the set of conditioning moulds 36 in Figure 2 and in this position the conditioning moulds are juxtaposed to a blow mould assembly 37 which has twelve cavities arranged in two rows of six. The parisons in the conditioning mould 36 may be transferred from that conditioning mould into the blow mould assembly by means now to be described.

Referring to Figure 1 , the transfer means is shown at 38 and comprises two rows of cores 39 having stretch rods 40. The cores and stretch rods are reciprocable by a fluid pressure cylinder 41 and the transfer means 38 is reciprocable horizontally on a guide 42. It will be noted from Figure 1 that the spacing between the rows of cores 39 is such as to be aligned with two rows of the cavities in the conditioning mould set which are separated by a third row. Thus as shown in Figure 1 the cores 39 are aligned with the rows of cavities indicated at 43 and 45.During each cycle of the machine the cores move downwardly into the cavities, pick up the parisons from the cavities in the conditioning mould set, move to the left in Figure 1, place the parisons in the cavities in the blow mould assembly 37, stretch and blow mould the parisons in the cavities and then return to a position similar to that shown in Figure 1 but aligned with the cavities in the rows 44 and 46, pick up the parisons in those cavities and transfer them to the blow mould for stretching and blowing.

While the transfer means 38 is returning to pick up another set of parisons from the cavities in the conditioning mould set 36, ejector means 47 which also slides on the guide 42 and which is also reciprocal vertically by a fluid pressure cylinder 48, picks up the blown articles in the cavities in the blow mould 37 and then moves to the left hand end of the guide 42 and presents the moulded articles in an oriented way, for packaging or secondary operations.

It will thus be seen that for each injection cycle there are two blowing cycles, the first cycle taking the parisons from the rows 43 and 45 of the conditioning mould set 36 and the next blowing cycle taking the parisons from the rows 44 and 46 of the conditioning mould set 36.

It will be appreciated that upon blowing of the parisons their diameters will considerably increase and it will be noted that the spacing of the cavities in the blow mould assembly is the same when considered vertically in Figure 2 as the spacing of the moulds in the conditioning mould sets but when considered horizontally in Figure 2 the spacing is greater. If the increase in size of the parisons when being blown is such that the arrangement shown in Figure 2 cannot be used and the cavities in the blow mould assembly 37 have to be spaced vertically in Figure 2 by a greater distance than the spacing between the cavities in the conditioning mould set 36, the transfer means 38 will be so arranged as to increase the spacing between the parisons as they are transferred from the conditioning mould set 36 to the blow mould assembly. This can be effected by fixed/fluid pressure cylinders.

A parison produced in the cavities in the first mould part 15 will be allowed to cool as the platen 21 indexes to bring the parison to a position to be placed in the conditioning mould set 33 and the cooling time will be somewhat over twice the cycle time of the injection step. The parison will then be conditioned in a cavity in the mould set 33 as this indexes round to the position shown for the mould set 36 and there will be plenty of time for the desired temperature conditions in the parison walls to be attained.

The cycle time of the machine is thus determined by the cycle time of the injection step and the parisons have plenty of time to cool and be conditioned before they are placed in the blow mould assembly 37.

The machine described has four second mould parts 27-30 and four sets of conditioning moulds 33-36. Other numbers could, however, be provided but there must be at least two second mould sets and two sets of conditioning moulds.

If one considers the machine without the mould parts then one may consider that the fixed platen 15 is at a first station, that the mould parts on the platen 12 are at second and third stations, assuming that there are two such mould parts, that the conditioning mould sets on the platen 32 are at fourth and fifth stations, assuming again that there are only two such mould sets, and that the blow mould assembly 37 is at a sixth station.

The machine has been described with stretch rods 40 which mechanically stretch the parisons just before or simultaneously with blow moulding but it is within the scope of the invention to provide a machine in which the stretch rods are omitted and blowing is carried out in the blow mould assembly 37 without mechanical stretching. The rods 40 could also merely centre the parisons during blowing. In either event, the parisons can be transferred to the blow mould at a very accurately controlled temperature conditions which will allow bi-axial onentatidn of the material to take place during blowing.

Claims (6)

1. A machine for carrying out injection-blowmoulding comprising a fixed platen having a first station to receive a first cavitied mould part; a first rotatable platen arranged above the fixed platen to rotate about a first vertical axis and having at least second and third stations for receiving second mould parts complementary to the first mould part and having cores thereon; means to index said first rotatable platen about said axis so that each of the second and third stations is brought in turn into alignment with the first station; clamping means to clamp together the mould parts which are in alignment; a second rotatable platen rotatable about a second vertical axis paced from the first axis and having at least fourth and fifth stations to receive sets of conditioning moulds; means to index the second rotatable platen about said second axis to bring each of said fourth and fifth stations in turn into juxtaposition with the second or third station on the first rotatable platen which is not aligned with the first station so that parisons carried by the cores of a second mould part at the second or third station may be transferred to a set of conditioning moulds at the fourth or fifth station; a sixth station to receive a blow mould assembly; the indexing means for the second rotatable platen bringing the fourth and fifth stations in turn to a delivery position juxtaposed the sixth station; and means to transfer parisons between the station on the second rotatable platen which is juxtaposed the sixth station to the sixth station.

2. An injection blow-moulding machine comprising a fixed platen a first mould part on the fixed platen and having cavities therein; a first rotatable platen arranged above the mould base to rotate about a first vertical axis and carrying at least two second mould parts complementary to the first mould part and having cores to enter the cavities in the first mould part; means to index said first rotatable platen about said axis so that each of said second mould parts is brought in turn into alignment with the first mould part; clamping means to clamp together the first mould part and the second mould part which is in alignment with the first mould part; means to conduct molten plastics material into the cavities in the clamped together first and second mould parts to form a parison on each core of the second mould part; a second rotatable platen rotatable about a second vertical axis spaced from the first axis and carrying two or more sets of conditioning moulds; means to index the second rotatable platen about said second axis to bring each set of conditioning moulds in turn into juxtaposition with a second mould part when the latter is not in alignment with the first mould part; means for transferring parisons from the cores of the second mould part which is in juxtaposition with a set of conditioning moulds into the moulds of said set of conditioning mould as the aligned first and second mould parts are clamped together; a blow mould assembly; the indexing means for the second rotatable platen bringing the sets of conditioning moulds in turn to a delivery position juxtaposed the blow mould assembly; means for transferring parisons from the juxtaposed conditioning moulds to the blow mould assembly; means for blowing the parisons in the blow mould assembly to make finished articles; and means for ejecting the finished articles from the blow mould assembly.

3. A machine according to Claim 2 wherein means is provided for mechanically stretching the parisons before or simultaneously with the blowing of the parisons in the blow mould assembly.

4. A machine according to Claim 2 or Claim 3 wherein there are four second mould parts on the first rotatable platen and four conditioning mould sets on the second rotatable platen.

5. A machine according to any one of Claims 2 to 4 wherein there are less cavities in the blow mould assembly than in each set of conditioning moulds and the means for transferring the parisons from the conditioning moulds to the blow mould assembly effects said transfer in stages.

6. A machine substantially as herein described with reference to and as shown in the accompanying drawings.