IES20040205A2 - A plastic blow-moulding process - Google Patents

Abstract

The process of the invention is for manufacturing a thin-walled plastics container comprising a bottle with a neck portion. In a mould (10) a parison of plastics material is formed about a blow pin and between a pair of spaced-apart mould halves. As the mould halves close low pressure pre-blow air is delivered thorough the blow pin for partially inflating the parison within the mould. Upon closure of the mould high pressure air is delivered through the blow pin to rapidly fully inflate the parison against an inner wall of the mould to form the bottle. Whilst the plastics material is still malleable the blow pin is advanced into the mould to gather and comprise plastics material at a neck of the bottle which is then separated from the parison material. Upon opening the mould (10) the bottle is removed and delivered by conveyor (12) and feeder (15) to deflashing station (16) at which excess waste plastics material is removed. Bottles are then delivered by conveyors (18,30) to a packaging station (32). <Figure 1>

Description

“A plastics blow-moulding process” This invention relates to a plastics blow-moulding process.

The invention is particularly concerned with the plastics blow-moulding of relatively thin-walled plastics bottles of the type used for example in the dairy industry for milk packaging. In blow-moulding such a plastics bottle a parison is extended downwardly about a blow pin and a pair of mould halves close together about the parison and blow pin. Air at a pressure in the order of 100 psi is blown through the blow pin to an interior of the parison to inflate the parison within the mould to take a bottle shape formed by an interior of the mould against which the plastics material of the parison is blown. A shear ring on the blow pin cooperates with a complementary shear collar at a neck opening of the mould, through which the blow pin passes, to cut a neck portion of the formed bottle away from the parison material. Usually blowing of the parison commences as the mould halves are closing together, the blowing being timed such that as the mould closes fully the bottle is fully blown and cut away from the parison at the neck portion. Particularly with thin-walled bottles getting the timing right presents difficulties and considerable wastage may occur in setting up the mould. Further, when the bottles are in use it is necessary to provide a good seal between the neck portion of the bottle and an associated cap of the bottle to prevent leakage of liquid from the bottle in use. With thin-walied bottles difficulties can arise due to lack of material at the bottle neck if the timing of the blowing and cutting of the neck is not very accurate leading to a relatively high reject rate. Also the sealing surface at the neck of the bottle which cooperates with a cap has a relatively coarse finish which can give sealing problems.

The present invention is directed towards overcoming these problems.

According to the invention there is provided a plastics blow-moulding process for manufacturing a thin walled plastics container comprising a bottle with a neck portion, including the steps: extruding a parison of plastics material downwardly about a blow pin and between a complementary pair of spaced-apart open mould OPEN TO PUBLIC INSPECTION I TStcl UNDER SECTION 28 AND RULE 23 JNL No. of IE 0 4 02 0 5 halves, closing the mould halves together, when the mould halves are partially closed pre-blowing the parison with low pressure air by injecting low pressure air through the blow pin into the parison for partially inflating the parison as the mould closes fully, sealingly engaging the mould halves with the blow pin when the mould is fully closed, injecting high pressure air at full blow pressure through the blow pin into the parison within the fully closed mould for rapidly fully inflating the parison against an inner side wall of the mould to form the bottle in the mould, after blowing the parison at full blow pressure for a preset period after closing the mould advancing the blow pin into the mould a preset distance for gathering and compressing plastics material at a neck of the bottle, and when the blow pin is fully extended into the mould a cutting ring on the blow pin cooperating with a complementary shear steel on the mould for cutting the neck of the bottle from the parison material, opening the mould, removing the bottle from the mould, cooling the bottle, de-flashing the bottle, and delivering the bottle for further processing and/or packaging. 0 4 02 0 5 In a preferred embodiment the time delay between closing the mould and advancing the blow pin into the mould within the range 0.4 to 0.5 seconds.

In another embodiment the process includes the step of moving the blow pin through a stroke of 15mm.

In a further embodiment the shear steel on the mould defines a tapered hole having a side wall which tapers outwardly at an angle of 15° to a central axis of the hole and the cutting ring on the blow pin has a right angle cutting edge for engagement with said side wall above the inner narrowest part of the hole.

In another embodiment the process includes engaging an exterior of a cylindrical cap part of the blow pin with an air seal formed in two associated seal parts mounted on the mould halves said seal parts engaging and forming an air seal with the cap part, the cap part slidably engaging the air seal parts for moving between a raised preblowing position and a lowered main blowing position.

In another embodiment the process includes starting injecting the low pressure preblow air into the parison as the closing mould halves are coming into contact with the parison.

In another embodiment the full blow pressure air is at about 10Opsi (6.89 bar).

In a further embodiment the preblow air pressure is in the range 20-25psi (1.38 bar 1.72 bar).

In a further embodiment the process includes the step of pressure testing the bottles downstream of the de-flashing station.

In another embodiment the process includes aligning a set of upstanding bottles in a number of rows and columns, pulling an outer plastics envelope about the set of bottles and sealing the envelope encasing the set of bottles.

The invention will be more dearly understood hy ths fallowing description of some embodiments thereof, given by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a schematic plan view of a plastics bottle blow-moulding production line according to the invention; Fig. 2 is a detail perspective view of a mould portion of the production line; Fig. 3 is an enlarged detail perspective view of portion of the mould; Fig. 4 is an exploded perspective view of a blow pin assembly for the mould; Fig. 5 is a perspective view of portion of the blow pin and mould; Fig. 6 is a detail diagrammatic illustration of the mould with the blow pin shown in a raised position; Fig. 7 is a view similar to Fig. 6 with the blow pin shown in a lowered neck cutting position; and Fig. 8 is an elevational view of a plastics bottle formed by the process.

Referring to the drawings a process and apparatus for canying out a plastics blowmoulding process for manufacturing a thin walled plastics bottle according to the invention will be described.

Referring initially to Fig. 1 a production line for the production of plastics bottles according to the invention is shown schematically. At a mould 10 plastics bottles are prepared by a blow-moulding process which will be described in more detail later. A plurality of bottles are blown together in a row. Formed bottles are lifted onto an inclined cooling conveyor 12 on which the bottles are allowed cool in air for a preset period.

IE 0 4 02 0 5 Immediately downstream of lh& cooling conveyor12 a row of hQttIes14 is transferrecL onto a feeder 15 for delivery to a deflashing station 16. At the deflashing station 16 excess plastics material at the top and bottom of each bottle are removed.

Cleaned bottles are delivered by a conveyor 18 to a selector 20 which directs the bottles as required and as preset to either a raw bottle delivery line 22 or a bottle labelling line 24.

Referring first to the raw bottle delivery line 22 bottles are conveyed to a testing station 26 at which the neck of each bottle is sealed and air at pressure 50 millibars is injected into the bottle for a period of two seconds. If there is greater than 8% drop in air pressure then the bottle is rejected into a reject bin 28.

Acceptable bottles are delivered by conveyor 30 to a packaging station 32. At the packaging station 32 a plurality of upstanding bottles are arranged in a number of rows and columns in a rectangular array 34. An envelope of plastics material is then pulled over the array 34 of bottles and sealed to form an envelope 36 containing the array 34 of bottles. This envelope 36 of bottles is then lifted onto a pallet 40.

Referring now to the labelling line 24, this is essentially similar to the raw bottle delivery line 22 except that a labelling station 42 is inserted belween the testing station 26 and the packing station 32. At the labelling station 42 a label band is pulled down over an exterior of the bottle, said label referring to the produce which is to be filled into the bottle subsequently.

Referring now in particular to Figs. 2 and 3 the moulding machine 10 and cooling conveyor 12 are shown. Robot transfer arms 45 are mounted at their inner ends on a rotatable spindle 46 having an associated drive motor 47. The arms 45 are mounted directly beneath associated pairs of mould halves 48, 49 in which the bottles are formed. Ram means (not shown) is provided in conventional fashion for moving the mould halves 48, 49 together and apart during the moulding process. After forming bottles within bottle shaped recesses in the mould 10 the mould halves 48, 49 open and the arms 45 grab a flashing tail at a bottom of each bottle and swing the bottles IE 0 4 0 2 ο 5 onto the cooling conveyor 12 when the spindle 46 is rotated by the motor 47. The botttesarereleased-onto4becoolingconveyor 12andthearms45 swing back beneath the mould halves 48,49 for engagement with the next set of bottles prepared in the mould 10. The bottles cool in air in travelling along the conveyor 12 belween an inlet 43 and an outlet 44 of the conveyor 12.

Referring now in particular to Figs. 4 and 5 a blow pin assembly for each bottle forming recess in the mould 10 is shown and indicated generally by the reference numeral 50. The assembly 50 includes a tubular blow pin 51 connected to a pressurised air supply (not shown). A blow pin cap element 52 is mounted on the blow pin 51, a central bore 53 of the cap 52 receiving the blow pin 51. Four radial air passages 54 are provided in a bottom face 55 of the cap 52.

A cutting ring 58 engages the bottom face 55 of the cap 52 and has a central through hole 59 for reception of the blow pin 51. A circular array of spaced-apart axially extending cooling air holes 60 pass through the cutting ring 58. A lower circular peripheral cutting edge 61 of the cutting ring 58 forms a right angle cutting edge, that is a side 63 and a bottom face 64 of the cutting ring 56 are substantially perpendicular.

Engaged against a bottom face of the cutting ring 58 is a neck bore calibration ring 62. The neck ring 62 sits in an associated rebate 65 at an upper end of a body element 66. The body element 66 has a central air passage 67 surrounded by a ring of cooling air holes 68 corresponding to the air holes 60 in the cutting ring 58.

A blow pin tip 70 has a stepped inner end 72 which engages and seats within a socket 73 formed at a bottom end of the body 66. The blow pin tip 70 has a central air through passage 75 with a number of radial air outlet slots 76 for directing air laterally and upwardly within the mould during the blowing process.

Mounted on the mould halves 48,49 for cooperation with the blow pin 50 is an air seal 80 and a shear steel 81. Each of these 80, 81 are generally disc shaped and are in two halves as shown in the drawing. Each overlying pair of halves 80, 81 is bolted to the top of an associated mould part 48,49 with central openings 83,84 in the air seal 80 and shear steel 81 aligning with a neck opening 85 at a top of the mould part 48,49 ΙΕ Η 02 0 5 as shown in Fig. 5.

An inside face 87 of the opening 84 in the shear steel 81 cooperates with the cutting edge 61 of the cutting ring 58 on the blow pin 50 for cutting the neck of the bottle from the parison material. The opening 84 in the shear steel 81 is a tapered hole having a side wall 87 which tapers outwardly from bottom to top at an angle of 15° to a central axis of the hole 84. The cutting ring 58 on the blow pin 51 has a right angle cutting edge 61 for engagement with said side wall 87 above the inner narrowest point of the hole 84.

In use, and referring in particular to Figs. 6 and 7, a parison 90 is extruded downwardly about the blow pin 50 belween the two mould halves 48,49. The mould halves 48,49 start closing inwardly together. As the mould halves 48, 49 are closing pie-blowing takes place with air at a pressure in the order of 20 psi being injected through the blow pin 50 into the parison 90. The low pressure preblowing air is switched on when the mould halves are about 50% closed and coming Into contact with the parison. When the mould halves 48,49 are fully closed the air seal 80 forms an airtight seal with tire cap 52 on the blow pin 51, engaging an exterior of the cap 52. The pressure of air being delivered through the blow pin 50 is then increased to a main blow pressure of approximately 100 psi to rapidly fully inflate the parison 90 thus forming a bottle 91 in the mould cavity 92. After at lest 0.4 seconds, and typically at about 0.5 seconds after closure of the mould and injection of high pressure air, the blow pin 51 is moved downwardly 15mm by means of a ram (not shown) the blow pin 51 gathering and compressing plastics material at the neck of the bottle 91 between the cutting ring 58 and the inside face 87 of the hole 84 in the shear steel 81 until the cutting edge 61 on the blow pin 50 cooperates with the face 87 on the shear steel 81 on the mould halves 48,49 to cut through the parison material at the neck of the bottle 91 (Fig. 7). This is typically about 1 mm above the bottom of the hole 84.

High pressure air is injected for about another 4 seconds for cooling the plastics material within the mould. The grooves 54 in the blow pin cap 52 allow air into the hole 83 in the air seal 80 to cool the plastics material immediately above the neck portion of the bottle so that it can be readily easily and quickly defiashed later. The mould is then vented and an arm 45 grips a flashing flange 93 at a bottom of each bottle, the flashing flange 93 projecting downwardly from the mould. When the mould opens the the bottle on the cooling conveyor 12.

A fresh parison is then extruded downwardly between the open mould halves and the cycle repeated.

Fig. 8 shows a plastics bottle moulded by the process of the invention. it will be appreciated that using the process of the present invention additional material is built up at the neck of the bottle 91. Also with the two step blowing the plastics material is partially solidified but still malleable so that it can be shaped and cut more accurately as the blow pin 30 moves downwardly. There is a dense compaction of material at the neck of the bottle to provide a smooth sealing surface.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail within the scope of the appended claims.

Claims (5)

1. A plastics blow-moulding process for manufacturing a thin walled plastics container comprising a bottle with a neck portion, including the steps: extruding a parison of plastics material downwardly about a blow pin and between a complementary pair of spaced-apart open mould halves, closing the mould halves together, when the mould halves are partially closed pre-blowing the parison with low pressure air by injecting tow pressure air through the blow pin into the parison for partially inflating the parison as the mould doses fully, sealingly engaging the mould halves with the blow pin when the mould is fully closed, injecting high pressure air at full blow pressure through the blow pin into the parison within the fully closed mould for rapidly fully inflating the parison against an inner side wall of the mould to form the bottle in the mould, after blowing the parison at full blow pressure for a preset period after closing the mould advancing the blow pin into the mould a preset distance for gathering and compressing plastics material at a neck of the bottle, and when the blow pin is fully extended into the mould a cutting ring on the blow pin cooperating with a complementary shear steel on the mould for cutting the neck of the bottle from the parison material, opening the mould, removing the bottle from the mould, IE Ο 4 Ο 2 ο 5 -10cooling the bottle, de-flashing the bottle, and delivering the bottle for further processing and/or packaging.

2. A process as claimed in claim 1 wherein the time delay between closing the mould and advancing the blow pin into the mould within the range 0.4 to 0.5 10 seconds.

3. A process as claimed in claim 1 or claim 2 including the step of moving the blow pin through a stroke of 15mm, and the shear steel on the mould defines a tapered hole having a side wall which tapers outwardly at an angle of 15° to a 15 central axis of the hole and the cutting ring on the blow pin has a right angle cutting edge for engagement with said side wall above the inner narrowest part of the hole, and including engaging an exterior of a cylindrical cap part of the blow pin with an air seal formed in two associated seal parts mounted on the mould halves said seal parts engaging and forming an air seal with the cap 2 0 part, the cap part slidably engaging the air seal parts for moving between a raised position and a lowered position.

4. A plastics blow-moulding process substantially as hereinbefore described with reference to the accompanying drawings.

5. Plastics containers whenever produced by the process as claimed in any preceding claim.