Method and apparatus for blow molding hollow articles

Abstract: A method and apparatus for blow molding plastic articles which utilizes one or more fixed needles and one or more micro vents associated with a blow mold cavity. Each needle has a first passage associated therewith through which vacuum is supplied to pull the molten plastic about the needle and a second passage therein through which air under pressure is introduced to tear the plastic and blow the article to the confines of the mold which has been closed about the plastic parison. Micro vents facilitate exhausting air which is about the parison. Preferably the second passage for compressed air is provided by a central bore and the first passage for the vacuum is provided by an annular space about the fixed needle. In a modified form, the fixed needle comprises dual air passages. Provision is made for utilizing plural molds with controls for supplying air and vacuum.

Description: Field of the Invention The invention relates to a method of blow molding hollow plastic containers according to the preamble of claim 1, and to an apparatus for blow molding containers from hollow plastic parisons according to the preamble of claim 9. Background of the Invention In the making of blow molded plastic articles utilizing blow molding machines, a hollow plastic parison of molten plastic material in the form of a tube is extruded between two complementary blow mold halves, the blow mold halves are closed and the tube is blown to the confines of the mold by utilizing a needle that pierces the tube, and air is introduced into the interior of the tube through the needle to form the article such as a hollow container. One commercially successful arrangement is of the type shown in US-A-3,737,275 and 3,873,661 wherein a movable needle is first advanced by air pressure to penetrate the extruded plastic tube and air is thereafter applied through a bore in the needle to inflate the tube. After blowing, the blowing air is exhausted and the blow needle is withdrawn. Such an arrangement not only uses multiple parts, but also requires critical timing to provide for the movement of the movable needle. A method and an apparatus according to the preambles of claims 1 and 9 is known from WO-A-90/07414. The blow needle is cam-actuated or rigidly fixed within the mold block. Furthermore, there are vacuum passages around the hollow plastic parison to extend same also in direction to the blow needle. However, no vacuum field is created around the blow needle. In a further known method and apparatus of blow molding hollow plastic containers (FR-A-1,475,911) after closing the mold about the plastic parison, a tube having a flange at its free end is moved from the mold wall to the adjacent parison wall, and vacuum is admitted into the tube so as to suck the parison wall and pull it to the blow needle for being punctured. Therefore, the vacuum field is made effective with moving parts. Summary of Invention It is an object of the present invention to provide a method and an apparatus for blow molding hollow plastic containers which do not require a movable blow needle nor movable parts around it. The invention is defined in claims 1 and 9. The apparatus of invention is simpler to construct and to maintain; it is less costly; it reduces mold costs by utilizing simplicity of placement, design and manufacture; it has less downtime; it is more reliable; it is more readily maintained; and it facilitates process start up. In the preferred embodiments of the invention, one or more fixed blow needles and one or more micro vents associated with the blow mold cavity are used. Each needle has a first passage associated therewith through which vacuum is supplied to pull the molten plastic about the needle and a second passage therein through which air under pressure is introduced to tear the plastic and blow the container to the confines of the mold which has been closed about the plastic parison. Micro vents facilitate exhausting air which is about the parison. Preferably the second passage for compressed air is provided by a central bore, and the first passage for the vacuum is provided by an annular space about the fixed needle. In a modified form, the fixed needle comprises dual air passages. Provision is made for utilizing plural molds with controls for supplying air and vacuum. Description of the Drawings FIG. 1 is a schematic of one embodiment in accordance with the invention. FIG. 2 is a schematic of another embodiment of the invention. FIG. 3 is a schematic of still another embodiment of the invention. FIG. 4 is a schematic of another embodiment of the invention. FIG. 5 is a top plan view of the lower mold half of a mold embodying the invention. FIG. 6 is a fragmentary part sectional view of a portion of the mold shown in Fig. 5. FIG. 7 is a fragmentary top plan view of the mold. FIG. 8 is a fragmentary top plan view of the lower mold half. FIG. 9 is a bottom view of the top mold insert. FIG. 10 is a fragmentary sectional view on an enlarged scale of a portion of the mold shown in Fig. 6. FIG. 11 is a fragmentary sectional view on an enlarged scale of a portion of the mold shown in Fig. 10. FIG. 12 is a fragmentary sectional view similar to FIG. 10 sharing the passage for providing a vacuum. FIG. 13 is a fragmentary sectional view similar to FIG. 12 showing a fixed needle in position. FIG. 14 is a part sectional elevated view of a fixed needle embodying the invention. FIG. 15 is a bottom plan view of the fixed needle. FIG. 16 is a top plan view of the fixed needle. FIG. 17 is an elevational view of the fixed needle shown in Figs. 14-16 with the O-ring removed. FIG. 18 is a fragmentary sectional view of the O-ring groove of the fixed needle. FIG. 19 is a sectional view taken along the lines 19-19 in Fig. 20. FIG. 20 is a plan view of a micro vent used in the invention. FIG. 21 is an elevational view of a double fixed needle. FIG. 22 is a bottom plan view of the double fixed needle shown in FIG. 21. FIG. 23 is a sectional view of the double fixed needle in a mold. FIG. 24 is a schematic diagram of vacuum and blow air as used in a rotary blow molding machine. FIG. 25 is a schematic view similar to FIG. 24 of a system used in a rotary blow molding machine having more molds than that shown in FIG. 24. Detailed Description of the Preferred Embodiments Referring to FIG. 1 which a schematic of one embodiment of the invention, the method comprises a blow mold 30 which comprises two mold halves 32, 34 which are closed about a plastic parison. A fixed blow needle 36 is provided in at least one mold half 34 and has an inner end extending in to the cavity of the mold 30. The needle 36 includes a first passage 38 surrounding the needle 36 which is connected to a source of vacuum through a line 40. Passage 38 extends to the interior of the mold 30. An exhaust valve 46 functions to exhaust the air in the second passage 42. The needle 36 includes a second passage 42 which is connected to a source of compressed air through a line 44. Passage 42 extends through the fixed needle 36 to the interior of the mold 30. A valve 50 is operable to control the flow of air through line 44. In addition, one or more micro vents 52 are provided in communication with the mold cavity to facilitate venting of the cavity. The method is preferably provided for use with rotary blow molding machines such as shown in United States patents 4,523,904; 4,549,865; and 4,648,831, incorporated herein by reference. In operation, a plastic parison of molten plastic in the form of a tube is extruded between the mold halves, the mold halves 32, 34 are closed and vacuum is provided through the first passage 38 to pull the plastic about the fixed needle 36. After a short time, for example, on the order of 0.5 second, compressed air is supplied through the second passage 42 to tear the plastic which has been stressed about the fixed needle 36 and the compressed air inflates the parison to the confines of the mold. After the shape of the article such as a plastic container has been set, the compressed air is turned off and another cycle can begin. A typical time cycle comprises 6 seconds. In the schematic shown in FIG. 2, vacuum and compressed air are supplied through a manifold 54. In all other respects the method is the same as that shown in FIG. 1. In the schematic shown in FIG. 3, plural micro vents are provided on mold halves 32, 34 as contrasted to FIG. 1. In the modified schematic shown in FIG. 4, the circuit is shown as a part of a wheel type blow molding machine such as that in the aforementioned patents, wherein the blow valve 50 and vacuum valve 60 of each pair of mold halves are controlled by cams as the wheel rotates as disclosed in said patents, incorporated herein by reference. In operation as shown in FIG. 24, the molds are provided about the periphery of a wheel in circumferentially spaced relation such that they move in a closed path in the manner of the aforementioned patents. A first cam is positioned at one station for actuating the air control star valve of each mold as it passes and a second exhaust cam is positioned at a circumferentially spaced station for controlling the exhaust valve of each mold when it passes that station. The star valve 50 associated with each mold 30 controls the vacuum valve of a subsequent mold to supply vacuum before blow air is supplied and during the first portion of the cycle when blow air is on. The operation is summarized as follows: The system is designed that when the BLOW AIR is OFF at the Operator Control Panel, vacuum will be ON to all station, IML vents and fixed needles. When the BLOW AIR is ON at the Operator Control Panel, vacuum will be ON only to half of the stations, IML vents and fixed needles. With the BLOW AIR On, the stations with vacuum ON will be the stations from 12 O'clock to 6 O'clock, clockwise. The vacuum to the mold IML vents and the fixed needle comes ON just before the IML assembly and shuts OFF at the bottom of the wheel. The chart below shows which station controls the vacuum in another station. It must be noted that the offset is 4 stations. Station Vacuum Valve Location Station Mold and Fixed Needle Vacuum ON/OFF Controlled by Star Valve Located in Station 1 1 11 2 2 12 3 3 13 4 4 14 5 5 1 6 6 2 7 7 3 8 8 4 9 9 5 10 10 6 11 11 7 12 12 8 13 13 9 14 14 10 Order of Operation: 1. Station #1 engages the Blow Cam. Station #1 blow air comes ON and Station #5 vacuum comes ON. 2. Station #1 engages the Exhaust Cam. Station #1 blow air shuts OFF and Station #5 vacuum shuts OFF. This operation is repeated for each mold in sequence as the wheel turns. In the schematics shown in FIG. 25, 18 sets of molds are provided and the placement of the blow valve, exhaust valve and vacuum valve are preferably positioned as indicated. Referring to FIGS. 14-18, a preferred needle 36 comprises a one-piece body 64 having a bore 66 defining the second or compressed air passage 42 (FIGS. 1-4). An annular passage 120 in the mold half (FIGS. 10-13) concentric with bore 66 and surrounding body 64 defines the vacuum passage. The nose 68 of the needle 36 is preferably shaped as truncated cone tapering to a sharp edge 70. Fixed needle 36 includes an ananular flange 72. Body 64 of the needle is formed with an annular groove 74 that receives an O-ring 76. Vacuum line 38 extends through a passage 100 (FIGS. 12-13) in mold half 106 to the area above O-ring 76, as presently described, such that vacuum is drawn through passage 120 about the annular flange 72. As shown in FIGS. 19 and 20, the micro vents 52 each comprise a threaded headed screw 78 with a central passage 80 that has a diameter on the order of 1.5875 mm (1/16 inch) to provide for venting of the area surrounding the molten plastic parison. Referring to FIGS. 21-23, a modified form of needle comprises a double fixed needle comprising a body 122 having an axial passage 124 defined by a tube 126 and engaging an axial air inlet 128 in mold 130 and an annular passage 132 about the tube 126 to which blow air is supplied by aa radial inlet 134 in the mold 130. Vacuum is provided about the body 122 by an annular passage 136. Such a double fixed needle has utility in hard to blow bottles and bottles requiring more exhaust area or passage. Referring to FIGS. 5-11, the invention is described with respect to molds utilized on a wheel machine made in accordance with the aforementioned U. S. patents 4,523,904; 4,549,865; and 4,648,831 for making a hollow container forming portion C with an integral hollow moil M which communicates with the container C. The needle 36 and micro vents 52 are associated with the moil forming portion of the mold. Each mold 100 comprises an upper mold half 102 and a lower mold half 104. Lower mold half 104 has a removable insert 106 in which a fixed needle 36 and a microvent 52 are positioned. The insert 106 includes a passage 108 which communicates with the bore 66 (FIGS. 14-17) of the needle 36 to provide compressed air and a passage 110 which communicates with the annular passage 120 (FIGS. 6 and 10-13) surrounding the needle 36 to apply vacuum. The upper half 102 includes a removable insert 114 which has one or more exhaust micro vents 52 to the exterior through passages 122. Among the advantages of the invention are: 1. The method and apparatus are simple and less complex, 2. There are no moving parts in the blow needle. 3. The cost of the blow needle is substantially less than a movable needle. 4. Mold costs are reduced because of the simplicity of placement, design and manufacturing. 5. The blow needle is more reliable. 6. Downtime for blowing failure is significantly reduced. 7. The operating window for blowing is wider which makes process start up easier. It can thus be seen that there has been provided a method and apparatus wherein does to require a movable needle; which has no moving parts; which is simpler to construct and maintain; which is less costly; which reduces mold costs by utilizing simplicity of placement, design and manufacture; which has less downtime; which is more reliable; which is more readily maintained; and which facilitates process start up.

Claims: A method of blow molding hollow plastic containers comprising the steps of: providing a blow mold (30, 100) comprising mold portions (32, 34; 102, 104) which when closed define a mold cavity, providing a fixed blow needle (36) in at least one mold portion (34, 104), said blow needle having an opening (42, 66), positioning a molten hollow plastic parison between said mold portions (32, 34; 102, 104), closing said mold portions (32, 34; 102, 104) about said plastic parison, providing vacuum to the mold cavity to extend the hollow plastic parison and pierce it by the blow needle (36), and thereafter providing air through the opening (42) in said fixed needle (36) to tear the plastic and to expand the parison to the confines of the mold cavity (30), characterized in that in the step of providing vacuum, a vacuum field about the periphery of the fixed blow needle (36) is made effective through stationary suction means (38, 120) surrounding the needle (36) to pull the parison wall adjacent to the fixed blow needle (36) about the needle (36). The method set forth in claim 1 wherein said vacuum about the periphery of said fixed blow needle (36) is provided through a fixed passage (40) to an annular space (120). The method set forth in claim 1 or 2 wherein the space about said parison in said cavity is vented (52). The method set forth in any of claims 1 to 3 wherein a second fixed blow needle in said mold cavity portion and a second passage about the periphery of said second fixed needle are provided, wherein vacuum is provided to both said passages (40) to draw said plastic parison about said needles at a moil portion and wherein air through said first and second needles is introduced to tear the plastic and expand the parison to the confines of the mold cavity. The method set forth in any of claims 1 to 4 wherein flow of air to and from said mold cavity is controlled by control valve means (46, 50). The method set forth in any of claims 1 to 5 wherein air and vacuum are supplied, respectively, through blow needle and passage means (38, 52) into in a plurality of molds to obtain a plurality of hollow containers which are blow molded. The method set forth in claim 6 including controlling the application of vacuum and air during the blowing cycle. The method set forth in claim 7 wherein said step of controlling the application vacuum and air comprises positioning said molds and their associated fixed passage means (38, 52) and fixed needles (36) in a closed path, providing a first cam at first position above the closed path, providing a second cam at another position above said path, providing an air control valve (46, 50) on each mold such that the first cam actuates said air control valve at said first position to apply air to the associated mold and said second cam actuates said air control valve (46, 50) at said second position to end application of air to the associated mold. Apparatus for blow molding containers from hollow plastic parisons, comprising a blow mold (30; 100) comprising portions (32, 34; 102, 104) which when closed define a cavity, a fixed blow needle (36) in at least one mold portion (34; 104), said blow needle having an opening (42, 66), means (40; 112) for providing vacuum in the mold cavity to extend the respective hollow plastic parison and pierce it by the blow needle (36) to pull the molten plastic about the fixed needle (36), means (44) for providing air through said opening (42) in said fixed blow needle (36) to tear the plastic and to expand the parison to the confines of the cavity mold, characterized in that suction means (38) is fixedly arranged in one of said mold portions (34, 104) around the fixed blow needle (36) and adapted to provide vacuum about the periphery of the needle (36) so as to pull the parison wall adjacent to the needle (36) about the needle (36). The apparatus set forth in claim 9 wherein said suction means (38) comprises an annular space (120) between mold wall and a flange (72) of the blow needle (36). The apparatus set forth in claim 9 or 10 including at least one vent (52) in said mold cavity to facilitate venting the space about a parison. The apparatus set forth in any of claims 9 to 11 wherein the mold (30, 100) comprises a moil cavity portion (M) and a body portion (C), said first mentioned blow needle (36) being in said moil cavity (M) of said mold. The apparatus set forth in claim 12 including a second fixed blow needle in said moil portion. The apparatus set forth in any of claims 9 to 13 wherein second suction means (38) is fixedly arranged adjacent to a second needle to draw the adjacent parison wall about said second needle before introducing air through said first mentioned needle and second needle to tear the plastic and expand the parison to the confines of the moil cavity portion and body cavity portion. The apparatus set forth in any of claims 9 to 14 wherein said means providing air comprises a valve (50) controlling the flow of air to said fixed needle (36). The apparatus set forth in claim 15 wherein said means for supplying air includes an exhaust valve (46) to exhaust air from said cavity. The apparatus set forth in claim 15 or 16 wherein the valve comprises a combined valve (50, 54) for controlling the flow of air and the vacuum. The apparatus set forth in any of claims 9 to 17 wherein said fixed needle comprises a fixed needle having dual air passages (124, 132) providing air. The apparatus set forth in any of claims 9 to 18 wherein dual air passages (124, 132) comprises concentric air passages in said needle. The apparatus set forth in any of claim 9 to 19 wherein each said mold includes a recess for receiving a fixed blow needle (36), an annular space (120) surrounding said recess, a first passage (110) to which vacuum is applied, being connected to said space (120) and a second passage (108) extending to the recess and being connected to the opening (66) of the blow needle (36). The apparatus set forth in claim 20 including a plurality of molds, each having a fixed blow needle (36) to which vacuum and air is supplied and means for controlling the vacuum and air to each said needle. The apparatus set forth in claim 21 wherein said means for controlling the application vacuum and air comprises means positioning said molds and their associated fixed needles in a closed path, a first cam at first position above the closed path, a second cam at another position about said path, and an air control valve (50) and an exhaust control valve (46) on each mold such that the first cam actuates said air control valve (50) of a mold at said first position and said second cam actuates said exhaust valve (46) at said second position.

Inventors: GILLIS ROBERT A, MCGLYNN DANIEL F, GILLIS, ROBERT A., MCGLYNN, DANIEL F.
Applicants: OWENS BROCKWAY PLASTIC PROD, OWENS-BROCKWAY PLASTIC PRODUCTS INC.
Application year: 1997
Main classification: B29C49
IPC codes: B29C49