BLOW MOLDING MOLD FOR FORMING HOLLOW DOUBLE-WALLED PRODUCT

Abstract: The present invention relates to a blow molding mold for a hollow doubled-walled product, comprising a pair of male and female mold members for holding a parison therebetween, said male and female mold members being movable toward and away from each other and having respective inner surfaces for shaping inner and outer layers of the parison therealong under the pressure of air injected into the parison, said female mold member being of a box-shaped structure compris­ ing two pairs of confronting peripheral wall segments and a single bottom, said peripheral wall segments being pivotally supported on said bottom by pivot shafts disposed outwardly of and extending parallel to edges of the bottom, said peripheral wall segments being angularly movable between an open position in which they are open outwardly and a closed position in which they engage said bottom and adjacent ones of said peripheral wall segments to form a female mold, one of said pair of peripheral wall segments having parison corner expansion prevention wall joined to opposite sides thereof and extending a predetermined dimension in a direction in which the parison is supplied between the male and female mold members.

Description: The present invention relates to a blow moulding mould for a hollow double-walled product as defined in the preamble of the independent claim 1. Various processes for manufacturing hollow double-walled products have been developed so far. Examples of such processes are disclosed in Japanese Patent Publications No. 46(1971)-14153, 49(1974)-18748, and 51(1976)-13495. However, there are known only few molds used to mold hollow double-walled products. There molds are shown in Japanese Patent Publication No. 49(1974)-41111, Japanese Laid-Open Patent Publications Nos. 60(1985)-67130, and 63(1988)-221020. According to Japanese Laid-Open Patent Publication No. 60(1985)-67130, a mold includes a female mold member having four separate peripheral wall segments and a bottom. When air is injected into the parison, the parison can be smoothly moved along the inner wall surfaces of the peripheral wall segments, so that a double-wall product having a uniform thickness can be molded. Double-walled products thus molded are stronger than those produced by conventional molds. All of the four peripheral wall segments are swingable outwardly, and they are required to swing in timed relation to the injection of air into the parison. The mold and a molding apparatus using the mold are therefore complex and expensive. Another problem is that a product molded by the mold has burrs on all four corners thereof. Though the molded product has a sufficient degree of mechanical strength, the burrs have to be removed in a subsequent step, and the product needs to be improved for its commercial value. The mold disclosed in Japanese patent Publication No. 49(1974)-4111 is only limited to the fabrication of a product having a body and a lid which share a hinge. This mold is therefore less versatile. The hinge of the molded product tends to be thin. The mold shown in Japanese Laid-Open Patent Publication No. 63(1988)-221020 also lacks versatility because it is used exclusively to form undercuts on molded parts. From JP-A-60-71223 a mold for blow molding of hollow doubled-walled articles is known, comprising a pair of male and female mold members for holding a parison therebetween, said male and female mold members being movable toward and away from each other and having respective inner surfaces for shaping inner and outer layers of the parison therealong under pressure of air injected in the parison, said female mold member being of a box-shaped structure comprising two pairs of confronting peripheral wall segments and a single bottom, said peripheral wall segments being pivotally supported on said bottom by pivot shafts disposed outwardly of and extending parallel to edges of the bottom, said peripheral wall segments being angularly movable between an open position in which they are open outwardly and a closed position in which they engage said bottom and adjacent ones of said peripheral wall segments to form a female mold. The blow molding mold of this document, however, has the disadvantage that again the molded product has burrs on all four corners thereof. Therefore, the product needs to be improved for its commercial value. It is, therefore, an object of the present invention to provide a blow molding mold of a relatively simple structure, which can manufacture a double-walled product in which little burrs are reduced or even prevented when the peripheral wall segments are erected, so that the corners of the molded product can easily be treated subsequently and neatly be finished for increased commercial value, and molded products can be manufactured with a better yield. This object is achieved by the characterising features of claim 1. The sub-claims contain preferred embodiments of the present invention. The above and other objects features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a female mold member of a mold according to an embodiment of the present invention; FIG. 2 is a cross-sectional view taken along line II - II of FIG. 1; FIG. 3 is a cross-sectional view of a blow-molding apparatus which employs the mold with peripheral wall segments being inclined outwardly during a blow molding process; FIG. 4 is a cross-sectional view taken along line IV - IV of FIG. 1; FIG. 5 is a cross-sectional view of the blow molding apparatus with the peripheral wall segments being erected during the blow molding process; FIG. 6 is a plan view of the female mold member shown in FIG. 1; FIG. 7 is a perspective view of a female mold member according to another embodiment of the present invention; FIG. 8 is a plan view of the female mold member shown in FIG. 7; FIG. 9 is a fragmentary plan view of a female mold member according to still another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Like or corresponding parts are denoted by like or corresponding reference characters throughout views. FIGS. 1 through 6 show a blow molding apparatus employing a mold according to an embodiment of the present invention. As shown in FIGS. 3 and 5, the mold comprises a female mold member 10 and a male mold member 20 which are fixedly mounted on a pair of support plates 30a, 30b, respectively, of a mold clamping device of the blow molding apparatus. As shown in FIGS. 1 and 6, the female mold member 10 comprises a bottom 11 and four peripheral wall segments 12a, 12b, 12c, 12d, confronting two of these peripheral wall segments being operable as a pair. The peripheral wall segments 12a, 12b, 12c, 12d are swingable or angularly movable outwardly from a closed position in which they form a box as shown in FIGS. 4, 5, and 6, about pivot shafts 13a, 13b, 13c, 13d, respectively. The pivot shafts 13a, 13b, 13c, 13d are positioned outwardly of and extend parallel to the respective side edges of the bottom 11, and join the peripheral wall segments 12a, 12b, 12c, 12d angularly movably to the bottom 11. The peripheral wall segments 12a, 12b, 12c, 12d can be angularly moved by respective fluid-pressure or hydraulic actuator in the form of cylinder units 14a, 14b, 14c, 14d connected between the peripheral wall segments 12a, 12b, 12c, 12d and the bottom 11. The paired peripheral wall segments 12b, 12d have pairs of parison corner expansion prevention walls 15b, 15d, respectively, disposed on their opposite sides and extending parallel to the direction in which a parison (described later on) will be supplied. The corner expansion prevention walls 15b, 15d in each pair project away from each other. In this embodiment, the peripheral wall segments 12b, 12d and the corner expansion prevention walls 15b, 15d lie substantially flush with each other as having substantially two-dimensional (flat) surfaces. The male mold member 20 shown in FIGS. 3 and 5 is of a known structure comprising a single block or a plurality of blocks. If the male mold member 20 is composed of a plurality of blocks, some of the blocks may move back and forth when the mold members 10, 20 are clamped. The male mold member 20 has a needle-shaped air supply/discharge nozzle 21 for being inserted into a parison, and a blow injection needle 22. However, only the air supply/discharge nozzle 21 may be provided, and the blow injection needle 22 may be dispensed with. A pair of parison pinching members 41 (FIG. 5) serves to flatten and fuse a portion of an extrusion-molded or injection-molded melted parison P transversely. The blow molding apparatus shown in FIGS. 1 through 6 operates as follows: The mold members 10, 20 are first fixedly mounted on the support plates 30a, 30b, respectively, in confronting relation to each other. At this time, the peripheral wall segments 12b, 12d with the corner expansion prevention walls 15b, 15d joined thereto are oriented parallel to the direction in which the parison P is supplied into the blow molding apparatus. More specifically, when the mold members 10, 20 are installed on the support plates 30a, 30b with mating faces 16, 26 (FIG. 5) of the mold members 10, 20 being directed vertically or obliquely (at an angle smaller than 50 to the vertical plane), the peripheral wall segments 12b, 12d are horizontally spaced from each other and the peripheral wall segments 12a, 12c are vertically spaced from each other. When a melted tubular parison P is to be supplied from a blow head 40 of an extrusion or injection molding machine, the support plates 30a, 30b are displaced from each other to space the mold members 10, 20 away from each other, and the peripheral wall segments 12a, 12b, 12c, 12d of the female mold member 10 are opened, i.e., angularly displaced outwardly in horizontal and vertical directions by the respective hydraulic actuators 14a, 14b, 14c, 14d. At this time, the opposite side edges of the vertically spaced peripheral wall segments 12a, 12c are positioned very closely to the walls 15b, 15d joined to the horizontally spaced peripheral wall segments 12b, 12d. In other words, the wall segments 12b, 12d are erected to some extent. Then, the parison P is extruded from the blow head 40 into a position between the mold members 10, 20. The leading end of the parison P is temporarily pinched by the parison pinching members 41 so that the leading end of the parison P is sealed off. Then the parison pinching members 41 are moved away from each other to release the parison P. Air is supplied from a second air supply/discharge nozzle 42 (FIG. 5) opening into the parison P so that the inner wall surfaces of the parison P will not adhere to each other. The parison P as it is extruded is moved along the inner surfaces of the peripheral wall segments 12b, 12d and positioned therebetween. After the parison P has completely been placed between the peripheral wall segments 12b, 12d, the trailing end of the parison P is sealed off by the parison pinching members 41. Thereafter, one or both of the support plates 30a, 30b are moved to displace the mold members 10, 20 toward each other until the parison P is lightly sandwiched between a projecting face 27 of the mold member 20 and an inner surface of the bottom 11 of the mold member 10 and the parison P is pierced by the air supply/discharge nozzle 21 on the mold member 20. The mold members 10, 20 are further moved toward each other to flatten the parison P. When the parison P is flattened to a desired size, the mold members 10, 20 are stopped temporarily. While regulating the air pressure in the parison P, the hydraulic actuators 14a, 14b, 14c, 14d are simultaneously operated to erect the peripheral wall segments 12a, 12b, 12c, 12d slowly. During this time, the layer of the parison P which faces the female mold member 10 is brought into contact with the inner surfaces of the bottom 11 and the peripheral wall segments 12a, 12b, 12c, 12d. The parison P may also contact with the corner expansion prevention walls 15b, 15d. As the peripheral wall segments 12a, 12b, 12c, 12d are progressively erected with respect to the bottom 11, the layer of the parison P which faces the male mold member 20 is also brought into wider contact with a main wall surface 28 of the mold member 20. The peripheral wall segments 12a, 12b, 12c, 12d are finally pressed against each other along their adjacent edges, and also against the adjoining side edges of the bottom 11. Portions of the parison P which are positioned along the adjacent edges of the peripheral wall segments 12a, 12b, 12c, 12d are borne by the corner expansion prevention walls 15b, 15d fully or substantially fully against outward expansion. These portions of the parison P may be wrinkled along the edges of the peripheral wall segments 12a, 12b, 12c, 12d, projecting into the parison P or increasing the wall thickness of the parison P. Since the parison P is not pinched between the adjacent peripheral wall segments 12a, 12b, 12c, 12d, no burr is formed on the parison P by these peripheral wall segments. Then, the support plates 30a, 30b are further moved toward each other to press the mating surfaces 16, 26 against each other. Any excessive parison layer then forms burrs between these mating surfaces 16, 26. Remaining air between the parison P and the mold members 10, 20 is removed, and air under pressure is injected from the air supply/discharge nozzle 21 or the blow injection needle 22 to inflate the parison P along the inner surfaces of the mold members 10, 20. Thereafter, the mold members 10, 20 with the parison P therebetween are cooled, the mold members 10, 20 are separated away from each other, and the peripheral wall segments 12a, 12b, 12c, 12d are opened or angularly moved outwardly by the respective hydraulic actuators 14a, 14b, 14c, 14d, after which the molded product is removed from the mold members 10, 20. The molded product of a double-walled construction has burrs on its edge around the open end thereof. Therefore, such burrs are removed. If any burrs are present on the corner edges between side panels of the product and the edges between the bottom panel and side panels thereof, such burrs are also removed. After the molded product has been deburred, it is presented as a finished product. In another blow molding process, the parison P may be supplied between the mold members 10, 20 in a direction across the peripheral wall segments 12b, 12d, i.e., the corner expansion prevention walls 15b, 15d joined thereto, and the support plates 30a, 30b may be vertically movable toward and away from each other. In this blow molding process, the support plate 30a lied horizontally as shown in FIG. 4. More specifically, the parison P is horizontally supplied toward the mold members 10, 20, and then over one of the peripheral wall segments 12b, 12d which are open and along the inner surfaces of the bottom 11 and the peripheral wall segments 12b, 12d. Thereafter, the blow molding process is carried out as described above. FIGS. 7 and 8 show a female mold member according to another embodiment of the present invention. The female mold member 10 shown in FIGS. 7 and 8 differs from the female mold member 10 shown in FIG. 1 in that corner expansion prevention walls 15b, 15d have partly conical or inwardly concave inner surfaces, the inner edges of which lie substantially flush with the inner surfaces of the peripheral wall segments 12b, 12d. In a blow molding process, the peripheral wall segments 12b, 12d are tilted more outwardly than those illustrated in FIG. 1. FIG. 9 fragmentarily shows a female mold member in accordance with still another embodiment of the present invention. The female mold member shown in FIG. 9 is substantially the same as the female mold member shown in FIGS. 7 and 8 except that each of corner expansion prevention walls 15b, 15d has a number of air outlet holes 19 defined therethrough and extending between its inner and outer surfaces. The air outlet holes 19 are connected to a pressurized air source 50 through a control valve 51. While the peripheral wall segments 12a, 12b, 12c, 12d are being tilted inwardly from an outwardly open position until adjacent ones of the peripheral wall segments 12a, 12b, 12c, 12d are pressed against each other, warm air supplied from the pressurized air source 50 is injected through the air outlet holes 19 into the female mold member. When the air is thus supplied, the layers, near the walls 15b, 15d, of the parison placed in the female mold member are kept out of contact with the walls 15b, 15d by the dynamic pressure and layer of the supplied air, and hence will not form burrs thereon. With the foregoing embodiments, since the peripheral wall segments of the female mold member are pivotally tiltable outwardly with respect to the bottom, the parison can be supplied between the male and female mold members with the peripheral wall segments opened outwardly. In operation, the parison as it is supplied is first brought into contact with the bottom and then held by the female mold member so as to face the male mold member. When the peripheral wall segments are lifted with respect to the bottom, they are brought into contact with the parison through a greater area of contact. Even when the peripheral wall segments are opened outwardly, gaps or spaces therebetween are closed by the corner expansion prevention surfaces or walls, which thus prevent the parison from being expanded between these corner expansion prevention walls. When the peripheral wall segments are fully erected with respect to the bottom, the corner expansion prevention walls hold the corresponding parison layers, reducing burrs on the parison. Alternatively, by regulating the air pressure in the parison, any burrs are prevented from being formed on the molded product at its corners and edges except the open end thereof. The edges between the peripheral walls or panels of the molded product are rendered strong since they are thick or wrinkled inwardly. The edges and corners of the molded product are not reduced in thickness, but the molded product has a substantially uniform wall thickness. Inasmuch as few burrs are formed on the product, the process is deburring the product is simplified and the material can be utilized efficiently. The female mold member shown in FIGS. 1 through 6 can easily be manufactured since the corner expansion prevention walls are simple in configuration. The female mold member shown in FIGS. 7 and 9 is advantageous in that the peripheral wall segments with the corner expansion prevention walls joined thereto can also be opened largely in the outward direction, and when the peripheral wall segments are opened, they are interconnected by the corner expansion prevention walls to prevent the parson from being overly expanded at the corners. Moreover, the peripheral wall segments are tiltable through a larger angle to form a molded product of a deeper double-walled construction. The peripheral wall segments may have substantially uniform surfaces, and may be attached to the support plate in an angular position which is 90 different from that shown in FIGS. 2 and 3. With the embodiment shown in FIG. 9, the corners of the parison are supported by the dynamic pressure or layer of air supplied from the air outlet holes, making the parison free of burrs. As the air outlet holes are connected to the pressurized air source through the control valve, the pressure of air to be supplied from the air outlet holes can be adjusted to a suitable level depending on the thickness, material, and shape of a parison to be introduced into the blow molding apparatus.

Claims: A blow molding mold for a hollow doubled-walled product, comprising a pair of male (20) and female (10) mold members for holding a parison (P) therebetween, said male and female mold members (20,10) being movable toward and away from each other and having respective inner surfaces for shaping inner and outer layers of the parison (P) therealong under the pressure of air injected into the parison (P), said female mold member (10) being of a box-shaped structure comprising two pairs of confronting peripheral wall segments (12a, 12b, 12c, 12d) and a single bottom (11), said peripheral wall segments (12a, 12b, 12c, 12d) being pivotally supported on said bottom (11) by pivot shafts (13a, 13b, 13c, 13d) disposed outwardly of and extending parallel to edges of the bottom (11), said peripheral wall segments (12a, 12b, 12c, 12d) being angularly movable between an open position in which they are open outwardly and a closed position in which they engage said bottom (11) and adjacent ones of said peripheral wall segments (12a, 12b, 12c, 12d) to form a female mold (10), characterised in that one of said pair of peripheral wall segments (12b, 12d) having walls (15b, 15d) for preventing expansion of the parison (P) at the corners of said female mold member (10), said walls (15b, 15d) being joined to opposite sides thereof and extending to a predetermined dimension in a direction in which the parison (P) is supplied between the male and the female mold members (20, 10). A blow molding mold according to claim 1, wherein said one pair of peripheral wall segments (12b,12d) extends parallel to said direction in which the parison (P) is supplied. A blow molding mold according to claim 1, wherein said one pair of peripheral wall segments (12b, 12d) extends perpendicularly to said direction in which the parison (P) is supplied. A blow molding mold according to claim 1, wherein said male mold member (20) has an outer surface which is spaced a predetermined distance from said peripheral wall segments (12a, 12b, 12c, 12d) in said closed position and said bottom (11), when said male and female mold members (20, 10) are positioned closely to each other. A blow molding mold according to claim 1, wherein said predetermined distance corresponds to the thickness of a wall of the hollow double-walled product. A blow molding mold according to any one of claims 1 to 5, further including actuators for angularly moving said peripheral wall segments (12a, 12b, 12c, 12d), said actuators being operatively connected between said support plate (30a) on which said female mold member (10) is mounted on said peripheral wall segments. A blow molding mold according to claim 1, further comprising hydraulic cylinders (14a, 14b, 14c, 14d) connected between said peripheral wall segments (12a, 12b, 12c, 12d) and said bottom (11), said peripheral wall segments (12a, 12b, 12c, 12d) being angularly movable between said open and closed position by said hydraulic cylinders (14a, 14b, 14c, 14d). A blow molding mold according to any one of claims 1 to 3, wherein each of said parison corner expansion prevention walls (15b, 15d) has an inner surface lying substantially flush with the inner surface of the peripheral wall segment (12b, 12d) to which it is joined. A blow molding mold according to any one of claims 1 to 3, wherein each of said parison corner expansion prevention walls (15b, 15d) has an inwardly concave surface, said inwardly concave surface having an inner edge lying substantially flush with the inner surface of the peripheral wall segment (12b, 12d) to which it is joined. A blow molding mold according to any one of claims 1 to 3, wherein each of said parison corner expansion prevention walls (15b, 15d) has a number of outlet holes (19) for injecting warm air into the female mold member (10). A blow molding mold according to any one of claims 1 to 10, further comprising a blow head (40) for supplying a tubular parison (P), a pair of support plates (30a, 30b) movable towards and away from each other, wherein said male and female mold members (20, 10) being detachably mounted respectively on said support plate (30a, 30b).

Inventors: KIKUCHI, MASANORI, OHTA, AKIRA
Applicants: KABUSHIKI KAISHA PLACO
Application year: 1989
Main classification: B29C49
IPC codes: B29C49