Process and apparatus for injection molding with melt filtration and mixing
A process and apparatus for injection molding of plastic material incorporate a perforated member for melt filtering and/or melt mixing during metering of plasticized material. The perforated member may be of a disk form mounted to a screw plunger provided within a machine body with the perforations arranged around the screw plunger. Impurities accumulated at the perforated member may be purged by rotating the screw plunger from a nozzle connected to the machine body via an annular recess formed at an inner surface of the machine body or directly from the machine body per se via a radial hole formed therein, when the screw plunger is in a predetermined position preferably in the most forward position, where the recess or the hole is located in the vicinity of the perforated member.
| Inventors: | Tsutsumi; Shigeru (Yonezawa, JP) |
| Assignee: | Seiki Corporation (Tokyo, JP) |
| Appl. No.: | 07/859,721 |
| Filed: | August 6, 1992 |
| PCT Filed: | January 28, 1991 |
| PCT No.: | PCT/JP91/00089 |
| 371 Date: | August 06, 1992 |
| 102(e) Date: | August 06, 1992 |
| PCT Pub. No.: | WO92/05940 |
| PCT Pub. Date: | April 16, 1992 |
| Oct 06, 1990 [WO] | PCT/JP90/01301 | |||
| Nov 16, 1990 [WO] | PCT/JP90/01503 | |||
| Current U.S. Class: | 264/328.17 ; 366/81; 366/82; 425/197; 425/207; 425/224; 425/562 |
| Current International Class: | B29C 45/20 (20060101); B29C 45/46 (20060101); B29C 45/52 (20060101); B29C 45/24 (20060101); B29C 045/24 (); B29C 045/52 () |
| Field of Search: | 264/328.1,328.16,37,328.17 425/197,204,207,582,583,587,562,563,224 366/81,82 |
| 3335461 | August 1967 | Schwartz |
| 3710988 | January 1973 | Moslo |
| 4112516 | September 1978 | Hotz |
| 4512733 | April 1985 | Eichlseder et al. |
| 4627916 | December 1986 | Dorsam |
| 4966539 | October 1990 | Pena |
| 0172925 | Mar., 1986 | EP | |||
| 2524746 | Dec., 1976 | DE | |||
| 2541738 | Mar., 1977 | DE | |||
| 1242329 | Aug., 1960 | FR | |||
| 1553319 | Jan., 1969 | FR | |||
| 2324443 | Apr., 1977 | FR | |||
| 9003879 | Apr., 1990 | WO | |||
Primary Examiner: Heitbrink; Jill L. Attorney, Agent or Firm: Kenyon & Kenyon
I claim:
1. A process of injection molding with melt filtration in a series of shot cycles, using an injection machine having a body provided with an injection screw plunger therein and a hollow extension, comprising a nozzle therefrom forming a nozzle passage, and a mold arrangement defining a cavity, the mold arrangement incorporated with the machine to communicate between the interior of the machine body and the mold cavity via the nozzle passage, the process comprising steps of:
having a plastic material, in every shot cycle, plasticized and metered while being heated within the machine body;
having the hot plasticized material injected under pressure toward and into the mold cavity through the nozzle passage; and
having the hot injected material held at least partially within the entire mold cavity under pressure while the mold arrangement is being cooled to thereby provide and freeze a molded article therein,
wherein said plasticizing and metering step is carried out such that the plasticized material is subjected to said melt filtration during the metering by passing the plasticized and metered material through a filter, the filter being mounted to a plasticizing and metering screw plunger,
characterized in that the melt with impurities accumulated adjacent and upstream of the filter is intentionally discharged from the machine body, when the filter is in a predetermined position with the screw plunger being intentionally rotated to move the melt with impurities toward the predetermined position, and with the machine body being provided with a by-pass passage at said position through which the melt can pass by the filter for discharge out of the machine body.
2. A process of injection molding with melt filtration according to claim 1, wherein said by-pass passage is provided by a radial recess formed at an inner surface of the machine body, and the melt is discharged from an axial outlet of the machine body defined by said nozzle through said recess where the melt is allowed to axially pass over the filter.
3. A process of injection molding with melt filtration according to claim 1, wherein said by-pass passage is provided by a radial hole formed in the machine body, and the melt is discharged from said radial hole at a position in the vicinity and upstream of the filter, when said radial hole is intentionally opened.
4. A process of injection molding with melt filtration according to any one of claims 1 to 3, wherein: the nozzle passage is interrupted midway therealong from communication between the interior of the machine body and the mold cavity, after said injection step but while said material pressure-holding step is being carried out; and upon or after said nozzle passage interruption, said plasticizing and metering step is carried out by the injection machine for a next shot or injection with the plasticized material subjected to said melt filtration during said pressure-holding step.
5. A process of injection molding with melt filtration according to claim 4, wherein in said pressure-holding step a closed space consisting of the cavity and a forward portion of the nozzle passage leading thereto is fixed in volume with said nozzle passage interruption to thereby have the injected material compacted therein exert an internal holding pressure.
6. A process of injection molding with melt filtration according to claim 5, wherein the material compacted in said fixed closed space in each shot is adjusted to a predetermined value in amount upon or after said nozzle passage interruption by discharging a possible excess part of the compacted material out of the machine system.
7. A process of injection molding with melt filtration according to claim 4, wherein:
a piston-cylinder is used in association with said nozzle passage so that a closed space variable in volume according to a piston stroke is defined by a combination of the cavity and said nozzle passage, or said combination with said piston-cylinder, with said nozzle passage interruption; and in said pressure-holding step the injected material compacted in said closed variable space is subjected to an external holding pressure by said piston-cylinder upon said nozzle passage interruption.
8. A process of injection molding with melt filtration according to claim 1, wherein said melt filtration is effected using a perforated filtering means which is likely to clog with impurities, and while said nozzle passage interruption is intentionally effected, the plasticized material is pressurized against the closed valve means by an instantaneous forward axial movement of the metering screw plunger to thereby have possible impurities clogging the perforated filtering means pressurized rearwardly in order to release the perforated filtering means from the clogging.
9. A process of injection molding with melt filtration according to claim 1, wherein the plasticizing and metering screw plunger also serves as an injection screw plunger by axial movement in a direction opposite to that of the metering movement.
10. A process for injection molding with melt filtration, comprising the steps of:
providing an injection molding machine having a machine body for receiving a material to be heated, plasticized and metered;
providing a plasticizing and metering screw having a filter mounted thereon, the plasticizing and metering screw being controllable to move axially through the machine body to plasticize and meter the material and to rotate about its axis to cause movement of material relative to the machine body;
heating the material received within the machine body;
utilizing the plasticizing and metering screw to plasticize and meter the heated material by moving the plasticizing and metering screw axially through the machine body in a metering direction;
utilizing the axial movement of the plasticizing and metering screw to cause the heated material to pass through the filter during metering of the heated material, to filter and remove impurities from the heated material and accumulate the impurities on an upstream side of the filter;
providing a by-pass passage in the machine body for discharge of the accumulated impurities from the machine body, the by-pass passage being arranged at a position in the machine body to cause the accumulated impurities to by-pass the filter and discharge from the machine body through the by-pass passage when the plasticizing and metering screw is positioned at a preselected impurities discharge position and the impurities are caused to flow axially within the machine body; and
rotating the plasticizing and metering screw about its axis when the plasticizing and metering screw is positioned at the preselected impurities discharge position to cause the accumulated impurities to flow axially within the body, by-pass the filter and discharge from the machine via the by-pass passage.
11. A process for injection molding with melt filtration, comprising the steps of:
providing an injection molding machine having a machine body for receiving a material to be heated, plasticized and metered;
providing a plasticizing and metering screw having a filter mounted thereon, the plasticizing and metering screw being controllable to meter the material;
utilizing the plasticizing and metering screw to plasticize and meter the heated material by moving the plasticizing and metering screw axially through the machine body in a metering direction;
utilizing the axial movement of the plasticizing and metering screw to cause the heated material to pass through the filter during metering of the heated material, to filter and remove impurities from the heated material and accumulate the impurities;
providing a by-pass passage in the machine body for discharge of the accumulated impurities from the machine body, the by-pass passage being arranged at a position in the machine body to cause the accumulated impurities to by-pass the filter and discharge from the machine body through the by-pass passage; and
purging the impurities from the machine body by causing the impurities to flow through the by-pass passage.
12. An injection machine for molding with melt filtration having a body provided with means for plasticizing, metering and injecting plastic material, the means for plasticizing comprising a screw rotatable in a cylindrical barrel,
characterized in that the screw is provided at its forward end with a filter for filtering impurities from the plasticized material as it is metered, and the cylindrical barrel is provided with a purging hole with means for opening and closing the hole, the hole being in a position which, in a purging operation for removal of the filtered impurities from the machine is adjacent the upstream side of the filter.
13. An injection machine for molding with melt filtration having a body provided with means for plasticizing, metering and injecting plastic material, the means for plasticizing comprising a screw rotatable in a cylindrical barrel, and a nozzle connected to the body,
characterized in that the screw is provided at its forward end with a filter for filtering impurities from the plasticized material as it is metered, and the cylindrical barrel has an annular recess at its inner surface, the recess being in a position where, in a purging operation of removal of the filtered impurities from the machine through a nozzle, the filter is received in the recess with a radial space gap between a periphery of the filter and a bottom face of the recess to thereby allow the filtered impurities to pass over the filter through the space gap.
14. An injection machine for carrying out plasticizing, metering and injecting steps of injection molding with a plastic material supplied therein, comprising a machine body forming a cylindrical barrel provided with a heating means, an exit passage and a screw plunger therein of a rod form with a helical screw thereabout for rotation and axially reciprocating movements, said screw plunger having a tip head portion and a main screw portion with a check valve therebetween, said check valve comprising a valve body member and a front valve abutment member and a rear valve seat member between which the valve body member is movably disposed and being provided to be opened for allowing a plasticized material to flow forwardly therethrough during the plasticizing and metering step where said screw plunger is allowed to move rearwardly against a back pressure with metered material being accumulated in an axially variable space downstream of said tip head portion, and to be closed for allowing said screw plunger to push the entire amount of the accumulated material forwardly through the exit passage for injection,
characterized in that a filter for effecting melt filtration while the plasticized material is subjected to the metering is provided on said screw plunger so that the filter is carried through the melt by rearward movement of the screw plunger during metering, and said melt filtering means comprises a perforated member having circumferentially arranged perforations for the filtration, and mounted to said screw plunger and slidably fitted to an inner surface of said barrel, and a radially extending purging hole formed in a cylindrical wall of said barrel with a means for opening and closing said purging hole, said purging hole being located in an axial position so that it opens to a local space zone of the interior of said barrel in the vicinity of a rear face of said perforated member, when said screw plunger is in the most forward axial position, in order to have the plasticized material, with non-filtered or residual foreign material or impurities accumulated on said perforated rear face, in said local space, discharged therefrom, intermittently during a long run molding operation, through said purging hole by rotating said screw plunger in the most forward position thereof.
15. An injection machine according to claim 14, wherein said valve body member forms said perforated member.
16. An injection machine according to claim 14, wherein said rear valve seat member forms said perforated member.
17. An injection machine according to claim 14, wherein said front valve seat member forms said perforated member.
18. An injection machine according to claim 14, wherein a member separate from the check valve and located upstream thereof provides said perforated member.
19. An injection machine according to claim 14, wherein said check valve is of a back-flow type with said valve body member forming an annular ring, and said front valve abutment member forming said tip head portion of said screw plunger, and said melt filtering means comprises said rear valve seat member having circumferentially arranged perforations for the filtration and being mounted to said screw plunger between said valve body member and said main screw portion to provide a valve seat for said valve body member, said perforations being positioned to communicate with both an annular valve passage of said check valve defined between a section of said screw plunger and said annular valve body member of solid form and a plasticizing space defined between said main screw plunger portion and said barrel, in which space the plastic material is plasticized by rotating said screw plunger, both said rear valve seat member and valve body member being slidably fitted to an internal surface of said barrel.
20. An injection machine according to claim 19, wherein said main screw portion of said plunger is an axially extending rod having a screw projection extending radially from a periphery thereof and extending helically thereabout, and said rear valve seat member has a peripheral portion extending radially from a level of the rod periphery, said peripheral portion having a conical face, as said rear face, which converges in a rearward direction and is exposed to said plasticizing space with a helical groove formed thereon, said perforations being arranged in said helical groove therealong, said radial purging hole being located in the vicinity of a periphery of said conical face when said screw plunger is in the most forward position.
21. An injection machine according to claim 14, wherein said check valve is of a back-flow type with said valve body member forming an annular ring, and said front valve abutment member forming said tip head portion of said screw plunger, and said melt filtering means comprises: said annular valve body member having circumferentially arranged perforations for the filtration and being axially slidably mounted to said screw plunger; and said circumferential rear valve seat member of a solid form being fixed to said screw plunger and slibably fitted to an internal surface of said barrel, said perforated valve body member being slidably fitted to both the internal barrel surface and a peripheral rod surface of said screw plunger with said preformations allowing the plasticized material to pass therethrough to thereby have the material pass through said check valve at an opened position thereof.
22. An injection machine according to claim 21, wherein said rear solid valve seat member has a circumferential axial projection extending forwardly, said circumferential projection providing said valve seat of a circumferential form and defining an annular recess about said screw plunger, and being radially positioned so that all of said valve body perforations are covered by said annular recess and opened to a local space zone defined thereby when said check valve is in the closed position with said circumferential valve seat abutting against said valve body member.
23. An injection machine according to any one of claims 12 to 22, comprising a second cylindrical barrel inclined to the first-mentioned cylindrical barrel, the two barrels being connected by a passage through which filtered plastic material in the first-mentioned barrel can be transferred by the screw into the second barrel which is provided with a piston or a screw plunger for injection of the transferred plastic material into a mold.
24. An injection machine for carrying out plasticizing, metering and injecting steps of injection molding with a plastic material supplied therein, comprising a machine body forming a cylindrical barrel provided with a heating means, an exit passage and a screw plunger therein of a rod form with a helical screw thereabout for rotation and axially reciprocating movements, said screw plunger having a tip head portion and a main screw portion with a check valve therebetween, said check valve comprising a valve body member and a front valve abutment member and a rear valve seat member between which the valve body member is movably disposed and being provided to be opened for allowing a plasticized material to flow forwardly therethrough during the plasticizing and metering step where said screw plunger is allowed to move rearwardly against a back pressure with metered material being accumulated in an axially variable space downstream of said tip head portion, and to be closed for allowing said screw plunger to push the entire amount of the accumulated material forwardly through the exit passage for injection,
characterized in that a filter for effecting melt filtration while the plasticized material is subjected to the metering is provided on said screw plunger so that the filter is carried through the melt by rearward movement of the screw plunger during metering, and said barrel is provided with a nozzle, and said melt filter comprises a perforated member having circumferentially arranged perforations for the filtration, and mounted to said screw plunger and slidably fitted to an inner surface of said barrel, and an annular purging recess formed at the inner barrel surface, said purging recess having an annular bottom face and being located in an axial position so that it provides an annular space gap between a periphery of said filter and said bottom recess face when said screw plunger is in the most forward axial position, said annular space gap allowing the plasticized material, with non-filtered or residual foreign materials or impunities accumulated on a rear face of said filter, to pass over said filter toward said nozzle through said annular space gap when said screw plunger is rotated, to thereby discharge the accumulated impurities from said nozzle.
25. An injection machine, which comprises:
a machine body having an interior for receiving a material to be heated, metered and plastisized;
a metering screw plunger arranged in the interior of the machine body for controlled axial movement within the interior to meter the material and controlled rotational movement to cause conveyance of the material within the interior of the machine body;
a filter mounted on the metering screw plunger to remove impurities from the material as the meter screw plunger meters the material; and
a by-pass passage formed in the machine body for controllably purging the impurities from the interior by controlled rotational movement of the metering screw plunger to convey material with impurities from the interior via the by-pass passage.
26. An injection machine, which comprises:
a machine body having an interior for receiving a material to be heated, metered and plastisized;
a metering screw plunger arranged in the interior of the machine body for metering the material;
a filter mounted on the metering screw plunger to remove impurities from the material as the meter screw plunger meters the material; and
a by-pass passage formed in the machine body for purging the impurities from the interior of the machine body.
TECHNICAL FIELD
The present invention relates to a process and apparatus for materials improved to provide effective melt filtration and mixing.
BACKGROUND ART
As described in, for example, U.S. Pat. No. 3,767,056, with an injection molding of plastic material in an injection molding apparatus, it is desired to filter hot running plastic to remove impurities or foreign materials, bits of unmelted plastic and the like during an injection step where the hot plastic material is forced to run toward a mold cavity. Otherwise, clogging of a melt passage leading to a mold cavity with such impurities is likely to occur with the result that a long run operation of injection molding is interrupted. This interruption may require replacement of a hot or cold runner mold and/or a manifold forming a section of the melt passage, and such replacement leads to an increased equipment or machine cost, and also leads to a reduction in molding productivity since the continuously repeated injection molding operation is interrupted.
In this regard, prior arts including the above U.S. patent incorporate melt filtering devices provided in a nozzle detachably connected to a barrel forming a body of the injection machine. The filtering device comprises a tubular member having a plurality of round or elongated perforations formed therethrough in a parallel and spaced relation The perforated tubular member is disposed in or connected to the nozzle so that the perforations communicate with the nozzle.
According to some of the prior arts, such a melt filtering device or means is provided with a means for purging the impurities accumulated upstream of, but in the vicinity of, the perforations, as needed. Such a purging operation, for example, is performed with the melt including the accumulated impurities discharged out of an outlet of the nozzle without passing through the perforations. This requires detachment of the nozzle with the barrel from a mold arrangement defining the mold cavity, and thus requires a relatively long period of time to reset up the injection molding machine for a normal injection molding operation.
In the meantime, it is noted that the conventional melt filtering device has an inherent problem in that it is subjected to a high pressure loss or exhibits a high pressure resistance against a hot plasticized material, the so called "melt", in the process of injection. Such a high pressure loss due to the filtration is increased as filtration performance is increased and also as an injection rate or speed is increased. The filtration performance relies on a size of the perforations.
With a nozzle provided with no such melt filtering device, an injection molding apparatus comprising a mold arrangement, including a cavity mold and a hot runner mold and/or a manifold, and an injection machine having the nozzle, is required to be subjected to a high fluid pressure loss or exert an injection pressure, for example, of 100 kg/cm.sup.2 to attain a desired injection rate. In this connection, the same injection molding apparatus but with a melt filtering device provided in the nozzle is required to exert a higher injection pressure of 115 or more kg/cm.sup.2 to attain the same injection rate. The increase in the injection pressure is due to the flow resistance of the melt filtering device, and with a higher injection rate an increased injection power is required accordingly. The higher injection power, naturally, requires an increased driving power to be exerted by the injection machine. This results in that some cases require a more powerful hydraulic driving apparatus to be incorporated in the injection machine for driving a screw plunger disposed in the barrel for rotation and axial reciprocation, resulting in increased machine cost.
Otherwise, or in a less powerful machine case, an apparatus with melt filtering means is likely to operate with an injection rate lower (for example, 60 to 65 g/sec) than that (for example, 70 g/sec) of the same apparatus but with melt filtering nozzle means provided. Such a decreased injection rate in the non-filtering apparatus affects production of a high quality molded article, particularly a thin product having a complicated contour.
Apart from the above, there is a problem in that it is not easy to provide a molded product, which is of a high quality due to a uniform distribution of different plastic materials and/or coloring pigments or the like therein. To solve the problem, there have been various efforts made in designing a screw plunger and providing starting materials which consist of a plurality of materials well mixed with each other in advance for enhancing the distribution degree of the materials in a molded product.
DISCLOSURE OF THE INVENTION
A first object of the present invention is to provide a process and apparatus for injection molding of plastic material with improved melt filtration for removing possible impurities contained in a plasticized material, which melt filtration is effected with no substantial increase in driving power for injection relative to a case where no melt filtration is effected.
A second object of the present invention is to provide a process and apparatus for injection molding of plastic material with improved melt filtering means which facilitates purging of accumulated impurities out of the machine system, and also removing impurities clogging the filtering means therefrom, resulting in increased long run productivity due to a decreased period of time during which temporary stopping of the operational run is effected for the purging and/or the removing and then for resetting the apparatus for normal injection molding operation. Both the purging and removing processes can be performed without substantially disassembling any part of the apparatus.
A third object of the present invention is to provide a means for admixing a variety of materials incorporated in an injection machine with a screw plunger before injection of the materials toward a mold cavity to thereby provide a molded product with a distribution of the materials therein mixed well with each other.
According to the present invention, there is provided a process of injection molding with melt filtration, using an injection machine having a body provided there with means for plasticizing, metering and injecting plastic material and a hollow extension, comprising a nozzle, therefrom forming a nozzle passage, and a mold arrangement defining a cavity, the mold arrangement incorporated with the machine to communicate between the interior of the machine body and the mold cavity via the nozzle passage. The process comprises the steps of:
having a plastic material, in every shot cycle, plasticized and metered while being heated within the machine body;
having the hot plasticized material injected under pressure for the mold cavity through the nozzle passage; and
having the hot injected material held at least partially within the entire mold cavity under pressure while the mold arrangement is being cooled to thereby provide and freeze a molded article therein.
The process is characterized in that the plasticizing and metering step is carried out such that the plasticized material is subjected to the melt filtration during the metering, and the injecting step is carried out with the filtered and metered material.
In this process the melt is subjected to the filtration not by passing the melt through a filter disposed in or connected to the nozzle but by passing a filter connected to the metering means through the melt as the metering means is withdrawn in the metering stage.
The process may be carried out in an injection machine in which the means for plasticizing, metering and injecting plastic material is a single screw plunger which may be rotated and reciprocated axially in a barred formed in the machine body to plasticize, meter and inject the plastic material. Using such a machine, a process having the above characterizing feature may be applied in a universality used non-pressure-holding chamber system where the nozzle passage is kept open to the barrel after the injecting step, and the pressure-holding is effected by a screw injection plunger of the injection machine per se.
However, it is more preferable to apply the above feature using such a single barrel machine provided with a pressure-holding chamber system which effects an increased productivity due to a considerably shortened shot cycle period relative to the above universally used system. According to the pressure-holding chamber system, the nozzle passage is interrupted midway therealong from communication between the interior of the machine body and the mold cavity, after the injection step but while the material pressure-holding step is being carried out; and upon or after the nozzle passage interruption, the plasticizing and metering step is carried out by the injection machine for a next shot or injection, the plasticized material being subjected to the melt filtration during the pressure-holding step.
With respect to such a pressure-holding system, there are three kinds of systems. One kind of system is disclosed in EP 0204133Al, GB patent No. 888,448 and the like, wherein: a piston-cylinder is used in association with the nozzle passage so that a closed space variable in volume according to a piston stroke is defined by a combination of the mold cavity and the nozzle passage, or the combination with the piston-cylinder, with the nozzle passage interruption; and in the pressure-holding step the injected material compacted in the closed variable space is subjected to an external holding pressure by the piston-cylinder upon the nozzle passage interruption.
Another kind of system is disclosed in an International Application (in English) No. PCT/JP89/01052 filed by the present applicant, wherein in the pressure-holding step a closed space consisting of the cavity and a forward portion of the nozzle passage leading thereto is fixed in volume with said nozzle passage interruption to thereby have the injected material compacted therein exert an internal holding pressure.
The third kind of system is an improvement on the above second kind of system, and is disclosed in an International Application (in English) No. PCT/JP90/00300 also filed by the present applicant, wherein with the above internal pressure-holding chamber system, the material compacted in the fixed closed space in each shot is remetered or adjusted to a predetermined value in amount upon or after the nozzle passage interruption by discharging a possible excess part of the compacted material out of the machine system.
The same principle of melt filtering can be applied in an injection molding process using a machine in which there are two inclined barrel, one containing a screw plunger for plasticizing and metering the hot plastic material and the other containing means such as a piston or screw for injection into the mold cavity hot plastic material delivered into the other barrel by the metering screw plunger. In this case the process of filtering the plastic material is analogous to that described above, namely it involves passing a filter connected to the metering screw through the melt as the metering screw plunger is withdrawn in the barrel in the metering stage.
According to the present invention there is also provided an injection machine for molding with melt filtration having a body provided with means for plasticizing, metering and injecting plastic material comprising a screw rotatable in a cylindrical barrel for plasticizing the material, the screw being provided at its forward end with a filter for fitering impurities from the plasticized material as it is metered, and the barrel being provided with a purging hole in a position which in a purging operation for removal of the filtered impurities from the filter, is adjacent the upstream side of the filter.
Further, according to the present invention, there is provided an injection machine for carrying out plasticizing, metering and injecting steps of injection molding with a plastic material supplied therein, comprising a machine body forming a cylindrical barrel provided with a heating means, an exit passage and a screw plunger therein of a rod form with a helical screw thereabout for rotation and axially reciprocating movements. The screw plunger has a tip head portion and a main screw portion with a check valve therebetween. The check valve may comprise an annular valve body member slidable along the screw plunger and a circumferential valve seat member fixed on the screw plunger, and is provided to be opened for allowing a plasticized material to flow forwardly therethrough during the plasticizing and metering step where the screw plunger is allowed to move rearwardly against a back pressure with a metered material being accumulated in an axially variable space downstream of the tip head portion, and to be closed for allowing the screw plunger to push the entire amount of the accumulated material forwardly through the exit passage for injection. The tip head portion of the screw plunger may form a front valve abutment against which the valve body member abuts in an opened position of the check valve, whereas the first mentioned valve seat member which may be called "a rear valve seat member" abuts against the valve body member in a closed position of the check valve. Alternatively, such a front valve abutment may be provided as a member separate from the tip head portion, which is located adjacent to and upstream of the tip head portion.
Alternatively the check valve may be of a back-flow ring type with the valve body member forming an annular ring or of a ball check type with the valve body member being in the form of a ball.
The machine is characterized in that means for effecting a melt filtration while the plasticized material is subjected to the metering is provided in the machine body or the barrel, and is carried through the melt during metering.
The melt filtering means may comprise a perforated member mounted to the screw plunger, and preferably fitted slidably to an inner surface of the barrel, so that on rearward movement of the screw plunger the filter is carried through the melt thereby to filter it. The perforated member may be incorporated with the check valve such that it provides the above mentioned rear valve seat member, the above mentioned valve body member, or the above mentioned front valve abutment member in the following manner.
That is, the melt filtering means may comprise the rear valve seat member having circumferentially arranged perforations for the filtering and being mounted to the screw plunger between the valve body member and the main screw portion. The perforations are positioned to communicate with both an annular valve passage of the check valve between a rod section of the screw plunger and the annular valve body member of a non-perforated solid form and a plasticizing space defined between the main screw plunger portion and the barrel therein in which space the plastic material is plasticized.
Alternatively, the melt filtering means may comprise: the annular valve body member having circumferentially arranged perforations for the filtration and being axially slidably mounted to the screw plunger; and the circumferential rear valve seat member of a solid form being fixed to the screw plunger and slidably fitted to an internal surface of the barrel. The perforated valve body member is slidably fitted to both the internal barrel surface and an peripheral rod surface of the screw plunger with the perforations allowing the plasticized material to pass therethrough to thereby have the material pass through the check valve at an opened position thereof.
As a further alternative, the melt filtering means may comprise the front valve abutment member separate from the tip head portion, having circumferentially arranged perforations for the filtering and being mounted to the screw plunger between the tip head portion and the valve body member and slidably fitted to the inner surface of the barrel. The perforations form the only outlet(s) of the check valve so that the plasticized material is allowed to flow out of the check valve only through the perforations for the metering. In the alternative case where the tip head portion forms the front valve abutment, the tip head portion is designed so as to be slidably fitted to the inner surface of the barrel and have circumferentially arranged perforations for the filtering as well as the metering.
Alternatively, the melt filtering means may comprise a perforated member slidably fitted to the inner surface of the barrel, but being a member separate from the check valve and located upstream thereof, preferably adjacent thereto at a forward end of the main screw portion of the plunger with perforations circumferentially arranged for the filtration so that the filtered material is allowed to flow toward an inlet(s) of the check valve.
For each of the above mentioned filtering means, there is provided a radially extending through-hole or purging hole formed in a cylindrical wall of said barrel and means for closing and opening the purging hole. The closing and opening means may be a plug to be detachably connected to the purging hole, or a conventional shut-off valve. The purging hole is located in a axial position so that it opens to a local zone of the interior of the barrel in the vicinity of a rear face of the perforated member, when the screw plunger is in the most forward position, in order to have a portion of the plasticized material, with non-filtered impurities or residual foreign materials accumulated on the perforated rear face, in the local zone, discharged therefrom intermittently during a long run operation, through the purging hole by rotating the screw plunger in the most forward position.
The perforations may be either of a round shape cross section or an elongated shape cross section.
The screw plunger for plasticizing and metering the plastic material may also serve to inject the plastic material into the mold. Alternatively it may serve to feed the material and fitered charge of plastic material into a second barrel inclined to the barrel of the plasticizing and metering screw plunger from which second barrel it is injected by a piston or screw plunger into a mold. Such a system may or may not be a pressure holding system.
With the above-mentioned kinds of pressure-holding systems, the melt filtering means of the present invention incorporated therein is more meritorious than when incorporated in the universal non-pressure-holding system in that as described in detail later, the former case enables the valve means for interrupting the nozzle passage to be utilized so that the filtering means being clogged with impurities is released from the clogging, that is the impurities are back-flushed or removed from the filtering means by effecting a quasi-injection operation while the nozzle passage interruption is effected intentionally, whereas in the latter case such a releasing process as above cannot be performed since no corresponding nozzle passage interruption is ever effected.
Preferably, such a quasi-injection operation may be instantaneous and can also be repeated.
According to the present invention, such a filtering means as above may, of course, be mounted to the screw plunger at a position upstream or downstream of the check valves, that is, it may be incorporated with the screw plunger but not incorporated in the check valve. In a preferable case where the filter is provided at the plunger head downstream of the check valve, it may be preferable to have accumulated impunities behind the filter discharged through the nozzle, when the nozzle is separated with the machine body from the mold arrangement. In this case, in place of the above mentioned discharging hole provided in the barrel, an annular recess is formed at the forward portion of the barrel, which allows the melt with the accumulated impurities to pass over the filter through an annular gap between the filter and an annular bottom face of the recess and then to be discharged from the nozzle extended from the barrel. The removal of the impurities is effected by rotating the screw plunger, when the nozzle is intentionally separated from the mold arrangement and also the filter is positioned at the recess. Preferably the recess and the filter are in the same axial position when the screw plunger is in the most forward position.
In connection with the above, it has been found that the melt filtering means of the present invention also works as a means for effectively admixing a variety of materials supplied in the machine body through a hopper before injection of the materials.
A metering chamber variable in volume defined by the barrel and the screw plunger in the machine body receives a melt through the perforations of filter, which melt is a mixture of the materials subjected to the plasticizing. The melt enters continuously into the metering chamber in the form of a plurality of melt streams axially moving and rotating about the axis of the body, and causes an accumulated part of the melt in the chamber to be stirred or agitated in various directions including both radial and axial directions. That is, due to the filter of the present invention, the different materials in the metered melt are effectively admixed to such an extent that they are uniformly distributed in the metering chamber. In comparison with the present invention, the prior art filter mounted in the nozzle for effecting the melt filtration during the injection of the melt also functions as an agitator for the melt, but does not cause the melt to be stirred substantially in the axial direction. This is because the filtration is effected during the injection process, and thus a local leading part of the filtered melt is not allowed to be mixed with a following local part of the filtered melt in the axial direction, although local melt parts filtered at the same time may be mixed with each other due to the filter in the radial direction. In this connection, the nozzle filter of the prior art does not ensure a molded product to be provided with uniformly distributed materials in practice.
The mixing effect of the filter according to the present invention may be enhanced, if the melt streams through the perforations of the filter are forced to flow out along a shape of a cone tip head of the screw plunger. In this regard, it is preferable to have the filter mounted to the screw plunger at a position adjacent to and upstream of the cone tip head with the perforations being oriented axially but inclined along the slope face of the cone tip head.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a cross-sectional diagram showing an
injection molding apparatus of an internal pressure-holding chamber system incorporated with a melt filtering means according to the present invention;
FIG. 2 is a plan view of a perforated disk forming the melt filtering means, seen in a direction A in FIG. 1;
FIG. 3 is a cross-sectional diagram corresponding to FIG. 1, showing another injection molding apparatus of an internal pressure-holding chamber system and a remetering system in combination with a melt filtering means according to the present invention;
FIG. 4 is a cross-sectional view of a portion of an injection molding apparatus corresponding to those shown in FIGS. 1 and 3, showing an embodied combination of a check valve of a back-flow ring type and a melt filtering means according to the present invention;
FIGS. 5 and 6 are cross-sectional views, each of a portion of an injection molding apparatus corresponding to FIG. 4, showing another embodied combination of a check valve of a back-flow ring type and a melt filtering means according to the present invention; and
FIGS. 7 and 8 are cross-sectional views, each of a portion of an injection molding apparatus, corresponding to FIG. 4 or FIG. 5, showing another embodied combination of a check valve of a ball check type and a melt filtering means according to the present invention;
FIG. 9 is a cross sectional diagram showing another molding apparatus having a metering and filtering system and an internal pressure-holding chamber system corresponding to those shown in FIG. 1 and also comprising an independent injection system;
FIGS. 10A, 10B and 10C are cross-sectional views of an injection molding apparatus according to the present invention, showing another embodied melt filtering means incorporated with a screw plunger and a barrel, FIG. 10A showing plasticiging, filtering and metering processes, FIG. 10B showing an injection process, and FIG. 10C showing an impurity discharging process;
FIG. 11 is an exploded perspective view of parts forming the filter as shown in FIGS. 10A to 10C; and
FIG. 12 shows another embodiment of an injection molding machine according to the present invention with a filter modified from that of FIGS. 10A for enhancing a stirring ability of the melt filter.
BEST MODE FOR CARRYING OUT THE INVENTION
FIGS. 1 and 3 show first and second embodiments of apparatuses according to the present invention. Referring to FIGS. 1 and 3, each apparatus for injection molding of plastic material has a conventional single barrel type injection machine 1 and a mold arrangement 10 incorporated therewith. The machine 1 is axially movable for a suck-back operation and for injection, plasticizing and metering operations, and comprises a body forming a cylindrical barrel 2 having a screw plunger 3 therein, a hydraulic piston-cylinder (not shown) with a piston connected to the plunger 3, and a cylindrical hollow extension 20 extending forwardly from the barrel 2. The apparatus further comprises a hot runner mold 13 incorporated with a manifold. The hot runner mold 13 is incorporated in the mold arrangement 10 in a thermal-insulating manner involving an air spacer 13a and solid spacer 13c.
The cylindrical extension 20 is in direct contact with the hot runner mold 13 at its forward end, but is connected with the mold arrangement 10 at its forward end via a solid thermal insulator 13c.
The mold arrangement 10 comprises a stationary mold half 11 and a movable mold half 12. The stationary mold half 11 is connected to the hot runner mold 13. Both mold halves have cooling means 14 and 15, and define at least one cavity 10a for a molded article, which cavity has at least one gate 10b. The gate 10b has a pointed heat-generating module 16, such as a so called "spear", received therein to thereby have the module heat a cold part of the material at the gate temporarily and instantaneously with the effect that the gate is opened to the cavity for a next shot, after the suck-back step is completed.
The hot runner mold 13 and the module 16 incorporated therewith result in a runnerless article being molded.
The cylindrical hollow extension 20, which provides an exit passage, is divided into three parts, that is, a forward part 21 connected to the hot runner mold 13, an intermediate piston part 22 axially disposed in the forward part, and a rear part 23.
The rear part 23 forms a head portion of the barrel 2, and the intermediate piston part 22 forms a so called "nozzle" detachably connected to the head barrel portion 23. The cylindrical extension 20 is designed so that its hollow space has an enlarged diameter portion 20A, and is provided with band heaters 25 at its periphery.
The hot runner mold 13 and the cylindrical extension 20 of the machine 1 in combination form a hollow extension defining a nozzle passage Y communicating the interior of the barrel 2 with the cavity gate 10b.
The rear cylindrical extension part 23 is incorporated with a valve means 40. The nozzle passage Y provides an internal pressure-holding chamber X between the valve means 40 and the cavity gate 10b.
The intermediate piston part 22 of the cylindrical extension 20, as the "nozzle", consists of a cylindrical body and a circumferential flange 22a provided to work as a stopper against the forward part 21 at an abutting end face thereof, and also as a sealing means for preventing leakage of the hot material when the material is injected. An axial position of the nozzle 22 relative to the forward part 21 is fixed when the flange 22a abuts against the abutting end face of the forward part 21. The machine 1 with the nozzle 22 is sucked back by a predetermined stroke from the above position.
Referring to FIGS. 1 and 3, the valve means 40 comprises a driving means, for example, a pulse motor (not shown) mounted on the rear cylindrical part 23, and a circular valve rod 42 extending vertically from the motor. The rear part 23 has a vertically circular hole 30 crossing the nozzle passage Y. The valve rod 42 is rotatably disposed in the vertical hole 30, and has a horizontal through-hole 42a. The valve hole 42a forms a portion of the nozzle passage Y when the valve means 40 or the valve rod 42 is in an opened position. The valve rod 42 effects a nozzle passage interruption or a chamber closing against communication of the barrel 2 with the cavity 20a, when it is in a closed position.
Immediately after a plasticized and metered material (melt) is injected from the barrel 2 using the screw plunger 3 toward the mold cavity 10a through the nozzle passage Y, the valve means 40 is forced to a closed position by the pulse motor to effect the nozzle passage interruption and to thereby have a closed space Z, consisting of the mold cavity 10a and the chamber X, fixed in volume. As a result, most of the injected material is compacted in the closed and fixed space Z to thereby exert an internal pressure against the melt filled in the mold cavity 10a, which pressure is called an "internal holding pressure".
In marked contrast, a conventional pressure-holding chamber system, shown, for example, in U.S. Pat. No. 4,632,652, comprises a piston-cylinder device in association with a corresponding chamber X'. Upon a corresponding nozzle passage interruption, the piston-cylinder exerts an external pressure against the melt in a corresponding space Z' which is not fixed but variable in volume. In this regard, the conventional pressure-holding chamber system may be called an "external pressure-holding chamber system" relative to the "internal pressure-holding chamber system" as shown in FIGS. 1 and 3.
Both kinds of the pressure-holding chamber systems incorporated in the injection molding apparatuses have a common advantage relative to a universal non-pressure-holding chamber system where a holding pressure is exerted by an injection machine per se with a screw plunger. The common advantage resides in that a period of one shot cycle is considerably shortened, leading to an increased productivity. This is because, while an external or internal pressure-holding step is performed, the injection machine is allowed to perform a plasticizing and metering step for a next shot. Therefore, it is preferable to perform such plasticizing and metering step upon the nozzle passage interruption which is to be effected immediately after an injection step in order to minimize a period of one shot cycle in a continuing cyclic injection molding run.
The universal non-pressure-holding chamber system, where an external pressure-holding is performed by an injection machine per se using a screw plunger for use in the plasticizing and metering and the injection, is substantially equivalent to the external pressure-holding chamber system in that the pressure-holding relies on an external hydraulic driving source such as the injection machine (in the non-pressure-holding chamber system) or the additional piston-cylinder device (in the external pressure-holding system), and thus the external driving source is likely to cause the weight of a molded product to be varied due to an inevitable pressure variation in the external holding pressure.
In marked contrast, the internal pressure-holding chamber system is advantageous relative to both the above systems in that such a pressure variation as the above does not occur during the internal pressure-holding operation, and thus variation in the weight of a molded product is considerably decreased. In this regard, the internal pressure-holding chamber system can be used effectively in production of precision molded products with high productivity. In this case, generally speaking, it is preferable to have a ratio of a spacial volume of the chamber X to that of the entire mold cavity(s) designed so as to be around 1 or greater.
The first embodiment as shown in FIG. 1 has no other valve means other than the valve means 40, in association with the internal pressure-holding chamber X. The second embodiment as shown in FIG. 3, has an additional or second valve means provided in the chamber X for remetering the melt. That is, as shown in FIG. 3, the head barrel portion 23 is provided with a remetering means associated with the first mentioned valve means 40. The remetering means comprises a pressure-sensitive check valve 50 of a valve seat type in association with the first valve means 40. The valve rod 42 of the first valve means 40 has a groove 42b formed at its surface portion. The head barrel portion or the rear part 23 has an outlet hole 30a extending horizontally therefrom to open to the vertical hole 30 in such a position that the groove 42b communicates with both the chamber X and the check valve 50, when the first valve means 40 is in the closed position, and when the first valve means 40 is in the opened position, the horizontal outlet hole 30a is closed by the valve rod 42.
The check valve 50 comprises a cylindrical valve chamber 51, having a vertical or radial opening (not shown) for discharging the melt out of the system, a piston valve body 52 of a seat type, and means 53 for urging or biasing the valve body against the melt in the chamber X at a predetermined pressure. The biasing means 53 comprises an inner rod 53a abutting against the valve body 52, an outer rod 53b, coil spring 53c encircling both the rods and sandwiched by the rods, inner and outer threaded housing cylinders 53d and 53e screwed to each other to form a housing for the spring and rods, and a load cell or pressure sensor 53f connected to a free end of the outer housing cylinder 53e and extending inwardly to abut against the outer rod 53b at a rear end thereof. A force of the spring 53c is adjusted by screwing the outer housing cylinder 53e relative to the inner housing cylinder 53d. In this connection the load cell 53f is provided to detect the spring force or the predetermined pressure for the remetering.
The piston valve body 52 has a circumferential chamfered edge at its free end, which edge is to be forced by the spring 53c to abut against a counterpart circumferential outlet edge of the horizontal hole 30a. When the first valve means 40 is in the closed position, but a pressure of the melt in the closed space Z is not more than the predetermined pressure, the melt is prevented from being discharged from the discharging outlet of the second valve means 50 through the groove 42, the outlet hole 30a and the interior of the valve chamber 51, that is the second valve means 50 is kept closed. Of course, when the first valve means 40 is in the opened position, the second valve means 50 is kept closed irrespective of the melt pressure. When the first valve means 40 is in the closed position and if the melt pressure is over the predetermined valve, the second valve means 50 is forced by the melt pressure to be in the opened position against the force of the coil spring 53c to thereby allow an excess part of the melt in the space Z to be discharged out of the machine system through the above mentioned passage route until the remaining part of the melt in the space Z is balanced with or reduced to the predetermined pressure exerted by the coil spring 53c. As a result, the melt compacted in the space Z upon the nozzle passage interruption, which is effected by the first valve means 40 immediately after injection, is regulated to a predetermined pressure or metered to a
