WO1992013700A1

WO1992013700A1 - Improved hot runner mold arrangement and use thereof

Info

Publication number: WO1992013700A1
Application number: PCT/JP1991/000166
Authority: WO
Inventors: Shigeru Tsutsumi
Original assignee: Seiki Corporation
Priority date: 1991-02-12
Filing date: 1991-02-12
Publication date: 1992-08-20
Also published as: CS169991A3; JPH05507445A; PT97997A; CN1064235A

Abstract

A hot runner mold arrangement (10) with a plurality of needle valves, particularly of a spring-biased type, for opening and closing corresponding gates (11B) of mold cavities (11A) is provided, wherein each needle valve body (170) extends from the interior of the mold arrangement to the exterior thereof through a corresponding sealing hole (13F) formed therein, and a common valve driving means connected to all of the valve bodies (170) is provided outside of the mold arrangement. The mold arrangement with the spring-biased type needle valves is used preferably in injection molding of an internal pressure-holding chamber system, wherein a valve (42) provided for effecting a nozzle passage interruption with a melt pressure against a spring force exerted by the valve driving means being reduced to a level low enough to effect the gate closing.

Description

DESCRIPTION

TITLE OF THE INVENTION

Improved Hot Runner Mold Arrangement and Use Thereof

TECHNICAL FIELD The present invention relates to an improved runnerless or hot runner mold arrangement incorporated with a plurality of needle valves, particularly of a spring-biased type and a process of hot runner injection molding using the same, preferably in a pressure-holding chamber system.

BACKGROUND ART

A pressure-holding chamber system for injection molding of plastic material, and a needle valve of a spring-biased type for opening and closing gates of a mold to be used in the injection molding, are known. The spring-biased means provides a valve driving means in cooperation with a melt pressure exerted in the injection molding.

There are known valve driving means in place of that of a spring-biasing type, such as those of hydraulic, pneumatic and electro-magnetic types.

A known injection molding machine has a machine body provided with means for plasticizing, metering, and injecting plastic material, a hollow extension, comprising a nozzle therefrom forming a nozzle passage, and a mold arrangement defining a plurality of runners and cavities having gates. The mold arrangement is incorporated to communicate between the interior of the machine body and the mold cavity via the nozzle passage including the runners. The machine carries out a process of injection molding 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 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.

Using such a machine, a process having the above characterizing feature may be applied in a universally used non-pressure-holding chamber system where the nozzle passage is kept open to the machine body 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 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.

With respect to such a pressure-holding chamber system, there are three kinds of systems. One kind of system is disclosed in EP 0204133A1, 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 Interna¬ tional 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.

U.S. Patent No. 3,800,027 discloses an original pointed intermittently heat-generating module having a probe with an axial tip, and U.S. patent No. 4,643,664 discloses an improvement from the original one. The conventional module is very effective in heating a cold part of the plastic material at the axial gate temporarily and instantaneously to open the gate for the injection-molding. The cold material part is a part integrated with a molded article in the cavity but separated therefrom after the mold is opened for removal of the article, and is integrated with a hot remaining part of the material staying in a mold arrangement.

The module has a longitudinal body forming a passage for the material therein with an outlet in the vicinity of the axial tip for communicating a runner of a hot runner mold, which communicates with a nozzle of an injection machine, with the axial gate so that a hot material is allowed to flow from the nozzle to the mold cavity through the runner and the annular space gap formed in the axial gate. The cold material part fills the annular space gap, which is designed to have a small thickness relative to the axial gate or the axial tip. Therefore, the cold material part can be easily and quickly fused or melted by the instantaneous heating of the axial tip.

According to a conventional art, the above mentioned pressure-holding chamber system involves a plurality of such pointed intermittently heat-generating modules, which are incorporated in the runners in the nozzle passage, in order to carry out a hot runner injection molding for producing a plurality of runnerless molded articles at the same time. The modules require a complicated and expensive controller controlling the timing of the instantaneous heating of the tips involved. The tips are heated instantaneously and concurrently every shot cycle just before the injection. The tip heating is desired to provide the effect that a cold material at each gate is melted instantaneously and concurrently but in practice it is not easy to attain such an effect. Further there is a problem in that the cold material at the gate does not work effectively as a plug for closing the gate contrary to expectation. In this regard, it is common practice to have the nozzle withdrawn with the machine body relative to the mold arrangement to effect sucking-back, with a melt pressure in the runners being reduced to thereby prevent a dripping of the melt with the cold material at the gate from occurring when the cavity mold is opened. It is possible to enhance the plug effect of the cold material at the gate by increasing a length of the tip so that such a sucking-back operation is omitted. However, there is another problem wherein it is not easy for the longer cold material at the gate to be melted instantaneously. As a result, the longer cold material is likely to move into the cavity without being melted completely with a following hot material or melt just before the injection. This would cause the cold material to damage a molded product. Under the circumstances, it is not easy to provide the module as well as the controller at a low cost, which in combination exhibit a desired effect of closing and opening the gate without such a damage of the molded product. The above mentioned needle valve of a spring-biased type for closing and opening the gate has been applied in a non-pressure-holding chamber system. Such a valve is alternatively called "a nozzle valve", and is disclosed in many patent publications, for example, Japanese Examined Patent Publication No. 62-13889 and Japanese Unexamined Patent Publication No. 58-65639. These needle valves are mounted in a runner mold, each with an individual spring-biasing means lodged in the runner mold, and are actuated by changing a melt pressure in runners formed in the runner mold.

There is another kind of a conventional needle valve of a piston cylinder type. A plurality of oil, air, or electro-magnetic piston-cylinders are mounted in a runner mold to actuate individual needle valve bodies for closing and opening corresponding gates.

The above two kinds of needle valves have a common problem in that it is not easy in practice to syn¬ chronize the opening and a closing operations of a plurality of the valves. A failure to synchronize the valves leads to concurrently molded products in a plurality of mold cavities varying considerably in weight, or defective molded products.

There is another common problem in that, since each needle valve has the individual means for driving its needle valve body, which driving means occupies a substantial radial space, a multi-cavity mold and a runner mold are obliged to have a size in the radial direction large enough to accommodate these valves. Further, in general it is not easy to design a runner mold so as to incorporate the valve driving means in a case where the valve driving means are mounted in the runner mold.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide an improved mold arrangement for use in various kinds of hot runner injection molding, which solves the before- mentioned disadvantages of the needle valves involved in the prior arts.

Another object of the present invention is to improve a process of hot runner injection molding in a pressure-holding chamber system, for producing a plurality of runnerless molded articles concurrently, using the improved mold arrangement of the present invention.

According to the present invention, there is provided a hot runner mold arrangement incorporated with a plurality of needle valves for opening and closing corresponding gates of a plurality of mold cavities defined therein, characterized in that the needle valves have a common valve driving means provided outside of the mold arrangement. In this case, a needle valve body of each valve is provided to extend from the interior of the mold arrangement to the exterior thereof through a corresponding hole formed in the mold arrangement and has a free end forming a valve head which is to cooperate with the gate and the other end fixed to the exterior .'valve driving means.

The valve driving means may be of a hydraulic, pneumatic, electro-magnetic or spring-biased type.

With respect to the mold arrangement incorporated with the needle valves of the spring-biased type, the present invention provides the following embodied mold arrangement.

According to the present invention, a mold arrangement for use in the above-mentioned hot runner injection molding is provided, which comprises: a cavity mold defining a plurality of cavities having respective axially extending gates; a runner mold involving a manifold which is detachably connected to the cavity mold and forms a plurality of axially extending runners communicating with corresponding gates of the cavity mold and a forward axial extension of the injection machine forming a nozzle; and a plurality of needle valves of a spring-biased type provided and actuated by changing a melt pressure for opening and closing corresponding gates. Each valve comprises an axially extending valve body of a needle or probe form disposed in a corresponding runner working as a valve chamber with a radial space gap therebetween. The needle valve body has a valve head at a forward end thereof, which head cooperate a corresponding gate. Each needle valve body extends axially and rearwardly out of the runner mold through a corresponding hole formed therein, and is axially movable through the hole but is radially fitted to the hole, so as to substan¬ tially seal the hole. The plural needle valves further comprise a common means provided so as to substantially seal the hole. The plural needle valves further comprises a common means provided outside of the runner mold for biasing the needle valve bodies against a first stopper provided outside of the runner mold to thereby have the valve heads close the gates. The common biasing means may comprise: a common axially movable flange of a radially extending plate provided outside of the runner mold for biasing or urging the needle valve bodies against the stopper provided outside of the runner mold to thereby have the valve heads close the gates. Preferably the common biasing means comprises: the common axially movable flange of a radially extending plate provided outside of the runner mold from which plate the needle valve bodies extend forwardly; a common stationary spring seat of a radially extending plate form provided outside of the flange plate with an axial space gap therebetween; the above mentioned first stopper and a second stopper provided to define forward and rear axial positions of the movable flange plate corresponding to common closed and open positions of the valves, respectively; means for radially supporting and axially guiding the movable flange plate, mounted to the stationary spring seat plate; and a plurality of axially extending springs provided in the space gap between both the flange plate and the spring seat plate to bias or urge the flange plate against the first stopper relative to the spring seat plate. Radial positions of the springs are allotted appropriately over the entire front surface of the spring seat plate.

The common biasing means further comprises a means for adjusting a main spring of a coiled form in respect to an axial length thereof to thereby adjust the entire force of the springs exerted against the flange plate. The spring seat plate has a central hole in which a combination of the nozzle and a rear hollow extension of the runner mold is disposed. The flange plate has a central hole coaxial with the central hole of the spring seat plate. Preferably, the spring adjusting means comprises: an axial hollow bolt extending rearwardly from the flange plate and enclosing the central hole thereof; and an adjusting nut screwed on the bolt. The hollow bolt is encircled by the main coil spring and located in an axial space gap defined between the adjusting nut and the spring seat plate.

Preferably, the supporting and guiding means comprises a plurality of axial rods extending forwardly from the spring seat plate. At least some of the rods are encircled by the springs other than the main coil spring, which are axial springs of a coil form. The spring-encircled rods are disposed in corresponding holes formed in the flange plate in which holes they are slidably fitted.

Preferably, the other rods are of a stepped form, each having a forward portion axially movable in a corresponding hole formed in the flange plate and a rear portion forming a shoulder providing the second stopper, which is to abut against the flange plate at the open position of the valves.

A spacer means may be provided for fixing an axial position of the spring seat plate relative to the cavity mold as well as the runner mold. The spacer means has a shoulder providing the first stopper, which is to abut against the flange plate at the closed position of the valves. Preferably, each needle valve body has a threaded portion which is screwed into a corresponding threaded hole formed in the flange plate, to thereby adjust a forward portion of the valve body extending from the flange plate in respect to an axial length thereof. In order to actuate the needle valves due to different melt pressures for opening and closing the gate, respectively, each needle valve body has a forward portion forming the frustum conical tip at a forward end thereof and a neighboring enlarged portion stepped therefrom to have a larger diameter. The enlarged portion is radially fitted to a corresponding hole of the flange plate. The flange plate with all of the needle valve bodies is axially moved toward the second stopper to open all of the gates, when the injection is effected, due to a melt pressure in the runners. The melt pressure is exerted against at least a total differential cross-sectional area between the enlarged portions and the forward portion. In this connection, it is preferable to design the total differential cross-sectional area so a _*s to be large enough to generate a predetermined melt force against the entire spring force plus a frictional force generated in the valve system involved to thereby have the flange plate commence a rearward movement for opening all of the gates.

Preferably, the runner mold has a plurality of axial forward extensions, each forming a corresponding runner therein and being provided with a body heater in the vicinity of a periphery of the runner. Each gate may be formed in a corresponding forward extension, in place of a cavity mold. Each needle valve body may be provided with a body heater therein. However, if each axial forward extension of the runner mold is provided with a tip heater therein in the vicinity of a periphery of a corresponding gate, for intermittently and instantaneously heating the material, the above body heater of the valve body may not be required.

These heaters are provided in order to have a friction generated at the gate and exerted against the valve head reduced when the gate is opened.

Preferably, additional heaters are provided in the runner mold, each in the vicinity of a periphery of a corresponding hole of the runner mold to which a corresponding valve body is radially fitted, for preventing a friction generated at the hole from being enhanced. An additional heater in place of the above additional heater of the runner mold may be provided in each needle valve body at a corresponding portion thereof, which is radially fitted to the hole of the runner mold to exert the same effect as the above. T e needle valve of the present invention may be of a seat type wherein the valve head is to abut against the gate at the closed position of the valve. Alterna¬ tively, the valve may be of a spool type wherein the valve head is to be disposed in the gate and radially fitted thereto when the gate is closed. In either case, the valve head may be forced to move forwardly and enter into the cavity at the open position of the valve. However, it is more preferable for the valve head to be withdrawn rearwardly in the runner from the gate when the gate is opened. This is because the valve head does not damage a mold product, whereas the valve head of the former case damages a molded product at a portion thereof corresponding to the gate. Therefore, in the former case, the valve head is required to be as small as possible to reduce such damage.

With respect to the spool type valves, wherein each valve head is of a cylindrical rod form and a corresponding gate forms a cylindrical hole to which the rod head is radially fitted, it is preferable that the gate at its cylindrical surface has a plurality of axial grooves, arranged around its axis and formed in its rear portion so that its forward portion is allowed to communicate with a corresponding runner via the axial grooves while the rear gate portion holds the cylindrical valve head coaxially at the open position of the valves. With respect to the needle valve body, it may be of not a single member or part but two separate parts. With the single part valve body, a straight sealing hole of a runner mold has a single axis, whereas with the two part valve body a corresponding sealing hole is of stepped form having forward and rear sections eccentric from each other so that they have different axes. The forward valve body part is radially fitted to the forward hole section, and the rear valve body is disposed'in the rear hole section with a radial space gap therebetween. The valve body parts have radially extending end faces at which they abut against each other due to the melt pressure and the spring force, while the rear part is allowed to radially move relative to the forward part within a radial gap between their different axes. In this connection, the two part valve body with the stepped sealing hole is advantageous in ensuring a smooth valve operation with a reduced resistance thereagainst in a long run injection molding, in a case where the runner mold is subjected to a thermal expansion with the result that there is a relatively large difference in the thermal expansion between forward and rear members of the runner mold.

Such a differential thermal expansion is likely to cause a resistance against a reciprocating movement of the valve body through the sealing hole to be increased. With the single part valve boby, it is likely to be bent relative to its original axis due to the differential thermal expansion, whereas with the two part valve body the radial movement of the rear part relative to the forward part is allowed to occur to compensate the differential thermal expansion. So long as the stationary spring seat plate is heated or thermally well connected to the runner mold body, such a differential thermal expansion can be reduced to a level low enough to substantially ensure the smooth valve operation with the single part valve bodies. With the above mold arrangement of the present invention, the synchronizing of the gate closing is ensured at every shot cycle, and a radial space occupied by each valve in the runner mold is considerably reduced, compared with the conventional valves. That is, each runner accommodates only the needle valve bodies, since the valve biasing means is out of the runner mold. There is another advantage that the biasing means is not damaged by the melt in the runners and/or the thermal energy imparted to the runner mold. Still further, it is easy to adjust a spring force and a length of each needle valve body as needed, whereas the prior art valves do not allow such an adjustment.

The above mentioned mold arrangement of the present invention can be effectively and advantageously used in both the commonly used non-pressure-holding chamber system and the pressure-holding chamber system. In a case of the non-pressure-holding chamber system, the mold arrangement of the present invention can be used in the same manner as that in the conventional hot runner mold arrangement. In this regard, the present invention also provides use of the above mold arrangement in the pressure- holding chamber system as follows:

According to the present invention, there is a process of hot runner injection molding in the above- mentioned second kind of pressure-holding chamber system, involving at least one mold cavity having a gate, preferably many cavities, characterized in that, using a needle valve of a spring-biased type for opening and closing the gate actuated by changing a melt pressure, the gate is forced to open by injecting the material or melt with a melt pressure exerted against a combination of the spring and a friction generated in the system involved, the gate is kept open during the pressure-holding step with the melt pressure being reduced, and is closed by releasing the nozzle passage interruption to thereby further reduce the melt pressure.

In the above process, the metering is completed during the nozzle passage interruption, which is then released to have the gate closed. Alternatively, an initial substep of the metering may be carried out during the nozzle passage interruption, and a final substep of the metering is carried out upon release of the nozzle passage interruption with the gate being closed.

The process may be applied in the above-mentioned third kind of the pressure-holding chamber system when the remetering is carried out in the chamber.

In the before mentioned first kind of the pres- sure-holding chamber system, a hot runner injection molding of the present invention is characterized in that the piston-cylinder involved in the chamber is actuated to reduce a melt pressure for closing the gate. BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a cross-sectional view showing hot a runner injection molding machine of an interval pressure-holding chamber system of the present invention, wherein two embodiments of a mold arrangement involved are illustrated;

Fig. 2 is an exploded perspective view, partially showing or needle valves of a spring-biased type of the present invention incorporated in one of the embodied mold arrangements of Fig. 1;

Fig. 3 is an enlarged cross-sectional view showing a rear-portion of the needle valve shown in Fig. 1;

Fig. 4A and Fig. 4B are diagrams showing enlarged cross-sectional views of a gate of the mold arrangement and a valve head of the valve shown in Fig. 1; and Fig. 5 is a diagram partially showing another embodiment of a hot runner mold arrangement according to the present invention; and Fig. 6 is a diagram showing a combination of a gate and a valve head of a spool valve type to be incorporated in the mold arrangement of Fig. 5, and alternative patterns of grooves formed in the gate. BEST MODE FOR CARRYING OUT THE INVENTION Fig. 1 show a hot runner injection molding machine of an internal pressure-holding chamber system according to the present invention. However, with respect to a mold arrangement incorporated in the machine, two embodiments are shown at an upper part of the drawing and a lower part thereof, respectively.

Referring to Fig. 1, the hot runner injection molding machine 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 at a nozzle 22. For injection, plasticizing and metering operations, the injection machine 1 comprises a machine body forming a 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 mold arrangement 10 comprises a cavity mold 11 and a runner mold 13 incorporated with a manifold 13a therein. The cavity mold 11 consists of a stationary mold half 11a (shown) and a movable mold half (not shown), both having cooling means 14 and defining a plurality of mold cavities 11A for molded articles.

The runner mold 13 has heating means 15. Each cavity has a gate 11B. The stationary mold half of the cavity mold 11 is detachably connected to the runner mold 13. The hollow extension 20 is divided into three parts, that is a forward part 21, so called "sprue bush", an intermediate piston part 22, so called "nozzle" axially disposed in the sprue bush, and a rear part 23 connected to the nozzle 22. The cylindrical holder extension 20 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 11B.

The rear cylindrical extension part 23 is incorporated with a valve means 40. The nozzle passage Y forms an internal pressure-holding chamber X between the valve means 40 and the cavity gate lib.

The intermediate piston part 22 of the cylindrical extension 20, as the nozzle, consists of a cylindrical body and a circumferential flange 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 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. 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 11A, when it is in a closed position.

Immediately after a palsticized and metered material (melt) in injected from the barrel 2 using the screw plunger 3 toward the mold cavity 11A 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 11A 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 11A, which pressure is called an "internal holding pressure" . in marked contrast, a conventional pressure-holding chamber system (not shown) 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 Fig. 1.

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 an 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 relys 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 occurring with the external holding pressure effected.

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 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.

In another kind of internal pressure-holding chamber system, so called "remetering pressure-holding chamber system" can be embodied by modifying the embodiment of Fig. 1 so that the hollow extension 23 has an additional or second check valve means provided in the chamber X for remetering the melt. In this case. 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 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 formed at its surface portion. The head barrel portion or the rear part 23 has an outlet hole 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 second check valve, 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 is closed by the valve rod 42.

The remetering and internal pressure-holding chamber system is advantageous, relative to the non-remetering internal pressure-holding system, in that an amount of the melt injected and compacted in the space Z, which amount is likely to vary due to an operational variation in the metering in every shot cycle, is remetered or regulated to a predetermined level so that the resultant or remetered melt has a reduced amount of variation. As a result, with the remetering system, the weight of variation in a molded product is more reduced than that with the non-remetering system, and thus the remetering system is more preferable in producing a precision molded article. In the embodied machine of Fig. 1, the screw plunger 3 has a filter 3c of a perforated member between a plunger head 3a and a check valve 3b. Due to the filter 3c, a metered melt is filtered from impurities included in a plasticized melt. Referring to Figs. 1 to 3, the mold arrangement 10 further comprises a plurality of needle valves 100 of a spring-biased type. The valves 100 comprise individual needle valve bodies 110, a common movable flange plate 120, and a common stationary spring seat plate 130. The seat plate 130 has a central hole 131 coaxial with the nozzle 22, through which the sprue bush or forward portion 21 of the hollow extension 20 is in touch with the nozzle or intermediate portion 22. The sprue bush 21 is a rear extension of the runner mold 13. The runner mold 13 is connected to the seat plate 130 via spacers 140. The seat plate 130 has a plurality of guiding rods 133 screwed into the seat plate 130 and extending forwardly therefrom. The seat plate 130 also has supporting and stopping rods 134 fixed by bolts and extending forwardly from the seat plate 130.

The flange plate 120 has a central hole 121 coaxial with the nozzle 22 through which hole the spruce bush 21 extends forwardly and is fixed to the runner mold 13, guiding holes 122 for the guiding rods 133 and supporting and stopping holes 123 for the supporting and stopping rods 134. The guiding holes 122 are designed so as to have corresponding guiding rods 133 radially fitted thereto and allowed to axially move therethough. Each supporting and stopping hole 123 is designed so as to have a radial gap with a forward portion of the rod 134 therebetween. A rear portion of the rod 134 is enlarged relative to the forward portion to form a shoulder 135 providing a second stopper for the flange plate 120. Preferably the rods 134 are designed to provide other kinds of spacers between the runner mold 13 and the seat plate 130 other than the spacers 140 providing the first stopper as shown in Fig. 1. That is, in this embodiment, the first (135) and second (141) stopper are provided by two kinds of spacers between the stationary runner mold 13 and the stationary seat plate 130 for the movable flange plate 120. The flange plate 120 has a hollow bolt 125 fixed thereto and extending rearwardly therefrom with the hole 121 and the sprue bush 21 being enclosed in the hollow bolt. The bolt 125 has an adjusting nut 126 screwed thereon. In a combination of the flange plate 120 and the seat plate 130 with the rods 133 and 134 disposed into the corresponding holes 122 and 123, a main coil spring 150 and a plurality of auxial coil spring 160 are provided to encircle the hollow bolt 125 and the rods 133, respectively.

The spacers 140 have shoulders 141 providing the above mentioned first stopper for the flange plate 120. An upper half of the mold arrangement in Fig. 1 shows a case where the flange plate 120 abuts against the shoulder 141 or first stopper, while a lower half of the mold arrangement in Fig. 1 shows another case where the flange plate 120 is displaced from the stopper 141, for convenience of understanding the mold arrangement.

In the above combination of the flange plate 120 and the seat plate 130, the auxial coil springs 160 encircling the rods 133 bias the flange plate 120 and are located between the flange plate 120 and the seat plate 130, and the main coil spring 150 encircling the hollow bolt 125 and located between the adjusting nut 126 and the seat plate 130 bias the flange plate 120 forwardly against the first stopper or the shoulder 141 of the spacers 140. A force of the springs 150 and 160 in total can be adjusted by changing an axial position of the adjusting nut 126 relative to the seat plate 130. The runner mold 13 has an axially extending central passage 13A, a forward portion of which is provided by the sprue bush 21, and radially extending delivery passages 13B branched from the central passage 13A and axially extending runners 13C communicated with the delivery passages 13B. The runner mold has a plurality of forward extensions 13D provided by runner bushes 112, each defining a forward portion of a corresponding runner 13C.

The cavity mold 11 has axial holes, each forming the gate 11B of the mold cavity 11A and an enlarged diameter portion with a shoulder formed therebetween. The forward extensions 13D of the runner mold 13 are disposed into the axial holes of the cavity mold and abut against the shoulders of the axial holes, respectively. Radial positioning of the forward extensions 13D relative to the gates 11B is effected by positioning pins 13E.

The needle valves have a plurality of needle valve bodies 170 having valve heads 171 for corresponding gates 11B, respectively. Each needle valve body has a threaded rear end portion 172. The flange plate 120 has a plurality of threaded holes 127 where the needle valve bodies 170 are disposed and screwed at the threaded ends 172 thereof.

The runner mold 130 has a plurality of holes provided by seal bushes 13F mounted in preformed holes and fixed to the runner mold. The needle valve bodies 170 extend forwardly through the seal bushes 13F toward the corresponding gates, respectively, and their enlarged diameter portions or sealing portions 173 are formed so as to radially fit to the seal bushes 13F and to be allowed to axially move.

As shown clearly in Fig. 3, it is preferably to design the enlarged diameter portion 173 of each needle valve body 170 so as to have a shoulder having a flat or radially extending surface 173A of an annual form, which is in contact with an internal surface of an assumed or phantom extension of the radially extending delivery passage 13B and does not project into the assumed extension, when the gate is closed or at a closed position of the valve as shown in the upper portion of Fig. 1 and Fig. 3.

The annular surface 173A of the needle valve body is a differential cross-sectional area between the enlarged diameter sealing portion 173 and a forward neighboring portion 174 of the valve body integrated with the valve head 171.

The annular surfaces 173A in total are designed to be large enough to have a melt pressure exerted against them to thereby commence a withdrawal of the flange plate 120 biased forwardly against the first stopper 141 by all of the springs 150 and 160 upon commencement of injection of the melt. When the withdrawal of the flange plate 120 is commenced, all of the needle valve bodies 170 start withdrawal to open the gates 11B, and then a total cress-sectional area of the sealing portions 173 is subjected to the melt pressure.

The needle valve bodies 170 are of a probe form having a frustum conical tip forming a valve head 171, and the gates 11B are also of a frusco-conical form as shown clearly in Figs. 4A and 4B. Preferably the gate has a diverging angle β smaller than θ ~ of the tip. Most preferably, both the gate and the tip are designed so that they are in a substantially circular line contact with each other at forward ends thereof when the gate is closed, with a tip end lying on an assumed or phantom surface portion of the cavity 11 A corresponding to the inner end of the gate 11B. That is, the tip does not project into the cavity nor is it retracted from the forward end of the gate, in order to let a molded product have no recess corresponding to the tip or no projection corresponding to the gate.

When each gate 11B is opened, a corresponding probe or needle valve body 170 is withdrawn rearwardly by a melt pressure in the runner 13C against a combination of the entire spring force and a frictional force generated in the needle valve system, until the flange plate 120 abuts against the second stopper 135 provided by the rod 134, as illustrated in the lower half of the mold arrangement of Fig. 1. In this gate opening or prove withdrawing process, the frictional force exerts so as to increase the combined force, whereas in a gate closing or probe advancing process the frictional force exerts so as to decrease the combined force. In this connection, the melt pressure must be reduced to a relatively lower level to close the gate which level corresponds to the entire spring force minus(-) the frictional force. This further means that the probe 170 does not move, while the melt pressure is decreasing to that lower level. A gap between the higher level and the lower level is dependent on the friction, and the entire spring force.

Under the circumstances, it is preferable in practice to design the needle valve bodies and determine the entire spring force so that an axial melt force exerted against all of the needle valve bodies by a predetermined melt pressure in the runners at a final stage of the internal pressure-holding step is equivalent or over the entire spring force at the open position of the valves. In such a case, each needle valve body is prevented assuredly from moving toward the gate even at the final stage of the pressure-holdig step. In a theoretical view, the first stopper 141 is expected to prevent the probe or needle valve body 170 from impinging against the gate 11B when the gate is closed, if the length of the probe is well or precisely adjusted in advance at the rear threaded end of the prove relative to the flange plate 120. However, in practice, there may a case where the probe 170 impinges against the gate 11B due to a thermal expansion of the probe in the axial direction. An impinging force does not exceed the entire spring force. In order to avoid such an undesired impinging, however, it is preferable to have the probe made of a relatively flexible metal.

With respect to heaters provided for the needles valves of a spring-biased type according to the present invention, a first embodiment of the valves is illustrated in the upper half of the mold arrangement as shown in Fig. 1, and a second embodiment is illustrated in the lower half of the mold arrangement.

According to the first embodiment, which illustrates the before mentioned state of the gate closing, the runner bushes 13D have body heaters 180 therein, and also probes 170 have body heaters 185 therein. Further, the sprue bushes 13F have body heaters 190 therein at the enlarged sealing portion 173. A pair of the body heaters 180 and 185 involved in each runner 13C are effective in reducing a friction generated at the gate 11B and the probe tip 171 due to a cold or semi-cold or frozen melt (material), while the other body heater 190 of each seal bush 13F is effective in reducing a friction generated at the seal bushes 13F and the enlarged sealing portion 173 of the probe due to a possible melt invading into a very small radial gap between the sealing portion 173 and the seal bush 13F. According to the second embodiment, which illustrates the before mentioned state of the gate opening, each runner bush 13D has a body heater 180 the same as that of the first embodiment, but it has a tip heater 181 at a forward end of the runner bush positioned in the vicinity of the cavity 11A and the probe tip 171. In turn, the prove 170 has no body heater. In the first embodied runner bush 13D has no forward end such as the above.

The enlarged sealing portion 173 of the probe has a body heater 191. In turn, the seal bush 13F has no body heater.

All of the above mentioned body heaters are means for effecting continuous heating, while the tip heater 181 is a means for effecting instantaneous and intermittent heating. The tip heater 181 is actuated just before every injection.

Thanks to a combination of the above heaters 180 and 185 of the first embodiment or heaters 180 and 181 of the second embodiment, and the tips 171 of frustum- conical form, an area of each probe 170 against which a melt pressure exterts for commencing the gate opening is increased over the above mentioned differential cross-sectional area between the enlarged sealing portion and the forward portion of the probe, due to a cold material at the gate being forced to melt.

With the above mentioned embodied injection molding machine as shown in Fig. 1, the valve 40 is actuated to open the nozzle passage Y as shown in a lower half of the machine, and then a melt is injected by the screw plunger 3. The melt is then filled under high pressure in each runner 13C. The high melt pressure exerts against each probe or needle valve 170, which is biased against the first stopper 141 via the flange plate 120.

All of the probes are forced to move rewardly with the common flange plate 120 until the flange plate 120 abuts against the second stopper 135.

As a result, all of the gates 11B are concurrently opened and the melt is injected into the cavities 11A.

The injection step terminates, and then is changed to an internal pressure-holding step when the valve 40 is closed as shown in an upper half of the machine. The internal holding pressure is decreased until the pressure-holding step is terminated, but the decreased melt pressure in the pressure-holding chamber is not small enough to have a combination of the entire spring force and the frictional force (which is a minus force) overcome the melt force, and thus the gates are kept open. In this connection, the valve 40 must be opened to thereby further decrease the melt pressure. The further decrease of the melt pressure occurs due to mixing of a melt in the chamber X at a higher-pressure with a metered melt at a lower pressure for a next shot cycle which has been prepared during the pressure- holding step. As a result, the entire spring force minus the frictional force overcomes the decreased melt pressure to thereby have the common flange plate 120 move forwardly with all of the probes 170 for concurrently closing all of the gates 11B.

In this process, there may be two cases. In one case, the next shot metering step is completed when the gates are opened. In the other case, the next shot metering step is not yet completed when the gates are opened. In the latter case, there is no substantial problem occurring in the metering. This is because a final sub-step of the metering can be continued just like a conventional metering step carried out in a non-pressure-holding chamber system, since the all of the gates are closed.

Of cause, in the above latter case, in place of the valve opening, a sucking-back operation may be carried out by withdrawing the nozzle 22 to thereby further decrease the melt pressure to a level low enough to allow the probes 170 to move forwardly for closing all of the gates 11B, during the metering with the valve 40 being kept closed.

Fig. 5 and Fig. 6 show another embodiment of a hot runner mold arrangement having a plurality of needle valves of a spring-biased type and a spool valve type, whereas Fig. 1 shows that having such valves as above but of a seat valve type. In Fig. 5, the same numbers as those of Fig. 1 denote members or elements substantially equivalent to those of Fig. 1.

Referring to Figs. 5 and 6, the mold arrangement is substantially the same as that of Fig. 1 except for the following features.

Each guiding rod 133 extends from a stationary spring seat plate 130 through a hole in a movable flange plate 120 and is disposed in a guiding hole of a stationary supporting and guiding plate providing a backing plate 13G of a runner mold. A plurality of coil springs 160 encircling corresponding rods 133 are mounted between the movable flange plate 120 and the seat plate 130. Each needle valve body 170' extends through an axial hole of the backing plate 13G and is disposed into an axially extending but radially stepped hole 13'F of a runner mold body. Spacers 140 are mounted between the back plate 13G and a spring seat plate 130. The backing plate 13G provides a first stopper 141 at its rear surface against the flange plate 120 at stopper rings 128 mounted thereto.

The seat plate 130 has a plurality of rods 135' extending forwardly therefrom, which provide, in combination, a second stopper 135 at free ends thereof against the flange plate 120. There is no main spring and no spring force adjusting means provided at a sprue bush 21. Preferably, such a means with a main spring 150 may be provided as illustrated in Fig. 1. 21A denotes a coil heater encircling the sprue bush 21. A runner bush 13'D, forming a runner 13'C and also a gate 11'B, has a body heater 180 of a coil form therein. Each gate 11'B is of a frustum conical form plus a cylindrical form extending forwardly therefrom. The frustum conical portion of the gate 11'B has grooves A, B, or C as shown in Fig. 6. A valve head or tip 171' is of a combined frustumconical cylindrical form corresponding to that of the gate 11'B but with no groove. The cylindrical tip of the valve is disposed into the cylindrical portion of the gate at a closed position of the valve. At a open position of the valve, the cylindrical tip is withdrawn rearwardly to such an extent that the grooves A, B, or C and the withdrawn tip, in combination, define passages open to the cylindrical gate portion as shown in Fig. 6. The axially extending but stepped hole 13'F of the runner mold body, through which a corresponding needle valve body 170' extends into a corresponding runner 13C, has a forward hole 130A section and a rear hole section 130B. The two hole sections have axes radially eccentric from each other.

Each needle valve body 170' consists of a forward part 170'A and a rear part 170'B separated therefrom. The two parts have abutting faces at facing ends thereof, respectively, and abut against each other at the abutting faces.

The rear part 170'B is disposed in the rear hole section 130B with a radial space gap, while the forward part 170'A is disposed in the forward hole section 130A and is radially fitted thereto. The forward valve body part 170'A is forced to abut against the counterpart

170'B due to a melt pressure exterted against a conical face portion of the valve head of tip 171' formed at a forward end of the part 170'A, even at the closed portion of the valve. When each valve closes a corresponding gate, the two parts of the valve body, in combination, are forced to move forwardly toward the gate due to a spring force exerted by all of the springs 160, which force overcomes the melt pressure plus a frictional force generated in the valve system involved. The above mentioned valve body 170' (170'A, 170'B) with the stepped hole 13'F having the sections 130A and 130B ensures the valve body to smoothly move forwardly and rearwardly in a long run injection molding operation, even if a radial position of the rear valve body part 170'B is shifted to a relatively large extent relative to a radial position of the forward valve body part 170'A from a predetermined relative position, due to a difference in a thermal expansion between the backing plate 13G and the runner bush 13'D. In this case, the valve body parts 170'A and 170'B are allowed to relatively slide at their abutting faces in a radial direction without any substantial bending of each part relative to the axis thereof.

Such a means involving separate parts forming, in combination, a needle valve body and eccentric sections forming a hole as above is not always required, but may be also applied in the embodiment of Fig. 1, as needed, in consideration of the thermal expansion of the runner mold. Further, the embodimens of the mold arrangement as shown in Fig. 1 may be modified so as to have a plurality of valves of a spool type as shown in Fig. 5 and 6, in place of the valves of a seat type.

Claims

CLAIMS 1. A mold arrangement of a hot runner type to be incorporated with an injection machine having a nozzle coaxial therewith for carrying out injection molding, said mold arrangement comprising: a cavity mold defining a plurality of cavities having respective axially extending gates; a runner mold involving a manifold, which is detachably connected to said cavity mold and forms a plurality of axially extending runners communicating with corresponding gates of said cavity mold and a forward axial extension of said injection machine including said nozzle; and a plurality of needle valves of a spring-biased type provided and actuated by changing a melt pressure for opening and closing corresponding gates, each valve comprising an axially extending valve body of a needle or probe form disposed in a corresponding runner working as a valve chamber with a radial space gap therebetween, said needle valve body having a valve head at a forward end thereof, which head cooperates with a corresponding gate, characterized in that each needle valve body extends axially and rearwardly out of said runner mold through a corresponding hole formed therein, and is axially movable through said hole but is radially fitted to said hole so as to substantially seal said hole, said plural needle valves further comprising a common means provided outside of said runner mold for biasing said needle valve bodies against a first stopper provided outside of said runner mold to thereby have said valve heads close said gates.

2. A mold arrangement according to claim 1, wherein said common biasing means comprises: a common axially movable flange of a radially extending plate provided outside of said runner mold from which plate said needle valve bodies extend forwardly; a common stationary spring seat of a radially extending plate form provided outside of said flange plate with an axial space gap therebetween; said first stopper and a second stopper provided to define forward and rear axial positions of said movable flange plate corresponding to common closed and open positions of said valves, respectively; means for radially supporting and axially guiding said movable flange plate, mounted to said stationary spring seat plate; and a plurality of axially extending springs provided in said space gap between both said flange plate and said spring seat plate to bias or urge said flange plate against said first stopper relative to said spring seat plate, radial positions of said springs being allotted appropriately over the entire front surface of said spring seat plate.

3. A mold arrangement according to claim 2, wherein said common biasing means comprises a means for adjusting a main spring of a coiled form, among said plural springs, in respect to an axial length thereof to thereby adjust the entire force of all of said springs exerted against said flange plate.

4. A mold arrangement according to claim 3, wherein said spring seat plate has a central hole in which a combination of said nozzle and a rear hollow extension of said runner mold is disposed, and said flange plate has a central hole coaxial with said central hole of said spring seat plate, said spring adjusting means comprising: an axial hollow bolt extending rearwardly from said flange plate and enclosing said central hole thereof; and an adjusting nut screwed on said bolt, said hollow bolt being encircled by said main coil spring and located in an axial space gap defined between said adjusting nut and said spring seat plate.

5. A mold arrangement according to claim 4, wherein said supporting and guiding means comprises a plurality of axial rods extending forwardly from said spring seat plate, at least some of said rods being encircled by said springs other than said main coil spring, which are axial springs of a coil form, said spring-encircled rods being disposed in corresponding holes formed in said flange plate in which holes they are slidably fitted.

6. A mold arrangement according to claim 5, wherein the other rods are of a stepped form, each having a forward portion axially movable in a corre¬ sponding hole formed in said flange plate and a rear portion forming a shoulder providing said second stopper, which is to abut against said flange plate at said open position of said valves.

7. A mold arrangement according to claim 6, wherein a spacer means is provided for fixing an axial position of said spring seat plate relative to said cavity mold as well as said runner mold, said spacer means having a shoulder providing said first stopper, which is to abut against said flange plate at said closed position of said valves.

8. A mold arrangement according to any one of claims 1 to 7, wherein each needle valve body has a threaded portion which is screwed into a corresponding threaded hole formed in said flange plate, to thereby adjust a forward portion of said valve body extending from said flange plate in respect to an axial length thereof.

9. A mold arrangement according to any one of claims 1 to 8, wherein said runner mold has a plurality of axial forward extensions, each forming a corre¬ sponding runner therein and being provided with a body heater in the vicinity of a periphery of said runner.

10. A mold arrangement according to claim 9, wherein each needle valve body is provided with a body heater therein.

11. A mold arrangement according to claim 9, wherein each axial forward extension of said runner mold is provided with a tip heater therein in the vicinity of a periphery of a corresponding gate, said tip heater being actuated intermittently and instantaneously.

12. A mold arrangement according to any one of claims 9 to 11, wherein said runner mold is provided with heaters therein, each in the vicinity of a

⁵ periphery of a corresponding hole to which a corre¬ sponding needle valve body is radially fitted, for preventing a frictional force generated at said hole from being increased.

13. A mold arrangement according to any one of ⁰ claims 9 to 11, wherein each needle valve body is provided with a heater therein in a corresponding portion thereof which is radially fitted to a corresponding hole of said runner mold, for preventing a frictional force generated at said hole from being '-^> increased.

14. A mold arrangement according to any one of claims 2 to 13, wherein said valves are of a seat type with each valve head being of a frustum conical tip and each gate providing a valve seat of a frustum conical 0 shape diverging toward said conical tip, said conical tip abutting substantially against said gate, when said flange plate abuts against said first stopper, to thereby close said gate.

15. A mold arrangement according to claim 14, 5 wherein each needle valve body has a forward portion forming said conical tip at a forward end thereof and a neighboring enlarged portion stepped therefrom to have a larger diameter, said enlarged portion being radially fitted to a corresponding hole of said flange plate, ⁰ said flange plate with all of said needle valve bodies being axially moved toward said second stopper to open all of said gates, when the injection is effected, due to a melt pressure in said runners, which pressure is exerted against a total dross-sectional area of said 5 needle valve bodies at said enlarged portions thereof to thereby generate a melt force against a spring force exerted by all of said springs at said flange plate plus a frictional force generated in the valve system involved.

16. A mold arrangement according to claim 15 wherein a total differential cross-sectional area between said enlarged portions and said forward portion is large enough to generate a predetermined melt force against said spring force plus said frictional force to thereby have said flange plate commence a rearward movement for opening all of said gates.

17. A mold arrangement according to any one of claims 14 to 16, wherein said conical tip diverges at an angle that is smaller than that of said gate so that it can be in a substantially circular line contact with said gate.

18. A mold arrangement according to any one of claims 1 to 13, wherein said valves are of a spool type with each valve head being of a cylindrical rod form having a uniform diameter, and a corresponding gate forms a cylindrical hole to which said rod is radially fitted, said cylindrical gate having at least one axial groove formed in its rear portion at a cylindrical surface thereof so that its forward portion is allowed to communicate with a corresponding runner via said groove while its rear portion holds said valve head coaxially at an open position of said valve.

19. A hot runner mold arrangement incorporated with a plurality of needle valves for opening and closing corresponding gates of a plurality of mold cavities jdefined therein, ^l characterized in that said needle valves have a common valve driving means provided outside of said mold arrangement, and a needle valve body of each valve is provided to extend from the interior of said mold arrangement forming a runner communicating with a corresponding gate to the exterior thereof through a corresponding sealing hole formed in said mold arrangement, said needle valve body having a free end forming a valve head which is to cooperate with said gate for the opening and closing thereof and the other end fixed to said common exterior valve driving means, said mold arrangement having a common stopper provided outside thereof for preventing said needle valve bodies from moving toward said gates.

20. A hot runner mold arrangement according to claim 19, wherein said valves are of a spool type or a seat type, and said valve driving means is of a hydraulic, pneumatic, electro-magnetic or spring-biased type.

21. A hot summer mold arrangement according to either one of claims 19 and 20, wherein each needle valve body is of a single member or part, which is radially fitted in a corresponding sealing hole formed in said mold arrangement.

22. A hot summer mold arrangement according to either one of claims 19 and 20, wherein each needle valve body consists of a forward part and a rear part separated therefrom and connected to said valve driving means, which parts have radially extending end faces where said body parts abut axially against each other, each sealing hole, through which a corresponding valve body extends to the extension of said mold arrangement, consisting of a forward hole section to which said forward body part is radially fitted at a rear portion thereof and a rear hole section in which said rear body part is disposed with a radial gap therebetween, both hole sections having axes radially eccentric from and communicating with each other.

23. A process of hot runner injection molding using an injection machine having a body provided with means for plasticizing, metering and injecting plastic material therein and a hollow extension, comprising a nozzle, therefrom forming a nozzle passage, and a mold arrangement defining at least one cavity having a gate, 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 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 provided and freeze a molded article therein, 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 during said pressure-holding step, characterized in that, using a needle valves of a spring-biased type incorporated in the mold arrangement and actuated by changing a melt pressure for opening and closing the gate, the gate is forced to open by injecting the material or melt with a melt pressure exerted against a combination of the spring and a friction generated in the valve system involved, the gate is kept open during said pressure-holding step with the melt pressure being reduced, and is closed by releasing said nozzle passage interruption to thereby further reduce the melt pressure.

24. A process of injection molding according to claim 23, wherein the metering is completed during said nozzle passage interruption, which is then released to have the gate closed.

25. A process of injection molding according to claim 23, wherein an initial substep of the metering is carried out during said nozzle passage interruption, and a final substep of the metering is carried out upon release of said nozzle passage interruption with the gate being closed.

26. A process of injection molding using an injection machine having a body provided with means for plasticizing, metering and injecting plastic material therein and a hollow extension, comprising a nozzle, therefrom forming a nozzle passage, and a mold arrangement defining a cavity having a gate, 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 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, 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 during said pressure-holding step, characterized in that, using a needle valve of a spring-biased type incorporated in the mold arrangement and actuated by changing a melt pressure for opening and closing the gate, the gate is forced to open by injecting the material or melt with a melt pressure exerted against a combination of the spring and a friction generated in the valve system involved, the gate is kept open during said pressure-holding step with the melt pressure being reduced, and is closed by with¬ drawing the nozzle with the machine body relative to the mold arrangement to effect sucking-back with the melt pressure being further reduced during said nozzle passage interruption.