JPH0136413B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an injection molding apparatus that injects molten synthetic resin directly from a molding machine nozzle into a cavity.

In injection molding of synthetic resins, runnerless molding, in which the resin between the injection head of the molding machine and the cavity of the mold is always kept in a molten state ready for injection, eliminates the loss of molding material due to sprues and runners. Since it improves the dimensional accuracy and strength of products, it has recently become widely adopted.

Conventional runnerless molding employs various systems, including an extension nozzle method in which the injection molding machine directly injects into the mold cavity, and an insulating system in which the resin around the sprue and runner is kept in an unmolten state. There is a well type nozzle method (or insulated runner method) which is used to keep the resin in the center in a molten state.A hot runner method which forcibly heats the runner to keep the resin in a molten state. .

Each of the above systems has its own advantages and disadvantages. For example, the extension nozzle method of Because it comes into contact with the biting plate, heat is easily conducted from the nozzle to the mold, resulting in a drop in nozzle temperature and clogging of the nozzle due to solidification of the resin, or conversely, solidification of the resin is hindered by conductive heat. There are disadvantages such as gate sealing may not be performed properly due to the heat transfer of the nozzle.

The well-type nozzle method does not always forcibly heat the molten resin in the well above its melting point, so there is a risk that the resin in the center of the well will solidify, and it may be difficult to use temperature-sensitive resin or the molding cycle. It is inappropriate for long ones. Also, usually only one piece can be taken.

In addition, in the insulated runner method, the runner diameter is made sufficiently thick to keep the resin in the center of the runner in a molten state during the next injection, but the gate part in particular tends to solidify, and most of the resin is It is limited to polyethylene and is unsuitable for molded products with high dimensional accuracy.

On the other hand, the hot runner method actively uses a heater to prevent the runner from solid cooling, so the pressure loss in the runner is small, the injection pressure is kept relatively low, and the internal strain of the molded product is minimized. can be made smaller. In addition, it has become possible to use a valve gate using a needle valve, which has many advantages, such as preventing nose sagging and greatly improving the precision and physical properties of molded products.

However, on the other hand, the mold structure is extremely complicated and the mold becomes expensive. In particular, when a valve gate is used in combination, there are problems such as the opening/closing mechanism is complicated and maintenance is not easy.

This development was made to solve the various problems of the conventional injection molding method as described above, and it incorporates a hot runner method and a valve gate method consisting of a floating nozzle chip into the extension nozzle method. By providing a new molding device, we can create inexpensive molds with an extremely simple structure.
The aim is to enable mass production of molded products with high dimensional accuracy and high physical properties in a high cycle.

The present invention will be explained below based on the drawings.

1 to 4 are diagrams showing one embodiment of the present invention. First, to explain the configuration, in the figure, 1 is the base of the in-line screw injection molding machine, 2 is the injection unit placed on the base 1, and 3 is the base of the in-line screw injection molding machine.
indicates the mold clamping device.

To explain the injection unit 2, 4 is a screw barrel, and a screw 7 is provided inside a heating cylinder 6 with a heater 5 wound around the outside. 8
is a heating cylinder support/material supply plate, and is provided with a hopper 9 for supplying molding material into the screw barrel 4. 10 is a drive motor that rotates the screw 7 via a reduction gear 11, and 12 is an injection actuator that moves the screw 7 back and forth within the heating cylinder 6, and has an injection piston 13 built therein.

The injection unit 2 configured as described above is attached to the slide base 14 fixed to the base 1 via the carriage 15.
By sliding the carriage 15 with a cylinder (carriage cylinder) 16 for moving the injection unit provided at 4, the injection unit can be moved back and forth. Furthermore, in this invention, as will be described later, it is necessary to move the screw barrel tip forward and backward within a regulated range for each molding cycle. Therefore, for example, a stopper 17 whose forward limit stop position can be adjusted with a screw,
A limit switch 18 that can adjust the reverse limit position (its contact point is connected to the carriage cylinder 1
A forward/backward movement control means 19 for the screw barrel 4 is formed on the slide base 14, and includes a solenoid valve opening/closing circuit inserted into an unillustrated hydraulic system 6). Of course, the forward/backward movement control means 19 is not limited to the above, and other general position detection/control means such as Magnescale (trade name) or photoelectric type may be used. I can do it.

Next, regarding the mold clamping device 3, 20 is a fixed plate fixed to the base 1, and 21 is this fixed plate 20.
It is a movable plate that holds the mold 22 in cooperation with the mold 22. This movable platen 21 is guided by tie bars 23 attached to the fixed platen 20, and is moved back and forth by a mold clamping ram 24 driven by a mold clamping piston (not shown). This opens and closes the mold 22.

Furthermore, the screw barrel 4 of the injection molding machine of the present invention will be explained based on FIGS. 2 to 4.

FIG. 2 shows a cross section of the tip of the screw barrel 4, which is inserted into a bore 25 provided in the stationary platen 20 and the mold 22 of the mold clamping device 3. 26 is a cavity arranged around this bore 25, 27 is a gate, and 28 is a gate land.
The band heater 5 is not wound around the tip of the screw barrel 4. An air gap G is formed between the outer periphery 4a of this tip and the inner wall 25a of the bore 25. 29
is a blind lid that seals the leading edge of the screw barrel 4. A plurality of through holes 30 are bored in the vicinity of the sealed end of the sealed screw barrel 4, intersecting the axis of the screw 7, and opening radially to the outside. (See Figure 3, six through holes are shown in the figure).

Reference numeral 31 designates a floating nozzle tip that is slidably fitted into each of the through holes 30. The outer end surface 3 of this floating nozzle tip 31
1a is a mold mating surface, which is concentric with the screw barrel axis, and which is concentric with the mold surface 25a (bore 25
It is formed into an arcuate surface with radius R being the distance up to the inner wall (Fig. 4).

Inside the floating nozzle chip 31, there are provided an orifice 32 that opens at the center of the mold mating surface 31a, and a hot runner 33 whose diameter is gradually reduced from the opposite end surface 31b toward the orifice 32. It has been formed. 34 is a notch provided in a part of the outer circumference of the floating nozzle tip 31, and the tip of the guide pin 35 screwed from the end face of the screw barrel 4 is applied to this notch to regulate the floating range of the floating nozzle tip 31. It is designed to prevent rotation.

36 is on the outer periphery of the tip of the screw barrel 4,
A heating element such as a cartridge heater 37, for example, is housed in a plurality of long grooves along the axis formed equally between the through holes 30. 38 is another groove along the shaft, which is also formed on the outer periphery of the tip of the screw barrel 4 so that one end is close to the floating nozzle tip 31.
For example, a thermocouple 39 is housed here as a heat sensitive body. Reference numeral 40 is a cover that covers all of the grooves 36 and 38 described above, forms a protruding hole for each floating nozzle tip 31, and is wrapped around the tip of the screw barrel 4 and fixed with a set screw (not shown). be. The lead wire of the heating element 37 and the heat sensitive element 3
The lead wire 39a of No. 9 is taken out from a lead wire insertion hole 40a formed in the cover 40.

Next, the effect will be explained. Note that a detailed explanation of the conventionally well-known contents of the molding cycle will be omitted. In the injection process, the carriage cylinder 16 of the injection unit 2 is driven by a hydraulic power source (not shown), and the carriage 15 is moved to the stopper 17 whose position has been adjusted in advance.
Move it forward until it touches the.

FIG. 6 shows the state of this injection molding apparatus during injection. That is, at this time, the orifice 32 of the floating nozzle tip 31 of the screw barrel 4
communicates with a gate land 28 leading to a cavity 26 of the mold 22. Under this condition, the screw 7 of the injection molding machine is advanced to pressurize the molten resin. This resin pressure causes the floating nozzle tip 31 to
protrudes, and its mold mating surface 31a is the mold surface 25.
Close contact with a. This adhesion force (that is, nozzle touch force) acts as a self-sealing force that automatically increases or decreases depending on the resin pressure, so that resin leakage from the mold mating portion can be prevented.

According to the present invention, the pressurization of the resin by the advancement of the screw 7 can be performed even before the orifice 32 of the floating nozzle tip 31 and the gate land 28 communicate with each other.

In that case, the preload force causes the orifice 32 to communicate with the gate land 28 and at the same time, the molten resin rapidly flows into the cavity 26 . The injection piston 13 of the injection actuator 12 follows and moves forward until the cavity is filled. The resin expands extremely quickly when the orifice 32 is connected, and the cavity 26 is quickly filled.Even if it is a thin-walled molded product, the cavity is completely filled before the injected resin solidifies, resulting in extremely high accuracy. Good molded products can be obtained.

Furthermore, since the floating nozzle tips 31 are arranged radially corresponding to each cavity, the reaction force applied during injection is canceled out, and it goes without saying that core runout and displacement of the screw barrel 4 can be completely prevented. In addition, the clamping force of the molding machine can also be small.

During pressure retention after injection, gate 2 of cavity 26
The resin No. 7 is first solidified to prevent the resin from flowing backward due to the resin pressure inside the cavity 26. When the pressure retention is completed, pressure oil is sent to the carriage cylinder 16, and the carriage 15 is moved back to the position regulated by the limit switch 18 and about 5 mm. With this retreat, the orifice 32 of the floating nozzle tip 31 also moves together with the screw barrel 4, and the semi-solidified injection resin in the gate land 28 is sheared at the orifice mouth. At the same time, the orifice mouth is on the mold side 2.
It is occluded at 5a. Therefore, in injection molding of extremely low viscosity molten resin, such as nylon resin, it is possible to completely prevent so-called "nose dripping" and "stringing" phenomena, which have been problematic in the past.

Since the operation of the floating nozzle tip 31 of the present invention is performed automatically according to the resin pressure, it does not require a complicated mechanism such as a hydraulic cylinder or a spring, which is required for conventional valve seats, and is simple. The structure fulfills the valve gate function. Therefore, during the subsequent cooling process, the next molding material can be introduced into the screw barrel 4, and the newly melted material can be pressurized in advance in preparation for the next cycle of injection. After cooling for a predetermined period of time, the mold 22 is opened and the solidified molded product B is taken out (FIG. 6). During this time, the temperature of the resin in the hot runner 33 of the floating nozzle tip 31 is appropriately controlled by the heat sensitive element 39, and the resin is forcibly heated sufficiently by the heating element 37 placed close to it.
It will not solidify.

Further, the contact portion between the screw barrel 4 and the mold 22 is limited to the mold mating surface 31a of the floating nozzle tip 31, so that the heat transfer area can be kept to a minimum. Therefore, there is no risk that the heat transmitted from the floating nozzle tip 31 will interfere with the solid cooling of the resin in the cavity 26, making it possible to shorten the cooling time and speed up the molding cycle. Of course, the resin in the orifice 32 of the floating nozzle tip 31 will not be solidified due to heat being taken away by the mold.

In the above description, a case has been described in which the molten resin is pre-compressed before injection, but the invention is not necessarily limited to this.
That is, as another usage mode of this injection molding apparatus, it can also be applied to a cycle in which the inside of the screw barrel 4 becomes a negative pressure state as the screw 7 of the molding machine retreats. In that case, the floating nozzle tip 31 slides within the through hole 30 in response to the pressure and retreats from its protruding position during injection. Thereby, the floating nozzle tip 31 is isolated from the mold 22 via the air goat, so that the insulation is more complete.

As described above, according to the present invention, the structure includes a screw barrel whose tip is sealed and inserted into the mold, and a screw barrel that intersects with the screw shaft in a radial manner near the sealed end. A floating nozzle tip is formed with a through hole opening to the outside and slidably fitted into the through hole, and the orifice of the floating nozzle tip is controlled by controlling the forward and backward movement of the screw barrel within a predetermined range for each shot. The injection molding device is equipped with a forward and backward movement control means that repeatedly connects and disconnects communication with the cavity.
Various effects such as the following can be obtained.

(1) The mold only needs to have a bore into which the screw barrel is inserted so as to maintain an air gap, and there is no need for the complicated configuration or precision machining required for conventional runnerless molds, so it is the most cost-effective method to date. High mold costs can be significantly reduced.

(2) Since the nozzle tip is inserted directly into the tip of the screw barrel, it has a simple configuration with a small number of parts, and can function as a hot runner and valve gate, resulting in a much lower cost and higher quality than conventional methods. We can mass produce molded products.

(3) Since the contact area between the screw barrel and the mold can be minimized, the heat input to the mold for each shot is reduced, the cooling time of the molded product is shortened, and the shot cycle is significantly saved.

(4) The orifice, which is the injection port, is opened and closed by controlling the forward and backward movement of the screw barrel, which prevents nasal drips and stringiness.

(5) By canceling out the reaction force caused by the nozzle touch force during injection, it is possible to create a molding device with less mold clamping force.

(6) Since forced heating and temperature detection can be performed very close to the floating nozzle chip, very precise temperature control can be achieved.

(7) The heater, heat sensitive body, nozzle chip, etc. can be easily taken out for maintenance.

(8) The effect of thermal expansion due to temperature differences can be absorbed by using a floating nozzle chip, making it extremely easy to fit the mold and injection end.

[Brief explanation of drawings]

Fig. 1 is a partial side view of one embodiment of the present invention, Fig. 2 is a cross-sectional view of a main part of what is shown in Fig. 1, Fig. 3 is a view taken in the direction of - arrow in Fig. 2, and Fig. 4 A is a floating Side sectional view of the nozzle tip, B is also a plan view, No. 5
Figure 6 shows how this invention is used.
FIG. 5 is a sectional view of the main part when the mold is opened and FIG. 6 is a sectional view of the main part when the mold is opened. 4... Screw Barrel, 7... Screw You,
19... Forward and backward movement control means, 22... Mold, 26...
...Cavity, 30...Through hole, 31...Floating nozzle tip, 32...Orifice, 33...Hot runner.

Claims (1)

[Claims] 1. A screw barrel whose tip is sealed and inserted into a mold, and a through hole that intersects the screw shaft and opens radially to the outside is bored in the vicinity of the sealed end. A floating nozzle tip is slidably fitted into the hole, and the forward and backward movement of the screw barrel is controlled within a predetermined range for each shot, so that communication and disconnection between the orifice of the floating nozzle tip and the cavity are repeated. An injection molding device comprising a forward and backward movement control means. 2. The injection molding apparatus according to claim 1, wherein the floating nozzle tip is provided with a hot runner that shrinks toward the orifice, and the end surface on the orifice side is an arcuate curved surface concentric with the screw barrel. .