JPS5939530A - Injection molding device - Google Patents

Abstract

PURPOSE:To provide the titled device capable of molding an article with a high dimensional accuracy and high physical properties by an inexpensive metallic force having a simple construction, provided with a screw barrel the tip of which is sealed and inserted into the metallic force, a floating nozzle tip and a forward and backward movement controlling means. CONSTITUTION:The forward and backward movement controlling means 19 for a screw barrel 4 is provided on a slidable base 14, and in an injecting step, a carriage 15 is forwardly moved until it comes into contact with a stopper 17. In the condition wherein the orifice 32 of a floating nozzle tip 31 for the screw barrel 4 is communicated with the gate land 28 leading to the cavity 26 of a metallic force 22, a screw 7 is forwardly moved to pressurized a molten resin. By this resin pressure, the tip 31 is protruded, and a mating surface 31a thereof is brought into close contact with the surface 25a of the force.

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, such as: ■ An extension nozzle system that injects directly from the injection molding machine into the mold cavity ■ The resin around the sprue launch is in an unmolten state Well-type nozzle method (or insulated runner method), which is used for heat insulation and keeps the resin in the molten state in the center ■ Hot runner method, which forcibly heats the launch part to keep the resin in the molten state There is a method.

Each of the above systems has its own advantages and disadvantages.For example, the extension nozzle method (■) has the advantage of eliminating the need for sprue bushings on the mold and simplifying the mold.
On the other hand, since the nozzle directly contacts the cavity plate of the mold, heat is easily conducted from the nozzle to the mold, resulting in a drop in nozzle temperature, which may cause the nozzle to shrink due to solidification of the resin. On the other hand, there are drawbacks such as the solidification of the resin being hindered by conductive heat, which may result in poor gate sealing, making it difficult to take heat transfer measures in the nozzle.

The well-type nozzle method described in (2) 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 may solidify. It is unsuitable for those with long cycles. Also, usually only one piece can be taken.

In addition, in the insulated launch method, the runner diameter is made sufficiently thick to keep the resin in the center of the runner in a molten state until the next injection, but the gate part in particular tends to solidify, causing the resin to melt. It is mostly 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 launch from falling on the same surface, so there is less pressure loss in the runner, and the injection pressure is kept relatively low, allowing the inside of the molded product to be Strain can be reduced. In addition, it is now possible to use a valve gate using a needle valve.
It 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 invention was made in order to solve the various problems of the conventional injection molding method as described above, and incorporates a one-way hot runner method and a valve gate method consisting of a floating nozzle tip into the extension nozzle method. By providing a new molding device, the aim is to mass produce molded products with high dimensional accuracy and good physical properties in a high cycle and with EJ capability using an inexpensive mold with an extremely simple structure.

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 11# configuration, in the figure, l is the base of the in-line screw injection molding machine, and 2d is this base!
The injection unit placed on the top, 3, indicates a mold narrowing device.

To explain the injection unit 2, 4 is a screw barrel, and a screw 7 is provided inside a heating cylinder 6 around which a heater 5 is wound around the outside. Reference numeral 8 denotes a heating cylinder support/material supply plate, which 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 inserted into the base 1 via the carriage 15, and is mounted on the slide base 14 using a cylinder (carriage cylinder) 16 for moving the injection unit. , by sliding the carriage 15, it can be moved back and forth. Furthermore, in this invention,
As will be described later, it is necessary to move the tip of the screw barrel back and forth 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 is used. , a limit switch 18 (the contact of which is incorporated into a solenoid valve opening/closing circuit inserted into the hydraulic system (not shown) of the carriage cylinder 16) that can adjust the backward limit position. The means 19 is formed on the slide base 14.However, the forward and backward movement control means 19 is not limited to the above, and may also be other types such as Magnescale (trade name) or a photoelectric type. General position detection/control means such as the above can be used.

Next, regarding the mold clamping device 3, 20 is a fixed plate fixed to the base 1, and 21 is a mouth J@ plate which cooperates with this fixed plate 20 to hold the mold 22. This -1 moving plate 21 is
Guided by the quiver 23 attached to the fixed plate 20,
$! +111. With this, mold 2
Open and close 2.

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

, Figure 2 shows the fixed platen 20 and mold 22 of the mold clamping device 3.
2 shows a cross section of the tip of the screw barrel 4, which is inserted into the bore 25 provided in the screw barrel 4.

26 is a cavity with VC arranged around this bore 25, 27
is Gate, and 2nd is Gateland. The band heater 5 is not attached to 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 chopstick 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 chip that is slidably fitted into each of the through holes 30. The outer end surface 31a of the floating nozzle tip 31 is a mold mating surface, and is an arc concentric with the screw barrel axis and having a radius R that is the distance to the mold surface 25a (inner wall of the bore 25). It is formed on the surface (Fig. 4).

Inside the floating nozzle tip 31, there is an orifice 32 that opens at the center of the mold mating surface 31a, and a hot runner 38 whose diameter is gradually reduced from the opposite end surface atb toward the orifice 32. It is formed. 34 is a notch provided in a part of the outer periphery of the floating nozzle tip 31, and the tip of the guide hinge 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 81. This is to prevent rotation.

36 indicates each through hole 3 on the outer periphery of the tip of the screw barrel 4.
With multiple long grooves along the axis formed equally through the 0,
Here, as a heating body, for example, a cartridge heater 37 is used.
Each is stored separately.

38 is also on the outer periphery of the tip of the screw barrel 4,
Another groove along the axis is formed such that one end thereof is close to the floating nozzle tip 31, and a thermocouple 39, for example, as a heat sensitive body is housed here. Reference numeral 40 denotes a cover that covers all of the grooves 36 and 38 and 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). The lead wires of the heating body 31 and the lead wires 39a of the heat sensitive body 39 are KL so that they can be taken out from the lead wire insertion holes 40a formed in the cover 40.

Next, the effect will be explained. Note that a detailed explanation of the conventionally 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 advanced until it comes into contact with the stopper 11 whose position has been adjusted in advance.

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 the gate land 28 leading to the cavity 26 of the mold 22. Under this condition, the molten resin is pressurized by advancing the screw 7 of the injection molding machine. The floating nozzle chip 31 protrudes due to this resin pressure, and its mold mating surface 31a is aligned with the mold surface 25.
Close contact with a. This adhesion force (i.e. nozzle touch force)
acts as a self-sealing force that automatically increases or decreases depending on the resin pressure, so resin leakage from the mold mating portion can be prevented.

According to this invention, the resin pressurization by the advance 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 +3 of the injection actuator 12 follows and moves forward until the cavity is filled. The resin expands extremely quickly when the orifice 32 is in communication, 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 hardens. Good molded products can be obtained.

In addition, 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. , the mold clamping force of the molding machine can also be small.

During pressure holding after injection, the resin at the gate 21 of the cavity 26 first solidifies, thereby preventing subsequent backflow of the resin due to the resin pressure within the cavity 26. When the pressure retention ends, pressure oil is sent to the carriage cylinder 16, and the carriage 15 is retreated approximately 511 degrees to the position regulated by the limit switch 18. During 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 closed by the mold surface 25a. Therefore, it is possible to completely prevent so-called "nose dripping" and "stringing" phenomena that have conventionally caused problems in injection molding of extremely low-viscosity molten resins, such as nylon resins.

The operation of the floating nozzle tip 31 of the present invention is performed automatically according to the resin pressure as described above, and does not require a complicated mechanism such as a hydraulic cylinder or a spring, as in the case of a conventional valve gate. It has a simple structure and 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 38 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, so that it is not solidified. There isn't.

Moreover, this screw barrel 4 and the mold 22. ! The contact part of : is limited to the mold fitting part 31a of the floating nozzle tip 31, and the heat transfer area can be kept to a minimum. Therefore, there is no possibility that the heat transmitted from the floating nozzle tip 31 will hinder the hardening of the resin in the cavity 26, and thus the cooling time can be shortened and the molding cycle can be accelerated. Of course, the resin in the orifice 32 of the floating nozzle tip 31
There is no possibility that the mold will absorb heat and cause it to harden.

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, as the screw 7 of the molding machine retreats, the b1 screw barrel 4
It can also be applied to cycles where the inside is in a negative pressure state. In that case, the floating nozzle tip 31 slides within the through hole 3o in accordance with the pressure and retreats from the protruding position at the time of injection. As a result, the floating nozzle tip 31 is isolated from the mold 22 via the air gap, so that the insulation is more completely achieved.

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 extends radially outward from the screw barrel near the sealed end, intersecting the screw shaft. A floating nozzle tip is slidably fitted into a through hole opening in the hole, and the forward and backward movement of the screw barrel is controlled within a predetermined range for each shot. Since the injection molding apparatus is provided with a forward and backward movement control means that repeatedly communicates and disconnects the oriice and the cavity, it is possible to obtain the following various effects.

(1) The mold has a bore into which the screw barrel is inserted.
It is only necessary to form the mold so as to maintain an air gap, and there is no need for the complicated structure or precision machining of conventional runnerless molds, so the mold cost, which traditionally had a high cost ratio, can be significantly reduced.

(2) Since the nozzle tip is directly inserted into the tip of the screw barrel, it has a simple configuration with a small number of parts, and can perform the functions of hot run force and pulp gate. We can produce high quality molded products.

(3) Since the contact area between the screw barrel and the mold can be minimized, the thermal force applied 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) Screw Controls the forward and backward movement of the barrel and opens and closes the orifice, which is the injection port, to prevent nasal drips and stringiness.゛(5) Offsetting the reaction force caused by the two nozzles during injection,
A molding device with small mold clamping force can be achieved.

(6) Since forced heating and temperature detection can be performed very close to the floating nozzle tip, extremely high P# temperature control can be achieved.

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

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

[Brief explanation of drawings]

Fig. 1 is a plan view of part I1 of an 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 along the ■-■ arrow in Fig. 2, and Fig. 4. (A) is a side sectional view of the floating nozzle chip, (B) is a plan view of the same, and FIG. FIG. 6 shows the mode of use of the present invention, in which FIG. 5 is a sectional view of the main part when the mold is injected and FIG. 6 is a sectional view of the main part when the mold is opened. ４・・・・・・・・・・・・Screw barrel 7・・・
・・・・・・・・・Screw 19・・・・・・・・・
Forward/backward movement control means 22...Mold 26...Cavity 30...Through hole 31...Floating Nozzle tip 32...
...Orifice 83...River...Hot runner

Claims (2)

[Claims] (1) A screw barrel whose tip is sealed and inserted into the mold; a through hole that intersects the screw shaft and opens radially to the outside near the sealed end; The forward and backward movement of the floating nozzle tip and the screw barrel that are slidably fitted together is controlled within a predetermined range for each shot, and communication and interruption between the orifice of the floating nozzle tip and the cavity is repeated. An injection molding device equipped with a speed control means -〇 (2) The injection molding apparatus according to claim 1, wherein the 711 nozzle tip has a hot run f'lce that contracts toward the orifice, and the end surface on the orifice side is an arcuate curved surface concentric with the screw barrel.