JPH0442096Y2 - - Google Patents

Description

[Detailed description of the invention] [Industrial field of application] This invention is a method that can absorb thermal expansion in the axial direction.
Regarding nozzle assembly for injection molding machine.

[Prior art]

An injection molding machine is equipped with an injection device that melts and injects supplied plastic material into a cavity of a die, and a mold clamping device that applies a predetermined mold clamping force to the die.

The injection device includes a hopper, a heating cylinder, an injection plunger, a nozzle, etc., and the plastic material is cut into pieces and supplied to the hopper. When the plastic material passes through a transport section called the feed zone, it is heated by heat transfer from the heating cylinder and frictional heat.
℃, plasticized and melted. The molten plastic is then injected into the mold cavity, for example through a nozzle at the tip of a heated cylinder.

As injection devices, plunger type, plunger pre-plastic type, screw pre-plastic type, and in-line screw type are known. Although the plunger type has a simpler structure, it has the disadvantage of narrowing the range of molding conditions because plasticization and injection are performed in the same process even though the plasticization conditions and injection conditions are different. . In order to eliminate this drawback, in the plunger pre-plastic type and screw-up pre-plastic type, plasticization and injection are performed in separate processes. In other words, in these pre-plastic types, the heating cylinder in which the torpedo (in the case of the plunger pre-plastic type) or the screw (in the case of the screw-in pre-plastic type) is installed is not coaxially arranged with the injection plunger, but is controlled by the reciprocation of the injection plunger. The injection cylinder is disposed at an angle above the injection cylinder to pre-plasticize the plastic. In the in-line screw type, the screw moves within a heating cylinder to perform plasticization and injection coaxially. Note that in the plunger type and in-line screw type, the heating cylinder also serves as the injection cylinder.

The nozzle is the tip of the heating cylinder (plunger type, in-line screw type), or
It is fixed to the tip of the injection cylinder (in case of pre-plastic type). The tip of the nozzle is brought into close contact with the mold to prevent liquid leakage between the nozzle and the mold.

As mentioned above, since the nozzle and the heating cylinder or the injection cylinder are arranged coaxially, the injection device has a considerable length in the axial direction. especially,
Some inline screw types are over 1m in length.

A heater is wrapped around the heating cylinder to heat the heating cylinder, and the plastic material is heated to 200 to 400°C by heat transfer from the heating cylinder and frictional heat from the rotation of the screw, and becomes plasticized.
melted. Further, a heater is also wrapped around the injection cylinder. The heating cylinder and the injection cylinder are heated by the heater and raised to a high temperature, so that they expand and contract due to thermal expansion. Also,
The nozzle itself is heated and expanded and contracted by heat transfer from the heating cylinder, the injection cylinder, and the molten plastic flowing therein. Due to the expansion and contraction of such heating cylinders, injection cylinders, and nozzles,
The injection device expands and contracts in the axial direction. However, since the nozzle is fixed to the tip of the heating cylinder or injection cylinder, and the nozzle is in close contact with the mold during molding, the heating cylinder, injection cylinder, and nozzle are
Unable to absorb axial elongation. Therefore, there is a risk that the nozzle, which is inferior in strength, may be destroyed.

Further, when the heating state changes and the heating cylinder etc. contracts due to thermal expansion, the nozzle is not brought into close contact with the mold, and a gap is created between the nozzle and the mold, causing liquid leakage.

Furthermore, in the known configuration, the pressing force of the nozzle that presses the mold, so-called nozzle touch force, varies due to expansion and contraction due to thermal expansion. A decrease in the nozzle touch force causes liquid leakage, whereas a sudden increase in the nozzle touch force destroys the nozzle.

Therefore, in known molding injection machines, for example,
A hydraulic cylinder and a piston are provided at the part where the heating cylinder is attached to the housing. With this configuration, the expansion and contraction of the injection device in the axial direction is absorbed by the relative movement of the hydraulic cylinder and the piston. The nozzle touch force is also kept constant.

Furthermore, a configuration is also known in which the heating cylinder is attached to the housing using a mechanical connection mechanism such as a link, and the expansion and contraction in the axial direction is absorbed by the connection mechanism.

Further, Japanese Patent Application Laid-Open No. 60-212316 discloses a plunger having an injection hole at the tip of the nozzle, which is provided with a mounting tube to make the plunger slidable. However, since the plunger was made to be able to slide freely inside the mounting tube, molten plastic entered between the plunger and the mounting tube due to the injection pressure through the gap that allowed the plunger to slide, making it difficult for the plunger to slide. There is a possibility that this will happen. And the molten plastic that got into it has no way out.
Due to the accumulation and accumulation, the plunger cannot move forward and moves backward.

[Problems with conventional technology]

However, in all of the above known configurations, the injection device tends to become structurally complex.

Incidentally, in order to prevent liquid leakage and damage to the nozzle, it is necessary to adjust the nozzle touch force according to the injection pressure. However, in the known configuration, the nozzle touch force is constant regardless of the injection pressure, and the nozzle touch force cannot be set in proportion to the injection pressure.

[Purpose of invention]

The purpose of this invention is to provide a nozzle assembly for an injection molding machine in which the nozzle is designed to absorb expansion and contraction in the axial direction of the injection device, and a nozzle touch force proportional to the injection pressure can be obtained.

[Summary of the idea]

In order to achieve this purpose, according to this invention, at the tip of the main nozzle, which corresponds to the conventional nozzle,
Irregularities are provided around the auxiliary nozzle, and the distortion of the auxiliary nozzle causes the main nozzle and the auxiliary nozzle to come into close contact with each other.

[Effect]

In such a configuration, expansion and contraction in the axial direction can be easily absorbed by sliding the auxiliary nozzle. In addition, nozzle touch force proportional to injection pressure can always be obtained.

〔Example〕

Hereinafter, embodiments of this invention will be described in detail with reference to the drawings.

As shown in the drawing, the nozzle assembly 10
is formed with a main nozzle 12 and an auxiliary nozzle 14, which correspond to conventional nozzles.

The auxiliary nozzle 14 has an outlet passage 16 at the tip of the main nozzle.
A small diameter flow passage 18 is formed in the auxiliary nozzle. In such a configuration, the auxiliary nozzle 14 is pressed by an external force due to the pressure (injection pressure) of the molten plastic in the main nozzle, and is brought into close contact with the mold 19. Therefore, even if the heating cylinder, the injection cylinder (both not shown), and the main nozzle 12 contract due to thermal expansion, the auxiliary nozzle 14 moves forward by the pressure of the molten plastic by the amount equivalent to the contraction, and molds the mold. 19 is still closely followed. Therefore, no gap is generated between the auxiliary nozzle and the mold, and liquid leakage is reliably prevented.

On the other hand, the elongation of the heating cylinder, injection cylinder, and main nozzle 12 is caused by the retraction of the auxiliary nozzle 14.
Absorbed. That is, when the heating cylinder or the like extends, the auxiliary nozzle 14 moves back against the pressure of the molten plastic by an amount corresponding to the extension, absorbing the extension of the heating cylinder or the like. Therefore, the auxiliary nozzle 1
4 is not forcibly pressed against the mold, and the auxiliary nozzle is prevented from being destroyed. Here, the main nozzle 12 is the mold 1
Not pressed by 9 and not destroyed.

In this way, in this invention, the auxiliary nozzle 14 is
It acts like a damper to absorb expansion and contraction of the injection device, reliably preventing liquid leakage and nozzle breakage.

Also, by moving the auxiliary nozzle 14 forward and backward,
The auxiliary nozzle is pressed with a nozzle touch force proportional to the injection pressure. In this way, the nozzle touch force
Since it is always proportional to the injection pressure and has an optimal value, there is no risk of liquid leakage. Further, the nozzle is not pressed with an unnecessarily large touch force, and the nozzle is not damaged.

In this invention, it is sufficient to attach the auxiliary nozzle 14 to the tip of the main nozzle 12 in a slidable manner at the beginning of installation, and the structure of the injection device is not complicated.

In this invention, the auxiliary nozzle 14 is formed small and thin. For example, the main nozzle outlet 16
When the diameter of the sprue 21 in the mold is 8 mm and the diameter of the sprue 21 in the mold is 3 mm, the diameter of the auxiliary nozzle 14 is approximately 2.5 mm, and the wall thickness of the auxiliary nozzle in the radial direction is 2.75 mm.
((8-2.5)÷2=2.75). Since the auxiliary nozzle 14 is formed thin in this manner, it responds sensitively to the pressure of the molten plastic and is sufficiently distorted in the radial direction. Then, due to the pressure of the molten plastic flowing in the flow path 18, the peripheral surface of the auxiliary nozzle is strongly pressed against the wall surface 16a of the outflow path, and is brought into close contact with the wall surface 16a of the outlet path. Therefore, the auxiliary nozzle 1
4. Reliable sealing (liquid tight) between the outflow channels 16
is ensured, and liquid leakage between the auxiliary nozzle and the outflow path is reliably prevented. In particular, if the peripheral surface of the auxiliary nozzle 14 is made into an uneven surface 20 as shown in the figure, the pressure of the molten plastic acts intensively on the convex portions of the auxiliary nozzle uneven surface 20, bringing the convex portions into close contact with the wall surface. ,
More reliable sealing can be obtained.

In the embodiment, as the uneven surface 20 of the auxiliary nozzle,
Although it is a wavy surface, it is not limited to a wavy surface as long as it has a shape that is easily distorted in the radial direction.

By the way, the pressure of the molten plastic, as the injection pressure (molding pressure), greatly influences the quality of the molding, and if the injection pressure is too low, short shots (insufficient filling), sink marks, weld defects, and air bubbles will occur. On the other hand, if it is too high, burrs, crazing, warping, jetting, etc. will occur. Therefore, it is necessary to accurately control the injection pressure.

However, the plastic materials themselves are not the same, and the particle size, water content, etc. vary from lot to lot, and it is difficult to obtain the same melt viscosity even when heated under the same conditions. Further, the residence time within the heating cylinder is not the same, and the melt viscosity also differs due to a difference in thermal history due to a difference in residence time. The injection pressure fluctuates due to such a difference in melt viscosity.

As mentioned above, in this invention, the auxiliary nozzle 14
is sufficiently strained, and a strain sensor 22 is arranged on the auxiliary nozzle to take note of this strain.
For example, the strain sensor 22 is embedded adjacent to the recessed portion of the uneven surface 20.

In this way, the strain sensor 22 is connected to the auxiliary nozzle 1.
4, the auxiliary nozzle is sufficiently strained and the strain is proportional to the pressure of the molten plastic, that is, the injection pressure, so the fluctuations in the injection pressure can be accurately determined from the detected fluctuations in strain.
Therefore, the injection pressure can be adjusted appropriately in response to changes in melt viscosity caused by changes in the lot, etc., and molding can be performed under a constant injection pressure. In particular, when detecting injection pressure using strain in the auxiliary nozzle 14,
Since the detection means (strain sensor) does not come into contact with the high-temperature, high-pressure molten plastic, there is no risk of damage to the detection means. Moreover, it is sufficient to simply arrange the strain sensor 22 on the auxiliary nozzle 14, and with an extremely simple configuration, fluctuations in melt viscosity, that is, injection pressure, can be accurately grasped.

The above-mentioned embodiments are for illustrating this invention, and are not intended to limit this invention in any way, and any modifications, modifications, etc. made within the technical scope of this invention are also included in this invention. Needless to say.

〔effect〕

As described above, according to this invention, the auxiliary nozzle is slidably attached to the tip of the main nozzle, and the auxiliary nozzle is pressed outward by the pressure of the molten plastic and brought into close contact with the mold. Therefore, the auxiliary nozzle acts like a damper and absorbs the expansion and contraction of the heating cylinder, injection cylinder, and main nozzle, thereby reliably preventing liquid leakage and destruction of the nozzle.
Note that the main nozzle is not pressed by the mold and is not destroyed.

Further, as the auxiliary nozzle advances and retreats, the auxiliary nozzle is pressed against the mold with a nozzle touch force proportional to the injection pressure. In other words, the optimum nozzle touch force is always obtained, and there is no risk of liquid leakage or nozzle breakage.

Furthermore, since it is sufficient to slidably attach the auxiliary nozzle to the tip of the main nozzle, the structure of the injection device is not complicated.

[Brief explanation of the drawing]

The drawing is a longitudinal sectional view of the nozzle assembly of this invention. DESCRIPTION OF SYMBOLS 10...Nozzle assembly, 12...Main nozzle, 14...Auxiliary nozzle, 16...Outflow path of the main nozzle, 16a...Wall surface of the outflow path, 18...Flow path of the auxiliary nozzle, 19...Fri Mold, 20... Uneven surface of auxiliary nozzle, 21... Sprue of mold, 22...
strain sensor.

Claims (1)

[Claims for Utility Model Registration] (1) In a nozzle assembly for an injection molding machine that includes a main nozzle and an auxiliary nozzle that is slidably attached to the tip of the main nozzle, unevenness is formed on the circumferential surface of the auxiliary nozzle. A nozzle assembly for an injection molding machine, characterized in that the auxiliary nozzle and the main nozzle come into close contact with each other due to the distortion of the auxiliary nozzle. (2) A nozzle assembly for an injection molding machine according to claim 1 of the utility model registration claim, in which a strain sensor is disposed in the auxiliary nozzle.