JPH07148801A - Injection molding machine screw - Google Patents

Abstract

PURPOSE:To uniformize a temperature distribution in the axial direction of a screw and enhance an ability of plasticizing a resin to obtain a high-quality article with little thermai deterioration. CONSTITUTION:In a screw 2 of an injection molding machine 100, a metallic material having a thermal conductivity of 130w/m.k or more and a tensile strength of 40kg/mm<2> or more is used as the material of the screw 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a screw for an injection molding machine, and more particularly to a screw for an injection molding machine, which is designed to efficiently disperse heat of the screw when plasticizing a resin.

[0002]

2. Description of the Related Art An injection molding machine 100, as shown in FIG. 3, has a barrel 1 having a nozzle 3 at its tip and a temperature adjusting device (heater 11) at its outer periphery. The barrel 1 is arranged so that the nozzle 3 can face the material injection port of the mold 4. The resin sent from the hopper 10 into the barrel 1 through the resin discharge port 10a is transferred from the material supply unit to the compression unit by the screw 2 which is rotationally driven by the motor 5, and the groove depth of the screw groove is formed in the compression unit. Is gradually compressed due to the gradual decrease. In this process, the resin between the screw flights 2a of the screw 2 transfers heat from the inner wall surface of the barrel 1 by the heater 11 and the resin itself due to the rotating action of the screw 2, and between the resin and the barrel 1 or the screw 2. Due to the frictional heat (generated by shearing energy) generated in step 1, a molten melt film is formed on the inner wall surface of the barrel 1, and is further collected by the screw flight 2a to form a melt pool in the screw groove 2b. In this way, the resin in the barrel 1 in the process of promoting plasticization is composed of three parts of the melt film, the melt pool and the solid bed which has not reached the melting point yet, and these are accompanied by the rotation of the screw 2, While being transferred further forward, the unmelted portion (solid bed) is continuously melted by the heating from the heater 11 and the rotating action of the screw 2.
In order to obtain a homogeneous molten plasticized resin by removing the unmelted portion in the measuring section of the screw 2.

[0003]

The screw 2 of the injection molding machine 100 as described above is usually made of steel, and although the strength is sufficient, the thermal conductivity is not necessarily sufficiently high. Therefore, for example, a screw having a heat pipe improved in a steel screw has been proposed (Japanese Patent Laid-Open No. 1-74117). However, in this proposal, the structure is complicated and expensive, and the strength is inevitably reduced. Further, in the case of a resin material having a large shear heat generation, a local temperature rise of the screw 2 occurs due to the shear heat generation and often exceeds a set temperature, and excess heat is difficult to be dispersed because the thermal conductivity is small, Although the temperature of the supply part is low, only the compression part and the measuring parts after it become high temperature, and the screw temperature is hard to fall. Therefore, the resin in the vicinity of the screw surface receives an excessive heat history and causes thermal deterioration of the resin. The present invention has a much higher thermal conductivity than steel instead of a screw made of steel, and by using a screw formed of a metal material whose structural strength is not so low compared to that of steel, This is intended to improve the plasticization efficiency of the resin by facilitating the axial diffusion of the heat of the screw whose temperature has risen locally and leveling the screw temperature.

[0004]

In order to solve the above problems, in the present invention, the screw of the injection molding machine is made of a material having a thermal conductivity of 130 w / m · k or more, and
It is a metal material having a tensile strength of 40 kg / mm ² or more.

[0005]

In the present invention, the heat generated by the shearing heat generated in the compression section following the supply section of the injection molding machine is distributed to the supply section at a relatively low temperature by the screw having a high thermal conductivity, so that the conventional steel As compared with the screw, temperature equalization in the longitudinal direction of the screw is promoted, and a temperature rise exceeding the set temperature in the measuring unit is avoided. Therefore, the plasticization efficiency of the resin is improved and deterioration due to excessive temperature rise is prevented.

[0006]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a longitudinal sectional view of an essential part of the injection molding machine, and FIG. 2 is a temperature distribution diagram of the screw. As shown in Figure 1,
The screw 2 of the injection molding machine 100 of the present invention has the same shape as the conventional one. However, while the conventional screw is made of steel such as chrome molybdenum steel, a material having a much higher thermal conductivity than steel is used. Specifically, a metal material having a thermal conductivity of 130 w / m · k or more and a tensile strength of 40 kg / mm ² or more is adopted. As a material satisfying these conditions, for example, an aluminum alloy (JIS H4040 A2014, A
2024, A2075) and beryllium alloy (JIS H
3270 C1720) and high strength brass (JIS H325)
0 C6782, C6783) can be used. The thermal conductivity and tensile strength of these metal materials and steel are as shown in Table 1.

[0007]

[Table 1]

The reason for limiting the numerical value of the screw material of the present invention will be described. The fact that the thermal conductivity is about 3 times or more that of the conventional type (made of steel) and the tensile strength is 40 kg / mm ² or more is conventional. This is because the structural strength is not significantly reduced as compared with that made of steel, and the strength has practically no hindrance.

In the injection molding machine 100 of the present invention having the screw 2 constructed as described above, for example, AB
When molding a resin material such as S resin, PC (polycarbonate) resin, nylon resin, or the like that generates a large amount of heat by shearing by heating and melting, the barrel 1 and the screw 2 in the compression section B
Shear heat generation caused by the reduction of the resin passage of is particularly large, and in the case of the conventional steel screw, as shown by the temperature curve C ₁ in FIG. In the screw 2 of the present invention, the heat generated by the shearing heat generated in the compression section B is transferred to the supply section A having a relatively low temperature through the screw 2 having a high thermal conductivity, and is shown by the temperature curve C ₂ in FIG. As described above, the temperature distribution of the supply unit A is relatively contributed, the excessive temperature rise of the compression unit B and the measurement unit C is prevented, and the temperature distribution is close to the set temperature S as a whole. As described above, by using the screw of the present invention, the temperature of the metering section or compression section, which tends to rise above the set temperature due to the heat generated by shearing of the resin, can be kept low near the set temperature. Therefore, the molten resin is not exposed to excess heat and thermal deterioration can be prevented. In addition, since the excess heat of the screw metering section and the compression section is transferred to the supply section that is much lower than the set temperature, the preheating effect on the resin pellets is improved, so that it is possible to improve the plasticizing ability. Furthermore, as well as being a material with good thermal conductivity, since a metal material having a tensile strength of a certain level or more can be used, it is possible to suppress the decrease in the strength of the screw as compared with the heat pipe method, and without requiring extra processing, It can be manufactured at low cost.

[0010]

As described above, the screw of the injection molding machine of the present invention equalizes the temperature in the longitudinal direction of the screw and avoids excessively high temperature, thus promoting plasticization of the resin. In addition, the deterioration of the resin is prevented, so that the quality of the molded product is improved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an essential part of an injection molding machine according to an embodiment of the present invention.

FIG. 2 is a temperature distribution diagram of a screw of the injection molding machine according to the embodiment of the present invention.

FIG. 3 is an overall vertical sectional view of a conventional injection molding machine.

[Explanation of symbols]

1 barrel 2 screw 2a screw flight 3 nozzle 4 mold 5 motor 10 hopper 10a resin discharge port 11 heater 100 injection molding machine A supply unit B compression unit C measuring unit S set temperature C ₁ temperature curve C ₂ temperature curve

Claims (1)

[Claims] 1. A screw for an injection molding machine, wherein the material of the screw is a metal material having a thermal conductivity of 130 w / m · k or more and a tensile strength of 40 kg / mm ² or more. Screw.