JPS602327A - Method of controlling temperature of mold for molding resin - Google Patents

Abstract

PURPOSE:To shorten the solidifying time of a melted resin in a cavity, by passing alternatively a heating medium having a temperature required for charging a resin and a heating medium having a temperature lower than that through a heating medium passage arranged adjacent to a cavity. CONSTITUTION:In a mold 1 that is used particularly in injection molding technique, a heating medium passage 3 is arranged adjacent to a cavity 2. A first heating medium 11 is passed to raise the temperature adjacent to the cavity to a temperature enough to charge a melted resin. Then immediately after the melted resin is charged into the mold 1 under a prescribed pressure, a second heating medium 12 is passed to lower the temperature adjacent to the cavity 2 so that the cooling speed of the resin is quickened to shorten the solidifying time. Immediately after the solidifying of the resin, the first heating medium 11 is passed to raise the temperature adjacent to the cavity so that the temperature may be restored to the prescribed temperature required for charging of the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION The object of the present invention is to significantly shorten the time required for molding a resin molded article, especially the time required for cooling and solidification, particularly in a mold used in an injection molding method.

As shown in Figure 1, the conventional method is to keep the entire mold at a constant temperature over time, and to protect the entire mold from thermal disturbances by installing a heat insulating material in the sealing part. The structure was designed to be resistant and practical. In this way, the general idea is that the entire mold is kept at a constant temperature, and the flow characteristics of the resin, molding shrinkage, molding distortion, and surface condition are stabilized over time in order to stabilize product quality. If you do it like this,
The minimum temperature required to fill the mold cavity while maintaining quality is determined by the temperature-dependent characteristics of resin fluidity and the flow path of molten resin into the cavity, and the cavity must be filled at this temperature. No. Further, the temperature of the molten resin filled in the cavity asymptotically decreases toward the mold temperature TO. This is cooled along the first exponential curve 001 shown in FIG. 2. Taking polyacetal resin as an example, the crystallization temperature T! Since the latent heat of fusion has a peak near l(+165°C), the temperature of the molten polyacetal resin stops decreasing by 40°al/! 1. ,. When the latent heat of fusion of No. 5 moves, the temperature of the polyacetal resin decreases again along the first cooling curve Moat. At this time, the polyacetal resin at the gate portion of the cavity solidifies and reaches the gate sealing temperature Tc, which requires a gate sealing time sc1. Thereafter, the product must be cooled to a solidification temperature TB at which the polyacetal resin in the cavity has enough elasticity or rigidity to resist the resistance force when it is extruded from the cavity by an ejector bin. This indicates that a solidification time of 8e1 or more is required, which is a characteristic contradictory to reducing the required molding time Elf1. As mentioned above, it is difficult to shorten the molding time Sf1 because the solidification time Se1 from filling the cavity to the solidification temperature TB is required while maintaining the flow characteristics necessary for filling the molten resin into the cavity. there were.

The present invention eliminates such drawbacks, and its purpose is to shorten the time required for cooling and solidifying without impairing the flow characteristics necessary for filling a cavity with molten resin due to its dependence on temperature. be.

The present invention will be described in detail below based on Examples. In FIGS. 3 and 4, the first heating medium 11 at a temperature t1 is passed through the mold at room temperature by the first directional control valve 5 (vl) to bring the temperature to tl. This is done in the same way as the conventional heating of the mold at the start of the operation. Next, the first heating medium 11 is stopped and its temperature reaches t2C.The second heating medium 12 is caused to flow and the temperature around the cavity is lowered to the second set temperature T. Further, the second heating medium 12 is stopped and the first heating medium 11 is allowed to flow, so that the temperature in the vicinity of the cavity becomes sufficient to fill the molten resin.
Raise the temperature to the set temperature Tyu. This allows the vicinity of the cavity to be at the same temperature as during cycle operation or a temperature close to it. Also, the temperature near the cavity is the first
The temperature reaches the set temperature T0, which is sufficient to fill the cavity with the molten resin. At this time, the molten resin is injected and filled into the cavity, and at the same time as the start of filling or the end of filling, the second heating medium 12 is caused to flow to lower the temperature around the cavity, speed up the cooling rate of the resin, and shorten the assimilation time 8e2. At this time, the temperature near the cavity is the first set temperature T
Exponential function curve C■2 from 1 to the second set temperature T2
The temperature drops in the swamp. The temperature of the molten resin is based on the second exponential function curve Co2, and the second cooling curve Oa2, which includes the internal latent heat near the crystallization temperature Ty and the temperature change near the cavity, moves to the solidification temperature via the gate seal temperature Tc. Reach TE.

As is clear from comparing Figures 2 and 3, the slope of the cooling curve differs depending on the temperature of the molten resin and the temperature near the cavity, and it is generally known that the slope of the cooling curve is proportional to the temperature difference and is an index of the elapsed time. Becomes a function. Comparing the solidification time to solidification temperature TE between the conventional method and the method of the present invention, in the case of polyacetal resin, it was shortened by about 60% to TE. The method of the present invention has the excellent effect of maintaining the fluidity of the molten resin without impairing it during filling, while lowering the temperature near the cavity during cooling and solidification, thereby shortening the solidification time. More specifically, as shown in FIG. 4, the mold 1 is comprised of a heat medium inlet 4a and a heat medium outlet 4b communicating with a heat medium passage 3 provided near the cavity 2. Further, a first pump 9 that pumps the first heat medium 11, a first pressure control valve 7 that controls the pressure below a constant pressure, and a first directional control valve 5 that communicates with the heat medium inlet 04α and the heat medium outlet 4b. and a second heating medium 1 configured in parallel with the first heating medium 11.
2, a second heat medium 12 circulation circuit constituted by two second pumps 1o, a second pressure control valve 8, and a second directional control valve 6. In the above configuration, the first heat medium 11 is the first pump? The first heat medium 11 that has passed through the first pressure control valve 7 and reached the heat medium outlet 4b via the heat transfer passage 3 is transferred to the heat medium inlet 4α by the first directional control valve 5. At this time, the first directional control valve 5 is in an operating state and the second directional control valve 6 is in a stopped state. Since the second directional control valve 6 is in a stopped state, the pressure of the second heat medium 12 pumped out by the second pump 10 becomes high and is sent back by the second pressure control valve. As described above, by alternately operating the directional control valves, the temperature in the vicinity of the cavity 2 can be changed periodically. Other circuit configurations can also meet the objective of the present invention as long as the method allows the heat medium to flow alternately in this manner. Furthermore, the first directional control valve 5
The switching timing between the operating state and the stopped state of the second directional control valve 6 can also be determined based on the temperature near the cavity B, and is included in the present invention.

As described above, the heating medium passage provided near the cavity is provided with the function of alternately circulating heating mediums of different temperatures, and the heating medium heated to a temperature higher than the temperature required for filling the resin and the heating medium heated to a temperature higher than the temperature required for filling the resin. By alternately circulating a heat medium cooled to a lower temperature, a method can be provided that can significantly shorten the solidification time of the molten resin in the cavity.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the state of conventional mold temperature. FIG. 2 is a diagram showing the temperature change of the resin inside the cavity obtained by the conventional mold temperature control method. FIG. 3 is a diagram showing the temperature change of the resin in the cavity according to the temperature control method of the present invention. Fourth
The figure is a diagram showing the relationship between a heating medium alternate circulation circuit and a heating medium path for periodically circulating heating mediums of different temperatures in the vicinity of a cavity. 1...Mold 2...Cavity 3...Heat medium passage 4α...Heat medium inlet 4h... ...Heat medium outlet 5...First direction control valve (vl) 6...
......Second directional control valve (v2)7...
...First pressure control valve 8 ...Second pressure control valve 9 ...First pump 10 ...Second pump 11 ... ...First heating medium 12...Second heating medium 1 figure 2 figure f: si! 1″f4 diagram

Claims (1)

[Claims] In a resin moldability method in which a cavity of a desired product shape of a mold is filled with molten resin at a predetermined pressure, a heating medium alternate circulation circuit is provided in which a heating medium passage is provided near the cavity and heating mediums of different temperatures are passed through the passage. Immediately after the molten resin is filled into the cavity, the second heating medium is passed through to promote cooling, and immediately after the resin solidifies, the first heating medium is passed through to raise the temperature around the cavity to a predetermined level necessary for filling the molten resin. A method for controlling the temperature of a mold for resin molding, characterized by returning the temperature to a temperature of .