Method and molding device for manufacturing foamed resin molded product

Abstract

To provide a method and molding device for manufacturing a foamed resin molded product that can shorten a molding cycle time and stabilize a detent distance at the same time.SOLUTION: In a method for manufacturing a foamed resin molded product, pre-expanded particles are filled into a cavity 15, steam is supplied into master frames 11 and 13 of each mold to heat and expand the pre-expanded particles, and when an expansion pressure rises, a movable mold 12 is retracted by the expansion pressure, after which a molded product is cooled and removed. The expansion pressure inside the cavity 15 is detected by a surface pressure gauge 18, and an opening of a steam valve 17 that supplies steam to the master frame is automatically controlled according to the detected expansion pressure, thereby stabilizing a detent distance d, which is a retraction distance of the movable mold.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method and a molding apparatus for producing a foamed resin molded product. [Background technology]

[0002] Foamed resin molded products such as foamed polyethylene and foamed polystyrene are manufactured by filling a cavity formed by a fixed mold and a movable mold with pre-foamed particles, supplying high-temperature steam into the master frame of each mold to heat and foam the pre-foamed particles, and then cooling the product before opening the movable mold and removing the molded product. However, as the thickness of the foamed resin molded product increases, the time required for the cooling process increases, which poses a problem of extending the molding cycle time and reducing productivity.

[0003] One solution to this problem is described in Patent Document 1, in which a mold plate for adjusting the cavity thickness, which defines one side of the cavity, is made slidable, and gradually slides due to the foaming pressure during the heating process. This technique is called "détente" because it releases the increased foaming pressure, and the sliding distance is called the "détente distance." The size of the cavity changes depending on the détente distance, which results in variations in the size of the molded product.

[0004] This technology has the advantage of reducing the energy stored in the molded product in the cavity by releasing the energy of the foaming pressure, thereby shortening the time required for the subsequent cooling process. However, because the properties of pre-expanded particles vary depending on various factors such as particle size and maturity, even if the amount of steam energy supplied is constant, variations in the degree of foaming are inevitable. As a result, the detente distance varies, resulting in inconsistent molded product sizes and the risk of defective products. For this reason, in the past, skilled workers controlled the detente distance by fine-tuning the molding conditions while monitoring the molded products, which left the problem of the defect rate depending on the worker's level of skill. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 2553754 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to provide a manufacturing method and molding apparatus for foamed resin molded products that solves the above-mentioned conventional problems, shortens the molding cycle time, and stabilizes the detent distance. [Means for solving the problem]

[0007] The method for manufacturing a foamed resin molded product of the present invention, which has been devised to solve the above-mentioned problems, involves filling a cavity formed by a fixed mold and a movable mold with pre-foamed particles, supplying steam into the master frame of each mold to heat and expand the pre-foamed particles, and when the foaming pressure rises, causing the movable mold to retreat due to the foaming pressure, and then cooling and removing the molded product.The method is characterized in that the foaming pressure within the cavity is detected by a surface pressure gauge, and the opening of a steam valve that supplies steam to the master frame of each mold is automatically controlled in accordance with the detected foaming pressure, thereby stabilizing the retreat distance of the movable mold.

[0008] It is preferable to evacuate the master frame to a vacuum before heating and expanding the pre-expanded particles.

[0009] The molding device for foamed resin molded products of the present invention, which has been made to solve the above-mentioned problems, is characterized by comprising a fixed mold having a master frame, a movable mold having a master frame, a steam valve for supplying high-temperature steam to these master frames, a surface pressure gauge for detecting the foaming pressure in the cavity formed by the fixed mold and the movable mold, automatic control means for controlling the opening of the steam valve in accordance with the detected foaming pressure, and means for releasing the clamping force of the movable mold when the foaming pressure is increasing or has reached its peak. [Effects of the Invention]

[0010] In the method for producing a foamed resin molded product of the present invention, the foaming pressure in the cavity during the heating and foaming process is detected by a surface pressure gauge, and the opening of a steam valve that supplies steam to the master frame is automatically controlled in accordance with the detected foaming pressure. Because the foaming process is driven by thermal energy imparted by the steam to the pre-expanded particles in the cavity, automatically controlling the opening of the steam valve to maintain the foaming pressure at a set value stabilizes the retraction distance of the movable mold. This stabilizes the detent distance even when the properties of the pre-expanded particles vary, eliminating the dependency of the defect rate on the skill of the operator. Furthermore, when the foaming pressure is rising or has peaked, the clamping force of the movable mold is released to retract the movable mold, thereby releasing the energy of the foaming pressure and significantly shortening the time required for the cooling process.

[0011] Furthermore, if the master frame is evacuated to a vacuum state after each molding cycle, the heating effect of steam will not vary due to air or water remaining in the master frame, stabilizing the heat-expanding process of the pre-expanded particles. This stabilizes the expansion pressure and further stabilizes the retraction distance of the movable mold due to the expansion pressure, i.e., the detent distance. [Brief explanation of the drawings]

[0012] [Figure 1]FIG. 1 is an explanatory diagram illustrating a device configuration according to an embodiment. [Figure 2] FIG. 10 is an explanatory diagram showing a state in which the movable mold is retracted. [Figure 3] 10 is a graph showing a change in pressure within a cavity. [Figure 4] 1 is a diagram showing a manufacturing process for a foamed resin molded product of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present invention will be described below, but first the configuration of a molding apparatus for molding foamed resin products will be described. In Figure 1, reference numeral 10 denotes a fixed mold having a master frame 11 on its back surface, and reference numeral 12 denotes a movable mold having a master frame 13 on its back surface. The movable mold 12 is opened and closed relative to the fixed mold 10 by a drive mechanism 14 such as a cylinder. A molding cavity 15 is formed by the fixed mold 10 and the movable mold 12. Figure 1 shows a state in which the interior of this cavity 15 has been filled with pre-expanded particles. The pre-expanded particles are filled through a well-known filling nozzle (not shown). Note that vent holes for steam inflow are formed in the surfaces of each of the molds 10 and 12 that form the cavity 15.

[0014] Reference numeral 16 denotes a steam supply source such as a boiler, which can supply high-temperature steam to each of the master frames 11 and 13 via steam valves 17. The supplied steam flows into the cavity 15 through the vent holes. The pre-expanded particles are heated by the thermal energy of the flowing steam, melt and foam inside the cavity 15, and the foamed particles fuse together to form a foamed resin molded product.

[0015] The fixed mold 10 is provided with a surface pressure gauge 18, which can detect the foaming pressure of the pre-expanded particles inside the cavity 15. The foaming pressure data is sent to automatic control means 19, and a steam control device 20 automatically controls the opening of the steam valve 17 so that the foaming pressure is maintained at the set value.

[0016] Reference numeral 21 denotes an exhaust means such as a vacuum pump, which is connected to the master frame 11 and the master frame 13 via an exhaust valve 22. In a preferred embodiment, the insides of the master frame 11 and the master frame 13 are evacuated to a vacuum prior to the supply of steam.

[0017] Next, the process for producing the foamed resin molded product of the present invention will be described in detail. First, the drive mechanism 14 closes the movable mold 12 as shown in Figure 1, forming a molding cavity 15 between it and the fixed mold 10. Next, pre-expanded particles are filled into this cavity 15 from a filling nozzle (not shown). Pre-expanded particles are made by pre-expanding raw material beads containing foaming ingredients and then aging them in an aging silo, and the amount filled is determined so as to achieve the target weight of the molded product. Aging refers to the process of replacing organic gas components such as butane and pentane contained in the foamed particles with air.

[0018] Next, the exhaust valve 22 is opened, and the inside of the master frame 11 and the master frame 13 is evacuated to a vacuum state by the exhaust means 21. This removes any air or water vapor remaining in the master frames 11 and 13, stabilizing the next heating and foaming process. This vacuum reduction is performed for each molding cycle. It is preferable to reduce the pressure inside the master frame 11 and the master frame 13 to -0.075 MPa or less, which allows for almost complete removal of any remaining air or water vapor, even if the shape of the cavity 15 is complex.

[0019] Next, the steam valve 17 is opened, and high-temperature steam is supplied from the steam supply source 16 into the interior of the master frame 11 and the master frame 13. The thermal energy of this steam heats the pre-expanded particles inside the cavity 15, causing them to foam and expand in volume. This causes the pressure inside the cavity to rise suddenly, as shown in the graph in Figure 3, and the expanded particles fuse together. This pressure inside the cavity is detected by a surface pressure gauge 18 attached to the fixed side of the mold 10. Automatic control means 19 automatically controls the opening of the steam valve 17 in accordance with the foaming pressure detected by the surface pressure gauge 18.

[0020] That is, if the detected surface pressure is higher than the set value, the opening of the steam valve 17 is reduced or the steam valve 17 is closed to reduce the steam pressure supplied, and conversely, if the detected surface pressure is lower than the set value, the opening of the steam valve 17 is increased or the steam valve 17 is fully opened to increase the steam pressure supplied. As a result, the thermal energy supplied to the master frame 11 and the master frame 13 changes, and the surface pressure can be controlled to approximately match the set value.

[0021] When the cavity pressure is rising or has reached its peak, the drive mechanism 14, which had been pressing the movable mold 12 against the fixed mold 10, is switched to neutral by the drive control means 23, releasing the clamping force on the movable mold 12 and making it movable by external force. At the same time, the foaming pressure in the cavity 15 causes the movable mold 12 to instantly retreat, as shown in FIG. 2 . This creates a detent distance d between the fixed mold 10 and the movable mold 12. In the present invention, the final retreat position of the movable mold 12 is regulated to coincide with the final thickness / height of the foamed resin molded product. In this embodiment, this detent distance d is set to a range of 0.5 to 3.0 mm, and the foaming energy of each foam particle allows the molded product to stably expand to the final thickness / height of the foamed resin molded product.

[0022] In this way, when the cavity pressure is rising or has reached its peak, if the clamping force of the movable mold 12 is released and the movable mold 12 is moved back by the foaming pressure, the cavity pressure will drop sharply as shown in Figure 3, and the time required for the subsequent cooling process can be reduced by half compared to the conventional method, thereby shortening the molding cycle time.

[0023] After cooling, the drive mechanism 14 opens the movable mold 12, and the molded product is removed from the cavity 15. The thickness of the molded product is affected by the detent distance d, but in this invention, the opening of the steam valve 17 is automatically controlled according to the detected surface pressure, reducing the variation in the detent distance d compared to the conventional method, and also reducing the variation in the dimensions of the molded product. Therefore, the defect rate is no longer affected by the skill level of the worker, as in the conventional method. The manufacturing process for foamed resin molded products of this invention is summarized in the process diagram in Figure 4.

[0024] As described above, the present invention has the effect of shortening the molding cycle time of a foamed resin molded product and simultaneously stabilizing the detent distance. [Explanation of symbols]

[0025] 10 Fixed side mold 11 Master Frame 12 Movable mold 13 Master Frame 14 Drive mechanism 15 Cavity 16 Steam source 17 Steam valve 18 Surface pressure gauge 19 Automatic control means 20 Steam control equipment 21 Exhaust means 22 Exhaust valve d Detente distance

Claims

1. A method for manufacturing a foamed resin molded product, comprising filling pre-expanded particles into a cavity formed by a fixed mold and a movable mold, supplying steam into a master frame of each mold to heat and expand the pre-expanded particles, causing the movable mold to retreat due to the foaming pressure when the foaming pressure increases, and then cooling the molded product to remove it, A method for manufacturing a foamed resin molded product, characterized in that the foaming pressure in the cavity is detected by a surface pressure gauge, and the opening of a steam valve that supplies steam to the master frame of each mold is automatically controlled in accordance with the detected foaming pressure, thereby stabilizing the retraction distance of the movable mold.

2. 2. The method for producing a foamed resin molded product according to claim 1, wherein the master frame is evacuated to a vacuum state before the pre-expanded particles are heated and expanded.

3. a fixed mold having a master frame, and a movable mold having a master frame; a steam valve for supplying high-temperature steam to these master frames; a surface pressure gauge for detecting the foaming pressure in a cavity formed by the fixed mold and the movable mold; an automatic control means for controlling the opening degree of the steam valve in accordance with the detected foaming pressure; a means for releasing the clamping force of the movable mold when the foaming pressure is increasing or reaches its peak; A molding apparatus for a foamed resin molded product, comprising:

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