JPH0261982A - Microwave-heated molding method - Google Patents

Abstract

PURPOSE:To heat a material with small dielectric loss and easily absorbing microwaves such as rubber or a pottery with microwaves by burying a heating element easily absorbing microwaves in an object to be heated which is hard to absorb microwaves and radiating microwaves from the outside. CONSTITUTION:An unbridged polyethylene layer 6 is formed between a tube section 2 and a hollow core forming shaft section 5 while unbridged polyethylene of an object to be heated, for example, is extruded from an extruding machine 1. The unbridged polyethylene layer 6 is heated by an electric heater 3 from the outer periphery of the tube section 2. Microwaves generated by a microwave generator 4 concurrently permeate the tube section 2 and the unbridged polyethylene layer 6 and radiate the hollow core forming shaft section 5 to heat the shaft section 5, and the unbridged polyethylene layer is heated by this heat from the inside. The whole unbridged polyethylene layer 6 is heated to the required temperature in a short period and uniformly bridged.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a microwave thermoforming method for thermoforming a substance by irradiating microwaves.

[Prior art] Conventionally, a method known as microwave heating molding involves mixing a substance with a large dielectric loss into a thermosetting resin and then irradiating it with microwaves to heat-cure it. It is used for manufacturing etc. This microwave heat forming method uses the principle of dielectric heating, and when an alternating current voltage is applied to the molecules that make up a substance, electricity is consumed due to friction caused by molecular vibration and heat is generated. . Such a phenomenon is called dielectric loss, and the dielectric loss P per unit volume is expressed by the following equation (1).

P-5,6X10" fE2 Xetan δ (W/m') = (1) However, (1
) In the formula, f is the frequency of the AC voltage, E is the applied voltage,
(is the dielectric constant of the material, and tanδ is the dielectric loss tangent.

However, as is clear from equation (1), the frequency f,
In a material having a small square of the applied voltage E, a small dielectric constant q, and a small dielectric loss tangent tan δ, the dielectric loss P will be a small value, and the microwave will be transmitted without being absorbed, so the amount of heat generated will be small. Therefore, materials such as glass, ceramics, and many plastics, which have a small dielectric loss P, are difficult to absorb microwaves and cannot be heated simply by irradiating them with microwaves.

[Object of the Invention] An object of the present invention is to provide a microwave heating forming method that eliminates the drawbacks of the above-mentioned conventional examples and makes it possible to heat-form a material with small dielectric loss and difficult to absorb microwaves. It's about doing.

[Summary of the Invention] The gist of the present invention to achieve the above-mentioned object is to embed a heating element made of a material with good microwave absorption characteristics inside a heated object that is difficult to absorb microwaves, and to This is a microwave thermoforming method characterized by heating the heating element by irradiating microwaves from the outer surface of the object to be heated, and heating the object to be heated by this heat.

[Embodiments of the invention] The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a sectional view showing a case where a crosslinked plastic vibrator with good heat resistance is manufactured by the microwave heating molding method according to the present invention. Extrusion 41! One end of a microwave-transparent tube section 2 made of ceramic or the like is connected to the outlet of the tube section 1, and a conventional electric heater 3 and a microwave generator 4 are installed outside the tube section 2. Further, the extrusion a1 is filled with uncrosslinked polyethylene or the like to which a crosslinking agent has been added as a raw material.

A rod-shaped shaft portion 5 for forming a hollow core is inserted into the center of the tube portion 2. This shaft portion 5 for forming a hollow core is made of a material such as ethylene vinyl acetate, which has a higher dielectric constant and dielectric power factor than polyethylene. It is preferable that

Here, extrusion 4I! While extruding the uncrosslinked polyethylene from 1, an uncrosslinked polyethylene layer 6 is formed between the tube part 2 and the shaft part 5 for forming a hollow core. Further, the uncrosslinked polyethylene layer 6 is heated from the outer circumferential portion of the tube portion 2 by the electric heater 3 . At this time, the microwave simultaneously generated from the microwave generator 4 is transmitted to the pipe portion 2 and the uncrosslinked polyethylene layer 6.
The hollow core-forming shaft portion 5 is irradiated with the light, causing the shaft portion 5 to generate heat, and this heat heats the uncrosslinked polyethylene layer 6 from within. In this way, the uncrosslinked polyethylene layer 6
Since the material is heated internally and externally, the temperature required for crosslinking can be easily reached and the entire product can be uniformly crosslinked in a short period of time. After crosslinking, the crosslinked polyethylene R6' is discharged from the other end of the pipe section 2 together with the shaft section 5 for forming a hollow core, and the shaft section 5 is removed to produce a crosslinked plastic pipe.

FIG. 2 is a perspective view of the case where the same method as described above is applied to the production of parts with complicated shapes. After covering it with water, irradiate it with microwaves from the outside. The microwaves pass through the heated material 8 and are absorbed by the heating element 7, and the heated material 8 is heated and molded from the inside by the heat generated by the heating element 7, so it is possible to easily obtain a #IH shaped molded product. can.

In the above embodiment, uncrosslinked polyethylene was used as an example of the material to be heated, but it can also be used for rubber, plastic, glass, and ceramics.

[Effects of the Invention] As explained above, the microwave heating forming method according to the present invention embeds a heating element that easily absorbs microwaves inside a heated object that does not easily absorb microwaves, and , it is possible to heat materials such as rubber, ceramics, many plastics, etc., which have low dielectric loss and are difficult to absorb microwaves, using microwaves. Furthermore, since the heating element is installed inside, heat can be generated from within, which is advantageous for molding complex shapes.

[Brief explanation of the drawing]

The drawings show an embodiment of the microwave heat forming method according to the present invention, with FIG. 1 being an explanatory diagram when applied to a pipe manufacturing method, and FIG. 2 being an explanatory diagram of another embodiment. Reference numeral 1 is an extruder, 2 is a tube section, 3 is an electric heater, 4 is a microwave generator, 5 is a shaft for forming a hollow core, 6 is an uncrosslinked polyethylene layer, 7 is a heating element, and 8 is a material to be heated. be.

Claims (1)

[Claims] 1. A heating element made of a material with good microwave absorption characteristics is buried inside a heated object that is difficult to absorb microwaves,
A microwave thermoforming method characterized in that the heating element is heated by irradiating microwaves from the outer surface of the object to be heated, and the object to be heated is heated by the heat.