CN1083767A - Be used for the Electric radiant Heating Film of Plastic Welding and manufacturing thereof and with the method for its welding plastic - Google Patents

Abstract

The electrothermal film for welding plastics is a mixture of plastic matrix and conductive filler. The filler is carbon black or metal powder; or carbon fiber or metal fiber; or a mixture of the above fillers. To manufacture the electric heating film, first mix the matrix with the filler, and then extrude, inject or calender it into an electric heating film that matches the welding surface; or directly extrude and injection mold it on the surface to be welded to form an electric heating film. Using the above-mentioned electric heating film to weld plastic parts is to energize the electric heating film and apply a certain pressure. The electric heating film heats up to the plastic welding temperature, so that the electric heating film and the welding surface of the plastic part are fully fused. After the power is cut off and cooled, the welding process is completed.

Description

The invention belongs to plastic welding, and in particular relates to a component for plastic welding and its manufacturing and application method.

Plastic products are used more and more widely in daily life, construction, aerospace and other aspects because of their low price, high quality and simple processing methods. How to connect materials to meet the performance requirements of the product, and the operation is simple and the cost is low has always been a key issue. Practice has shown that, in addition to mechanical fastening and bonding and other connection methods, welding is a high-quality, high-efficiency plastic connection technology. At present, there are many welding methods for plastics, which can generally be divided into three categories: thermal welding, friction welding and electromagnetic welding. Among them, electric heating wire welding, which belongs to electromagnetic welding, is also called electric fusion welding. Its industrial application began in the early 1980s. Due to the simple construction operation, light field equipment, and fast welding speed (generally <20 seconds), large and complex products can be welded. , this welding method was quickly developed and promoted. The basic principle is: pre-embed the high-resistance metal wire into the plastic surface to be welded or the inner wall of a special plastic sleeve. After the power is turned on, the electric heating wire heats up and melts the surrounding plastic and fuses with each other. This welding technology has been used in many countries for the welding and repair of small-diameter air supply pipes and sewer pipes, and the effect is good. However, there are many disadvantages in electrofusion welding: 1) the main reason is that the cost is high, and the injection molding process and mold of the heating wire embedded in the plastic are quite complicated, which will inevitably lead to high production costs of the parts to be welded; 2) when the plastic melts and a small amount of flow occurs, Closely arranged heating wires overlap each other to cause short circuit and often cause welding failure; 3) After welding, the heating wire remains in the weld seam, which affects performance on the one hand, and causes unnecessary waste of alloy materials on the other hand.

The task of the present invention is to provide a kind of electrothermal film for plastic welding and its production and welding use method, welding plastic products to be welded with it, can simplify the manufacturing process of the parts to be welded, reduce Cost, while avoiding the short circuit of the heating wire and other bad phenomena.

The electrothermal film of the present invention is a composite material, which is a mixture composed of a plastic matrix and a conductive filler. The plastic matrix is made of the same plastic as the plastic product to be welded or another plastic with good welding performance with the piece to be welded. The conductive filler is made of carbon black with a particle size of less than 0.3 μm, or metal and its alloy powder; or the long diameter Carbon fiber or graphite fiber or metal and its alloy fiber with a ratio greater than 21-30 or a mixture of the above-mentioned conductor fillers.

The above composite electric heating film has the following properties:

1. It has a good welding effect with the parts to be welded, so the type of substrate is selected;

2. Has good electrical conductivity;

3. Has good mechanical properties, because the electrothermal film remains in the weld, its mechanical properties often determine the welding strength;

4. The resistivity cannot have too strong positive temperature coefficient effect (ie PTC effect) in the range from room temperature to melting temperature.

The type and content of conductive filler can be selected from the last three items. The weight content of the conductive filler in the composite electrothermal film is generally between 10% and 60%. If the content is less than 10%, the electrical conductivity is too poor, the input power of the electric heating film is too low, and the welding speed is too slow; and if the content is more than 60%, the mechanical properties of the electric heating film are too low, which affects the welding strength, so the electric heating film formula needs to be overall considered . An electrode is respectively arranged at both ends of the electrothermal film to connect the power supply.

The manufacture method of above-mentioned composite electrothermal film:

First, the plastic matrix and conductive filler are uniformly mixed, and then the mixture is extruded, injected or calendered to form an electric heating film that matches the welding surface of the plastic product to be welded; or the mixture is directly extruded or injected on the surface to be welded to form an electric heating film membrane. Before the plastic matrix is mixed with the conductive filler, the conductive filler can be treated with a coupling agent such as silane or phthalate.

The method of welding plastic products with composite electric heating film:

When welding, connect the power supply to the electrodes at both ends of the electric heating film, and the electric heating film will heat up rapidly, so that the plastic to be welded When the material product reaches the welding temperature of the material, add a certain pressure P. After a certain period of time, the two sides of the electric heating film and the welding surface of the plastic product to be welded are fully fused, and then the power supply is cut off. After the welding area cools down, the welding process is completed.

Compared with the contrast technology, the present invention has obvious effect:

The invention not only has various advantages of electric fusion welding, but also the production of electric heating film is far less complicated than that of electric heating wire embedded in plastic, so the production cost is low; at the same time, problems such as short circuit of electric heating wire will not occur in the welding process, and the safety of welding The reliability is improved; the mechanical strength of the plastic products welded by the present invention is relatively high, and its tensile strength is generally about 0.8 of the parent plastic, even up to 0.9, which is also inferior to that of electric heating wire welding.

Graphic description:

Fig. 1 is the schematic diagram that applies the present invention to carry out butt welding;

Fig. 2 is a schematic diagram of applying the present invention for lap welding.

Embodiments of the invention are described with reference to the accompanying drawings:

Example 1: As shown in FIG. 1 , the electrothermal film 2 of the present invention is arranged on the butt joint surface of the workpiece 1 to be welded.

Welding conditions:

Input the electric heating film voltage V=150V;

The pressure P on the welding surface is 1.5~3.0kg/cm ² (press lightly by hand);

The power-on pressurization time is 30 seconds.

Welding performance:

Butt tensile strength 25.0MPa;

Base metal tensile strength 28.8MPa;

The welding strength factor is 0.87.

Example 2: As shown in Figure 2, plastic parts 1 to be welded are overlapped, and the electrothermal film of the present invention is arranged at the overlapping surface.

Welding conditions:

Input voltage 150V;

Apply pressure P1.5～3.0kg/cm ² to the overlapping surface;

Pressurization and energization time is 30 seconds.

After welding, the shear failure test was carried out on the lap joints, and it was found that the lap joints were not fractured, but were broken on one of the sample strips.

It can be seen from the above two embodiments that the welded plastic products produced by the present invention have higher welding strength and can meet complex engineering technical requirements.

Claims (3)

1. An electric heating film for plastic welding, which is characterized by a mixture of plastic matrix and conductive filler. The plastic matrix is made of the same plastic as the plastic product to be welded or has good welding performance with the piece to be welded. Another kind of plastic, the conductive filler is carbon black with a particle size of less than 0.3 μm, or metal and its alloy powder; or carbon fiber or graphite fiber or metal and its alloy fiber with an aspect ratio greater than 20-30; or the above-mentioned conductive filler The weight content of the conductive filler in the total mixture is 10-60%, and electrodes are respectively arranged at both ends of the electrothermal film. 2. A method of manufacturing an electric heating film for plastic welding: (1) Evenly mix the plastic matrix with the conductive filler; (2) Extrude, inject or calender the homogeneous mixture to form an electric heating film that matches the welding surface of the plastic product to be welded; or directly extrude or inject the mixture on the surface to be welded to form an electric heating film. 3. A method of welding plastics with electric heating film: when welding plastic products, connect the power supply to the electrodes at both ends of the electric heating film, and the electric heating film will heat up rapidly, so that the plastic parts to be welded reach the material welding temperature. The two sides of the electric heating film are fully fused with the welding surface of the plastic product, and then the power supply is cut off. After the welding area cools down, the welding process is completed.

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