CN1008051B - Production method of automatic temperature-limiting heating belt and product thereof - Google Patents

Abstract

The present invention discloses a method for manufacturing an automatic temperature-limiting heating belt and its product. The heating element of the heating belt uses two long metal wire cores with equal spacing as electrodes, on which a layer of thermistor switch material (i.e., PTC material) is continuously laid as a heating element, and the switching temperature of the material is Ts=85±5°C. A polymer sheath is coated on the outside of the electric heating element, and then the whole is radiated and cross-linked to form a finished heating belt. This product has three thermal properties: electric heating, power self-adjustment, and automatic temperature limiting. Its self-limiting temperature (Tr) is 80±5°C, and it can be widely used in heating and heat preservation projects such as antifreeze and anti-condensation in the petroleum and chemical sectors, and gas and liquid transportation pipelines.

Description

The invention relates to a manufacturing process of an electric heating device and the electric heating device thereof.

The electric heating element of the traditional electric heater uses metal resistance material as the heating element, and its resistivity changes little with temperature. Under the rated voltage, the electric heating power is basically constant. Only by adding electronic control equipment can the automatic adjustment of power be realized, but the technology is relatively complicated, the cost is high, and it is inconvenient to maintain. In 1961, F. Kohler used low-pressure polyethylene (HDPE) to fill the composite material made of carbon black (CB), and found that its resistivity had a positive temperature coefficient (Positive Temperature Coefficient), referred to as PTC material. The resistivity of this material not only increases with the increase of temperature, but also increases sharply in a specific temperature zone, so that it can block the current, and has the characteristic of thermosensitive electric switch. The temperature at which the resistivity jumps is defined as the switching temperature (Ts) of the PTC material. Different PTC materials have different switching temperatures (Ts), which mainly depend on the raw material composition and manufacturing process. The earlier prototype of the self-limiting heater made of PTC material as the heating element in the United States (USP3, 243, 753). The self-limiting heater made of PTC material can not only heat when it is powered on, but also automatically limit the maximum heating temperature, which is defined as the self-limiting temperature (Tr) of the heater. The height of the self-limiting temperature (Tr) depends on the switching temperature (Ts) of the PTC material, which can make the maximum heating temperature of the heater work stably near Ts. The self-limiting temperature Tr is a main indicator of the self-limiting temperature heater, which determines the adaptation range of the heater. In 1974, the United States has developed a self-regulating heater (Self-Regu-lating Heater) suitable for industrial use. In USP3,914,363 patent literature, the disclosed self-limiting conductive extrudate manufacturing method makes the completed heater must be annealed at a temperature of 120～150°C for more than 15 hours, thus requiring the jacket material of the heater ( The melting point of high polymer) must be tens of degrees higher than that of the internal PTC material to ensure that the PTC heating element does not soften and deform under the annealing temperature. At present, foreign countries (such as the United States) have commercially produced different types of self-limiting heaters with Tr of 65°C, 110°C, 120°C and 150°C. Since 1980, China has been involved in the above fields, and developed a self-limiting heating zone with Tr equal to 65°C. Because the heater (belt) has the special performance of automatic temperature limit and compensation heating, it has been widely used in antifreeze, anti-condensation, gas-liquid transportation pipelines, oil exploration and many other projects that require heating and insulation, and has been recognized excellent effect. In terms of civil use, self-limiting heaters have also been more and more widely developed and applied, which has attracted the attention of domestic and foreign science and technology and business circles. Zhao 57-21441, JP Zhao 56-8443) and the working life of the heater (JP Zhao 55-98801), etc. However, there is still a lack of self-limiting heaters with Tr=80°C in the prior art and commercial products, and the production process of such heaters has not been disclosed.

In view of the above situation, the task of the present invention is to propose a production method of an automatic temperature-limiting heater, and use a PTC material with a switching temperature (Ts) of 85°C as a heating element to manufacture a heater that can automatically limit the maximum heating temperature to 80°C. The self-limiting heating belt in the temperature zone of ±5°C can meet the requirements of the heater in the temperature zone for civil and various heat preservation projects.

The gist of the invention is: between two parallel metal wire cores with a certain distance, a PTC material layer is laid continuously and evenly to form a PTC core strip of an electric heating element. Then, a layer (or multiple layers) of polymer material (or metal braided mesh) is coated on the outside of the core belt as a heating belt coat, and finally the entire heating belt is irradiated and cross-linked, so that the PTC characteristics of the core material have a memory function. That is, the finished product of the self-limiting heater is made. Said metal wire core can be selected multi-strand stranded wire as two electrodes of heating belt. The PTC core belt and the polymer jacket use the same thermoplastic polymer (PE) as the base material. The invention is completed through the three-step process of drawing the PTC core belt, covering the jacket and irradiating cross-linking. Its production steps are:

A. Drawing the core belt: first preheat the single-screw extruder, and keep the temperature of the head of the extruder at 210-250°C, the temperature of the body at 150-180°C, and the temperature at the tail of the extruder at 80-110°C. Then load the pellets of PTC material whose switch temperature (Ts) is 85±5℃ from the tail of the machine. Use two equidistant conductive wire cores to pass through the extrusion mold of the machine head in parallel, and at the same time pull the wire cores to move at a constant speed, and the linear speed is stable at 30-50m/min. The viscous flow PTC material is extruded from the mold of the machine head and evenly laid on the two wire cores to form a strip-type heating element with a PTC material tail and two parallel electrodes (ie wire cores) on both sides, and then The drawn hot-state electric heating element is cooled by the water bath, and becomes the PTC core belt.

B. Covering jacket: Polymer jacket material, high pressure polyethylene (LDPE) cable sheath material can be selected. Use the above extruder of the same type, keep the head temperature of the extruder at 210-230°C, the body temperature at 150-170°C, and the tail temperature at 90-100°C, and apply an appropriate amount of talcum powder to the drawn PTC core belt , through the outer mold of the machine head, the shape of the outlet of the mold is the same as that of the core belt mold (section), and the size is slightly larger. The PTC core belt passing through the outer mold has the same pulling speed as the drawing speed of the PTC core belt. As the core belt is pulled out, the viscous sheath material in the extruder is continuously and evenly extruded on the PTC core belt through the outer mold, and the formed hot jacket is rolled and formed by a pair of cylindrical rollers. Make it close to the surface of the PTC core belt, then enter the water tank to cool down, and get the basic heating belt.

C. Radiation cross-linking: put the above-mentioned PTC core tape coated with the outer jacket in a radiation field under normal temperature, normal pressure and atmospheric atmosphere, and carry out overall uniform radiation cross-linking. The radiation source can be electron beam or gamma rays such as ⁶⁰ Co, ¹³⁷ Cs, etc. During irradiation, according to the different radiation sources used, the irradiation can be terminated when the cumulative irradiation dose of the body reaches 5-20Mrad. The degree of cross-linking of the PTC material and the coat should be in the range of 45% to 65%, that is, the production process of the self-limiting heating belt is completed.

The automatic temperature-limiting heating belt produced by the above steps is composed of a PTC core belt and a jacket with two electrodes on both sides. The self-limiting temperature (Tr) of the heating belt is 80±5°C. The core belt and the polymer jacket The same kind of thermoplastic polymer (PE) is used as the base material, and the cross-linking degree is 45-65% after the overall radiation cross-linking. The heating belt has a self-weight of about 40g/m, and is suitable for conventional AC and DC power supplies, and the working voltage is 220±20V. Its output power can be automatically adjusted with temperature changes. The continuous working life of the heating belt is more than 30,000 hours, and the intermittent working life is more than 2,000 times (one power-on and power-off cycle is one time). The finished heating belt is tested with AGA780 thermal imager. The self-limiting temperature distribution along the length of the belt is in the range of 80±5°C. It is qualified by the relevant testing unit according to the standard method of GB2951 and GB3048. And it has been tested by relevant units, and the effect is good, and it can be widely used in projects that require heating and heat preservation in industries, national defense and other departments. According to needs, it can also be made into heating and heat preservation devices of other shapes, so as to adapt to various special purposes.

Description of drawings:

Fig. 1 is the basic structure of an embodiment of an automatic temperature-limiting heating belt, wherein 1 is an electrode, 2 is a PTC material layer, and 3 is a jacket.

Fig. 2 is a sectional view of the PTC core tape A-A in Fig. 1, 1 is an electrode, and 2 is a PTC material layer.

Figure 3 is the relationship between the automatic temperature-limiting heating belt heating power P (W/m) and the temperature T (°C).

Example: Use Ts=85±5°C PTC material as the raw material for the core tape, use 19 regular strands of tinned round copper wires as the core, and use φ=0.26mm for each round copper wire, and use 2401 black polyethylene cables for the jacket Sheathing material (PE-H), using a φ45 single-screw extruder to draw the core belt and the covering jacket, irradiating and cross-linking with a ⁶⁰ Co γ-ray source, and stopping the irradiation when the cumulative dose reaches 15 Mrad, and measuring the cross-linking with a Soxhlet extractor. The degree of linking, the degree of cross-linking is greater than 45%. Using the above production steps, the temperature of the extruder is shown in Table 1 (see the text below):

When the drawn PTC core tapes in Examples 1 to 4 are coated with a jacket, the temperature of the extruder is kept at 230°C at the nose, 170°C at the body, and 100°C at the tail.

Example 1 2 3 4

Drawing PTC Head 220 210 220 250

Ribbon temperature (°C) Body 170 150 160 180

Tail 90 80 90 110

Claims (3)

1, a kind of automatic siding temperaturing heating belt production method, this method is that to carry out integral body with radiation method crosslinked, the electric heating element that it is characterized in that the heating tape, using switch temperature (Ts) is that 85 ± 5 ℃ ptc material is raw material, its overcoat uses the thermoplastic macromolecule material similar with ptc material (PE) to be base material, and production stage is:

A. draw the core band

(1) the single multiple screw extruder of preheating, and keep 210～250 ℃ of head temperatures, 150～180 ℃ of body temperatures, 80～110 ℃ of tail temperature; From tail

(2) switch temperature (Ts) of packing into is 85 ± 5 ℃ a ptc material pellet;

(3) pass the extruded mould of head abreast with two equidistant conductor wire cores, the draught line velocity-stabilization that makes this core is at 30～50m/min; Simultaneously

(4) plastic extruding machine is extruded the viscous state ptc material by extrusion die, on these two cores that are laid in equably continuously, forms the banding pattern electric heating element that there are two parallel poles ptc layer and both sides;

(5) the hot electric heating element that (4) are drawn cools off through tank, promptly becomes PTC core band.

B. coating outer cover is selected polyethylene from high pressure process (LDPE) class cable jacket material for use

(6) used plastic extruding machine is with (1), and the temperature that extrudes overcoat keeps 210～230 ℃ of heads, 150～170 ℃ on fuselage, 90～100 ℃ of tails.

(7) the PTC core band that (5) are drawn is coated with an amount of talcum powder, passes the outer mold that size is big slightly, export shape same (3); And make

(8) this PTC core band draught line speed is with (3); Simultaneously

(9) the viscous state protective cover material in the plastic extruding machine is extruded on the core band through outer mold; Again

(10) through the roll forming of a pair of column type roller, make it be close to PTC core belt surface; Enter immediately

(11) heating tape basic model body is made in tank cooling.

C. crosslinking with radiation

(12) with the heating tape of (11) coating outer cover, under normal temperature, normal pressure, air atmosphere, place and carry out whole irradiation in the radiation field;

(13) look used radiation source classification, wait to accumulate the irradiation accumulated dose when reaching 5～20Mrad, irradiation stops.Make from limitting the heating tape finished product.

2, production method according to claim 1 is characterized in that made basic model heating tape behind whole irradiation, and its PTC core and the overcoat degree of cross linking are 45～65%.

3, the automatic siding temperaturing heating belt that utilizes claim 1,2 methods to produce, this heating tape is to have the PTC core band and the overcoat of two electrodes to constitute by both sides, the temperature of limit certainly (Tr) that it is characterized in that said heating tape is 80 ± 5 ℃, said core band and overcoat use similar thermoplastic polymer (LDPE) to make base material, and its degree of cross linking is 45～65%.

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