RU2597836C2 - Method of producing flexible electric heater - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to production of flexible electric heaters, creating temperature of up to 150 °C, which are used to maintain preset temperature of onboard hardware and structural components of spacecraft, air, sea or ground transport, etc. Method includes formation of a resistive element, connection to it of at least two sheets of electric insulation material arranged on both sides thereof, and providing current lead to resistive element. Formation of a workpiece from resistive material is carried out through application of electrical insulation with subsequent formation of resistive element configuration by removing part of resistive material and connection of at least a second sheet of electrical insulation. Sheets of electrical insulation are made of flexible heat-radiation resistant high-insulation material consisting of one or more different, with low gas emission in vacuum.

EFFECT: invention simplifies technology of making high-technology electric heater with high reliability, reduced dimensions with increase in power, heating of objects of different shapes to different temperatures and during operation in wide range of temperatures.

5 cl, 3 dwg, 4 ex

Description

The invention relates to flexible electric heaters that create temperatures up to 150 ° C, which are used to maintain the set temperature of on-board equipment and structural elements of spacecraft (SC), structural elements of air, sea or ground transport, vacuum installations of scientific and technological purposes, temperature control in spacesuits , domestic use (heating car seats, floor heating, etc.).

Of all the fields of application, the most stringent operating conditions are typical for on-board equipment and spacecraft design elements, therefore, the aforementioned application of a flexible electric heater is discussed in more detail below.

In the process of operating the spacecraft onboard spacecraft while the spacecraft is in the shadow of the Earth or other space objects, the surfaces of the spacecraft are cooled to cryogenic temperatures. At the same time, the operating temperature range of most devices is quite narrow and for their normal functioning it is necessary to raise their temperature to the values specified by the technical operating conditions. This is possible with the help of electric heaters placed either directly on the device’s body or on the spacecraft’s body in the immediate vicinity of the device. These surfaces can be either flat or curved, for example spherical. For example, the following requirements are usually imposed on electric heaters of spacecraft onboard equipment (the most critical and severe conditions for all types of operation):

1. The working temperature of the heated surface is from 0 to 80 ° C.

2. Conditions under which the electric heater must remain operational:

- temperature range from minus 70 to 150 ° C (for individual applications - from minus 269 to 200 ° C);

- residual gas pressure 10 ^-12 Pa;

- absorbed dose of ionizing radiation up to 6 · 10 ⁶ Gy.

3. The minimum weight.

4. Minimum thickness.

5. Minimum gas evolution in a vacuum during testing according to GOST R50109-82 (mass loss of not more than 1%, volatile condensed matter content of not more than 0.1%).

6. Manufacturability.

A known method of manufacturing a flexible heater, consisting of two layers of an insulating base, placed between them a conductive resistive layer and electrically connected current leads (RF patent No. 2213432, Н05В 3/00, publ. 09/27/2003), in which the layers of the insulating base are connected to resistive layer with glue. The method consists in the fact that the resistive element, in the form of which charcoal tows act, is laid on an insulating base made of fabric with asbestos, basalt or glass fibers, and then it is applied, for example, with a fluoroelastomer, or with an organosilicon elastomer or liquid glass, or with flame retardant elastic glue. Then, a second layer of insulating base is applied to the surface of the heated layer, with non-combustible elastic glue or liquid glass applied to it, and glued to smooth the surface.

The disadvantages of this method include:

- low technical and operational parameters, since the adhesive joints do not provide uniformity of thermophysical parameters on the surface of the electric heater (due to areas of non-adhesive);

- insufficient elasticity, which is created when the glue hardens, which affects the fastening to complex heated surfaces (with curvature of the surface).

A known method of manufacturing a flexible heater, consisting of at least two sheets of electrical insulation made of multilayer electrical insulation coatings: from a fiberglass cloth with a layer of thermoplastic polymer, which in the heated state wets with respect to the material of the fiberglass cloth, and the resistive element of the heater is made of conductive paper and metal electrodes are fixed on it (RF patent 2058674, Н05В 3/36, publ. 10.04.1998), which consists in hot pressing of all layers of the blank wki heater at the same time.

The disadvantages of the described method of manufacturing a flexible electric heater:

- the implementation of the resistive element of conductive paper leads to low heating efficiency;

- the heating element is cut from conductive paper, which leads to an increase in the complexity of manufacturing the product;

- the complexity of the connection of the resistive element of paper with metal electrodes, which leads to a decrease in its reliability, which is unacceptable for the intended purpose;

- poor adhesion of the connection of the fiberglass cloth with a layer of thermoplastic polymer that does not impregnate the fiberglass in bulk;

- pressing blanks on a snap that does not take into account the relief of heated surfaces, incl. curved surfaces, which reduces the efficiency of the entire device as a whole.

A known method of manufacturing a flat electric heating element (RF patent 2082282, Н05В 3/34, publ. 06/20/1997), in which the resistive element is formed by cutting on the foil tape counter-parallel transverse relative to its longitudinal axis grooves (zigzag shape). Die cutting is carried out on a stamp with a given width of the notched groove and matrix.

The disadvantages of this method include:

- when the operational parameters of the electric heater change, the shape of the resistive element changes, for the manufacture of which it is necessary to make new dies;

- do not provide a high packing density of the resistive element, and therefore, electric heaters have low power;

- the inability to manufacture electric heaters for complex curved surfaces, for example spherical;

- complication of the technological process in which the resistive element, even for flat electric heaters, is cut down separately from the sheets of electrical insulation, and then placed on them.

- during die cutting, as a rule, a sharp edge is formed on which the electric field increases and as a result the electric strength of the electrical insulation decreases.

Closest to the technical solution is RF patent 2058674.

The objective of the present invention is to simplify manufacturing technology, increase reliability and operational capabilities (including with the possibility of heating objects of various shapes) of an electric heater with a simultaneous reduction in size and a reduction in the cost of an electric heater.

This problem is solved due to the fact that the method of manufacturing a flexible electric heater includes forming a resistive element, attaching to it at least two sheets of insulating material, placing them on both sides of it, and providing a current lead to the resistive element; the formation of the resistive element is carried out by attaching a layer of resistive material to the sheet of electrical insulation followed by the formation of the configuration of the resistive element by removing part of the resistive material from the workpiece without damaging the sheet of electrical insulation and the material of the resistive element and attaching at least a second sheet of electrical insulation, and the above-mentioned sheets of electrical insulation are made of flexible thermo-radiation-resistant highly insulating material, consisting of one material or several their heterogeneous, with low gas evolution in a vacuum.

The invention is illustrated by drawings of FIG. 1-3, where in FIG. 1 shows a cross section of a blank of a resistive element in one embodiment, including an electrical insulation sheet 1 and a layer of resistive material 2; in FIG. 2 shows a blank of several electric heaters on one sheet of electrical insulation; in FIG. 3 shows the finished electric heater.

In this case, sheets of electrical insulation material in an electric heater are made of flexible heat-resistant radiation-resistant high-electrical insulation material with low gas evolution in a vacuum and can consist of one material or several dissimilar ones, for example:

- from one material, for example - thermoplastic polyimide type PI-PC, polysulfone, thermoplastic fluoroplastic, polyetheretherketone;

- of several heterogeneous, for example, a film of thermosetting polyimide with a thermoplastic layer of fluoroplastic, or thermoplastic polyimide, or polyetheretherketone; fiberglass or organoplastic with a thermosetting or thermoplastic binder, for example epoxy, cyanate or polyether etherketone; a sheet of silicone rubber, pure or with a dielectric filler (fabric, fibrous, powder).

In the case of using dissimilar materials, as is clear from the above examples, they are either arranged in layers - if there are several dissimilar materials, or if one dissimilar material is used, it is made in the form of a composite material in which one material acts as a filler and the second as a binder (the filler may be in the form of fabric, fibers, powder). In addition, there can be several fillers - for example, in the form of a fabric and in the form of a powder, from one or different materials. In a layered arrangement, the materials are joined together by a welding method, if at least one of them is thermoplastic, or connected by pressing with simultaneous polymerization of the binder in at least one of the two layers.

Depending on the embodiment determined by the operating conditions, the electric heater may have a flat or curved shape, contain two or more sheets of electrical insulation. At the same time, the need to make the electric heater in a curved or flat shape, as well as the number of sheets of electrical insulation, is determined by the design of the electric heater based on operating conditions (shape of the heated surface, electrical insulation strength, supply voltage, material of the heated surface, operating temperature range).

In an electric heater containing two sheets of electrical insulation, a resistive layer is attached to the first sheet of electrical insulation. In the embodiment with three or more sheets of electrical insulation, the resistive layer is attached to the third (intermediate) sheet, and at least the first and second sheets of electrical insulation are attached on both sides of it (in layers) after the configuration of the resistive element.

The most difficult is the implementation of the electric heater of a curved shape, and the sequence of manufacturing steps depends on the selected design of the electric heater, for example:

a) a sheet of electrical insulation, to which a resistive layer is attached, is previously given a curved shape by molding on appropriate equipment. Then the same shape is given to the resistive material layer, followed by attaching the resistive material layer 2 to the electrical insulation sheet 1 (see example 3), or the resistive layer is attached by applying directly to the electrical insulation sheet in the form of a coating;

b) the resistive layer is attached to the electrical insulation sheet in the process of joint molding on the appropriate equipment (see example 2).

The preparation of the resistive element of the required size can be obtained both by attaching the foil to the electrical insulation sheet, and by applying a metal or alloy directly to the electrical insulation sheet in the form of a coating (for example, magnetron sputtering in vacuum, electric arc spraying, galvanic deposition, etc.). The attachment of the layer of resistive material 2 in the form of a foil can be carried out, for example, by thermo-contact welding with a thermoplastic layer of electrical insulation sheet 1 or by molding onto electrical insulation sheet 1 containing a polymerizable binder, while polymerizing it, for example, by hot pressing on a thermal vacuum press.

The choice of metal or alloy for the resistive element 2 is determined by the design of the electric heater. The most common case is when it is enough to choose a resistive alloy such as nichrome, constantan, inconel, as shown in examples 1-3. But in some cases, their use does not ensure the achievement of the required technical result. For example, with a low supply voltage and the requirement of high uniformity of surface heating, it is possible to use metals or alloys with low resistivity, such as copper, aluminum, chromium bronze, or with an intermediate, such as platinum, nickel. Example 4 shows a heater device with an aluminum resistor element.

By choosing an alloy with the desired specific electrical resistivity, the parameters of the resistive element are optimized for a given supply voltage. Thus, the choice of metal or alloy for the manufacture of a flexible electric heater is due to the device (design) of the manufactured electric heater, which, in turn, is selected in accordance with the operating conditions.

In FIG. 2 shows embodiments of resistive elements 3 (a case with the simultaneous formation of three blanks of electric heaters of different configurations from one blank of a resistive element).

The configuration of resistive elements 3 is not limited to the presented options and is determined by the operating conditions of electric heaters (operating temperature; shape and area of the heated surface, its thermal conductivity and heat capacity, specific power, supply voltage, etc.).

The configuration of the resistive elements 3 is formed by removing part of the resistive material 2 from the blank of the resistive element by any method that does not damage the electrical insulation sheet and the future resistive element itself, for example, by lithography, in which the modes of the removal process, for example, chemical etching, are selected so as to obtain the desired configuration and the geometric shape of the cross section of the resistive element, uniform in thickness and without defects in the material itself in the resistive element (without burrs, thinning, jumpers between sednja lines and others. defects).

Then, in one embodiment, to the electrical insulation sheet with the formed resistive element (to the billet of the electric heater) can be connected to the lead wire 5, for example, by soldering or welding. Then additionally attach one or more sheets of electrical insulation.

In another embodiment, the lead wires are connected after the manufacture of an electric heater (Example 2). For this, technological holes are left in the sheet or sheets of electrical insulation on one side of the electric heater, which make it possible to connect the wires to the contact pads of the resistive element, followed by their sealing with electrical insulation material, for example, by filling with a compound, varnish or by attaching electrical insulation pads.

During operation of the electric heater, an electric current passes through the current-carrying wires 5 (Fig. 3) and the resistive element 3, the generated heat is removed through the insulation sheets 1 to one or two heated surfaces (depending on the installation location).

For an electric heater containing two sheets of electrical insulation, the joining of the second sheet of electrical insulation to the workpiece of the electric heater is performed on the side of the resistive layer. For an electric heater containing more than two sheets of electrical insulation, molding of the electric heater is carried out with the addition of sheets of electrical insulation located on both sides of the third (intermediate) sheet with a resistive element 3 attached to it. The connection of sheets of electrical insulation can be carried out by molding, for example, by hot pressing on thermal vacuum press or thermal contact welding.

The connection of the sheets of electrical insulation, the connection of the resistive layer of the electric heater, shaping (if necessary) is carried out at temperature-time regimes and pressure corresponding to the physicomechanical and thermophysical characteristics of the materials constituting the electric heater, the choice of materials themselves is determined by the design, taking into account operating conditions.

The electric heater made according to the present method has the form shown in FIG. 3. It includes sheets of electrical insulation 1 from a flexible heat-resistant radiation-resistant highly insulating composite material with a resistive element 3 located between them, having contact pads 4 to which current-conducting wires are connected 5. Option a) - with an upper sheet of electrical insulation from a less elastic (flexible) material ; option b) - with a top sheet of electrical insulation made of a more flexible (flexible) material and with a resistive element, the cross section of which is made with smooth corners.

By obtaining the desired configuration of the resistive element 2 by removing part of the workpiece material of the resistive element in any way that provides the desired configuration without damaging the resistive element and the electrical insulation sheet, for example by laser microprocessing or lithography, the reliability of the resistive element increases (it remains uniform in structure and properties, has no weak places in the form of bends, burrs, cuts), manufacturability is increased (the removal technology is well developed, about provides high reproducibility and accuracy of the picture). In addition, it allows you to get resistive elements of any complex configuration, with high accuracy of the picture, including several types of resistive elements on the same workpiece at the same time, which reduces the complexity of manufacturing electric heaters.

Thanks to the implementation of electrical insulation sheets 1 from a flexible heat-resistant radiation-resistant highly insulating material with low gas emission in a vacuum, maximum mechanical and electrical strength is achieved with a minimum weight in extreme operating conditions (due to the high electrical insulation properties of electrical insulation sheets with their small thickness and the strength of their connection to each other), it is possible installation of an electric heater on surfaces of various shapes to ensure maximum thermal contact (due to flexibility), the efficiency of the electric heater is achieved in the harsh conditions of outer space (due to radiation resistance and heat resistance), pollution of the spacecraft’s own external atmosphere is minimized by gas products of the electric heater materials (due to the small gas evolution of the material).

Giving shape to the blank of the resistive element separately from the sheet of electrical insulation and then attaching them to each other or shaping the blank of the resistive element at the same time as the sheet of electrical insulation makes it possible to produce electric heaters of complex shape mounted on curved surfaces, including spherical, despite the significant difference in the coefficients of thermal expansion of the material resistive element and electrical insulation material.

The introduction of a third (intermediate) sheet of electrical insulation makes it possible to manufacture electric heaters with minimal deviations from a given shape, for example spherical, without the appearance of defects in the material of the resistive element (without tensile, compression, thinning, micro folds, corrugations, scoring, dot dents and thickenings, etc. .) and without defects in geometric dimensions (thickness, inconsistencies in the cross-sectional dimensions of the resistive element specified by the operating conditions of the configuration). This is achieved by simultaneously connecting, for example, by forming sheets of electrical insulation on both sides of the resistive element. In this case, the thermal stresses arising during the formation of the electric heater (due to shrinkage of the electrical insulation sheets, differences in the coefficients of thermal expansion of the resistive element and electrical insulation) balance the two sides of the resistive element.

Due to the hot-formed molding of the electric heater on a thermal vacuum press, interlayer air penetration into its electrical insulation is excluded and, accordingly, the formation of non-adhesive spots, which subsequently lead to local heating of the electric heater and reduce its reliability and service life.

Variants of manufacturing electric heaters with connecting wires before or after forming the electric heater make it possible to use wires of various cross-sections - depending on the operating voltage (on the type of wire, its cross-section and insulation) - thin wires can be connected before forming the electric heater, for connecting thicker wires left technological holes in the electrical insulation sheet, followed by their termination.

The manufacture of electric heaters for operation in different conditions - in certain temperature ranges (lower and higher), at certain radiation levels, is made of different materials. Thus, the cost of materials, electricity and equipment for the manufacture of electric heaters are selected based on operating conditions, which is economically feasible.

Example 1. The design of a flexible electric heater is made of two sheets of electrical insulation material from a polyimide thermosetting film with a heat-sealable fluoroplastic layer PMS-S-351 40/50 TU 6-19-226-89 and a resistive element made of nichrome in the form of a "snake" with a width a conductor of 0.42 mm and a distance between adjacent turns of 0.42 mm. In this case, the shape of the electric heater and, accordingly, the placement of the “snake” of the resistive element is selected depending on the shape of the seat — rectangular, circular, round, etc.

A method of manufacturing this electric heater consists of the following sequential operations:

1) the blank of the resistive element is carried out by attaching a foil of nichrome to a polyimide thermosetting film with a heat-sealable fluoroplastic layer PMS-S-351 40/50 TU 6-19-226-89 by hot pressing;

2) the formation of the configuration of the resistive element by lithography;

3) the connection of conductive wires by welding;

4) the formation of an electric heater occurs: by attaching a second sheet of electrical insulation from a polyimide thermosetting film with a heat-sealable fluoroplastic layer PMS-S-351 40/50 TU 6-19-226-89 by hot pressing.

Example 2. The design of a flexible electric heater consists of three sheets of insulating material (two of fiberglass heat-resistant cushioning STP-4 TU 2296-006-11436290-02, one - fiberglass E1-30P GOST 19907-83) and a resistive element made of constantan foil 12 μm with a track width of 1.2 mm, the distance between the tracks is 1.2 mm and has a curved shape (cut from a sphere with a diameter of 1.2 m, size 30 × 150 mm).

A method of manufacturing this electric heater consists of the following sequential operations:

1) the blank of the resistive element is carried out by attaching the constantan foil to the first sheet of electrical insulation from fiberglass heat-resistant cushioning STP-4 TU 2296-006-11436290-02 at the same time giving the complex shape to the resistive material together with the first sheet of electrical insulation on a snap size 35 × 160 mm, having view of the cut from a sphere with a diameter of 1.2 m, by hot pressing;

2) the formation of the configuration of the resistive element by lithography;

3) the electric heater is formed by simultaneously attaching a second sheet of electrical insulation from fiberglass to heat-resistant cushioning STP-4 TU 2296-006-11436290-02 from the side of the resistive layer and a third from fiberglass E1-30P GOST 19907-83 from the side of the second sheet by hot pressing on the above snap;

4) the connection of conductive wires through the technological holes using soldering;

5) termination of technological holes after connecting conductive wires.

Example 3. The design of a flexible electric heater consists of two sheets of electrical insulating material - APTIV 2100 polyetheretherketone and a resistive element made of constantan in the form of a quadruple "snake" with a conductor width of 1.7 mm and a distance between conductors of 1.7 mm and has a curved shape ( performed in the form of a decorative element of complex shape - bas-relief).

A method of manufacturing this electric heater consists of the following sequential operations:

1) giving a complex shape to the resistive material from constantan separately from the sheet of electrical insulation on metal equipment having the form of a bas-relief;

2) the blank of the resistive element is made by attaching a constantan foil with an irregular shape to the first sheet of electrical insulation - APTIV 2100 film polyetheretherketone by hot pressing of APTIV 2100 polyetheretherketone on the appropriate equipment;

3) the formation of the configuration of the resistive element by laser microprocessing;

4) the connection of conductive wires by soldering with solder;

5) the electric heater is formed by attaching a second sheet of electrical insulation from APTIV 2100 film polyetheretherketone by hot pressing on the appropriate equipment.

Example 4. The design of a flexible electric heater consists of two sheets of electrical insulation material, one of which consists of polyimide, the other of a polyimide thermosetting film PM-1EU TU 6-05-2015-86 with a heat-sealable layer of polyimide adhesive PI-PK TU 6-05- 211-1449-87 and a resistive element made of sprayed aluminum, a thickness of 2 microns, a track width of 0.5 mm (with a fill factor of 0.55). Based on the shape of the heated surface, the configuration of the resistive element is chosen in the form of a spiral.

A method of manufacturing this electric heater consists of the following sequential operations:

1) the blank of the resistive element is made in the form of a coating of aluminum by vacuum deposition on the surface of the first sheet of electrical insulation from a polyimide thermosetting film PM-1EU TU 6-05-2015-86;

2) the configuration of the resistive element of the laser microprocessing;

3) the connection of conductive wires using conductive glue;

4) molding of the electric heater occurs by attaching a second sheet of electrical insulation of the polyimide thermosetting film PM-1EU TU 6-05-2015-86 with a heat-sealable layer of polyimide glue PI-PK TU 6-05-211-1449-87 by thermal contact welding.

The enterprise has developed and manufactured prototypes of electric heaters. The tests showed: high temperature uniformity over the area of the electric heater, high electrical strength of electrical insulation, the possibility of mounting on curved surfaces, low gas evolution in vacuum, good reproducibility of properties and manufacturability, high resistance to storage factors (exposure to variable temperatures and humidity) and operation (cyclic temperature change in vacuum (from minus 150 to 150 ° C), ionizing radiation absorbed dose up to 6 · 10 ⁶ Gy).

From known to the authors of patent information sources, the totality of features similar to those of the claimed subject matter is not known.

Claims (5)

1. A method of manufacturing a flexible electric heater, including forming a resistive element, attaching to it at least two sheets of electrical insulation material, placing them on both sides of it, and providing a current lead to the resistive element, characterized in that the formation of the resistive element is carried out by applying blanks from a resistive material on an electrical insulation sheet, followed by the formation of a configuration of the resistive element by removing part of the resistive material from the blank without damage to the electrical insulation sheet and the material of the resistive element and the attachment of at least a second electrical insulation sheet, wherein said electrical insulation sheets are made of a flexible thermo-radiation-resistant high-insulation material consisting of one material or several dissimilar materials having low gas emission in a vacuum. 2. A method of manufacturing a flexible electric heater according to claim 1, characterized in that the blank of resistive material and electrical insulation sheets give a complex shape to a curved surface on the appropriate equipment, while the blank of the resistive element is formed by applying a resistive material in the form of a coating of metal or alloy directly on electrical insulation sheet, for example, by vacuum deposition or by attaching a foil, and the configuration of the resistive element is carried out, for example, by lithograph ui. 3. A method of manufacturing a flexible electric heater according to claim 1, characterized in that at least two electrical insulation sheets, for example, by hot pressing, are attached to the electrical insulation sheet with the resistive element formed on it simultaneously from two sides. 4. A method of manufacturing a flexible electric heater according to claim 1, characterized in that the electrical insulation sheet on which the resistive element is formed is made of a uniform hot-melt material. 5. A method of manufacturing a flexible electric heater according to claim 1, characterized in that the current supply is carried out by connecting the current-conducting wires to the contact pads of the resistive element after attaching the sheets of electrical insulation through the technological holes in the latter, followed by their termination with electrical insulation material.

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