DE1103479B - Electric tubular heater and process for its manufacture - Google Patents

Description

GERMAN

The invention relates to tubular heating elements with one or more heating wires, which are surrounded by a metal jacket and electrically insulated from it by glass fibers, which are characterized in that the cross section of the heating conductor (s) is at least 10% of the cross section that is compressed in the jacket tube in order to achieve sufficient thermal conductivity _{accommodated glass fibers that contain more than 90% SiO 2} and less than 10% metal oxides for the purpose of achieving sufficient electrical insulation properties and thermal stability, so that the glass fiber insulation maintains its stated electrical and thermal properties without significant deviations up to temperatures of 1065 ° C, and the invention relates to an extremely simple process for the continuous manufacture of large or endless lengths of these radiators.

It is already known to use glass fibers to insulate heating conductors. However, because of the low softening and melting point of conventional glasses, such insulation can only be used at relatively low temperatures. It has now been found that thermally stable electrical insulation that can be used even at high temperatures can be achieved by using glass fibers which _{contain more than 90% SiO 2} and less than 10% metal oxides. Such glass fibers can be produced by methods known per se. As a result of the very good electrical insulation properties of such fibers, the insulating layer can be made relatively thin, that is, with tubular heaters, the heating conductor and jacket move closer together, the heat dissipation from the heating conductor is improved, and overheating of the heating conductor is avoided. The electrical resistance of an insulation made of such glass fibers freed from metal oxides does not decrease during use.

The invention is described in more detail below with reference to the drawing.

Fig. 1 is a longitudinal section through a tubular heater according to the invention;

Figure 2 is an enlarged cross-section through the tubular heater taken along line 2-2 of Figure 1;

Figures 3 to 9 are cross-sections through tubular heaters of various designs according to the invention;

FIG. 10 is a schematic representation of an apparatus for producing a tubular heater according to FIG Figures 1 and 2 and also illustrates the various stages of manufacture of the radiator;

Fig. 11 shows in a side view and in an enlarged Scale shows the arrangement of the various deforming rollers of the device according to FIG. 10;

Figs. 12 to 16 are enlarged cross sections taken along

Electric tubular heater
and its method of manufacture

Applicant:

General Electric Company,
Schenectady, NY (V. St. A.)

Representative:
Dr.-Ing. A. v. Kreisler, Dr.-Ing. K. Schönwald,

Dipl.-Chem. Dr. phil. H. Siebeneicher

and Dr.-Ing. Th. Meyer, patent attorneys,

Cologne 1, Deichmannhaus

Claimed priority:
V. St. v. America July 26, 1954

Charles Herbert Yohe, Glen Ellyn, 111. (V. St. Α.),
has been named as the inventor

the lines 12-12, 13-13, 14-14, 15-15 and 16-16 of FIG. 11 and illustrate the individual deformations ;

17 is an enlarged longitudinal section through the various pressure rollers of the device according to FIG Fig. 10, and

Figures 18-23 are enlarged cross-sections through the radiators along lines 18-18, 19-19, 20-20, 21-21, 22-22 and 23-23 and illustrate the individual cross-sections of the tubular heater during its manufacture.

In Fig. 1, 30 is the jacketed heater made of the metallic resistance wire 31, one of these Wire surrounding layer 32 of predominantly silica-containing threads and a tubular metallic sheath 33, which surrounds both the wire 31 and the layer 32 and the Layer 32 compresses around conductor 31 so that wire 31 is central and spaced from the jacket 33 is held. In the finished heater 30, the metallic resistance wire 31 can be via the Ends of the sheath 33 protrude and an electrical connection 31 ß (see. Right side of Fig. 1) form. The ends of the jacket 33 can be closed moisture-tight with porcelain or glass stoppers,

109 538/461

as indicated at 34. The closure 34 can be formed in a known manner.

The heating wire 31 consists, for example, of a chromium-nickel alloy, the jacket 33, for example, made of copper, brass, aluminum or iron-chromium-nickel alloy.

The layer 32 of threads predominantly containing silica can be in the most varied of forms; it preferably consists of a textile-like structure, such as a braided sheath made of yarn or thread containing _{more than 90% SiO 2.} The layer 32 can, however, also consist of a covering made of textile tape made from yarn or thread containing _{more than 90% SiO 2.} In any case, however, the layer 32 of predominantly SiO ₂ -containing material surrounds the heating wire 31 and is held in place by the jacket 33, which, as a result of the processing described below, strongly compresses the flexible layer 32, which nevertheless remains flexible. so that in addition to the best electrical insulation, high thermal conductivity is guaranteed.

The Si O ₂ -containing threads of the layer 32 thus consist of glass fibers from which the main part of the glass-forming metal oxides has been leached. Such products are manufactured in such a way that glass fibers _{are leached with a mineral acid, preferably HCl or HNO 3} , for several hours at elevated temperatures. The product obtained has a softening point of about 1290 ° C and a melting point of about 1650 ° C. A typical composition of such a product is given below:

Silica (SiO ₂ ) 95.68%

Aluminum oxide (Al ₀ O ₃ ) 1.43%

Titanium oxide (TiO _n ;. "... '0.08%

Iron oxide (Fe ₂ O ₃ ) 0.09%

Calcium Oxide (CaO) 0.00%

Magnesium oxide (MgO) 0.08%

Alkali as sodium oxide (Na ₂ O; .. 0.32%

Boric anhydride (B ₂ O ₃ ) .. ". 0.00%

97.68%

The remaining 2.32% consists of hydration water, absorption water, unburned carbonaceous Residues, unspecified impurities and minor analytical errors.

Another glass fiber suitable for leaching has a softening point of a little below 600 ° C and has a melting point of about 760 ° C and is composed as follows:

Silicic acid (SiO ₂ ) 53.76%

Aluminum oxide (AUO ₃ ; 15.29%

Titanium oxide (TiO ₂ ). "... '0.08%

Iron oxide (Fe ₂ O ₃ ) 0.23%

Calcium Oxide (CaO) 16.80%

Magnesium oxide (MgO) 5.10%

Alkali as sodium oxide (Na ₂ O) .. 0.42%

Boric anhydride (B ₂ O ₃ ) 6.60%

98.28%

The remaining 1.72% consists of unburned carbonaceous residue, made up of impurities the original glass mix and minor analgesic errors.

This glass is treated with hydrochloric acid at an initial concentration of about 11.2% for about 5 hours about 60 ° C leached. The acid-leached product is then washed acid-free in air dried and heated to about 925 ° C for about 8 hours. The main part of the glass-forming Metal oxides leached, so that in the end product the silica is about 99% in addition to low glass-forming metal oxides, d. i.e. the end product consists practically of pure silica.

To produce a heater 30 of normal length, it is sufficient to use the layer 32 predominantly To apply silica-containing threads to the heating wire 31 and the whole in the preformed to bring tubular jacket 33. Then the whole thing is cold processed, for example cold rolled or cold forged. The cross section of the jacket 33 is reduced and the layer 32 around the Heating wire 31 compressed. In this way, the heating wire 31 is solid and concentric within the Sheath 33 stored. After cold working, the ends of the jacket 33 are somehow removed, a power connection at the ends 31a of the heating conductor 31 to be able to attach, and the jacket 33 is at the ends with plugs 34 made of porcelain or Glass closed. In the manufacture of the radiator 30, steel clamps, not shown, are usually used attached to the ends of the heating wire 31, which are then embedded in the porcelain or glass stoppers 34 will.

To produce endless lengths of tubular heating elements 30, a continuous process is used which can be carried out with an apparatus 40 as shown in FIG. 10. The device 40 consists of a feed roller 41 from which the heating wire 31 runs off, a braiding or cladding head 42 to which the SiO ₂ -containing fibers are fed in the form of threads or ribbons from 44 in the direction 43, a supply roller 45 from which the strip 33 a forming the jacket 33 is pulled off, a series of deforming rollers 47, an electric seam welding device 48, a series of compression rollers 49 and a winding roller 50, onto which the heating element 30 is continuously wound. The heating wire 31 is continuously fed from the roll 41 to the head 42, to which the Si O ₂ -containing fiber material 43 from 44 is fed and in which the textile layer 32 is produced in the form of a covering or a jacket on the heating wire 31. The heating wire 31 with the layer 32 of siliceous material is then fed from the head 42 via the guide roller 51 to a series of deforming rollers 47. The band 33 a forming the jacket 33 is continuously fed from the supply roll 45 via the guide roller 52 to the deformation rollers 47, in which the band 33 a is continuously deformed to form the jacket 33 over the flexible layer 32 of silica-containing fibers. Then the whole thing is continuously fed to the electric seam welding machine 48, in which the adjacent longitudinal edges of the strip 33 a are welded together to form a tubular jacket 33. From the continuous seam welding machine 48, the whole arrives at the compression rollers 49, in which the whole is transferred into the finished heating element 30 by cold working. This is wound onto the supply roll 50 via the guide rollers 53.

The operation of the deforming rollers 47 is best understood with reference to Figs. 11-16,

in which the arrangement of the individual deformation rollers is shown diagrammatically. According to FIG. 11, five individual pairs of deforming rollers 61-62, 63-64, 65-66, 67-68 and 69-70 are arranged one behind the other. The flat belt 33 α is inserted between the first pair of deforming rollers 61-62 and then migrates through the subsequent pairs of rollers while deforming the belt, as shown in FIGS. 11, 12, 13 and 14. Between the third pair of rollers 65-66 and the fourth pair of rollers 67-68 , the heating wire 31 , which is covered with the textile covering 32 made _{of SiO 2} -containing threads, is introduced into the preformed belt 33 α via the guide roller 71. In the fourth pair of forming rollers 67-68, the preformed band is 33 α further deformed tubular, and in the fifth pair of forming rollers 69-70, the deformation is terminated at the closed tubular sheath 33rd The adjacent edges form the longitudinal seam of the jacket 33.

These abutting edges are welded in the electric seam welding device 48.

The operation of the compaction rollers 49 is best understood with reference to Figures 17-23, in which the arrangement of the individual compaction rollers is shown diagrammatically. According to Fig. 17, five pairs of compaction rollers 81-82, 83-84, 85-86, 87-88 and 89-90 are arranged one behind the other. The heater 30 passes through the various pairs of compression rollers one after the other, gradually reducing its cross-section. In the compression shown, the rollers are arranged in such a way that the tubular heating element 30 is given, one after the other, elliptical cross-sections rotated by 90 °, as shown in FIGS. 19, 20, 21 and 22. Accordingly, the diameter of the jacket 33 entering the compression rollers 81 and 82 (cf. FIG. 18) is significantly larger than that of the jacket which leaves the compression rollers 89-90 (cf. FIG. 23). The orientation of the various elliptical passages prevents burrs from forming on the jacket 33 when its diameter is gradually reduced and the flexible layer 32 of silica-containing fiber material around the heating wire 31 is compressed. In this way, the heating wire 31 is firmly embedded in the jacket 33.

If it is necessary to use a lubricant such as wax or the like when applying the yarn or thread in the wrapping head 42 , this lubricant should be removed again before the jacket 33 is applied. The lubricant can simply be burned off by guiding the sheathed heating wire, for example through a furnace (not shown), between the sheathing head 42 and the guide roller 51. Attention is drawn to this possibility, since it is desirable that no foreign substances, in particular no moisture, are enclosed in the finished tubular heating element 30 under the jacket 33.

As an example it should be stated that the tubular jacket 33 according to FIG. 18 has an outer diameter of approximately 4 mm and according to FIG. 23 an end diameter of approximately 3.2 mm. The inner diameter of the jacket 33 is in the final state, for example, about 2 mm and the outer diameter of the heating wire 31 0.76 mm, that is, the cross section of the heating wire makes up slightly more than 16% of the cross section of the embedding layer 32 made of siliceous fibers. The final density of the compliant layer 32 is, for example, 1.2 to 1.4 g / cm ³ .

The described continuous process for producing the heating conductor 30 is particularly advantageous because it allows the production of endless lengths of the heating conductor and because the heating wire 31 is centrally embedded in the tubular heating elements produced and an insulation of constant thickness is formed between the heating wire 31 and the metallic jacket 33 .

The tubular heating element according to the invention can be made very different with respect to the number of heating wires which are arranged in the casing and with respect to the casing, ίο as can be seen from FIGS. 3 to 9. In any case, each individual heating wire is surrounded separately by its own flexible layer of SiO ₂ -containing fibers; several such heating wires with their sheathing made of SiO ₂ -containing fibers can be enclosed together in a single sheath. This is followed by cold processing in the manner described in order to reduce the cross-section and to compress the silicic acid-containing fibers around the heating wires.

According to FIG. 3, the tubular heating element 100 consists of three individual heating wires 101 of circular cross-section, three individual flexible layers 102 of silica-containing fibers and a common metal jacket 103 of circular cross-section.

The tubular heating element 110 according to FIG. 4 contains seven individual metallic heating wires 111 of circular cross-section, seven individual flexible layers 112 of SiO ₂ -containing fibers and a common metallic jacket 113 of circular cross-section.

According to Fig. 5, the tubular heater 120 consists of

a single metallic resistance wire 121 of oval cross-section, a single resilient layer 122 of siliceous fibers and a metal jacket 123 of oval cross-section.

The tubular heating element 130 according to FIG. 6 contains three individual metallic heating wires 131 of circular cross-section, three individual flexible layers 132 of SiO ₂ -containing fibers and a common metal jacket 133 of triangular cross-section.

In Fig. 7, a heater 140 is shown, which contains the three metallic heating wires 141 a, 141 b and 141 a, three separate flexible layers 142 made of siliceous fibers and a common metallic jacket 143 of circular cross-section. In the heating element 140 , the heating wires 141 α have a circular cross-section and are arranged on opposite sides of the heating wire 141 b located in the center and have an oval cross-section. The heating wires 141 α have a slightly smaller cross section than the heating wire 141 b located in the middle.

According to Fig. 8, the heater 150 includes three individual metallic heating wires 151 a, 151 b and 151 a, three individual flexible layers 152 made of siliceous fibers and a common metal jacket 153 of square cross-section. The heating wires 151a have square cross section and are arranged on a side of the radiator, while the filament 151 b of rectangular cross-section on the other side of the radiator is arranged. The heating wires 151a have b smaller cross section than the heating wire 151st ~

According to FIG. 9, the heating element 160 consists of two individual metallic heating wires 161 of circular cross-section, two separate flexible layers 162 of silicic acid-containing fibers and a common jacket 163. The jacket 163 is bent in the shape of a figure eight, and the longitudinal edges 7oJJl63a are in the figure Center compressed so that the

two heating wires 161 are housed in two separate rooms.

Claims (2)

Claims ·. 1. Electric tubular heater with one or more heating wires which are surrounded by a metal jacket and electrically insulated from this by glass fibers, characterized in that the cross-section of the heating conductor or conductors is at least 10% of the cross-section of the glass fibers compacted in the jacket tube in order to achieve sufficient thermal conductivity _{that contain more than 90% SiO 2} and less than 10% metal oxides for the purpose of achieving sufficient electrical insulation properties and thermal stability, so that the glass fiber insulation has its stated electrical and thermal mix retains properties without significant deviation up to temperatures of 1065 ° C. 2. A method for producing electrical tubular heating elements according to claim 1, characterized in that that glass fibers, the glass-forming metal oxides of which have largely been leached out, applied continuously to the heating wire or wires, then the one or those with the glass fibers surrounded heating wires continuously by a metal jacket by flanging the edges of a Metal band are surrounded and finally the cross section of the metal jacket by cold working is reduced. Considered publications:
German Patent Nos. 709177, 744 460, 014, 758 724, 895 798. 1 sheet of drawings © 109 538/461 3.61