US2097981A - Immersion heater for salt baths - Google Patents

Description

Nov, 2, 1937. A. KARcHER 2,097,981

IMMERSION HEATER FOR SALT BATHS Filed Sept. 5, 1935 3 Sheets-Sheet 1 Int/o1 tor Azf'red Kiz'rcher A Home 5- Nov. 2, 1937. A. KARcHER 2,097,931

IMMERSION HEATER FOR SALT BATHS 7 Filed Sept. 3, 1935 3 Sheets-Sheet 2 In umhri Nov. 2, 1937.

A. KARcHER 2,097,981

IMMERSION HEATER FOR SALT BATES Filed Sept. 3, 1935 5 Sheets-Sheet 3 V WV VVVVVVVW MIMM MMMMA \MMMM MM Ag Inventor- Alfred lfiz'rchvr 1 Aflorntjs is considerably prolonged and Patented Nov. 2, 1937 UNITED STATES PATENT OFFICE assignor to firm Dentsche Gold- Scheideanstalt vormals Roessler, Frankforton-the-Main, Germany, a corporation of Germany Application September 3, 1935, Serial No.

In Germany September 3, 1934 15 Claims.

The invention relates to electrically heated immersed heating elements for the heating of baths which like salt melts tend to intrude into heating bodies and have the faculty to destroy the heating plants.

It is a known fact to heat liquids, more especially water by means of electrically heated immersed heating elements consisting of an immersed pipe and eventually with suitable additional immersible pieces such as spiral pipes of suitable material, for instance of metal in which the heating elements e.g. the resistance windings are lodged. These heating elements have however not proved satisfactory for the heating of salt melts and the like, though in various directions they have great advantages. the suitability of such lieatingelements for bath liquids similar to salt melts is, as has been found out, essentially due to the fact that the arrangement of the heating mantle e. g. the pipe with numerous windings and the like that are meant to enlarge the surface, requires a number of welds-and that these welds form exactly the favorable points of attack for the obnoxious ingredients of such baths. No such difliculties have been experienced by the use of water baths or in the heating of liquids that do not attack the mantle pipes. With such heating bodies therefore an exchange of the actual heating elements is not necessary. For the treatment of salt melts, however, an easy possibility to exchange the heating elements is of special importance, inasmuch as differences of temperature of some duration become very detrimental and first of all may bring about a stiffness of the smelt.

By the heating element according to the invention the aforesaid disadvantages are obviated and thus the use of electrically heated immersed heating elements for the treatment of salt melts is made possible.

It has been found that by avoiding forms of construction e. g. branchings of the pipes, mouth pieces and the like and thus doing away with welds, the life of the immersed heating elements what is even more, the exchangeability of the heating gear is possible without any interruption of the working.

The heating element according to the invention consists of a pipe closed at its immersed end, that lies-only with one simple curvature in the bath, in the interior of which a heating gear body of resistance spirals is located easily to be pushed in or else just as easily removed, which are kept in suitable position by thimbles of ceramic The fault of material and facilitate the moval of the heating gear.

By this arrangement is attained that m the whole heating element only one simlc 'elded should become necessary, it can easily be taken out of the bath region, as the only profitably but slight curving offers no resistance. The exchange of the heating gear can therefore be effected without interruption of the working of the bath especially if the heating element consists of several heating bodies according to the invention which warrant in case of short circuit or the like the maintenance 'of temperature of the bath.

As has furthermore been shown short circuits are inmost cases .by the peculiarity of salt melts to intrude into the pipes after a long period of working only created in the plane of touch between bath and the air outside. It has been found that important concentrations of salt take place just at such points of the heating gear that are located in the level of the salt surface or in its immediate neighbourhood preferably above, while at the other points of the heating gear such concentrations are not yet to be found.

' It has therefore been proved to be of advantage not to fit the heating gear that consists of several resistance spirals that are kept in position by thimbles of ceramicmaterial, with distance mem-.

berswithin the region of the strong salt concentrations just mentioned, since by these distance members the saturated salt steam is enabled to condensate and thus to form, as it were, bridges that provoke a short circuit.

As another suitable form of execution has been found one in which the heating gear from the closed end in the interior of the bath is continued only up tojust below the surface of the bath, but close below the surface of the bath straight metal rods are connected with the heating gear by current connecting terminals. By such an arrangement salts or other bath liquids that could intrude into the interior of the heating gear are deprived of the possibility of any such influence and furthermore, even if such substances could intrude, a concentration on such parts is precluded by which the current conductors among themselves or against the earth could get short circuit. A deposit at the hot parts of the heat- REISSUEB puttinginorthcreprevents permeation.

ing gear while in operation is only slightly noticeable and involves practically no disturbances.

Another possibility to prevent to a large degree a deposit of salts or the like and at the same time to facilitate the exchangeability of the heating gear is effected by fitting the heat conductor supports i. e. the thimbles with one or'several broken edges in such a way that at least one edge remains. Thereby will be attained that these supports offer but a slight resistance to the insertion of the whole heating gear into the pipes, that they possess comparatively but little mass and thus show warmth and finally offer no too high resistance to the immediate radiation of warmth from the heating conductor on the pipe walls.

By leaving at least one unbroken edge of the three or more edged e. g. plate like thimbles it is possible to hold the heating gear by the various thimbles in the wanted position within the mantle body. The number of touching points and thus also the shifting resistance of the heating conductor supports on the inside wall of the pipe is thereby reduced to a minimum while the position of the heating conductor remains warranted. Furthermore the mass of the distance bodies is at the same time reduced and the space for the immediate radiation of warmth, as mentioned, is enlarged.

As specially advantageous has been proved to break one of the edges e. g. of a quadrangular distance plate to such an extent that the heating conductor lies completely free at that point. It is profitable to arrange the sequence of the supports, one after the other, of the heating gear in such a way against one another that the un- It has been.

broken edges lie in a screw like line. shown that thereby the insertion of the bendable heating gear more especially in tightly bent pipes is considerably facilitated.

To increase the free space for the immediate radiation from the heat conductor to the pipe wall it is furthermore of advantage to form the heat conductor support in such a way that its cross out along the axis of the pipe to be heated at the ends touching the inner wall of the pipe runs out as it were in a point.

Furthermore the choice of material for the mantle body especially the part of the heating body to be immersed into the bath is, as has very often been proved, of particular importance. In working it has been shown that a permeating of salts through the heated walls of immersed heating bodies cannot suficiently be avoided even by using special iron alloys. This resulted in the fact that immersed heating bodies for salt baths and the like have practically not been used any more.

It has however been proved that by covering of material which like nickel can be attacked but little by the melts, also in' such baths an excellent security against the permeation of salts is efiected. Tests have shown that a nickel covering of preferably a thickness of more than .08 mm.

More especially by. galvanization to such thick layers of nickel perfectly cheap heating bodies of this kind may be manufactured. It is well known that for so called immersed heaters as they are for instance used in households for heating water and similar liquids, nickeled mantles are used. In this case the covering of such heaters with layers of nickel means however only to prevent rusting or rather to produce apleasant appearance. The use of inside heating bodies as heating bodies on a large but little accumulated aoemsi scale of smelting baths forms however in various directions different tasks. The question of prevention of rust is here of minor importance.

It was immaterial to use therefore instead of the hitherto used protecting pipes of iron for these forms of use, pipes of nickel or pipes with nickel covering. It is known first of all that for instance saltpeter containing baths at certain temperatures lead to exotherme reactions with iron, that can become the reason for a sudden melting of the iron and even for explosions. It could hardly be foreseen, how these apparitions that hitherto have not been cleared up, would be changed by using nickel. It is therefore surprising that covering layers of nickel or other material belonging to the type of tinder free alloys do not lead to overheating, explosions and the permeation of salt and the like. It has been shown that by coverings of such kind of material also existing welded joints are so securelycleared that they are practically immune to any destruction by the salt. As has been shown such protecting layers are fitted with advantage not to the heating bodies only but also in the reservoirs i. e. preferably on the surfaces of the reservoirs that face the heating body.

The proposed use of layers of material of the kind mentioned has yet the further advantage that the. thermo-pressure existing between the protecting cover and'the wall material may be used as is usual with thermo elements to immediately measure the temperature of the wall and of the bath. Such measuring at the walls has the advantage that overheating of the walls may easily be found and quicker regulated than it was possible by the usual manner of .measuring the temperature of the salt bath, because here the rises of temperature at the walls came only by a round about way over the salt to the thermo element.

By increase of the thermo currents these ap- Fig. 2 shows a down view of a heating body arrangement.

Fig. 3 shows the arrangement of several heat conductors with distance members, showing broken edges in a heating pipe.

Fig. 4 is anaxial cut through a piece of pipe with several distance members.

Fig. 5 is a pipe cross cut as per Fig. 4.

Fig. 6 represents a special form of execution of a heat conductor support.

Fig. '7 shows a scheme of a bath with an immersed heating body in longitudinal cut in which several level parts of the heating body as well as of the reservoir are fitted with protecting layers.

According to Fig. 1 the bath reservoir I with the salt melt la which reaches up to the bath surface lb through the heating body 2 is heated by four single pipes. These pipes consist each of a horizontal side which represents the actual heating division and a vertical side which serves as supply main. The sides are bent towards one another in such a radius that a bendable heating gear can be inserted from the open end of the pipe.

Two of these pipes are shown in the drawings in Fig.

denser cut open. In the upper one of the cut open pipes lies the heating gear in the manner hitherto usual. This heating gear consists of the heating wire spirals 3 as such, which are held in the desired position to one another and to the pipe 2 by the thiinble 4 of ceramic material.

As mentioned before, with such an arrangement in the neighbourhood of the bath surface, marked 5 a specially preferably at the point strong deposit of salt in the pipe shows itself. In the lower cut open pipe the heating gear is according to the invention not brought up right to the surface of the bat but the heating wire spirals 3 are continued by permit simply by a single distance support (thimble) below the bath surface to secure the position of the currentconductor in the pipe. These metal rods are furthermore far outside the bath held by a corresponding holder. By this arrangement it is impossible that at the endangered point salts are deposited at such parts which connect the current conductor.

The open ends of all pipes 2 are embodied in a closed casing I which contains also the collector rails 8 lying on tension, with which the heating wire spirals are connected.

In the detailed drawings according to Fig. 3 the single heating conductors e. g. wire spiral 9 are kept in the desired position in pipe Ill by the thimbles II. The thimbles or supports of heat conductor 9 consist of quadrangular plates, the one end of which is to a large extent cut off. These plates contain openings l2 through which the heating wires are led. These openings are arranged in the supporting bodies in such a was that they form a ring around the centre of the quadrangle having equal distance from one another, by the shortening of the one edge of the quadrangle, there is however no room for an opening left for one of the wires. Thus the wire gets no lead at that point.

arrayed here on the four drawn wires in such a way that the supports following one another are in each. case transposed by one hole portion. Thereby the unbroken edges in the longitudinal the pipe lie on a screw line.

In Figs. 4 and 5 shown.

are broken 011', 'while the other two neighbouring edges are kept. As will beseen from Fig. 4 the three thimbles arranged one above the other e. g. soap stones or preferably stones of even mass are arranged one against the other so that the corresponding unbroken edges of the stones in succession form a screw line; as shown 4 are furthermore theedges of the heat carriers pointed adjacent to the pipe wall, so that the level piece of the pipe which is getting radiation immediately from the heat conductor is covered aslittle as possible. The longitudinal cut through a supporting body as per Fig. 6 shows a further minimizing in order to reduce the mass obstructing the radiation. The body I! is, as will be seen, formed in its middle on both sides concave, the one edge I8 is unbroken, while the other I9 is broken. As shown in Fig. 4 for the strengthening of the opening'for a supporting wire on both sides of this openinga flange .may beprovided.

- tecting layer 25 in the metal rods 6, which coverings on the The sinheat conductor supports H are however direction of.

In the example of execution as per Fig. 7 the heating body I8 is fitted with a junction pipe 20 in ring form. The pipe 2| acts as conductor main. In the heating part 20 the electric heating gears 22 are placed. The bath reservoir 23 can, if needs be, be surrounded by a heat wiring. Its outside walls may in this case be fitted with a protecting layer of material immune to corrosion 24. It is also provided on the inner surface towards the heat carrier with such a protecting layer 24 for instance of nickel.

The immersed heating body has such a proactual heating part viz., inside as wellas outside.

The protection on the inside of the pipe has double the effect, viz., in the first instance to prevent the permeation of salt through the wall and at the same time to protect the wall side facing the'heat bodies from smoldering. Nickel outside of the bath reservoir have proved of advantage only, if heating from outside is resorted to.

I claim:

1. An electrical heating element for immersion heating of salt bathscomprising a curved pipe supported by spaced insulators extending therein, said insulators being substantially flat, and thin in section, and being formed with a plurality of corners which provide substantially point-like bearings for said insulators against the inside walls of said pipe.

2. An electrical heating element as in claim 1, in which said insulators are substantially rectangularly shaped, but have at least one corner removed, whereby the number of point-like bearings for each insulator is reduced.

less than the cross sectional area of the interior. of said pipe on a plane lying normal to said axisand the bearing surfaces between said insulating elements and said wall being substantially fine areas of contact.

4. A heating element as in claim 3, successive insulating elements being angularly displaced about the axis of the pipe whereby the engaging portions of said insulating elements with said pipe are in staggered arrangement.

5. A heating element as in claim 3, said insulators being substantially polygonal-in shape but having at least one corner thereof removed whereby the number of contact points of eachinsulating element is reduced.

6. A heating element for immersion heating of salt baths comprising a curved pipe and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductorsahd substantially fiat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe, at least one heating conductor passing through each of said insulating elements, the maximum pmjected area of each of said insulating elements in the direction of the longitudinal axis of said pipe being less than the cross-sectional area of the 75 said elements being said axis and the bearing surfaces between said 1 insulating elements and said wall being substantially fine areas of contact.

'7. A heating element for immersion heating of salt baths comprising a pipe having a single curve therein and being closed at one end, and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe, at least one heating conductor passing through each of said insulating elements, themaximum projected area of each of said insulating elements in the direction of the longitudinal axis of said pipe being less than the cross-sectional area of the interior of said pipe on a plane lying normal to said axis and the bearing surfaces between said insulating elements and said wall being substantially fine areas of contact.

8. A heating element for immersion heating of salt baths comprising a curved pipe closed at one end, and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining the heating conductors spaced from pipe, at least one heating conductor passing through each of said insulating elements, said insulating elements mounted on said conductors extending ironl the end of the heating conductors to a point below the level of a bath in which said heating element isadapted to be immersed, the maximum projected area of each of said insulating elements in the direction of the longitudinal axis of said pipe being less than the crosssectional area of the interior of said pipe on a plane lying normal to said axis and the bearing surfaces between said-insulating elements and said wall being substantialy fine areas of contact. 9. A heating element for immersion heating of salt baths comprising a pipe having a single curve therein and being closed at one end, and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe, and the maximum projected area of each of said insulating elements in the direction of the longitudinal axis of said pipe being less than the crosssectional area of the interior of said pipe on a plane lying normal to said axis, at least one heating conductor passing through each of said insulating elements, and at least one heating conductor passing through a space between an insulating element and the inner wall of the pipe.

10. A heating element for immersion heating of salt baths comprising a curved pipe and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductors and substantialy flat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe. said insulating elements being polygonal in shape with at least one corner removed, and at least one heating conductor passing through each of said insulating elements, successive insulating elements being angularly displaced about the axis of the pipe.

each other and from said aoergoai 11. A heating element for immersion heating of salt baths comprising a curved pipe and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining theheating conductors spaced from each other and from said pipe, the maximum projected area of each of said insulating elements in the direction of the longitudinal axis of said pipe being less than the cross-sectional area of the interior of said pipe on a plane lying normal to said axis, the bearing surfaces between said insulating elements and said well being substantially fine areas of contact, at least one heating conductor passing through each of said insulating elements, and a supporting wire passing through said insulating elements.

12. A heating element for immersion heating of salt baths comprising a curved pipe and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe, the maximum projected area of each of said insulating elements in the direction of the longitudinal axis of said pipebeing less than the cross-sectional area of the interior of said pipe on a plane lying normal to said axis the bearing surfaces between said insulating elements and said wall being substantially fine areas of contact, at least one heating conductor passing through each of said insulating elements, said heating conductors being adapted to and arranged to terminate in a heating bath below the surface thereof and said pipe to extend above the surface of the bath, and supply leads connected in said pipe with the heating conductors.

13. A heating element for immersion heating of salt baths comprising a curved pipe and a uniform flexible heating element movably arranged in said pipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe, said insulating elements being in substantially point-like contact-with the inner wall of said pipe, and at least one heating conductor passing through each of said insulating elements, said insulating elements being pointed toward the contact points.

14. A heating element for irmnersion heating of salt baths comprising acurved pipe and a uniform flexible heating element movably arranged in saidpipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe, said insulating elements being polygonal in shape with at least one corner removed and being in substantially point-like contact with the inner wall of said pipe, and at least one heating conductor passin said pipe, said heating element consisting of at least two heating conductors and substantially flat insulating elements spaced from each other for maintaining the heating conductors spaced from each other and from said pipe, said insulating elements being in substantially point-like contact with the inner wall of said pipe, and at least one heating conductor passing through each of said insulating elements, the successive insulators being disposed at equal angles about the axis of the pipe, the surface of the pipe being coated by a material resistant to the corrosive action of a melting bath, and said insulating ele ments being adapted and arranged to terminate in said bath below the surface thereof.

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