Autogenous Welding of Iron

T. I. Tikhonov.

(With 5 tables.)

Autogenous welding of iron over the last decade has begun to be used more and more widely for various boiler-making operations. Preliminary melting of the metal at the joint is carried out either by means of an electric current¹ or by means of a blowpipe. In the latter case, the worker, directing the jet of burning gas from the blowpipe onto the place of the joint, melts the metal at the edges of the joint and, as soon as the particles of molten metal join together and fill the seam, the worker immediately stops the action of the blowpipe, allows the seam to cool slowly, and only in some cases, when the edges of the seam are bevelled, and when working with two blowpipes from both sides of the seam, the latter, for closer contact of the seam edges, is subjected to light hammering.

According to the kind of gas used, blowpipes may be: hydrogen, acetylene, using illuminating gas or gasoline vapor. In all these blowpipes the gas is mixed with oxygen, but the gas is always present in considerable excess, so that the working flame has a strongly reducing character. The oxygen necessary for such work with blowpipes is ordinarily supplied in an almost pure compressed form at a pressure of 140–150 atmospheres in special metal cylinders. (Usually such compressed oxygen contains 96% and 4% N). The cylinders are provided with a reducing valve, and the oxygen, after passing through it, usually enters the blowpipe at a pressure of from 1/2 to 2 atmospheres. Pure oxygen for the indicated purposes has recently been obtained by Linde’s method from air, i.e., by fractional distil—

distillation of liquid air, based on the difference of 32°C in the boiling points of liquid oxygen and nitrogen¹.

As the combustible gas in blowpipes for the autogenous welding of iron, hydrogen and acetylene are chiefly used, as gases with the highest flame temperature; illuminating gas and gasoline vapors are most often used for welding metals more fusible than iron, or for iron up to 4 m/m in thickness. Hydrogen for the indicated brazing works is supplied in special metal cylinders in compressed form, at a pressure of 140–150 atmospheres, and enters the blowpipe from the cylinder through a reducing valve at a pressure of up to 1/2–2 atmospheres. Hydrogen is obtained as a by-product of many chemical processes or by the electrolytic decomposition of water; however, the products obtained from the decomposition of water cannot be used directly for brazing operations, and the quantity of hydrogen must be increased so that in the blowpipe the ratio of hydrogen to oxygen gases would be close to 4:1, for at such a ratio of the gaseous mixture the flame, having a reducing character and developing a combustion temperature of about 1900°C, can give a good dense seam. The mixing of the gases usually takes place in a special cavity of the blowpipe tip, into which the gases are fed through rubber hoses from the cylinders. Oxygen enters the cavity of the blowpipe under a higher pressure, as a result of which it vigorously draws in the hydrogen and, after thoroughly mixing with it, proceeds to the brazing orifice of the blowpipe itself. To prevent explosions that may occur during work with such burners, it is necessary to make the outlet openings with such a cross-section that the rate of combustion (i.e., the rate of propagation of the combustion process of the prepared mixture) would be less than the rate of outflow, in order to prevent the flame from passing back into the burner. Recently, for the mixing of hydrogen and oxygen, a special reservoir has been arranged before the blowpipe, into which the mixed gas enters, and from such a reservoir it is supplied to the blowpipe through a common rubber hose.

The hydrogen flame is usually used in practice for brazing work comparatively rarely, owing to its considerable cost in comparison with acetylene, generally where such work is temporary or periodic in character and a permanent acetylene installation cannot pay for itself.

The difference in the operating cost of hydrogen and acetylene autogenous welding can readily be seen from the following table¹.

The reducing valve-manometer for oxygen is screwed onto the branch of the valve fitted on the oxygen cylinder, by means of the attached connecting nut $a$ in Fig. 1, Table A. Upon opening the shut-off valve of the cylinder, the oxygen rushes through the narrow channel $б$ into the reducer, the oxygen entering the reducer only after the pin $u$ (which closes the channel $б$) has been withdrawn from its seat. The manometer $д$, connected directly with the channel $б$, indicates the pressure of the oxygen issuing from the cylinder. The reduction of the high pressure of the oxygen coming from the cylinder is effected by the lever $e$, which, owing to the greater or lesser pressure of the spring $ф$, presses on the pin $u$ and closes the channel $б$; the spring $ф$ is acted upon by the pressure screw $i$; when the spring $ф$ is completely relieved, it presses the spring $x$, lying on the other side of the lever, against the lever $e$ and the pin $u$, so that oxygen cannot penetrate at all into the space $i$. As already stated, owing to the pressure on the spring $ф$, the pin $u$ comes out of its seat, as a result of which the oxygen gains access to the space $i$; this latter space is separated from the space $к$ by a rubber membrane $a$. The pressure of the oxygen in the space $i$ is transmitted to the membrane $i$ and is balanced, i.e. the corresponding pressure of the spring on the membrane $ф$ is established on the other side; thus the lever $e$, by means of the pin $u$, establishes the required opening of the channel $б$. With the space $i$, by means of the channel $м$, is connec—

day, a manometer that indicates the pressure of the oxygen reduced by the method described above.

Acetylene for work with a blowpipe in welding iron cannot be supplied in compressed form, since in that state it is highly explosive; very rarely is acetylene taken for the indicated work in a solution of acetone, but in that case it is placed in a cylinder filled with some porous substance (coke), which, by virtue of its capillarity, retards the propagation of an acetylene explosion. Usually, to obtain acetylene, a special generator made of thin boiler iron is set up not far from the soldering apparatus. One such generator from the factory of Messer & Co., Frankfurt am/Main, is shown in Fig. 2, Plate A.

The generator consists of a gas producer, a water basin 1, to which is riveted a gas holder 2 with a gas bell 3.

To the generator it is also necessary to attach a gas purifier 4; in doing so, attention must be paid to ensuring that the outlet cock 5 between the generator and the purifier is installed in place, so that, when the purifying mass is newly charged, the small quantity of gas contained in the gas holder may be released by means of this cock.

The gas holder 2 is filled with water, pouring it into the space between the walls of the gas holder and the gas bell 3 up to a level that would stand 100 mm below the edges of the gas holder. When filling with water, both cocks located before and after the gas purifier must be kept open, so that the air contained in the gas bell can escape freely. If gas is subsequently contained in the gas bell, then the water level rises to a height 20–30 mm below the edges of the gas holder.

After the cock for draining sediment has been screwed shut, the basin of the gas holder 1 is filled with water to a level 150 mm below the edges of the gas producer. The carbide reservoir 9 must be taken out of the gas producer while it is being filled with water.

If there is no purifying mass in the gas purifier, its cover must be removed, it must be filled with this mass, and the cover screwed on again. Most often the factory sends the purifier already filled with the mass.

After all these preliminary operations, the carbide reservoir is filled with carbide; for filling, the reservoir is placed with its opening upward, the guide rod is raised upward and the open—

move it aside, after which the bottom piece 7 and the conical valve 8 are removed. Then the entire space 9 is filled with carbide down to the bottom 10, and the carbide valve (the conical plug 8) is put back in place; likewise, with the bottom piece 7 and by clamping the valve stem 8 in the coupling of the guide rod 6, the carbide reservoir is closed. Holding the handles of the carbide reservoir 11 and of the guide rod joined together in the hand, the reservoir is lowered with its opening downward and shaken several times. The handle 6 must be pressed against handle 11, so that the carbide in space 9 cannot get into the lower part of the carbide reservoir; thanks to this, when the reservoir is suspended in the gas generator, losses of gas are avoided.

The carbide reservoir is suspended from the gas holder by means of two hooks to the iron 12. During this suspension it is still necessary to keep valve 8 closed, and to bring the lower part of the reservoir up to the gas holder in such a way that the gas-directing trough 13 comes under the concave bottom of the gas holder. Only then is the guide rod 6 slowly lowered, i.e., in this manner the inlet carbide valve 8 is slowly opened.

Gas generation begins. The acetylene that is produced displaces from the generator the air which (as indicated above) is to have a free outlet through the open cock located behind the gas purifier. Then, when the sharp odor of acetylene appears, valve 8 is again pressed into place and cock 5 (on the path from the generator to the purifier) is closed; by alternately lowering and raising rod 6, gas is obtained until the gas bell begins to rise and the guide rod by itself remains motionless in the upper position.

The entire gas bell is hermetically closed on all sides; only to a height of several centimeters is the lower part of the carbide reservoir filled with water, since the walls of the gas-directing trough 13 are perforated.

At the moment the carbide valve is opened, the carbide from the upper space of the reservoir falls into the lower part, filled with water, and then gas generation begins. The acetylene rushes through the openings of the perforated bottom piece 7, along the directing trough 13, and under the bottom of the gas holder, through pipe 14, into the gas bell 3. As can be seen from the drawing, the gas must pass through the water of the gas holder to a height of several centimeters, since the gas-outlet openings in the float 15 are below the water level. In this way a water seal is created, preventing ob—

to the reverse outlet of gas into the gas generator. Following the rise of the gas bell, the float 15 also rises and carries with it the regulating rod 16, which is firmly connected to it. This rod pulls up the guide rod 6, pressing it against the bottom of the reservoir and thereby closing the carbide valve 8. As the gas is consumed, the gas bell descends, presses on the float, and lowers the regulating rod 16 connected with the float; the guide rod is released, descends, and valve 8 opens. A new portion of carbide falls into the water, and as a result of the new gas generation the bell rises together with the float and locks the carbide valve.

Thanks to the described alternating lowering and rising of the gas bell and of the float connected with it, during operation of the generator the carbide inlet valve is alternately opened and closed; that is, gas production proceeds according to the demand for gas.

The alternating movements of the gas bell are guided by the axle, the guide post 18, and the safety tube 17. In the event that gas should be produced in an amount not corresponding to the capacity of the bell, this safety tube 17 is provided, through which the excess gas can escape to the outside, preventing the bell itself from emerging from the water, since the safety tube is shorter than the height of the side walls of the bell, as a result of which it enters the gas space (above the water level) earlier than the walls of the bell.

In the room for the generator, above tube 17, it is necessary to install a ventilation pipe that would conduct the excess escaping gas safely to the outside space; the formation of excess gas is explained only by the small consumption of it by the burners in operation.

The apparatus may be filled with carbide at any time, i.e., even when not all the carbide located in the reservoir has been consumed. From the weight of the reservoir one can always determine whether it contains much or little carbide.

In order to fill the reservoir with carbide, it is necessary to remove it from the gas-generating basin 1, keeping handle 8 and rod handle 6 closed, so that conical valve 10 is closed and the carbide cannot fall into the water; the lower part of the reservoir, the gas-guiding trough 13, must first be moved away from beneath the bottom, and only then should the reservoir be removed.

After removing the reservoir, it is turned over, the guide rod 6 is set aside, and the bottom 7 and valve 8 are taken out. The entire lower part of the reservoir is carefully cleaned with a dry rag of lime residues from the carbide, and especially the inner surfaces of the valve 8 itself and of the funnel 10. When these latter are kept clean, the generator works most reliably. Then carbide is poured into the reservoir and, as indicated above, the generator is put into operation. If gas still remained in the gas bell at the moment the generator was put into operation, then when the rod 6 is released it does not descend, and the carbide valve 8 remains closed.

After 5–6 charges of carbide, much lime residue and foam forms in the gas generator, which becomes noticeable even in the lower part of the carbide reservoir after it is removed from the gas generator; in this case it is necessary, after opening the drain cock of the gas generator, to let the water out of it and replace it with fresh water, filling it, as indicated above, to a level 150 mm below the edges of the gas-generator basin.

From time to time it is necessary to pay attention to the height of the water level in the gas holder; namely: when there is water in the gas bell, the water level in the gas holder should stand 30 mm below its edges.

The operability of the apparatus, as is clear from the foregoing, depends chiefly on the cleanliness around it and on careful maintenance; therefore it is desirable, every 2–3 years, to subject the apparatus to complete disassembly and thorough cleaning, as well as painting.

Acetylene from the generator is delivered by a rubber hose to the torches and, there, having mixed with oxygen supplied to the torches likewise from its own cylinder by a rubber hose, is ignited. Torches intended for this purpose are fairly uniform in construction. Thus, in Fig. 3, plate A, a torch of the above-named plant is shown. As can be seen from the drawing, the admission of both gases into the torch is effected by one common cock. Oxygen passes through tube a, nozzle b, into the mixing chamber d; the acetylene gas passes through the channel intermediate between tubes a and u and through the slots f to the mouth of nozzle b; here the jet of oxygen issuing from the nozzle, like an injector, draws with it the acetylene gas into the mixing chamber d; from there the gas mixture exits through the tip and is ignited to obtain the welding flame.

With the valve completely open a long flame is obtained; it is shortened to a length of 6–10 mm by locking the common valve for both valves of the stopcock.

During work with the torch, the end of the latter may become clogged, and the discharge of gas may cease. Under such conditions oxygen, as entering under a higher pressure than acetylene, can penetrate into the bell of the acetylene generator and form an explosive mixture with the latter. To prevent the combination of acetylene with oxygen, in addition to the torch tip, torches of special construction are used, in which the acetylene in the body of the torch passes through a series of capillary tubes and then combines with the oxygen; such capillary tubes hinder the propagation of an acetylene explosion. Fig. 4, Table A, shows a torch of such construction from the Schumacker works.

Acetylene enters through tube \(A\). Often, for the same purpose, a check valve is placed in torches at the opening of the channel for acetylene. Fig. 5, Table A. Finally, often, in order to prevent the access of oxygen into the bell with acetylene, a water seal is placed on the acetylene pipeline, playing the role of a safety device in case of an explosion. Fig. 6, Table A, explains the arrangement of this apparatus: acetylene gas flows through tube \(a\), which with its lower part is immersed in water, and through this latter enters space \(b\). The rubber hose carrying the gas to the torch is attached to the upper valve \(u\); the lower valve \(d\) is a water gauge for indicating the water level in the apparatus—the water must stand in the apparatus at the level of this valve. A second tube \(e\) is inserted into the water, which enters with its lower end into vessel \(\phi\) (the upper cover of vessel \(\phi\) is somewhat below the water level) and at the top ends in an open funnel. As soon as the above-mentioned case occurs, i.e., oxygen from the hose rushes into the generator, then, entering space \(b\), it will force the water out of tubes \(a\) and \(e\). With the increasing pressure, water will begin to be forced out of vessels \(b\) and \(\phi\) through tube \(e\), owing to which tube \(e\) will open outward and give free passage outward to the oxygen rushing in. Meanwhile, however, in tube \(a\) the water rises so high that it forms a reliable seal for the generator. As soon as the pressure in space \(b\) again decreases, the water contained in the outlet funnel, and also in tube \(a\), will flow back into vessels \(\phi\) and \(b\), and the normal standing of the water will be restored under normal—

...at low pressure. The same pressure will also occur in the event that an explosion arises in space b. By means of the water seal described, complete protection of the generator against explosion is achieved.

Recently, gas cutting of metal has been widely used in many boiler works. The principle of gas cutting consists in the following: if a jet of pure oxygen is brought up to iron (or steel) heated to the melting temperature, then the latter, oxidizing and burning the material, cuts it, as a saw does, as it moves over the iron. The cutting apparatus shown in Fig. 7, Plate A, is arranged as follows: oxygen enters the apparatus i, passes through tube b and nozzle d. Here the oxygen is held back by means of the conical valve x, which closes channel i, owing to the corresponding pressure on lever n. Through channel k, with cock l open, a thin jet of oxygen passes, carrying with it into the mixing chamber m the acetylene gas which has entered the apparatus at a and, having passed through the intermediate space between tubes b, c, and channel e, proceeds to the cutting nozzle f. The gas mixture emerging from the nozzle of the apparatus is ignited, and the iron to be cut is heated by the resulting cone of flame to the melting temperature. Immediately upon attainment of such heating, by the corresponding pressure on lever n, valve x is raised from its seat, and pure oxygen rushes toward the heated place of the metal.

In the jet of oxygen the iron burns. With further movement of the apparatus, we obtain further combustion of the iron and thus its cutting. The jet of pure oxygen must follow the jet of the heating flame, so that all particles of the iron being cut can first be heated to incandescence before the cutting oxygen jet is released.

Regulation of the inflow of the cutting jet of oxygen is carried out by means of the corresponding greater or lesser pressure on lever n, i.e., by greater or lesser opening of the orifice of valve k. The construction of the apparatus cutting iron more than 100 mm and up to 300 mm thick is completely identical with that described.

The section of the nozzle of the cutting apparatus with two outlet openings for the heating acetylene-oxygen flame, shown in Fig. 8, Plate A, shows the arrangement of the apparatus for cutting metal of great thicknesses in all directions.

Cutting apparatuses of similar construction can also operate on...

in a hydrogen flame, with corresponding changes in the cross-sections of the blowpipe outlet openings.

As for the actual course of the autogenous-welding process, in general outline it is as follows: the edges of the sheets to be welded are carefully fitted to one another before welding, and this work is usually done on machine tools. Then the edges of the sheets to be welded are brought tightly together and, by means of two blowpipes, one from below and the other from above, the weld seam is thoroughly heated; the heating of the metal is made as uniform as possible, for which purpose the blowpipe flame is made to act over as broad a heating zone as possible. If the sheets to be welded are thicker than 8 mm, then after the edges have been fitted closely, but before the blowpipes are used, they are first heated to a temperature of 400–500° C. When the metal at the joint of the sheets begins to melt, the seam is lightly struck with a hammer along its plane, for greater compaction of the metal and for closer cohesion of the particles of the heated metal. The plane of the weld seam of the sheets is beveled, and one edge is placed upon the other, or the edges are joined end to end; when the sheets are more than 10 mm thick, both edges of the sheets to be welded are beveled in such a way that a free gap with a triangular cross-section remains between them at the top; this gap is then filled with soft Swedish iron, and at this point the weld produces a certain thickening of the sheet. The soft iron for filling the seam in the latter case is taken from a special rod, which is held in the flame of the upper blowpipe. To obtain greater density of the seam, it is useful, at high heat, to compact it with light hammer blows.

Autogenous welding may be applied in practice for filling blowholes and other defects in cast-iron and steel castings; in this case, filling is carried out with soft iron analogously to the last method of welding iron, but the repair of such defects must always be preceded by preliminary heating of the articles to be repaired.

As for the consumption of acetylene and oxygen for welding and cutting iron, depending on the thickness of the sheets this consumption is expressed on average by the following figures (see table, p. 11).

To produce one cubic meter of acetylene, 3½ kilograms of calcium carbide are required. One kilogram of carbide costs on average about 35 kopecks. Oxygen in steel cylinders under pressure up to 125 atmospheres is delivered in Russia at an average pri—

not for 1000 liters about 3 rubles 50 kopecks.

When purchasing carbide, serious attention must be paid to the purity of the carbide, for even a slight content of phosphorus in the latter has a very bad effect on the quality of the seam obtained. With sufficiently pure acetylene the burner flame has a dark-blue color, with a sharply defined inner white cone. If, however, the outer envelope of the flame takes on a dirty yellow coloration, this serves as a clear sign of insufficient purification of the gas; phosphorous-hydrogen compounds are burning in the flame, with the formation of acids, and the place of welding, as a result of the action of phosphorus, becomes cold-short.

Autogenous welding of iron is considerably better than ordinary forge welding, and, in the hands of an experienced worker, gives good mechanical results. At the Schulz Knaudt works in Essen autogenous welding is widely used, and extensive experiments were carried out there to test the mechanical properties of acetylene welding. ¹)

¹) Stahl und Eisen 1909. V. 1814. Journal of the Russian Metallurgical Society, No. 2, p. 342.

T. I. Tikhonov.

A special feature of autogenous welding, and at the same time an advantageous aspect of it, is the possibility of obtaining a thickened seam, whereas in ordinary forge welding with water gas the seam obtained is thinner than the edges being welded.

Owing to this feature of autogenous welding, the usual mechanical tensile test of welded specimens does not give a correct idea of the actual mechanical strength of the welded iron. For mechanical testing the thickening of the seam is machined off; therefore fracture always takes place at the weld. In this case a reduced tensile strength and a very small elongation are obtained. It would be more correct to carry out tensile testing of unmachined specimens, and still better to test the welded articles themselves.

From boiler iron 15 mm thick, a boiler was made by autogenous welding (diam. 1200 mm, length of the cylindrical part—1500 mm) with convex bottoms; three seams were obtained—one longitudinal and two transverse. The boiler was filled with water, the pressure of which was gradually brought up to 91.5 kg per sq. cm. Although the circumference of the boiler in the middle part increased by 6.3%, no damage was found in it.

After the test, specimens for tensile tests were cut from the boiler, both at the welds and in sound places; the welded specimens were subjected to tensile testing both in the unmachined and in the machined condition.

From these figures it is evident that, first, the pressure test of the boiler was reflected most of all in the welds and that, second, machined and unmachined specimens show a considerable difference in mechanical properties. True, this difference is obtained only when fracture occurs at the weld; if, however, fracture occurs not at the weld, then no difference between machined and unmachined specimens is observed, as is clear from the figures given above.

This is also confirmed by mechanical tests of welded iron sheets (10, 13, 16, 19, and 22 mm thick)—machined

and unmachined welded specimens give quite identical mechanical properties, provided only that the rupture does not occur at the place of welding.

Comparative experimental investigations of welded specimens have shown that the hydrogen seam is stronger than the acetylene one. The test specimens welded with hydrogen were prepared in the laboratory of the Griesheim-Elektron chemical factory in Frankfurt, and those welded with acetylene—in Fouché’s laboratory. The average results of the tests are given in the following table. ^5)

Thus from the last table it is evident that the acetylene seam is considerably worse than the hydrogen seam in respect of:

Elastic limit by . . . 30.5%
Tensile strength by . . . 22.3%
Elongation by . . . 24.8%

Hence it is evident that with acetylene welding the tensile strength of the material decreases by 23%, and the elongation by 84%; with hydrogen welding the tensile strength almost does not decrease, while the elongation falls by 60%.

The mechanical properties of autogenous welding of iron depend to a considerable degree on the experience and skill of the worker conducting the soldering process. With insufficient supervision on the part of the worker, gas or slag cavities remain in the soldering seam; not infrequently even unwelded places remain in the seam. Thus Figs. 1, 2, 3 and 4 of Table I give a clear picture of the nonuniformity of the autogenous seam of acetylene welding. All the following polished sections likewise relate to acetylene welding and cutting of iron. Even in a favorable case the structure of the seam differs characteristically from the structure of the parts of the metal being joined.

^5) Borovich. Boiler Production. p. 420.

In poor welding the seam abounds in substantial defects (Fig. 3). The temperature of the torch has a noticeable effect on the change in the structure of the metal of the iron sheets being joined, and the lower the temperature of the flame, the farther from the seam the structure of the joined parts of the metal is altered.

Thus, when hydrogen is used for autogenous welding, the change in the structure of the joined parts of the metal extends to a greater depth from the seam than is observed with an acetylene flame, for in the latter case the temperature is incomparably higher, as a result of which the process also proceeds noticeably faster than with an acetylene flame.

In autogenous welding, fluxes are usually not used to remove scale and slags from the seam, because the temperature is so high that these bodies are usually in a liquid state during soldering and are easily removed from the seam. If, however, the temperature during soldering remains comparatively low, then these foreign bodies (slag and scale) are only weakly separated from the seam, and a large amount of them remains among the metal particles in the seam.

The latter is especially clearly revealed after a low and prolonged (about \(500^\circ C\)) annealing; thus Figs. 6, 5 of Table II depict the macrostructure of one of such seams in acetylene welding, the section of the seam in Fig. 5 having been annealed, as a result of which the presence of foreign bodies in the seam is clearly noticeable.

Fig. 7 of Table II depicts the macrostructure of an acetylene autogenous weld of iron; the heterogeneity of the structure of the metal is clearly noticeable and is revealed especially strongly at high magnification in Figs. 8 and 9 of Table II.

Moreover, Fig. 8 clearly indicates the considerable hardness of the metal in the middle of the seam; Fig. 9 shows the transition of this structure into a softer one belonging to the joined parts of the iron.

A similar very hard structure is shown by Fig. 12 of Table III, but this structure refers to place \(A\) of the macrostructure of Fig. 6 of Table II. The same structure, of the same section after annealing, is shown in Fig. 13 of Table III; the defect of welding with a large accumulation of slags on the latter polished section is clearly noticeable. At place \(B\) of the macrostructure of Fig. 6 of Table II, the structure of the seam after annealing is distinguished by greater homogeneity and purity (see Fig. 14 of Table III). Finally, Fig. 15 of Table III depicts an unwelded place of the seam after annealing of the same section of Fig. 6 of Table II from place \(C\). Figs. 16 to 21 of Table IV give a vivid picture of the heterogeneity of the structure of the acetylene-

Autogenous Welding of Iron

…of an autogenous seam, of very good workmanship. The structure of the joined parts of the iron near the seam, as can be seen in Fig. 18, changes considerably, and the metal in this place, as is evident from the structure, undergoes slight hardening.

Quite analogously to the last case, the structure of the iron changes along the edge of the cut to a depth of from 3 to 5 mm, as can be seen from the phototypes of Figs. 10 and 11 of Table III; moreover, the first polished section was prepared without annealing, and the second with annealing at a temperature of \(600^\circ C\) for 2 hours. As is seen from a comparison of the last two polished sections, the metal along the edge of the cut made with an acetylene torch greatly changes its structure in the direction of increased hardness, and in responsible boiler work this edge should be removed to a thickness of 3–5 mm, or, in the extreme case, the cut sheets should be annealed.

Thus, summarizing all the foregoing, we arrive at the following conclusions regarding the autogenous welding of iron:

1. Autogenous welding of iron with the use of hydrogen or acetylene, when carried out by an experienced and good workman, possesses good mechanical properties and is considerably better than ordinary manual forge welding of iron.

2. The autogenous-hydrogen weld in iron welding is considerably better, in terms of seam strength, than the acetylene weld, all other conditions being equal.

3. In acetylene welding, the tensile strength of the material at the place of joining decreases by 23%, and the elongation by 84%; in hydrogen welding the tensile strength decreases almost not at all, while the elongation falls by 60%.

4. The structure of the metal in the sections of the seam of autogenous welding of iron is very heterogeneous in constitution and, in poor welding, abounds in foreign inclusions.

Fig. 1. \(1 \times 2\).

Fig. 2. \(1 \times 3\).

Fig. 3. \(1 \times 3\frac{1}{2}\).

Fig. 4. \(1 \times 1\).

Table 1

Fig. 5. 1×4.

Fig. 6. 1×5.

Fig. 7. 1×5.

Table III.

Fig. 10. \(1 \times 100\).

Fig. 11. \(1 \times 100\).

Fig. 12. \(1 \times 100\).

Fig. 13. \(1 \times 100\).

Fig. 14. \(1 \times 100\).

Fig. 15. \(1 \times 100\).

Autogenous Welding of Iron. T. Tikhonov.

Table IV.

Fig. 16. 1×2.

Fig. 17. 1×50. Place A.

Fig. 18. 1×50. Place B.

Fig. 19. 1×50. Place C.

Fig. 20. 1×50. Place D.

Fig. 21. 1×50. Place E.

Autogenous Welding of Iron. T. Tikhonov.

Table A.

Fig. 7.

Fig. 8.

Fig. 5.

Fig. 2.

Autogenous welding of iron. T. Tikhonov.

Fig. 1.

Fig. 6.

Fig. 4.

Fig. 3.

1. Zeitschrift für Werkzeugmaschinen und Werkzeuge. 1910. No. 6. p. 82. ↩↩↩