Brazing Iron and Steel.

Fig. 62.—Home-made Brazing Hearth

In the back, near the bottom, atS, cut a hole for the nozzle of one of the bellows, and above the shelf cut another hole atS1to take the nozzle of the other bellows. The bottom bellowsCshould have the top handle extended by a piece of stout bent ironNto act as a pedal, and should be screwed to the base. A central hole about 3 in. in diameter should be cut atPto allow the air to reach the valve. Now get a piece of lead pipe1⁄2in. inside diameter, and, having cut down the nozzle to just under that diameter, force the mouthof the pipe over it as atS, and bend the pipeFas shown, to reach the centre of the shelfBand enter the holeGuntil flush with the top. Remove the lead pipe and get a block of wood about 3 in. square. Cut off the corners and bore a hole in the middle, so that the lead pipe will just pass through it, and countersink the hole. Broach out the mouth of the lead pipe until it becomes bell-shaped and fits the block of wood, so that its edge is flush with the wood when pressed hard against it. This is clearly shown atG, where the dark shading represents the wood block. Cut a leather washer the size of the block, with a1⁄2-in. central hole, and lay this over the hole in the bottom of the top bellows where the leather flap valve is. Bore two holes in the wood block, and screw this down tightly to the bottom of the bellows, so that the bell-mouth of the lead pipe faces the hole and has the leather between it and the block. This should make an air-tight joint for the fixing of the pipe to the bellows.

Next, push the nozzle of the bellows through the holeS1, and screw the bellows down tightly to the shelfB. Join the lead pipe to the nozzle of the bottom bellows, and make an air-tight joint with glue and tape bound round. Between the top of the upper bellowsDand the top of the packing case atV, a stout sofa springEis fixed to keep the top bellows shut down tight till air is pumped in from the bellows below.

From a screw near the top of the case stretch a house-bell coil springM, and attach its lower end to the foot-plate or pedalN. This spring tends to keepthe lower bellows open. When pressure is put on the foot-plateN, air is pumped from the lower to the upper bellows, and thence along the flexible pipeRto the bunsen blast nozzle described in detail later. If it were not for the upper bellows, the air would come to the nozzle in puffs, but the springEkeeps the pressure constant, and a steady blast is secured. The rubber pipeRshould be of sufficient length to reach the hand conveniently, and allow room for movement.

The hearthKcan be made from sheet-metal, with the edges bent upwards to form a tray; or an old frying-pan will answer very well. Whichever is employed, four iron stays or legsHmust be used to raise it above the top of the packing case as shown. These legs should be screwed at one end to the sides of the case, and at the other to the pan, and if a frying-pan is used, the handle may be cut and bent to form a hook as atL; it then acts as a support for the blast nozzle.

Fig. 63.—Blowpipe or Blast Gas Nozzlefor Brazing Hearth

For use with the brazing hearth, a blast gas nozzle on the bunsen principle is required, and this is easily made from two pieces of gas-piping, a right-angle joint, and two mouthpieces to take flexible pipes. First, get 1 ft. of3⁄4-in. brass (or iron) pipe and an elbow, internally threaded at both ends. Cut 2 in. off the brass pipe, and cut a thread at one end of the short piece and one end of the long piece, to screw into the elbow as shown inFig. 63. At the other end of the long tube solder in a cock or mouthpiece to take a large diameter flexible pipe from the gas bracket. Next get 1 ft. of1⁄4-in. brass pipe, and bend it to the shape shownatB, soldering a mouthpiece atFto take the smaller diameter air-pipeR(Fig. 62) from the bellows. Bore a hole through the elbowC, and push the pipe in, making a tight fit, and so that it passes centrally through the larger brass tube until it nearly reaches the end as shown atD. Run a shoulder of solder to hold the small tube firmly in the larger one as atE, and unite with a drop of solder the large tubeAand the small tubeBwhere they cross atG.

The gas passes up the large pipe, and out atD, and a blast of air is forced through the centre of the flame through the small pipeB. The shape of the small pipe allows of it being readily hung up on the hookL(Fig. 62) when not in use. Instead of the mouthpiece shown atH(Fig. 63), a cock will be found more convenient; but it should not be too small, or it will restrict the flow of gas, which should be as great as possible. No gas-cock should have less than1⁄4-in hole.

The “fuel” (heat conservers) consists of chunks or cubes of asbestos, and when these are blown upon with the gas flame, the heat is quite sufficient for moderately heavy brazing. Be careful not to get any kinks in the flexible tubes, or the air and gas will be reduced in quantity, if not stopped altogether.

A square of thick asbestos (sheet) is useful for laying on small articles whilst brazing, and a piece or two of charcoal will be handy for silver-soldering.

—Before attempting to braze either iron or steel the surfaces should be thoroughly cleaned by filing or grinding, etc. Brass orcopper may be cleaned by dipping in a solution of 1 part nitric acid and 2 parts of sulphuric acid. This same solution can be used to remove the scale after brazing. The parts should be fastened together in the position they are to occupy when joined. The fastening may be effected by the use of wires, screws, bolts, clamps, etc. If practicable, the parts should be held in such a way that they can be turned over during the brazing process without disturbing the relation of the parts, thus affording a better chance to apply the flux and brazing material.

In brazing sheet metal, if the seams are not required to stand much working after soldering, they may be joined edge to edge. When seams are formed in this way, little nicks, about1⁄2in. apart, should be filed out along the edges, so that the solder flowing through the nicks will render the joint sound. If the seam is to be worked after soldering, a small lap is necessary to ensure adequate strength. To form seams of this type, first thin the edge of the metal along the ends that are to form the seams, about1⁄8in. in from the edge, so that when the two edges are lapped over each other the combined thickness at the seams will bethe same as the single thickness of the metal at other parts. Cut a small cramp at the top and bottom of the seam, and fit the opposite edge in these cramps. After preparing the seams by either of the above methods, fasten binding wire round the articles so as to hold the seams securely in position. Now powder some borax flux, mix equal parts of the borax paste and grains of spelter, and along the seams place sufficient of the mixture to solder them when melted. Some dry borax should also be kept ready at hand, so that a little may be taken and thrown on the solder at any point where the material does not appear to be flowing freely. Gently heat the article by some suitable means, such as foot bellows and blowpipe, so that it will expand equally, and not disarrange the seam; increase the temperature until the metal is a dull red, and the spelter runs. If necessary, with a piece of wire flattened at one end gently rub the solder along the seam until every part is joined.

—For uniting two pieces of copper rod,1⁄4in. or3⁄8in. in diameter, first prepare the joint as atAinFig. 64, and file the surface of the copper clean in the immediate vicinity of the joint. A mixture of borax and water and spelter should now be applied to the joint, which should rest on a small heap of broken coke, the coke being also built round it. The flame of the blow-lamp should be directed at first on the coke surrounding the joint, and then gradually brought to bear on the joint itself. If necessary, add a little more spelter before any of it fuses, and whenthe copper begins to get red hot, throw just a pinch of dry borax on the joint to facilitate matters.

Fig. 64.—Dovetailed Joint in Copper Rod

Fig. 65.—Dovetailed Joint in Key Stem

—In brazing together the broken parts of a key stem, first it is necessary to file the fractured ends quite true; this may entail the shortening of the key by1⁄4in. or1⁄2in., and as another1⁄4in. will be lost in making the joint, it may be advisable to use another key bow having a longer piece of stem than the one that was broken off. With a warding file cut a dovetail on each of the ends to be joined, as shown byFig. 65. A small, half-round file will assist in making the edges true and square. The pieces must interlock perfectly, and when this is the case, very lightly hammer the joint, round which then bind seven or eight turns of brass wire to act as spelter. Wet the joint, sprinkle powdered borax on it (this is to serve as the flux), and, holding the key in a pair of tongs, place it in a clear part of a forge fire made with charcoal, small coke, or coal cinders, and commenceto blow steadily the forge bellows or blower. Failing a forge fire, use a blowpipe, the key being placed on a piece of charcoal or pumice-stone whilst the heat is being applied. If the forge fire is used it is as well to support the key on a guard of thick iron plate having a hole in its centre over which is the joint to be brazed. By this means the necessary local heating is obtained, and much labour in cleaning the key afterwards is avoided. On being heated, the borax swells and boils up, and should be pressed down with a spatula, previously dipped in cold water to prevent the hot borax adhering to it; a suitable spatula is made by flattening one end of a 1-ft. length of a1⁄4-in. round rod, having at its other end an eye by which it may be hung when not in use. With this spatula, also, powdered spelter may be added to the joint if required. When the brass wire begins to run, assist the flow by adding powdered borax, and when all the brass has run into the joint, rub off superfluous molten metal from underneath and allow the joint to cool gradually. When cold, file up and clean the stem of the key until only a thin bright line of brass can be seen.

—In cycle brazing, the first consideration is the means of heating the heaviest joint to a brazing heat. This may be done in several ways, by a paraffin blow-lamp costing at least 35s. to 40s., or, what is better, a gas blowpipe7⁄8in. or 1 in. in diameter, with at least1⁄2in. gas supply pipe and a fan or bellows to supply the necessary air pressure. A small fan is far preferable to a bellows of any description, the flamebeing steady and constant, and the operator being able to devote his entire attention to the job. In the absence of power, obtain a small circular double-blast bellows and hearth, costing with blowpipe about £5.

The brazing materials are brass spelter. No. 3 size, or brass brazing wire and powdered borax; a tin to hold the mixture of spelter and borax, and one for the plain borax; a piece of iron wire about1⁄4in. by 18 in., flattened at one end to feed the spelter and borax to the joints; and a brazier’s brush, which is desirable, but not absolutely necessary, to brush the superfluous borax and brass from the outside of the joint as soon as it is removed from the hearth; this saves much work in filing up, and saves the files immensely. Do not purchase the borax ready powdered, but buy lump borax, as that purchased ready powdered is likely to be adulterated. In making the brazing mixture, use about equal parts, in bulk, of No. 3 spelter and borax.

In preparing the work for brazing, see that the surfaces are bright, clean, and free from scale. The joints should be a good tight fit, free from shake, and where a joint such as the back forks to the bridge lugs is being made, see that the tube edges fit close up to the shoulder of the lugs all round, and do not depend on the brass to fill up a badly fitted joint.

The chief things to observe are to make a sound joint the full depth of the lug, and not merely to get a thin film of brass round the outer edge. To do this, the flame should be directed on to the thickest part of the lug first before getting the tube too hot, and feedingthe joint with borax before the metals get hot enough to scale. As soon as the lug and tube begin to get a dull red, feed with borax only, then with brass and borax, when it should flow almost like water and penetrate to the deepest part of the joint.

Another very important thing is not to “burn” the tube by getting it too hot, which will spoil it and cause an early fracture. If the above method of heating the lug first is observed, and the tube near the lug kept “wet” with borax to prevent it scaling, this should not happen.

Where the joint to be brazed lends itself to inside loading with the spelter, the work should be so placed on the hearth that the brass inside, when it melts, will tend to flow to the outside of the joint. Then if borax only is used on the outside until brass appears round the edges, it will be fairly certain that a sound joint will result. As soon as this comes through, feed a little brass-and-borax mixture to the joint, and, as soon as this melts, stop the flame and remove from the hearth. If the flame is kept on too long after this, there is a possibility of “soaking” all the brass out of the joint, especially so if the joint is not a very good fit.

Some braziers use a blacklead mixture for protecting thin tubes whilst brazing; but care must be taken to keep it out of the actual joint, as brass will not adhere to metal where this is present.

Cycle frame joints can be brazed on an ordinary smith’s hearth, but it is rather risky, and requires more skill than with a gas blowpipe. It also requires a goodclear fire and a light blast. The job should be kept well fed with borax to prevent the tubes scaling and burning. The joint should be loaded from the inside with about a thimbleful or less of crushed borax and No. 3 spelter mixed in the proportion of about half of each in bulk. The heaviest part of the lug should be heated first, and the work must be turned frequently in the fire so as to avoid burning the tube. If the joint is fed from the outside with borax until the brass flows round it, a sound joint is ensured. This applies to a joint where the lug is fitted inside the tube. Where the tube is fitted inside the lug, a little brass and borax should be applied outside the joint just as the inside charge has melted, which can be seen with some joints by looking down the inside of the tube. When the tube is closed both ends, such as the last joint of a frame, the job is more difficult and requires careful judgment and skill to ensure a sound joint.

—Although it has been dogmatically asserted both that cast-iron can and cannot be brazed, it may be stated that the general results of attempting this process are so indifferent as to warrant the conclusion that this process cannot be recommended. In brazing, one of the conditions essential to success is that the metal to be brazed and the spelter should unite to form an alloy just where the brazing occurs, and that this should take place spontaneously. This actually happens when brazing copper, brass, wrought-iron, etc., but not in the case of cast-iron. If, however, the reader desires to experiment in thisdirection, the following hints may be useful. First of all, remove all dirt and grease from the cast-iron, and then chemically clean it by immersion in hydrochloric acid, afterwards well rinsing it in clean cold water. A mixture of borax and water and spelter should now be applied where the brazing is required, and gentle heat then brought to bear on it until the water is evaporated. The heat should now be increased until the casting is red hot in the neighbourhood of the brazing; and some workers claim that at this juncture the best results are obtained by dusting the red hot cast-iron liberally with boric or boracic acid powder. A hard spelter should be used in preference to a readily fusible one, otherwise the spelter would be fused much too soon, and before the casting is raised to a sufficiently high temperature.

An experienced worker who believes that it is possible to make a sound joint in cast-iron by brazing, states that he has brazed articles with equal parts of borax and boracic acid. The chief difficulty is the flux. He has tried one called “Ferroment,” which seems to give good results. The first casting brazed with it was 3 in. wide and5⁄8in. thick, and this casting at the time of writing had been in work six months for fifteen hours per day. This same worker prefers to roast borax before use, as it stops on the work better. Also, when a deep, wide joint is being dealt with, he finds it an advantage to smear on a little clay underneath and the side, as should the joint get slightly hotter in one part the spelter will run through and make an unsoundjoint. The heat required to braze cast-iron varies somewhat with the spelter used. If brazing by means of a smithy fire, the spelter will show a blue flame when it starts to run, and the article must then be removed from the fire. In using a blowpipe or blowlamp, the blue flame does not show, and one has to look for the spelter melting, and see that it flows well along the joint before removing the flame. Spelter which has been kept in stock a good time may not flow well. The worker in question prefers brazing wire to grain spelter, as by means of warming the end of the wire and dipping in the flux (which will adhere to the hot wire), it may be put just where desired. He collects all the soft brass turnings from his lathe and uses them for brazing.

Another worker has stated that those who have a forge of any kind will find the following an effective method of repairing an iron casting. A flux may be made of chlorate of potash 4 oz., boracic acid 1 lb., and carbonate of iron 3 oz. These should be mixed well together and pounded. The parts to be brazed together should be carefully cleaned by scraping them, and brought to a bright-red heat. Then apply the flux and spelter and increase the heat.

Still another worker says that in brazing cast-iron, if powdered soda is used instead of borax, the result will be a perfect joint.

Iron and steel can be joined by heating until they become plastic and then consolidating the two members of the joint by hammer blows, the work being supported on an anvil. Correct heat and cleanliness are the chief requisites. The “welding heat” corresponds with that temperature at which the metal is in a state of partial fusion on the surface. The better the quality of the iron, the higher the temperature it can stand without being burned and ruined. Iron at a welding heat gives off dazzling sparks, whereas ordinary cast steel is only an intense yellow, but few sparks being evolved. Sufficient lap for the proper making of the joint must always be allowed. When heated in a perfectly clear fire, the metal may need no treatment prior to hammering; but otherwise it may be necessary to sprinkle sand or some special flux over the work. At the proper moment the iron is transferred to the anvil, and the union of the two members of the joint immediately effected; delay means an imperfect joint. In lifting the work out of the fire, remove it vertically and so as not to collect particles of dirt on it. Keep a switch of brushwood at hand for removing adhering matter.

—Some steels will “stand the fire” better than others, which means that they will stand more heat before they reach the point when they begin to burn.

The different kinds of steel used in a general way may be summed up as blister, spring, shear, double shear, and cast steel. Blister steel will, as a rule, stand the most heating before beginning to burn, and the others follow in the order given. The difference in heating will vary from nearly a white heat on blister to the yellow heat of cast steel.

A simple method of ascertaining what heat a steel will stand before beginning to burn is as follows: Heat the steel to its burning point, and at various stages, beginning at the yellow stage, lay it on the anvil and give it a few blows with the hand hammer. Repeat the process until a heat is reached that will cause the steel, when struck with the hammer, to give off sparks like small fireworks. When this stage is reached it will show that the burning point is arrived at.

Careful observations of these points will enable the smith to know just when to begin to use the flux for welding, which, by the way, must be just before the steel reaches the burning point.

Another important point is the formation of the scarfs. These should not be fullered down so thin or left in the same form as the scarfs as when joining iron, and should be shorter (compareAandB,Fig. 66).

Fig. 66.—Scarfs for Iron and Steel

In bringing the steel up to its welding point, care must be taken to have it at a uniform heat throughoutat the part for welding; and, to get this, the blast should not be forced at the start, but used gently. In some cases the blast should be stopped occasionally, to allow the steel to soak. Then restart the blast, and gradually force it when beginning to use the flux, continuing so until the welding point is reached. Only light blows should be given at the start, just to cause the two parts to stick together; but when stuck, the harder the blow the better the weld.

An idea seems prevalent that the flux has a certain influence on the steel, and converts it into a form that makes it more weldable. The real use of a flux in this case is simply to retard the heat, and form a coat or shell on the steel, and so counteract and prevent the burning action which takes place when heating steel in an ordinary blast fire.

The reason why different fluxes are required for different brands of steel is no doubt due to the differences in manufacture. As a rule, the greater the heat the steel will stand before burning, the less it requires a flux to protect it, so that in a great many cases a flux consisting of some clean, sharp sand is all that is required; but the steels that will burn at a lower heat require something more than sand to protect them. Hence arises the necessity of adding burnt borax, crushed glass, powdered marble, etc.

The method of welding steel is as follows; but before proceeding to get the heat make a point of having a shallow tin on the forge large enough to hold a sufficient quantity of the flux, so that it will coverthe scarfed end when being dipped in same. Have a clean fire and plenty of firing on the hearth, so that the heat can be well covered. Start with gentle blast until the heat is nearly up to burning point. If necessary, stop the blast and let the heat soak for a few seconds so as to ensure a uniform heat. Gradually force the blast, and keep withdrawing the “heats” and roll them well in the flux, and so continue until it is thought that the heat is plastic enough to unite. Place the scarfs in position, give a few light blows until the parts stick together, then hammer well home and move smartly so as to ensure the proper joining together whilst in a plastic state. When welded, do not continue the hammering or tooling at too low a heat; but if further hammering is necessary, re-heat the work.

These hints are not applicable to every make of steel. With the special steels manufacturers issue particular instructions.

A flux for welding cast steel consists of 2 oz. each of powdered chalk, soda and burnt borax, mixed with 1 lb. of silver sand.

A firm of steel manufacturers recommend a mixture of 21 oz. of sand and 7 oz. of salt, moistened; the steel is to be treated in a fire of sulphurless coal.

How to Make a Bench Gas Blowpipe.—The blowpipe illustrated byFig. 67gives a powerful flame. It can be clamped to the edge of the workbench by means of a winged nut, a hole being made near the edge of the bench to accommodate the bolt. A piece of hard woodA, 5 in. by 2 in. by 1 in. thick, has a strong iron boltBpassed through at one end. A 2-in. cubeC, which should also be of good hard wood, is screwed firmly to the other end ofA, the combined block being perforated through the centre to take a length of gas tubeD, which carries a gas-bracket with flange, elbow joint, and tapE. The flange should be screwed down to the top of the block. The elbow joint allows the direction of the flame to be adjusted within a wide range movement. The arm of the bracket is removed, and a shorter tubeF, 3 in. long, is substituted. This carries a1⁄2-in. ironT-pieceG. The tubeH, which is 3 in. long, should be of brass, threaded at one end to fit into theT.

Fig. 67.—Bench Gas Blowpipe

The air is conveyed through an 8-in. brass tubeJ1⁄4in. in diameter, which should be smooth inside. This latter point is of some importance, and, if preferred, a glass tube may be used instead of brass, the current of cold air having a sufficient cooling effect to preventundue heating. The end should be cut off sharp with a file in the ordinary way and left in that condition. Smoothing the edge by fusion in a flame will not improve matters, but rather the reverse. Of course, the other end, which comes outside, must be smoothed to prevent injury to the indiarubber tube used for making connection with the bellows. The air tube must be held firmly in the centre of the gas tube, while capable of being moved in or out for the purpose of adjusting the flame. This can be done quite satisfactorily by means of a short brass tube or nippleK, threaded to screw into theT(seeFig. 67). A sound cork should be driven into this short tube so as to entirely fill it, a hole being made with a cork-borer to admit the air tube. This hole must be exactly central, and the cork must grip rather tightly.

A foot-bellows is generally used for supplying the air, the bellows being connected with the air jetJby means of an indiarubber tube. The tubeD, which should extend an inch or so below the bench, is to be connected with the gas supply.

—A simple form of gas blowpipe is shown inFig. 68, the rubber tube connecting it with the gas supply being fixed on the pipe at the point of connection with the cock. To construct the appliance, one end of a piece of brass gas pipe of the required length with, say, a3⁄8-in. bore, is bent as shown, whilst at the back of the curve thus made a hole is drilled to admit a tubeA5⁄16in. in diameter. This should have one end (seedotted lines) bent tocorrespond with the angle previously formed in the larger tube, whilst its other extremity should be bent upwards. Make these pipes red hot where they are to be bent, and, if they are afterwards plunged in cold water, the material will to some extent be softened, and its tendency to split will be obviated. The smaller tube is passed through the hole in the bend of the larger one, the ends being almost flush and quite concentric. Solder the parallel portions of the tubes together, and then fix a gas-regulating cock to the larger one, as inFig. 68. The end is then connected to an ordinary bracket or burner by means of an indiarubber tubeG, and a short piece of tubing is fitted with a bone or other mouthpiece, and attached to the projecting end of the air tube. This instrument will do any soldering, and will be suitable for melting gold, silver, and brass, or brazing odd jobs in iron or steel. Of course, when used for the last-named purpose it would be in conjunction with asbestos tubes or other supports.

Fig. 68.—Simple Form of Gas BlowpipeFig. 69.—Larger and more efficient Blowpipe

Fig. 68.—Simple Form of Gas Blowpipe

Fig. 69.—Larger and more efficient Blowpipe

—As regards the relative volumes of gas and air for blowpipes, the late Mr. Thomas Fletcher said that, speaking roughly, but still sufficiently near to make a correct rule by which to work, a blowpipe requires one volume of gas to eight of air. If the gas is supplied at a pressure equal to 1 in. of water, and the air at eight times that pressure, then, to get the best effect, the area of the gas and air pipes should be equal. If the air supply is equal to 16 in. of water pressure, the gas pipe must be double the area of the air, and so on in proportion. Somemakers assert that a better working flame is produced by using ten volumes of air to one volume of gas; but, of course, if the blowpipe is fitted with taps, the supplies can be adjusted easily. It will be found, however, that any practical departure from Fletcher’s rule will result in a loss of power.

—It has been said, a blowpipe with a1⁄8-in. air jet, if worked with an air pressure of 10 oz. per square inch—that is, 15 in. of water—will braze up to about1⁄2lb. total weight; or in other words, will securely unite two pieces of brass each weighing1⁄4lb. With the same pressure a1⁄4-in. bore air-jet will braze a total weight of about 2 lb., and so on in proportion. It will be understood that the air jet is measured at the point at which the blast leaves the air tube, whilst the area of the gas supply is that of the annular space between the two tubes. When the air tube is thus carried inside the gas tube (seeFig. 69), the tool appears to be much larger than it really is, and this accounts for the fact that a1⁄2-in. size blowpipe with the air tube fixed outside the gas supply is just as effective as one of the3⁄4-in. size which carry the air tube inside the stem. All indiarubber tubing must be perfectly smooth inside, for if it is wired or in any way rough, the resultant friction will cause a loss of pressure. It should also be of as large a bore as is convenient.

—A large and efficient blowpipe that can be made in a few minutes is shown byFig. 69, the only materials required beingaT-coupling and diminishing socket, an elbow, and one or two pieces of pipe. The air tubeA(represented for the most part by dotted lines) passes through the diminishing socket until it almost reaches the nozzle of the blowpipe, with which it is concentric. By using the elbowD, the two supply pipes are brought parallel to each other, so that the indiarubber connecting tubes can be more easily held in the hand like reins, as by simply squeezing them the flame can be readily regulated. Sometimes, in cases of emergency, a plug drilled to meet the air tube is used in place of the socket. The plug is thrust into the end of theT-socket; but in all cases it must be airtight. This blowpipe can be used efficiently only in conjunction with a foot blower.

The stoves and lamps burning paraffin in the form of vapour have become very popular on account of their good heating properties, portability, and little attention required. They consist of a container holding paraffin, a burner with a heating tube attached is screwed to the container, and a tube leading almost to the bottom. A small air-tube, similar to a cycle-pump, is fixed in container, the handle and cap only being in sight. When the burner tubes are heated, a thumbscrew on the filler caps is closed, and a few strokes of the pump puts a slight pressure on the oil in the container. The oil is forced up the central tube to the burner; but before reaching this it has to flow round the heating coils, and in so doing is turned to vapour. The outlet at the nipple being very small, causes the vapour to issue with some force, and it mixes with the air, forming a mixture which burns with a non-luminous flame similar to that of a bunsen burner. This flame plays on the heating coils, and once started, the lamp is practically automatic; a stroke or two from the pump will keep it going until the oil is consumed.

There are patterns that use petrol or benzol, their action being slightly different. Petrol and benzol are light spirits, which give off inflammable vapour at amuch lower heat than paraffin does. Advantage is taken of this fact by causing burner and nipple to be in one solid brass casting, so that when the nozzle is heated, the brass conducts the heat back to the nipple and so vaporises the petrol, which is fed to the nipple by a thick wick contained in a tube which reaches almost to the bottom of the container, the wick touching the bottom.

To start either paraffin or petrol lamps, the exit tube or nozzle is heated. The petrol lamp has no coils round the nozzle; but comes straight from the holder to the exit nipple. The size of flame is regulated by a needle valve fitted with a wood or fibre handle. The petrol lamp has no pump, except on high-power brazing lamps whose use requires expert handling.

The chief trouble with lamps using paraffin is that the burner becomes choked; this is shown by the lamp jumping out or the flame not attaining sufficient heat. The makers supply a proper cleaning needle, a sheet stamped to form a handle and a piece of fine steel wire fixed at one end. Nothing else, such as pins, etc., should be used, or the hole in the nipple becomes enlarged, and emitting too much gas, causes a smoky flame. The cleaner should be used each time before lighting. A good way to avoid this trouble is to use a small funnel with fine brass gauze soldered in the body when filling. White Rose is a quite satisfactory oil for these lamps.

After considerable use the heating coil becomes choked with carbon deposit. A new heater tube canbe obtained, or the old one cleaned by drilling two or three holes in the ends and passing a piece of flexible wire (such as Bowden brake wire) through the heater and removing the obstruction. After getting it clean, tap out the holes and fix suitable screws, flat under the head, with a piece of asbestos to make a tight joint.

If a larger flame is not obtained by pumping, take the cap off the pump and draw out the plunger; the leather is probably worn. Fit a new one; or it may have become hard, in which case apply a little oil and open out carefully. The retaining valve is in the centre of the pump bottom, and is removed by using a long key down the pump barrel. The valve is in four pieces. See that the spring is free and that the cork is in good condition. When replacing, take care not to get it cross thread, and screw firmly home. The washer under the filler cap is of rubber and cuts through in time. Do not use pliers to screw down; it will go gas-tight with the fingers if the washer is good.

To remove the nipple from which the gas issues is almost impossible without a proper key. This has a universal joint, which allows it to be rotated, although the handle is almost at right angles with the burner. Keys and all other parts mentioned can be obtained from any dealer in these lamps.

With the lamps using petrol, the only parts requiring attention are the plate from which gas issues and the wick. Unlike the paraffin nipple, this is a circular stamping of brass approximately3⁄4in. in diameter with a fine hole in the centre. To removethis disc, pass a long flat screwdriver blade through two openings in the nozzle and turn to the left (anti-clockwise), holding the body of the lamp firmly on the bench. Before fitting a new disc, thoroughly clean recess and remove any deposit from the inside of the valve box. Unscrew the needle and gland if there is any leak there, and clean and repack with asbestos yarn. A little glycerine on the packing appears to be an advantage. Place the disc in position, dip an asbestos washer in water, and screw the nozzle firmly down.

The wick inside the lamp filters the spirit before reaching the nipple and occasionally needs replacing. Remove the cap from the bottom of the lamp, and with a piece of thick wire flattened at one end and filed to a hook, push it up the tube and withdraw the old wick. The new one is simply put in its place and the cap screwed tight. The washer under the filled cap is of cork and rarely gives any trouble.

A Paraffin Brazing Blow-lamp.—The brazing blowlamp shown inFig. 70was made at a total cost of less than 4s. The illustration is printed to a scale of about one-quarter full size. The lamp illustrated is not a mere experiment, as the writer of this description had a similar one in use for over two years, and during that time brazed hundreds of jobs with its aid.

The container is of tinplate, and adapted from a workman’s tea can. When purchased this will have a wire handle and two hinges, and these should be removed and soldered up. The handle shown atHis made from a strip of iron,1⁄8-in. by5⁄8-in. section, bent round to the shape shown and riveted to the side of the container. These rivets should be well soldered over inside to prevent leakage. The joint of the longer strip is shown atX. The lid should next be taken in hand, a5⁄16-in. hole being drilled at one side close to the handle, to take an ordinary Lucas cycle valve. A leather washer is fitted inside, and also one outside under the lock nut, the latter being then tightly clamped up.

AtEis shown the filling cap, the body part of which was taken from an old paraffin oil-lamp container, and the screw cap made at the local brass works; but thisfitting can be obtained in a finished state from many model-fittings manufacturers. This is soldered to the lid in the position shown, a hole being afterwards drilled in the tin to suit it.

Fig. 70.—Paraffin Brazing Blow-lamp, the container being shown in section

The cock shown atDis an ordinary gas-cock, with a length of3⁄8-in. outside-diameter copper piping screwed and sweated in beneath. This is passed through a hole drilled in the lid for its reception, and the base of the cock is then sweated in position. Note that the length of this pipe is such that when the lid is in place it clears the container bottom by1⁄8in.

The coil of piping atPis3⁄8in. diameter copper tubecoiled round to the shape shown, the lower end being tightly screwed into the top of the cock. The opposite end is screwed for a short length of3⁄8-in. gas thread, and very tightly fitted with a screw plug such as that used by plumbers for shutting off a portion of gas piping. Before screwing this on, a small hole about1⁄32in. in diameter should be drilled in the middle of same; this is the nipple for the exit of gas to the burner.

The3⁄8-in. copper tubing should not require filling with anything before bending; this operation is best done round a mandrel of wood. No heating is necessary. A certain amount of flattening of the tube will no doubt occur, but this is immaterial. The end of the flame tube is, of course, open, otherwise the flame could not emerge. The nipple end of the flame tube is also quite open, with the nipple end of the coil just projecting inside. The portion of tubing shown dotted inFig. 70takes the vapour from the coils to the nipple; it does not pass through the coils, but at the back of them, and bends round as shown.

The lid of the container should now be carefully soldered down all round, and then the3⁄16-in. brass stay rod shown atSmust be fitted and both ends sweated over. It is essential that this stay is not omitted, as otherwise the pressure to which the container is subjected would bulge out the ends.

The flame tubeAshould now be made of1⁄32-in. sheet-iron, being held in place by two or three clips riveted on and bent over the coil ends as shown atC,only one of which is shown for clearness. The flame tube does not taper, nor is the back end closed up. Its diameter should be 11⁄4in. and length 31⁄2in., but this depends on the size of the hole in the nipple. No holes are required in this tube, as all the air is drawn in at the end. The nipple has a gas thread cut inside it, and it is screwed tightly on to the end of the copper coil. The length of the pipe from tap to coil is not important; about 9 in. will be satisfactory.

The best means of joining the nipple to the tube is to screw the end of the tube before bending it round at the end, and then to screw the nipple on tightly. The pipe can afterwards be bent as shown.

The jet hole in the nipple should be about1⁄32in. bare, and should be so drilled that the issuing gas passes through the centre of the flame tubes. The tube is open at both ends, to allow air to be drawn down and complete the combustion of the paraffin vapour, the mixture igniting and burning properly when the vapour passes out at the other end and comes into contact with the atmosphere.

To use the lamp, it should be filled about two-thirds or one-half full of paraffin oil, and the container cap then screwed hard down with a leather cap as a washer. A cycle pump should then be connected to the valveV, and a few strokes given, the cockDbeing meanwhile closed. The copper coil should next be put into a gas flame or the fire for a few minutes until nearly red hot, and then the cockDshould be opened a shade, which will allow the paraffin to rise up the pipeIandenter the coilsP, where it will become vaporised, and the gas will then issue from the nozzleN, and burn at the mouth of the coils.

The lamp may then be applied to the job, and five or six more strokes given to the pump, when the flame should burn with an intense heat and give out a roaring noise.

The theory of action of lamps of this character is as follows: The pressure of air in the container forces the paraffin up the copper tube into the coil, where it is vaporised by the red-hot piping. The vapour then issues at some pressure from the nipple hole and, passing down the flame tube, an ejector action is caused which draws air in with it. This air mingles with the paraffin vapour, and when the mixture issues at the other end, and comes into contact with more air, combustion takes place.

The heat produced by the lamp should be quite sufficient to braze the bottom bracket of a motor-cycle frame and other similar jobs. The size of nipple with relation to the size of the flame tube is most important. If the flame tube be too large in proportion, the result is an excess of air, which cools the gas unduly and the flame dies out. A candle is put out in a draught from the same cause. On the other hand, if the flame tube is too small, or the nipple hole too large, the result is an excess of gas, causing incomplete combustion and a partly luminous and smoky flame, with less heating power. To ascertain if the nipple hole is too small, take a strip of tin and, whilst the lamp is burning, holdthe tin partly over the end of the flame tube, so as to restrict the amount of air entering, and note the result.

If the drawing (Fig. 70) be regarded as 4 in. to 1 ft., and the lamp made accordingly, it will be of ample size to braze small and model boilers. It must be understood, though, that the size of the lamp alone does not govern the size of the flame, this depending entirely on, firstly, the size of the nipple, and secondly, the pressure of air in the container forcing the vapour out. The larger the container, the longer the lamp will burn without refilling, and, incidentally, the larger it is the weaker the container will be, and vice versa.

Should this lamp be required for brazing and silver-soldering articles about1⁄2in. in diameter, it must be altered, as it is obviously much too large. The same container will do, of course, although perhaps rather unwieldy. If preferred, another container just half the size could be made; this will be handier in use, although it will not allow the lamp to burn for so long a period without recharging as the larger pattern. For the tubing,3⁄16-in. copper tube, preferably solid drawn, will be suitable. This should be heated to a dull red and then quenched in water to anneal it, this making the task of bending it much simpler. If it kinks too much in the bent portions, pour some molten resin into the tube, one end being plugged up for this purpose, and when set, bend to the shape desired. The resin can be heated and run out afterwards. The flame tube may be half the diameter and length of the one illustrated, but no hard and fast rule can be given for the dimensionsof this part of the lamp, as the size of the nipple hole has everything to do with this. Make the latter just big enough to admit a fine needle. A simple method is to drill the cap almost through, and then punch the rest through with the point of a needle. By experimenting, it will be easy to find the right proportions of flame tube and nipple hole. The screwed joints should be a metal-to-metal fit as it is termed, that is, they should fit so tightly when screwed home that no leakage is possible. This can be ensured by seeing that all male threads are a tight fit in their respective holes.

Contact Welding.—The electric welding of iron strips and sheets is usually done by the Thomson process of “contact-welding.” In this process the metal is brought to a welding heat by passing a very large current through the joint to be welded, which, by virtue of its high resistance in relation to other parts of the circuit, develops great local heat. When the correct temperature for welding is reached, the joint is pressed together by mechanical means, and the current interrupted. InFig. 71the necessary arrangements for the welding of a steel rim are sketched.Ais the iron core of an alternating current transformer andBthe primary winding supplied with alternating current either from a works dynamo or a public supply, and controlled by a double-pole switchC. The transformer has a secondary winding consisting of a single copper strip of very heavy sectionD, in which secondary currents of low voltage but very large volume are induced. This windingDterminates in two heavy metal clampsE, one fixed and the other capable of movement by rack and pinion or screw, and the clamps must be shaped to the contours of the workFthey are intended to hold, so as to fit well and present as little electrical resistance there as possible. The butt ends of thewheel rim are brought into contact, current switched on at the transformer primary, and immediately a very heavy secondary current passes round the “winding”D, generating intense heat at the junction of the metal rimGheld in the clamps, where the electrical resistance is comparatively high. In a few moments the joint will arrive at welding heat and the screw feed is then operated, driving the joint together and completing the weld, except so far as a little hand dressing may be found necessary. Directly the weld is established the current is switched off at the mains and the job allowed to cool out. Nothing less than 5 kilowatts to 10 kilowatts is likely to be very satisfactory for hoops about3⁄4in. by No. 16 gauge, and the current must be alternating. The primary voltage and frequency is immaterial, as the transformer can be wound to suit the circuit conditions whatever they may be.

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