OXY-ACETYLENE WELDING.
Page 27
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A Long and Valuable Contribution from a Regular Reader.
REMARKING that oxy-acetylene welding is more popular in commercial motor repair shops than the
electric method, " A.E.," of Manchester, offers the following hints for the consideration of readers of this page, and his.contribution is of such a length that it occupies the whole of the space
devoted to this feature this week, a,ncl thus automatically secures the nremiel
• award.
A weld well prepared, he says, is a weld half done, for preparation in this work is half the job. Moreover, if the preparation be not well carried out, the • weld will most likely fail. The accom ' panying sketches show how . various forms of welded joints should be effected.
To• join thin sheet metal, turn up a shallow flange; as shown in Fig. 1, at least as deep, above the main surface of the material, 'as the thickness of the sheet; preferably, the depth of flange is a little in excess of that thickness. Fig. 2 illustrates the appearance of such a-joint after the welding has been corn pleted. In some cases, where. it is feared that the metal might buckle or spread during the prpcess of welding, the flanges should be tacked together here and there. by light rivets, as shown in Fig. 3.
For sheet. metal approximating in thickness to in., the plain butt joint, illustrated by Fig. 4, makes a good' sound job, but above that thickness and up to about in. the edges should be bevelled off at 45 deg., so that the angle between the two bevelled surfaces, when the edges of the metal are 'together, ready for welding, is 90 degrees. The
ipipdrtance of keeping to the proper a"ngle for this bevel cannot be over
estimated; it is particularly essential that the angle between the two faces be not less than 90 degrees, as too acute an angle involves difficulty in effecting the wehl over the full face of the metal. The welder in such circumstances, in endssavouring to penetrate right to the corner, may easily burn the material.
Fig. 5 sllosys a piece of metal bevelled off to the proper angle; as it should be,
whilst Fig. 6 illustrates what. is meant by saying the angle between the sur faces is too acute. When the material exceeds g in. in thickness; then it should 'be' bevelled at
both sides, as shown in Fig. 7, which indicates the proportions of a welded . joint to be 'effected in material which is i-in. thick. Welding .in such, circum stances can, and should be, effected on both sides: If,' as the result of the configuration of the article which iato be welded, it is impossible to Weld, on both .. sides, then the joint should be prepared as shown in Fig. 8. . .
The lap-jointed weld shown in Fig. 9 . should be avoided, as it has:several disadvantages. In such a joint tha.weld rarely extends across the whole face of the joint, which is, therefore, of doubtful efficiency and uncertain strength.
Fig: 10 shows how •a cylinder and angle-iron ring, which is to be welded to it, should be prepared. It has been assumed, in this case, that the metal of the cylinder and that of the angle is of the same thickness. In the event of one being thicker than the other—as, for eXample, is shown in Fig. 11—bevelling is Unnecessary. The dotted lines in • this figure show how the filling material ,should be built up during the operation of welding. • .
• These examples sufficiently indicate
• the .general• principles involved in the . operation al preparing to effect a welded joint Their application is indicated in riga. 12 and 13;which show how. (12) the end of a cylinder. or tube may be stapPed by welding-a circular piece into place, and how that piece should be bevelled along its edges before welding is commenced, and (13) how a flange should be prepared for welding to a pipe or tube.
other examples are afforded by the
repairing of cracks in plates or cylinders. The metal on each side of the crack should be treated as has been explained. See that the crack is bevelled throughout its length and to the full thickness of the metal. In some cases it may make a better job,to fit a patch. A -patch should always be slightly " bellied," with concave part towards the piece which is being repaired, and
• shouldhave all its edges correctly bevelled.
' In all oxy-acetylene welding operations, the parts which are being welded together should be carefully set in proper. alignment one with another before the 1)low pipe flame is applied. Too often this precaution is overlooked, with the result that, although the weld, as such, may be perfect, the job as a whole is useless, because the parts are not properly in line.
'Welding by this process differs from the same operation as carried out in the old-fashioned way by the blacksmith, in that. it is of much wider application, being capable of being used in connection with all metals, not even excepting aluminium. The' conditions which are necessary, if good work is to result, vary very considerably, as might be expected, according to the metal upon which the operation is, to be, performed.
When steel is being welded, a know ledge of the quality clf the material . and of the alloys of which -it is constituted is a 'great help., but there arc
• several. essential ,precautions which should be observed .
In the case of aluminium castings, it is necessary to take • extra precautions to ensure cleanliness of the parts to be , welded, as this metal, on account of its . porosity, often retains oily. and fatty materials .below its surface . To prevent . trouble from this cause, heat the work with the blow-pipe, or with a blow-lamp, so as to burn off all the grease.
A suitable flux for use when welding aluminium castings 'is made up as follows :—Sodium chloride, 30 parts, potassium , chloride, 45 parts ; lithium chloride, 15 parts; potassium fluoride, 7 parts; bisulphate of potassium, 3 parts..
The flux is best applied by means of the welding rod. This can be arranged well if the rod be slightly warmed in the flame of the blow-pipe, when the flux will readily adhere to it.
Care must be taken to avoid contact of the white cone of the blow-pipe flame 'with the Metal, as this isart-of the flame is very hot indeed; so that contact would : actually -result in ,holesbeing. burnt' in • the metal. . The actual distance between this ..cone and the Metal should, vary in accordance with the power, of the blowand in. are the limits. -.When welding -alurninitini Crankcases or gearboxes, it is adviiable to support the casting underneath the crack, or fracture.' This is best done by' means .of sheet iron or steel, bent to fit,' and -covered with asbestos.. This 'bent metal, in turn, may be blocked up on fire
bricks. • .
Directly after welding, the repaired parts should be wall washed with warm water, in orderto remove all _remaining traces of the flux,' which Continues its chemical action after the* welding.