Notes on Welding PracticeIII

J.G. Waterworth; A.R. Mowbray

doi:10.1108/eb030427

Waterworth, J.G.; Mowbray, A.R.

1939-01-01 00:00:00

January, 1939 AIRCRAF T E N G I N E E R I N G Workshop and Production Section By J. G. Waterworth and A. R. Mowbray HE materials commonly employed in the steels with high chrome-nickel content are tubing fabrication of aircraft structures are t o specifications D.T.D.97 and 102 and sheet to confined for the main part to steels of low T D.T.D.146. As with the high tensile tubes already carbon content (i.e., mild steel, manganese steels mentioned, these require greater care in weld treat of a medium carbon) and chrome-molybdenum ment , both with regard to the ability of the welder steels. The content of carbon steels tha t are weld- and regulation of the flame since it is essential that able cannot be exactly laid down, since the amount oxidation and carburization be avoided ; the which can be contended with by the oxy-acetylene former condition having the effect of readily process ma y rise t o as much as 0·8 pe r cent, although destroying chromium. Fluxes such as calcium this does no t occur in the examples given here where carbonate , fluoripar, etc., must be applied to stain only steels within the region of 0·3 per cent carbon less steels either in paste form or by coating the exists. filler rod, as in arc-weldiqg. These fluxes break These are found in the following ranges regularly down the resisting oxide film by covering the in service: molten metal with a fluid slag and so preventing Sheets D.T.D., 124A, 12A, 141, S3 . th e oxide causing a non-almalgamation of the filler Tube s D.T.D.41, 178, T26, 35, 45. rod with the base metal. While the use of the flux S3 and T26 are particularly adaptable, since their is essential excess of it creates hard spots in the purit y and low carbon make them readily weldable weld, which on being worked afterwards is prone to and give the operator more scope. Should a fracture. Early experiments on welding this steel slight excess of acetylene be permitted the flame seemed to show that a slight excess of acetylene does not introduce a sufficient carburizing effect on is advantageous in effecting the regular deposit th e weld to alter materially the characteristics. desirable in aircraft work ; but with the intro Moreover, the normalizing of the steel after welding duction of improved flux it was found tha t a neutral taneously makes it about 20 per cent harder, flame produced superior results. Another feature has the effect of raising its maximum tensile thereb y reducing its ductility by approximately t o be observed with this steel is that, owing to its strengt h by about 8 per cent ; the unwelded metal 66 per cent. Although the tensile figures of this greate r thermal conductivity, much skill is required havin g a figure of 26 tons. (D.T.D. 178) should give 35 tons minimum after in the application of the heat if distortion is to be Wit h the highly stressed parts demanded by the tensile heat treating, it does no t compare favourably avoided. modern conditions under which military aircraft with the low-carbon mild steels in fatigue values; perforin, the use of manganese and chrome- coupled with which it has the disadvantage of air- Coupled with fabrication in steel is that of molybdenum steels must be considered. These, hardenin g in the area adjacent to the weld and a aluminium and its alloys on which some hints may two specifications D.T.D. 41 an d 178 ar e very applic tendenc y to develop cracks. It is possible for bo included. These are t o be found in specifications able, provided tha t a carbon content of 0·25 to 0·27 these latter faults to be eradicated, where practic 3T9 for tubes and 2L4, 2L16 for sheets. It should is not exceeded, but call for more precise regulation able, by subsequent heat treatment. Observations be remembered that by reason of the low melting of flame content since the introduction of 0·04 per take n of the hardness of the affected area show this poin t of aluminium (650 deg. C.) certain difficulties cent more carbon into th e latter metal may increase a t times to be in the region of 350-380 Brinell value. presen t themselves even to an operator who is its tensile strength by about 10 tons, but simul Included in the corrosion-resisting, or stainless, adep t in the welding of steel. Whereas the nozzle employed for steel of 16 s.w.g. is 50-litre capacity, it is policy to use one of 25-litre capacity on aluminium of similar gauge. It will then be easier t o control the metal as, its heat-conductivity being high, the heat given off by the larger nozzle would be quickly dissipated over the area, resulting in a preheatin g along the length of the proposed weld. As a result, should the operator pause unduly to make good a small hole, for example, the prolonged hea t over the remainder of the job may cause a collapse of the metal when he resumes the running of the weld. Furthermore , since it is not evident to the eye when aluminium is molten, the point at which the filler rod should be applied is not obvious. An indication may be gained from the appearance of a slight tremor on the surface of the metal. Immedi atel y this occurs th e operator should begin t o apply th e filler rod ; taking care that bulbous deposits ar e not allowed to form, otherwise adhesions will result and no penetration be effected. The use of a flame containing an excess of acetylene, contrary to practice with steel, is found to be both beneficial and effective on aluminium, as thereby better fluidity of the metal is obtained, coupled with more certain penetration. I t is a practice in some shops, when welding aluminium sheet, to place steel or copper some ⅜-in. thicknes s on each side of the seam, beneath, an d or on top. (See Fig. 1.) By this means the hea t is additional bulk of metal and conducted away, thereby giving a less intensity of heat to the aluminiu m and favouring an easier run of weld with ou t the possibility of the sheet collapsing. The application of this is naturally only practicable on straigh t runs such as in th e welding up of tan k seams, etc. Another method of facilitating a seam weld (although not in accordance with A.I.D. standards, since they require a proud deposit on all metals) is t o turn up a lip abou t 1/32 in . high, or equal to gauge thickness, along the entire length of the seam. When using the blowpipe this edge is run to form th e joint without the addition of the filler rod. The flux must in this case be applied to the underside of th e sheet, the reason being that an unobstructed view of the edges is obtained and the flux is drawn through by the application of the heat on the top side and assures the whole depth of weld being rid of the oxide resistance. In preparing the metal it is imperative that the edges be filed or scratch- brushed to give an oxide-free surface, even on new material , and for the operator to refrain from handling the surface where the weld is to be made.

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Notes on Welding PracticeIII

$January, 1939 AIRCRAF T E N G I N E E R I N G Workshop and Production Section By J. G. Waterworth and A. R. Mowbray HE materials commonly employed in the steels with high chrome-nickel content are tubing fabrication of aircraft structures are t o specifications D.T.D.97 and 102 and sheet to confined for the main part to steels of low T D.T.D.146. As with the high tensile tubes already carbon content (i.e., mild steel, manganese steels mentioned, these require greater care in weld treat of a medium carbon) and chrome-molybdenum ment , both with regard to the ability of the welder steels. The content of carbon steels tha t are weld- and regulation of the flame since it is essential that able cannot be exactly laid down, since the amount oxidation and carburization be avoided ; the which can be contended with by the oxy-acetylene former condition having the effect of readily process ma y rise t o as much as 0·8 pe r cent, although destroying chromium. Fluxes such as calcium this does no t occur in the examples given here where carbonate , fluoripar, etc., must be applied to stain only steels within the region of 0·3 per cent carbon less steels either in paste form or by coating the exists. filler rod, as in arc-weldiqg. These fluxes break These are found in the following ranges regularly down the resisting oxide film by covering the in service: molten metal with a fluid slag and so preventing Sheets D.T.D., 124A, 12A, 141, S3 . th e oxide causing a non-almalgamation of the filler Tube s D.T.D.41, 178, T26, 35, 45. rod with the base metal. While the use of the flux S3 and T26 are particularly adaptable, since their is essential excess of it creates hard spots in the purit y and low carbon make them readily weldable weld, which on being worked afterwards is prone to and give the operator more scope. Should a fracture. Early experiments on welding this steel slight excess of acetylene be permitted the flame seemed to show that a slight excess of acetylene does not introduce a sufficient carburizing effect on is advantageous in effecting the regular deposit th e weld to alter materially the characteristics. desirable in aircraft work ; but with the intro Moreover, the normalizing of the steel after welding duction of improved flux it was found tha t a neutral taneously makes it about 20 per cent harder, flame produced superior results. Another feature has the effect of raising its maximum tensile thereb y reducing its ductility by approximately t o be observed with this steel is that, owing to its strengt h by about 8 per cent ; the unwelded metal 66 per cent. Although the tensile figures of this greate r thermal conductivity, much skill is required havin g a figure of 26 tons. (D.T.D. 178) should give 35 tons minimum after in the application of the heat if distortion is to be Wit h the highly stressed parts demanded by the tensile heat treating, it does no t compare favourably avoided. modern conditions under which military aircraft with the low-carbon mild steels in fatigue values; perforin, the use of manganese and chrome- coupled with which it has the disadvantage of air- Coupled with fabrication in steel is that of molybdenum steels must be considered. These, hardenin g in the area adjacent to the weld and a aluminium and its alloys on which some hints may two specifications D.T.D. 41 an d 178 ar e very applic tendenc y to develop cracks. It is possible for bo included. These are t o be found in specifications able, provided tha t a carbon content of 0·25 to 0·27 these latter faults to be eradicated, where practic 3T9 for tubes and 2L4, 2L16 for sheets. It should is not exceeded, but call for more precise regulation able, by subsequent heat treatment. Observations be remembered that by reason of the low melting of flame content since the introduction of 0·04 per take n of the hardness of the affected area show this poin t of aluminium (650 deg. C.) certain difficulties cent more carbon into th e latter metal may increase a t times to be in the region of 350-380 Brinell value. presen t themselves even to an operator who is its tensile strength by about 10 tons, but simul Included in the corrosion-resisting, or stainless, adep t in the welding of steel. Whereas the nozzle employed for steel of 16 s.w.g. is 50-litre capacity, it is policy to use one of 25-litre capacity on aluminium of similar gauge. It will then be easier t o control the metal as, its heat-conductivity being high, the heat given off by the larger nozzle would be quickly dissipated over the area, resulting in a preheatin g along the length of the proposed weld. As a result, should the operator pause unduly to make good a small hole, for example, the prolonged hea t over the remainder of the job may cause a collapse of the metal when he resumes the running of the weld. Furthermore , since it is not evident to the eye when aluminium is molten, the point at which the filler rod should be applied is not obvious. An indication may be gained from the appearance of a slight tremor on the surface of the metal. Immedi atel y this occurs th e operator should begin t o apply th e filler rod ; taking care that bulbous deposits ar e not allowed to form, otherwise adhesions will result and no penetration be effected. The use of a flame containing an excess of acetylene, contrary to practice with steel, is found to be both beneficial and effective on aluminium, as thereby better fluidity of the metal is obtained, coupled with more certain penetration. I t is a practice in some shops, when welding aluminium sheet, to place steel or copper some ⅜-in. thicknes s on each side of the seam, beneath, an d or on top. (See Fig. 1.) By this means the hea t is additional bulk of metal and conducted away, thereby giving a less intensity of heat to the aluminiu m and favouring an easier run of weld with ou t the possibility of the sheet collapsing. The application of this is naturally only practicable on straigh t runs such as in th e welding up of tan k seams, etc. Another method of facilitating a seam weld (although not in accordance with A.I.D. standards, since they require a proud deposit on all metals) is t o turn up a lip abou t 1/32 in . high, or equal to gauge thickness, along the entire length of the seam. When using the blowpipe this edge is run to form th e joint without the addition of the filler rod. The flux must in this case be applied to the underside of th e sheet, the reason being that an unobstructed view of the edges is obtained and the flux is drawn through by the application of the heat on the top side and assures the whole depth of weld being rid of the oxide resistance. In preparing the metal it is imperative that the edges be filed or scratch- brushed to give an oxide-free surface, even on new material , and for the operator to refrain from handling the surface where the weld is to be made.$

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Notes on Welding PracticeIII

Notes on Welding PracticeIII

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Notes on Welding PracticeIII

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