The Art of Lead Burning / A practical treatise explaining the apparatus and processes.

by C. H. Fay

The object sought is to get a light fusion between the two sheets before attempting to burn the lead clear through the seam. If this is not done, the lead will run from the upper sheet and cause holes, or at least will seriously weaken the upper sheet, as shown in cross section at b. After fusion is once obtained it is a simple matter to go over the seam a second time, which can then be fused clear through without much danger of burning holes through the sheet. Lead can be added in the same manner as in upright seams if necessary.

Inverted Butt Seam.

This seam is used extensively in joining waste pipes which conduct the acid from tanks to the drain. These pipes are usually in a horizontal position and the seams must be burned in place. The most difficult part of the seam is in starting it. When fusion has once taken place the balance of the seam is easy. The seam is prepared the same as described for other butt seams. Care must be taken to have the edges butt close. The board can then be supported in the required position by any convenient device.

The blow pipe flame must be made as short as possible and still melt the lead. The point of the inner flame is then placed squarely on the seam. Both edges must be heated at once. If the edges begin to brighten and do not show an inclination to fuse, the flame should be drawn quickly to one side, and the melted drop will follow the point of flame and unite with the adjoining edge. This seam, in common with the other butt seams, should be gone over the second time to assure a perfect seam. It is difficult work to add lead to the flat inverted seam. When necessary to do so, however, it can be added by burning the end of the lead strip to the seam. The strip is then melted off, leaving a drop of lead affixed to the seam, which can then be drawn to the required spot with the flame.

The characteristic inverted seam shows pits upon examination of the reverse side of the sheets. These are caused by overheating. The operator will often be surprised at the inverted butt seam showing a remarkable fullness. This is accounted for upon the examination above referred to. The lead, upon the application of the heat, runs from the upper or back side of the sheet and forms a very full seam. For that reason the inverted butt seams always appear stronger than they really are. See inverted lap seam, Fig. 27.

Lap Seams.

The lap seams are the seams commonly used on all classes of work. When the beginner becomes proficient with the blow pipe no trouble will be experienced in making lap seams that will show when cut a joint equal in thickness to the sheets that are joined. The lead sheets for the flat lap seam are prepared by shaving clean the exposed edge; also, shave the sheets where they touch each other. The upper edges can then be shaved for a distance of ⅛ inch each side of the lap, which will make the finished seam ¾ inch wide, as shown at a in Fig. 23. The sheets should be lapped ½ to ¾ inch, according to the weight of the stock. It is very evident that light weights would not require as large a lap as would heavier sheets, as the object of lapping the sheets is to leave the sheets practically as one piece, and the lead, to accomplish this object, is to be melted from the upper sheet.

Fig. 27.—Burning an Inverted Lap Seam.

From the foregoing it will be seen why a 12-pound sheet requires a ½-inch lap, while a 24-pound sheet would require a ¾-inch lap. The flame, when regulated to the work, is brought to bear squarely on the edge of the upper sheet, slanting slightly in the direction of the lower sheet, as shown. When the edge has brightened almost to the fusing point the blow pipe should be drawn quickly to one side and from the upper sheet to the lower sheet. If the metal is sufficiently hot the melted drop will follow the point of the flame and instantly fuse with the lower sheet, and if properly done the seam will resemble b in Fig. 23. This process is repeated, advancing about ⅛ to ¼ inch each time. Do not attempt to fuse a large surface at a time. Experts cannot do such a thing satisfactorily, so why should a beginner try to? Rather, try to fuse small surfaces quickly and strongly, as better work and more of it can be accomplished in that manner.