An important advance has recently been made in the method of lead welding or autogenous fusion of lead.

For some years the practice has been to use as a heating medium either coal gas or hydrogen. In the case of coal gas, it is taken either from town mains, or compressed in cylinders, and used in conjunction with oxygen through a special blowpipe. Coal gas taken from town mains lacks portability, and can only be used in places where town mains exist. The consumption of oxygen is very high, and the speed of work is slow on account of the relatively low heating value of coal gas. In the case of coal gas in cylinders, the advantage of portability is counterbalanced by increased cost.

Over a century ago hydrogen combined with air was used for lead burning. The hydrogen and air were mixed before entering the blowpipe by means of foot-bellows or pumps. The system, however, was slow, wasteful and dangerous, and was succeeded by the oxy-hydrogen process.

Hydrogen used for leadburning is either generated in a special apparatus, or obtained in commercial cylinders. The former is gradually being replaced on account of the difficulty of obtaining sufficient pressure and the excessive consumption of oxygen, and though the apparatus is portable it is somewhat cumbersome. Where hydrogen is used from trade cylinders, the sources of supply are few, and the gas is, in consequence, difficult to obtain, and the cost fairly high.

The introduction of the Oxy-Acetylene blowpipe for this purpose is due largely to the possibility of using both gases, Acetylene and Oxygen, at pressures much lower than those which are required for other purposes. The consequence is that advantage is taken of the high calorific value of Acetylene, whilst the consumption of both gases is kept at a minimum. Both Acetylene and Oxygen are readily obtainable in conveneint cylinders from numerous works and stores.

A series of experiments recently conducted in the welding of lead over a wide range of specimens, from the thinnest sheet up to 1 inch thickness, and covering a working period of 14 days, gave the following comparative results. The specimens were welded by a skilled operator, previously experienced in the Oxy-Coal Gas and Oxy-Hydro-gen methods, and a similar range of work was done by each of the following methods :- Oxy-Coal Gas, Oxy-Hydrogen, Oxy-Acetylene.

Consumption Of Gas

From careful observation, the volume of Dissolved Acetylene required was only 2b per cent, of the volume of Coal Gas, and only 15 per cent, of the volume of Hydrogen required for a given amount of work. The volume of Oxygen consumed with Dissolved Acetvlene was onlv half of the volume consumed with either Coal Gas or Hydrogen.

Working Capacity

The working capacity of the operator, i.e.. the amount of work produced in a given time, was increased by Dissolved Acetvlene over Coal Gas bv 50 per cent., and over Hydrogen by 40 per cent.

Operating Costs. Taking the cost as represented by the total of gases consumed together with labour employed, the cost of operating in the case of Oxy-Acetylene shows an increase of Id. per hour over Oxy-Coal Gas, and a decrease of l|d. per hour below Oxy-Hydrogen.

In all these calculations, Coal Gas was taken from town mains and not compressed. The use of the latter would probably make the operating costs of Oxy-Coal Gas equal to, or greater than that of Oxy-Acetylene.

Comparison

After taking into consideration the working capacity of the operator with the operating costs, it will be seen that a saving is effected by the use of Dissolved Acetylene amounting to about 30 per cent, compared with the use of Coal Gas, and about 33£ per cent, compared with the use of Hydrogen.

Applications Of The Process

The process of lead fusion or welding, better known as leadburning, is principally employed in three trades -chemical manufacturing, electrical or accumulator manufacturing and building and plumbing.

In the case of chemical lead, some of the heaviest sections are used, and the operators employed are usually highly skilled. It will be found that by the use of the Oxy-Acetylene blowpipe t he increased temperature of the flame combines with the skill of the operator to produce quicker and better work, and tends at the same time to increase the operator's skill.

The manufacture and repair of accumulators is a class of work.

I which has recently increased in volume, and in which the advantages of the portable Oxy-Acetylene apparatus are fully appreciated.

In building, the use of an apparatus suitable for jointing sheet lead rooting and lead rain-water or soil pipes, etc., and artistic lead work such as that in the superior types of buildings, is becoming essential in practice, and needs a portable apparatus of the highest efficiency.

" Alda " Oxy-Acetylene lead-burning equipment enables the operator to carry out the burning or welding of sheet lead in flat, horizontal, vertical or overhand seams with equal facility. The speed at which the work is carried out increases the strength whilst at the same time reducing the risk of cutting through acid tanks whilst operating upon them, e.g., in the presence of sulphuric acid fumes. The range covered by the apparatus is from the thinnest to the heaviest lead employed in chemical work, and the only alteration required in order to deal with a different thickness of lead is to change the tip of the blowpipe, which in itself provides 5 blowpipes in one instead of requiring a separate blowpipe for each of several different thicknesses of metal.

In addition to lead, the same blowpipe is found to be highly efficient for other metals in their thin sections, including zinc and aluminium and also block and sheet tin in various sections (see also Vol. III., page 65).

(Messrs. Allen-Liversidge Ltd.)