CORRUGATED IRON. Although many millions of galva nized corrugated sheets are now in use all over the world, this industry is less than ioo years old. British makers were the pioneers. At first the sheets were made from wrought or puddled iron (not steel), and corrugated in the black, then galvanized by hand dipping in an open bath of molten zinc. The output naturally was small, and the cost high, but the quality was excellent, so much so that galvanized corrugated iron sheets are known to be still in use although they were fixed in position 5o years ago.
After the steel making process became a commercial proposi tion about 186o, steel sheets were produced in the heavier gauges but it was not until about 3o years later that they were made suc cessfully in the lighter gauges. The output per shift was so much larger and the cost so much lower than iron, that steel sheets very quickly ousted the old-fashioned iron sheets. But it must be admitted that the life of ordinary quality galvanized corrugated steel sheets is only about 25% that of the original iron sheets. Iron sheets, of higher purity than ever, are being made not only in Great Britain but on the Continent and in America, for those who see the wisdom of paying a higher price for an article of longer life, but 95% of the so called "corrugated iron" is really steel. The corrugating process enables much lighter gauges of sheets to be used because it makes them very rigid and portable.
Exact figures of output of corrugated sheets in other countries are not obtainable, but the tonnage as yet is comparatively small. A few years ago Germany was exporting 3,000 to 4,000 tons monthly but in 1927 this had fallen to about 5oo tons monthly. Belgium, however, since she entered the corrugated sheet business has made fairly rapid progress, and in 1928 was producing at the rate of 75,000 tons per annum. Japan, which formerly bought her galvanized corrugated sheets principally from Great Britain, is now buying the bulk of her sheets in the black condition from Britain and America and doing the galvanizing and corrugating in Japan. These sheets are specially light, namely 28 to 31 gauge, which is only about half the thickness used in other countries. Galvanizing and Corrugating.—The black sheets are first put through the pickling process. This is done in a stone or timber tank which is filled either with sulphuric or hydrochloric acid to remove all scale, oxide or rust. This operation can be carried out either by hand pokers or by an automatic pickling machine. After being cleansed in a water tank, the flat sheets are then fed into the galvanizing bath either by hand or by an automatic feeder, one at a time. The galvanizing bath is made of steel plates from 'in. to thick and of a size to suit the width of sheets to be treated. Inside the bath there is the galvanizing machine with rollers which revolve in the molten spelter or zinc which is heated to 85o° F. The sheets pass rapidly through the zinc and emerge at the other side of the bath through two exit rollers; these rollers, together with the speed of the machine and temperature of the bath, regulate the quantity of zinc covering, viz., from to 21oz. per square foot. A flux is used in the process made from muriate of ammonia and this causes the zinc to flow freely and gives the sheet a smooth surface. When sheets are wanted with a bright flowery spangle, it is necessary to add a small proportion of tin to mix with the zinc. The sheets automatically pass through a tank of hot water to wash off any flux stains and then they pass on to a drying fire and finally they are examined by inspectors.
The sheets then pass to the corrugating department. The gal vanized flat sheets are here corrugated to the size of corrugation required, either by powerful presses when several sheets are cor rugated at a time or in rotary corrugated rollers usually doing one sheet at a time. In either case the process is rapid and a large tonnage is obtained. The corrugated sheets are then weighed up, bundled or packed for shipment ; or they are put into store in their various sizes and gauges.
Bolts, nails or screws should always be placed in the top corru gation. Wood screws or nails should be placed 6in. apart. Bolts for fixing sheets together should be about i5in. apart along the side corrugation. Hook bolts for iron framed buildings should be about i2in. apart. All screws and sheet bolts should have at least one iron or lead washer under the head; one of each is recom mended. Hook bolts should have curved washers, either round or diamond shaped. In laying sheets the workman should begin at the bottom row, and work towards the ridge of roof.
Galvanized sheets should be stored very carefully in a dry, well-ventilated place, and any sheets which have become damp or wet in transit should be wiped thoroughly dry before storing. On no account should they be stored in bundles in a damp atmosphere. If sheets must be stored in the open air or under poor conditions, they should be stacked in such a manner as to allow a good air space between them. (See also GALVANIZED IRON AND STEEL.) (D. McM.)