PLYWOOD

Korero (AEWS), Volume 2, Issue 24, 29 January 1945, Page 8

PLYWOOD

A KORERO Report

Up in the air in a plywood plane. Down in the ground in a plywood coffin. Across the sea in a plywood ship, eating from a plywood table, your luggage in a plywood suitcase, your beer from a plywood cask, washing in a plywood bathtub, rescued in a plywood lifeboat. Plywood railway carriages, bus bodies, tram-cars. Stairways, furniture, ceilings, floors, pictures ; boxes, barrels, chests, reels, baskets, traysall plywood. It’s a handy sort of product. But in New Zealand it’s not as handy, as widely used, as this list of goods might suggest. Not yet. It’s made in New Zealand, has been for some time, but only since the war has production been on anything like a big scale. Now there are three companies very busy in the business ; the war increased the demand for the product, and it is for the fighting of the war that millions of square feet of the material have been used. One day, though, production will be switched from a military to a civilian basis, and then the list in the first paragraph will probably be as incomplete for New Zealand as it is now for several countries overseas. Plywood timber in its latest, most scientific, most economical form — is one of the strongest and most adaptable of materials made by man ; it has the natural strength of wood and does away with most of its weaknesses. To make the product, thin layers of wood are glued to each other with the grain of each layer running at right angles to the grain of the next layer. An examination of the present-day ply board shows little more than a development of the veneered panel which has been made by craftsmen through the ages. In Egypt of the fifteenth century B.C. veneering was known and highly regarded. Excavations have brought to light furniture built on the plywood principle that has stood the test of centuries ; how the wood of those mummy coffins and royal tombs was sawn or cut, how the glue has managed to stick tight

for thousands of years is a mystery that will always confound the modern craftsman. Through the ages plywood-built furniture has been made. It was fashionable with the Romans. It was fashionable in the eighteenth century —Thomas Chippendale, Thomas Sheraton, and Jean Henry Riesener were three of the worldfamous craftsmen to make furniture which has given ample proof of the lasting qualities of this product. But the purpose of their use of the product was chiefly decorative. Few of the old veneer workers realized that thin sheets of wood glued together with the grain at right angles had advantages other than beauty, not the least of which is strength. In 1884 a small factory built for the manufacture of plywood chair seats was probably the first commercial venture. However, large sheets of plywood did not become available until about 1890 when the rotary-cutter was invented. It was then apparent that by using these sheets and applying this idea of cross-grained construction, material of exceptional size and strength could be built up. Threeply tea chests were the first result. Commercial three-ply wood on a large scale followed soon afterwards. The manufacture and use of plywood is a war baby. But not of this war. In the Great War material had to be found for aeroplane manufacture. Plywood was the strongest available for its weight ;

in short time aeroplane factories were using it. The development of the plywood industry kept pace with that of the aeroplane. It is questionable if plywood could have been the sound product it is to-day but . for the intense research work in the early days of the last war. Serious difficulties arose that in spite of the merits of the material could not be overcome. Plane construction required that flat pressed plywood be steamed to “ compound curvature.” A tendency for the material to return to its original pressed condition at the time could not be overcome satisfactorily. With changes in temperature or humidity the plane was liable to alter shape or to wrinkle. An aeroplane that changed shape would not do. Manufacturers turned to aluminium. For fifteen years little was heard of plywood planes. Now they have zoomed and soared into the news again. New Zealand has three factories. A Korero representative went to look at one in Auckland. It can produce 1,000,000 square feet of plywood a month, it has more orders than it can possibly fill. This factory was noisy, steaming hot, at times the smell was rather strong, but there was much to see, all of it interesting. Cut ’em up, cook ’em up, slice ’em up, dry ’em up, stick ’em up. That’s the recipe. But there’s more to it than that. Giant tree-trunks wriggle along a creeper-track from the railway siding to be sliced into the required lengths by a saw which rips through the huge girths. It’s as easy as a bread knife cutting through a loaf—and the sawdust makes a lot of crumbs. Rimu and matai trunks from National Park and Rotorua are used mostly ; they have been found suitable and they are the most readily available. Cooking the logs comes next. To soften the wood for the cutter the pieces of tree are swung with a huge winch into pots to be left in water (of 150 degrees temperature) for anything between twelve and twenty hours, depending on the size. Hot and steaming, cooked to a turn, the logs are now swung over t _> the rotary cutter ; they call it a lathe and it works on the same principle. After the bark has been removed, the log roughly rounded, it is fitted between two shafts in the way a block of wood or metal is fitted into a

lathe. A push of a button, the log starts to turn, faster and faster ; slowly it edges across the & ft. knife, razor-sharp. It’s strange to watch, the lack of effort is hard to understand. A wide ribbon of wood peels through the knife from the turning log along a flat tray. This ribbon is as wide as the log is long, about | in. thick ; - it comes through continuously. With this operation there are none of the flying chips or sawdust usual with woodcutting ; for all the effort there is the knife might be cutting cheese. A comparison is the unwinding of a roll of carpet over a smooth floor. The whole process is as easy as rolling off a log. The moisture content of the wood is high, sap froths and bubbles from under the cutting knife. The next process is the drying. Large ovens do the job. The long sheets, clipped to the required lengths on the cutter, are stacked singly on trays which move slowly through one of two giant ovens. The time of drying varies from twenty-five minutes to forty-five minutes in a temperature of between 225 degrees and 280 degrees. One thousand dive bombers all diving and bombing could not cause more noise, more disturbance, more clenching of teeth and blocking of ears than the machine that trims and glues the edges of the smaller sheets. It rips its way through a large compressed stack with

only a flash of that saw. These small sheets are then stuck together until the required size has been obtained. The spreader covers the surface with glue, the sheets are placed on top of each other (the number depending on whether it is three-ply or five-ply that is required), and all is ready for the next process—pressing. A steam hydraulic press does the work. A 1,300 lb. pressure to the square inch and a high temperature hardens the glue. In eleven minutes there is a solid panel. Except for a further period of drying and the last process of trimming and squaring, the product is now ready for the market— ready for delivering in plywood crates and plywood packing. Plywood is split proof. It is not hard to split a piece of timber in the direction of the grain ; it takes a lot of cutting and chopping to cut wood across the grain. Plywood profits from that fact ; it is for this reason that when the sheets are laid together the grain of one sheet is at right angles to the grain of the succeeding sheet. It is strong. As you know from the wooden handle of your metal teapot,' wood is a good insulator ; plywood, of course, has that advantage over metals, too. It is pliable to work with, easily pressed into rounded forms ; and when it is properly made it is durable and slow to decay.

The strength or weakness of any plywood depends on the bond holding the sheets together — glue. In the .last war and many years after when plywood aeroplanes changed their shape and wrinkled in the air, when other products for various reasons were not satisfactory, the main trouble was the glue. \ There were three principal typesstarch glue (made from tapioca), casein glue (made from milk products), and glue made from slaughterhouse waste. Each of them had their limitations : they were not temperature and • humidity proof, they were not waterproof, they were susceptible to bacteria, or they simply came unstuck. It was a problem. Progress in the plywood industry could not be made until there was an improvement. From Germany came the answer in 1930. It was a newly developed plastic glue, a synthetic resin. This glue is the same sort of plastic used to make fountain pen barrels, unbreakable tumblers, and telephones ; it is not only waterproof but bacteria resistant as well. However, the one drawback of this plastic glue is the high cost and complex nature of its production, and although the cost has been reduced in recent years synthetic resin glue is still used only for the manufacture of high-quality products such as planes and boats. At the Auckland factory, for instance, casein glue is found -satisfactory for much of the production, with the plastic resin kept only for special orders. Prefabricated houses which allow for individual design and ideas. Motor-car bodies of molded plywood which are cooler in summer and warmer in winter. Railway carriages and tram-cars. Film scenery. Fuel and water tanks. Boat building (plywood assault boats have been built by the thousand since the beginning of this war). To list fully all the present uses of plywood and- the experiments in new fields now being made would be tiresome. But the most spectacular prospects for plywood are in aeroplane construction. It is not suggested the plywood plane will overnight replace the metal machine, but the wood product (with the bond of plastic glue) has advantages over alumin-

ium that at present are becoming recognized as of great importance ; their wide application in the future is certain. In the plywood plane costly and difficult riveting, which reduces strength, is eliminated. Metal tends to weaken with vibration and to corrode with exposure to weather does not take place with plywood. Manufacture is faster, simpler, and less costly. It is claimed that because of the absence of complicated wing braces, and with wings and fuselages hollow and curved, the plywood plane needs 25 per cent, less power. Change of design can be made without trouble. Less labour is necessary and wood-working machinery only is sufficient ; planes can be made in piano and furniture factories which have idle capacity. Plywood planes are in the air at present. But after the war, with time for further experiment and more rigorous testing,

these planes may be the answer to the demand by thousands of pilots for lowpriced machines.