USES OF PLYWOOD

Te Awamutu Courier, Volume 58, Issue 4191, 31 May 1939, Page 9

USES OF PLYWOOD

RAPID EXPANSION OF THE TRADE. NEW WAREHOUSES OPENED AT LONDON DOCKS. (From P.L.A. Monthly) The ancient Egyptians, who have done so much to .account for the theory that there is nothing new in the world, also forestalled more recent claims to the invention of plywood. Plywood is generally regarded as a comparatively modern development of the timber trade, but excavations in Egyptian tombs, the happy hunting ground of archeologists, show that the Egyptians not only “had a word for it,” but had already experimented in the glueing together of thin layers of wood to make coffins and panels. It was not, however, until the beginning of the present century that possibilities for the utilisation of plywood began to be realised, and later still that the industry embarked upon phenomenal development. Like a number of other modern industries in which method of manufacture rather than primary materials are concerned, plywood was for many years regarded as a “substitute,” and the trade had to fight hard to live down its infant reputation of cheap inferiority. The rough plywood packing cases of the early days are no more representative of the specialised industry of to-day, than Wright’s spindly aeroplane is classed with the Empire flying boat of 1939. Both were pioneer attempts in the evolution of a new medium, and the rapidity of progress in both industries can be aptly compared. It was the aeroplane industry during the War which gave the first intense impetus to the plywood trade which has now grown to such astounding proportions. Plywood is made by glueing together a number of veneers, or thin sheets of wood, in such a manner that the grain of each sheet runs at right angles to that of the one before it. Timber is a living substance long after the tree has been felled, and the varying degree of moisture in the wood causes the fibres to swell or contract and the material to warp or twist. This action, is much more marked across the grain than in the length of the wood. In the manufacture of plywood, the alternate placing of the sheets in such a way that the grain runs in opposite directions reduces these tendencies, and greatly increases the strength and reliability of the wood when subjected to changes of temperature and humiity. The main supplies of imported plywood arive in this country from Northern Europe, especially Finland, and Russia; there are considerable shipments also received from Canada. The timber used varies according to the country of origin. ■ In Finland, where the mass production of plywood has attained the highest stand nrd, birch is used. Sweden’s forests are mostly pine, so it is natural that this should be the basis of the industry in that country. Alder and g-aboon are also used, and from Canada comes plywood made of Oregon pine.

The Finnish plywood industry in particular has developed on the most progressive and scientific lines. State research laboratories have been established for technical and experimental purposes, and for the training of chemists, and most of the big mills have their own testing stations. The training of skilled labour is also efficiently organised, and great attention is paid to the changing demands of the consumer with whom the Finnish manufacturer maintains close touch. Every phase of the process is carefully controlled to eliminate unnecessary waste and improve the standard of efficiency of the factories and the quality of the output. When the cut logs arrive at the plywood factory, they are examined, sorted and peeled. Methods of cutting veneer from the tree trunk vary. The log may be sawn down the centre into two halves for flat cutting. As the expression denotes, the sheets are then cut from the flat inner surface of the wood. In the case of large logs, these can be quartered and again flat cut or placed on the rotary lathe. Alternatively, the whole log can be rotary cut so that the veneer peels off like a long ribbon. As these thin sheets of wood unroll under the saw or knife, they are dispatched. through mechanical drivers to reduce the moisture in the veneers to a uniform degree. The glue used to stick the different plies together is one of the most important factors in the manufacturing process. It is applied in most carefully controlled quantities by machinery. Chemists in the research laboratories are for ever experimenting with different types of glue. The new synthetic re< siif glues, for instance, have proved very successful, especially for ply-

woods used for outdoor purposes, as the glue knits together the wood fibres and forms a hard waterproof sheet. This type of plywood is. now made up to 2in. thick and is used for brake blocks, cogs, etc., because of its extreme hardness. When the veneers have been glued together, the “timber sandwiches” are put into hot or cold hydraulic presses and then redried. The finished sheets of plywood arc trimmed by guillotine knives and parcelled ready for dispatch. The packages, consisting of a number of sheets of equal size, weighing between 1 and 12 cwt. are bound together by metal hoops with solid wood battens to protect the ends, and are known as crates. Plywood is one of the most adaptable materials known. Its uses are being added to almost month by month. Lightness, great strength and easy handling are the main virtues of plywood which commend its use for such, widely divergent purposes as aeroplane manufacture and model making.