Pressure should be distributed as evenly as possible. Presses may be had in almost every style for every need—open on one side, or on two sides; for veneered stock; sectional presses; etc. Very excellent presses are being made of structural steel. They are practically indestructible, very efficient, and yet simple in operation.
In selecting a veneer press equipment the amount of pressure per square inch must first be determined. Opinion varies with different manufacturers, some using 100 pounds, some 200 pounds, per square inch. The best general results are obtained by using 150 pounds per square inch. All presses made with a 2-inch screw should be designed to withstand a pressure of 8 tons or 16,000 pounds per screw. To find the tonnage of press that you require, multiply the length by the width of stock, this by the pressure per inch you desire and divide the results by 2,000. This will equal the tons pressure required. The number of screws per press can then be determined.
DISTRIBUTING GLUE IN LARGE PLANTS
Glue is used in the wood-working industry mainly for making joints and veneers.
In large establishments, where many workmen are employed, a good plan for distributing the melted glue is to arrange a battery of small glue-pots, or warmers, strung along a pipe line running from the steam boiler or gas heater.
Individual pots of copper which are filled at the central source of supply fit into cast-iron jackets, kept warm by steam which comes from the pipe line. The requisite temperature is thus maintained at minimum cost.
The valves may be so arranged as to cut off any warmer not in use, avoiding waste of heat. The arrangement is very satisfactory even in comparatively small establishments, and may be adapted to any number of individual pots.
ADVANTAGES OF ELECTRICAL EQUIPMENT
When steam is used as the heating agent, only about one-fifth the amount of heat generated is actually used for heating the glue. Four-fifths of it radiates through the pipes and creates a heat so intense that the efficiency of the workmen is reduced fully one-half in summer. With gas as the heating agent, the same conditions are present as with steam, plus the fire risk, which in itself is so great as to make gas extremely inadvisable.
Electricity is coming into greater favor every year, with the improvement of electrical glue-heating appliances. Electricity is still too expensive to justify its use as a heating agent, except for the exact purpose desired, but modern electrical devices, including the jacketed, heat-retaining glue-pot, make it possible to use electricity without waste.