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.
The cost is less than either steam or gas and its advantages are so great that thousands of institutions are now using these “fireless” glue-heaters. The best electric glue-heaters are made of copper and brass, the greatest conductors of heat. They require much less heat than any other pot and the heat is required for just about one-fifth the time, owing to the heat-retaining jacket.
CHAPTER VI
WHICH GLUE TO USE
The answer to this question depends so largely on the individual conditions, that only very general suggestions may be given. We have already suggested the need of experimenting and accurately recording the results of using various kinds of glue. Once again, your dealer will give you good advice nine times out of ten—and your own experience should afford the most valuable check on his suggestions.
In general, the following glues are indicated:
Wood joints—High test hide glues. They make strong, firm joints, which is extremely important, as joints are subject to more or less tension; and they set rapidly.
Veneers—A moderately high test mixture of bone and sinew or bone and hide. The higher test glues set too quickly for this particular kind of work. If a spreading machine is used, avoid a glue that tends to foam. Sometimes foaming is caused by its spreading too fast. Overheating glue also tends to foam it. This can be overcome by the addition of sweet oil or vaseline, paraffine or wax candle, but it is objectionable when veneering. It is best to be sure you have a glue that will not foam. Your dealer can tell you what glue to use.
Sizing—Use a glue free from grease and foam and one that flows freely.
Paper Boxes—A quick-setting hide glue is indicated for setting-up. For covering, a lower test bone glue is preferred, as it does not set so quickly. Paper box manufacturers are troubled more or less with foaming glue and can use the remedy suggested in the paragraph on veneers, as this will not be objectionable in paper box work.
Belting and Other Leather Goods—Here the principal requirements are flexibility, resistance to moisture and tenacity. The higher test glues are generally preferred.
Bookbinding—For pasting covers, a low-grade bone glue answers all requirements sufficiently well. For rounding and backing, where strain is exerted, a high-grade hide glue should be used.
For Emery Purposes—Very high-grade glue that has been carefully prepared to eliminate all acids, alkalies and impurities. A good emery glue possesses superior water-absorbing qualities. To test a glue for emery purposes, soak an ounce in about five times its weight of water at room temperature for 48 hours. If at the end of the time the water shows discoloration, or if decomposition is evidenced by a disagreeable odor, the glue is not adapted to emery use; otherwise it may safely be used. Weigh glue after the operation, to get an idea of its water-taking properties.