The simplest, cleanest, and cheapest method in the long run is to have rolls with corrugated surface; even spread is thus assured, and there is practically no “wear-out” to them.
In order to keep glue at right temperature during use, it is best to have the glue-pans surrounded by heating coils. These may easily be connected with the steam boiler or gas heater; or electricity may be used.
A further improvement is to have the spreader connected with the glue-heater, as then only a minimum quantity of glue need be carried in the pans. By this method a quantity of glue sufficient for a day’s work or half-day’s work may be melted in the morning and maintained steadily at uniform thickness and temperature until used. The melted glue is fed to the pans only as needed, through open copper troughs.
Glue pans should of course be made of copper, for the reasons already mentioned. Another advantage is that copper pans are self-cleaning, as glue does not adhere to this material.
Spreaders may be had as a single-roll machine, for coating one side of stock, or as a double-roll, for coating both sides, or as a combination single and double-roll. They may be operated by hand or with power. When used with power a good operator can coat 13,500 lineal feet per day, with a good machine. The results with a glue spreader are largely due to the proper adjustment of the scrapers.
Glue spreaders can be used to coat flats, edges, straights and mitres equally well.
For coating plain and straight surfaces, use a solid roll. For tongued and grooved pieces, V-shaped stock, dovetails and other irregular shapes, use a brush roll. Some spreaders are fitted with combination solid and brush roll; a very convenient and economical arrangement.
The spreaders should be kept scrupulously clean, and also the brushes, if any are used. Clean brushes by filling glue pan with hot water and revolving the brush in it until all the glue has been removed.
CLAMPS AND PRESSES
After gluing, the work should be kept under pressure for a sufficient length of time to insure perfect adhesion. In the case of hide glues the time required is from three to four hours. The time varies with variations in the glue, in condition of stock, and in temperature of room. No general statement can be made to cover the case; experience is the best guide. Either retaining clamps or presses are used.