One of the largest glue manufacturers in the country makes the following comment on this subject:
“In regard to the effect of live steam turned into a pot of glue, whether flake, ground, or jelly—the glue would become overheated, and you know that always has a disastrous effect. The temperature of live steam is 212°, and under pressure it is even higher, so that at least the glue around the pipe will attain a temperature of 212°. The effect will be that the glue will be cooked to death and lose its strength. We would certainly discourage the application of live steam for dissolving glue as there is nothing to gain by it and everything to lose.”
Opinions of other manufacturers are unanimous on this point.
“We know of factories where they have made a careful test,” writes one, “and the results obtained from glue where it was melted with a live steam jet and where it was dissolved in a jacketed kettle were so greatly in favor of the latter method that it is used universally today.”
A further vital objection to the use of steam direct is that the steam contains acids from boiler compounds, dirt, pipe-rust and sediment, all of them injurious to the strength and to the elasticity of glue.
Then too, glue always takes up moisture from steam. This changes the consistency of the glue. It leads to guess-work. The quantity of water added to glue must always be exactly regulated. Turning live steam on glue prevents proportions of glue and water remaining constant.
USE A THERMOMETER
The only safe procedure in melting glue is to use a thermometer. If glue is melted in an open pot, or one in which the contents of the glue chamber can be reached easily, an ordinary drop thermometer, encased in a frame for protection, may be used.
It is preferable, however, to have the thermometer a part of the apparatus, with the mercury tube extending into the glue chamber. In this way it is easy to keep watch on the temperature of the glue mass at all times.
An improvement even on this method is found in the automatic temperature controller that may be had with some glue-melting appliances, by which the supply of heat is automatically regulated. When the temperature in the glue chamber passes 150° F.—the absolute maximum of safe temperature—the valve automatically closes and shuts off the heat, re-opening again when the temperature has lowered from 5° to 10°. By the use of the automatic temperature controller the temperature is kept at the proper point, and there is no necessity of making observations with the thermometer except to verify your controller.