Modern glue-room equipment
ITH the increased knowledge of the nature of glue, and of proper methods of handling, has come a great improvement in apparatus used. The primitive way of melting glue was to heat it in an open pot over a fire. No heed was given to the loss through evaporation; nor to the scalding of glue; nor to the dirty condition of the glue-pot, and consequently contamination of fresh glue by the remains of former melts frequently occurred.
We say "primitive" methods advisedly in speaking of this old-time way of melting glue; for in the light of modern knowledge such methods belong to a day gone by. Yet some glue-rooms still use the old open glue-pot, and many others use apparatus which shows little, if any, improvement.
Modern glue-room appliances are now available for every glue-room, for every purpose. No glue user, large or small, can afford to use any but modern, scientific equipment. The saviI in time, and in materials, and in improved quality of the completed work, and in the greater respect and increased efficiency of workers in the glue-room, all these things result in quickly repaying the increased outlay required.
ONLY COPPER, BRASS, ALUMINUM SHOULD COME INTO CONTACT WITH GLUE
The advantage of using copper, brass, and aluminum in glue-room appliances, due to their self-cleansing properties, already has been mentioned.
In apparatus designed for melting glue the use of copper, brass, and aluminum is absolutely required for economy and good results. Copper, brass, and aluminum are the only materials available that are not affected unfavorably by the action of acids in glue, steam and water; by boiler compounds, dirt, pipe-rust and sediment.
An iron agitator or stirrer in a glue heater is corroded so quickly by the acids in glue, water and steam that in six months it is unfit for use.
A brass agitator, on the other hand, will last practically forever. So it is with every part of the glue heater with which glue comes into direct contact.
The glue user who has had experience with galvanized iron heaters does not need to be told that the iron quickly is eaten away and the apparatus rendered unfit for use. It is certainly the part of wisdom to invest in copper, brass, and aluminum equipment, to which metals there is practically no "wear-out."
Glue-room equipment of iron is still sold, but only because there are still some users who are so blinded by the initial small saving in outlay, as not to see the saving that accrues in the end from using indestructible materials - and the additional saving due to good work and economy of glue.
A SCIENTIFIC GLUE-HEATER
The facts already mentioned about the melting of glue should be borne in mind in choosing a glue 'miter, or glue- heater -- always remembering in particular that it is of utmost importance that the heating agent should not come into direct contact with glue, and that the glue should not be overheated in preparation.
The glue-beater that has been proved most economical and efficient in widespread use has an air-tight glue chamber (to prevent evaporation), surrounded by a water-jacket (to prevent burning or scalding glue), the water in the jacket being heated either by direct injection of steam or by the use of copper heating coils. Electricity is also used successfully as a heating agent.
The heater is made of copper and brass throughout, and is therefore not affected by the harmful effect of acids in glue, steam and water, dirt, grease, pipe-rust, sediment and other harmful substances. In this heater glue is reduced to a uniform and correct working consistency, and with unusual speed, if desired; 5 gallons of glue may be melted in less than 15 minutes, and as much as 50 gallons in less than one hour.
It has already been noticed that excessive speed in heating requires a degree of beat that is injurious.
A thermometer is provided with this heater that gives accurate readings of the temperature within the glue chamber, so that the beat may be turned off when the danger point of 150Ã‚Â° F. is reached.
THE AUTOMATIC TEMPERATURE CONTROLLER
A still more recent and valuable improvement is the automatic temperature controller, a thermostatic valve which operates automatically to keep the temperature in the glue chamber between 145Ã‚Â° F. and 150Ã‚Â° F., or at any temperature for which it is set.
Not only overheating of the glue is prevented, but expense of supervision is reduced. The heater does not need to be constantly watched for, fear glue will not be kept at correct temperature.
This particular heater is also provided with a brass agitator (hand or power) for keeping glue thoroughly mixed while melting, and with a special faucet by means of which the melted.glue is drawn off without .jdripping or clogging. It is made in sizes from 2 gallons to 500 gallons liquid capacity, and for use with any heating agent - gas, electricity, or steam.
An apparatus of this kind not only facilitates economical melting of glue, by preventing evaporation, waste, formation of scum, sour and dirty glue, but it also insures uniform "spread." Furthermore, it is a great incentive to accuracy and cleanliness on the part of workmen, encouraging them to good work by providing them with a neat and clean glue melting appliance, in contrast with the old-fashioned, unsightly and ill-smelling "glue-pot;" and providing them also with glue that has been properly prepared.
KEEPÃ‚Â STEAM AWAY FROM GLUE
Above all, keep steam away from glue. Some glue-melting devices are on the market in which glue is prepared by subjecting to the direct application of steam. This produces only bad results. All authorities are now agreed on this subject. It is safe to say that the chief development in glue-room methods of the past ten years hinges entirely on the discovery of these facts: that steam ruins glue; that glue never should be heated above 130Ã‚Â° to 150Ã‚Â° F. at the utmost; that the other properties in steam - boiler compounds, acids, dirt, pipe-rust, sediment, and grease - are absolutely injurious to glue.
Do not let the argument of speed blind you to the damage resulting from the live steam type of dissolver. If you want speed, use a type of instantaneous dissolver that prevents steam from coming directly into contact with glue. The very best practice, the one generally recommended by experts, is tm heat glue slowly, with a heat not above 130Ã‚Â° to 150Ã‚Â° F. Then the glue is in the very best possible condition for work.
The effect of acids is such that they have been known to turn a pot of good glue black.
In wood-working establishments where much glue is used, it should be applied mechanically, by means of glue spreaders.
Some spreaders are made with Brussels carpet covering for rolls, but this is not good practice. The carpet covering absorbs dirt quickly, is difficult to keep clean, is liable to tear, is sure to stretch and eventually rots and wears out.
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 oth sides, or as a combination single and double- roll. They may be operated by band 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.
CLAMPSÃ‚Â 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.
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 beating 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 isiso 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 purpdse 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.