T is quite certain that glue-room methods in many factories are years behind the times. This is due to poor equipment, to ignorance and to carelessness. Many factories could not continue in business if the hit-and-miss methods of the glue-room prevailed in other departments.
It is possible to spoil the very best glue by improper methods of preparation; and not only is a vast amount of glue rendered totally unfit for satisfactory work, but a great deal is wasted; the total loss, through faulty methods, being about 25% of the entire amount used.
There is no reason why there should be such loss in the glue-room. The proper methods of procedure have been definitely established. Putting them into effect not only saves glue, but it enables better work; saves time of workmen, and increases greatly the general efficiency of glue-room operations. The following rules are a guide to correct practice.
ALWAYS SOAK GLUE IN COLD WATER BEFORE MELTING
The function of soaking is to get back into the glue the liquid it originally contained.
Soaking in cold water gets the glue into proper condition to dissolve readily when heats applied. If glue is soaked in warm water, or if melted without soaking, the glue on the outside will dissolve at once, and this will coat the remainder with a film, so that it will not readily dissolve, except when heat is applied in a degree that is harmful.
Glue has an affinity for cold water. Good glue will absorb from 13 times to 22 times its weight of cold water.
If glue is in flakes or strips, break up into small pieces. Soak the pieces from 10 to 12 hours in cold water. Soak ground glue 1 to 4 hours in cold water. Naturally the thinner the glue the less time required for thorough soaking. The glue should be soaked through thoroughly and not merely moistened on the outside. You can determine whether the soaking has been completed by breaking a piece in two and noting conditions at the centre. If pieces are permitted to stick out beyond the level of the water, the natural result is that such pieces will be only partially softened. As the melting proceeds, these will slip to the bottom of the kettle, and in order to melt them long heating and high temperature are required. This means damaging the strength and adhesiveness of the glue.
In soaking ground glue it is a good plan to keep stirring as the glue is added to the water in the soaking vessel, as this helps to keep the fine particles of glue immersed in the water, instead of floating on the top. This is true also of thin- cut, high-test glues.
USE ONLY PURE, COLD WATER
In soaking and thinning glue, use only pure, cold water. Unless heater is provided with pure water attachtnent or pure water chamber, avoid using water from the glue heater. Do not use water from boilers, for such water contains pipe-rust, acids from boiler compounds, sediment, and other matter extremely harmful to glue. See to it that all soaking vessdls are scrupulously clean.
TESTING GLUE BY WATER ABSORPTION
The soaking of glue in cold water before using is employed in some factories as a basis for comparative test of working quality. The amount of water absorbed may vary as much as 10 ounces in half a pound. Other things being equal, the glue that absorbs the most water is of course the cheapest to use. As a comparative test, melt up say 10 pounds of glue and see how much work it will do compared with the glue you are now using.
A SIMPLE GLUE TESTER FOR DETERMINING WATER ABSORPTION
A simple and accurate apparatus may be had for determining the amount of water the glue will absorb for best working results, and also whether the amount of water actually used is the proper amount for this particular glue.
It is important to know these facts, since the more water a glue will absorb under proper working conditions, the cheaper that glue is to use.
The apparatus in question is illustrated on the next page. It consists of a copper pot and a hydrometer arranged for a temperature of 75°C., or 167°F. A sample of the glue to be tested is poured into the pot and the hydrometer is slowly allowed to sink into the solution until it finds its correct position. If the glue solution is, for instance, 1 part glue to 3 parts water, the hydrometer will drop to 25 on the hydrometer scale. This will show that you have 25% dry glue in the solution. The hydrometer is
fitted with a temperature correction scale
that enables the readings to be adjusted
to the temperature of the glue ,solution.
By noting the working qualities of glue prepared with various proportions of water, you can determine what is the correct amount of water to use, ‘and then by using the hydrometer as each batch is prepared, you can be sure that the correct proportions are always being used. By making readings from time to time with the hydrometer, you can also determine the amount of evaporation that is going on, and in this way guard against the glue becoming too thick for proper use.
No special skill is required to use the hydrometer, and the readings are so quickly made, that tests can be made in every department in which glue is used without loss of time.
MELTING, OR DISSOLVING, GLUE
After the glue has been soaked in the manner described, the most important part of the process is undertaken – that is, the melting of the glue by application of heat.
The words “most important” are used advisedly. It is safe to say that most of the damage done to glue occurs in the melting process. There are all kinds of ways of melting glue, but many of them absolutely ruin glue for practical work. As this is a very important subject, it is well to get the rudiments thoroughly in mind – and for this purpose the reader should remember what has been said about the nature of glue – that it is made from animal matter; and that it is composed of innumerable small fibres on whose strength the holding power of the glue depends.
Whatever injures and brealls down these fibres inevitably weakens the glue; so that in melting, every care must be observed to avoid the breaking down of the glue fibres.
The most common destructive agent is heat. Just as the application of heat breaks down ale fibres of a roast of beef, rendering it “tender” as the saying is, so the prolonged application of heat, or heat of too great an intensity, will destroy the glue-fibres, and therefore radically impair their value for actual use.
So, it is absolutely necessary to employ no more heat in melting glue than is required to reduce the soaked mass to the proper working consistency.
DO NOT HEAT GLUE HIGHER THAN 150°F.
By actual experience it has been determined that a temperature of 130°F to 150°F. is all that is required to melt the glue to the requisite consistency ; any greater heat is actually harmful, as it assists just so much more in the process of disintegration.
The term “boiling,” or “cooking,” never should be applied to the process of glue melting. These words imply a temperature of 212°F. – and such a temperature is ruinous to glue. In producing glue from the original stock – from the hides, bones, sinews, etc., – boiling is necessary, in order to extract the gelatinous matter but as we have already seen, the longer the stock is boiled, the weaker the product. “First boilings” are always best. In preparing for use, however, boiling is not necessary; therefore, never heat glue above 150°F.
APPLY HEAT INDIRECTLY
Heat never should be applied directly, as this results in burning, or scalding, the glue.
Some glue melting appliances have been constructed in which steam is turned directly upon the glue mass. This is bad practice of the most harmful kind.
Steam never should come into direct contact with glue. The temperature of steam is always at least 212°F. – under pressure it is much higher and consequently it cooks the glue and destroys the fibres. Live steam burns glue just as it burn’ your hand if turned directly upon it.
The destructive effect of live steam upon glue may not be noticed at once, but work on which overheated glue has been used will eventually pull apart on account of the destruction of the glue fibres.
LIVE STEAM RUINS GLUE
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°F, and under pressure it is even higher, so that at least the glue around the pipe will attain a temperature of 212°F. 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 take’s up moisture from steam. This changes the consistency of the glue. It leads to guesswork. 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.
The temperature controller not only permits the scientifically correct preparation of glue, preventing overheating and ruined work, but saves also in expense of supervision.
HEAT GLUE SLOWLY
Glue should be heated slowly, requiring about 30 minutes. Rapid heating dissolves the outer portions of the glue quickly, and a scum is then formed over the rest of the glue, preventing its proper melting.
The following precautions will be found useful to put into practice.
CLEANING THE MELTING POT
Dirt ekers the melting pot through the glue itself, the introduction of dirty brushes, or the exposure of the pot to dust, etc. If glue is melted in a dirty pot, the skin forming on the surface of the glue liquor gradually accumulates at the sides of the kettle and slowly decomposes. This may or may not fall into subsequent melts, thus contaminating them. The only way to make sure that it will not do so is to clean the pot.
Much unnecessary waste of glue may be avoided through observance of the following procedure. The contents of the melting-pot exhausted, scraps of dried glue, as well as scraps of partially dried jelly adhering to the sides should be detached mechanically, as thoroughly as possible, and examined. If clean, they may be replaced in the bottom of the kettle; if dirty, they are to be set aside temporarily.
In the first instance, they are covered with the minimum of water necessary to soften, and the sides of the kettle swabbed with a little water in order to soften any glue that has dried and has not been detached mechanically. The pot is then gently heated in order to bring the scraps into solution, this solution used in work, and the pot thoroughly washed out with hot water and cooled before soaking a fresh portion of glue.
If the scraps have proved dirty, but not sour, they may be kept warm enough to permit the dirt to settle, when the glue may be used without risk. If sour they must be thrown away. If the glue pot is properly cleaned there is no danger of souring and all the glue may be used without waste.
It may be contended that much labor may be saved by adding sufficient water for the next melt, and through this means soften all glue adhering to the kettle in connection with that added fresh. It will be found, however, that the freshly added glue will absorb the bulk if not all of the water, leaving adhering scraps practically unsoftened, which in this way continue to accumulate, interfering with the proper working of the glue.
Pots, kettles, brushes, everything that comes into contact with glue, should be regularly and rigidly inspected, and kept absolutely free from dust and dirt. This is extremely important.
USE COPPER AND BRASS OR ALUMINUM
An important aid to cleanliness is the use of copper, aluminum or brass for all parts of the apparatus with which glue comes into contact. Not only are copper, aluminum and brass the cheapest materials to use in the long run, due to their resisting acids in glue, water and steam which quickly corrode iron, but copper, aluminum and brass are practically self- cleaning.
Iron equipment is especially bad. It is most expensive in the end, for iron is quickly eaten away by acids in glue and water. Iron rusts, and the rust impairs the color and quality of the glue liquid. Do not use iron vessels under any conditions.
GUARD AGAINST EVAPORATION
A great deal of waste in the use of glue is due to evaporation. If glue is heated in open pots, evaporation is very great. Evaporation weakens glue; makes it too thick for use, and also makes it very uneven in quality. Glue should always be melted in a closed vessel.
DO NOT MELT TOO MUCH AT ONE TIME
As glue deteriorates quickly if ‘allowed to stand, no more should be prepared than is needed for a single day’s work. It is even better to prepare it twice or oftener during the day.
If glue is dissolved at the proper temperature and kept at that same temperature after melting, no noticeable deterioration result during the course of the working day. But if allowed to stand over night its value decreases, and it should not be mixed with fresh glue, as it is not of the same consistency.
With practice and observation you can easily determine each day’s needs in advance and prepare each morning just the right amount.
CLEANLINESS OF FIRST IMPORTANCE
Glue is extremely sensitive to impurities.
Cultures of germs are grown by bacteriologists in gelatine glue because they afford an ideal breeding place for germs.
Clue quickly absorbs odors, and decays rapidly if exposed to impurities.
Decayed or decaying glue is not only extremely unpleasant to handle, but it is worthless to work with. Keep your glue clean. Keep it away from strong odors. Glue will keep sweet and clean before melting just as long as you care to keep it so.
KEEP GLUE-ROOM WARM AND FREE FROM DRAFTS
Glue can not be expected to do good work if not kept at uniform temperature. See that the glue-room is of a temperature that facilitates uniform consistency of glue. Avoid possibility of drafts and consequent chilling of the melted glue.
Do not let glue freeze. If glue-jelly is frozen through it will crumble and act about like overheated glue. Glue frozen only around the edges does not show pronounced deterioration. Do not take any chances. Keep the glue-room temperature above freezing at art times.
USE BY WEIGHT
Glue is sold by the pound and should be used by the pound. Weigh not only the glue, but weigh the water as well.
Keep an accurate record of weights.
Glue should be stored in a dry place. Barrels should not be unheaded prematurely, and after having been opened should be kept covered when not in use.
All surfaces to which glue is to be applied should be warm and dry. Hot glue will chill if applied to a cold surface, and if wood is being glued, moisture will have the effect of clogging the pores of the wood. Heat dries and expands the pores, allowing the glue fibres to penetrate deeply, thus insuring perfect adhesion.
At the same time there is danger of getting wood too dry, making it absorb too much glue, and too speedily. This causes a very quick setting, and may result in “starving” the glue joint.
Some users on this account recommend adding a little moisture to the surface of stock, by steaming or by application of a little warm water. There is more or less uncertainty on this subject. As a general conclusion it is safe to say that stock must always be warm; surplus moisture must be expelled; no “green” stock must be used.
Here again, as in so many other problems of the glue-room, observation of results under actual conditions should be the guide to practice.
SECURING WORKERS’ CO-OPERATION
One more thing of extreme importance the employer should do everything possible to secure the co-operation of every worker in the glue-room, from the foreman down, in using proper methods. A little personal interest here will be rewarded a thousand fold. Provide your workmen with proper equipment, which in itself encourages cleanliness, and show them how the quality of work may be improved.
Show them that an unclean, ill-smelling glue pot, is unnecessary. Show them that there is a right way, and a wrong way, to prepare glue – and the right way is the way to use. Introduce system into the glue-room, as into every other part of the plant.
Many workers are still ignorant of modern glue methods. It is the duty of the employer to know what the correct practice is, and to see that it is employed in his glue-room.