Extract from Modern Printing by John Southward.
IT is of the very greatest importance that the printer should possess thoroughly good rollers, for without them he cannot produce respectable work.
Qualities of a good Roller. The following qualities should be possessed by a good roller:-
In shape it should be perfectly cylindrical, and exact in mechanical form from one end to the other.
It should never shrink or swell. Shrinking or swelling causes loss of time in setting the roller in the machine, and is always accompanied by a variation in the quality of the roller.
Its elasticity, if not absolutely perfect must at least be good, so that it can adapt itself perfectly to the pressure of the forme.
It must have a sufficiently strong affinity for ink to take instantly a sufficient supply from the ink table.
It must part with its ink properly to the forme.
It should be able to withstand the action of proper detergents.
It should preserve these qualities under varying conditions of temperature, and of humidity in the atmosphere. Great improvements in this respect have been lately made, but when some kinds of composition are used summer rollers and winter rollers are necessary.
Mr. Earhart says in "The Colour Printer":- “A roller when in the best condition for taking up the ink and freely giving it off again, should be firmly elastic, and should feel tacky when the hand is, gently pressed upon its surface; at the same time, if the hand is moved rapidly along its surface; it should feel smooth and polished, as if it was not very tacky. A forme roller should be nicely adjusted, so that it will evenly pressed by the vibrator along its full length without flattening its surface; at the same time, it should firmly but evenly press the face of the forme without depositing any ink below the actual face of the type, cuts, &c., contained in the forme.”
At the present time printers very seldom make their own roller composition, preferring to use special composition, produced by firms which devote themselves to this branch of manufacture. Nor as a rule do many printers make their own rollers. It is found advantageous to obtain them from firms which possess special apparatus for manufacture, and employ persons experienced in this kind of work.
Various roller compositions are supplied under trade names, but they all belong to one of two kinds. In one glue and treacle are the principal ingredients; in the other glue and glycerine. The first kind of rollers are the oldest, but the latter, which are the newest, are now by far the most widely used.
In regard to the constituents, glue is hard when cold. To render it soft and springy fluid ingredients are used. Treacle, called molasses in America, is a syrup containing about a quarter of its weight of water in an ordinary temperature and is adopted for admixture with glue to keep it in a soft, elastic condition. Both the glue and treacle in a roller when kept in a dry place rapidly became hard. Constant washings with water become necessary, but the unavoidable evaporation of the liquids also soon destroys the power of the glue to gelatinise. The composition then acquires a hard face, and if detergents, such as lye and water, are frequently applied it becomes cracked. The cracks not only cause the roller to give an imperfect coating of ink to the forme, but retain ink after the surface has been washed. A roller in this condition cannot be used for colour, such as red, after it has been used for black.
Glycerine, on the other hand, is a permanent liquid which, under ordinary circumstances, does not volatilise or lose bulk. With several admixtures it forms compounds which are, insoluble in water, which is one of its chief advantages in roller-making. It may be deprived to a certain extent of. its property of absorbing moisture, and rollers made from this modified substance will not swell or refuse to take ink when there is an excess of dampness in the atmosphere.
The old glue and treacle composition gave much trouble. owing to its susceptibility to changes of the weather. It was generally necessary when such rollers were used to have several sets of rollers fit for working, some in hot weather, some in cold. The newer kind of rollers maintains a more equable consistency during all the seasons of the year. They also last much longer, and produce much better work. Although the first cost of the composition is higher, it is doubtful whether they are as expensive as the old kind when the losses in time connected with the use of the treacle-and-glue rollers are taken into account.
Another advantage of using the glycerine instead of treacle rollers is that the latter require far more care and experience in getting them into condition and maintaining them so. Modern conditions of printing demand that, as far as is practicable, rollers should be always in workable condition. A futher advantage is that the newer kind of rollers last many times longer than the old one.
The following recipes for making roller composition have been found satisfactory, but much depends on the quality and of the ingredients used. Glue, glycerine, and treacle occasionally much adulterated, and sold in an unsuitable condition.
Recipe for treacle roller :
|Glue||… … … … … …||9||parts by weight|
|Treacle||… … … … …||14||” ”|
|Paris white||… … … …||11||” ”|
Recipe for glycerine roller:
|Glue||… … … … … …||2||parts by weight|
|Refined sugar||… … … … …||10||” ”|
|Gycerine||… … … …||12||” ”|
The dry glue must, after being weighed out, be put in soak. A good way to soak glue is to put it into clean cold water for about twenty minutes, take it out and place it upon a board, covering it with a damp printer's blanket, and let it remain all night. In the morning it will be of the consistency of india-rubber, and will stretch like it.
Put the kettle on and bring the water to all but boiling point, and keep it at that temperature. Then put the glue into the composition pot and stand the latter in the water. As the glue melts, keep it stirred till all traces of the water are out of it. Then add the glycerine, stirring it till it is well mixed with the glue. Next add the sugar, and keep the whole well stirred for from thirty to forty minutes. If it remains much longer it will probably "candy."
The appliances for roller casting, as used in ordinary printing offices, are a melting kettle and roller moulds.
The melting kettle, which should be provided with a stirrer, may hold from 2½ to 10 gallons of melted composition. It may be heated by steam, or by gas, or a coal fire.
The moulds require to be most accurately bored and fitted. They should have vice-handle "dogs" and stout screws. Hand-press roller moulds are made of either cast-iron or stout brass. They range from 12 to 30 inches in length. Machine roller moulds are generally of cast-iron. They may be from 36 to 72 inches in length, and occasionally may be even longer.
Preparations before Casting. The melting kettle is on the principle of the carpenter's glue pot, consisting virtually of two vessels, one within the other. They are separated by water, so that the inner one is not touched by the fire. A moist heat is desirable for reducing or liquefying the composition, to get it into a state fit for pouring. The material must be boiled, not baked. It must not be heated more nor longer than is absolutely necessary. Roller casting is a simple operation, if a little forethought is exercised.
Casting should always be done in a warm place. Before consigning it to the melting pot, the composition should be cut up into small pieces, somewhat about the size of a large jujube. This is done to facilitate thorough and quick melting.
If a small roller only is wanted, the composition may be cut up and put into a large jug, which might be placed in a metal pail of water and stood over a gas or other stove.
After the composition has been put in the kettle and whilst it is melting, the mould should be prepared. Care should be taken to see that it is perfectly free from rust or dirt. It should then be heated just hot enough to comfortably bear one's hand upon it. Carefully grease all over the inside -with sperm oil, using as little as possible. The roller stock is then placed inside the mould. If an iron stock, it should be heated first. It should be painted with white lead, which must be allowed to dry, and a piece of coarse twine or tape wound round it. There will then be something for the composition to hold on to and keep there-otherwise it might come off the stock.
The mould should stand in an upright position when casting, and the composition poured over the roller spindle so that it is filled from the centre and the oil is not washed from the sides. Have the composition only just fluid enough to pour it on the spindle. If it is poured too hot and too quickly air bubbles will probably make their appearance.
In pouring the composition into the mould, see that the spindle of the roller is exactly in the centre, so that there will then be an equal amount of composition round the spindle. Pouring slowly prevents any holes and flaws. The mould is filled an inch or two higher than is required to allow for shrinkage and trimming.
When the roller has cooled sufficiently, it is carefully removed from the mould and trimmed at the ends with a sharp knife. After being kept from three to seven days it will be ready for use.
If the composition gets loose near the ends of the roller, and it is in good condition elsewhere, a rough-and-ready remedy is to make a common table knife almost red hot, insert it on the side of the composition nearest the stock so as to make it sticky; withdraw the knife, and encircle the roller with the hands for a few minutes so as to exclude the air. If the adhesion is complete the roller will last for some time.
In drawing the roller from a tubular mould it is astonishing how it will stick sometimes. Many a roller has been spoilt in the drawing. No one who has not actually witnessed it could imagine the tenacity with which it sticks to the tube. The novice is sometimes disposed to facilitate the removal [...]
Text from Modern Printing by John Southward.
Find us on Google Maps