The Preparation of Plantation Rubber

by Sidney Morgan

MACHINES

The number of manufacturers of machines for preparing rubber would seem to be on the increase, and there can be little doubt that this competition will result in a continued improvement in the design of machines. It cannot be denied that there has been room for such improvement, and it is believed that manufacturers will display judgment in putting only their best quality into the work. While design and finish are very excellent in their way, it is to be regretted that in a number of cases in the past the material of rolls has been found to be of inferior quality. Generally, the complaint seemed to be that the rolls were too soft, and that the “grinding” effect was far too great. The damage to pale rubber in such cases is considerable, as it is impossible to keep the rolls free from fine dark powder. The effect is generally noticed more in the smooth rolls with which a finish is put upon the crepe.

Cases have occurred frequently in which rolls have been returned, because of the injury caused to pale rubber, and there can be little doubt that the life of quite a large number of rolls is even now far too short in comparison with the expense involved.

It is a moot point, however, in many instances how far the quality of the rolls is actually responsible for the damage done to the rubber. In the experience of the writers it is certain that complaints regarding the rolls were unjustifiable, and that the injury had been caused by carelessness in the “feeding” of the machine. Especially in the case of smooth finishing rolls, it is clear that if the rolls are allowed to run idle for more than the briefest possible interval grinding must take place.

The complaints apply not only to the rolls themselves, but also to the brass linings for shaft-bearings. Cases are known in which a brass “liner” was so worn within a few weeks as to be quite useless. If the matter ended there it would not be so bad; but there is always the possibility of particles of brass finding their way into trays, and so into the rubber. The damage which ensues to the rubber is quite irreparable. This particular defect arising from the presence of brass will be dealt with in a [later chapter]. But here again it is necessary to point out that such wear on brass liners may be caused by the standards (ends) of the rolls being eccentric; and the case may be analogous to the placing of “new wine in old bottles.”

En passant it may be remarked that in any case brass liners are not strictly necessary. White-metal alloys are in use on rubber machines, and cast-iron bearings have been employed satisfactorily for years.

It would be well for managers to remember, therefore, that when machines have to be ordered, nothing but the best is good enough, and that the difference between good machinery and passable machinery is probably immensely greater in effect than any saving in expenditure would warrant.

Adequacy of Machines.—In general, the factories which prepare sheet rubber are usually equipped with adequate machinery. This arises from the fact that machines are necessary for preparing all grades below the first, even if they are not necessary for the making of sheet. Thus all the necessary macerators and finishing machines are installed, but the major part of the output is in sheet form. For the preparation of sheet, no heavy machinery is required; all that is necessary are light machines for rolling the sheets and expressing as much moisture as possible. To obtain a pattern on the sheet, another light machine may be used. It may be imagined, then, that the work of rolling sheet rubber by power machines is small, and that a large quantity of rubber can be worked off in a comparatively short time. It follows, therefore, that the preparation of the lower crepe grades can be proceeded with at once, and that the whole work of the factory is expedited.

The case of factories which have to prepare all first-grade rubber in crepe form is quite different, especially when thin rubber has to be made. The care which has to be exercised in preparing pale crepe rubber is very great in comparison with what is demanded by sheet rubber. The rubber has to go first through the uneven-speed macerators, from there to the intermediate rollers, thence to the finishing rollers. Considerable ingenuity has to be displayed in the arrangement of the machines, so that one section will not work faster or slower than another. More often than not, the attempt to arrive at such a desirable arrangement fails, owing to an insufficiency of machines. Such a statement will probably read strangely to the uninitiated; but an example will make it plain. A factory may have a battery of six machines, one only of which is a finishing machine (smooth rolls). With five macerators and intermediate machines working continuously, it will be more than the work of one finishing pair of rolls to keep pace, especially as so much more care has to be exercised in finishing than in rough crepe-making. The obvious course to adopt is to substitute a pair of smooth rolls, with suitable gear ratio, for a pair of macerators or “intermediates.”

If, however, the macerators and intermediates are already fully occupied the whole of the time, any such change would be of small benefit. What is really needed in this case is more machinery.