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.

It might be pertinently asked what constitutes an adequate equipment of machines for crepe-making. The writers cannot give a number, but have no hesitation in stating that if a factory cannot complete its whole day’s work before dark, it is inadequately equipped. No work should be done after dark, if possible, as it cannot receive the supervision which crepe-making demands. To make comparison between the number of machines in any two factories and their respective outputs is not sound argument, as the out-turn of two similar machines will depend upon the speed at which the rolls travel—i.e., the gearing between the machines and the engines. Thus, while one machine will out-turn 40 lbs. of crepe per hour, another may only have an output of 30 lbs., although the machines may be identical in pattern. To make calculations based on a rate per hour for any known make of machine, and to apply those calculations to the existing machinery in any factory, in an attempt to judge whether there is a sufficient number of machines, would be a mistake, unless one were also supplied with the relative speeds at which the rolls work.

Finally, on the question of adequacy of machines, it must be pointed out that an insufficient number of machines must result in a poor product, since all rolls have to be used for all grades. Even with the greatest possible care it happens that pale crepe is sometimes spoiled because it is contaminated with foreign matter, resulting from the working of lower grades on the same machines. This is one of the great arguments in another direction for the installation of a scrap-washer.

In conclusion, the writers can only give their opinion that one must not decide the question of adequacy by the number of existing machines, but by the time taken each day in working off the rubber, providing one can be satisfied that the best arrangement of the existing machines has been made.Ideal Arrangement.—As to what this best arrangement may be, guidance can be obtained from the results of experience here given. It must be premised that the output of any factory preparing fine pale crepe is limited by the output of the smooth finishing rolls. Broadly, it will be recognised that if there is any excess of capacity in a battery it should be found in the smooth-roll machines. This sufficiency, or excess of capacity, may sometimes be attained by an alteration in the gearing of the drive of the rolls from the back-shaft, or by an addition to the number of machines. In the former case, there are practicable limits of speed, beyond which the second alternative measure must be adopted.Speed.—The usual speed at which the back-shaft travels ranges from 60 to 70 revolutions per minute. Taking first the macerating machines, the intermediate gearing between the shaft and the rolls should give a driving speed of about 20 revolutions per minute on the faster-travelling roll. This is equivalent, with a 15-inch diameter roll, to a peripheral speed of about 60 to 65 feet per minute.

The intermediate and smooth rolls can be arranged to travel more quickly, but the maximum comfortable speed for proper feeding and control appears to be about 25 revolutions per minute on even-speed rolls. In view of the fact that the rubber at each successive machine becomes longer and thinner, it will be seen that a smooth-roll machine could not cope with the output of a macerator in the same period of time. If, therefore, the macerator is fully occupied for the greater part of the time, an additional smooth-roll machine must be installed, even though the existing one has been “speeded up” to practicable limits.

For the information of the uninitiated it might be explained that in the macerating and intermediate machines the cog-wheels driving the two rolls are of different sizes (i.e., differentially geared), as opposed to the smooth rolls on which the cog-wheels are usually of the same size (i.e., even speed). The idea in the one case is to exert a “working” influence upon the rubber while it is being washed by the stream of water coming from above; in the smooth rolls a squeezing action only is effected.

To give an idea of the ratio of the speeds of the rolls in each machine in a typical working battery, the following particulars may be noted:Gear Ratios.—

It will be seen that the so-called “even-speed” smooth rolls run at approximately the same rate.

It is advised that in all cases the gear wheels should be cut helically. Those who have experience of the noise of some batteries after they are slightly worn will appreciate such a remark.Grooving of Rolls.—Concerning the choice of grooving, there is divergence of opinion, some managers preferring one type, which others reject in favour of another type. Provided any particular type can be shown to be as effective as required, no necessity for laying down hard-and-fast rules seems to exist.

The following particulars serve to describe a battery well known to the writers, and accustomed to produce the finest quality of thin pale crepe and lower grades:

The actual rate of output of this installation is the capacity of the last smooth machine. This is about 180 lbs. per hour, while the output of the macerator is approximately double this amount. Thus the macerator only works for about half the time. This applies also to the two intermediate machines. After a study of the preliminary remarks, it would not be difficult to suggest methods for improving the condition of affairs. It would appear that, in order to obtain a uniform rate of working in such a battery, the relative peripheral speeds of the several machines should be—(1), (2), and (3) 100; (4) 150; (5) and (6) 200. The remarks on the practical limits of speed should be borne in mind. In this case the smooth rolls travelled at 23 revolutions per minute.

As already stated, it is not intended to lay down definitely that, e.g., horizontal grooving alone should be cut on macerating rolls. Some estates employ with satisfaction a deep square-cut spiral 1/4 inch by 1/4 inch by 1/4 inch or 1/2 inch spacing; others use a large diamond pattern. Similarly various types of grooving are cut in the intermediate rolls.

It has been remarked in the chapter dealing with crepe preparation that much depends upon the condition of the coagulum. There is no necessity, or desirability, for having a standard higher than 2 lbs. dry rubber per gallon, and it has been argued that it would be better to select a standard of 11/2 lbs. The tougher the coagulum, the more the power required, and the slower the rate of output of the leading machines.

In ordering machines for crepe-making, only large rolls should be considered—e.g., rolls having a diameter of 12 inches to 18 inches and from 15 inches to 18 inches face.Rolls Running Hot or “Free.”—If the rolls are found to become hot, work on that machine should be stopped, and an examination made, otherwise there is the possibility of the crepe becoming sticky and “tacky” when dry.

Although comparatively cold water may be flowing upon the rubber and the rolls, little alleviation may be noticed, inasmuch as the source of heat lies generally at the bearing ends of the rolls. This may be tested by placing the hand on the top of the “standard” of the machine. The development of the heat may be due to lack of lubrication, worn bearings, or sometimes faulty setting-up of the machines.

Allusion has been made to the necessity for avoiding the running “free” of rolls—i.e., in the absence of rubber. The grinding of the rolls, when working close together, produces a fine powder, which causes a more or less pronounced deposit on pale crepe. When the rolls have been in action for some time and become slightly worn, this deposit may be confined only to the edges of the rubber.Sheeting Machines.—The foregoing paragraphs have dealt entirely with machines for crepe preparation. Concerning machines for use in sheet-making, the ground has been mainly covered in Chapter IX.

Where both crepe and sheet are made, it is permissible and advantageous to use the heavy smooth rolls for the rolling of the sheets, and it is only necessary to instal one or two light machines for placing a pattern on the rubber.

Where a heavy battery does not exist, light machines with smooth rolls may be employed satisfactorily. Even engine-power is not necessary for the preparation of excellent sheets, but the output is limited where hand-power only is employed. Estates are known on which upwards of 1,000 lbs of sheet rubber are made daily with hand-power machinery in one station. Beyond this figure, it is deemed advisable to instal a small engine, say of 7-9 horse-power. This is ample to drive a battery of three smooth-roll machines and two markers, and yet have sufficient reserve to actuate a small pump for the water supply.Lubrication of Machines.—It must always appear to those inexperienced in engineering matters that existing methods for lubricating rubber machinery are distinctly crude, when one considers the delicacy of the material to be prepared. Many existing machines are still lubricated with oil, which has to be administered in generous quantities. Generally, such machines have been so designed that the excess of oil may find an easy passage into the tray which receives the rubber. If not, it drops just outside the tray to the floor, and is washed away in great gouts. Even where grease-cap lubricators are fitted it is common to find that the excess can often be transferred from the bearings to the trays and so to the rubber. One would have expected from the attention which is being given to machinery for rubber estates that some improvement in lubrication methods would have been devised.

It is probable, however, that a great deal of the disabilities attaching to present methods of lubrication might be obviated if closer attention were given to the actual operation of the lubricators. Coolies should not be allowed to handle them, and the responsibility should be placed upon a foreman or the engine-driver.Trays.—The most unsuitable and damage-causing part of the vast majority of machines, without doubt, is the tray. On nearly all machines the tray is wider than the effective portion of the rolls, so that any excess of lubricant may drop into it. On others, not only is the tray wider than the rolls, but its edge either is in contact with the shaft of a roll or just a small distance away. The edge of the tray is thus favourably situated for acting as a “wipe,” and the lubricant is transferred to the inside of the tray. Considering that the effective portion of rolls is about two-thirds of their length, it must be unnecessary to have trays wider than the length of the rolls. For the preparation of fine crepe trays are quite superfluous, and their place can be taken by a narrow piece of board if required. If the bed of the machines has been covered with glazed tiles, even a piece of board is not necessary. Where trays have been removed from the fine-crepe rolls on a number of estates, a marked decrease in the number of spoiled pieces of rubber has resulted.

It must be recorded that the foregoing paragraph appeared in our 1913 publication. After a lapse of over seven years, the remarks remain as true as when originally written. One of us is continually meeting with cases in which the defects are plainly attributable to the cause indicated above, and the fault often lies with the management of estates. On most machines the trays are not fixtures, and could be removed if desired.Arrangement of Machines.—In considering the future arrangement of machines, the first care should be to see that machines and windows are to be found together.[16] Of all the factory operations, rolling of rubber should be given the maximum light. At the same time it would not be advisable always to choose a southern aspect, unless outside shades were supplied. The best position for setting up machines, therefore, is along a wall having a number of windows. This is extremely convenient also from the view of power transmission, and gives the maximum free floor space to the factory. In setting up machines, foresight must be displayed, otherwise one may find, when future extensions are made, that the extra machines may obstruct an entry or exit.

[16] Windows imply the existence of walls. Such is the conventional design of factories. It may be pointed out that walls are not necessary. The roof may be supported on pillars between which expanded metal of large size may be placed. This fulfils all requirements and gives the maximum of light and air. Many new factories have been erected to such a design.