The Preparation of Plantation Rubber Part 16

Some ingenuity can be displayed in the packing of sheet rubber in order to avoid folding the sheets, which, besides increasing the difficulty of sampling, leads to loss of s.p.a.ce. Endeavours are being continually made on estates to prepare sheet of such a size as to obtain the maximum benefit of s.p.a.ce both in smoke-house accommodation and in packing. A few estates employ tanks of such calculated dimensions as will yield uniform sheets which pack flat and fill the superficial area of the case.

In view of the contamination which sometimes characterises the employment of wooden cases it is sometimes advised that the interior should be lined with sheets, or pieces of crepe, the ends of which are later folded over the top of the ma.s.s. In this manner it is stated that contamination is confined only to the exterior of the contents of the case.

WEIGHT OF CONTENTS.--The dimensions of average cases are 19 inches by 19 inches by 24 inches, giving a capacity of 5 cubic feet.

In these it is possible to pack 150 lbs. of crepe rubber and 200 lbs. of sheet rubber (about 5 per cent. more in cases of three-ply wood). It may be noted that boxes arrive in better condition when fully packed. The foregoing figures are not adhered to strictly. For example, some estates find it expedient to s.h.i.+p rubber in actual ton lots, and for this purpose pack only 140 lbs. of crepe per case, giving sixteen cases to the ton.

Other estates, using presses, pack more per case than the quant.i.ties noted above. At present there does not appear to be any definite regularity in practice.

[Ill.u.s.tration: ON ITS ROAD TO THE RAILWAY: BULLOCK-CART TRANSPORT.]

In all instances it should be the invariable rule that the rubber should be weighed before packing, and that all cases should contain uniform nett quant.i.ties of any particular type of rubber. Invoicing, etc., will thus be greatly facilitated. If these practices are followed, and the rubber always weighed on the same scales (a.s.suming it to be perfectly dry when packed) complaints of "short-weight" should be infrequent.

"SHORT" WEIGHTS.--In some cases the occurrence of "short" weights on arrival at ports would appear to be inexplicable. It often happens that the const.i.tuent parts of wooden cases have been in stock for a considerable period. If for no other reason than that indicated below, all cases, either before or after a.s.sembling, should be thoroughly dried in the sun.

"Short" weight could be accounted for to some degree by a lack of observance of this elementary rule, as it is most probable that there would be a perceptible difference in weight of the wooden case in a drier atmosphere.

(_a_) If rubber is weighed in the box, and the average tare of the case deducted from the gross weight (in order to obtain the nett weight), any loss in the weight of the timber would appear as a deficiency of rubber at the distant port.

(_b_) Whether the same effect would be produced eventually in the case of rubber which is weighed before packing will depend upon the method of weighing at the warehouse. If the rubber is weighed in the box, any observed deficiency would be attributed to a loss of weight in the rubber.

PART III

MACHINERY AND BUILDINGS

CHAPTER XIII

_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 compet.i.tion 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 finis.h.i.+ng 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 bra.s.s linings for shaft-bearings. Cases are known in which a bra.s.s "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 bra.s.s 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 bra.s.s will be dealt with in a later chapter. But here again it is necessary to point out that such wear on bra.s.s liners may be caused by the standards (ends) of the rolls being eccentric; and the case may be a.n.a.logous to the placing of "new wine in old bottles."

_En pa.s.sant_ it may be remarked that in any case bra.s.s 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 pa.s.sable 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 finis.h.i.+ng 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 quant.i.ty 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 finis.h.i.+ng 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 finis.h.i.+ng machine (smooth rolls). With five macerators and intermediate machines working continuously, it will be more than the work of one finis.h.i.+ng pair of rolls to keep pace, especially as so much more care has to be exercised in finis.h.i.+ng than in rough crepe-making. The obvious course to adopt is to subst.i.tute 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 const.i.tutes 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 sc.r.a.p-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 finis.h.i.+ng 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.--

_Machine._ _Differential Ratio._

1. Macerator 32-17 2. Intermediate (coa.r.s.e grooved) 32-17 3. " (fine grooved) 30-19 4. Smooth (uneven speed) 30-19 5. " (finis.h.i.+ng) 25-24 6. " ( " ) 25-24

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:

-----------------+-----------------------------------+------------- | |_No. of Times _Machine._ | _Grooving._ |Rubber pa.s.ses | | through._ -----------------+-----------------------------------+------------- 1. Macerator | Deep horizontal grooves; | | square-cut, 5/16 inch 5/16 inch | | 5/8 inch s.p.a.ces | 3 2. Intermediate | Horizontal grooves; 3/16 inch | | 3/16 inch 3/8 inch s.p.a.ces | 2 3. " | Fine spiral grooves; 1/8 inch | | 1/8 inch 1/4 inch s.p.a.ces | 2 4. Geared smooth | Nil | 1 5. "Even" smooth | " | 1 6. " " | " | 1 -----------------+-----------------------------------+------------- | Total | 10 times -----------------+-----------------------------------+-------------

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 s.p.a.cing; others use a large diamond pattern. Similarly various types of grooving are cut in the intermediate rolls.

[Ill.u.s.tration: A BATTERY OF MACHINES.

On the left, light marking rolls for sheet rubber; on the right, heavy machines for crepe preparation. In the middle background, "sc.r.a.p-was.h.i.+ng"

machines outside the main building.]