The Preparation of Plantation Rubber Part 12

Owing to the existing differences in equipment and speed of drive, etc., the regular practice of any one estate may be unsuitable for another. It remains, therefore, a matter of study for each estate to discover the minimum number of times which rubber should pa.s.s through the machines, consistent with the factors indicated above. In any case it may be a.s.sumed that if any factory cannot prepare a good crepe by pa.s.sing the rubber, say, twelve times through the rolls, there is some deficiency in the machines, or of speed; the coagulum may be too hard, or the rolls may be badly worn.

LOWER GRADES OF CREPE RUBBER.--Even a few years ago it was plain that the lower grades of crepe (_i.e._, all grades lower than first latex rubber) were not sufficiently appreciated in the market. There was often a marked difference in price between a first-grade crepe and crepe made from naturally coagulated lump. This arose chiefly from lack of knowledge. It has since been recognised in some measure that no reason exists for such a wide difference in price, and more recently the margin between even the first-grade rubber and the lowest grade of sc.r.a.p rubber has been a gradually diminishing one. Providing sufficient care is exercised in the preparation of the lower grades, one would expect to see but very small difference in prices between any two grades. It is true that adequate attention has been given to the preparation of the sc.r.a.p grades only in comparatively recent years, and it is acknowledged that when high prices were ruling for first-grade rubbers sufficient attention was not generally given to the subject of the preparation of the lower grades.

NATURALLY COAGULATED LUMP RUBBER.--The grade of rubber made from the naturally coagulated lump which forms in buckets and carts is usually of a mixed colour, due to the fact that the lumps oxidise very quickly. When they are allowed to remain overnight before being machined, it can be imagined that the colour of the dry crepe would be very dark, or would contain very dark streaks. Such is ordinarily the case, unless special precautions are taken.

Providing that the coagulated lump is free from bark, leaves, and leaf-stems, and certain other precautions taken, the difference in price between coagulated-lump crepes and first-grade crepes should be very slight. Too often, however, not sufficient supervision is given to the coagulated-lump rubber, and it is common to see it come into the factory containing leaves and bark. These should be picked out before the latex is strained, but obviously it would be better to ensure that they did not enter the buckets in the first place.

It would seem reasonable to suppose that if some means could be employed for preventing or checking the surface oxidation of naturally-coagulated lump rubber, there would be a corresponding improvement in the colour of the dry crepe. That such a method is practicable has been demonstrated on many estates. The lump when lifted out of the latex is allowed to drain for a few minutes, and is then (without squeezing) placed in a dilute solution of sodium bisulphite. A 1 per cent. solution is sufficiently powerful. It is not to be thought for a moment that by the use of sodium bisulphite any previous oxidation will be counteracted; all that is claimed for the treatment is that any further surface oxidation will be checked, and the rubber may be allowed to remain until the next day, for working, if it is so desired. It will probably be found that quite a quant.i.ty of latex has been expressed from the lumps by contraction, and acid may be added to obtain the rubber from this. On other estates the lump rubber is worked on the machines as it is received, and the resulting crepe is submerged in a weak solution of sodium bisulphite over-night. It is then rinsed in water and hung to drip before weighing and placing in the drying house. Under certain conditions some of the lump rubber darkens rapidly during transport to the store, and any such oxidised portions must be rejected if a uniform colour is to be expected in the crepe.

Following the procedure indicated above, some estates find it possible to prepare from naturally coagulated lump rubber a crepe which can be cla.s.sed as No. 1 grade.

SKIMMINGS AND WASHINGS.--The skimmings of tanks, as already shown, may be prepared sometimes as a second quality of smoked sheet; but generally they are amalgamated with the rinsings of cups and buckets, treated with sodium bisulphite and acid, and made into crepe form.

The cup-washings, as they arrive at the store, represent a very dilute latex, the rubber from which is generally of a greyish colour.

Bucket-washings should yield a good type of pale rubber if they are obtained properly. To obtain the maximum quant.i.ty of good rubber the buckets should first be rinsed. A gang should be taken, a small quant.i.ty (say a quart) of water poured into the first bucket, and this dilute latex used progressively in all the buckets of that gang of tappers. The result is a fair latex which can be added to the bulk of No. 1 latex, provided it is free from dirt. Where sheet rubber is being prepared, carefully strained cup-washings or bucket-washings may be utilised in the dilution of the latex to the required standard, thus increasing slightly the percentage of first-grade rubber.

TREE-Sc.r.a.p.--As tree-sc.r.a.p is a naturally coagulated rubber, it should be expected to show up well in quality. This is usually the case; but from what has been said of the effect of sun-heat it will be understood that if trees are not regularly "sc.r.a.pped," there is a danger that the crepes may be found to contain tacky streaks due to the inclusion of old sc.r.a.p which has been sun-baked. In hot dry weather, on widely planted areas tapped on alternate days, it has been noticed that sc.r.a.p remaining for two days often exhibits a resinous appearance, and feels sticky to the touch.

If tree-sc.r.a.p is to be made as a separate grade, as used to be the general custom, care should be taken to see that it is free from bark and dirt. On some estates where sc.r.a.p-rubber is paid for per pound collected, it is usually the rule to insist that sc.r.a.p shall be washed free from dirt and picked free of bark. This course is to be commended, but might probably prove impracticable to the majority of estates. Theoretically, of course, the operation of machining should rid the sc.r.a.p of all traces of bark; but in practice it does not do so.

Some proportion of the tree-sc.r.a.p is usually found to be heavily oxidised, and naturally if a crepe of uniform colour is to be obtained these dark sc.r.a.ps must be rejected, otherwise dark streaks will be formed. Coolies should be instructed to sort out the dark pieces before arriving at the store.

BARK-SHAVINGS.--It has been intimated in a previous section that the method of obtaining and collecting bark-shavings varies with the type of labour employed.

Where the sc.r.a.p is removed from the edge of the bark on each occasion before tapping, the amount of rubber to be extracted from the dry shavings is very small--so small, in fact, that when the price of rubber is low, it is doubtful whether it pays to collect and work the material.

On the other hand, where trees are not "sc.r.a.pped" before tapping, the bark-shavings and tree-sc.r.a.p are collected together, and the amount of rubber derived from the mixture may be 30 to 40 per cent. upon the gross weight--depending chiefly upon the quality of the tapping (_i.e._, in this case, the thickness of the paring). Another factor influencing this figure would be the effect of using an anti-coagulant on the cuts.

Bark-shavings entail such wear upon the ordinary machines during working, especially if fairly free from rubber, that unless the factory is equipped with a special "sc.r.a.p-washer" it is advised that this material should be sent for working to a factory having the necessary equipment. Whenever possible, bark-shavings should receive treatment on the day of collection.

It used to be quite common to see heaps of bark-shavings acc.u.mulating on the floor of a factory, and generating excessive heat. Yet these heaps were allowed to stand about for a day or days. Is it any wonder then that tackiness was found to develop when the rubber was dry? It is here definitely laid down that no heaps of bark-shavings should be acc.u.mulated even for half a day. Tanks should be provided in which the shavings should be submerged in water.

EARTH-Sc.r.a.p.--Of all grades of crepe this is the one most liable to become tacky in transit. This tackiness to a large extent cannot be avoided, as old pieces of earth-sc.r.a.p may be brought in amongst the bulk. Probably these old pieces have been exposed to the sun for days, and have become quite resinous. It would be practically impossible to go through all earth-sc.r.a.p in order to find these odd pieces, but unless this were done one could not guarantee that the earth-rubber would always be free from tackiness. The difficulty does not appear, however, on estates where earth-rubber is collected systematically at very frequent intervals.

FIBROUS MATTER IN LOW-GRADE RUBBERS.--It is sometimes found in this and other lower grade rubbers that pieces of cloth or cotton-waste are concealed. Coolies may have used them for cleaning cups, or the store coolies may have been at fault. Earth-sc.r.a.ps especially should be examined, before working, for such extraneous matter.

Sc.r.a.p-WASHERS.--These are heavy machines specially devised for the treatment of lower grade rubbers. In these the raw rubber is well masticated and freed from impurities, if the machine functions efficiently.

There are several types of these machines, all of which are efficient. That best known is the "Universal" washer, made by Joseph Baker, Sons, and Perkins, Ltd. (formerly Perkins Engineering Company). Coming into local favour during the War, the "U.E." sc.r.a.p-washer, made by the United Engineering Company (Singapore), gives very good service. The "C.C.C."

washer, made by the Colombo Commercial Company, is suitable for the purposes of an average estate. There are others, less well known. Most of these machines are made in varying sizes to meet the requirements of small, medium, or large estates; and if funds are available, a sc.r.a.p-washer should be regarded as an essential item in the machinery of any estate employing engine power.

The rate of output of sc.r.a.p-washers will depend mainly upon the speed at which they are driven, and when ordering the equipment it would be advisable to state the ordinary speed of the back-shaft, length of drive, etc. It does not follow that the larger the rate of output, the greater is the efficiency of the washer. The point is not as to what quant.i.ty of rubber can be taken out per hour, but what quant.i.ty is actually freed from impurities.

It is advisable for the superintendent to obtain a thorough knowledge of the general construction and principles of the particular sc.r.a.p-washer employed. In the past it was not uncommon to find superintendents innocent of the fact that a certain type of washer possessed movable parts upon which the efficiency of the cleansing largely depended. It was often found that these parts, which were intended to be removed and cleaned at intervals, had become firmly fixed and could not be removed for inspection.

It must be recognised also that the machines are liable to considerable damage if extraneous substances are allowed to enter--for example, tapping-knives, stones, pieces of iron, spouts, etc., which are sometimes present in the loose sc.r.a.ps of rubber or shavings, owing to the carelessness of coolies. Under the best regulated-system, such accidents occasionally occur, but a great deal of trouble could be avoided by having it understood that each charge must be sorted over before entering the washer.

Again a deal of extra work, and much wear and tear, is caused by the _abuse_ of the sc.r.a.p-washer--_e.g._, in the cleansing of earth-sc.r.a.p. As this reaches the factory it often contains a quant.i.ty of internal or adhering earth. Before entering the washer a good proportion of the external soil could be removed if the sc.r.a.ps were thrown into a tank and given a thorough soaking and stirring. In a similar manner dry bark-shavings, which have been allowed to acc.u.mulate, could be softened.

In the actual working of sc.r.a.p-washers instructions are generally given by the makers. These sometimes advise the introduction of warm water (or of steam into the cold water supply) for an interval during the working of each charge. Where possible, such instructions should be followed, as by this means the individual pieces of rubber are ma.s.sed together, in the final stage, into a "sausage" form which is easy to transport and to manipulate in the ordinary crepeing battery.

COMPOUND CREPES.--The att.i.tude of both buyers and sellers with regard to the types of lower grade rubbers appears to be changing. In the past, from any one estate there might be obtained as many as six grades of crepe below No. I. These comprised:

(1) A pale rubber (often streaked) obtained from coagulation of cup washings and bucket rinsings.

(2) A pale rubber (often streaked) obtained by coagulation of the skimmings from the surface of the No. 1 latex.

(3) A streaked and dull rubber prepared from naturally-coagulated clots found in cups, buckets, and latex carts.

(4) A streaked rubber prepared from sc.r.a.p which had coagulated upon the face of the cut bark.

(5) A brownish and streaked rubber made by maceration of bark-shavings to which pieces of tree-sc.r.a.p adhered.

(6) A dark rubber, often tacky, prepared from sc.r.a.p found in or on the ground near the base of the trees. As it is often a matter of weeks between any two regular collections, it is easy to understand why the dry rubber was more liable to be "tacky" than any other grade of crepe.

It will have been evident to all who have acquaintance with these grades, as shipped from many different estates, that the diversity in the various shipments must have been rather bewildering. There appeared to be a regrettable lack of uniformity, even in the appearance of, say, a bark sc.r.a.p rubber from any two estates. When, in addition to these variations, the further complication of condition of cleanliness is introduced, one may realise the difficulty attaching to the evaluation of these rubbers as they appeared upon the market.

Although the foregoing paragraph is written in the past tense, it should be pointed out that within certain limits the trouble continues to exist with respect to the output of a great number of estates.

In the case of many, it has been realised that the manufacturer does not want to buy a large number of "parcels," all differing in some respect. It is probably correct to state that what a manufacturer requires is a big "parcel" uniform in appearance and treatment, even though the colour may not be so light as that of many smaller lots. This statement is modified with the proviso that the rubber, no matter what its colour or appearance may be, must be free from dirt, grit, and bark.

The difficulty of making a uniform product from several types of lower grade rubbers has been successfully solved on several estates by the preparation of a "compound" crepe composed of a mixture of the best lower grades in approximately definite proportions daily. Naturally the shade of colour of this compound crepe will depend largely upon the types of rubber employed, but as a rule it is somewhat darker than the highest of the types employed in the mixture. To the writers this seems immaterial as long as the manufacturer is offered a larger and more uniform lot which can be given uniform treatment in vulcanisation processes. Neither would it appear that the seller suffers any monetary loss. In point of fact it will be found probably that the reverse is the case. For instance, supposing it were decided to mix for a compound crepe--

(_a_) Naturally coagulated lump rubber.

(_b_) Tree-sc.r.a.p.

(_c_) Bark-shavings sc.r.a.p.

The product would be darker in colour than (_a_) and slightly better than (_b_). Let it be granted that there might be a monetary loss on (_a_), it is probable that there would be a slight gain in comparison with the usual prices obtained for (_b_) and (_c_). Now, as a general rule, the actual percentage of crop made into (_b_) is appreciably less than that made into (_c_) and still less than (_b_) and (_c_) together. Apparently, therefore, there would be a margin of profit on the whole by making a compound crepe.

It may be pointed out, on the other hand, that there might be expended on the manufacture of this crepe more time and labour, but as against this the labour of sorting and grading would be simplified.

Unfortunately this process is not open to estates which do not possess a sc.r.a.p-washer. _It is essential that the rubber should be free from grit, sand, and bark particles._ In the absence of a sc.r.a.p-washer for the cleansing of the bark-shavings, it would be futile to attempt to make a compound crepe containing that type of rubber, as one would run the risk of spoiling the whole. It seems certain that in course of time a sc.r.a.p-washer will be considered as necessary a piece of machinery as an ordinary crepeing machine in the factories of estates having sufficient means. Until that time the preparation of compound crepes must be the privilege only of well-equipped estates, unless other estates can send their lower grade rubbers for treatment in a sc.r.a.p-washer to their more fortunate neighbours.

In previous publications a diminution in the number of grades of crepe rubber has been advocated, and it is gratifying to find that in many cases the amending grades suggested have been improved upon. Many estates now make only three grades of crepe--viz.:

(_a_) No. 1. From latex coagulated in the store.

(_b_) No. 2. Compound.

(_c_) No. 3. Earth-rubber.

It will be seen that the compound crepe includes all types between fine pale crepe and earth-rubber. Naturally one could not safely recommend the inclusion of earth-rubber in any compound crepe, as the risk of possible "tackiness" in the whole would be serious. In the case of the bark-shavings rubber to be incorporated, it is first cleaned alone in the sc.r.a.p-washer.

Then all types are mixed together again in the sc.r.a.p-washer in proportions ruled by the experience of the usual average percentages of each grade of the crop.

Besides the estates having only three grades, there are others which make four--viz.: