Figures obtained from the actual working of a drier in Ceylon are given below:
| Chamber 1.—Temperature 160°-180°F. | Chamber 2.— Temperature 150°-165°F. | ||||||
| No. of Tray. | Drying Period. | Weight of Wet Rubber. | Weight of Dry Rubber. | ||||
| Hrs. | Mins. | Lbs. | Lbs. | ||||
| 1 | 1 | 22 | 7 | 1⁄2 | 6 | Worked similarly | |
| 2 | 1 | 42 | 7 | 1⁄2 | 6 | to No. 1. Yielded | |
| 3 | 1 | 57 | 7 | 1⁄2 | 6 | in 2 hrs. 23 mins. | |
| 4 | 1 | 57 | 7 | 1⁄2 | 6 | 703⁄4 lbs. dry rubber, | |
| 5 | 1 | 57 | 7 | 5 | 3⁄4 | from 871⁄2 lbs. wet | |
| 6 | 1 | 57 | 7 | 1⁄2 | 6 | rubber. | |
| 7 | 2 | 0 | 7 | 1⁄2 | 6 | ||
| 8 | 2 | 0 | 7 | 1⁄2 | 6 | ||
| 9 | 2 | 11 | 6 | 1⁄2 | 5 | ||
| 10 | 2 | 11 | 7 | 1⁄2 | 6 | ||
| 11 | 2 | 11 | 7 | 1⁄2 | 6 | ||
| 12 | 2 | 18 | 7 | 1⁄2 | 6 | ||
| 88 | 1⁄2 | 80 | 3⁄4 | ||||
It will be seen, therefore, that the drier had an output in 2 hrs. 23 mins. of 1411⁄2 lbs., which is at the rate of 1 lb. per minute approximately.
As the rubber leaves the driers it resembles vacuum-dried rubber in being surface-sticky. This stickiness is only temporary, and is got rid of by passing the crepe through wet rolls. Opinions differ as to when this rolling should be given. On some estates the rubber is only allowed to cool a little before passing through the rolls; on others it is given a day or so before rolling. The methods of rolling also differ. In some factories the rubber has been cut to lengths before drying, and these lengths are merely rolled together by simple pressure. Other estates prefer to re-macerate the crepe while still fairly warm and soft. It is probable that little harm, if any, results from this re-maceration while the rubber is soft, as it is more easily worked in this condition. The thick rubber is then generally hung for a few days to air-dry before packing. As most of the moisture taken up by the dry rubber is surface moisture, three or four days is usually found ample for air-drying.
Michie-Golledge System.—The Michie-Golledge system comprises a process of preparation and drying. The latex is diluted with two, three, or four volumes of water and coagulated with acid in a vessel which is rotated with a churning motion. In this cylinder there are curved and fixed blades. The revolving cylinder and its ribs force the latex against the curved blades so as to cause an eddy in the middle of the machine. Here the rubber coagulates and accumulates, the remaining liquor whirling round outside the blades. It can be imagined that with such dilute latex, the coagulum is very soft and spongy. This soft mass is passed through a machine which cuts it into “worms” about 3⁄16 inch in section. These are placed upon wire trays and dried by means of hot air. The “worms” when dry are re-macerated and built up into medium and thick crepes. The colour of the rubber prepared by this process is usually very good. When treated in a Colombo drier the “worms” usually require about two hours to dry, so that crepe rubber may be packed at latest on the fourth or fifth day, as in the case of vacuum-dried rubber.
Rate of Air-Drying of Crepe Rubber.—In spite of the facts that some estates have been making thin pale crepes for years, and that so much has been written concerning the preparation of this grade of rubber, one occasionally meets with a case in which an estate seems to be unable to prepare thin pale crepe, or if it does the period of drying is much longer than obtains on most estates.
Again, when cases of infection by spot disease in fairly thin crepes are submitted, it is usually found that the particular crepes are of that type which, though fairly thin, show whitish spots of moisture when the bulk of the rubber is nearly dry. This type of crepe is to be noted for the excessive period of drying in comparison with other crepes of equal thinness. It has been advanced elsewhere[12] that a factor of the most considerable importance in the rate of drying of crepe rubber is the type of drying-house and its situation. This accounts very largely for observed differences in the rate of drying of thin crepes on different estates. Yet even where two drying-houses may be of the same type, and the situations may be comparable, one still observes that one thin crepe dries more quickly than another. It has been remarked also that a thin crepe in one old drying-house dries in a shorter period than a similar crepe in another more modern house, although the methods of coagulation and preparation exhibit no apparent diversity. In all these conflicting cases allowance is made for the weather conditions, and the observed differences seem to be inexplicable. It has always been the opinion of the writers that the actual rolling of the rubber plays an important part in determining the rate of drying of crepe, apart from the question of thinness; and it seemed possible that this factor would account for the discrepancies noted above, either partially or wholly.
[12] “Preparation of Plantation Rubber,” Morgan, 1913, chapters xii. and xiii.
With a view to determining to what degree the drying of crepe rubber was hastened by the extent to which the rubber was rolled, experiments were made. It was hoped, also, that some idea would be gained of the particular stage in crepe rolling which had the greatest effect upon the rate of drying. In preparing crepe in the estate in the ordinary way the coagulum is passed through three sets of rollers, and the stages may be described as:
(1) Rough rolling.