On the left, light marking rolls for sheet rubber; on the right, heavy machines for crepe preparation. In the middle background, “scrap-washing” machines outside the main building.
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.