200 



THE INDIA RUBBER AVORLD 



[April 



1 90 1. 



pass it once more between the calender rolls. The new strip 

 or facing now spreads over the surface of the packing and com- 

 pletes the process. Care should be exercised again in regard 

 to bubbles of air, as indeed should be the case whenever a new 

 layer is applied to any roll. 



The calender rolls should always be adjusted so as to make 

 the sheet a trifle thicker than is required in the finished goods. 

 This is to allow for shrinkage — and also for compression which 

 the packing undergoes while confined between the plates of 

 the hydraulic press. 



Next we may take up the C. I. packing, which differs from 

 the above in several ways. The sheeting used in this packing 

 is frictioned on both sides, as the rubber is applied to both 

 sides of the cloth. With this packing we have two facings, 

 also, instead of one as in the above. 



We now take this roll of sheeting and hang it up in front of 

 the calender as before, then take the batches — those made from 

 the trimmings — and warm them up on the mill as before, and 

 when at the proper heat feed into the calender, at the same 

 time the sheeting is passed into the rolls and the compound 

 spreads over the surface of it. When one side of the sheeting 

 has been covered, turn the roll around and run a coating on 

 the other side. Continue this process until the desired num- 

 ber of plies isobtained. Thus the sheeting becomes imbedded 

 between the various layers of rubber. These layers are calen- 

 dered sufficiently thin to permit of the two facings being still 

 added to the outside and yet have the desired thickness when 

 finished. All is now ready for the outside layers or facings, 

 and these are applied to the roll as described in the case of 

 C. O. S. packing, except that a facing is run on each side of 

 the roll instead of one side as in the former case. 



The third kind, or C. B. S. packing, is constructed in much 

 the same manner as described, the exception being found in 

 the facing, which, instead of being composed of rubber, has a 

 layer of sheeting, frictioned on one side, applied to each side of 

 the sheet of packing. The friction side of the sheeting, of 

 course, goes next to the packing. This completes the con- 

 struction or building-up process. 



These three kinds of packing constitute the so-called cheap 

 grades of sheet packing, and the vulcanization is the next pro- 

 cess it undergoes. This description has been reserved until 

 now, as the curing process is the same in case of all the three 

 different kinds. 



The roll of packing is now taken to the hydraulic press ; but 

 before this process begins the surfaces of the packing ar« dusted 

 with powdered talc or soapstone, to prevent the plates of the 

 press from sticking to it. 



There is used generally for this purpose a belt-press. This 

 press is made in various lengths; but, for convenience, we 

 shall select one of 25 feet. The upper plate of the press is 

 made stationary by numerous supports or legs on either side, 

 securely fastened into the floor or base of the press. The lower 

 plate is made to move up and down between these two rows of 

 supporters, so that when raised to the level of the upper plate 

 the two plates will meet perfectly flush. The lower plate is 

 raised and lowered by means of hydraulic pressure. These 

 plates are several inches in thickness, and are hollow to permit 

 steam to circulate evenly against the surfaces of the plates for 

 the purpose of heating them. 



In use, first heat the plates of the press to the temperature 

 desired. The bottom plate is then lowered and the end of the 

 packing pulled through to the opposite end of the press. Now 

 turn on the hydraulic pressure, and the plate rises until the 

 packing is firmly pressed against the upper one where it remains 

 until sufficiently cured. 



This done, again lower the plate and pull through one more 

 length of packing, and so on, until the roll is completed. The 

 pressure of these polished plates gives to the packing a smooth 

 surface while the heat is curing it. The roll should now be 

 taken to a long zinc covered table, where the rough edges are 

 trimmed ofl with a sharp knife ; giving the packing a neat ap- 

 pearance. One of the most important features in the manu- 

 facture of cheap packing is this curing process. The tendency 

 is to over-cure, and this should be avoided ; because cheap 

 packing, being composed largely of shoddy, and in many in- 

 stances semi-cured stock, will very naturally become hardened 

 with little age. Therefore, it should have a soft cure to insure 

 pliability and longer life. 



[CONTINUED NEXT MONTH.] 



DRYING WASHED RUBBER. 



BY AN ENGLISH CONTRIBUTOR. 



THE subject of the drying of washed rubber is an important 

 one, and I read what Mr. Pearson has to say on the sub- 

 ject with much interest. In the present state of business it 

 would of course be quite impossible to revert to the old order 

 of things, and allow the rubber a long period of time for drying 

 and maturing, even if the advantages attending such a proceed- 

 ing could be considered as demonstrated beyond doubt. It may 

 be taken that the average duration of time occupied in drying in 

 British works is five or six days, though this would be shortened, 

 if there was plenty of drying room available, by rolling out the 

 sheets thinner. Nine-tenths of the water can be removed in 

 a warm chamber supplied with a fan in the space of a few 

 hours, as the bulk of the water is loosely attached to the sur- 

 face of the rubber. It is the small portion which is in the pores 

 of the rubber which is difficult to remove, as, if not chemically 

 combined as a sort of hydrate, it is certainly tenaciously held. 

 The more or less speedy removal of this portion depends upon 

 the thickness of the sheet, and the heat of the drying chamber, 

 the presence of a current of air doing but little to effect its 

 removal. One prominent British firm dries its rubber in half 

 the time taken by a neighboring rival firm by rolling it out 

 much thinner, but then the one firm has plenty of available 

 drying room, while the other is somewhat cramped and would 

 find any extension a decidedly expensive proceeding. Where 

 there is a rush of business the amount of time taken in drying 

 is a matter of great import, and considerable interest therefore 

 attaches to the process of drying for a few hours at a high heat, 

 which is mentioned by Mr. Pearson as having been done for 

 some years in a certain works. I have not heard of anything of 

 the sort being tried in England, and cannot imagine that it 

 would prove desirable for any but the best rubber. I did not 

 notice any reference in the book to the vacuum system of dry- 

 ing rubber, originating in Germany, and which has been so per- 

 sistently exploited and advertised. It has certainly been 

 adopted by one or two firms who did not allow themselves to 

 be alarmed by the initial outlay, but it cannot be said that it 

 has been extensively adopted in Great Britain, whatever may 

 be the case elsewhere, and I am inclined to believe that first 

 cost of plant is not the only fact which has militated against 

 its wider use. 



A NEW schedule of export duties was to go into effect in 

 Colombia on March i, in which the rate levied upon India- 

 rubber is 5 pesos per quintal of 100 pounds. The peso was 

 quoted lately at 42.7 cents. United States gold, which would 

 make the duty equal to $2.1^/4 cents per 100 pounds. The ex- 

 port of Colombian rubber is about 1,000,000 pounds a year. 



