May 



1901.] 



THE INDIA RUBBER 'JVORLD 



231 



THE MANUFACTURE OF RUBBER PACKINGS. 



By John S. McClurg, M. S. 



[ CONCLUDED FROM LAST MONTH. 1 



ANOTHER grade of packing, commonly known as " pure 

 gum," is that which has neither cloth insertion nor 

 cloth applied to the outside. This usually has a much 

 better quality of stock than any of those already de- 

 scribed, as the rubber must give to the packing the strength 

 and firmness which in other cases have been imparted by the 

 sheeting. Here, also, more care should be exercised in the 

 preparation of the batches. They should be well ground and 

 mixed, and then permitted to dry and season before making up. 



When ready, a batch is taken to a mill and warmed up, pre- 

 paratory to building up the packing on the calender. The 

 writer has found that not enough importance is attached to this 

 w«rming up process by most manufacturers. If it is done prop- 

 erly and carefully, much of the difficulty in calender work can 

 be overcome. When the calender is at the proper heat, begin 

 to feed the compound into it and run out a thin layer of gum 

 to the length required in the roll. The roll is now run through 

 the calender again and another layer applied to it, and so on, 

 until the desired thickness is obtained, care being taken, of 

 course, while running, to prick all the air bubbles, thus permit- 

 ting the plies to come closely together, and also preventing 

 blisters in the curing. This layer process has a great advan- 

 tage over the process of running the full thickness at one time, 

 because it secures for the packing a more compact body and 

 greatly reduces the possibility of defects in the finished 

 product. 



The packing is now rolled up on a drum provided for the 

 purpose and, after being well wrapped with several thicknesses 

 of wet muslin cloth, it is consigned to the vulcanizer to be 

 cured, or rather semi-cured, before taking it to the press to be 

 plated, and the cure completed. This having been done, the 

 roll is now taken to the hydraulic press where the process is the 

 same as previously described, except that with pure gum pack- 

 ing the edges of the sheet should be well blocked up. By 

 blocking up is meant that two bars of iron the length of the 

 press, and the same thickness as the packing, are placed against 

 each edge of the packing one on each side in the press. This 

 prevents the packing from spreading or becoming porous on 

 the edges while subject to the heat and pressure. It is also a 

 saving as it does away with much of the trimming at the finish. 



The next, or the highest and best grades of packing — those 

 designed for resisting excessive heat — are, perhaps, the most 

 important of all the different varieties now manufactured* 

 These packings usually contain in their composition finely pul- 

 verized asbestos or some other material not readily affected by 

 heat. They are invariably subjected to high temperatures and 

 very often for considerable lengths of time. It is important, 

 therefore, that the composition should receive much attention 

 as to the ingredients which enter into it. Unusual care should 

 be exercised in milling and grinding the compound to insure 

 the even distribution of the various ingredients through the 

 entire body of the batch and to render it smooth and even. 

 After this has been done the batches should be piled up in a 

 dry place to season, dry, and harden. A couple of weeks is not 

 too long and will be found very beneficial. 



When the batches have been sufficiently dried they are taken 

 to a mill and warmed up as other packings, before sheeting it 

 out on the calender, and the roll is ready to be started. The 



heat of the calender rolls is an important item in the manufac- 

 ture of this packing, as much care must be exercised to prevent 

 any extraordinary swelling or shrinkage of the stock. Here, 

 too, the sheet is run off in layers as before described. As the 

 finished sheet comes from the calender it is wrapped upon an 

 iron drum, as are other pure gum packings, and then the out- 

 side is well wrapped with several thicknesses of wet muslin 

 cloth, and then consigned to the vulcanizer to be cured. After 

 this has been done the packing may be taken to the hydraulic 

 press and plated. With this packing the pressing process is 

 discarded in many cases and the packing is completed with the 

 removal from the vulcanizer. This leaves it with the impres- 

 sion of the muslin lining upon its surfaces, instead of the 

 smooth shiny surface imparted by the press. 



Experience long has taught that a long curing process at a 

 low temperature is the best of this quality of packing, as indeed 

 it is for any compound which contains a considerable propor- 

 tion of crude rubber. A short cure at a high temperature is 

 very liable to produce porousness and other defects, while the 

 long cure insures a solid compact body, more pliable and per- 

 fect. Pure gum square packing, which is so largely used, is 

 made in much the same manner as the pure gum packing. 



The batches are prepared and afterwards warmed up for the 

 calender in the same way, and are then sheeted out on the cal- 

 ender in lengths ranging from 12 to 20 feet, or whatever length 

 is desired in the finished coil. Here, also, these slabs are built 

 up in thin layers one top of the other until the desired thick- 

 ness is obtained. It is then sent to the vulcanizer to be cured, 

 after which it is taken to the hydraulic press and plated as be- 

 fore described. 



This being done, the slabs are laid aside to be cut up into 

 square sections. These slabs are never less than % inch in 

 thickness and range from that on up to 1 inch, and in some rare 

 cases to \% inches. To cut these strips the slab is laid on a 

 wide table where it is securely fastened to prevent motion 

 while being cut. The cutter is usually in the shape of a plane 

 provided with an adjustable knife which can be set at any 

 length. With this instrument the slab is cut into strips corre- 

 sponding in width to the thickness of the slabs. These strips 

 are now coiled up and securely tied, which completes the 

 process. 



This very nearly completes the list of rubber varieties ; the 

 next kinds to be considered are the duck packings or those va- 

 rieties composed largely of duck. Square duck packings pro- 

 vide for the consumption of large quantities of otherwise waste 

 pieces of frictioned duck which must naturally accumulate dur- 

 ing the manufacture of rubber belting. These odds and ends 

 of duck are cut into convenient sizes and filled into the center 

 or body of the slab of packing. The duck used in making this 

 kind is usually light weight belt duck — about 22 or 24 ounces. 



This duck is run over a series of hot iron rolls to eliminate 

 all the moisture, after which it is taken to the friction calender 

 to be coated on each side with rubber friction, which causes 

 the layers of duck to vulcanize securely together in the curing 

 process. The roll of duck is now taken to a room provided 

 with a table 50 feet or more in length, on which the duck can 

 be unrolled. The duck is stretched out on the table and cut 

 into bias strips about 3>^ feet in length until the roll is cut up. 

 These bias pieces are now laid end to end, lapping each over 



