March I. 1921 



THE INDIA RUBBER WORLD 



423 



REPAIRING BLOW-OUTS IN TRUCK TIRES 



Repairing a blow-out in a truck tire is accomplished in practi- 

 cally the same manner as for small type cords of passenger sizes ; 

 that is. cut the plies of cords square across from bead to bead 

 according to location of injury and simply make a lay-back nearly 

 the full length of the mold. Step down the necessary number of 

 plies outside and replace in the same manner, reinforcing the inside 

 with a cord shoe of as many plies as necessary, Repairing each 

 injury must necessarily be a case of judgment on the part of the 

 repair man. 



Number of Plies of Cords in Truck Tires 



6 and 7-inch tires usually have 10 plies of cord fabric 



8-inch lires usually have 12 plies of cord fabric 



9-incIi tires usually have 14 plies of cord fabric 



10-inch tires usually have 16 plies of cord fabric 



Table of Cures Showing Length of Time and Amount of 



Steam Pressure Where Combination Steam and 



Air Bag Is Used 



Tread Cuts 



Air Bag Cure 

 /C 



I \ 



Hours Minutes 



Where injury is ^-inch deep 1 ... 



Where injury is J^-inch deep 1 .^5 



Where injury is ^-inch deep 2 10 



Sections 



.Air Bag Cure Steam Bag Cure 



< ^- V , * ^ 



Hours Minutes Hours Minutes 



On 6-inch tire cure 1 '... 1 30 



On 7-inch lire cure 1 ... 1 40 



On 8-inch tire cure 1 ... 1 SO 



Sections Where Cord Patch or New Cord Fabric is Used Inside the 



Tire 



Air Bag Cure Steam Bag Cure 



, * ^ , * > 



Hours Minutes Hours Minutes 



On 6-inch tire cure 50 I 10 



On 7-inch tire cure 1 ... 1 10 



On S-inch tire cure 1 ... 1 10 



(Note : Cure with air in bag first, then tap bag and turn in steam. 



BUILDING UP RETREADS ON GIANT PNEUMATIC TRUCK TIRES 



No attempt is made to give a chart of specific widths to cut 

 stock for the building up of treads on the giant pneumatic truck 

 tires for the simple reason that the tires are of so many different 

 percentages of over-size as to make each job a case of judgment, 

 and also for the reason that the operator who is retreading these 

 large tires will have had sufficient experience in the other sizes, 

 so that specific sizes and directions are not necessary. 



The most important thing to bear in mind in building the tread 

 on a giant pneumatic tire is that the treads are semi-flat in design, 



Six-Inch Combination Non-Skid Retread and Section Mold 



thus making a shoulder on each edge of the tread and, therefore, 

 necessitating the application of more rubber on each side of the 

 tread. 



After the -tire is cemented, apply cushion gum from 3/32 to 

 5^-inch thick in the center and tapering off on the side wall to 



1/32-inch. Next, apply a breaker strip of about 5 inches on the 

 6-inch tire, 534 inches on the 7-inch tire and bY^ inches on the 

 8-inch tire. A wide breaker is necessary to avoid tread separation 

 on the edge of the tread. 



In building up the tread itself the best and easiest method of 

 getting the proper contour with sheet stock is to start out with 

 narrow strips on each edge of the breaker, cutting each additional 

 strip somewhat wider than the preceding one until a semi-flat 

 contour is obtained on the tread of the tire. Then by cutting 

 strips which lap from one side of the tire to the other, and each 

 ply a little wider than the preceding one, the proper shape tread 

 will be obtained. 



It is a good idea, in learning the amount of stock to apply, to 

 set the tire in the mold after it is cut down, noting carefully the 

 points which need the thickest application of rubber. It is also 

 a good idea to make a teinplate of metal or cardboard the shape 



Six-Inch Section Mold — Semi-Flat Type 



of a cross-section of the mold to place over the tire to determine 

 the shape of the tread to be applied. On the 6-inch tire the 

 shoulder should be approximately 3/16-inch thicker than the cen- 

 ter of the tread ; on the 7-inch tire, K-inch and on the 8-inch 

 tire, S/16-inch thicker. 



A very excellent retread may be produced by having a special 

 stock for building these shoulders on the tire, that is, a cross in 

 compound between cushion gum and tread stock, or cushion gum 

 may be used for this purpose if no other resilient compound can 

 be obtained. This shoulder acts as a "shock absorber" for the 

 hard knocks to which a tire is subjected and eliminates the pos- 

 sibility of the tread separating at the edges on flexing point of 

 the tire. Tire manufacturers are now making camel backs for 

 truck tires, which eliminate a lot of the difficulties of building 

 from sheet stock. 



SOME "DO'S" AND "DON'TS" TO OBSERVE 



It isn't necessary to put the tire in the sectional mold, provided 

 a shoe is being cured to the inside of the casing and only a small 

 spot on the outside, as this can be very easily done by putting 

 the combination steam and air bag inside the tire, applying the 

 bead molds and cross-wrapping the tire and bead molds with 

 muslin, skipping the place where the raw stock on the exterior 

 must come in contact with the curing surface. The tire may 

 then be placed on the tube plate, so that the plate covers the 

 raw spot, the steam connection made to the steam bag and cured 

 in this manner. The weight of the tire itself will furnish suf- 

 ficient pressure to cure the tread spot. 



Inside sections may be cured in the sectional mold with the 

 steam bag without heat in the mold, provided there is no break 

 or cut to be repaired on the outside of the casing. 



An electric light attached to a long cord and covered with a 

 wire guard is a very valuable instrument to use in inspecting the 

 interior of casings, as it will show up every defect of the casing. 



