THE INDIA RUBBER WORLD 



435 



Practical Advice to Repairmen. 



By A. B. Zwebell. 



IN MY LAST article' I related my experience of calling on some 

 fifty-odd tire repairmen throughout the East, and I will now 

 cover the high spots governing tire rebuilding, which should 

 interest both the user of retreaders, as well as those contemplat- 

 ing going into this line of business. 



Retreading is bound to be popular this year, and so long as 

 tires are high in price, and there appears to be no reduction in 

 cost of labor and material, and as worn treads represent only a 

 fractional part of the actual tire — 25 per cent to be exact, there 

 remains 75 per cent of the actual tire to be used, which, after 

 retreading will deliver from 2,500 to 5,000 miles service. An 

 economical person would not throw away a perfectly good suit 

 of clothes just because the lower edge of his trouser cuff was 

 worn. He would have them repaired, because it represents only 

 a fractional cost of the suit. 



The tire manufacturer aims to build a balanced tire — one in 

 which the tread is just thick and tough enough to last as long 

 as the carcass. It would be poor business to follow another 

 line, for if the tread was two inches thick (where one inch would 

 suffice), a customer would naturally say the fabric was rotten 

 if the tread was good and the fabric broken, or separated at 

 the end of 5,000 miles. Reverse the situation ; too much fabric 

 is just as bad as not enough, for the tire could not perform the 

 dutj' it was designed for, and instead of flexing it would be too 

 stiff and eventually break down. Ask any tire manufacturer 

 and he will tell you what has made the six-, seven- and eight- 

 inch truck tire possible — cord construction, for one thing, and 

 development. So you as a tire rebuilder, should be able to 

 develop along the same line as the tire manufacturer, and soon 

 be able to rebuild a tire giving 6,000 to 8,000 miles. What exper- 

 ience has done for the manufacturer it will do for you. 



Data gathered from Te.xas to Canada and from New York 

 to Seattle demonstrated that many combinations of repair 

 material were being used. One repairman used one brand of 

 cement, another brand of breaker fabric, another brand of 

 cushion gum and still another brand of tread stock. This practice 

 I should be discouraged, for a manufacturer or jobber who sells 

 you a cushion gum with a recommended cure of 50 pounds at 

 50 minutes, and a tread stock with a SO pounds at 50 minutes 

 cure is not giving you a combination that will make a successful 

 retread. The cure recommendation no doubt was based on a flat 

 pipe ; in other words, when the uncured rubber comes in direct 

 contact with the mold itself (rubber being a non-conductor of 

 heat), the tread would be sufficiently cured, whereas the breaker 

 fabric and cushion, not forgetting the cement, would be greatly 

 undercured. 



Retreading stocks are then not merely ordinary repair 

 materials, but "specially compounded retreading stocks," de- 

 signed, compounded and balanced. A retreaded tire requires a 

 tread stock that is softer than the ordinary run of repair material. 

 It resists road shocks and saves the carcass from bruising. It is 

 important to use not too much or too little material; an extra 

 ply of tread gum will not necessarily add a thousand miles of 

 extra wear. It may decrease the wear of the tire even to a 

 greater extent, for it will have a tendency to undercure the 

 cushion and cement, which is a vital part of the entire job. 



Don't use cheap repair materials and expect your retread to 

 stand up. Tread stock that can ordinarily be purchased at 35 

 cents to 40 cents a pound will be expensive compared with tread 

 stocks selling at 80 and 90 cents a pound. Comparing these 

 stocks on a 34 by 4 carcass, the cost was found to be 35 cents 



> "Practical Hints on Retreadi 

 1919, page 159. 



ig," The India Rubber World. December 



more than when retreading with the 80- and 90-cent stock, but 

 the results were worth the difference. Forget you are getting 

 a bargain when a salesman offers you repair stocks at 35 cents 

 a pound. Good crude rubber costs around 50 cents a pound, 

 and when you buy retread stock make up your mind you are 

 buying something else besides rubber. Analyze your own situa- 

 tion, cut off a pound of cheap gum, and a pound of high-grade 

 stocks, compare the gage of the stock and figure the difference 

 m yardage. Remember, rubber is one of the lightest ingredients 

 going into the compound, and the lighter in weight per yard 

 the higher the rubber content. Rubber stock has always been 

 sold by the pound, but I contend it should be sold by the square 

 yard or per tread of given dimensions. 



The proper selection of a carcass is another vital matter, and 

 while we can't look between the plys of fabric, we can avoid a 

 lot of trouble by being careful, making a thorough examination 

 and turning out a satisfactory job. 



Start your work with a good foundation. Give the cement 

 a clean new surface to cling to ; remove the outside ply of fabric 

 and you eliminate one of the worst enemies— dirt. Make up for 

 the loss of the oUcside ply by vulcanizing a 3-ply liner inside, 

 strengthening and building service into your tire. Vulcanize 

 the liner in. Do not merely cement it in. By vulcanization it 

 becomes a part of the tire, strengthening the weakness you over- 

 look and cannot see. 



Rebuild your tire. Do not simply retread it. When the tread 

 is gone, your tire needs an overhauling and the cost of rebuild- 

 ing is only a trifle more than retreading. Repairs should be 

 made after the tread has been removed. Do not make a repair 

 and retread at the same time. Your cure is not long enough 

 to reach through to the inside of the tire. Make all repairs first 

 and semi-cure, then rebuff the tire previous to cementing the 

 carcass for the retread in the usual way. 



Rim cuts can be successfully repaired, but judgment should 

 be exercised by the repairman. A rim cut caused through acci- 

 dent, such as a bad bump or curb bruise, can be successfully 

 repaired, for the chances are that the balance of the tire is 

 HI first-class condition. But a rim cut caused by a tire being 

 run underflated is very much of a gamble to repair, for the 

 chances are it is weak in another place and will soon blow out 

 from the strains. 



Resetting treads can be accomplished very successfully on the 

 following occasions : 



1. If the side walls of the carcass were oil-soaked and the 

 rubber pulled off while being removed from the mold. 



2. Where the carcass blew out at the bead after running a 

 short distance. 



3. When the fabric separated due to moisture. 



To remove the tread, cut along the tread line with a knife 

 around each side of the tire to the fabric. Pry loose with a prod- 

 ding tool or screw driver and work a section loose. Then insert a 

 broom handle and, with a little effort, time and patience this 

 entire tread can be removed in one piece. An easier method is 

 to cut across the tread and pull it off in the regular manner. 

 The latter way is much easier, and the results are as good, the 

 only difference being the fact that you have to resplice the tread, 

 hut tliis is an easy accomplishment. 



In resetting a tread use one new ply of cushion gum only, as 

 the breaker fabric will come off and adhere to the tread. It is 

 advisable to let the cushion gum extend down the side of the 

 tire one-half to three-quarters of an inch in order to piece in 

 new strips of tread stock, trimming them off flush so as to 

 make a neat job, otherwise there will be an offset. Don't over- 



