812 



THE INDIA RUBBER WORLD 



August 1, 1931 



Set-Screw io 

 hold Knife 



\T-Slide 



Fig. 



3. Flat Die-head for 

 Tubing Treads 



TUBING MACHINE TREADS 



There are two kinds of treads, the tubing and the calender 

 machine tread. The tubing-machine tread which is less costly 

 than the latter, is not always uniform in shape, due to carelessness 

 in feeding and main- 

 taining uniform tem- 

 perature of the stock. 

 A tubing machine can 

 be operated more effi- 

 ciently and give the 

 desired results if the 

 temperature of the ma- 

 chine can be kept con- 

 stant. Although it is 

 water-cooled, the op- 

 erator is usually relied 

 upon for his sense of 

 touch and feeling. 



A very good design 

 of a flat die head 

 for tubing treads is 



illustrated in Fig. 3, and has been used with a great deal of satis- 

 faction. 



ALLOWANCES FOR TREAD MEASUREMENTS 



After the treads are extruded from the tubing machine they are 

 put into books and placed on racks to cool. This is to allow for 

 variations in width and shape while cooling. When the treads are 

 cool they are cut to a given weight, plus or minus one ounce, 

 with a variation in specified length of plus or minus three inches. 

 The treads are then replaced in books and sent to the tire room 

 where they are to be assembled on the tire carcass. 



Before the tread is put on the tire carcass it is again weighed 

 for specified weight with no variations, except that of length in 

 which an allowance of plus or minus three inches is still main- 

 tained. This is a final check to avoid error— a rule that is not 

 always adhered to by the weighers as many cases have been seen 

 where a tread was stretched as much as ten inches. 

 ASSEMBLING TREADS 

 There are two methods of assembling treads used by the tire 

 finishers. The first, which gives the best result, is to stretch the 

 tire as it is put around the carcass, first one end and then the 



other. The second, which should 

 be barred and actually is pro- 

 hibited by some of the inspectors, 

 is to stretch the tread around 

 the carcass until the ends meet 

 .-ind then pull the tread from the 

 carcass, thereby shifting the 

 stretch. Here again the operator 

 is relied on to give the uncured 

 tread an even stretch so as not 

 to aflfect the contour of the tire. 

 If it is stretched too much at one 

 spot, it may be the cause of a 

 shy tire. Stretching the tread is 

 essential so that the edges of the 

 tread can be rolled down on the 

 sides without wrinkling. Some 

 tire companies have eliminated 

 this variable by a mechanical de- 

 vice. 



MAKING AND ASSEMBLING 

 CALENDER TREADS 



The calender tread, which is 

 the best-formed tread and can 

 be kept very near constant, is a 

 more costly operation. The most 

 common method of running calender treads results in many treads 

 being scrapped, due to air blisters. To eliminate this a tubing 



machine arranged back of a calender could be used. The tread 

 is then applied to the tire in the same manner as the tubing- 

 machine tread. 



CALCULATING WEIGHT OF UNCURED TREAD 



A formula for figuring weight of cured or uncured tread is 

 shown in Tabic 1. To use this formula a lay-out of the tire has 

 to be made similar to that shown in Fig. 4, first laying out the 



Fig. 4. Pneumatic 

 Tire Lay-Out 



RUBBEK 



Specific 

 Gravit-y 

 1.35 

 1.36 

 1.37 

 1.38 

 1.39 

 1.40 

 1.41 



1.4: 



1.43 

 1.44 

 1.45 

 1.46 

 1.47 

 1.48 

 1.49 



1.51 

 1.52 

 1.53 

 1.54 

 1.55 

 1.56 

 1.57 

 1.58 

 1,59 

 1.60 

 1,61 

 1.62 

 1.63 

 1,64 

 1.65 

 1.66 

 1,67 



Weight 



in Lbs. 



Per Cu. In. 



.04883 

 .04919 

 .04955 

 .04990 

 .05027 

 .05064 

 .05100 

 ,05 1 36 

 .05172 

 .0520S 

 .05245 

 .05281 

 .053)6 

 .05353 

 .05389 

 .05425 

 .05462 

 .05498 

 .05534 

 .05570 

 .05606 

 .1)5642 

 ,05679 

 .05715 

 .05751 

 .05787 

 .05823 

 .05860 

 .05895 

 .05932 

 .05968 

 .06004 

 .06040 



Table 1 



Formula for FtcuRiNc Weight of Cvred or 

 I'ncured Tke,\d 



Area reading of plantmetcr for uncured tread. 



.^rea reading of planimeter for cured tread. 



Circumference of tire. 



Cubical contents of uncured tread. 



Cubical contents of cured tread. 



Weight of uncured tread. 



Weight of cured tread. 



Diameter cf core. 



Thickness of plies of fabric. 



Thickness cvf padding. 



Thickness of breaker. 



Weight of cubic inch of uncured rubber. 



Weight of cubic inch of cured rubber. 



C 



V 



W: 



K —. 



P = 



n — 



R - 



C : 

 V : 

 W : 



[K 4- 2(F -f-P 4- B)] X 3.1416 

 CXA v=CXa 



V X R w = V X r 



(W) should correspond to (\v) \vithin 2 or 3 ounces. 

 If there is more difference in weight than that speci- 

 fied above, use the following formula to get proper 

 area for uncured tread, which will make (W) and 

 (wO correspond. 



: A 



R X (C — 3) 

 Note — [Explanation of (C — 3)] — Three is sub- 

 tracted to allcav stretch on uncured tread so that 

 the edges of tread can be relied down on sides 

 without wrinkling. 



core outline and then the contour of the tire from the dimension 

 on the mold. Then around the core lay out the thickness of the 



Result of Using 50% Scrap in *378 Stock 

 on Vh'-T>A Non-Skid S,S. Tires 



To obtain tiie following results, ttvo 4h"-S4 Tires */,34S,SS0 



and *l,i^S,464 were used. 

 From each tire, fVe sections were tafren and all the 



rubber was removed from fabric anct readings were 



taken with micrometer. 



S Plies Fabric 

 .047"6age 



Tire*I.I4S.580 



Section 



I 



2 



3 



4 



S 



A ye rage for S-Ply 



Actual for l-Ply 



Compression tor l-Ply 



Difference 



A B C D E 



181 



m 



IS2. 



.181 

 l8(\l7T[nS\l7i[l8} 

 .ISS 

 .178 

 182.173 

 047. m 



me 

 on 



.17^180 



ns 



I7SJ82 

 J7S\l78.m 

 .047mi\041 

 016 



.oil 



.oil 



.010 



Tire,*l.34S.464 



Section 



Average for S' Ply 



Actual for l-Ply 



.OSS 037 Ccmprtssion for I'Ply 



Difference 



ABODE 



.010 



.178 

 .181 

 .I8S. 

 .189 

 .131 

 .18S 

 .047 

 on 037 



.010 



I87\.l73 

 184 



ne\.iT7. 



.182. 



'.I9S 



J86 



047\O4T\.047 .047 



.on 



010 



181 J9£ 



Pesult:- Compression of each ply from .010" to .Oil" 



7 9 12 IS 17 20 21 21 !S 27^-.,f,^^u.^ .f gjfi,^ :„ :„^^., 

 6\ 8 \12' 11 16 I8\?l\22\24\26\ TS"' """"""^ "' ""'^^ '" ""^'^" 



: Other half exactly the same 



?0 19 18 n 16 15 14 IJ 12 1 110 9 8 7 6 5 4 3 2 1 <— Corresponding with reference numbers 

 Y. Tread 4^8" wide on section of tire layout 



Fig. S. Upper— Method of Obtaining Thickness or Fabric 

 Plies. Lower — Lav-Out for Determini.vg Tread 



Measurements 



various plies of fabric. The thickness of the fabric should not be 

 laid out for its actual thickness but for the thickness of the 

 fabric after it is vulcanized, or when it has received its final cure. 

 To give a clear idea of how this is established, two tires are 

 generally cut up, taking at least five sections from each tire and 

 stripping off all the rubber, tread, breaker and padding. Then 

 measure the thickness of the plies of fabric dit A, B, C, D and E 

 as shown in Fig. S. The average per ply is then taken which 

 gives the desired resuh. The padding and breaker are then laid 

 out as shown in 8 and 9 in Fig. 4 and then comes the side-wall 10 



