August 1, 1921 



THE INDIA RUBBER WORLD 



813 



that leaves the cavity for the tread 11. To get the correct 

 measurements and area of this cavity, construction lines are drawn 

 every one-quarter inch on the bottom of the tread cavity, as 

 shown in the hne construction in Fig. 4. Using these construction 

 hues as points of measurements in the thickness of tread, a lay-out 

 such as shown in the lower part of Fig. 5 will give a correct 

 form of tread as it should come from the tuber or calender. In 



Fig. 6. Cord Tire TRE.\n Profiles 



like manner shapes and forms of treads can be figured out and 

 designed for cord tires, as shown in Fig. 6. 

 THE PLANIMETER 



A word might be said here as to the planimcter instrument. 

 Quite a number of people interested in the rubber industry are not 

 familiar with this instrument which is illustrated in Fig. 7. 



This ingeniously devised instrument is an indispensable aid to the 

 calculations and computations necessary in the work of tire con- 

 struction engineers, as it affords the most simple and convenient 

 method of measuring the area of plane surfaces on drawings and 



Fig. 7. Pl.-\nimeter for Me.\surixg .Are.\ of Pl.\ne Surf.^ces 



plans. -Accurate results can be obtained when the instrument is 

 properly used. In cases of irregular surfaces, the results ob- 

 tained cannot be equaled in accuracy by any compass and scale 

 method of mensuration ; and the time saved by using the instru- 

 ment in such cases is very considerable. There are two types of 

 planimeters : the polar planimeter and the rolling planimeter. 



The polar planimeter, as its name implies, revolves with its 

 tracer arm around a role, and is therefore limited in its application 

 by the length of the two arms, so that larger areas have to be 



Fig. 8. Dirty Cokes Cause Shy Side-Walls 



measured in sections. The rolling planimeter differs from the 

 polar planimeter in that it moves on two broad rollers. As the 

 travel of these rollers is not limited, areas of any length, but not 



exceeding in width the movement of the tracer arm, can be 

 measured in one operation. Contrary to the prevalent idea, plani- 

 meters are not difficult to use, but are very simple to operate. 

 THE NEED OF CL£AN CORES 



Although a tire may be accurately designed and perfectly con- 

 structed, it does not always follow that the vulcanized tire will be 

 a perfect product. One reason for shy tires is illustrated in Fig. 

 S. If the cores are covered with cement and dirt when assembled 

 in the shells, the result is shown at A, and consequently there 

 will be a large opening at B, allowing too much overflow, which 

 prevents proper compression, causing shy sidewalls. The remedy 

 is to keep the cores perfectly clean. 



IMPORTANCE OF PERFECT CORE ALINEMENT IN MOLDS 



.\nother instance of a perfectly good tire Ix-ing spoiled in cur- 

 ing is illustrated in F'ig. 9, where the core and built-up tire are 

 placed ofF-ccnter in the lower shell with the result shown at A 



A ij- - Upper Shell 



' in 



-Core 



~- Louver Shell 



Fig. 9. — Misplacing Tire in Lower Mold Causes Imperfect 



Tires 



and B. Thus when the upper shell, guided by dowel pins, is ap- 

 plied to the lower shell, the misalinement shown at D and £ 

 occurs, causing a greater overflow at A than at B. Uneven over- 

 flow results in open spaces through which live steam enters, 

 causing shy tires. The remedy is perfect alinement of the tire 

 and core, and the avoidance of moisture or water at P, which 

 would turn into steam under this heat and cause imperfect beads. 



A BATTERY TESTER NOT EASILY BROKEN 



Car owners whose cars are equipped with a storage bat- 

 tery will be interested in the 

 "Break-Not" battery tester. 

 This hydrometer syringe is 

 so constructed as to elimi- 

 nate to a large extent the use 

 of glass, and make it pos- 

 sible to carry in a tool box 

 without danger of breakage. 

 The manufacturer guarantees 

 the accuracy of the tester. 

 The float has large figures 

 on the scale which are easily 

 read and red danger marks 

 indicate whether the battery 

 is empty, half charged or 

 fully charged. The bulb is 

 large and made of strong 

 red rubber. The other parts 

 are: glass jar, hydrometer 

 and rubber jar or tip; all of 

 which are interchangeable 

 and replaced without diffi- 

 culty. The "Break -Not" 

 comes packed in a strong 

 chip-board mailing tube, with 

 metal screw cover, and com- 

 plete directions for making 

 storage battery tests. — E. 

 Edelmann & Co., 341 East 

 Ohio street, Chicago, Illinois. 



The "Break-Not" Battery Testei 



