August 1, 1920.] 



THE INDIA RUBBER WORLD 



The Manufacture of Battery Jars. 



|N 1919 there were in round numbers 7,000,000 passenger cars 

 I in use in the United States. If one-half of this number were 

 equipped with lighting and starting batteries that cost $40 

 each, the outlay would In; $140,000,000 for batteries. The esti- 

 mated number of starting and lighting batteries now in use is 

 5.253.073. valued at $236,388,285. Allowing three jars to a bat- 

 tery, 15,759,219 hard rubber jars, valued at $20,000,000, would 

 be required. 



It is estimated that there are 100,000 electric vehicles in the 

 United States, of which 50,000 are passenger and 

 50,000 are commercial. The cost of the average bat- 

 tery is about $600 for a passenger car and $1,000 

 for a commercial car: a total expenditure of $30,- 

 000,000 for passenger and $50,000,000 for commer- 

 cial cars. The average number of cells is 32 in a 

 passenger car and 44 in a commercial, or a total 

 of 3.800,000 jars. The average cost of a jar is 

 about $2, therefore the total expenditure for hard 

 rubber jars for electric vehicles will be $7,800,000. 

 There are other uses for storage batteries, such as 

 supplying light and for power and ignition purposes 

 in a great variety of applications. No substitute has 

 been found as yet that will replace hard rubber for 

 battery jars. 



Battery jars are made mostly on white metal forms 

 constituted of lead, tin and antimony. These forms 

 are easily made and with very little machining. 

 White metal is used in preference to cast iron al- 

 though cast iron is more durable. The reason for 

 this is that there are so many changes of sizes tnade 

 by customers and a variation of shrinkage allow- 

 ances due to the different kinds of raw material used, 

 that it is easier to melt and cast a core over than 

 it is to machine it. 



The core is shaped as shown in Fig. 1. The walls A are about 

 f^-inch thick and the grooves B vary in number from two to as 

 many as the customer specifies. At the bottom of the groove B 

 two or more small holes are drilled into the air chamber D so 

 that the ribs of the jar can be cured more easily, and then two 

 larger holes are drilled in the sides as shown at C. This is done 

 so that when the air expands in chamber D, while curing, it will 

 have a chance to escape and when the jar is being pulled from the 

 core, it allows an inlet of air so that no vacuum is created 

 between the jar and the core, thus making it easier to re- 

 move the jar. These holes can also be used with a mechanical 

 device to remove the battery jars from the forms after curing. 



four of which are used and then D is inserted to act as a core 

 for the air chamber. This core is slightly tapered on the sides 

 to draw easily when removing it from the mold. The core and 

 angle-irons should be heated up to very near the temperature of 

 inolten metal. This can be done by immersing them in a pot of 

 molten metal. .\s white metal has a greater specific gravity than 

 iron, the iron parts will float. These parts will, therefore, take 

 up enough temperature so as not to allow the molten metal to 

 chill too quickly when pouring and will then give the surface of 

 the form a very smooth finish. The metal is then 

 poured in this form and a long wire rod is pushed 

 in and out in the molten metal to remove any trapped 

 air that would cause air holes in the cores. 



The angle-irons A should be made very accu- 

 rately and of sufficient strength so that they will not 

 warp because of constant heating and changing of 

 temperature. 



.\ great deal of tin-foil about .OOS-inch thick is 

 used throughout the manufacture of articles made 

 from hard rubber, and the making of battery jars 

 is no exception to this rule. It helps to handle the 

 sheet rubber and is an asset in the vulcanization. It 

 also gives the outside surface a polished effect. At 

 one time the specifications for battery jars stipulated 

 this surface condition but now it is not required. 

 Before putting the jars in series into containers, the 

 acid sometimes splashed and frequently ran over the 

 sides, and if the jar was perfectly smooth the acid 

 would run off, but if the sides were rough as they 

 are when the jar is not made with tin-foil, the drops 

 of acid would adhere to the sides and make a rather 

 unsightly appearance. 



AhtT the stock is compounded it goes through a 

 process illustrated in Fig. 3. The stock is first warmed in a mill 

 shown at A and the operator then feeds the stock to the calender 



B. To keep the thickness of rubber more uniform and to 

 eliminate all air pockets, the stock is plied, two or more plies, 

 depending on the thickness required, on a large drum shown at 



C. This drum runs at the same speed as the calender B and is 

 approximately 3 feet 6 inches in diameter and is water-cooled. 

 The calender man applies a sheet of tin-foil to the drum C and 

 the rubber sheet is plied on this tin-foil. Another man handles a 

 hand operated conveyor shown at D and cuts the stock from 

 the large drum in two pieces and lays it on a tray. The width 

 of stock nm from tlie calender is the correct length for wrap- 



The molds used are of a collapsible type as shown in Fig. 2. 

 Various sizes of angle-irons A are made to agree with the va- 

 rious sizes of jars being made. The base B acts as a gage to 

 set up the angle-irons A and forms the rib places in the core. 

 The angle-irons .\ ar 



then clamped with special clamps C. 



ping around the core for making jars. It requires three men to 

 operate these machines. 



The next step is to cut these sheets to correct widths for the 

 jars allowing a surplus for trimming top and bottom. This is 

 done by laying the stock on a fiat, smooth table, marking with a 



