May I, 1908.] 



THE INDIA RUBBER WORLD 



251 



The Tubing Machine in Insulation Work. 



By a Factory Superintendent. 



THE usefulness of the tubing machine is not confined to the 

 production of tubing for the druggists' sundries trade, or 

 to tlie material from which jar rings are made, or to the 

 solid bodies which evolve into solid carriage tires, and the great 

 number of articles that are cured in molds. It is possible to 

 produce in a day's run from a modern tubing machine rubber 

 for the insulation of as much as six or seven miles of wire. 



While speed is desired and essential, in no work done by the 

 tubing machine are the conditions more exacting. Where the 

 tubing machine is used in preparation of stock for mold work, a 

 certain latitude may be allowed. Then, too, the enclosing walls of 

 a mold and the pressure of the curing plates exert a powerful in- 

 fluence toward making a stock behave itself. In the ordinary run 

 of insulation for wire, however, a higher standard is required. 



In the first place, stock for this purpose must be so compounded 

 as to eliminate possibility of "blowing" or departing in any par- 

 ticular from the outside diameter required, for there are in the 

 curing process no inclosing walls to enable it to keep its shape 

 or size. In common with other stocks, that used for insulation 

 must be prepared upon the mixing mills until it is of the requisite 

 softness to work readily in the tubing machine. An intractable 

 compound not only delays the speed with which the machine may 

 be run but, by remaining longer in process than usual, develops a 

 tendency to "cure" in the body of the machine, or break up into 

 checks or corrugations on the wire, thus reducing to minimum its 

 qualities as an insulator. 



The tubing machine for this work does not differ essentially 

 from that used in mechanical lines, except in the "head." The 

 ordinary tubing machine head is so arranged that the compound 

 is forced out in a line with the machine body or barrel. In fact, 

 in the early days of seamless insulation the attempt was made 

 to cover wire in the same manner, but results were unsatisfactory. 

 Machines were constructed with 3 hole in the center of the drive 

 wheel which continued through the screw or worm, permitting the 

 passage of the wire to be insulated to, and through the die in the 

 head of the machine. This worked all right with certain com- 

 pounds, but it was found difficult to control the thickness of in- 

 sulation thus placed upon the wire. 



An inventive genius finally suggested that the wire, instead of 

 passing through the body should pass through the head only, at 

 right angles to the plane of the machine. When tried it was 

 found that this style of tubing machine head when supplied with 

 a die that could be depended upon, furnished practically a uni- 

 form thickness of insulation on any size wire, and that this new 

 and peculiar method of ejecting the contents of the machine re- 

 sulted in a more compact covering for the wire than it had been 

 possible theretofore to obtain. Dies for this work are made in 

 two parts, occupying opposite sides of the head of the tubing ma- 

 chine, and so adjusted as to permit of the insulation contents is- 

 suing in but one direction. 



The adjustment of the die is a nice operation, for, unless it is 

 properly and securely centered, the insulation will be thicker on 

 one side than upon the other, and a uniform thickness of wall is 

 essential to secure the best dielectric resistance of which a com- 

 pounded stock is capable. It is equally necessary that the ma- 

 terials entering into the compound be free from anything tending 

 to interfere with the passage of the electric current. For a 

 grain of sand, a minute particle of bark, wood, or fabric, obstruct- 

 ing the die might throw hundreds of feet of insulation "out of 

 center" before discovery. This means always delay and loss. 

 Submarine cables are sometimes made up from conductors run in 

 mile lengths. This insulation must be perfect, and where the tube 



machine work is interrupted as described, the entire run is re- 

 jected and the wire stripped. 



A tubing machine equipped for insulation work would have the 

 following accessories : In front a revolving table holding the coil 

 of wire to be insulated and an automatic device for measuring 

 quantity of wire used. Back of the machine is a table 15 feet long, 

 one foot wide, along which passes the newly covered wire to be 

 wound upon a drum or into a pan. This narrow table has, imme- 

 diately back of the tubing machine, a closet with sliding doors, 

 and supplied with heat from the steam pipes, for holding the com- 

 pounded stock that is to be used in the machine. This warmed 

 closet is necessary that its pliability or ductility may be retained 

 until used. The last third of this table is without top, which per- 

 mits the wire in its passage to sag, more or less, forming slack. 

 This is necessary that the soft insulation material be not marred, 

 nor wound upon thfe drum so tightly as to flatten it. Winding 

 upon a drum or in a pan is done by hand. 



These drums are of steel, and consist of a cylinder with raised 

 sides to hold the wire in place. They are two feet wide and dif- 

 ferent diameters, and sometimes made so as to telescope, that is to 

 say, each drum fitting into the hollow interior of the next larger, 

 thus permitting a large quantity to be vulcanized at one heat. As 

 a rule drums are used for the harder, cheaper stocks. The work- 

 man stands on a small platform that he may work upon the up- 

 per surface of the drum. This he turns, matching the speed with 

 which the wire comes to him. He guides the wire, laying it 

 closely in course, and layer on layer. 



.\ tubing machine is sometimes fitted with speed pulleys, but the 

 insulation stock really sets the pace. If it is a "rich" stock, that 

 is, one containing a large percentage of rubber, it could be run 

 upon the wire at great speed, say, three-quarters of a mile per 

 hour. Such a stock, however, would be placed in a pan rather 

 than upon a drum. As the rubber covered wire is coiled into the 

 pan, it is bedded in talc, the greatest pains being taken to avoid 

 abrasion. These pans are made of heavy galvanized iron rein- 

 forced with strip and angle iron. They are pivoted to an iron 

 stand and take their speed of revolution from an overhead pulley. 



-A rare but none the less valuable addition to the equipment 

 of a tubing machine is a thermometer. By drilling a small chan- 

 nel in one corner of the head, large enough to hold it, the oper- 

 ator can, at any time, ascertain the heat and thus intelligently 

 govern one of the essentials to first class production. There is 

 doubtless a lot of intelligence at the command of an experienced 

 operator who uses his sense of touch as guide to proper condi- 

 tions, but the use of a thermometer has much to recommend it. 



It has been urged that a point in favor of insulation applied in 

 the form of strips lay in the application of successive layers in 

 one operation. The chance that an extra coat or two would close 

 possible outlets for escape of electric current was worth while 

 considering. The efficacy of more than one coat, moreover, is 

 thoroughly well established. But the strip machine has no mon- 

 opoly in this particular. Insulation material can be applied in 

 one, two or three coats or layers at the same time by tubing ma- 

 chines operated in tandem or triplet. That is to say, the ma- 

 chines are placed in line with each other, so that the wires to be 

 insulated passes in succession through all, receiving in each an 

 individual layer, which, however, in the vulcanizing process be- 

 omes an integral part of a solid body of insulation. 



In this manner stocks possessing different characteristics and 

 differing in cost can be applied to advantage. It is a common 

 practice to have the first insulation coat (next to the wire) of 

 pure Para rubber,, or a white stock, known as "white core," with 



