DEPOSITING THE SHELL
Those who are not technically familiar with electrochemistry are prone to think that the length of time a mold is kept in the electrolytic bath, i. e., the copper bath, determines the thickness of the shell deposited thereon. As a matter of fact, one electrotyper may keep his molds in the copper bath for three hours and get only as thick a shell as another who keeps his in but two hours. The element of time does not determine the thickness nor quality of the shell deposited.
The determining factors in this phase of electrotyping are the composition of the electrolytic bath, its temperature, and the current density applied. In addition, the purity of the materials, the cleanliness of the batteries, the perfection of the electrical connections as well as the distance between the anode and the cathode are all matters of importance. These factors are all variables and must be confined between narrow limits.
This important phase of manufacture in The Rapid Electrotype Company is under the supervision of an electro-chemical engineer.
Plus this fact is the accuracy of mechanical operation in handling wax molds from the time they are put into the batteries until they are taken out with the shell deposited thereon and ready for tinning and backing-up.
The molded cases are suspended at regular intervals of twenty inches from an endless chain-conveyor operating directly over the batteries. This conveyor carries the cases edge-wise through the electrolytic bath between two rows of anodes which are four inches apart. At the end of each battery the conveyor automatically lifts the cases out and over into the next battery in the series, of which there are seven. The eighth tub contains pure running water for washing the case after the complete deposition of the shell.
The speed of this conveyor is regulated so that when the molded case has reached the end of its journey through the series of seven batteries, the other factors also being regulated, a shell of uniform thickness and texture throughout is deposited thereon.
This automatic handling of the cases in the batteries eliminates the necessity of the battery-man pulling the case out of the bath by hand from time to time in order to peel back a corner of the shell to see if it is thick enough, which is the common practice. In other words, the element of human guess-work is eliminated, and in addition, the items of time and handling are greatly reduced.