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.
BACKING UP THE SHELL
Backing-up the shells with the metal base, i. e., casting, is done automatically by The Rapid Electrotype Company.
A rotary casting-table with a capacity of ten pans revolves around its axis on a plane that brings each pan immediately below a spout through which the required metal is automatically flowed from the bottom of the metal pot on the tinned shell placed therein. When the required metal backing has been flowed, the table turns to bring the next pan with its shell under the metal-spout. The amount of metal flowed is exactly regulated. As the casting table completes a circuit, the first shell backed up has cooled so that it can be removed to the scrubbing machine.
This method, of course, eliminates the hand-ladling of hot metal from the metal-pot to the casting-table, as is the ordinary practice, and obviates any possibility of the oxidized metal or dross on the surface getting into the casts, besides effecting a marked economy in time and handling. In addition, it casts the plates flat, thereby eliminating about 75 per cent of the finishing, which, of course, means a better printing plate. Three of these machines are used.