Anodizing apparatus

Claim 1

AN ELECTRICAL ENERGIZING AND CONTROL CIRCUIT FOR ANODIZING THE SURFACE OF A WORKPIECE IN AN ELECTROLYTIC ANODIZING CELL, FIRST AT A CONSTANT CURRENT WITH INCREASING APPLIED VOLTAGE UNTIL A DESIRED FILM THICKNESS HAS BEEN REACHED AND THEN AT A CONSTANT VOLTAGE WITH DECREASING CURRENT FLOW THROUGH THE CELL TO EQUALIZE THE THICKNESS OF THE FILM, THE CIRCUIT COMPRISING: A CONSTANT-CURRENT D.C. SOURCE CONNECTED ACROSS THE CELL FOR APPLYING A CONSTANT ANODIZING CURRENT THERETO OF SUFFICIENT MAGNITUDE TO ANODIZE THE WORKPIECE AT A DESIRED RATE, THE VOLTAGE DROP ACROSS THE CELL, AND CONSEQUENTLY THE APPLIED VOLTAGE, INCREASIN AS THE ANODIZING PROCESS PROCEEDS TO A VALUE DEPENDENT ON THE THICKNESS OF THE ANODIZED FILM AT ANY TIME; AN ADJUSTABLE CONSTANT-VOLTAGE D.C. SOURCE CONNECTED ACROSS THE CELL IN PARALLEL WITH THE CONSTANT-CURRENT SOURCE, AND HAVING AN OUTPUT VOLTAGE THAT IS PRESET TO EQUAL THE VOLTAGE DROP ACROSS THE CELL WHEN THE DESIRED FILM THICKNESS HAS BEEN REACHED; AND A UNIDIRECTIONAL CONDUCTING DEVICE CONNECTED IN SERIES WITH THE CONSTANT-VOLTAGE SOURCE SO AS TO BLOKC THE FLOW OF CURRENT FROM THE CONSTANT-VOLTAGE SOURCE OF THE CELL AT ALL TIMES, WHILE PERMITTING THE FLOW OF CURRENT FROM THE CONSTANT-CURRENT SOURCE THROUGH THE CONSTANT-VOLTAGE SOURCE AFTER THE VOLTAGE DROP ACROSS THE CELL HAS RISEN TO THE PRESET VOLTAGE OF THE CONSTANTVOLTAGE SOURCE, INDICATING THAT THE DESIRED FILM THICKNESS HAS BEEN REACHED, THUS MAINTAINING THE VOLTAGE DROP ACROSS THE CELL CONSTANT AT THE PRESET VALUE AFTER THE DESIRED FILM THICKNESS HAS BEEN REACHED SO AS TO EQUALIZE THE THICKNESS OF THE FILM.