Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

Issue link:

Contents of this Issue


Page 649 of 707

Belville washer assembly and the device. Note that the Belville washer is made up of four parts: a centering section, a flat washer, and two concave washers. 3. Clean the surfaces of both bus bars and the new thyristor or diode. Clean both clamping bars, and check that the insulated surfaces of the clamp have not been damaged. 4. Apply heat sink compound sparingly to both surfaces of the device and to the bus bars. 5. Place the new flat pack in the clamping mechanism, ensuring that the device is oriented properly. Check the other devices to verify this. There are typically roll pins in the bus bars that align with depressions in the device. Make sure the roll pins do not damage the flat-pack surfaces. 6. Reassemble the Belville washers as shown, making sure the two concave washers are back to back. Now place the washers in the clamp. 7. Finger tighten the clamp nuts, ensuring all parts are situated properly, and tighten the nuts with a wrench one-quarter additional turn. Check that approximately the same number of threads are visible beyond the nuts on each stud. 8. Using a depth gauge, measure through the center of the hole in the bus bar and Belville washer system. Note this reading. 9. Tighten each nut one-half turn, and recheck with the depth gauge. Continue this tightening procedure until the difference from the orig- inal reading is 0.048 ± 0.004 in. for a 10,000 lb clamp, and 0.026 ± 0.002 in. for a 5,000 lb clamp. 10. Reattach the gate and cathode thyristor leads. PREVENTIVE MAINTENANCE Nothing is more important to rectifier reliability and longevity than a consistent program of preventive maintenance. The efforts expended in taking periodic care of any equipment, especially those operated in the aggressive environments typ- ically found in metal-finishing processes, will be returned many times over. The following provides a brief outline of the minimum maintenance that should be performed every month and every 6 months. The program you imple- ment should take into consideration the number of rectifiers, how many shifts, what type of processes, and the duty cycles of your particular operation. Monthly 1. Ensure that all doors and panels are on the rectifiers and that the area around the rectifier is free and clear of items that would hinder proper airflow or operation. 2. On air-cooled systems, wash or replace the air filters. Refrain from using inexpensive cardboard framed filters, as the thin metal facing can quickly deteriorate and be drawn into the rectifier. Also, check that the fan blades are secured to the fan motor shafts and that they run with- out vibration. 3. On water-cooled systems, remove and clean or replace the inlet water strainer. Check all water lines for signs of leaks or contamination accu- mulations. If contamination is evident, determine the source and correct if possible. 648

Articles in this issue

view archives of Metal Finishing Guide Book - 2011-2012 Surface Finishing Guidebook