Dry Lube Makes Draw Rings into Workhorses
Early in 2010, the dry-lubricant coating line at toll processor Voss Taylor became extremely busy, as the firm took on all of the coating work for Bristol Compressors, Bristol, VA. Voss Taylor, with 400,000 sq. ft. under roof in Taylor, MI, and annual capacity of 720,000 tons on its pickling line, has developed a unique application process for the dry lube that optimizes coating consistency—an absolute must for Bristol’s demanding deep-draw and redraw operations. The process is used to form compressor housing components that are robotically welded with minimal allowable weld gap. Therefore, dimensional tolerances are extremely tight in order to ensure good fitup in the welding fixture, and consistently high weld quality.
A QA technician at Bristol Compressors performs a chemical test on dry lubed blanks to check for coating consistency, before the blanks head to one of the firm’s eight hydraulic-press deep-draw production lines.
“Draw consistency is critical to our robotic-welding department downstream from the housing department,” notes Counts. “Dimensional tolerance is just 0.030 in., and we rely on the consistency of the dry lube applied to the blanks, at the required coating thickness, to contribute to a repeatable draw process throughout all eight lines.”
Each production line features a 250- to 400-ton AP&T hydraulic press with varying degrees of automation. Draws reach 14 in. on blanks from 16.4- to 20.5-in. dia., of hot-rolled steel (HRb 40-70) 0.100 to 0.200 in. thick. Four of the press lines are fed blanks manually by Bristol operators, the other four are robotically loaded with AP&T press robots. Cycle time in the press is 10 to 11 sec.—an initial first draw followed by a redraw to resize and reconfigure the part. Capacity is 14,000 to 15,000 drawn parts per 24-hr. period across all eight lines. A conveyor carries the drawn parts route to a shear trimmer that trims the parts to specified height, to a piercing unit, and finally to a wash station.
Dry-Lube Line in Sync
One of eight draw-redraw lines at Bristol Compressors prepares to form a blank into a compressor housing; press cycle time is 10 to 11 sec.
Bristol allows a liberal range on coating thickness (or weight) of 400 to 800 mg/sq. ft., and Voss Taylor has no problem meeting that range, says Ed Sikina, director of quality assurance at the toll processor.
“We routinely apply the Tru-Chem product at 300 mg/sq. ft. to a tolerance of ±100 mg/sq. ft.,” Sikina says, “with a 1.33 or better Cpk. We run 6000 to 7000 tons of steel/month through the coating line, of which Bristol accounts for about one-third.”
Application and QA Processes
Voss Taylor’s coating equipment mounts on rails to allow it to be moved into and out of the pickling line quickly and efficiently. The process begins by leveling the coil prior to the material entering the acid bath. A rinse station follows the pickling process, then the material is dried and the dry-lube coating applied. An accumulator builds up 100 ft. of the coated steel to allow it to dry before recoiling.
Quality-assurance technicians at Bristol inspect incoming coated blanks before they make their way to the press lines. They test both sides of two blanks per every fifth lot of blanks; lot sizes range from 360 to 500 based on blank size. A technician also inspects blanks periodically throughout each shift.
A drawn compressor housing is ready for post-processing—a conveyor will carry the drawn part to a shear trimmer, a piercing unit and then to a wash station.
Tru-Chem’s T.C. 1800-3 comprises a water-soluble powder applied as a solution. Die buildup, peeling, powdering and sticking “are virtually eliminated,” says the company, “leaving no lubricant marks on drawn steel parts.” Compared to applying lube at the press, Bristol Compressors enjoys a much cleaner, safer process.
Prolonged Draw-Ring Life“Not only are we holding the tight fitup tolerances required for welding the housings,” says Counts, “but we’re also more than quadrupling draw-ring life, running our draw rings for as long as 3 yr. This is due in part to the consistency of the dry-lube coating, as well as recent change in draw-ring radius. We went to a longer, softer radius on the rings to prevent the lube from being wiped off during the forming process. MF
See also: Tru-Chem Company, Inc.
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