It started with a bang at 3 a.m. on August 13 when excessive powder fines exploded at the Frigidaire Range Products/Electrolux plant (Springfield, TN). Ironically, finishing veteran, Larry Cornett was traveling to Springfield to join Bob Reece, the company's manufacturing engineer, the next day to evaluate the overtaxed production line and recommend improvements. Because of increased sales, the paint shop had been working three shifts a day, six to seven days a week for months to keep the assembly lines supplied, relegating maintenance to emergency situations only.
The work pieces for 30-inch ranges being painted were predominantly flat panels, including door fronts and frames, drawer fronts and instrument panels. To accommodate the wide range of part sizes, the overhead conveyor had 56-inch spaces between hang points. This was necessary to keep the larger parts from touching on the inclines and declines of the line. To increase the 24 fpm line speed would ease the demand pressure for parts but would reduce the quality of the finished parts. In addition, this spacing arrangement was also causing other serious difficulties. When the smaller parts were finished, a high percentage of the powder was being lost to overspray, and its continuous recovery created excessive fines. To compensate for this condition, the powder particle grind size was adjusted up from the normal 35 microns. The excessive fines also caused more than safety problems. The 12 canister filters kept blinding out and had a 50% reduction in operating life. At a cost of $2,400 each, this was unacceptable.
Mr. Reece had heard of AP Conveyor and its hanging tool that could greatly reduce the space required between parts. If this were possible, it could clearly reduce both the production demand situation and the excessive powder problems and costs.
The Angle-Pivot tool uses a simple bearing mechanism acting with gravity to rotate parts or hangers on inclines and declines. The hanging device uses a mechanical bar that is mounted near and parallel to the conveyor chain with hooks on each end of the bar. The simplest version of the bar has a formed angle in the center with a bushing attached at the formed angle. The rack or part hooks engage the bushing hole and are free to rotate. On the horizontal sections of the line, the parts or racks face outward as on most conventional processes. As the racks begin to climb an incline, the hook in the angled bushing rotates the part or rack up to 70 degrees so that the parts or racks proceed in a column. This action is reversed on the decline.
Traditionally, overhead conveyors with inclines and declines required space between parts or racks to avoid overlapping or touching. A rule of thumb is to allow 50% of the part or rack width for clearance. The hanging tool used at Frigidaire reduces this requirement to a nominal clearance, usually a little over the thickness of the part or loaded rack and presents a solid wall of parts for increased production and paint efficiency.
"At Frigidaire, we installed these hanging tools on a trial section of the porcelain line and began testing the system," Mr. Cornett noted. "There were some initial bugs to work out, which we expected. But, what really impressed us was the personal support that we received from AP Conveyor. Their willingness to work with us was one of the deciding factors to proceed quickly with the conversion of the much larger powder line."
In Frigidaire's case, the fixed 56 inches of spacing between hang points on the conveyor was costly, resulting in a sparse arrangement when parts larger or smaller than normal were run. To give the system maximum flexibility, the single mechanical Angle-Pivot bar was extended to a longer load bar with pivots on 2-inch centers. This made it possible to retrofit the entire line to accept hooks at any of the 2-inch positions for maximum hanging coverage of all parts. "Because of the flexibility of continuous 2-inch hook centers, we are currently developing a more creative hanging arrangement for a new range model. Instead of hanging a family of similar parts, we can now hang various parts by combinations of models based on sales demand. This avoids additional storage and sorting labor and delivers a complete set of parts directly to the assembly operations as needed," according to Ted Wolowicz, Frigidaire's senior finishing engineer.
"Because of the greatly increased production rates, we found it necessary to add an automatic lubrication system for the pivot tools. This was a small cost compared to the overall benefits," said Mr. Wolowicz. "The concept is wonderful and works with very little maintenance or wear. The few problems we've experienced so far are with simple things like worn conveyor wheels or chain and damaged hangers."
When the new retrofit was completed, the production rate was increased significantly from the tooling change alone. As the paint shop hours returned to normal, other subsequent enhancements to the system have more than doubled output with no increase in floor space. The powder particle grind size was returned to the normal 35 microns and the problem of excessive fines from repeated overspray was eliminated.
"We simply could not meet our current production capacity without this hanger tool," stated Mr. Wolowicz. "The powder line overhead conveyor is a ½ mile long and can handle the 1,100 hangers of parts. At several junctions, we have to incline/decline 60 degrees to cross other finishing operations. I've been in the finishing business for 20 years, and this simple development is a major breakthrough for our industry. We've been able to significantly increase production on our existing lines with a minimum of investment."