May/June_AMP_Digital

FEATURE A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 1 8 4 5 gen has sufficient time to penetrate the steel microstructure. Commonly accepted practice is to start the baking process within 1 to 2 hours after plating. Because the heating soak time of 8 hours is greater than the 2-hour maximum allow- able delay (between plating and baking), a batch process would not work because the oven would be occupied for 8 hours for each load, well beyond the 2-hour maximum. For this reason, anddue to the high volume of lugnuts beingpro- duced, a continuous oven was chosen as the best solution. To process 1100 pounds of parts per hour, the goal was to load themas deeply on the conveyor as practical, without restricting the flow of heated air through them. A depth of approximately 2.5 in. was chosen, as it did not overly restrict the air but provided a load density of 85 lb/ft 2 of conveyor belt, near the maximum for a conveyor belt of its type. To minimize oven length, a wide conveyor belt was suggested. A belt width of 7 ft was decided on because any wider would make the oven toowide to economically ship to the required location. Calculations showed that with this configuration the conveyor would need to move at 1.85 ft per hour in or- der to process 1100 pounds of lug nuts per hour. Therefore, the 8-hour soak time would require 14.8 ft of heated length (8 × 1.85). But this was only part of the story. With the above pa- rameters established, the next question was: How long will it take for parts to heat up? This information was required to finalize the oven length because the oven heating chamber must be sufficiently long to not only provide the 8-hour soak time, but also to heat parts up to temperature. Because the lug nut manufacturer did not have data on this, Wisconsin Oven performed heatup testing on the parts. Once the time required to bring parts up to temperature was determined, total oven length could be finalized. To set up the test, a representative sample of parts was placed into a basket at a loading of 85 lb/ft 2 , and thermocouples were placed into five of the lug nuts, in holes that were drilled into the parts. The oven was set at a temperature of 400°F and the basket was loaded into the Wisconsin Oven test oven. The goal was to determine the time required to get the parts to heat within 5° of the 400°F oven temperature, or 395°F. Testing revealed that the parts took 1 hour and 10minutes to reach the target temperature (Fig. 3). With this information in hand, the engineers at Wiscon- sin Oven could now determine the oven length required to heat the lug nuts to temperature and to provide the neces- sary soak time. By adding the soak time of 8 hours to the hea- tup time of 70 minutes, total heating time was calculated as 9.2 hours. It could now be determined that the oven heating chamber would need to be a minimum of 16.9 ft (9.2 × 1.85). To account for end effects near the oven openings, the oven chamber was set at 18 ft 6 in. CONCLUSION The oven was designed and built to the above speci- fications and the Factory Acceptance Test (FAT) performed prior to shipment verified the results were achievable in the new oven (Fig. 4). When sizing a conveyor oven, part testing is often necessary to determine the heating time, and there- fore the oven length. Reputable oven manufacturers often perform testing for a nominal fee and assist users in inter- preting the results. ~HTPro For more information: Mike Grande is vice president of sales and engineering, Wisconsin Oven Corp., 2675 Main St., East Troy, WI 53120, 262.642.3938, mgrande@wisoven.com , www.wisoven.com. Fig. 3 — At a loading of 85 lb/ft 2 , parts took 70 minutes to reach temperature. Fig. 4 — Part testing was used to determine the length of a new hydrogen embrittlement relief oven. 13