Metal Finishing Guide Book

2012 Organic Finishing Guidebook Issue

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Page 191 of 331

Fig. 3. Machine length for sample design of three-stage washer and dryer. (ambient), one-minute phosphate (heated), 30-second rinse (ambient), and 30-sec- ond rinse/inhibit (ambient) will be required Spray versus Immersion In general, spray processing provides the most effective cleaning and rinsing ca- pabilities owing to increased mechanical action, liquid impingement, and natur- al draining; however, for impingement of recessed or hidden surfaces of complex parts and assemblies, immersion processing is more appropriate. The addition of ul- trasonics or agitation can enhance the impingement capability, but it is costly. When processing complex parts or heavily loaded baskets of parts a combination of immer- sion and spray stages is often required. Testing dirty parts in a laboratory will provide proper selection. Sample Three-Stage Washer The first step in the design is to lay out the system (using a conveyor speed of 4 fpm and a largest part size of 2½ ft x 18 in. x 18 in.). The entrance profile should include a 3-in. clearance around the part. This will provide flexibility to process larger parts if required (see Fig. 2). A housing space of 1 ft on each side of tunnel openings allows for spray risers and piping. The cleanout section can be 2 to 2½; 3½ ft from the floor to the bot- tom of the tunnel opening will provide enough space to have the tank capacity to keep the pump-to-tank ratio around 3:1. The overall height of the machine is 7½ft, but we need to allow another 3 ft minimum for ventilating ductwork. The machine length for a three-stage washer, allowing three minutes of drying, is shown in Fig. 3. You know that one minute in the wash stage is required and that the conveyor is traveling at 4 fpm, so you can size the wash stage at 4 ft. Similarly, Fig. 4. Five-stage monorail-type zinc phosphating machine (see Table I for details). 190

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