Metal Finishing Guide Book


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Fig. 3. Machine length for sample design of three-stage washer and dryer. and 30-second rinse/inhibit (ambient) will be required Spray versus Immersion In general, spray processing provides the most effective cleaning and rinsing capabilities owing to increased mechanical action, liquid impingement, and natural draining; however, for impingement of recessed or hidden surfaces of complex parts and assemblies, immersion processing is more appropriate. The addition of ultrasonics or agitation can enhance the impingement capability, but it is costly. When processing complex parts or heavily loaded baskets of parts a combination of immersion 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 2�� 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 2��; 3�� ft from the floor to the bottom 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 7��ft, 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, rinse stages are 30 seconds; thus, they are each sized at 2 ft in length. Fig. 4. Five-stage monorail-type zinc phosphating machine (see Table I for details). 810

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