Metal Finishing Guide Book


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finishing equipment & plant engineering PRETREATMENT SYSTEM DESIGN FOR OPTIMUM END-USE PERFORMANCE CINCINNATI INDUSTRIAL MACHINERY, DIV. OF EAGLE PICHER, CINCINNATI A finishing system may have many possible arrangements, but only one is best suited to the user���s plant conditions and needs. Only after working closely with the user and suppliers are you able to determine the system best suited to your requirements. Finishing systems are comprised of washers, dry-off ovens, incinerators, pretreatment, electrocoating, spray booths, flowcoaters, dip tanks, cure ovens, conveyors, waste treatment, and air makeup. A complete paint finishing system consists of an integrally designed combination of equipment (or single compact machine) that conveys parts through the cleaning, pretreatment, paint application, and baking steps to deliver a finished part ��� often without labor between loading and unloading. Systems can include makeup air equipment to replace exhausted air, loading and unloading devices, and other related equipment. A typical schematic is pictured in Fig.1. DEFINING PARAMETERS Pretreatment can be accomplished in many different ways involving several technologies (see Table I). The optimum design for a family of parts evolves from understanding the following parameters and applying them with consistent design integrity: (1) quantity and configuration of parts; (2) material composition of parts; (3) desired material handling methods; (4) understanding soils and cleanliness desired; (5) facilities and utilities available; and (6) environmental considerations. Each of these parameters will influence the design of the system. Early involvement of competent representatives from chemical suppliers, equipment manufacturing companies, and paint companies will improve the design phase and enhance your objective. Once the parameters have been defined the design can begin. Quantity and Configuration of Parts The production rate obviously determines the level of automation, capacity of the equipment, energy consumption, chemical usage, etc. Selection for today���s requirements may be inadequate for tomorrow���s needs and sizing the system too large can waste money. Long-term planning will help determine production rate, future designs, and available financial resources. The proper analysis is essential. List all parts, their sizes, and annual production rate that you plan to process with the system. This will give you the yearly production requirements. Then, based on one, two, or three shifts, determine production time available. When comparing production requirements with production time available you can establish rate in feet per minute. The smallest, the largest, and the average part size must be defined in terms of dimensions. This allows equipment manufacturers to size the openings for washers (to minimize overspray), determine optimum drain length (minimize solution carryover), and size heaters, pumps, and fans. The overall weight of the part or batch of parts being conveyed must be known to calculate heat loss through the washer and ovens. Unusual shapes must be identified for early consideration. For example small, blind holes on surfaces could negate the power wash approach, whereas large, open or flat surfaces that can drain are ideal. Small parts that can withstand tum806

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