Metal Finishing Guide Book

2013

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Fig. 8. Conventional powder booth system. Multi-Axis Machines Both oscillators and reciprocators provide movement in one plane only. Multiaxis machines were developed to provide increased coating flexibility and meet a demand for total automation. Multi-axis machines have been successful in eliminating some or all of the manual touch-up necessary on some products. Though costly, this increased automation often will pay for itself by providing consistent part coating with minimal, if any, touch-up. The multi-axis machine design is made up of two or three reciprocators that will move the gun(s) in two or three planes. The convention used to label the three axes of motion is as follows (see Fig. 7). X = parallel to the conveyor travel Y = up and down Z = in and out The design of these units is the same as reciprocators with respect to the control of speed and stroke adjustment; however, because the units must track parts moving along the conveyor, the addition of a programmable logic controller (PLC) is required. The PLC will accept inputs from encoders (that determine conveyor speed) and photo cells or limit switches (that determine part position). This information is used to determine at what speed the multi-axis machine must run to track the part and when the multi-axis motion program is to be executed. The purpose of this complex tracking and motion system is to provide gun dwell time and powder pattern direction. Robots Most robots provide six axes of gun motion by adding wrist movement. Robotic machines can be electrically or hydraulically driven. Because of their cost and complexity, these units are rarely used in powder coating systems. Another detriment to these units is that hydraulic fluid is not something you want to have around powder. Also, powder coating material is very abrasive and can play havoc with hydraulic seals and pistons. POWDER RECOVERY A powder booth/recovery system must accomplish two specific goals: contain the powder overspray within the booth and remove the powder from this containment air so that it can be reused or disposed of properly. Powder booths are designed using several filtration techniques to separate the overspray powder 216

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