Products Finishing

OCT 2013

Products Finishing magazine is the No. 1 industrial finishing publication in the world. We keep our readers informed about the latest news and trends in plating, painting, powder coating, anodizing, electrocoating, parts cleaning, and pretreatment.

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Page 72 of 115

PARTS CLEANING Wet blasting combines abrasive media with water to form a special slurry for removing burrs, scale, oxidation and rust, marks, paint and coatings. nozzles targeting specific areas. The part can also be manipdepend heavily on controlling and monitoring several ulated in front of blast streams with a robot, or a robot can specific machine functions. Ensuring consistency in terms manipulate the nozzles. In any machine configuration, the of media, air and water pressure are critical to precise and part or nozzle movement must be monitored in real time. consistent finish results. Part Rotation within the Blast Streams: Look for a The following guide outlines key considerations and VFD-controlled drive system where the drive is external to recommendations when selecting slurry blasting machines: the cabinet and uses a belt and sheaves. In addition, a zeroPart Fixturing: Finding a method to hold the part firmly speed sensor located on an idler sheave and in a consistent position in the blast will confirm table rotation and help stream is essential and will require the ensure even, consistent coverage. end-user and blast equipment vendor to The slurry-blast Media Concentration Control: work together to identify the best solution. process virtually Low-level warning sensors for the slurry Part fixturing can be combined with eliminates embedded concentration are an important feature to masking techniques to protect surfaces ensure a precise and consistent result. If that do not require a profile. media issues the media concentration falls below the PLC-Controlled Machine with commonly found in dry set percentage, more media is automatiOperator Interface (HMI): This imporblasting systems. The cally added from the hopper. The system tant aspect provides part process and should allow for roughly three additions machine parameter setup and editing, process does not create of media, but if concentrations remain too then saves the parameters to form part dust, and chemicals low, the system should trigger a shutdown process "recipes." Part processing is are not required. and display a warning. accomplished through enabling the Media Size Control: Media within assigned recipe number. The control the slurry must be the correct size. Look system must monitor all machine paramfor equipment with a hydrocyclone, which separates the eters during the process cycle as well as the machine slurry stream into two outlets: one with the fine particles shutdown and status/fault display on the HMI screen. and water, and the second with the large particles, typically Machine Configurations: Consistent process results the remaining good media. The large particles are returned require that the developed part-to-blast stream relationto the machine sump, while the fines are sent to a vibratory ship be repeated cycle after cycle. There are several ways classifying screener where a screen recaptures any good to control the process by manipulating the part. Most media and returns it to the sump. The remaining water and often, the fixture part rotates on a powered table with fixed PRODUCTS FINISHING — 71

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