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(c) Media Types I through V
To get plastic abrasive media material refer to Section VII Table 706 Consumables.
(3)
Equipment Required
(a)
Blast Equipment: Blast equipment must be of proper type and adequately sized for the task. It must allow the operator ease of control over the intensity and targeting of the blast stream.
(b)
Screening: Screening or filtering equipment is essential for media maintenance. It is mandatory to screen or filter new and used media prior to remove undersize, or broken abrasive particles, corrosion debris, coating debris, metal particles or any other media contamination.
WARNING: INHALING DUST PARTICLES IS HAZARDOUS. DUST PARTICLES CAN ALSO BE EXPLOSIVE. SUITABLE DUST COLLECTION AND VENTILATION SYSTEMS ARE ESSENTIAL TO PROTECT PERSONNEL FROM THESE HAZARDS.
(c)
Dust Collection and Ventilation: Provisions must be made to collect the dust formed during blasting and provide adequate dust free ventilation to personnel. Filtering type respirators should be used.
(4)
Process Parameter Development
CAUTION: NOZZLES LARGER THAN 0.375 INCH (9.52 MILLIMETERS) DIAMETER CAN PROVIDE SUCH A LARGE AMOUNT OF MEDIA THAT CAN CAUSE DAMAGE TO COMPONENTS AND ARE NOT RECOMMENDED.
Test blast a small area using 30 psig (208 kPa), a 3/8 inch diameter nozzle, a 60 degree blast angle, Type I media and 12 inch standoff distance. An acceptable removal rate is typically 0.50 to 0.75 square feet (0.047 to 0.070 square meters) per minute for metal substrates (approximately 0.30 square feet (0.03 square meters) per minute for organic matrix composites). If the removal rate requires improvement, adjust the following process parameters (a) through (d), and select the best combination that will provide an acceptable removal rate while not harming the substrate or the sub coatings. Record the process parameters giving the best results.
NOTE: Nozzle sizes range from 0.25 to 0.625 inch (0.635 to 15.88 millimeters) diameter and each will have their own characteristic removal rate and blast energy.
(a)
Plastic blast media are grouped according to increasing hardness and abrasiveness. (See Step (2)) Therefore, if Type I removal rate is too slow, try Type II.
(b)
Blast pressure at the nozzle directly affects the removal rate and may be varied from 25 to 45 psig (172 to 310 kPa) for pressure blast systems. Higher pressures are necessary for suction type blasters. Excessive pressure will damage the media. Pressures should be kept on the low side; in the range of 25 to 30 psig (172 to 207 kPa).
NOTE: Use less pressure to avoid damaging delicate substrates.
Cleaning
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CAUTION: USING HIGH SPRAY ANGLES (75 TO 90 DEGREES) WILL IMPART MORE ENERGY TO THE SUBSTRATE THAT MAY CAUSE WARPAGE OR CRACKING.
(c)
Blast angle has a proportional effect on removal rate. The higher the angle, the higher the removal rate. On delicate substrates, it is advisable to use low blast angles of 45 degrees or less.
(d)
Standoff distance typically ranges from 6 to 24 inches (153 to 610 millimeters) and has a significant influence on removal rate. It is recommended that a range be selected and maintained as close as possible during the entire blasting operation.
(5) Areas to be blasted must be dry and free of moisture, grease, oil, or any loose contaminants.
WARNING: AVOID PROLONGED INHALATION OF SOLVENT VAPORS. WEAR RUBBER GLOVES AND USE PROTECTIVE HAND CREAM TO PREVENT CONTACT WITH SKIN. DO NOT HEAT SOLUTION.
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