TASK 70-21-05-120-002
1 . General.
A.Abrasive blast cleaning is a mechanical technique for removing scale, corrosion, oxidation and carbon deposits from all kinds of materials.
B.Abrasive blast cleaning is often employed for surface preparation of steels that have a breaking strength greater than 210000 psi (1450 MPa) and which cannot be cleaned by chemical processes.
CAUTION:
SUBSTITUTION OF A DIFFERENT METHOD FOR THE ONE RECOMMENDED IS DANGEROUS AND CAN DAMAGE PARTS.
C.The Engine/Shop Manual specifies the particular process to be used in each case. The choice depends upon:
(1)The standard of cleanliness desired.
(2)The nature of the part.
(3)Part shape and degree of fragility.
(4)Surface finish to be obtained.
D.Approved wet abrasive blast methods are:
(1)Method No. 5A - Fine.
(2)Method No. 5B - Medium.
2 . Equipment.
Subtask 70-21-05-120-021
E.The following equipment is required for the application of this process.
CAUTION:
TO PREVENT CONTAMINATION OF PARTS BEING PROCESSED, A BLASTING BOOTH SHOULD BE RESERVED FOR THE USE OF A GIVEN MATERIAL (ALLOYED STEEL, ALUMINUM ALLOY, OR TITANIUM PARTS) WHENEVER POSSIBLE.
(1)Important considerations:
(a)It is recommended that wet blasting operations are performed using installations specifically designed for the process, such as a blasting booth or cabinet with features including sound suppression, mist extraction, material handling, and adequate lighting.
(b)To provide good process control, there shall be devices to separate and discard undersize grit and a pressure regulator to control and adjust blast air pressure. The capability to measure the concentrations of abrasives in the blast stream shall also be provided. This can be separate from the machine.
(c)It will be very difficult to remove abrasive residues from parts unless the parts are thoroughly rinsed immediately after grit blasting and before drying. Rinsing may be performed using clean water from a spray gun or by immersion in a water rinse tank. Attention must be given to abrasives caught in recesses and cavities. A suction device may be necessary for the complete removal of all abrasive residue from such areas.
(2)Some of the optional additives allowed in this process make it important for personnel operating the facility to wear appropriate Personal Protection Equipment (PPE). See the contents listed in the specified solutions.
(3)Parts that may corrode or rust should be dried immediately after rinsing.
(a)Remove any masking that could be damaged by the drying process.
(b)Alternative procedure available. Flash drying may be performed by immersion in hot water as follows:
1Immerse parts in hot water at minimum 150ºF (66ºC).
2Keep the part submerged until the part reaches a temperature sufficient to provide for flash drying.
NOTE:
The time required will vary with part size, water temperature and tank size. Proper flash drying is indicated by seeing the water on the surface of a part start to "flash" or "whisk" off as the part is being removed from the hot water tank.
3Remove the part from the water. The part will flash dry as soon as it is removed from the water.
(b).A.Alternative procedure:
1Use a steam cleaner or a hot pressure washer to clean the part.
2Remove excess water by using a suction device or a blast of clean, compressed air, then finish drying the part with a hot air blower or an oven dryer.
NOTE:
Maximum drying temperature should not exceed 200°F (93°C) for plastic/composite parts or 300°F (149°C) for metal parts.
TASK 70-21-05-120-A02
1 . General - Method No. 5A - Fine.
NOTE:
When you do this procedure (5A) you must also obey the instructions in TASK 70-21-05-120-002, Cleaning Method No. 5 - Wet Abrasive Blast Cleaning.
CAUTION:
THIS PROCEDURE IS USED FOR THE PREPARATION OF SURFACES FOR PAINTING. IT MUST BE CARRIED OUT IN ACCORDANCE WITH SPECIFICATIONS AND IN INSTALLATIONS RESERVED SOLELY FOR THAT PURPOSE.
CAUTION:
IT IS ADVISABLE NOT TO CLEAN DIFFERENT MATERIALS (STEELS, ALUMINUM, TITANIUM) IN THE SAME INSTALLATION TO AVOID POSSIBLE CONTAMINATION.
CAUTION:
AVOID EXCESSIVE ABRASIVE BLASTING. OPERATE THE EQUIPMENT SO THAT THE ABRASIVE JET IS NOT LOCALIZED ON THE SAME SPOT. DO NOT DWELL FOR MORE THAN 2 SECONDS. BLASTING IS DONE BY SWEEPING OBLIQUELY OVER THE ENTIRE SURFACE AND NOT NORMAL TO IT.
F.The surface finish achieved by this process is smoother than that obtained with the medium process.
G.The blasting parameters are variable depending on the blasting material and the shape of the part. For thinner parts, reduce the pressure.
2 . Equipment.
Subtask 70-21-05-120-022
H.See Subtask 70-21-05-120-021, Equipment.
3 . Materials.
Subtask 70-21-05-120-023
 
Solution
No.
Operating Temp °F (°C)
 
TASK 70-00-99-801-048, Wet Abrasive Blasting - Aluminum Oxide 1200 Mesh
S1048
Ambient
4 . Procedure.
Subtask 70-21-05-120-024
I.Cover all ports, pockets, cavities, or tube ends to prevent entry of abrasive which may be difficult to detect and remove after cleaning. Mask all surfaces, if required, as indicated in the Engine/Shop Manual. The part must be free of oil and grease to prevent the quality of the abrasive from deteriorating.
WARNING:
DO NOT BREATHE THE PARTICLES FROM BLASTING OR LET THE PARTICLES TOUCH YOU. THE PARTICLES CAN CAUSE DAMAGE, INJURY, OR IRRITATION TO YOU. USE PERSONAL PROTECTION EQUIPMENT. USE LOCAL MECHANICAL EXHAUST VENTILATION OR AN APPROVED RESPIRATOR.
CAUTION:
AVOID EXCESSIVE ABRASIVE BLASTING. OPERATE THE EQUIPMENT SO THAT THE ABRASIVE JET IS NOT LOCALIZED ON THE SAME SPOT. DO NOT DWELL FOR MORE THAN 2 SECONDS. BLASTING IS DONE BY SWEEPING OBLIQUELY OVER THE ENTIRE SURFACE AND NOT NORMAL TO IT.
J.Wet-blast parts using solution listed in Subtask 70-21-05-120-023, Materials. Maintain air pressure at 60-90 psi (415-620 kPa) with the nozzle held at a distance of 6-8 inches (150-200 mm) from the part. The recommended angle to the surface being blasted is between 50 to 70 degrees.
K.Rinse the part with hot or cold water.
L.If parts are not likely to rust or corrode, dry the part using either of the following procedures:
(1)Alternative procedure available. Remove excess water by using a suction device or a blast of clean, compressed air, and then allow part to air dry.
(1).A.Alternative procedure. Remove any masking that can be damaged by the heat and then dry the part using heat drying.
NOTE:
Maximum drying temperature should not exceed 200°F (93°C) for plastic/composite parts or 300°F (149°C) for metal parts.
M.If parts are of a material that will rust or corrode easily, they should be heat dried immediately after rinsing.
(1)To heat dry a part that can rust or corrode:
(a)Remove any masking that could be damaged by the drying process.
(b)Alternative procedure available. Flash drying can be performed by immersion in hot water as follows:
1Immerse parts in hot water at 150° to 200°F (66° to 93°C).
2Keep the part submerged until the part temperature reaches the water temperature.
3Remove the part from the water. The part will flash dry as soon as it is removed from the water.
(b).A.Alternative procedure:
1Use a steam cleaner or a hot pressure washer to clean the part.
2Remove excess water by using a suction device or a blast of clean, compressed air, then finish drying the part with a hot air blower or an oven dryer.
NOTE:
Maximum drying temperature should not exceed 200°F (93°C) for plastic/composite parts or 300°F (149°C) for metal parts.
5 . Quality Assurance.
Subtask 70-21-05-120-025
N.Visually check that the part has been evenly cleaned and no blasting residues have accumulated.
TASK 70-21-05-120-B02
1 . General - Method No. 5B - Medium.
NOTE:
When you do this procedure (5B) you must also obey the instructions in TASK 70-21-05-120-002, Cleaning Method No. 5 - Wet Abrasive Blast Cleaning.
CAUTION:
WHEN THIS PROCEDURE IS USED FOR THE PREPARATION OF SURFACES FOR PAINTING IT MUST BE CARRIED OUT IN ACCORDANCE WITH SPECIFICATIONS AND IN INSTALLATIONS RESERVED SOLELY FOR THAT PURPOSE.
CAUTION:
IT IS ADVISABLE NOT TO CLEAN DIFFERENT MATERIALS (STEELS, ALUMINUM, TITANIUM) WITH THE SAME EQUIPMENT SO AS TO AVOID POSSIBLE CONTAMINATION.
O.The surface finish achieved by this process is not as smooth as than that obtained with the fine process.
P.The blasting parameters are variable depending on the blasting material and the shape of the part. For thinner parts reduce the pressure.
2 . Equipment.
Subtask 70-21-05-120-026
Q.See Subtask 70-21-05-120-021, Equipment.
3 . Materials.
Subtask 70-21-05-120-027
 
Solution
No.
Operating Temp °F (°C)
 
TASK 70-00-99-801-050, Wet Abrasive Blasting - Aluminum Oxide 325 grit
S1050
Ambient
 
TASK 70-00-99-801-054, Wet Abrasive Blasting - Aluminum Oxide 500 grit
S1054
Ambient
4 . Procedure.
Subtask 70-21-05-120-028
R.Cover all ports, pockets, cavities, or tube ends to prevent entry of abrasive which can be difficult to detect and remove after cleaning. Mask all surfaces, if required, as indicated in the Engine/Shop Manual. The part must be free of oil and grease to prevent the quality of the abrasive from deteriorating.
WARNING:
DO NOT BREATHE THE PARTICLES FROM BLASTING OR LET THE PARTICLES TOUCH YOU. THE PARTICLES CAN CAUSE DAMAGE, INJURY, OR IRRITATION TO YOU. USE PERSONAL PROTECTION EQUIPMENT. USE LOCAL MECHANICAL EXHAUST VENTILATION OR AN APPROVED RESPIRATOR.
CAUTION:
AVOID EXCESSIVE ABRASIVE BLASTING. OPERATE THE EQUIPMENT SO THAT THE ABRASIVE JET IS NOT LOCALIZED ON THE SAME SPOT. DO NOT DWELL FOR MORE THAN 2 SECONDS. BLASTING IS DONE BY SWEEPING OBLIQUELY OVER THE ENTIRE SURFACE AND NOT NORMAL TO IT.
S.Wet-blast parts using one of the solutions in Subtask 70-21-05-120-027, Materials. Air pressure must not exceed 90 psi (620 kPa) with the nozzle held at a distance of 6-8 inches (150-200 mm) from the part. The recommended angle to the surface being blasted is 50 to 70 degrees.
T.If parts are not likely to rust or corrode, dry the part using either of the following procedures:
(1)Alternative procedure available. Remove excess water by using a suction device or a blast of clean, compressed air, and then allow part to air dry.
(1).A.Alternative procedure. Remove any masking that can be damaged by the heat and then dry the part using heat drying.
NOTE:
Maximum drying temperature should not exceed 200°F (93°C) for plastic/composite parts or 300°F (149°C) for metal parts.
U.If parts are of a material that will rust or corrode easily, they should be heat dried immediately after rinsing.
(1)To heat-dry a part that may rust or corrode:
(a)Remove any masking that could be damaged by the drying process.
(b)Alternative procedure available. Flash drying may be performed by immersion in hot water as follows:
1Immerse parts in hot water at 150° to 200°F (66° to 93°C).
2Keep the part submerged until the part temperature reaches the water temperature.
3Remove the part from the water. The part will flash dry as soon as it is removed from the water.
(b).A.Alternative procedure. Clean and dry the part as follows:
1Use a steam cleaner or a hot pressure washer to clean the part.
2Remove excess water by using a suction device or a blast of clean, compressed air, then finish drying the part with a hot air blower or an oven dryer.
NOTE:
Maximum drying temperature should not exceed 200°F (93°C) for plastic/composite parts or 300°F (149°C) for metal parts.
5 . Quality Assurance.
Subtask 70-21-05-120-029
V.Visually check that the part has been evenly cleaned and no blasting residues have accumulated.