TASK 70-47-03-380-018
1 . General.
A.This procedure is recommended for increasing the coefficient of friction between 2 faying surfaces of a bolted assembly. It should be used when specified in the Engine/Shop Manual.
NOTE:
As an alternate method, wet abrasive blasting per TASK 70-47-02-380-017, Wet Abrasive-Blast Surface Finishing, may be used in lieu of dry blasting.
2 . Equipment.
Subtask 70-47-03-380-181
A.The following equipment, or its functional equivalent, is recommended:
NOTE:
Functionally equivalent equipment for this process includes alternatives to the suction blast equipment defined below and also includes the use of direct pressure blast equipment. Equipment must get the uniform matt surface texture required for this process.
(1)Manually operated blast cabinet.
(2)Blasting gun having a suction nozzle with a 1/2 inch (13 mm) inside diameter at the discharge end and a 7/32 inch (6 mm) inside diameter air jet.
NOTE:
The nozzle lines shall be replaced when inside diameter at outlet end is worn to 5/8 inch (15.8 mm).
(3)Source of compressed air should be sufficient to maintain controlled pressure of 25-30 psi (172-207 kPa) for direct pressure type equipment and 50-60 psi (345-414 kPa) for suction type equipment during blasting.
3 . Materials.
Subtask 70-47-03-380-182
 
Consumable Product
No.
 
Abrasive Grit Aluminum Oxide 120 Mesh
C04-114
 
Abrasive Grit Aluminum Oxide 150 Mesh
C04-283
NOTE:
Grit size should be monitored and if finer than 150, it should be replaced.
4 . Procedure.
Subtask 70-47-03-380-183
A.Parts must be completely finish machined and free of burrs and sharp corners before abrasive blasting. Parts should meet all surface finish requirements before blasting. Proceed as follows:
(1)Clean all parts so they are completely free of dirt, oil, and grease. Steam cleaning (TASK 70-21-03-160-001, Cleaning Method No. 3 - Steam Cleaning) is preferred in all cases. Vapor degreasing (TASK 70-21-02-110-002, Cleaning Method No. 2 - Vapor Degreasing) is acceptable for cleaning non-titanium parts.
(2)Mask all markings that are to be retained after blasting, such as identification and inspection markings. No other masking is required unless otherwise specified by Engine/Shop Manual.
(3)Dry blast the parts using any of the products listed in Subtask 70-47-03-380-182, Materials, in the following manner:
NOTE:
The process parameters defined in the following paragraphs are for use with the suction blast equipment defined in paragraph 2.0. If functionally equivalent equipment is used, then parameters can be modified to get the uniform matt surface texture required for this process. It is ordinarily expected that suction blast equipment will require a higher pressure than direct pressure blast equipment to achieve the same surface texture.
CAUTION:
PRESSURE OF 25-30 PSI (172-207 KPA) FOR DIRECT PRESSURE TYPE EQUIPMENT AND 50-60 PSI (345-414 KPA) FOR SUCTION TYPE EQUIPMENT TO BE MAINTAINED DURING BLASTING TO AVOID EXCESSIVE EROSION.
(a)Direct the blast nozzle at 40-60 degrees to the part, and 3-5 inches (76.2-127.0 mm) from it. When blasting disks or spacers, direct the blast radially outward to avoid blasting into dovetails, and to cut across circular tool marks.
(b)Avoid letting the abrasive blast dwell in one place on the workpiece. If the blast cabinet incorporates a rotating work table, it should be turning during the blasting operation.
(c)Blast only those surfaces specified by the Engine/Shop Manual. Holes and corner radii should be avoided during blasting.
(d)Unless otherwise specified by the Engine/Shop Manual, make sufficient passes to remove existing machined surface finish and attain a uniform matt surface finish.
(4)Completely remove all residual grit after blasting.
(5)Visually check blasted surface for uniformity of finish.