Preliminary Requirements

Safety Requirements

WARNING

FACE MASKS AND RUBBER GLOVES MUST ALWAYS BE WORN BY THE OPERATORS DURING THE BLASTING OR PEENING PROCEDURES, OR WHEN THE EXHAUST FILTERS ARE CLEANED.

WARNING

THE OPERATORS MUST NOT TOUCH THE POWDERED GLASS.

WARNING

ALL EQUIPMENT MUST BE FULLY GROUNDED, TO REMOVE HEAVY ELECTRICAL CHARGES THAT CAN OCCUR DURING THE PROCEDURE.

WARNING

DRY NON-METAL BLASTING CAN BE USED ON TITANIUM PARTS IF THE FINE METAL POWDER, MADE DURING THE PROCEDURE, IS CLEANED THROUGH A CYCLONE WATER SYSTEM. ALSO, THE CABINETS MUST BE SUPPLIED WITH EXPLOSION RESISTANT DOORS AND A CONTINUOUS LOW SPEED AIR EXTRACTOR.

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURERS MATERIAL SAFETY DATA SHEETS FOR CONSUMABLE MATERIALS INFORMATION SUCH AS, HAZARDOUS INGREDIENTS, PHYSICAL/CHEMICAL CHARACTERISTICS, FIRE, EXPLOSION, REACTIVITY, HEALTH HAZARD DATA, PRECAUTIONS FOR SAFE HANDLING, USE AND CONTROL MEASURES AND ALSO TO TAKE LOCAL REGULATIONS INTO CONSIDERATION.

Procedure

1. SUBTASK 70-38-04-300-001 Controlled Wet or Dry Abrasive Blasting

   1. General.

      1. Controlled abrasive blasting is used to remove dressing or etch marks and give a non-direction surface finish; to a specified roughness value. A secondary use is to apply a compressed force into the surface of a part to give it better fatigue resistant properties.

   2. Procedure.

      1. Apply CoMat 02-001 ADHESIVE TAPE (MASKING), or a mask, to all parts that are not to be blasted.

         NOTE

         1. For blades or vanes, blast each side for 5 seconds; if this time is more than that specified above.

         2. Apply the blast longitudinally along the airfoil at an angle of 45 degrees, to make sure it includes the root and shroud radii.

         3. Reject the nozzle, when the diameter has worn to 0.500 in. (12.7 mm).

      2. Apply CoMat 05-003 ABRASIVE MEDIUM ALUMINUM OXIDE, 120/220 GRADE, with a 120 to 220 mesh, to give a smooth abrasive blast to the surface of the part. Use a blast nozzle diameter of approximately 0.375in. (9.0 mm) and a nozzle to work-piece distance of approximately 6 to 8in. (150 to 200 mm). Blast each sq in. (650 sq mm) of area for approximately 1 second. Use an air pressure of 60 to 80 psi (414 to 552 KPa), for wet abrasive blasting, or 30 to 40 psi (207 to 276 KPa), for dry abrasive blasting, unless specified differently in the Engine Manual.

      3. When the part is dry blasted: apply clean, dry compressed air to remove all the particles.

      4. When the part is wet blasted: immediately flush with a clean, cold water flow.

      5. Dry the parts:

         1. Put steel parts into dewatering oil (refer to the SPM TASK 70-38-05-380-501).

         2. Put non-ferrous parts into clean, hot water; then remove and dry with clean dry, compressed air.

      6. Examine the parts:

         1. Visually examine, to make sure the procedure is completed and that all dressing marks are removed.

         2. Examine, to make sure that the subsequent 'centerline average' (CLA) quality of finish is available; unless a grit other than 120-220 grade is specified in the Engine Manual.

            Titanium: 40 to 80 micro-inches.

            Aluminum: 60 to 80 micro-inches.

            Steel: a maximum of 63 micro-inches.

            Nickel alloys: 60 to 80 micro-inches.

2. SUBTASK 70-38-04-300-002 Controlled Shot/Glass Bead Peening

   1. NOTE

      The parts to be peened must be clean, dry and free from particles and surface coatings such as paint or plating.

      General.

      1. Peening is to hit the surfaces of a part with a flow of rounded steel shot or spherical glass beads supplied by air pressure or a centrifugal force, from a nozzle. It is used to apply a compressed force into the surface of a part to give it better fatigue resistant properties. It also gives better frettage resistant properties and prevents stressed corrosion cracks.

      2. Masking and peening per TASK 70-38-13-380-501 is permitted where shot peening per TASK 70-38-04-300-503 is specified.

   2. Procedure.

      1. Apply CoMat 02-003 ADHESIVE TAPE BLACK WATERPROOF, or a mask, to all parts that are not to be peened.

      2. Find the conditions specified in TASK 70-38-04-200-502, SUBTASK 70-38-04-200-001 Step 2.B., to get the necessary peening intensity specified in the Engine Manual by the Almen test-strip procedure.

      3. Put the parts into the peening cabinet and attach them to the fixtures. Peen the necessary areas, to the conditions specified in step (2), to get a smooth finish.

      4. After peening, remove the parts from the peening cabinet. Remove the steel shot or glass beads by the procedures that follow:

         1. Use clean, dry compressed air to remove all of the peening medium. Alternatively a soft brush, with suction when necessary, can be used.

         2. To remove the wet glass beads, flush the parts in a cold water flow. Remove the adhesive tape or mask and flush in clean, cold water. Put into clean, hot water, then dry with clean, dry compressed air.

         3. As an alternative to step (b), clean the parts with an air/water gun then put them into dewatering oil (refer to the SPM TASK 70-38-05-380-501).

            NOTE

            Wet or dry glass bead peening can be used as an alternative to steps (a) to (e) that follow.

            A second alternative for aluminum parts is wet abrasive blasting with CoMat 05-004 ABRASIVE MEDIUM, ALUMINUM OXIDE, 140/400 GRADE (150 to 400 mesh).

      5. When recommended in the Engine Manual iron contamination can be removed from aluminum, nickel base alloy, stainless steel and titanium parts by the procedures that follow:

         1. Remove the grease from the parts (refer to the SPM TASK 70-11-01-300-503).

         2. Put the parts into a 25 percent nitric acid solution (refer to the SPM TASK 70-11-07-300-503) for 15 minutes at a temperature of approximately 68 deg F (20 deg C).

         3. Flush the parts in a clean, cold water flow then pressure-blast with air and water.

         4. Put the parts into a 3 percent sodium metasilicate solution made from CoMat 01-044 SODIUM METASILICATE Na2SiO3.5H2O.

         5. NOTE

            Alternatively, unusual parts can be dried in an oven at a temperature of 239 to 275 deg F (115 to 135 deg C).

            Put the parts into clean, hot water at a minimum temperature of 176 deg F (80 deg C). Remove the parts and dry them with clean, dry compressed air.

      6. Examine the peened surface:

         1. Visually examine the peened surfaces to make sure the procedure is completed and that the steel shot or glass bead marks overlap.

         2. Visually examine the peened surfaces, at 5X magnification, to make sure that they are not rough.

         3. When peening is used to give an anti-galling surface, examine at 10X magnification; as a roughness check.

      7. Apply protection to the parts:

         1. As a protection against corrosion, do not touch the peened parts but apply a temporary protection, as specified in the SPM TASK 70-38-05-380-501.