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.

THE OPERATORS MUST NOT TOUCH THE POWDERED GLASS.

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

DRY NON-METALIC 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.

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, EXPLOSING, REACTIVITY, HEALTH HAZARD DATA, PRECAUTIONS FOR SAFE HANDLING, USE AND CONTROL MEASURES AND ALSO TO TAKE LOCAL REGULATIONS INTO CONSIDERATION.

Procedure

1. SUBTASK 70-38-04-200-001 Control Procedures

   1. Check the wet abrasive mixture.

      1. Collect a sample from the nozzle, with the air shut off.

      2. Allow the sample to settle, in a graduated tube, so that the proportions of abrasive, fines and water can be determined.

      3. When renewing the abrasive in a wet cabinet, the interior of the cabinet must be thoroughly washed with clean water. The pump must then be filled with clean water and the new abrasive added.

   2. Control and testing of shot and glass bead peening procedures.

      1. Control procedure:

         1. Peening develops a compressive stress on the surface of a part, which must be controlled and measured. Too much peening can cause deformation, especially with thin parts, while insufficient peening may not achieve the necessary resistance to fatigue.

         2. Full control is essential, during all parts of the peening procedure, to make sure that the amount and uniformity of stress, together with the depth of layer are consistently maintained. Automatic peening procedures must always be used, when possible, to make sure that uniform and constant results are obtained. The equipment must therefore be mechanically controlled and capable of moving either the parts to be peened, or the shot stream. The areas to be peened are specified in the Engine Manual, together with the type and size of peening medium to be used and the peening intensity (that is, the Almen 'arc height' and coverage required).

         3. Peening control means that the depth of the compressive stress is held constant; which is achieved with Almen strips, made from cold rolled spring steel (SAE 1070) heat-treated to 45 to 50 HRC. These strips are identified as N, A and C; which are 0.031in. (0.74 mm), 0.051in. (1.30 mm) and 0.094in. (2.38 mm), thick respectively (refer to Figure).

         4. The measurement of the peening intensity is made, by inserting an Almen strip into the fixture (refer to Figure) where one side of the strip is saturated with a specified particle size of shot or glass bead, at a specified air pressure. This then causes the strip to bend or arc, according to the amount of peening (that is, the compressive stress applied). The peening intensity is thus expressed in terms of 'arc height' of the curvature of the Almen strips, as measured on a standard Almen gage (refer to Figure). The intensity is expressed as, for example, 6-10A (that is, an 'arc height' of 0.006 to 0.010in. (0.15 to 0.25 mm)). The use of Almen strip measurements allow the peening intensity to be repeated (that is, at different times, with different equipment and operators) but always with the same results.

         5. To establish the peening conditions necessary for the required intensity; test several Almen strips, supported in the correct fixtures, using the specified peening medium at a constant air pressure or impeller speed and for different periods of time.

         6. The tests must be repeated for different air pressures or impeller speeds and the results plotted to give an intensity curve (refer to Figure) from which the optimum air pressure or impeller speed and exposure time can be determined.

         7. The Almen test strip 'arc height' must be satisfactory before the engine parts are peened, using the parameters established.

         8. Control sheets must be kept to record the following parameters as a minimum for each peened part.

            Details of equipment and set-up.

            Details of peening medium.

            Working pressure.

            Nozzle-to-work distance.

            Nozzle diameter.

            Air jet diameter.

            Impingement angle of blast.

            100 or 200 percent saturation.

            Duration.

            Almen 'arc height'.

            Area treated.

            Other important information.

      2. Test procedure:

         1. Vapor degrease the strips (refer to the SPM TASK 70-11-01-300-503).

         2. Secure the strip in the fixture (refer to Figure), before applying the same procedure as for the parts.

         3. After peening, remove the strip from the fixture. Measure the curvature of the unpeened surface using the Almen gage (refer to Figure).

         4. Peen several strips for each determination.

         5. Plot the results to give an intensity curve (refer to Figure).

         6. Determine the optimum air pressure or impeller speed and exposure time.

         7. When the machine is calibrated, periodic checks must be made during the peening procedure:

            Glass beads - one determination after every 2 hours of operation.

            Cast steel - one determination after every 8 hours of operation.

            At least one determination at the beginning and end of each batch.

            At least one determination after any control setting change or shot replacement.

            .

Figure: Almen test strip

Almen test strip



Figure: Test strip fixture

Test strip fixture



Figure: Almen gage

Almen gage



Figure: Intensity determination curve

Intensity determination curve