Preliminary Requirements

Safety Requirements

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURER'S MATERIAL SAFETY SHEETS FOR THE CONSUMABLE MATERIALS. THESE CONTAIN 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 70-38-41-380-051 Material Preparation, CoMat 07-177 Slurry, Aluminium-Silicon

   1. Make sure you keep the CoMat 07-177 Aluminum Silicon Paint tightly sealed in the initial container in a cool place when not in use. Shelf life is unlimited, but the solid particles in the slurry will fall (settle) to the bottom of the container.

   2. Before use, stir or agitate the CoMat 07-177 Aluminum Silicon Paint in the initial container to suspend the powder or break up agglomerates. Stir or agitate until all solids are equally dispersed. It is recommended to stir or shake the slurry during use to keep the powder in suspension.

2. SUBTASK 70-38-41-380-101 Surface Preparation

   1. Aqueous degrease the part. Refer to the SPM TASK 70-11-03-300-503.

   2. Apply masking tape from the SPM TASK 70-34-18-380-501, to areas that are not to be coated. Make sure you apply the mask tape with an overlap of 0.010 in. to 0.100 in. (0.254 mm to 2.540 mm) around the defect.

   3. Dry abrasive blast the surfaces to be coated. Use TASK 70-12-09-120-501 dry grit blast (No. 240 or No. 320 Aluminum Oxide Grit). The grit blast material used shall be either new or used and not contaminated with impurities. This can be obtained with appropriate filters or cyclone systems.

      1. Component specific blasting data is specified on the operation sheet.

      2. During all operations following the dry abrasive blast in Step, the surfaces to be coated shall be handled with clean gloves only. Contamination by chlorides (hand sweat) shall be avoided.

      3. If the part will not be oxidized by the Oxidizing step in Step, the interval between blasting and coating shall not be more than 8 hours.

      4. Protect the part from dust until the start of the next operation and during the intervals between all subsequent operations in this task.

   4. Remove masking

   5. Oxidizing

      1. If Step or Step will be performed in 8 hours or less after the abrasive blast, then continue to Step.

      2. If Step or Step will be performed more than 8 hours after the abrasive blast, then do the subsequent procedure:

         1. Oxidize the component for a minimum of 30 minutes at 250 C - 350 C (482 F - 662 F).

         2. The interval between oxidizing and coating shall not be more than 8 hours.

   6. Apply a masking tape again or mask to the areas that are not to be coat. Make sure you apply the masking tape or mask with an overlap of 0.010 in. to 0.100 in. (0.254 mm to 2.540 mm) around the blasted area.

3. SUBTASK 70-38-41-380-151 Application of Aluminium-Silicon Slurry

   1. The CoMat 07-177 Aluminum Silicon Paint shall be applied in steps. In the process, make sure not to apply too much slurry at a time, as this may cause segregation of the constituents of the coating applied.

      1. If such segregation has taken place and the coating is subjected to diffusion annealing, deposits or speckling may form on the component, which irreversibly damages the component.

      2. If the specialist personnel is uncertain about the exact amount of slurry to be applied in each step, specimens shall be coated prior to and/or during slurry application and inspected.

   2. The areas exposed by dressing shall be covered completely with slurry.

   3. Apply the slurry by Step or by Step.

4. SUBTASK 70-38-41-380-151-001 Coat By Brushing

   1. A high-quality paint brush shall be used for paint application.

   2. A uniform coat shall be applied by brush onto the component surfaces prepared by Step.

   3. The components shall then be aired at room temperature until the color of the paint has changed from dark grey to light grey or until the paint coat is dry.

      NOTE

      The color change may be affected by both the temperature and the humidity of the room.

5. SUBTASK 70-38-41-380-151-002 Coat By Spraying

   1. A uniform coat shall be applied with a spray gun onto the components which have been prepared by Step. Make sure the coating is wet and does not show a sandy structure.

      1. Spray gun nozzle diameter: 0.020 in. - 0.060 in. (0.508 mm - 1.524 mm).

      2. Working pressure: 1 bar - 3 bar (100 kPa - 300 kPa, 14.503 psi - 43.511 psi).

   2. Dry at 60 C - 150 C (140 F - 302 F) for a minimum of 10 minutes.

   3. Apply a second uniform coat with the spray gun.

   4. Dry at 60 C - 150 C (140 F - 302 F) for a minimum of 10 minutes.

   5. If necessary, apply a third uniform coat with the spray gun, then dry at 60 C - 150 C (140 F - 302 F) for a minimum of 10 minutes.

6. SUBTASK 70-38-41-370-001 Curing

   1. After airing and pre-drying, the painted components shall be cured at 180 C - 220 C (356 F - 428 F) for a minimum of 30 minutes.

7. SUBTASK 70-38-41-220-001 Visual Inspection By The Person Executing The Work

   1. Extreme dark discoloration, blisters or cracking are not acceptable. Coatings exhibiting such non-conformances shall be removed using a soft brush and water.

      1. If required, an additional coat shall be applied by Step or Step, and then cured by Step to achieve the required coating thickness.

8. SUBTASK 70-38-41-370-051 Diffusion Heat Treatment

   1. The diffusion heat treatment may be performed in argon or in hydrogen.

   2. Prior to the diffusion heat treatment, the air shall be removed from the retort by flushing with argon, or by evacuation. Heating may commence as soon as an oxygen content of 0.2 percent by volume maximum is attained in the retort.

   3. Before production is commenced, trials shall be carried out to determine the heat treatment temperature and the soaking time needed to produce the specified coat thickness on the component being processed.

   4. Heat treatment temperatures: 870 C - 900 C (1598 F - 1652 F).

   5. Typical soaking times: 2 hours - 4 hours.

9. SUBTASK 70-38-41-120-051 Cleaning Of The Components After The Diffusion Heat Treatment

   1. Use one of the subsequent procedures to remove (clean off) undiffused powdery residues and oxide film.

   2. Scrub with a stiff brush and water, and then dry with a blast of shop air.

   3. Blasting of the coated surfaces by SPM TASK 70-12-09-120-501 dry grit blast (No. 240 or No. 320 Aluminum Oxide Grit).

10. SUBTASK 70-38-41-200-051 Quality Assurance And Process Inspection

    1. Definitions

       1. Batch: A group of parts which have been processed together through a complete diffusion heat treatment cycle in the same furnace at the same time.

    2. Acceptance limits

       1. If a specimen from a batch does not fulfill the acceptance limits, the entire batch represented by the specimen in question shall be rejected.

       2. Visual Inspection

          1. Unacceptable conditions are:

             1. Flaking

             2. Chipping

             3. Blisters

             4. Uncoated areas

             5. Exceptionally speckled appearance (leopard fur)

          2. Steps in the transition area between old and new coating that can be felt with the finger are not permitted.

          3. Components exhibiting visually discernible steps that can, however, not be felt shall be subjected to cosmetic blasting. Following this blasting operation, no steps are permitted.

          4. Surfaces that were covered by adhesive tape or paste have a dull, dark grey appearance, whereas the repair coated areas can be lighter.

          5. The repair coated areas can be surrounded by a light, metallic bright strip several millimeters in width.

       3. Coating Thickness (measured on a representative process sample by metallographic evaluation)

          1. In the area of the new coat, measured at not less than three places, however outside the old/new coating overlap, refer to the repair procedure.

          2. If the thickness is not specified in the repair it shall be between 0.040 mm and 0.120 mm.

    3. Imperfect coatings

       1. If inspection shows that the diffusion coating is too thin, the components may be recoated provided the coat is satisfactory in all other respects. If possible, the same quality control specimens should be recoated with the components. Otherwise, a component from the same batch shall be used as quality control specimen. The diffusion heat treatment parameters shall be determined by Step.