Preliminary Requirements

Safety Requirements

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 70-31-16-310-001 Application

   1. Primary for vacuum furnace brazing of structures for use up to 1500 deg F (816 deg C). Induction brazing in argon can be used when specified.

2. SUBTASK 70-31-16-310-002 Materials

   NOTE

   Preforms must be used for tube-to-fitting joints.

   Specified wide gap filler materials can be used in addition to identified filler metal for vane and shroud assemblies, and for other parts when specified.

   Flux must not be used.

   1. Filler metal must be identified by this specification number and suffix number as follows.

      1. Identification PWA 36950-3 (Ref), Braze filler metal (See note 1.) CoMat 03-249 BRAZING FILLER MATERIAL,Ni-BASE or CoMat 03-150 DELETED, or CoMat 03-251 BRAZING FILLER MATERIAL,Ni-BASE. Wide gap filler metal (See note 2.) CoMat 03-250 BRAZING FILLER MATERIAL,Ni-BASE.

3. SUBTASK 70-31-16-310-003 Brazing Atmosphere

   1. Refer to Figure.

4. SUBTASK 70-31-16-310-004 Preparation

   1. Surface roughness.

      For joints not prepared by nickel plating, a surface rougher than 60 microinches is recommended, but not necessary.

   2. Prepare surface.

      Surfaces to be brazed must be prepared before assembly. Refer to TASK 70-31-20-301-501.

   3. Nickel plating (where specified).

      1. Refer to Figure.

      2. For induction or furnace brazing in a protective atmosphere, or in a vacuum, surfaces of these materials to be joined by silver, gold, or nickel braze alloy must be nickel plated in the brazing area (TASK 70-33-06-300-503) to the applicable thickness specified in Figure.

5. SUBTASK 70-31-16-310-005 Procedure

   NOTE

   Part temperature must not be more than this maximum during brazing cycle.

   Time at brazing temperature must be more than 30 minutes. When extended time at temperature is necessary to aid diffusion, it must be as specified in note 3.

   When suffix letter D is specified after suffix number, total time at brazing temperature must be 170 to 190 minutes.

   1. Heating of parts to be brazed must be done in a furnace apart from alloys which do not get hard by heat treatment which can be heated by electrical induction. Parts must be heated to a stabilization temperature and held until both temperature and pressure have stabilized as follows. Identification PWA 36950-3 (Ref). Stabilization temperature 1675 deg to 1750 deg F (913 deg to 954 deg C). Brazing temperature maximum (See note 1) 1950 deg F (1065.6 deg C). Temperature must then be raised quickly to the brazing temperature (See note 2).

6. SUBTASK 70-31-16-310-006 Cooling

   1. 

      CAUTION

      COOLING RATES SPECIFIED BY THE ENGINE MANUAL MAY BE DIFFERENT FROM THE STANDARD PRACTICES/PROCEDURE MANUAL (SPM). ADHERENCE TO ENGINE MANUAL REPAIR INSTRUCTIONS SUPERSEDES THE SPM REPAIR INSTRUCTIONS.

      Decrease the temperature of assemblies to the "Braze Quench" temperature at a rate (slow or fast) to prevent cracks and minimize internal stress and distortion.

   2. Brazing atmosphere must be kept until parts have cooled to below scaling temperature.

   3. Alloys which get hard by heat treatment must be cooled at a rate not less than 35 deg F (19 deg C)/minute from below the "Braze Quench" temperature to 1100 deg F (593 deg C) and not less than 15 deg F (8 deg C)/minute from 1100 deg F (593 deg C) to 1000 deg F (538 deg C). Use any rate below 1000 deg F (538 deg C). There is no requirement to hold parts at the "Braze Quench" temperature during cooling from the braze temperature.

7. SUBTASK 70-31-16-310-007 Rebrazing

   1. Brazed joints can be rebrazed using initially necessary heating procedure and brazing alloy. Maximum of two rebraze cycles for each part is permitted.

   2. Local rebrazing of compressor vane and shroud assemblies is permissible to fill braze voids using critical braze alloy wire. Heating must be by plasma or gas tungsten arc torch for each approved procedure. Assemblies which include materials which get hard must be solution heat treated or austenitized, as applicable after rebrazing.

8. SUBTASK 70-31-16-310-008 Properties

   1. Brazed parts must agree to the subsequent specifications.

      1. Appearance.

         1. A check of the exterior of the joint must show a full line or ring of brazing alloy between the component parts at end of joint to which brazing alloy was put in use and when applicable, must show at least a metallic stain of brazing alloy at opposite end of joint, to show full entry of brazing alloy in the joint.

      2. Coverage.

         1. Area joined by brazing alloy must not be less than 80 percent of the area of the mating portions of the assembly. Procedures to find that this specification is met must be as agreed upon by the purchaser and the supplier.

         2. Tube wear sleeve and bracket-washer joints with 50 percent minimum area of coverage and not a complete line of brazing alloy at joint bond line are permitted.

9. SUBTASK 70-31-16-310-009 Quality

   1. Depth of alloying at joint must not be more than 0.004in. (0.102 mm) when measured from initial parent metal surface and undercutting must not be more than 0.002in. (0.051 mm), but the depth of alloying plus undercutting must not be more than 0.004in. (0.102 mm).

   2. Brazed joints must be sound, clean and free of cracks and other defects dangerous to usage of assemblies.

   3. Surfaces of parts must be free of pitting, burning, oxidation, decarburization, alloy loss and excessive brazing alloy. Some change in color is permitted.

Figure: Brazing atmosphere

Brazing atmosphere



Figure: Nickel plating

Nickel plating