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 70-31-15-310-001 Application and Preparation

   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. Materials.

      1. Refer to Step (Table 1).

      2. Filler metal must be identified by this specification number and suffix number as in Step.

   3. Brazing atmosphere.

      1. Refer to Step (Table 2).

   4. Preparation.

      1. Surface roughness.

         1. For joints not prepared by nickel plating, a surface rougher than 60 microinches (0.000060in. or 0.0015mm) is recommended, but not necessary.

         2. If surfaces are prepared by abrasive blasting refer to the SPM TASK 70-31-20-310-501.

      2. Surface cleaning.

         Surfaces to be attached must be cleaned before assembly. Refer to SPM TASK 70-11-26-300-503.

      3. Nickel plating.

         1. Refer to Step (Table 3).

         2. Joints must be prepared by nickel plating as AMS 2403 or AMS 2424.

         3. Brazing alloy must be put into from internal surfaces of tube-to-fittings joints.

2. SUBTASK 70-13-15-310-002 Nickel Brazing Procedure

   1. Refer to Step (Table 4).

   2. Heating of parts to be brazed must be done in a furnace but alloys which do not get hard by heat treatment can be heated by electrical induction. Parts must be heated to a stable temperature (Refer to SUBTASK 70-31-15-301-006) and held until the temperature and pressure have become stable. Temperature must then be raised quickly to the brazing temperature in SUBTASK 70-31-15-301-006 Note 1.

   3. 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 keep to a minimum internal stress and distortion.

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

   4. Re-brazing.

      1. Brazed joints can be re-brazed using the initial necessary heating procedure and brazing alloy. Maximum of two rebraze cycles for each is permitted.

         1. Local rebrazing of compressor vane and shroud assemblies is permitted to fill braze voids using the initial brazing alloy wire. Heating must be by plasma or gas tungsten are torch for each procedure made. Assemblies which include materials which can be made hard must be solution heat treated or austenitized, as applicable, after rebrazing.

   5. Properties.

      Brazed parts must agree to the subsequent specifications.

      1. Appearance.

         Examine the joints externally and they must show a full line or ring at brazing alloy between the component parts at the end of the joint to which the brazing was put and when possible, must show at least a metallic stain of brazing alloy at opposite end of the joint, to show the brazing alloy went fully through the joint.

      2. Coverage.

         Area attached by brazing alloy must not be less than 80 percent of the area of the mating parts of the assembly. The supplier and purchaser must agree to find a procedure which is to be met for the necessary step given before.

         Tube wear sleeve and bracket-washer joints with 50 percent minimum area of cover and a not complete line of brazing alloy at the point edge are satisfactory.

   6. Quality.

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

      2. Brazed joints must be good, clean, and free of cracks and other defects dangerous to the use of assemblies.

      3. Surfaces of parts must be free of pitting, burning, oxidation, decarburization, alloy depletion and to much brazing alloy. Some changes in color is permitted.

3. SUBTASK 70-31-15-310-003 Table 1 Filler Metal

   Designation	Braze Filler Metal *	Wide Gap Filler Metal **
   PWA 36950-2	CoMat 03-249 BRAZING FILLER MATERIAL,Ni-BASE	CoMat 03-250 BRAZING FILLER MATERIAL,Ni-BASE
   * Preforms must be used for tube-to-fitting joints.
   ** Specified wide gap filler materials can be used in addition to designated filler metal for vane and shroud assemblies, and for other parts when specified.
   Flux must NOT be used.

4. SUBTASK 70-31-15-310-004 Table 2 Brazing Atmosphere

   Type	Dew Point Maximum (see Note 1)	Pressure/Purity	Application
   Vacuum		5x10-4 Torr (0.5 Micron Hg) Or Better (See Notes 2 and 3)	Furnace Brazing
   CoMat 03-010 ARGON GAS CoMat 03-117 ARGON GAS Argon	-35 degrees F (37C) or Better	99.99 percent Minimum	Induction Brazing and Vacuum Furnace Back-Fill
   1 Shall be determined on gas being exhausted from the brazing chamber.
   2 Leak up rate shall not exceed 60 microns Hg/hour determined at room temperature after pumping down to one micron Hg or lower pressure and blocking pumps.
   3 Partial pressure of Argon permitted by back-filling with argon after attaining required vacuum.

5. SUBTASK 70-31-15-310-005 Table 3 Nickel Plating

   		Nickel Plating Thickness in Inch (mm)
   Alloy		Vacuum	CoMat 03-010 ARGON GAS Argon CoMat 03-117 ARGON GAS Argon
   Precipitation Hardenable Iron Base Alloys		0.0006 (0.0152) maximum	0.0004-0.0006 (0.01016-0.0152)
   Titanium Stabilized Stainless Steels		Optional (See Note 2)	Optional (See Note 3)
   Precipitation Hardenable Nickel Base Alloys	(a) Ti+Al Content Less Than 4 Percent Nominal	0.0006 (0.0152) maximum	0.0004-0.0006 (0.01016-0.0152)
   	(b) Ti+Al Content More Than 4 Percent Nominal or Greater	0.0008-0. 0012 (0.0204-0.0304)	0.0008-0.0012 (0.0204-0.0304)
   Non-Precipitation Hardenable Nickel Based Alloys, Ti+Al Content Up To 1 Percent		Optional (See Note 2)	0.0001-0.0006 (0.0026-0.0152)
   All Other Alloys		Optional (See Note 2)	Optional (See Note 2)
   1 Nickel plating in areas other than joints is optional and can be incomplete.
   2 If Nickel plating is used , plating thickness must be 0.0001-0.0006 inch (0.0026-0.0152mm).
   3 If Nickel plating is used, plating thickness must be 0.0004-0.006 inch (0.0102-0.0152mm).

6. SUBTASK 70-31-15-310-006 Table 4 Heating Procedure

   Designation	Stabilization Temperature	Brazing Temperature, Maximum *
   PWA36950-2	1675 deg F to 1750 deg F (913 deg to 954 deg C)	1950 def F (1066 deg C)
   * Part Temperature must not be more than this maximum during brazing cycle.
   1 Time at brazing temperature must not be more than 30 minutes. When extended time at temperature is required to aid diffusion, it must be as specified in Note 2.
   2 When suffix letter D is specified after suffix number, total time at brazing temperature shall be 180+/-10 minutes.