Preliminary Requirements

Safety Requirements

WARNING

IT IS THE RESPONSIBILITY OF THE OPERATOR TO OBTAIN AND OBSERVE THE MANUFACTURER'S MATERIAL SAFETY DATA SHEETS FOR CONSUMABLE MATERIALS INFORMATION. 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 70-31-09-310-001 Deleted

2. SUBTASK 70-31-09-310-006 Preparation

   1. General.

      1. It is necessary to keep the work area clean before vacuum brazing. Components which are cleaned and degreased must not be touched by hand unless clean gloves are used.

   2. Dimensional inspection.

      1. Inspect the components to make sure the brazing gap is correct to the drawing limits.

   3. Cleaning.

      1. The brazing joints must have no corrosion, scale, oxide layers, oil, grease or paint. For the vapor degrease of the parts refer to the SPM TASK 70-11-01-300-503, or clean in CoMat 01-060 ACETONE (CH3)2CO. Components which show oxide formation on the surface can be removed by Step and Step.

   4. Bright annealing.

      1. Steel components must be bright annealed in a vacuum at a temperature of 1832 to 2192 deg F (1000 to 1200 deg C) for 5 to 10 minutes. The annealing temperature will be specified in the Engine Manual.

   5. De-oxidizing.

      1. Surfaces must be descaled or deoxidized, if necessary by the applicable procedures.

   6. Mechanically clean.

      1. Mechanical treatment with felt polishing wheels is permitted. These must be used on one applicable material only and will be identified. The components must be then cleaned with vaporous trichloroethane.

   7. Blasting.

      1. The use of silicon carbide or quartz for blasting is permitted. Do not use aluminum oxide.

   8. Assembly.

      1. Where wettability is thought to be low, the components can be nickel plated in the brazing areas (to a maximum of 0.0004 inch (0.01 mm)).

      2. Tacking can be done by TIG welding or resistance welding which use capacitor spot welding units or AC welding units. Other tack welding procedures (spot welding which uses balls of nickel-base materials) must have the authority of the Engine Manual Authority. Capacitor discharge welding units will give good results when tack welding sheet less than 0.002 inch (0.05 mm) thick.

   9. Brazing alloy.

      1. NOTE

         The use of fluxes is not permitted in a vacuum furnace.

         Prepare the braze alloy.

         1. Mix brazing alloy powder with CoMat 03-290 BINDER, BRAZING ALLOY or CoMat 03-291 BINDER, BRAZING ALLOY or CoMat 03-292 BINDER, BRAZING ALLOY or CoMat 03-293 BINDER, BRAZING ALLOY or an equivalent binder. A prepared mixture which contains these binders can be applied with a metering unit.

      2. Limit the brazing alloy.

         1. Use stop-off to keep the braze alloy in position when brazing. The permitted stop-off materials are CoMat 03-295 STOP-OFF MATERIAL, CoMat 03-294 STOP-OFF MATERIAL, CoMat 03-296 STOP-OFF MATERIAL and CoMat 03-297 STOP-OFF MATERIAL.

         2. If you are not sure which stop-off to use, test a sample of stop-off on a test piece.

         3. Stop-off, where possible must be applied before the brazing alloy. Make sure that the stop-off does not get in to the braze joint and affect the joint. Use a wire loop artists brush or rapidograph or injector to apply the stop-off. Some types of stop-off (nicrobraz) are adhesive tape.

3. SUBTASK 70-31-09-310-002 Vacuum Furnace

   1. The type of furnace must do modern brazing work (cold wall construction).

   2. The furnace and loading racks must be of heat resistant alloys (L605, INCO600, TZ molybdenum or equivalent) or graphite. The bottom to hold the furnace load is to be made of graphite or AL2O3.

   3. The necessary thermal tolerance is for a maximum of plus or minus 50 deg F (10 deg C). To monitor the furnace, position four thermocouples in important heat areas on to the components. The use of digital voltmeters to get the instrument quality necessary is recommended. Select the thermocouples to get the thermal range for which they are used.

   4. The serviceable vacuum must be a minimum of 1.33 x 10-4 mbar.

   5. After full heat for a number of hours, the leakage and gas given out rate in the furnace, with the main vacuum valve closed must not be more than 1 x 10-3 mbars l/s. The test temperature at the time must be below 8640 deg F (150 deg C). When heated up, the furnace must not be opened before the measurement for leakage.

4. SUBTASK 70-31-09-310-003 Brazing

   1. Test example.

      1. When brazed components do not have sufficient time-tested furnace settings, a test piece braze joint must be used to record the data. The data can be heat rate, soak temperature and time, brazing temperature and dwell time, cool pattern and the position of parts.

   2. Leakage test.

      1. Leakage tests must be done at given times. When a process is very important a leak test must be done before each brazing operation.

      2. The leakage rate is usually tested when the furnace is at an operation temperature of 122 deg F (50 deg C) above the process temperature. Heat for three hours at full temperature. In special processes make an estimate of the vacuum through the analysis of the make-up of the remaining gas (mass spectrometer).

   3. Load the furnace.

      1. When the furnace is loaded, the position of the components must be selected so that the flow of brazing alloy is helped by gravity. Component surfaces that are not to be wetted but can get brazing alloy on must have stop-off applied.

   4. The heat and hold of the temperature.

      1. The heat rate that is used until the balanced soak temperature is got to, can change with the material, the shape of the component and the size of the furnace load.

      2. To make sure a constant temperature during the load is got, a constant temperature soak point must be selected. The soak point temperature must be 86 to 104 deg F (30 to 40 deg C) below the solidus point of the brazing alloy used. The balance must be got within 30 minutes. When 4 thermocouples are used on the load, at least three of them must show the selected soak temperature. If the thermal balance is not got to, the cycle must be stopped and the load cooled in a vacuum. When a cycle is stopped, tell the necessary functional department, who will give the correct procedure to use.

      3. When joints are brazed on thin components, the brazing alloy can cause bad erosion which will make the component unserviceable. Careful calculation is necessary for the amount of brazing alloy, the brazing temperatures and the soak times when brazing thin components. The operation sheet will give the heat and cool rates in the solidus-liquidus range.

   5. Brazing time.

      1. For nickel base brazing alloys the brazing time is 10 to 15 minutes. For precious-metal brazing alloys a number of minutes will be sufficient.

   6. Cool rate.

      1. The cool rate that is used after brazing is different for each component. It will be necessary to find the cool rate by the use of test pieces and then record data on the operation sheet. On some materials it can be possible to mix the brazing operation with other heat treatment operations to make a single cycle.

   7. Partial-pressure operation.

      1. When using brazing alloys with high vapour pressure (brazing alloys containing silver, manganese or copper), the brazing alloy begins to evaporate at the brazing temperature in a high vacuum, causing undesirable deposits in the interior of the furnace. When evacuated, the furnace shall be flushed with argon to achieve a partial pressure of 1 x 10-1 mbar before the solidus point is reached.

5. SUBTASK 70-31-09-290-001 Acceptance Limits

   1. General.

      1. Each initially brazed part shall be inspected metallographically. This also applies when the brazing conditions are changed.

         1. Test specimens may be used for the assessment of the braze if the shape, size and nature of mated materials fully represent the brazed joints of the original parts.

   2. Maximum allowable defects.

      1. The total surface area of discontinuities, pores, or inclusions, shall not be greater than 20 percent of the brazed area. A single defect shall not be in longer than 20 percent of the length of the total joint in any one ground and polished test section. These limits apply to visual and radiographic inspection of joints.

   3. Visual inspection.

      1. The acceptance limits for visual inspection with a 2x illuminated magnifying glass are as follows:

         1. All fillets must be continuous. Fillets extending into the area of the parallel gap are not allowed.

         2. Pores in fillets are allowed if the distance between pores is greater than the diameter of the pores.

         3. Braze residue (for example, splashes, tears) is permitted on non-rotating parts and vanes if it is firmly attached and blended (approximately 20 micro braze thickness). Braze residue is permitted on functional surfaces only if the function is not impaired. All forms of braze residue is permitted on surfaces that are to be machined.

         4. Braze residue is not permitted on rotating parts and functional surfaces of blades. In case of uncertainty with regard to functional surfaces, contact IAE.

            1. NOTE

               Inspection with fluorescent penetrant can produce large amounts of background fluorescence because of the rough surface of the braze. If this occurs, contact IAE for instruction for additional processing or finishing prior to crack inspection.

               Crack inspection.

            2. Fluorescent penetrant inspection, or magnetic particle inspection must not indicate cracks in the base metal or the braze.

      2. Ball test.

         1. Use balls to test for pipeline constrictions. Constrictions are permitted if the restriction is not greater than 10 percent of the rated diameter.

      3. Pressure test.

         1. Do a pressure test if specified in the engine manual. The test pressure shall be specified by the engine manual.

6. SUBTASK 70-31-09-310-004 Post treatment

   1. Post treatment is usually not necessary on vacuum brazed components. If components have stop-off applied before brazing it can be removed by wet blasting to the SPM TASK 70-12-03-120-501, or mechanically by felt or rubber polishing wheels. Felt wheels must be used for special materials and must be identified.

7. SUBTASK 70-31-09-310-005 Rework

   1. Defective braze joints can be repair-brazed two times. The brazing alloy is only to be applied in the defective area. With some nickel-base brazing alloys, the alloy used in the repair-brazing can be the same as that used initially. With other nickel-base brazing alloys, the alloy used for repair-brazing must be lower in solidus point and fillers can be added. When you are not sure, contact the Production Methods Department of the Materials Laboratory.

      1. To break and rebraze a defective braze joint (which could be with silver alloys of low melt point) will usually result in damage to the component.