Standard Blending Procedure [CFML]

TASK 70-28-00-910-808-A
Standard Blending Procedure

1. Reason for the Job
Self explanatory
2. Job Set-up Information
A. Fixtures, Tools, Test and Support Equipment

REFERENCE	QTY	DESIGNATION
No specific	AR	ABRASIVE STONE
No specific	AR	CLOTH-CROCUS
No specific	AR	CLOTH-EMERY, FINE
No specific	AR	FILE - FINE
No specific	AR	PAPER - ABRASIVE, FINE
No specific	AR	TAPE - MASKING

B. Referenced Information

REFERENCE	DESIGNATION
TASK 70-25-00-910-802-A	Fluorescent-Penetrant Inspection-Portable-Water Washable
TASK 70-27-00-910-811-A	Swab Etching Procedure and Cleaning
Blending Procedure

3. Job Set-up
Subtask 70-28-00-941-050-A

A. General
(1) This task gives instructions for these four types of blending:
(a) Hand blending.
(b) Power blending.
(c) Component specific requirements - Blending Airfoils.
(d) High metal removal.
(2) General Information

NOTE: Refer to the engine/aircraft manual section or Service Bulletin for the blending limits of the part you will blend. Use the limits in this procedure only when no limits are specified in the applicable manual or Service Bulletin.

(a) Blending is a repair procedure you use to remove stress concentrations on critical parts. These stress concentrations are caused by nicks, scratches or other sharp edged damage marks. When you blend a part, you remove material around the stress concentration. You blend the sharp edges into a smooth contour which releases the stress concentration. This will decrease the chance of a crack starting on the part and allows you to extend the life of the part.
(b) You also blend to remove sharp edges that occur when you machine or drill a part. A blend procedure will also repair the original contour and surface finish to parts. This can be necessary after parts are welded or brazed.
(c) The finish on the blended area must be as close as possible to the original finish of the part.

4. Procedure

WARNING: WHEN YOU DRILL, MACHINE, BLEND, GRIND OR SAND PARTS, USE PROTECTIVE CLOTHING, GLOVES, DUST MASK AND GOGGLES. BE CAREFUL NOT TO BREATHE THE DUST OR LET IT TOUCH YOUR SKIN. DUST AND PARTICLES ARE DANGEROUS FOR YOUR HEALTH.

Subtask 70-28-00-320-050-A

A. Blending Procedure
(1) If there is more than one defect, measure the distance between the defects and follow these steps:
(a) Blend separately defects that are more than 0.25 in. (6.3 mm) apart.
(b) Blend together defects that are less than 0.25 in. (6.3 mm) apart (except splines).
(c) Blend separately defects on splines that are closer than 0.25 in. (6.3 mm).
(2) Do these steps for hand blending:
(a) Use ABRASIVE STONE, PAPER - ABRASIVE, FINE, FILE - FINE or a CLOTH-CROCUS to blend the sharp edges on the part:
1 Use a coarse abrasive or a FILE - FINE to remove metal quickly.
2 Use a less coarse abrasive or CLOTH-CROCUS to make a smooth surface finish.
(b) When you blend rotor blades, stator vanes or equivalent type parts, do these steps:
1 Refer to the applicable inspection and repair procedures for blend limits on each part of the engine.
2 Make the blend in the radial direction.
3 When you remove metal from an airfoil section, make sure that the edges do not become thin or sharp.
4 Make sure that you do not change the original contour of the airfoil section.
(c) When you blend a part with a cylinder shape, blend in a circumferential and not along the axis of the part.
(d) Try to make the finish on the completed blend equivalent to the finish on the remaining area of the part.
(e) When you blend on a part that has a radius, do these steps:
1 Keep the radius as specified in the repair procedures.
2 If the radius is not specified, keep it as near as possible to the original contour.

NOTE: If necessary, refer to an equivalent part to find the original radius.

(f) After you blend, do these steps:
1 Clean by swab etching (Ref. AMM TASK 70-27-00-910-811).
2 Inspect using fluorescent penetrant (Ref. AMM TASK 70-25-00-910-802).
(3) Do these steps for power blending:

CAUTION: WHEN YOU DO THE POWER BLENDING PROCEDURE ON AN AIRFOIL SECTION, ALWAYS REFER TO THE SPECIFIED AMM TASK. IF YOU DO NOT REFER TO THE AMM TASK, YOU CAN CAUSE DAMAGE TO THE PART.

CAUTION: WHEN YOU USE POWER GRINDING OR BLENDING TOOLS, MAKE SURE THAT THE ENGINE BLADE DOES NOT BECOME TOO HOT. IF THE BLADE BECOMES TOO HOT, LET IT COOL BEFORE YOU CONTINUE THE REPAIR. TOO MUCH HEAT DURING GRINDING OR BLENDING CAN MAKE THE BLADE WEAKER.

(a) Use points made of an abrasive material bonded to rubber to blend most parts:
1 Use the points with a power drive to blend and polish the parts.
(b) If there are special instructions to blend a part, make sure that you follow those instructions.
(c) Use the coarser grades of the abrasive tools or materials to start the blend of the part.
(d) Use the less coarse grades to complete the blend of the part.
(e) When you blend with power tools, make sure you follow the same specifications as when you blend the part manually.
(f) After you complete a power blend on titanium, you must blend the area 0.002 in. (0.05 mm) more in depth manually.

NOTE: This will remove the remaining stress in the surface material.

(g) After you blend, do these steps:
1 Clean by swab etching (Ref. AMM TASK 70-27-00-910-811).
2 Inspect using fluorescent penetrant (Ref. AMM TASK 70-25-00-910-802).
(4) Do these steps for component specific requirements for blending airfoils:

NOTE: Refer to the engine manual, airplane maintenance manual or service bulletin for the blend limits of the piece part. Use the limits in this procedure only when no limits are specified in the manual or applicable Service Bulletin.

(a) Refer to the applicable part inspection paragraph for the specifications of the airfoil damage limits.
(b) A manual or power blend can repair these types of airfoil damage:
1 Nick
a A V-shaped depression in the airfoil with a sharp edge.
2 Pit
a A circular hole with sharp edges with a rounded bottom caused by erosion.
3 Scratch
a A V-shaped line or furrow made by a sharp object that touched the surface of the airfoil.
4 Dent
a A smooth, circular depression made by a circular object that hit the airfoil. If there is a sharp edge in the depression, then the damage is a nick. If the leading edge or trailing edge has a wave shape, the damage is a dent.
5 Erosion
a The effect of sand or dust that goes through the engine. Sand or dust will wear down the leading edges and the leading part of the concave side.
6 Torn Metal
a A separation of material by force that has left jagged edges.
(c) Do a manual blend of the airfoils as follows:
1 Blend the airfoil to remove nicks, pits and scratches.
2 Blend to remove high metal and to straighten the dents (where permitted).
a Make sure that you repair the airfoil shape to as near as possible to its initial aerodynamic contour.
3 Complete the blend with a fine ABRASIVE STONE or CLOTH-CROCUS as follows:
a Use coarser tools for the initial removal of material.
b Complete the blend in a direction along the length of the blade or vane.
c Make sure to remove all marks on the airfoil that you made during the initial steps of the blend procedure.

CAUTION: KEEP THE SHAPE OF THE BLENDED AIRFOIL LEADING EDGE AS NEAR AS POSSIBLE TO THE ORIGINAL CONTOUR OF THE MATERIAL AIRFOIL. IF THE SHAPE OF THE BLENDED AIRFOIL IS DIFFERENT FROM THE ORIGINAL CONTOUR OF THE AIRFOIL, ENGINE STALLS AND ENGINE DAMAGE CAN OCCUR.

4 Do a check of the airfoil dimensions after you blend:

NOTE: The procedure gives the blend limits as depth dimensions. This makes it easy to see the quantity of damage you can repair. You can use the depth limits for rework. The minimum chord limit is the most important dimension. Make sure that you do not blend more than this limit. If you blend an area that shows signs of a previous repair, make sure that you obey the minimum chord limit. The procedure gives depth limits and minimum chord limits in decimal and fraction forms. If the depth and chord limits do not agree, use minimum chord dimension to find if the part is serviceable.

NOTE: The procedure gives defect limits as depth dimensions since this dimension has an effect on the strength of the part. Special equipment is necessary to measure a depth limit accurately. You can compare the depth of the defect with the thickness of a known item. You can use a thickness gage or a piece of lockwire to make a good estimate of the depth.

a If there is more than 0.25 in. (6.3 mm) between the defect areas, do not blend them together.
b If there is less than 0.25 in. (6.3 mm) between the defect areas, you can blend the areas together.
c All blends must have a minimum radius of 0.25 in. (6.3 mm).
d You can decrease the chord width on only one side of the part or divide it between the two sides.
e The minimum limit of the chord width controls the quantity of blend work you can do.

The procedure gives the minimum permitted chord for the root and tip of the airfoil. The minimum chord at the other points is proportional.

f Make sure that you do not change the contour of the airfoil section.

NOTE: This will help prevent an engine stall.

5 Swab etch cleaning:

CAUTION: YOU MUST USE A BRUSH OR SWAB TO APPLY THE PENETRANT ON THE PARTS THAT HAVE OPENINGS FOR AIR FLOW. IF YOU DO NOT USE A BRUSH OR SWAB, THE PENETRANT WILL FILL THE OPENINGS AND CAUSE DAMAGE TO THE PART.

a Do a swab etch procedure on the area where you did the blend repair (Ref. AMM TASK 70-27-00-910-811).
6 Examine the part again as follows:
a Inspect using fluorescent penetrant (Ref. AMM TASK 70-25-00-910-802).
(d) Power blend the rotor blades, the variable vanes, and the vane segments as follows:
1 Apply TAPE - MASKING on the airfoil adjacent to the area that you will do the blend procedure.

NOTE: This will prevent damage to the airfoil during the blend procedure.

2 Use a coarse grade silicon carbide soaked rubber wheel or point for the initial blend the blades or vanes.
3 Use fine to extra-fine grades of an abrasive wheel to complete the blend of the defects.
a Remove only the minimum necessary quantity of material to repair the defect.
b Apply light pressure on the wheel to make a radius on the leading and the trailing edges of the airfoil.

NOTE: This will let the cushion effect of the abrasive wheel blend the radius and buff the defect.

4 Swab etch cleaning:

a Do a swab etch procedure on the area where you did the blend repair (Ref. AMM TASK 70-27-00-910-811).
5 Examine the part again as follows:
a Inspect using fluorescent penetrant (Ref. AMM TASK 70-25-00-910-802).
6 If there are loose parts, put the repaired blades and the vanes in containers for protection.

NOTE: This will help to prevent damage when you move the parts.

7 Carefully do a check on the blades and the vanes.
(e) Do the blend procedure on small indications in tubing as follows:
1 Use a fine ABRASIVE STONE, a FILE - FINE, CLOTH-EMERY, FINE or CLOTH-CROCUS to blend.
2 Blend around the circumference of the tubing.

NOTE: Try to make the finish on the completed blend equivalent to the finish on the remaining area of the part.

(5) Remove high metal as follows:

NOTE: High metal is metal that is above the usual surface of the metal. You usually find high metal around nicks and scratches.

(a) Use a fine ABRASIVE STONE, CLOTH-EMERY, FINE or CLOTH-CROCUS to remove high metal.
(b) Remove only the material that is above the initial surface contour.

[Rev.10 from 2021] 2026.04.01 13:09:15 UTC