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A
747-400
MAINTENANCE MANUAL
B. Consumable Materials
(1)
G02330 Brush, Stiff Bristle Non-metalic
(2)
C00934 Burring Polishing Compound (PMC 3061)
(3)
C00000 Compound, Silicon Carbide Deburring
(PMC3088)
C.
Blending
NOTE: Blending is an operation that is used to remove nicks,
____ scratches, and other surface irregularities by intentional removal of base metal. Manual or mechanical methods are used to produce shallow and smooth surface depressions that reduce the stress concentration from the damaged area by the distribution of the stress concentration over larger, more tolerant areas.
S 122-007-N00
(1) General Guidelines (unless specified differently)
(a)
Cracks are not repairable by blending.
(b)
Non-toleranced enclosed areas defined in blend repairs are to corners, points of tangency between surfaces, or at points opposite one of these locations. Enclosed areas will assume tolerance of plus 0.125 inch in all directions unless adjacent areas are specified as areas where blending is not permitted.
(c)
It is better to blend sharp impact damage that is within acceptable limits than it is to accept that damage. The sharper the impact, the better it is to blend the damaged area.
(d)
The best blends are the ones which are smooth, continuous, and round-bottomed that extend outboard from the damage area as much as necessary.
(e)
It is recommended that you make one single blend when the adjacent damage is so close together that the minimum length-to-depth blend ratio cannot be done independently.
(f)
The depth of the blend must be as deep as necessary to remove the damage with the repair limits specified. The only time it is permissible to increase the depth of the blend to remove material that is not damaged is when there are unwanted surface stresses (at high temperature or high force) that are a result of the damage; then, it is permissible to remove an additional 0.002-0.003 inch minimum beyond the depth of the damage.
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A
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MAINTENANCE MANUAL
(g)
For rotating parts, the length of the blend must be a minimum of 15 times the maximum depth of the blend in all directions. For non-rotating parts, the length of the blend must be a minimum of 10 times the maximum depth of the blend in all directions.
(h)
The surface finish of the blended area must be as smooth as, or smoother than, the initial surface. You can compare the surface finish with the adjacent non-blended surface.
(i)
All transitions from blended to nonblended areas must be smooth and continuous.
(j)
If the blended area intersects adjacent radii, the initial radius contour must be restored. Butterfly polish holes by SPOP 502, as necessary.
(k)
If the blended area intersects a corner, break the sharp edges 0.003-0.015 inch.
(l)
For local damage in the form of raised material, manual blending (blending by hand) is the preferred method.
(m)
When blending on a cylindrical surface, blend in the
circumferential direction.
(n)
Blend engine radial menbers in a radial direction.
(o)
For parts that are smaller than 1.75 inches in length, the manual blending method is recommended.
S 122-008-N00
(2) Manual Blending (Blending by Hand)
(a)
Manual blending is done with abrasive stones, abrasive paper, abrasive pads, files, and/or crocus cloth.
(b)
Blending can be done with more than one grade of abrasive (coarse to fine, as necessary) to remove damage and get the specified surface finish. Be sure to start with the least aggressive abrasive needed to remove the damage.
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