(10)
Rubber block (durometer reading of 35 + 5, Shore A scale) or wood block
(11)
Buffing wheels
(a)
Stitched muslin wheels - 4 inches to 10 inches diameter
(b)
Unstitched muslin wheels - 4 inches to 10 inches diameter
(12)
Buffing compounds
(a)
Learock No. S-30 (Ref 20-30-51)
(b)
Learock No. 888 (Ref 20-30-51)
(c)
0000 rouge
(d)
Dupont 7 (Ref 20-30-51)
(e)
Polysand (Ref 20-30-51)
(13)
Wax - Simonize (Ref 20-30-51)
C. Examine the lens for cracks to determine if the lens is repairable.
NOTE: Do these repairs before the defects are more than the crack limits.
(1)
Cracks in acrylic plastic not longer than five inches are repairable.
(2)
Continuous cracks in the acrylic plastic, which extend across the lens from one fastener hole to another in multiple locations, are acceptable provided a minimum of two fasteners are on each side of the crack.
(3)
If a continuous crack is found, inspect the lens during each subsequent A check and replace the lens at the next C check.
D. Prepare for Repair
(1) Prepare cement PS-18 (Component A - base, Component B - catalyst, Component C -promoter).
(a)
Add one capsule (2.4 grams) of component B to 4 fluid ounces (118cc) of component A and dissolve by stirring. This mixture can be stored up to 24 hours at 35-40oF.
(b)
Just before using, add 5 cc of component C to the above mixture and stir thoroughly. The pot life of this cement at 75oF is 10 minutes.
WARNING: THE FOLLOWING PRECAUTIONS MUST BE OBSERVED IN USING THIS CEMENT: DO NOT MIX COMPONENT B DIRECTLY WITH COMPONENT C AS A VIOLENT REACTION WILL OCCUR. AVOID CONTACTING THE SKIN WITH COMPONENT C. WASH CONTACTED SKIN AREAS IMMEDIATELY WITH SOAP AND WATER.
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May 01/01 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 57-21-11 Page 801
(2) Prepare Cement EC-2216B/A
(a) Blend equal parts by weight of EC-2216B (base) and EC-2216A (accelerator). Pot life of the blended adhesive is about 90 + 10 minutes at 70-800F.
E. Repair Cracks in Forward Fairing
(1)
Stop drill the crack by drilling a 1/4 inch or 3/8 inch diameter hole at the end of the crack.
NOTE: CARE MUST BE TAKEN IN DRILLING AS THE ACRYLIC IS EASILY CRACKED. IT IS SUGGESTED THAT PRACTICE HOLES BE DRILLED IN 0.10 INCH THICK PLEXIGLASS 55 SHEET MATERIAL.
(2)
Smooth hole by sanding to eliminate all cracks or chips in the acrylic.
(3)
Cut out a 0.10 inch thick Plexiglass 55 plug to fit hole drilled in acrylic. The fit must be accurate.
(4)
Bond the plug in the fairing with either cement using the following method:
(a)
Roughen faying surface with 240 grit wet-or-dry paper.
(b)
Clean faying surface with aliphatic naptha or soap and water followed by aliphatic naptha.
(c)
Let faying surfaces dry.
(d)
Mask surrounding plastic covering the surface to within 1/32 inch of the bonding area with tape.
NOTE: Masking shall extend a minimum of one inch parallel to the joint.
(f)
Apply a light coat of adhesive to both faying surfaces.
(g)
Join the surfaces immediately after coating.
(h)
Wipe excess cement onto the masking material if possible. Cover exposed cement with cellophane to prevent inhibition of cure by the air.
F. Restore Airplane to Normal
(1)
Parts cemented with PS-18 may be machined after five hours at room temperature.
(2)
Parts cemented with EC-2216B/A must be cured 24 hours at room temperature, or 130 + 10 minutes at 160 + 100F before handling or use.
(3)
If the cement greatly reduces the transmission in the repaired area, it should be sanded and polished per the following to restore original surface smoothness:
(a)
Remove masking and flush all unmasked areas with clean water to remove dirt and grit.
(b)
Wash with soap and water. A soft cloth, or chamois may be used in washing, but only as a means of carrying the soapy water to the plastic. Go over the surface with a bare hand so that any adhesive can be quickly detected and removed.
(c)
A clean, damp chamois should be used for drying. A clean cotton-flannel cloth may be used if care is taken to avoid rubbing after the acrylic is dry.
(d)
Remove oil and grease by wiping lightly with a cloth saturated with aliphatic naptha. Dry with a clean cotton-flannel cloth.
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