Page 244 - Handbook of Adhesives and Sealants

Surfaces and Surface Preparation 213

TABLE 6.5 Surface Preparaton of Aluminum Substrates vs. Lap Shear Strength 3
, X s, C v ,
Group treatment lb/in. 2 lb/in. 2 %
1. Vapor degrease, grit blast 90-mesh grit, alkaline
clean, Na 2 Cr 2 O 7 –H 2 SO 4 , distilled water ............. 3.091 103 3.5
2. Vapor degrease, grit blast 90-mesh grit, alkaline
clean, Na 2 Cr 2 O 7 –H 2 SO 4 , tap water ................. 2,929 215 7.3
3. Vapor degrease, alkaline clean, Na 2 Cr 2 O 7 –H 2 SO 4 , 307
distilled water .................................... 2,800 10.96
4. Vapor degrease, alkaline clean, Na 2 Cr 2 O 7 –H 2 SO 4 ,
tap water ........................................ 2,826 115 4.1
5. Vapor degrease, alkaline clean, chromic–H 2 SO 4 ,
deionized water................................... 2,874 163 5.6
6. Vapor degrease, Na 2 Cr 2 O 7 –H 2 SO 4 , tap water ........ 2,756 363 1.3
7. Unsealed anodized ................................ 1.935 209 10.8
8. Vapor degrease, grit blast 90-mesh grit ............. 1,751 138 7.9
9. Vapor degrease, wet and dry sand, 100 240 mesh
grit, N 2 blown .................................... 1,758 160 9.1
10. Vapor degrease, wet and dry sand, wipe off with
sandpaper........................................ 1,726 60 3.4
11. Solvent wipe, wet and dry sand, wipe off with
sandpaper (done rapidly) .......................... 1,540 68 4
12. Solvent wipe, sand (not wet and dry), 120 grit ...... 1,329 135 1.0
13. Solvent wipe, wet and dry sand, 240 grit only ....... 1,345 205 15.2
14. Vapor degrease, aluminum wool.................... 1,478
15. Vapor degrease, 15% NaOH........................ 1,671
16. Vapor degrease ................................... 837 72 8.5
17. Solvent wipe (benzene) 353
18. As received....................................... 444 232 52.2
X average value. s standard deviation. C v coefficient of variation. Resin employed is
EA 934 Hysol Division, Dexter Corp.; cured 16 h at 75 F plus 1 h at 180 F.

6.3.3 Evaluation of treated parts before
and after bonding
The common goals of surface treatment are to produce a clean and
wettable surface. There is, unfortunately, no standard procedure or
equipment available to tell when a surface is clean. Thus, the term
‘‘clean’’ is difficult to define. One can try to define clean as no visible
soil or foreign matter on the surface when inspected with the naked
eye. Since this is very subjective, the quality of the surface treatment
process will ultimately be dependent upon rigid process controls and
well-trained operators. These process controls include the monitoring
of critical parameters such as solvent purity, temperature, and time;
equipment maintenance; the accumulated number of parts or bond
area being treated with the same solution; and the handling and stor-
age of the clean parts prior to application of adhesive or sealant. Pe-
riodically through a production run, the bond strengths of prototype
parts should be tested to determine if the surface treatment process
is still working as expected.