Page 450 - Handbook of Adhesives and Sealants

388 Chapter Ten

+2
o
Fe + Methylacrylic acid → Fe (Rust)

+2 +3 - .
Fe + ROOH → Fe + OH + RO

CH 3

. .
RO + Methylacrylic acid → RO − CH 2 − CH

COOH

CH 3

.
RO − CH 2 − CH + Tetraethylene glycol dimethacrylate → Crosslinked polymer

CH 3
Figure 10.8 Proposed mechanism for cure of anaerobic adhesives. 4

(some metals and plastics) and on inhibiting surfaces, such as bright
platings, chromates, oxides, and certain anodizes. Phenolic plastics
and some plated metals, such as cadmium and zinc, require a primer
such as ferric chloride.
Table 10.15 lists properties and curing characteristics of these ad-
hesives. Anaerobic resins are noted for being simple to use, one-part
adhesives, having fast cure at room temperature and very high cost
on a dollars/pound basis. However, the cost is equivalent to only frac-
tions of a cent per square inch of bonded area because only a small
amount of adhesive is required. Anaerobic adhesives do not cure when
gaps between adherend surfaces are greater than approximately 30
mils. These adhesives are available in various viscosities. Cure speed
is largely dependent on the chemical nature of the parts being joined.
The anaerobic adhesive formulations can cure in minutes to hours
without primer at room temperature. Application of primer and/or
heat will speed up the cure. The primers are generally catalysts dis-
solved in degreasing solvent.
Anaerobic adhesives are available in machinery and structural
grades. Machinery grades provide high strength in threaded assem-
blies and other closed machinery joints. Structural grades provide
high shear strength characteristics in flat joints. The most important
use of anaerobic adhesives is as liquid lock washers for screws and
bolts, flange sealing, and retaining. Because of their strong penetrat-
ing ability, they can be applied either before or after assembly of the
mechanical fasteners. These resins have also been used as sealants to
seal porosity in metal castings.
Certain anaerobic adhesives can withstand continuous aging at
450 F. However, generally their service temperature limit is 300 F.