Page 241 - Handbook of Adhesives and Sealants

210 Chapter Six

preparations can range from simple solvent wiping to a combination
of mechanical abrading, chemical cleaning, and acid etching. In many
low- to medium-strength applications, extensive surface preparation
may be unnecessary. However, where maximum bond strength, per-
manence, and reliability are necessary, carefully controlled surface-
treating processes are required. As shown in Fig. 6.5, high strength
durable bonds generally require aggressive and expensive surface
treatment processes. These optimized processes also require prolonged
production time and provide safety and environmental concerns. Thus,
one should be careful not to over-specify the surface treatment re-
quired. Only the minimal process necessary to accomplish the func-
tional objectives of the application is required. The following factors
should be considered in the selection of a surface preparation:

1. The ultimate initial bond strength required
2. The degree of permanence necessary and the service environment
3. The amount of and type of contamination initially on the adherend
4. The type of adherend and nature of its surface
5. Production factors such as cost, cycle time, safety and environmen-
tal compliance, training, monitoring and control

Any surface treatment used for bonding or sealing requires the com-
pletion of one or more of the following operations: cleaning, mechan-

Surface Treatment Cost Quality
None Inexpensive Poor

Dry Rag Wipe
Solvent Degrease

Vapor Degrease
Mechanical Abrasion

Plasma

Chemical Etch
Conversion Coating

Anodizing Expensive Excellent
Figure 6.5 The objective of surface preparation is to provide a
consistent, reproducible adherend surface that when bonded
meets the strength and durability required for the application.