Surface Preparation Methods

As the epoxy/substrate bond is mechanical, not chemical, it is absolutely necessary that the surface be clean, dry, oil-free, and have a recommended surface profile. Surface preparation is one of the most important factors in performance of any coating. It includes  

Hand and power tools Loose rust, mill scale, loose paint 

High pressure water jetting Marine fouling, loose rust and paint 

Ultra high pressure water jetting Rust, tight paint 

Abrasive blasting Rust, Mill Scale, tight paint 

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In Section 4.3 several recently developed and experimental surface preparation methods for steel such as conversion coatings, plasma spray and sol-gel that attempt to simultaneously improve durability and bond strength over grit blasting will be discussed. 

Despite the progress outlined in this chapter, much work remains to be done in the metal surface preparation arena. For example, there is still no ideal surface preparation method that does for steel what anodization processes do for aluminum and titanium. The plasma spray process looks encouraging but because it is slow for large areas and requires rather expensive robot controlled plasma spray equipment, its use will probably be limited to some rather special applications. For more general use, the sol-gel process has potential if future studies confirm recently reported results. 

Electrode Surface preparation method Electrolyte vs. SHE (dEnJdcy (mV dm3 mol-1) fpz Atomic density/cm2 Method References... 

The surface preparation method must be carefully considered, especially if the completed weldbond is to have long-term durability to hostile environments. The surface preparation should provide an optimal surface for both adhesion and welding. Thus, the choice of surface treatment is crucial, and there can be a conflict of requirements. The spot welding process requires a low electrical surface resistance, and many adhesive surface preparation processes provide a high surface resistance because of oxide layer buildup. When it is impossible to harmonize on a surface treatment, current practice tends to favor treatments that yield good weld nuggets at the expense of the adhesive bond. 

For most adhesive bonded metal joints that must see outdoor service, corrosive environments are a more serious problem than the influence of moisture. The degradation mechanism is corrosion of the metal interface, resulting in a weak boundary layer. Surface preparation methods and primers that make the adherend less corrosive are commonly employed to retard the degradation of adhesive joints in these environments. 

As with metal substrates, the effects of plastic surface treatments decrease with time, so it is important to carry out the priming or bonding as soon as possible after surface preparation. The surface preparation methods suggested in App. F are recommended for conventional adhesive bonding. Greater care must be taken in cleaning thermoplastics than... 

To obtain a usable adhesive bond with polyolefins, the surface must be treated. A number of surface preparation methods, including flame, chemical, plasma, and primer treatments, are in use. Figure 16.4 illustrates the epoxy adhesive strength improvements that can be made by using various prebond surface treatments to change the critical surface tension of polyethylene. 

Polyphenylene sulfide parts are commonly bonded together with adhesives. A suggested surface preparation method is to solvent-degrease the substrate in acetone, sandblast, and then repeat the degreasing step with fresh solvent. The polyphenylene sulfide surface that forms next to a mold surface is more difficult to bond than a freshly abraided surface. This is possibly due to a different chemical surface structure that forms at high temperature when the resin is in contact with the metal mold surface. 

One surface preparation method that is unique for composites employs a peel or tear ply.77 Utilization of the peel ply is illustrated in Fig. 16.5. With this technique, a closely woven nylon or polyester cloth is incorporated as the outer layer of the composite during its production layup. This outer ply is then torn or peeled away just before bonding. The tearing or peeling process fractures the resin matrix coating and exposes a clean, fresh, roughened surface for the adhesive. This method is fast and eliminates the need for solvent cleaning and mechanical abrasion. 

SURFACE PREPARATION METHODS FOR COMMON SUBSTRATE MATERIALS... 

TABLE FI Surface Preparation Methods for Metal Substrates... 

TABLE F2 Surface Preparation Methods for Plastic Substrates ([Pg.502]

TABLE F3 Surface Preparation Methods for Elastomeric Substrates Continued)... 

Historically, surface treatments to improve adhesion of coatings to plastics consisted of mechanical abrasion, solvent wiping, solvent swell that was followed by acid or caustic etching, flame treatment, or corona surface treatment. Each of these treatments has limitations, thus providing a strong driving force for the development of alternative surface preparation methods. Many of the common methods mentioned are accompanied by safety and environmental risks, increased risk of part damage, and expensive pollution and disposal problems. 

V. Sattabanasuk, V. Vachiramon, F. Qian, S.R. Armstrong, Resin-dentin bonding strength as related to different surface preparation methods, J. Dent. 35 (2007) 467-475. 

The edl at PC Zn-H20 interfaces has been studied in many works, but the situation is somewhat ambiguous and complex. The values of Amin depend on the surface preparation method. The value of A =o for PC Zn lies between A =o values for single-crystal planes, and at Amin, lo pcl < 0-01 C m [1-5, 7, 51, 52]. 

BS EN ISO 8504-1 2001, BS 7079-DL2000 Preparation of steel substrates before application of paints and related products. Surface preparation methods. General principles. 

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