Primers chromate

If dielectric separation of fasteners in noncompatible joints cannot be implemented readily, fasteners should be coated with a zinc chromate primer and exposed ends encapsulated. This is illustrated in Figure 2.4. 

The purity of the zinc is unimportant, within wide limits, in determining its life, which is roughly proportional to thickness under any given set of exposure conditions. In the more heavily polluted industrial areas the best results are obtained if zinc is protected by painting, and nowadays there are many suitable primers and painting schemes which can be used to give an extremely useful and long service life under atmospheric corrosion conditions. Primers in common use are calcium plumbate, metallic lead, zinc phosphate and etch primers based on polyvinyl butyral. The latter have proved particularly useful in marine environments, especially under zinc chromate primers . 

Modified pretreatment primer plus zinc chromate primer plus two coats of micaceous iron oxide/polyurethane. 

Zinc chromate primer plus micaceous iron oxide/alkyd or phenolic. 

Zinc chromate primer in quick- Airless spray. 2 80-100... 

These paints, submitted by exhibitor A, consisted of one coat of a fire-retardant chromate primer, followed by application of a fire-retardant white paint. 

A study was conducted on 977 male painters who had worked for at least 3 months within 10 years prior to 1959 at two U.S. military aircraft maintenance bases where spray painting utilized zinc chromate primer paint. They were followed through 1977. There were 21 deaths due to respiratory cancers, compared with 11.4 expected based on national rates (SMR=184, p<0.01). When compared with national proportionate cancer mortality rates, however, the excess (SMR=146) was not significant (Dalager et al. 1980). 

Figure 28.7 Schematic of corrosion process on chromated primer coated on chromate conversion coated A1 alloys surfaces.

A nonchromated, water-borne primer applied to [2B] alloy samples, with the appropriate surface preparation and plasma deposition of an ultrathin plasma polymer, was also compared to controls prepared by depositing a chromated primer on chromate conversion-coated A1 substrate. The same comparison was also performed for IVD Al-coated 2024-T6 substrates (pure aluminum is deposited by ion vapor deposition process on aluminum alloy 2024-T6). In the latter case, the primer could not be removed from the IVD Al-coated panels that were treated with the plasma polymer prior to spray primer application. It is interpreted that the water-borne spray paint penetrates into the column structure of the top surface of the IVD Al-coated substrates when the surface energy was modified by the application of a plasma polymer. This effect could be viewed as interactive coating with a porous surface. 

Figure 28.9 Comparison of chromated primer coated A1 panel ([7B](Dox)/T/F/A) with nonchromated primer coated A1 panel ([7B]y(Dox)/Tfs/(Ar)/X) after Prohesion salt spray test primers were removed after the test.

The main aim of SAIE is the complete elimination of heavy metals from the coating systems an approach that primarily relies on tenacious water-insensitive adhesion and good barrier characteristics of a primer has been taken. It should be pointed out that this approach is theoretically incompatible with the approach that utilizes the primers with corrosion inhibitors, e.g., chromated primers. This is because a primer with super barrier characteristics would not allow the migration of inhibitors and would not provide enough water for their electrochemical reaction to form corrosion protection products, as described in Chapter 28. In order to further elucidate the SAIE concept, both chromated and nonchromated spray primers were employed to generate two types of plasma coating-modified systems, and their corrosion protection behaviors were investigated in this study. 

Figure 31.27 shows the comparison of average corrosion widths of (1) SO2 salt spray-tested and (2) Prohesion salt spray-tested A1 alloy panels and their corresponding control panels. After 4 weeks of SO2 salt spray test, most of the chromated primer-coated [2B] and [7B] panels, including those with excellent... 

Tabie 31.2 Adhesion Test Results of Chromated Primers [Deft 44-GN36 (A) and 44-GN-72 (Al)] to No Anode Assembly Plasma-Treated 7A(Ace/0)... 

Table 31.3 summarizes the adhesion test results of nonchromated primers [Spraylat EWAE118 (D) and Dexter 10-PW-22-2(X)] to plasma coatings deposited without an anode assembly, which were produced in both flow and closed system deposition processes. As noted in Table 31.3, closed system TMS plasma polymers (Tcs) showed superior primer adhesion performance to similar ones obtained from a flow system (Tfs). Similar to chromated primers, summarized in... 

Table 32.8 Adhesion Performance in Various Adhesion Tests, Indicating the Influence of Second Plasma Treatment Effects of TMS Plasma Films (Under IVD Conditions) on their Adhesion Performance to Chromated Primers (Deft 44-GN-36 and 44-GN-72) ...

In order to produce chromate-free plasma coating systems, the adhesion of closed system TMS coatings to nonchromated primers (Spraylat EWAE118 and Dexter lO-PW-22-2) was also investigated, and the adhesion test results are summarized in Table 32.9. Closed system TMS plasma polymers showed superior primer adhesion performance to those obtained from a flow system. Similar to chromated primers, summarized in Table 32.8, excellent primer adhesion was always achieved with closed system TMS plasma polymers treated with subsequent Ar plasma applications. 

The cabinets for cellular telephones are made of steel or aluminum. A double system of galvanizing and painting steel cabinets is applied for corrosion protection. Surface preparation by grinding and the application of zinc chromate primer is done prior to galvanizing. There are nearly 4000 cabinets for cellular telephones in use, and the estimated cost for corrosion is approximately 4 million. 

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