Metal Finishing Guide Book


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Table II. Three-Stage TMC System Process Stage 1 Option 1 2 3 Comments Clean Rinse TMC For dry-in-place time TMC Rinse/Optional Seal Clean-coater TMC Option 2 Clear/TMC Rinse Table III. Three-Stage Spray Application Methods Stage One Process Time Temperature Concentration pH Stage Two Stage Three Clean 90 sec 95-130��F 2%-4% Alkaline Rinse 30-45 sec Ambient n/a Neutral TMC (Dry-In-Place) 45-60 sec Ambient 2%-4% Acidic The most common way of using TMC in three-stage pretreatment processes is to apply them in the final stage. The clean, rinse, coat configuration is ideal for manufacturers that have tough to remove soils and inconsistent sources of steel. A custom coater with 3-stage washer is a good example of an organization that could benefit. Users of these technologies report varying degrees of satisfaction, but with creative use of vestibule space for misting risers to provide better rinsing, and good chemical product selection, a 3-stage washer can give satisfactory service. The 5stage washer configuration will give much more flexibility in the application of TMC pretreatments. Of particular interest are conversions of legacy zinc phosphate systems to TMC pretreatments. With performance of TMC pretreatments approaching that of zinc phosphate, without the detriments of heavy sludge, high process cost, and need for onsite waste water treatment, these old washers are being converted with increasing frequency. The most important consideration is the removal by acidic descaling of the old sludge and activator products from the washer surfaces. Using a hot recirculating solution of muriatic acid will dissolve old zinc phosphate scale, corrosion products, titanium salts, and other deposits, leaving the washer ready to accept the new TMC pretreatment. Failure to descale the washer will cause contamination and compromise performance of the new pretreatment. CONCLUSION TMC are now widely used across the globe by hundreds of users in a broad range of industries. This technology is the fastest growing powder coating and paint pretreatment and is firmly established in the finishing market. It is no longer considered ���new���. The technical support to convert existing metal phosphate pretreatment systems is well established. The newest TMC products are easy to run, so there are no barriers to enjoying the benefits to your process offered by TMC. If you are interested in improving the corrosion resistance of your product and the environmental profile of your pretreatment program, you may consider TMC. 118

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