” )- I 9 FmU” LC 7 T POWDER COATING, April 1995 17

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chemicals and water costs takes carefid planning

Brad Gmss Fremont Industries

Water constitutes most of the solutions in a powder coat- ing surface preparation system. As a result, water plays a major role in your ability to clean, rinse, phosphatize, and seal-rinse parts before powder coating. Overuse of this natural resource not only wastes water but also drives up energy and chemical use. As a result, your costs go up. This article points out ways to conserve water and chemicals to cut costs. It includes information on raw- water quality and improvement options, water-use docu- mentation, soils and pretreatment chemistries, TDS (total dissolved solids) and pH variables, system design, and chemistry selection.

queous surface preparation chemistries require judicious use of water. Rinsing is a critical step in A nishing because a part is ultimately no cleaner

than the quality of rinse water used. Realizing the necessity of water in the surface preparation process places significance on the control and conservation of its use. A majority of finishers make several mistakes that lead to overuse of water and an increase in pretreatment chemistry costs. Following is a list of the most common mistakes finishers make:

*They use high-temperature cleaners that not only shorten chemistry life but also increase evaporation, water use, and maintenance and energy costs.

*They use poor quality cleaners and conversion coating chemistries that lead t o frequent dumping and recharging. This increases water use and places a greater burden on treatment than is necessary.

*They don’t use water meters on individual process stages, which leads to overuse of rinse water.

*They control rinse-water quality visually, rather than by “DS and pH readings, which causes ineffective rins- ing or water waste.

*They hang parts improperly and use poorly designed hangers, which causes drag out, drainage, and water- cupping problems.

*They have systems with inadequate and undersized tank volumes and improper drain vestibule lengths that create water and chemical waste and a subse- quent decrease in powder performance.

Several factors are crucial in conserving water and chemicals

To conserve water and chemicals and reduce costs, you should know or investigate several factors when design- ing or improving a surface preparation system. These factors include raw-water quality and improvement options, actual water use, soils and chemistries, TDS and pH, and system design.

Raw-water quality and improvement options. One of the factors you should know about is the quality of the incoming raw water. Have an independent source or your chemical pretreatment vendor analyze your water and explain why its constituents behave in a negative or positive way. By understanding this resource, you can elect to treat the incoming water in one of three ways: (1) sofiening, (2) reverse osmosis, or (3) deionizing. [Editor’s note: For a comparison of the three methods, see Brad Gruss, “HOW t o minimize pretreatment problems to maximize powder performance,” Powder Coating? vol. 5, no. 2 (April 1994): 37-46.1

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desirable when large volumes of an improved water source are necessary. In many cases, a blend of reverse- osmosis and raw water is used to improve the water source for active chemical stages.

18 POWDER COATING, April 1995

Softening. This method exchanges high amounts of cal- cium, magnesium, or other minerals found in your water for sodium. A common industrial-sized softener can be used to remove those water constituents that lead to scale buildup in the nozzles, the tank walls, and the heating apparatus found in heated washers. Sodium is more soluble and less likely to produce hard scale than the minerals it replaces. If you have hard water and use alkaline cleaning baths, you are a good candi- date for softened water, which is typically in a hardness range of 15 grains per gallon or more.

However, the exchange of calcium and magnesium for sodium raises the TDS level. This rise in TDS is typical- ly due to lack of adequate or complete back flushing when removing excessive sodium. Make sure your soft- ener is well designed, sized, and maintained. A softener is usually not recommended for the rinse preceding and following the phosphate stage and for final seal-rinse stages because the dissolved solids left behind are more soluble and conducive to corrosion than the original hard-water minerals.

Reverse osmosis. This form of water conditioning can produce high-quality water for finishing. Basically, reverse osmosis is a process in which water is passed between semipermeable membranes. These membranes can be designed to remove hardness, minerals, and other constituents that interfere with high-quality pre- treatment. Reverse-osmosis systems tend to be most

Typical water meters

Deionizing. Basically, deionizing water relies on reac- tions. The first reaction uses a cation-exchange resin regenerated with an acid to remove all metal ions and replace them with hydrogen ions. The second reaction is an anion exchange to remove the acids produd. This reaction is regenerated with an alkali solution. Deionized

water in the final rinse stages of surface preparation. F’rimaril~ it’s beneficial in cleansing a substrate before dry- ing. This step removes unreacted deposits and leaves the substrate virtually h e of dissolved and undissolved solids.

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water is the most fiequently used source of high-quality ~~

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Actual water use. Water use should be documented. How can you conserve water if you don’t know what amount is used in each part of the surface preparation process? Effective rinsing is difficult to evaluate without documenting gallons consumed. Leaking tanks, stuck float valves, and excessive exhaust can lead to disagree- ments and excessive chemical use because the active chemical stages become diluted. ‘Jh document water use, install a water meter (Figure 11, a flow meter (Figure 2), or both. The devices will help you control costs and pre- dict volumes for posteffluent treatment.

A typical flow meter

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Soils and chemistries. Soils and surface preparation chemistries have a direct bearing on water consump- tion. Soils such as drawing and stamping lubricants that contain heat-sensitive waxes require higher cleaning temperatures than some other soils. Higher tempera- tures create more evaporation and water use than lower temperatures. Surface preparation chemistries, espe- cially cleaners, must have dual functions. That is, they must remove, replace, or digest soils and provide free rinsing.

Cleaners with poor or excessive wetting can lead to increased volumes of water to provide adequate rinsing. The best option is to match the cleaners to the soils, or change soils to be more compatible with the process and its control.

TDS and pH. Indicators of water cleanliness, TDS and pH should be checked and recorded daily. As stated ear- lier, visual observation causes ineffective rinsing and water waste. After your chemical vendor has analyzed the incoming water, the vendor should provide you with specific guidelines for checking TDS and pH. The pH of water shifts up or down when it’s effectively used as a rinse following an active chemical stage. This shift depends on many factors. Following are the factors with the most impact

.Alkalinity or acidity strength of preceding chemical stage

.Part shape, size, length, and configuration

.Rinsestage volume

.Rinse-stage design

Overflow volume

Ideally, TDS and pH in rinse tanks should be the same as incoming water. Obviously, this isn’t typical in actual pro- duction. In general for most situations, rinse-tank pH should be within ? 1.5 to 2 points of incoming-water pH, and TDS should be no more than twice the initial read- ing for rinse stages between active chemical tanks. Of course, the real answer can only be found with a series of tests comparing TDS and pH values with adhesion, chemical use, and humidity and corrosion test results.

System design. Surface preparation system design plays a significant role in chemical and water use. [Editor’s note: For information about effective rinse design and back-flow options, see Gus Lissy, ‘Water- and energy-saving washer designs for the 1990’s ecology: Powder Coating, vol. 5, no. 2 (April 1994): 19-34.1

Reducing initial costs when considering a new system inadvertently increases operating costs throughout the service life of the equipment. Water meters, rinse-tank

volumes, and racking and drain lengths are often over- looked when designing a new system.

Water meters. The installation of water meters in each stage will help you control costs and balance any back- or counterflow process you employ. Water meters can also help detect tank leaks, malfunctioning level indicators, and excessive moisture drift caused by exhaust stacks. -

Rinse-tank volumes. Undersized rinse tanks lead to quickly contaminated rinses. Small tanks simply can’t keep up with the drag in and have to be dumped and recharged daily in some cases. This leads to increased water use and added maintenance.

Racking and drain lengths. Tilting parts front down, rather than front up, causes excessive stage-to-stage contamination. This problem is further exaggerated when drain lengths are shortened to reduce overall washer length. Figure 3 shows an example of poor rack- ing (notice part drainage forward of the floor apex).

Parts tilted front down, such as the one at the top center of the photo, don’t drain adequately. At the top right of the photo, the part is draining forward of the floor apex (the part is moving left to right inside the surface preparation system).

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Pretreatment chemicals should be cost effective and have little

environmental impact Before you select your surface preparation chemistries, you should conduct a detailed investigation or needs analysis. You should ask yourself several questions. For example, does your current process meet your needs? If not, what improvements in quality, cost, and production do you need to make? Following is a list of other ques- tions you should ask yourself before you select surface preparation chemistries:

*Do I know my current surface preparation process thoroughly?

*Did I establish finishing specifications?

*Did I conduct a soil audit?

*Did I conduct a substrate audit?

*Did I pretest and evaluate pretreatment chemistries?

*Did I pretreat, coat, and test parts?

*Are there any local environmental restrictions?

*Did I get MSDS technical data from vendors?

*Do I know my total powder coating process capabilities?

*What support and services are available from vendors?

*Are the vendors IS0 certified?

Establish finishing specifications to meet the needs of your products and customers. Typically, these should include color, gloss, adhesion, durability, and corrosion resistance. By being realistic and communicating your true needs to your powder coatings and pretreatment vendors, you can achieve your goals. Bear in mind that you may have to make trade-offs that impact costs, qual- ity, or environmental concerns.

A major part of selecting the right chemistries deals with the soil and substrate audits. You should choose the final chemistries for the right reasons+quality and performance, cost, environmental impact, safety, and vendor service. Any proposed chemistry should be tested and evaluated in a way to assure similar production results. Following are some tips that deal specifically with selecting cleaners and conversion coatings.

Selecting cleaners. As a guiding principal, you should select the most cost-effective cleaner with the least envi- ronmental impact. New process development for today’s finishing can’t be accomplished with old cleaner tech- nology. High-temperature, high-alkaline, and old sur-

POWDER COATING, April 1995 21

factant-type cleaners aren’t suitable anymore. Today’s finishers base their cleaner choices on the following:

*They are nonreportable through the Superfund Amendments and Reauthorization Act (SARA) of 1986.

*They have the right surfactant technology.

*They can split oil.

*They are chelate, caustic, and phosphate free.

A cleaner formulation must contain a balance of deter- gents and surfactants to offer fast, efficient wetting. Cleaning simply can’t take place without a wetting func- tion. Figure 4 shows a cleaner impeding a soiled surface. The wetting function is accomplished because the deter- gency causes the soil to move and sh r ink into globules. Oil tends to gather into a shape of greatest stability (spheres, or globules). Eventually, the oil is completely displaced and a majority of the soil floats to the surface of the solution (see Figure 5).

Detergents must also be capable of floating oil in the solution to ease oil removal and extend solution life. This

In surface wetting, detergency causes the soil to move and shrink into globules.

The soil is wetted out when it is displaced from the substrate.

Cleaner solution

22 POWDER COATING, April 1995

fact emphasizes the importance of a careful soil audit. Some metalworking fluids that ultimately become clas- sified as soils are either partially emulsifiable or totally emulsifiable. In cases such as this, the detergent or sur- factant used is incapable of floating the soil. The deter- gent portion of today’s industrial cleaners also con- tributes to the overall level of organics in the solution. Because surfactant packages are proprietary in nature, you should work with your chemical vendor to select the right one for your operation.

Selecting conversion coatings. Finishing specifica- tions, soils, substrates, and coating choices impact the type of conversion coating required. General industry has gone in the direction of iron phosphate and powder coatings, primarily for their high quality and low envi- ronmental impact.

Chrome conversion coatings, both hexavalent and triva- lent, have their places, as do zinc phosphate and other heavy-metal treatments. The trend, however, is to use iron phosphate whenever possible. The key questions to ask when investigating an iron phosphate conversion coating are as follows:

*Is it nonreportable through SARA?

*Does it contain molybdate1?

Nonchrome seal rinses on panels A and B pass corrosion testing when looking at the top half of the panels only. However, a tape-pull test on the bottom half of the panels reveals a significant difference between their performance.

A B

*Is it low sludging?

*Is its coating weight within 35 to 70 milligrams per square foot?

Certain iron phosphates have more SARA-reportable ingredients than others. Those of you who want to reduce this reporting task should look at alternatives. In addition, iron phosphates that are accelerated with molybdate are very common in industry. They have lim- itations and benefits. Currently, the elimination of molybdate is under discussion; a few bans on this mate- rial exist in localized geographic areas. Proactive ven- dors of surface preparation chemicals recognize this and offer nonmolybdate versions. Low-sludging irons that produce high-quality deposits of phosphate are also important as powder coaters seek to reduce the volume of potentially hazardous materials in their operations.

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In conclusion Finally, if you are considering a nonchrome reactive chemistry for your operation, you need to conduct tests and do product comparisons. It’s important to carefully evaluate panels. For example, the panels in Figure 6 indicate that both nonchrome seal rinses A and B pass corrosion testing when looking at the top half of the pan- els. However, a tape-pull test on the bottom half of the panels indicates that a significant difference in perfor- mance exists between seal rinses A and B.

As with any part of your surface preparation process, it pays to test, and then evaluate test results accurately. Do this and you’ll get the best surface preparation chem- icals for your operation. Equally important, you’ll reduce water, chemical, and energy use and cut down on main- tenance. And that means lowering overall costs. PC

Endnote 1. Molybdate. A sal t of the element molybdenum, which resembles

chromium and tungsten in many properties. Definition from F.C. Mish, ed.-in-chief, Webster’s Ninth New Collegiate Dictionary (Springfield, Mass.: Merriam-Webster, 1990).

Brad Gruss is vice president of Fremont Industries, 4400 N. Valley Industrial Blvd., Shakopee, M N 55379; 6121445-4121. In his 20 years with the company, he has made numerous presentations on surface preparation for powder coating. He holds BS degrees in business admin- istration and marketing and a BFA degree in art adver- tising from Mankato State University, Mankato, Minn. He is chairman ofthe board of advisors of the Association for Finishing Processes of the Society of Manufacturing Engineers and is a member of the Powder Coating Institute and the Chemical Coaters Association.