cleaning, pretreatment & surface preparation

ENSURING READINESS FOR

PHOSPHATE-FREE CONVERSION COATINGS

BY KEN KALUZNY, PRODUCT MANAGER,

CORAL CHEMICAL COMPANY, ZION, ILL.

Most everyone involved with metal finishing processes is aware of the newpretreatment technologies available. Several names have been used to identifythese alternatives to phosphate-based treatments. Within this article I will usethe acronym TMC, transitional metal conversion, as it describes what is on thesubstrate after treatment similar to using the terms iron or zinc phosphate.There are dozens of companies that have this technology. Anyone who mixeshydrofluorozirconic and/or hydrofluorotitanic acid in water can say they havethe new pretreatment technology. However, there is more to the formulationfor success. What matters is performing on your line day after day. It is veryimportant that you roll smoothly into this change. Most TMC line conversionsare made without incident. However, there are situations that can create issuesfor a successful TMC implementation. All I am asking you is to know why you’rechanging and that it is a sound business decision.

CONSIDERING CHANGE

The features and benefits of the new pretreatments are hard to ignore. Whodoesn’t want to reduce energy consumption, phosphate usage and washermaintenance? Increasing water discharge regulations and energy costs makeTMCs very appealing. Before changing your pretreatment to a TMC, it is prudentto know your current pretreatment cost per unit as well as your first-passefficiency. If your goal is to reduce cost, then you need to know your currentcosts to determine if you were successful. The cost to treat or haul away wasteis also a factor. If your pretreatment change is motivated by environmentalrestrictions then perhaps there is no reason to take the time to calculate youroperating costs.

Identify Benefits and Savings

Unless your goal is to become a “greener” neighbor or manufacturer, if thereare no significant benefits or savings then why change your process? Phosphaterestrictions and POTW surcharges could motivate a change in pretreatmenttechnology. If you’re operating a wastewater treatment system, then the changeto TMC will reduce and possibly eliminate your wastewater treatment costs.Newly imposed environmental restrictions may require your company to treatyour wastewater. The capital investment for a wastewater treatment systemmight be avoided by changing to a TMC.Cost savings are really what drive the change to TMC. Unless you are using azinc phosphate process, the savings from switching to TMCs are usually fromprocess-related savings rather than from the TMC product cost and consumption.Energy savings is heavily marketed and realized from eliminating appliedheat to the treatment stage and potentially from reduced heating requirementsfrom the dry off oven. The TMC treatment has a lower surface tension thanphosphate surface conversions due to lower TMC coating weights requiringless heat to dry the parts.Maintenance-related costs are generally lower for a TMC. The absence orextreme reduction of phosphate in the treatment solution significantly reducesthe formation of precipitates that accumulate as sludge that makes scale. If youhave particulate filtration for your phosphate system, then this cost is virtuallyeliminated. Washer descaling frequency will by substantially reduced and perhapseliminated as you won’t have the sludge that forms scale.

Product – Process Research

Start your research by determining potential vendors and products. Get references—good and bad. I wouldn’t be shy to ask the hard questions of where theyhave had problems and how they were resolved. We’re talking about new technologyand manufacturing—stuff happens. You need to find ways to shorten yourTMC learning curve. This is one of the reasons I think you should ask for “bad”references. It is helpful to know what has gone wrong and how those issues wereresolved. You also want to know how your vendor will respond in times of need.It may or may not relate to your situation. At the very least, the discussion canmotivate questions that need addressing prior to implementation. If your riskis substantial, you should consider taking some tours.Somewhere in the same time frame you should conduct testing of the chosenTMCs. You can use laboratory panels as control panels but should includeproduction substrates to make sure the process is viable. If possible, treat yourown parts through an existing TMC production pretreatment system. Whenyou compare lab-prepared TMC panels to a production phosphate panels youare not only comparing the pretreatment technologies but also the washers.You need to also research the requirements of the chosen TMC. Will theconstruction of your existing washer be compatible with the TMC’s chemistry?

Some products require stainless steel construction and all products have betterbath life when used in acid-resistant construction. Water quality is also anissue. Most TMCs will require RO or DI water. Solution control equipment andprocedures should also be reviewed to make sure you have, or are capable ofconducting, pertinent solution control procedures.Successful implementation requires vendor support. Prior to implementationyou need to define support for the start-up and in the following days or weeks.Generally you don’t need a representative for weeks but a plan for the vendor tocheck in on the process is warranted.

Implementation Strategy

Once you have a viable product and process, you should conduct some trainingprior to charge-up. Include wash line operators as well as painters and appropriatemanagement to familiarize them with the TMC operation as well as the treatment’sappearance. The appearance will most likely be different from what theyare accustomed. There will probably be several questions that would be betteraddressed prior to charging up the TMC. Discuss your and your vendor’s concerns.They know their product, requirements and limitations. You know yoursystem, requirements and constraints. These need to be fully discussed to makesure that all the necessary steps are taken to ensure a successful implementation.Those who have used iron phosphates for a substantial time have probablyseen something unusual and perhaps unexplainable despite the long history ofiron phosphating. The chance for something unforeseen with TMC is possible.If there is still uncertainty about how the new technology will perform on yourline, then conduct a short-term trial. Consider a 5-stage pretreatment systemwith the traditional alignment of cleaner, rinse, phosphate, rinse, final rinse.With some effort and a garden hose for auxiliary rinsing you can conduct ashort-term TMC after a shift or on a weekend by putting the TMC in stage 4.Run for an hour or two or set a number of parts to treat, test and set the reston the side for eventual use. In other words, try it on for size to see if it fits youroperation. This will help reassure that a change over has a chance of success orwhether some modifications are required. If you have multiple paint lines thenperhaps you can start your testing on the smallest line or the line with the leastamount of risk.

WHAT CAN GO WRONG

Water quality is very important for most if not all TMCs. Cations such as calcium,iron, and magnesium can precipitate vital ingredients of TMCs. If the waterhardness isn’t too hard then you might not need it. Even if the TMC can toleratesome water hardness, there is concern about its use in the final rinse. The watercations dried on the substrate are hygroscopic and will absorb moisture to formblisters in moist environments, compromising paint adhesion which leads tocorrosion. The anions such as sulfate and chloride can initiate corrosion.Poor rinsing and excessive carry over can also create performance issues. TheTMC products operate with very low solids in the treatment solution. In otherwords, they don’t handle contamination very well especially alkaline carry overas it precipitates the active metals in the TMC solution. Lines with insufficientrinsing from lack of stages, poor riser/nozzle performance, or short drain zoneslead to quality or product usage issues. High chemical usage can also occur ifthe solution control procedures aren’t adequate.Insufficient cleaning causes most finishing issues. Obviously all organicsoils need to be removed. Inorganic soil removal is more important for TMCsthan for phosphating. Phosphate-based surface conversions are more forgivingfor metal variations simply due to the phosphate reaction etching the substrateto start the phosphate conversion. The TMCs do not etch the substrate to thisextent to produce a surface conversion. If there is a thin layer of organic orinorganic soil, the phosphate etching will undermine the residual soil to giveyou a passivation. Inorganic compounds formed on the substrate from aging

or from reaction with certain lubricant components can interfere with the continuityof the surface conversion. The inorganic compounds and transitional metal oxides are electro-chemically different. The electro-chemical differenc

can create corrosion cells. All thatis needed is water or moisture andcorrosion initiators such as chlorideor sulfate commonly found in

untreated water. Depending on thequality of your paint and your product’sservice environment this maybe an issue.

WAR STORIES

I’m not going to mention any namesof companies or vendors. The TMCshave been around long enough thatthe stories have made it around ourmetal finishing world. Vendors are more in tune to this as we are all competingfor business with new technology. There is an adage used by pretreatmentvendors: every line is unique. As much as suppliers do research, it would beunreasonable to expect a research chemist to anticipate every unique situation.Before I start relating war stories, I want you to understand that I’m telling youabout the bad things. My intent is not to make you paranoid but rather preparedfor a TMC. Most TMC installations go without incident if there is sufficientplanning and resources.The quality issues aren’t always unique to TMCs as they also happen withiron phosphating. Adhesion issues generally stem from improper cleaning andrinsing. Loose deposits will cause paint adhesion issues. Line stops can createflash rusting that is loosely bonded. Ergo, flash rusting can cause paint adhesionissues. A quick test for TMC adherence can be simply done with tape. If you canpull the coating off exposing silver metal underneath, then you will have a paintadhesion problem. This is pretty obvious but leads into a situation where a metal

finisher had over a dozen consecutive line stops due to paint color changes. Thequestion was posed: was there a particular area of the 5-stage washer where linestops create adhesion issues.Laboratory testing was conducted to determine if there was a particularlybad area for parts during a line stop. Lab variations simulated 3-minute line stops in the process stages with normal transfer times, 3-minute line stops in

the drain zones with normal stage exposure, and three minute stops in both thestages and drain zones. A fourth set was prepared with normal sequence timesas a control. Used production TMC solution was utilized for the lab treatment.The time increment of 3 minutes was used as this was the time it took to handspray a rack of parts and change colors. Adhesion testing and salt spray testing

was performed to compare the variations.To my surprise, all of the cross- hatch adhesion (ASTM D3359) results wereperfect. This was not expected and was most likely due to the differences betweenthe laboratory and the production washers. The neutral salt spray (ASTM B117/

D1654) results at 336 hours demonstrated better variation. The test data suggeststhat the line stops in between stages have a greater impact on performancethan stopping in the stages that continued to spray solution. Spray impingementprevents the formation of loose deposits that can interfere with paintadhesion and corrosion resistance.Other process-related issues include flash rusting. Figure 1 illustrates a uniform

coating on HRPO rims and an appearance that is not uncommon withTMCs. The HRPO substrates were treated in a 5-stage washer with the TMCin stage 4, followed by a reverse osmosis rinse. As the parts continued towardsthe e-coat tank their color changed. You couldn’t wipe off the TMC coating,although it was evident that the reaction continued. About the same time thee-coat ultra-filters were beginning to plug with an iron containing residue.Drippings were collected to determine how much iron was in the residual waterentering the e-coat tank. A high number was 10 ppm and values were typically2–3 ppm. Assuming 10 ppm of iron was constant, it would have taken 52,000gallons of iron containing water dragged into the 7,000 gallon e-coat tank tomatch the amount of iron in the e-coat tank. The metal finisher was conductingTMC trials with multiple vendors. It was unknown how much came from thefirst or second vendor.Based on material balance, there was no way that water on parts alone establishedthe iron levels in the e-coat tank. High iron loading had to be related toline stops, and I suspect that the parts were rusty due to line stops in pretreatmentand then dissolved in the cathodic e-coat tank. A power and free conveyorwould eradicate this situation. Iron entering an e-coat tank is a concern you needto consider. Not all lines have this issue, but I have heard of at least four e-coaters

having this issue. In one instance, the e-coat solution had to be replaced. Ironaccumulation in rinse tanks has also been seen. In as much as I’ve heard of thisproblem, one would think that it could be remediated with better rinse overflow.This is not always the case and generally leads to the use of “rinse aids” or rustpreventatives.High operating cost has also been observed. High water usage was seen on aline where the total RO water usage in the stage before and after the TMC was52 gpm. This metal finisher also had extreme TMC usage as well. There was highcarry-over from the parts processed on this line. High carry is a concern not onlyfor product usage but for quality as well. Phosphate discharge wasn’t a concernfor this finisher. They were solely interested in energy savings. Once they convertedto an ambient iron phosphate they reduced chemical purchases by 58%.This is the crux of this article. I believe in being green. I reduce, reuse, andrecycle whenever I can. But I also believe you need to run your line efficiently tosurvive and prosper. You need to make good decisions so that you aren’t the guyat yet another company saying the conversion to TMC “was a mistake.”Ancillary processes associated with your pretreatment line may also be affectedby changing to the new technology. If you continue to treat your wastewaterafter implementing a TMC you need to consider the water treatment chemistry.The implementation of TMC changed how the coagulant worked. Figure 2shows what happened to the right and how the sludge should look on the left.The result was that the sludge became dense and sticky making a mess in theclarifier and sludge thickening tank.

WRAP UP

Transitional metal conversions potentially can save you money while improvingquality. I believe in the new technology. However, in the last two years I’ve seenlines converted in many ways from iron or zinc phosphate to TMC and somewent back to phosphating. The common denominator for failed implementationis carry-over contamination and in-process rusting from slow transfertimes. I have also seen TMCs replace with competitive TMC’s. The reason forthis transition is that the original product’s capabilities were oversold. It is thesesituations that motivate my topic.In closing, do your research, make a plan and roll with the changes withopen eyes.

BIO

Ken Kaluzny is the General Industrial Product Manager for Coral Chemical Company inZion, Ill. He received a Bachelor of Arts degree in Chemistry from Knox College in 1982.Since then he has held various positions at Coral Chemical. Ken is a member of the ChemicalCoaters Association International, the Electrocoat Association, Powder Coating Institute, and the Porcelain Enamel Institute.