ASTM DO 1.53

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In the last article, the need for involvement in other committees that affected coil coating was discussed as a result of the downgrading of the Hunter L,A,B method in Committee E12. Fortunately the “do not use” recommendation was rescinded as a result of paying attention outside coil coating’s immediate sphere of influence. On the flip side, in recent months several topics have arisen in ASTM committees other than D01.53, where specifications have been revised or discussed that required the expertise of the coil coating world. These discourses often led to significant changes to long standing specifications that were requested by both our international and domestic members. With ASTM truly an international organization, many perspectives and interpretive questions arise weekly that allow ASTM specifications to improve and become even more relevant for the future. It is particularly important for experts in the world of coil coating to lend their knowledge and experience to committees that tangentially touch D01.53. The specification worlds of steel, aluminum, post-painting, mechanical testing, accelerated corrosion testing and disciplined laboratory methodology all benefit from the unique perspective provided by coil coating. And these are not just intellectual exercises. Winning business can sometimes depend upon being able to perform and pass requirements defined within ASTM specifications. In the past, some of these ambiguities were explained contextually by long standing members within the various disciplines. Unfortunately, many of these experts are now retired or about to retire. The world of coil coating is losing hundreds of years of collective knowledge that may not be written clearly enough for adjacent industries and for those that are new to the coil coating industry.

___ For example, a coil coater was unable to win business due to the mandatory testing defined in Annex 1 of A755/A755M because it was specified by the potential customer. A755/A755M is the “Standard Specification for Steel Sheet, Metallic Coated by the Hot-Dip Process and Prepainted by the Coil-Coating Process for Exterior Exposed Building Products” housed in Committee A05. As you can see from the title, the painting portion of this specification is very critical to providing prepainted building products that can be warranted. Unfortunately, some of the mandatory testing was not possible on a coil coated product. One of the mandatory tests was to measure the mechanical properties of the paint film itself as a quality control test – a misinterpretation of D2370, a test specification that actually governed thick polymer films. Once the comparatively thin paint film adhered to the substrate it was impossible to perform the “required” testing. Unfortunately, the coater’s customer was unconvinced because it was listed in the mandatory testing annex. Another part of that annex required measurement of the durometer hardness of the paint film according to D2240. Again, this was an inappropriate test for coil coated sheet. Both of these misappropriated requirements were causing the coater to lose significant business potential. As a result of this inquiry, this annex was revised to incorporate appropriate testing for coil coating along with updating the specification with modern film thickness measurement techniques. In this case, the steel committee benefited from the expertise of the coil coating industry. The specification was rewritten and appropriate testing will facilitate a conversion from alternate materials to coil coated building product. The resulting ballot that closed last month provided the votes needed to officially revise the specification.

___ Another example of a seemingly unrelated specification that benefited from coil coating knowledge of passivation chemistry and corrosion resistant zinc coated products is the current endeavor to clarify and revise A1003 “Standard Specification for Steel Sheet, Carbon, Metallic and Conversion Coated for Cold-Formed Framing Members”. This specification, also housed in Committee A05, was originally written to provide a standard for metallic coated framing products. Written by segments of the steel industry, many of the terms and information related to the conversion coatings themselves were confusing. Through the collaboration of a combination of steel, metallic coating, coil coating and framing experts, the specification is undergoing a significant revision that will allow the industry to have a clear definition of the requirements of this product that incorporates both old and new technology. This cooperative effort will allow a ballot item to come forward in the third quarter after several years of confusion and controversy.

ASTM D01.53 Coil Coating Subcommittee Review
___ With all the tangential activity, D01.53 has not been quiet. There are now 45 members of this subcommittee, four of which are new coil coater company members. Two test methods have successfully passed main committee balloting and are located in the ASTM/NCCA Collaborative Portal: D7639 “Test Method for Determination of Zirconium Treatment Weight or Thickness on Metal Substrates by X-Ray Fluorescence” and D6665 “Practice for Evaluation of Aging Resistance of Pre-stressed Prepainted Metal in a Boiling Water Test”. Nine other standards are in various stages of review and or revision and will be balloted during the fourth quarter of this year. Once these standards are approved, the latest versions will be available on the ASTM/NCCA Collaborative Portal.
Through the D01.53 Accelerated Weathering Task Group, new work item has been initiated in order to provide a document listing a collection of outdoor accelerated test sites as a service for ASTM members. NCCA members will also benefit from this document. This work was begun in response to a myriad of questions around the industry as to the identification, location, certification and reputation of exposure testing facilities. The objective is to have a relatively complete listing for members to access on the D01 home page and through the ASTM/NCCA Collaborative Portal.

___ Finally, as always, new ASTM D01.53 members are always welcome. The $75 yearly membership is well worth the cost. Not only can you become involved directly with coil coating by joining D01.53, you can lend your expertise to tangential disciplines and keep coil coating knowledge alive for the next generation.

Online Wet Film Measurement

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__ The coil coating industry is increasingly facing tougher competition and a more demanding client base. Short production runs are more common and customer quality expectations have not relaxed, so there is a drive towards improved efficiency and cost savings. Increasing product yield by avoiding downgrades represents a real opportunity for increased profitability. When there is sufficient market demand, having additional capacity from within existing production shifts also provides an opportunity for additional profit.
___ Delivering the tools needed to meet these opportunities and challenges is what motivates Wolf Innovation. At Wolf Innovation we have recently launched a fourth new product for the coil coating quality control sector called WFM2™. This is a patented, automated, wet film thickness instrument that replaces WFM1™. In combination with PVS1™ (paint volume solids instrument) this provides a significant new opportunity for savings by eliminating out of specification product from the start of a production run. It can take several hundred metres of strip before a thickness related defect is detected and a correction is made. The reason is simple – it is not possible to defect a defect until painting has commenced.

WFM2™ Data and Modes of Operation
WFM2 Provides 3 thickness output values:
• Wet film thickness on the coater roll
• Wet film thickness on the strip, and
• Dry film thickness on the strip (in combination with PVS1™)
Primary measurements are made on the coater roll. Modes of operation include:
• Forward and reverse coating mode, and
• Measurement before and during painting.
The measurement range extends to thin films so measuring primer thickness is very reliable.

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Coater Head Set-Up Procedures and Potential Losses
___ When it comes to coater set-up prior to painting there is a heavy reliance on experience, and only a few approaches are available. Replicating coater set-up conditions from run to run is a common approach, but this also has limitations. The variables that affect coater set-up, apart from the obvious ones, include coater roll diameter, roll hardness, paint volume solids, coater roll swelling (due to solvent absorption), and mechanical inconsistencies such as coater roll eccentricity. If any one of these is not in line with expectations, the initial film build target may not be achieved. Instances do occur where fully instrumented servo controlled coaters deliver film builds that vary to a significant level from one side of the strip to the other – this is both surprising and unexpected for this type of technology. The only sure way to hit target film build from the onset of coating is by direct film thickness measurement during coater set-up.
In common use, the wet film thickness wheel applied to the strip after painting commences provides a basic approach to measuring wet film-build on the strip. This is a destructive test that relies on operator skill. The method has a significant error band. Since the measurement is made after painting has commenced many metres of strip will have been painted before any correction can be made, that is, a correction to dry film build. Separate readings are needed on each side of the strip adding to the time required for the measurement whilst increasing the amount of lost product.
___ For a 100,000 tpa paintline operating at full capacity 5 metres of wet film wheel track lines every 20 tonnes equates to over 80 tonnes of lost product per year, excluding any out of spec product at the start of a painting run. This is a conservative estimate. Instances of ‘out-of-specification’ product are not avoided.
___ Another approach is ‘the test strip’ in which a section of coil is painted once the coater has been set up. The coil for the test strip is loaded onto the line between threader strips. A sample is cut from the test strip for measurement of film thickness, colour, and other paint physical properties. The cost of test strips is high and production cannot proceed while the line is stopped waiting for the test strip results. The advantage of test strips over the wet film wheel is that dry film thickness on the strip and colour can be assessed accurately in the laboratory.
___ For a 100,000 tpa paintline operating at full capacity 20 metres of test strip every 50 tonnes equates to about 130 tonnes of lost product per year. It also equates to about 500 hours of lost production time. That equates to a potential 10,000 tonnes of additional capacity within existing shifts.

WFM2™ – Paint Coater Set-Up Before Painting
___ WFM2™ uses an intrinsically safe confocal sensor to measure the surface of paint on the coater roll and the surface of the elastomeric roll at the same location. This data provides a measured value for wet film thickness on the coater roll. Coater and line speed set-up values are imported into WFM2™, which allows determination of wet film thickness on the strip. PVS1™ values of paint volume solids are then used to determine dry film thickness on the strip.
The three coating thickness values given by WFM2™ are shown in Figure 2.

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To be of value the measured wet film thickness on the coater roll has to be correct and there are some hurdles to overcome to achieve the integrity of this measurement:
1. The paint wet film thickness on the roll before painting is not equal to the wet film thickness during painting – shown in figure 3. To overcome this WFM2™ uses a very soft pneumatically operated doctor blade to wipe a narrow band of paint from the roll upstream of the sensor – this mimics painting.

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2. The wet film thickness on the coater roll has to take account of roll and bearing eccentricity and roll shape problems. The instrument measures and stores thousands of reference readings to characterise the roll shape and bearing wear in order to take these out of the equation.
3. Conversion of the wet film thickness on the coater roll to the equivalent wet film thickness on the strip requires a one-off calibration for each coater. During reverse coating not all of the paint is wiped off the coater roll onto the strip – shown in figure 3b, above. The residual paint on the coater roll after the kiss point is known as leakage. As part of the calibration process WFM2 characterises leakage for a coater and accounts for its effect. Figure 4, below shows the distribution curve for leakage values from a coater across 100 paint runs covering most topcoat types applied on this coil paint line.

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4. Conversion of the wet film thickness to dry film thickness on the strip requires an accurate value for paint volume solids (PVS). PVS1™ reliably measures paint volume solids in a production environment. PVS1™ is the only PVS instrument and method to fully cure the paint to an equivalent degree as occurs in a paint line oven. This is particularly useful with plastisols that are cure-sensitive.
Accurate prediction of dry film build before painting commences has the added benefit of significantly reducing off color defect caused by out of specification paint thickness. The value of this benefit should not be underestimated.

WFM2™ – In Use
___ WFM2™ does not interfere with coater room operations including coater roll cleaning and change over. To achieve this:
• The sensor components are designed to slide into and out of position on a linear bearing usually mounted off to the side of the coater. The brackets are tailored for each coater design.
• The sensor has hands free operation.
• The small doctor blades can be cleaned quickly and easily.

Typical Performance – Repeatability Under Production Conditions
___ After setting up a coater ready for production WFM2™ was used to take 8 sequential film thickness readings without altering the set-up between readings. The purpose of the test was simply to check and illustrate repeatability of the reading. The results, given in table 1 below, speak for themselves. Deviation of WFT ROLL is consistently within +/- 0.012mils across all paint types.

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Production Data – Comparing WFM2™ and Phaeton™ Dry Film Measurements
___ A random selection of nine results from a 16-day period of production compares dry film thickness measurements with Phaeton™ dry film thickness measurements. The results shown are typical for WFM2™ in terms of strip DFT results verses lab thickness results. The largest variance here is 0.03 Mils, and the least is 0.004 Mils. On average, results were within +/- 0.015 Mils of the lab measurement. This capability of measuring and setting strip dry film thickness before the commencement of painting provides a significant and new opportunity for improved prime product yield and for significant gains to the bottom line.
___ WFM2™ wet film measurement in combination with rapid in plant paint volume solids assessment has now been introduced on a coil line in Asia to determine dry film thickness before painting commences. The results from WFM2™ are in good agreement with independently measured values of dry film thickness determined with the off-line Phaeton™ DFT instrument. This provides validation for both WFM2™ and for Phaeton measurements.

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PVS1 is the only paint volume solids instrument to cure a paint sample to the same degree of cure as occurs on a coil paint line. Consequently results from PVS1 together with WFM2 provide dry film build results with a high level of confidence.
___ Out of specification product from the early part of each new production run can now be effectively eliminated with this new and effective QC tool. When things do go wrong, start up losses in the order of hundreds of metres of strip can easily occur. Savings in substrate, paint, and a reduction of field and customer complaints, and downgrades will provide an attractive payback for WFM2™.
___ Improvement in production yield shows the real value of this ‘new-to-the-world’ leading-edge quality control innovation.

Unique Demands of Small Lots in Coil Coating

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___ In the article “Minimizing Cleaning Costs in Modern Coil Coating Operations”, which appeared in Coil World’s September/October 2012 issue, we noted:
“…the coil coating marketplace has changed significantly. Extreme economic pressures have resulted in a great deal of consolidation within the industry, and some coaters have failed entirely. Those that remain live in a significantly different competitive environment. Nowhere is this more evident than with toll coaters. Gone are the days of the 72-hour run. Customers are striving for leaner operations with lower inventories. As a result, they are demanding smaller, more frequent shipments with shorter leadtimes. Faced with the same business constraints, coaters are being forced into shorter runs – often just a portion of a coil…”1
___ In fact, this has become the norm in the industry for virtually all coaters, resulting in operational issues which include:
• more frequent color changes
• more partial drums to handle and store
• increased cleaning costs
• increased setups and quality checks
• reduced available run time
___ These issues drive reduced efficiency at a time when excess production capacity in the marketplace is forcing razor-thin margins, and they require innovative strategies if a coater is to remain viable.

Improving Efficiencies
___ There are many ways that coaters can improve their efficiency. That particular article compared various cleaning methodologies, analyzing them to identify the most time efficient and cost effective option available to the coil coater. Moreover, the introduction of simple, non-intrusive, effective point-of-application temperature control in 2005 has enabled many coaters to also realize gains by:
• reducing solvent additions
• reducing paint consumption
• improving film quality and appearance
• improving batch-to-batch repeatability
___ So how has the addition of temperature control enabled forward-thinking coaters to realize all of these benefits? The answer lies in the relationship between temperature and viscosity and the relationship between viscosity and film.

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Temperature, Viscosity, and Film
___ “…all coaters understand the importance of fluid viscosity to the coating process. Performance parameters such as coating film build, color match, voids, chemical resistance and the like can all be linked directly to the viscosity of the [liquid] coating material when it was applied. In addition, process parameters such as pressure, flow rate and coating speed are all dependent on coating material viscosity. For these reasons, virtually all coating processes begin with the measurement and/or adjustment of coating viscosity.”2
___ Given this understanding, it is common for a coater to adopt a policy of running similar coatings at the same viscosity in an attempt to stabilize other process parameters, like roll speeds and nip pressure, thus simplifying setups and increasing the efficiency of color changes.
___ Unfortunately, what’s often misunderstood is that this relationship varies for each color formulation – even within the same paint type. Figure 1 shows the Viscosity vs. Temperature curves for a group of related paint colors. These are all of the same resin base type, yet they display very different viscosity characteristics as a function of temperature. As demonstrated in the May/June 2012 Coil World article “Adjusting Coating Viscosity” quoted above, if all of these colors are to be run at a 26-second viscosity and the temperature is below 70°F, all will require viscosity reduction – likely through the addition of solvent – in order to reach that 26-second target. As the topic of solvent addition is covered in depth in that article, suffice it to say here that the addition of solvent runs counter to the efficiency and cost-containment objectives of coaters in today’s marketplace. As a result, many have turned to temperature control as a means of controlling viscosity. In the example shown in Figure 1, if a constant 26-second viscosity is desired, the Black must be run at 70°F, the Muslin and Warm Beige must be run at 75°F, the Charcoal must be run at 80°F, and the Putty must be run at 85°F. This produces a consistent viscosity across all colors without the time and cost of adding solvent, which is ultimately “burned-off” in the curing process anyway.
___ Another issue is the significant friction that is generated in the roll coating process. This adds energy to the paint and causes its temperature to vary widely. Figure 2 below shows a typical 2-roll reverse (indirect) coating configuration:

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_ Here, the coating is picked up from the pan by the pickup roll, and then transferred to the applicator roll, which in turn, applies it to the passing strip. The pickup roll has a hard surface, usually constructed of steel and sometimes ceramic coated. The applicator roll has a compressible surface, usually constructed of steel with a thick urethane (or other polymer) coating. These two rolls are forced together at the “nip” under significant pressure, often in the 2,000 – 3,000 PSI range. When the pickup roll carries the coating from the pan to the nip, it is squeezed down so a thin film remains on the applicator roll to be applied to the strip. That film thickness is determined by the pressure between the rolls at the nip, the durometer (firmness) of the urethane applicator roll, and the viscosity of the coating. The balance of the coating on the pickup roll is sheared away by the action of the nip and falls back into the pan.
___ The texture of the pickup and applicator roll surfaces and the pressure between them results in a great deal of friction, which generates heat. Additionally, as the coating is applied, the friction between the applicator roll and the strip, which is intensified by their opposing directions of travel, also generates heat. Much of the heat generated by this process is carried back to the pan, first by the coating squeezed out of the nip, and then by the pickup roll, which is submersed in the coating in the pan.
___ The flow of coating in the pan is determined by numerous factors, including the geometry and volume of the pan itself, the rate at which the coating is being pumped into the pan, the location of the inlet, the location of the outlet, the speed of the pickup roll, and the rate of coating usage – but the flow is almost never directly from the inlet to the outlet. Because of all the rotational vectors generated by the various motions in the system, significant swirls and eddy currents are spawned in the coating. As such, the heat produced is unevenly distributed throughout the pan. Saint Clair Systems has developed specialized methods for measuring the resulting temperatures at multiple points throughout the application system, and these measurements have repeatedly shown that significant temperature variations are presented to the nip along the width of the strip.

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_ Because of the relationship between temperature and viscosity, as discussed above and demonstrated in Figure 1, the warmer coating presented to the nip will be at a lower viscosity than the cooler coating. As a result, the film of coating allowed to pass through the nip will be thinner. Because of the compressible nature of the applicator roll, it is possible to have different displacements in adjacent areas across its width. This results in variation of the film across the width of the applicator roll, which is subsequently applied to the strip. Figure 3 shows how this variation in temperature across the width of the pickup roll, called the Thermal Profile, results in variation in the film build across the width of the strip.
___ To complicate matters further, coaters and suppliers are continuously creating higher-volume-solids coatings in an attempt to drive down the solvent content and, therefore, reduce the cost and environmental impact of VOC’s in the process. These higher volume solids mean steeper viscosity vs. temperature curves, which in turn, results in even greater film variations as a result of edge-to-edge and head-to-tail temperature variations. These conflicting objectives can create a “vicious circle” of increasing processing difficulties for the coater to handle.

Correcting the Thermal Profile
___ In order to break this vicious circle and reduce variations in film, it is necessary to minimize thermal variations in the system. Research performed on literally hundreds of coating heads has shown that the best thermal profiles (those with the smallest edge-to-edge temperature variation) are found on heads operating in a 3-roll reverse (indirect) nip-feed coating configuration, as shown in Figure 4. In fact, the thermal profile measured on the head in Figure 4 is shown in Figure 5.

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Here we can see that the edge-to-edge variation is on the order of ±0.1°C (±0.2°F). This assures that the film variations across the width of the strip as a result of coating viscosity variations are virtually non-existent. Unfortunately, the head-to-tail performance of these systems is as bad as their 2-roll reverse counterparts. The thermal performance over time of this same system is shown in Figure 6.

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From this graph we can see that, though the edge-to-edge profile is very tight, the temperature of the coating (and therefore the viscosity) is continually changing. The friction of the system, increased due to the use of two nips, drives the temperature of the coating up until cool coating is added from bulk supply to the pit (break) drum. This cools the coating temporarily, but between fills, the cycle repeats itself. This means that, without adjustments to parameters like nip pressure to compensate for the change in viscosity caused by the varying temperature, the film build on the strip will continually vary from the head (start) of the coil to the tail (end).

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This can obviously be addressed through the implementation of temperature control. Figure 7 shows another 3-Roll Reverse (Indirect) Nip-Feed Coater both without and with temperature control. In the left-hand graph (without temperature control) we can see the same temperature variation over time demonstrated in Figure 6 above. In the right-hand graph (with temperature control), however, we can see that both the edge-to-edge and head-to-tail variations have been eliminated. In this situation, the coil will be coated evenly over its entire surface – with no adjustments required. Furthermore, this consistency will be independent of the length or width of the coil being coated and can be repeated from coil-to-coil. Best of all, this allows the same coater “recipe” to be used every time that product is run, through every season, which optimizes the setup efficiency.

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So why doesn’t everyone just switch to a 3-roll nip-feed configuration? In spite of its advantages, there are still many issues with 3-roll systems:
• Not all coating heads are set up for 3-roll operation
• Additional rollers are expensive
• Additional energy is required to run the third roller
• Additional maintenance is required with a 3-roll system
It’s difficult to operate 3-roll configurations reliably without temperature control.

 

The Best of Both Worlds
___ “[To] Promote the global competitiveness of manufacturing companies by controlling fluid temperature and viscosity at the point of use.”4
This is Saint Clair Systems’ published Mission Statment, which clearly delineates our long standing commitment to making our customers more efficient and effective. In keeping with this stated objective, we have taken these lessons learned and applied them to the development of our patent-pending Profile Correction Module (PCM). Shown in Figure 8, this innovative new device creates 3-roll nip-feed coating configuration performance on a standard 2-roll coater – with none of the complexities.
___ This unique, patent-pending design achieves this objective in three fundamental ways:
1) As shown in Figure 9, coating is metered to the surface of the pickup roll through a carefully controlled gap created by the physical location of the PCM in relation to the pickup roll face. This adjustable gap supports any film build, allowing it to be used with coatings as thin as Epoxies and Lacquers used for beer & beverage stock, Urethane and Epoxy Primers, common Polyester, Modified Polyester and Fluoropon based architectural coatings, and even high-viscosity, thick-film coatings like PVC’s and Plastisols.
2) This gap is continuously flushed with fresh, temperature-controlled coating from the center to the ends to drive out any material that has been in contact with the roller long enough to absorb energy and increase its temperature. This stable temperature coating in constant contact with the pickup roller helps to bring roll swell to equilibrium more quickly than in either standard 2-roll or 3-roll configurations.
3) The pan is lowered into a “catch-basin” configuration so that the coating in the pan is no longer in contact with the pickup roll and, therefore, temperature variations in the pan created by swirls and eddy currents cannot be transferred to the applicator roll by the pickup roll. Furthermore, the volume of coating in the pan no longer has any impact on the coating result, so it can be driven down to an absolute minimum. In fact, reductions in system fill-volume of up to 80% are possible.

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The detailed configuration of the system is shown here in Figure 10:

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The proof that this new system emulates 3-roll performance is best shown in the thermal profile graph in Figure 11, which shows less than ±0.15°F variation across the width of the “nip”.
The advanced features of this new system include:
• Low initial cost
• Smaller fill volumes
• Quick-release mountings
• Positive repositioning stops
• Fast initial install (<2 hours)
• Negligible edge-to-edge temperature variation
• No third motor, so no added energy to operate
• Removal & reinstall < 1 minute (total) at color change
• Faster, more efficient cleanup

rlw1-12_ By combining the best of the 2-roll and 3-roll coating systems, the PCM system improves on the benefits of each with features that directly address the issues associated with the short-run requirements of today’s coating marketplace. A quick recap is in order:

 

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A Better Way of Coating
___ By combining the best of the 2-roll and 3-roll coating systems, the PCM system improves on the benefits of each with features that directly address the issues associated with the short-run requirements of today’s coating marketplace. A quick recap is in order:

BIBLIOGRAPHY
1 – Bonner, Michael R. Minimizing Cleaning Costs in Modern Coil Coating Operations. Coil World, September/October 2012.
2 – Bonner, Michael R. Adjusting Coating Viscosity. Coil World, May/June 2012.
3 – Paint Viscosity vs. Temperature data provided courtesy of Sherwin-Williams Corporation.
4 – Saint Clair Systems, Inc., M