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AUTOMATION COST JUSTIFICATION FOR TODAY'S POWDER FINISHER

Cynthia A. Skelton-Becker & Sergey Guskov

Manager, Controls Engineering Nordson Corporation

Amherst, Ohio

Presented at: FINISHING '95 CONFERENCE AND EXPOSITION

September 18-21, 1995 Cincinnati, Ohio

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Automation Cost Justification for Today’s Powder Finisher

Cynthia A. Skelton-Becker Sergey Guskov

Introduction

Automatic controls have found an important place in modem factories. They often provide the consistency required to meet ever growing quality requirements of powder finishing customers. Controls provide material cost savings by controlling the application of powder and monitoring the coating environment. They also reduce downtime by notifying operators of problems when they occur and before they can result in significant equipment or product damage.

It is often difficult to justify investing in controls based on payback. Some benefits realized (such as material savings) can be easily projected based on anticipated production volumes and expected efficiencies. Other issues (such as downtime and cost of quality) are subjective and based on information that is difficult to estimate and even more difficult to project or measure. However, those issues become extremely important once the system is down for repair or when rejects start populating the load stations. Unfortunately, sometimes this realization comes too late.

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Automatic control features available today can be divided into three broad categories: Gun Control, Booth Control and Gun Positioning. Here we analyze these categories providing material useful if a powder mater is considering the purchase of automatic controls. Where applicable, spreadsheets of cost analysis are provided. In every case, we try to provide the information to allow engineers to estimate cost savings and quality improvements that can be realized from utilization of each control feature.

Gun Control: Simple Triggering

The most obvious cost savings realized from the use of automatic gun controls are those associated with turning “on” the application equipment only when required. Typically, automatic guns can remain “on” as long as the conveyor is running. However, better quality finish and reduced powder use can be achieved simply by tuming the guns “off and “on” in a controlled manner (triggering). Several products are available from powder application equipment suppliers to provide this function. Almost all automatic application equipment can be controlled by an outside source (for example, a PLC).

The major savings in triggering can be associated with saving material typically sprayed to waste with non-triggering automatic guns. Appendix 1 provides a spreadsheet showing calculations of savings that can be realized from gun triggering in a powder system where guns are automatically triggered “on” only when a part passes before them. Savings are associated not only with powder lost in non-reclaim systems, but also in systems where material is recovered.

Additional savings can be achieved by using what is called restrained or extended wrap illustrated in Figure 1. Extended wrap allows an increased system efficiency by increasing a wrap-around effect of electrostatic powder coating process. Restrained wrap provides users with a reduction in the “picture frame” effect that is frequently observed if parts are not hung close togetber and excess powder builds up on the part edges. Given that the material flow rate is usually set to provide minimum required coating thickness on the most dificult to coat areas, the excess powder deposited on protruding parts and edges of coated objects can be rather significant, resulting in dramatic reduction of economic benefits. Uniformity of the coating thickness is extremely important for reducing the everyday cost of a powder coating operation. When the oversprayed powder is being reclaimed, the cost of the excess powder deposited on the substrate becomes the major waste element. Appendix 2 illustrates how savings from better uniformity of the coating thickness can be calculated.

Reduction or elimination of the picture frame effect using gun triggering also often results in finish quality improvements. These improvements are particularly pronounced when applying powder on textured substrate or using textured coating materials. In such cases the excess paint can affect finish quality by “overflowing” and hiding the pattern.

Other savings can be achieved, even if fixed equations cannot be developed generically. First, powder application equipment uses both electricity and compressed air. Many plant managers are aware of their electricity and air costs. Savings can be calculated on a case-by-case basis if the engineer knows the costs associated with air and electricity use. One simply calculates the percentage of time g u n s would be “off due to a mater’s product mix and computes the total electricity and air costs. Second, reducing amount of material sprayed results in lower load on recovery system, extended filter life, reduced cleaning time and wear on parts of application equipment.

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Figure I I

Extended Wrap Restrained Wrap

- H Spray Duration Spray Duration

Gun Control: Other Parameters

In addition to tuming the guns “on” and “off, other factors can affect system and quality costs. Almost all automatic powder applicators provide for adjustment of KV or current settings and pump air control. The intention is to adjust the applicator to provide the appropriate coverage for a particular part. If an automatic powder system is coating parts with similar geometries, requiring the same coverage, with the same powder, then adjustments are not required. Often this is aot the case and there are a number of factors that require a powder water to adjust parameters of coating application equipment to achieve maximum economic efficiency and quality. Some of these parameters are:

+ Powders of different colors can have different specific gravities and require different amounts of material sprayed to achieve the same efficiency of coverage.

+ Parts of different geometries and structures require different electrostatic parameters’ settings to combat Faraday cage effect, achieve better wrap-around, increase coating thickness or optimize final finish quality.

+ Changes in line speed or coating thickness requirements can be accommodated by adjusting powder flow rates.

On parts with developed surface profiles, changes of electrostatic and pneumatic settings of application equipment may be required across a single part to achieve coating uniformity and optimize material utilization. (See Figure 2)

+

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Where batching allows, the line operators can certainly adjust settings on automatic guns between changes. With this approach, whenever the color, part, or line speed dictates, the operator adjusts the multiple settings for each gun on the line. Hopefully, the correct information was recorded so that the same settings are used for each batch. Inaccuracies may result when the adjustments are either forgotten or made incorrectly.

If batching is not possible, then a compromise is found. A “best set” of parameters is found to put the best overall finish on the part mix. The settings are often selected to accommodate the most visible or difficult to coat part or to provide above the minimum required wating on all parts. In either case, many parts are produced with excess coating material on them.

I [Without Idout gun positioning, higherflow I bte may be required to coat recessed area. I

Comparisons can be made and savings computed to examine if an automated method of adjusting gun and pump parameters is cost effective for an application. Appendix 3 illustrates the savings calculation for a typical powder coating system if the ability to program powder flow rates for different parts based on coating thickness requirements is used.

In the case of a production facility currently making changes by an operator, one can review the effectiveness of the current program and compare it to 100% change. Also, an automatically adjusting system allows a facility forced into batch finishing to move towards a Just - In - Time or non-batched work flow.

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In a powder coating system currently compromising its finishing requirements due to mixed parts on a line or difficult part geometries, each part can be reviewed for the cost of current powder usage versus desired powder usage. It is often surprising to a powder coater how much savings is incurred by providing this sophistication.

Other savings also should be estimated in determining whether advanced controls are cost effective. For example, in a facility where the compressed air pressure fluctuates based on compressor load, thc fan patterns for a pneumatic pump system fluctuate when the feed air pressure changes. Many of thc control systems that provide pump parameter adjustment also provide closed loop control over the air input. The transducer/regulator device will adjust itself to provide consistent pressure to the pump even as the. input air pressure varies. With this consistency, powder coaters can set gun parametcrs for a minimum coverage and not find excessive rework due to light coatings.

The cost of quality issues brought upon by compromises are often measurable, even if it is difficult to provide a formula that is applicable to all lines. Does your facility have an estimated cost for each repainted part that requires more labor and takes up valuable conveyor space? What docs Marketing have to say about improved surface finish that can be provided by better control of the applicator parameters?

Siecor Case Study

Siecor Corporation is a leading manufacturer of optical fiber cable, hardware and accessories for voice, data and video communications applications. Siecor powder coats thousands of parts each day and is dedicated to total quality. Operating on a just-in-time (JIT) principle made it difficult to rack parts into batches with the same application parameters. In addition, Siecor sprays six major colors (each requiring different pneumatic and electrostatic parameters) onto two different material substrates: ferrous metal or aluminum. Diversity of part configurations, colors and substrates made it impossible to manually adjust application equipment settings, One compromising regime of powder application was found and used on all parts and with all colors. As a result, virtually all parts had to be manually reinforced. Although overall reject rate at Siecor amounted to only 3 percent of production volume, for Siecor this translated into thousands of parts annually.

To make the operation more efficient, reduce manual reinforcement and reject rates, in June 1994 Siecor installed at its plant a fully automated, PLC based control system. The system is capable of storing up to 256 different sets of application parameter for different parts. At Siecor, thirty-eight (38) different parts were assigned part ID numbers based on part configuration and color category. As the system recognized a different part ID entering the booth, gun settings changed automatically.

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Results at Siecor:

1. Manual touch-up was virtually eliminated. Difficult-to-coat deep boxes, which previously had to be manually reinforced over the entire surface, were coated automatically with only minimal manual reinforcement on deep-inside comers. Figure 3 illustrates reductions in manual and automatic guns use.

2. Significant results were achieved in improving consistency of coating thickness on parts. Figure 4 shows variations in the coating thickness before and after an automatic PLC controller was installed.

3. Overall first-pass reject rate on the powder coating line was reduced by 50 percent (Figure 5) declining from 3 to 1.5 percent.

4. Film build was reduced in the range of 0.02 to 0.5 mils for different parts (See Figure 6) resulting in significant overall material savings.

AWRAGE HOURS USED PERDAY 7.00 6.00

5.00 E 4.00 8 3.00

2.00

1.00

0.00 4/21 - 6/23 f 6/23 - 812

Automtic PLC Cantroller is Installed

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1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 ~ 2 3 2 4 2 5 ~ 2 6 ~ 2 8 2 9 3 1

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(Figure6 I Material Savings After Automatic PLC Installation

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b. 0 h P) .a 6

0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00

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Booth Control

Although we usually equate User Friendly with computer systems, the ease of use of factory equipment was important before the computer was invented. However, as machines and processes became more complicated, computers (PLCs, dedicated microprocessors, or Personal Computers) were required to make human tasks more manageable and user friendly. Various computer-based control systems have been designed in the industry to monitor and control working parameters of powder spray booths. Implementation of such sophisticated controls results not only in improved user friendliness of the coating system but also in sizable cost savings.

Most of the cost savings realized from automatic controlling a booth are difficult to express and calculate in a formula format. However, these savings can be assessed on a plant-by-plant basis. There are a number of a spray booth control features available through the use of sophisticated, PLC - based, automatic control systems. Some of those features are:

t Monitor and alarm on cartridge and final filter pressure.

t

t Dew point monitoring.

Powder level control and alarm in hoppers and reclaim modules.

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4 Automatic airflow management.

4 Pulse-ondemand of collector cartridges

4 Statistical data analysis.

Booth control features can be divided into two broad categories: Diagnostics and Monitoring, and Air Flow Management.

Diagnostics and Monitoring

Automatic booth diagnostics and monitoring can provide both tangible cost savings and benefits that are less easily quantifiable. Like most machine control, much of the benefit is in the case of use. Operators can easily locate problems as devices and processes are monitored. By locating problems quickly, down time is reduced.

This category of control features results in major savings for a powder coater due to (1) ability to plan preventative maintenance, (2) reduction of overall downtime, and (3) reduction in reject rates. Features include:

Monitoring the motor control devices and safety interlocks. If any of these fail, the booth control Operator Interface Panel (OIP) would notify the operator of the errant device. Instead of an electrician with a meter ringing out an interlock string, the OIP will clearly tell the operator where the failure is located. This can save minutes or hours.

Monitoring of a pressure drop across cartridge and final filters. The cartridge pressure can be viewed over time, allowing maintenance to plan downtime for replacement. If the pressure drop exceeds a certain maximum level it can lead to poor powder material retention inside the booth, contamination of plant environment, damage to equipment and disruption of the manufacturing process.

Powder level control and monitoring in feed hoppers and reclaim modules warrant against down time and quality problems caused by low powder levels in feed hoppers or by powder spilling out of hoppers and collectors.

Dew point monitoring. The compressed air dewpoint can be measured and examined over time, telling the engineer how well the air dryer is working. Moisture in the air supply affects every major element in a powder coating system. Excess moisture can make the powder material agglomerate and cause surging spray patterns and clogging of cartridge and exhaust filters, fluidizing plates, and pneumatic lines.

Statistical data analysis or alarm log records assist in planning preventative maintenance for reduced downtime and facilitate data collection for IS0 9000 certifications and quality control. Savings of data collection cost can be rather significant for a large manufacturer.

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Air Flow Management

Air Flow Management systems allow users to select an optimal airflow through booth openings and automatically maintain it constantly at this level regardless of changes in the pressure drop across the booth and recovery system. Typically, in a standard powder booth without airflow controller, fan speed is fixed. As a result, depending on cartridge loading, static pressure and airflow in the booth will change. Automatic airflow control system provides constant air velocity across the booth and improves consistency of the first pass transfer efficiency of the coating operation, material utilization, and uniformity of the finish.

Moreover, major savings are realized from reduced energy consumption as the system allows users to operate at a lower than a maximum capacity of the exhaust fan motor. Appendm 4 provides an example of calculations of savings realized from reduced energy consumption.

Pulse-ondemand of cartridge filters is yet another valuable feature of the automatic airflow control system. When this feature of the control equipment is used, cartridge filters are pulsed only when the static pressure drop across the cartridges reaches a preset level. Monetary savings from pulsing on demand are difficult to calculate although benefits of it are easy to understand. This feature provides reduced compressed air consumption, extended life of cartridge filters, and lower noise levels. Moreover, if the load on the reclaim system is low (amount of powder sprayed), there is a possibility that the cartridge filters will be “over pulsed‘‘ if no automatic pulse control is used. Over pulsing cartridges results in lower cartridge efficiency, more powder going to the final filters, shorter service life of the filters and additional powder material waste.

Gun Positioning

Gun - to - Part Distance

Gun-&part distance is one of the critical working parameters of a powder coating system. It strongly affects the first pass transfer efficiency and the size of the effective pattern of the gun. Experiments have shown that a 50 percent reduction in the distance between a spray gun and the object being coated may result in 25-30 percent reduction in powder transfer efficiency.

Such changes in transfer efficiency mean that if a flat panel is followed by a deep box and the guns are fixed along the horizontal axis, unless adjustments are made to the pump and electrostatic parameters, coverage will vary. This means that, to achieve minimum required coating thickness on all the parts, some parts will have to be coated with an excess amount of deposited powder. The economic consequences of this have been discussed earlier in this paper. -

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Figure 7 illustrates yet another effect of changes in a gun-to-part distance. The guns are typically spaced vertically by a distance that would provide for a certain overlap of patterns from adjacent guns. Required pattern overlap is determined based on the size of the spray pattern and the distance between the gun and the part. If the latter changes, the size of the overlap zone also changes. Therefore, if the part passes closer to the guns, the coating thickness in the overlap zone will be greater than on the rest of the surface. If the part is farther from the guns, the overlap zone of the adjacent patterns shrinks and may even disappear resulting in thinner than required deposited coating thickness. In either case the coating becomes uneven and wavy.

In addition, with a corona gun, the closer the distance between a gun and a part, the bigher the density of the free ion current and the faster the development of back ionization on the deposited powder layer. Back ionization limits the ability to achieve thicker films, disrupts finish quality, hinders ability to coat Faraday cage areas and often results in rejects.

To combat the negative consequences of the vatying gun-to-part distances, modern automatic system control equipment includes a feature that continuously monitors and maintains a fixed distance between the gun and the coated surface. Although it is difficult to quantify the savings that are realized from implementing this feature, it results in greater coating thickness uniformity, better finish quality and reduced reject rate.

\I . -. -. . . . . . . . . . . . . . . . . . .. . -. . -. . . . . . . .. .........II. Overiap zone of pawms ofadjacent guns shrinks or cvcn

disappcan if tho part is moved cioser to the guns iesuhing in an; uneven coating thickness

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Increased automation with Servo Systems/Robotics

In the early ~ O ’ S , robots were considered one of the more effective tools to reducing costs and improving quality in US manufacturing with painting robots being one of the two main applications. Today, because of the expense and maintenance requirements, manufacturers look carefully and robots are used where specifics of the manufacturing process make it imperative or the benefits realized are greater than the extra operating cost.

Servo systems, whether 7-axis robots or 3-axis gun movers, are still useful in replacing manual touch- up and to coat some extremely difficult parts. For example, there are fast conveyor applications with deep parts (oven cavities, washer tumblers) that an automatic gun placed outside the opening will not coat sufficiently. However, using manual gun operators to perform the coating could result in a high probability of occurrence of industrial diseases like Carpel Tunnel Syndrome even if an applicator used is very light. If changing the conveying system and part hanging configuration is not an option, then a servo system is one of the few options available in powder coating today.

Other applications can be identified where a simple one or two-axis servo system can be used to replace two manual operators. The increased capital cost is then compared to wages and benefits of two employees each shift.

If a poor internal finish affects the cost of quality for your product, the use of a servo system can provide further cost benefits. Like all robotics systems, servo systems perform the same motion each time. A powder water is not dependent on the accuracy of an operator who may tire and slow down or change motion patterns to avoid additional fatigue and motion related illness. As a result, cost of quality is often reduce when servo systemshobotics are implemented in an industrial coating process.

Cost Savings Decision

Powder coaters must decide which options are cost effective for their particular product mix and their specific manufacturing process. Customizing a control package to meet the needs of each customer can provide additional savings necessary to justify the initial capital cost. Modular design of automatic control equipment allows powder finishers to choose the particular options that provide the most savings for each specific application.

Another valuable aspect of controls is an easy adaptability of a control system. Should a product line of a manufacture change, causing a new product mix or new colors, additional controls can be evaluated to upgrade an existing system. By planning ahead, additional savings can be realized later from the flexibility of upgrading.

In all cases, sizable cost savings that become realizable through the implementation of controls move the automatic controls system from a Nice-to-Have status to the ranks of Cost Saving options.

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Bibliography

Reddy, Vishu, et al. “Nordson Smart-Coatm System: Value Analysis at Siecor Corporation.” Copyright 1994 Nordson Corporation, Amherst, OH.

Reddy, Vishu, et al. “Controls and Productivity.” Powder Coatings ‘92 Conference Prodceedings. October 6-8, 1992. Copyright 1992, the Powder Coatings Institute. p93.

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Appendix 1

A I B I C I D I E

Gun Triggering Benefit Analysis. 66

- 67 BR

Sprayed with Triggering (loo0

sz ICost of Powder Wasted ( %/year) I $105,524.OO I I I I

Continued

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Appendix 1 (Continued)

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Appendix 2

I Example of Value Analysis of I I Restrained Overspray I

The entire surface required 1 Mil. of coating.

A - is coated with 1 Mil. B - is coated with 3 Mil.

Applied cost of Excess Film Buildmart.

- - (CostLb.) x (Volume of Excess Film Build) (CoverageLMil.) x (Transfer Efficiency)

- -

- $0.14mart 3 x (0.5 x 3) x 2 63 x 0.90

- - -

- - - 192.3 Where - Coveragmil (Specific Gravity) x (Excess Film Build)

192.3 - 63 - - - 1.4 x 2

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Appendix 3

~ - L

"2- powder flow rate according to coating thickness requirements -

__ 134 for different parts. 133 --

A I B 1 C I D I E 130

Savings which can be realized from automatic adjustment of

. .. .. . . . -. - - . , .. . . . .

I I M a x i " Cmting T h i c b (cut of all parts) 3.00

Automatic Flow Rate Control

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Appendix 4

4000 CFM

0.060 15 6

4680 390.0

7.5 6.3

$147 $1,766

60% 2.2 1.8

$43 $510

$105 $1,256

71%

ILOW MANAGEMENT ESTIMATED COST SAVINGS ANALYSIS 5500 CFM

0.060 15 6

4680 390.0

IO 8.4

$196 $2,355

60% 2.7 2.3

$53 $632

$144 $1,722

73%

I SYSTEM CAPACITY Operation Data: * Electricity Cost (Nkwbr)

Operation HourslDay * Operating Daysmeek Annual Operating Hours: Monthly Operating Hours:

System Performance NO AIRFLOW MANAGEME1 Horsepower Energy Consumption (kw) Monthly Operating Cost: Annual Operating Cost:

System Performance WITH AIRFLOW MANAGEll * Airflow (60-100%) Typical Horsepower Energy Consumption (kw) Monthly Operating Cost: Annual Operating Cost:

AIRFLOW MANAGEMENT 4 Savings: Monthly Cost Savings ($) Annual Cost Savings (S) Percent Savings

NOTES :

0.060 15 6

4680 390.0

15 12.6

$294 $3,532

0.061 1:

4681 390.1

21 16.:

$392 $4,709

liT 60% I 60% 5.3 4.5

$105 $1,258

:RATING

$189 $2,274

64%

5 . ( 4.'

$109 $1,312

COST

$283 $3,397

729

14400 CFM 7

0.06( l!

t 468(

390.C

25 21.c

$491 $5,886

60% 9.t 8.C

$188 $2,260

$302 $3,626

61 ?4

1. Typical airflow for a booth with large openings is 90-95%. 2. Typical airflow for a booth with small openings is 60-70% 3. ( * ) indicates the parameter is adjustable. 4. The calculations are estimates that will vary with application. 5. 100% flow is approximately the system flow rating.

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