Metal Finishing (Electroplating)
P2 Workshop
Part 1
Ohio EPA
Division of Hazardous Waste Management
Office of Pollution Prevention
Good morning, welcome to the Metal Finishing Sector Pollution Prevention Workshop
Whats in it for Me?
Understanding of Metal Finishing Unit ProcessesSkills for Identifying Process Optimization (P2!) OpportunitiesKnowledge of Tools and Resources for Providing Technical Assistance
Value of this training. This training should make you more comfortable in identifying potential pollution prevention opportunities at metal finishers and coaters that you inspect. We hope to give a broad but accurate overview of plating processes and situations that you may encounter. Each section will have some basic keys to look for when visiting a plating facility. We want you to be confident in suggesting options for facilities to pursue and know where to find resources and assistance should a facility be open to considering P2 opportunities.
Metal Finishing Process Unit
9
This is a very basic input output diagram to begin to consider opportunities for reductions in raw materials and subsequent waste streams.
Metal Finishing Processes
Surface Preparation and Cleaning:
alkaline cleaning
electropolishing
oxide removal
Metal Plating:
electroplating
electroless plating
Protection and Finishing Treatments:
anodizing
chromate conversion
phosphating
Basic metal finishing process usually incorporate these 3 major steps
Some type of cleaning and preparation step, in order to allow the work piece to accept a coating. The coating or Plating process where metal ions are attached to the surface by a bond Some sort of protective coating to seal the finish
Surface preparation will usually start with removal of fluids from machining and or shipping protective coatings. This step should be the beginning of the P2 focus at a facility. Carry over from the cleaning or preparation phase will impact the plating solution and possibly subsequent rinses.
Alkaline cleaning: oil, dirt, coating removal
Electropolishing: reverse plating process, remove thin coating of metal from part, shiny surface (from which the name is taken)
Oxide removal: acid stripping of rust also done for surface preparation, longer is pickling.
Electroplating is the electronic deposition of a metal ion on the surface of a negatively charged work piece.
Electroless plating is the same deposition process except current is not used, a solution of metal ions still deposits on the work piece.
Anodizing: this process is basically the same as electropolishing except the purpose is to form a thin oxide on the surface of the part.
Chromate Conversion Coating: this process uses chromic acid to form a thin gel like film of chromic oxide and aluminum oxide on the part surface. This is frequently used so that paint or adhesives will adhere to aluminum parts.
Phosphating: a thin layer of phosphate crystals on the metal surface, for coating adhesion.
Typical Plating Line
Slide 17
Plating Line/Department Except for vapor degreasing, which normally is performed off-line, plating operations are normally incorporated into a sequence of tanks, called a "line."
A plating line may be designed to produce a single coating or a number of coatings. While not always the case, the process line contains tanks lined up in sequential order. Automated lines may or may not contain tanks in sequential order.
A zinc plating line may therefore consist of 13 tanks, each containing a chemical processing solution or rinse water, soak clean, electroclean, rinse, acid, rinse, zinc plate, rinse, bright dip, rinse, chromate, rinse, hot water rinse, and dry. If the line is for barrel plating, each tank may have one or more "stations," that is, places to put a barrel. A six-station zinc plating tank can plate six barrel-loads of parts at one time. To economize, some shops may have one cleaning line that services several plating lines. There also are tanks for rack stripping, stripping rejects, purifying contaminated solutions or holding solutions that are only sporadically used. The entire lineup of tanks and lines creates a "layout" of the shop, with parts entering the plating department from one direction, traveling through the process lines, and leaving the plating department.
Common Metal Finishing Wastes
Rinse water effluentSpent plating baths Spent alkaline and acidic etchants and cleanersSpent strippersSolvent degreasersWaste and process bath treatment sludgesMiscellaneous wastes (filters, empty containers, floor grates, off-spec chemicals)
* Some of these may be Persistent Bio-accumulative Toxic substances such as Cadmium, Chromium, Copper, Lead, Nickel, Zinc & Cyanide
Rinse water effluent receives metals loading, cleaners, etchants and often requires pH adjustment. Volume of the waste water is a key, along with any alternative chemistries for cleaning, coating, etc. Always ask if a process step is required by the customer, or if alternatives would be acceptable.
P2 Principles for Metal Finishing
Use the least toxic/easiest to manage chemicals
Extract the most life (use) out of process chemistries
Keep process chemistry solutions where they belong: in the tanks
Return as much escaping solution (dragout) as possible to the tanks
Use the least amount of rinse water required for good rinsing
28
Least toxic chemicals, starting with coolants fluids or lubes if parts are machined, then cleaners, etchants, and plating solutions themselves. A key is to ask how solutions are prepared and maintained. (If they describe their process as a number of glugs, jugs, scoops, handfuls etc.) Take note, process chemistries should be carefully maintained. If they are proactive they will talk about extending the life of their baths and rinses. Be alert to fixed dump or batch replacement schedules. (like we dump that bath every Thursday) solution life is variable based on use, soil loading.
Rack Plating
Workpieces hung or mounted to frames (racks)Most common and versatile processing methodDragout rates and rinse water use easier to control
Dragout most easily managed due to ability to drain or rinse properly, covered in more detail in the drag-out control areas
Barrel Plating
Parts processed in containment barrelTypically small parts with low level of plating or processing tolerance requirementsDragout rates and water use relatively high
Consequently, poor drainage and difficulty in rinsing make barrel plating a challenge.
Manual Plating
Process steps performed by handSmaller size parts, lower production
Basically un-automated rack plating. Keys are agitation, withdrawal rate, hang time and tilting. Manual process changes must be addressed as a training/management issue. (Worker controlled) Can be potentially very effective if implemented properly.
Automated Plating
Fully Automatedonly requires manual racking and unrackinghigh production quantities and ratesSemi automatedrequires manual control of hoists and railslarger parts, lower production rates, and varied parts
Automated or Semi-automated plating could be either racks or barrels. Main features of automated plating both good or bad is consistent withdrawal rates, rinsing, agitation etc. Semi-automated with hoists has the same procedural constraints as manual plating (worker controlled) training issue.
Keys to Identifying P2 Opportunities at Metal Finishing Facilities
Basics of Metal Finishingdoes the facility monitor and measure their plating or coating solutions, how are additions madedoes the facility have specifications for each part they finish, mil thickness, quality standards?does the facility have procedures and training in place for coating time, withdrawal rate, drain time, rinsing, part orientation?does the facility know addition and flow rates for water in their cleaning and plating solutions and rinses?
Measuring and Understanding Dragout
Now that you have seen an introduction to dragout, we can discuss how to measure and understand it better. If you can measure dragout, you can identify material losses and wastes, and establish a baseline data point so you can measure improvement
Dragout Impacts
Increased plating chemical useIncreased rinse water use or decreased rinse qualityIncreased dragin into next bathIncreased wastewater generation
1.psd
Now lets look at the metal finishing diagram shown earlier during the Metal Finishing the Basics portion of our training.
Dragout from the process or plating bath has multiple impacts.
As shown in the video, dragout causes material losses. The material in this case is the process/plating chemicals. Plating chemical additions are more frequent because of these losses.
The dragout decreases rinse water quality which leads to an increase rinse water flow and use
The excess chemicals from dragout and increase rinse water flow send more rinse water to wastewater treatment
Dragout Impacts (continued)
Increased WWTS treatment chemicalsIncreased WWTS filter cakeIncreased WWTS effluent metal concentration
Increase wastewater generation has a direct correlation to wastewater treatment chemical use. This use increases because more gallons must be treated and there is a higher metal ion concentration from the dragout plating bath.
More chemicals and plating solution in the effluent produces more wastewater sludge and more disposal responsibilities including cost, paperwork, and liability.
Dragout Measurement
Direct volume measurement (dragout volume drained from parts)Metal concentration/conductivity in rinse tanksWastewater contaminant concentration
Once a metal finishers is aware of dragout, they should measure it to establish baseline data and can measure improvements and reductions.
There are 3 methods of measurement;
Direct volume measurement (dragout volume from parts)
Metal concentration/conductivity in rinse tanks
WW contaminant concentration
Conductivity measurement is the easiest and most effective. Direct volume is time consuming and difficult to measure total volume and Wastewater concentration can be expensive because of lab testing. Also, with WW concentration, targeting a particular plating line or solution is difficult.
Calculating Dragout
Vd = (DC)(Vr)/Cp
where:
Vd =dragout volume (L/rack)
DC =increase in rinse water metal concentration per rack or barrel(mg/L/rack)
Vr =rinse tank volume (L)
Cp =process bath metal concentration (mg/L)
Calculating dragout volume in L/rack is possible. The estimated slope of the stagnant rinse tank is 1.5 mg/L/rack. That is delta C. We can assume that the rinse tank volume in 1000 L and the process bath metal concentration is around 70,000 mg/L. Dragout volume is about 21 mL/rack.
Conc = [0.0021 x (conductivity)] + 0.423
0
1
2
3
4
5
6
7
0
500
1,000
1,500
2,000
2,500
3,000
Conductivity (
m
S)
Zn Concentration (ppm)
Good News: conductivity versus concentration is linear.
More Good News: conductivity is easy to measure!
Measuring dragout with conductivity works because conductivity versus concentration is linear. This make measurement easy yet effective.
Using Dragout Measurements
Estimate costs of dragout for particular partsMake cost/benefit decisionsLower dragout vs. slower withdrawal rates Lower dragout vs. longer hang timeWorker trainingIncentive programsWWTS Recovery technologiesBenchmarking
By measuring with conductivity, dragout costs can be estimated for particular parts. This can help when anylyzing what changes are most cost effective and/or save the most money.
Its may help a company make cost/benefit decisions;
Which will have the largest and most effective impact?
Lower Dragout or slower withdrawal rates
Lower dragout or longer hang time
Working training?
Incentive programs?
WWTS?
Recovery technologies to reclaim plating bath
Benchmarking is an important part of dragout measurement. A standard of measurement must to set to establish a reference point for future reductions and improvements.
Dragout Reduction Techniques
Identifying and measuring dragout is the first step. From here, dragout reduction techniques can be applied.
You have a copy of this diagram in your manual.
It is important to look at the 4 ms that cause raw material loss through dragout
Methods, Man, Materials, and Machine
Dragout Reduction:Parts Racking and Handling
Rack maintenancePart geometryPart overlap and angleBarrel rotation and hang time
35
How parts are placed and positioned on a rack effects dragout rates.
Racks are made of metal and be receive the plating solution themselves as shown in the video. This leads to odd shape clusters that increase surface area for dragout to collect. Maintaining the racks are significant
The parts geometry themselves can attribute to dragout. Certain shaped parts like the ones on this slide and collect excess plating solution. They must be racked accordingly, for instance, with a different angle. Also, part overlap is critical so that the plating solution doesnt drip directly onto the next part below.
Finally, barrel rotation and hang time are important factors also. As seen in the video, a few extra seconds on hang time can reduce dragout significantly.
Impact of Barrel Rotation
Barrel rotation also has impacts on dragout. 8 ppm/rack difference or nearly 20% reductions will be significant over a months and years production time.
Dragout Volume vs. Drain Time
Chart1
4.71.61.30.7
5555
2.210.60.4
1.80.80.40.3
20202020
25252525
1.20.60.20.1
35353535
40404040
1450.145
50505050
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Barrel 1, Part 1
Barrel 1, Part 2
Barrel 2, Part 1
Barrel 2, Part 2
Drain Time (seconds)
Dragout (mL)
Sheet1
Dragout (milliliters)
Drip Time (seconds)Barrel 1, Part 1Barrel 1, Part 2Barrel 2, Part 1Barrel 2, Part 2
04.71.61.30.7
5
102.210.60.4
151.80.80.40.3
20
25
301.20.60.20.1
35
40
4510.1
50
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Title
Best Practices for
Metal Finishing
Line Operators
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InfoInput
Facility Name:ABC Metal FinishingDate:05/08/01
UNIT COSTS
1)Type of process solution:Nickel
Unit cost of process solution:$ 7.47/gallon
2)Unit cost of water:$ 3.49/1,000 gallons
(Includes purchase price and
sewer fee)
3)Unit cost of wastewater treatment:$ 51.37/1,000 gallons
(Includes treatment chemicals, maintenance,
permitting, and sludge disposal)
PROCESS INFORMATION
1)Concentration in Process Bath84000.0mg/L
2)Volume of Rinse Tank473.1Liters
(formula includes a conversion from gallons to liters)
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Cal Numbers
DilutionConductivity (microS/cm)Concentration (mg/L)
5001601.00200.00Line Equation
7501420.00100.00slope0.4855794599
10001310.0053.00y-intercept-581.9710495594
20001190.000.00
3000
4000
Blank
City water used for calibration curve
Concentration of metal in plating solution =84,000mg/L
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Cal Graph
200.00
100.00
53.00
0.00
Concentration (mg/L)
Conductivity [microSiemens]
Metal Concentration [mg/L]
Calibration Curve
Ex.1-Racking
FIRST RINSESECOND RINSE
Parts Racked HorizontallyParts Racked VerticallyHorizontalVertical
No. of RacksMetal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)
01445.0119.70.001343.070.20.00Start122.011.7124.011.9
11478.0135.733.01365.080.822.0Finish128.012.3128.012.3
21490.0141.545.01376.086.233.0Increase6.000.604.000.40
31512.0152.267.01395.095.452.0
41535.0163.490.01410.0102.767.0Rinse Improvement =0.20mg/L
51560.0175.5115.01430.0112.487.0% Improvement =33%
10.7mg/L/rack8.2mg/L/rack
Process Solution Dragout Calculations
HorizontalVertical
10.7mg/L/rack8.2mg/L/rack
473.1L473.1L
84,000mg/L84,000mg/L
0.060L/rack0.046L/rack
0.016gal/rack0.012gal/rack
WORKSHEET CALCULATIONS
1) Dragout Losses
Parts Racked Horizontally
0.016gal/rack
=55.8gal/month
Parts Racked Vertically
0.012gal/rack
=42.8gal/month
Reduction
Dragout Reduction =13.0gal/month
Percent Reduction =23%
2) Rinse Quality Improvement (second rinse)
Parts Racked Horizontally
Initial =11.67mg/L
Final =12.27mg/L
Increase =0.60mg/L
Parts Racked Vertically
Initial =11.87mg/L
Final =12.27mg/L
Increase =0.40mg/L
Improvement in Rinse Quality
Improvement =0.20mg/L
3) Rinse Water Use Reduction
% Reduction in Dragout
% Dragout Reduction =23%
Parts Racked Horizontally
Flow rate in 2nd rinse =4.0gpm
=42,240gal/month
Parts Racked Vertically
Flow rate in 2nd rinse =3.1gpm
=32,395gal/month
Rinse Water Reduction
Reduction =9,845gal/month(based on % drag out reduction)
4) Process Solution Cost Savings:Nickel
Parts Racked Horizontally
Dragout =56gal/month
Cost =$417/month
Parts Racked Vertically
Dragout =43gal/month
Cost =$320/month
Cost Savings
Savings =$97/month
5) Rinse Water Use Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$147/month
Parts Racked Vertically
Water Use =32,395gal/month
Cost =$113/month
Cost Savings
Savings =$34/month(based on % drag out reduction)
6) WWTS Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$2,170/month
Parts Racked Vertically
Water Use =32,395gal/month
Cost =$1,664/month
Cost Savings
Savings =$506/month(based on % drag out reduction)
7) Summary Table
Parts Racking Position
HorizontalVerticalDifference
Dragout Volume
for 5 racks (gal/rack)0.0160.012
per month (gal/month)55.842.823%
0.60.433%
Rinse Water Use (gal/month)42,24032,39523%
Chemical Costs ($/month)$417$320$97
Water Costs ($/month)$147$113$34
WWTS Costs ($/month)$2,170$1,664$506
Total Savings ($/month) =$637
(These are graph reference numbers below; do not alter!!)
HorizontalVertical
Chemical Costs$417$320
Water Costs$147$113
WWTS Costs$2,170$1,664
Graph1a
0.000.00
33.0022.00
45.0033.00
67.0052.00
90.0067.00
115.0087.00
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HorizontalVertical
Conductivity Increase (mS/cm)
Conductivity Increase (mS/cm)
Racks
Conductivity (mS/cm)
Parts Racking
Graph1b
416.60319.50
147.42113.06
2169.871664.13
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Horizontal
Vertical
Cost per Month
Parts Racking
Ex.2-Drain Time
FIRST RINSESECOND RINSE
0-Second Drain Time3-Second Drain TimeNo Drain Time5-Second Drain Time
No. of RacksMetal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)
01445.0119.70.001560.0175.50.00Start123.011.8122.011.7
11467.0130.422.01570.0180.410.0Finish126.012.1123.011.8
21490.0141.545.01581.0185.721.0Increase3.000.301.000.10
31512.0152.267.01605.0197.445.0
41535.0163.490.01623.0206.163.0Rinse Improvement =0.20mg/L
51560.0175.5126.01650.0219.287.0% Improvement =67%
11.1mg/L/rack8.8mg/L/rack
Process Solution Dragout Calculations
No Drain Time5-Second Drain Time
11.1mg/L/rack8.8mg/L/rack
473.1L473.1L
84,000mg/L84,000mg/L
0.063L/rack0.049L/rack
0.017gal/rack0.013gal/rack
WORKSHEET CALCULATIONS
1) Dragout Losses
Parts Racked Horizontally
0.017gal/rack
=58.2gal/month
Parts Racked Vertically
0.013gal/rack
=46.0gal/month
Reduction
Dragout Reduction =12.2gal/month
Percent Reduction =21%
2) Rinse Quality Improvement (second rinse)
Parts Racked Horizontally
Initial =11.77mg/L
Final =12.07mg/L
Increase =0.30mg/L
Parts Racked Vertically
Initial =11.67mg/L
Final =11.77mg/L
Increase =0.10mg/L
Improvement in Rinse Quality
Improvement =0.20mg/L
3) Rinse Water Use Reduction
% Reduction in Dragout
% Dragout Reduction =21%
Parts Racked Horizontally
Flow rate in 2nd rinse =4.0gpm
=42,240gal/month
Parts Racked Vertically
Flow rate in 2nd rinse =3.2gpm
=33,381gal/month
Rinse Water Reduction
Reduction =8,859gal/month(based on % drag out reduction)
4) Process Solution Cost Savings:Nickel
Parts Racked Horizontally
Dragout =58gal/month
Cost =$434/month
Parts Racked Vertically
Dragout =46gal/month
Cost =$343/month
Cost Savings
Savings =$91/month
5) Rinse Water Use Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$147/month
Parts Racked Vertically
Water Use =33,381gal/month
Cost =$116/month
Cost Savings
Savings =$31/month(based on % drag out reduction)
6) WWTS Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$2,170/month
Parts Racked Vertically
Water Use =33,381gal/month
Cost =$1,715/month
Cost Savings
Savings =$455/month(based on % drag out reduction)
7) Summary Table
Drain Time
None5-SecondDifference
Dragout Volume
for 5 racks (gal/rack)0.0170.013
per month (gal/month)58.246.021%
0.30.167%
Rinse Water Use (gal/month)42,24033,38121%
Chemical Costs ($/month)$434$343$91
Water Costs ($/month)$147$116$31
WWTS Costs ($/month)$2,170$1,715$455
Total Savings ($/month) =$577
(These are graph reference numbers below; do not alter!!)
No Drain Time5-Second Drain Time
Chemical Costs$434$343
Water Costs$147$116
WWTS Costs$2,170$1,715
Graph2a
0.000.00
22.0010.00
45.0021.00
67.0045.00
90.0063.00
126.0087.00
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No Drain Time5-Second Drain Time
Conductivity Increase (mS/cm)
Conductivity Increase (mS/cm)
Racks
Conductivity (mS/cm)
Drain Time
Graph2b
434.50343.37
147.42116.50
2169.871714.77
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No Drain Time
5-Second Drain Time
Cost per Month
Drain Time
Ex.3-Spray Rinse
FIRST RINSESECOND RINSE
No Spray RinsingSpray RinsingNo Spray RinsingSpray Rinsing
No. of RacksMetal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)
01382.089.10.001318.058.00.00Start134.012.9134.012.9
11404.099.822.01333.065.315.0Finish140.013.5136.013.1
21419.0107.137.01352.074.534.0Increase6.000.602.000.20
31434.0114.352.01356.076.538.0
41452.0123.170.01368.082.350.0Rinse Improvement =0.40mg/L
51468.0130.986.01382.089.164.0% Improvement =67%
8.2mg/L/rack6.0mg/L/rack
Process Solution Dragout Calculations
No Spray RinsingSpray Rinsing
8.2mg/L/rack6.0mg/L/rack
473.1L473.1L
84,000mg/L84,000mg/L
0.046L/rack0.034L/rack
0.012gal/rack0.009gal/rack
WORKSHEET CALCULATIONS
1) Dragout Losses
Parts Racked Horizontally
0.012gal/rack
=42.8gal/month
Parts Racked Vertically
0.009gal/rack
=31.2gal/month
Reduction
Dragout Reduction =11.6gal/month
Percent Reduction =27%
2) Rinse Quality Improvement (second rinse)
Parts Racked Horizontally
Initial =12.87mg/L
Final =13.47mg/L
Increase =0.60mg/L
Parts Racked Vertically
Initial =12.87mg/L
Final =13.07mg/L
Increase =0.20mg/L
Improvement in Rinse Quality
Improvement =0.40mg/L
3) Rinse Water Use Reduction
% Reduction in Dragout
% Dragout Reduction =27%
Parts Racked Horizontally
Flow rate in 2nd rinse =4.0gpm
=42,240gal/month
Parts Racked Vertically
Flow rate in 2nd rinse =2.9gpm
=30,766gal/month
Rinse Water Reduction
Reduction =11,474gal/month(based on % drag out reduction)
4) Process Solution Cost Savings:Nickel
Parts Racked Horizontally
Dragout =43gal/month
Cost =$320/month
Parts Racked Vertically
Dragout =31gal/month
Cost =$233/month
Cost Savings
Savings =$87/month
5) Rinse Water Use Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$147/month
Parts Racked Vertically
Water Use =30,766gal/month
Cost =$107/month
Cost Savings
Savings =$40/month(based on % drag out reduction)
6) WWTS Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$2,170/month
Parts Racked Vertically
Water Use =30,766gal/month
Cost =$1,580/month
Cost Savings
Savings =$589/month(based on % drag out reduction)
7) Summary Table
Spray Rinsing
NoneSpray RinsingDifference
Dragout Volume
for 5 racks (gal/rack)0.0120.009
per month (gal/month)42.831.227%
0.60.267%
Rinse Water Use (gal/month)42,24030,76627%
Chemical Costs ($/month)$320$233$87
Water Costs ($/month)$147$107$40
WWTS Costs ($/month)$2,170$1,580$589
Total Savings ($/month) =$716
(These are graph reference numbers below; do not alter!!)
No Spray RinsingSpray Rinsing
Chemical Costs$320$233
Water Costs$147$107
WWTS Costs$2,170$1,580
Graph3a
0.000.00
22.0015.00
37.0034.00
52.0038.00
70.0050.00
86.0064.00
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No Spray RinsingSpray Rinsing
Conductivity Increase (mS/cm)
Conductivity Increase (mS/cm)
Racks
Conductivity (mS/cm)
Spray Rinsing
Graph3b
319.50232.71
147.42107.37
2169.871580.43
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No Spray Rinsing
Spray Rinsing
Cost per Month
Spray Rinsing
Ex.4-T&D
FIRST RINSESECOND RINSE
No Tilting and DrainingTilting and DrainingNo Tilting and DrainingTilting and Draining
No. of RacksMetal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)Metal Concentration (mg/L)
01532.0161.90.001478.0135.70.00Start120.011.5120.011.5
11551.0171.219.01486.0139.68.0Finish125.012.0121.011.6
21567.0178.935.01497.0144.919.0Increase5.000.501.000.10
31586.0188.254.01509.0150.831.0
41602.0195.970.01520.0156.142.0Rinse Improvement =0.40mg/L
51626.0207.694.01532.0161.954.0% Improvement =80%
8.9mg/L/rack5.3mg/L/rack
Process Solution Dragout Calculations
No Tilting and DrainingTilting and Draining
8.9mg/L/rack5.3mg/L/rack
473.1L473.1L
84,000mg/L84,000mg/L
0.050L/rack0.030L/rack
0.013gal/rack0.008gal/rack
WORKSHEET CALCULATIONS
1) Dragout Losses
Parts Racked Horizontally
0.013gal/rack
=46.6gal/month
Parts Racked Vertically
0.008gal/rack
=27.9gal/month
Reduction
Dragout Reduction =18.7gal/month
Percent Reduction =40%
2) Rinse Quality Improvement (second rinse)
Parts Racked Horizontally
Initial =11.47mg/L
Final =11.97mg/L
Increase =0.50mg/L
Parts Racked Vertically
Initial =11.47mg/L
Final =11.57mg/L
Increase =0.10mg/L
Improvement in Rinse Quality
Improvement =0.40mg/L
3) Rinse Water Use Reduction
% Reduction in Dragout
% Dragout Reduction =40%
Parts Racked Horizontally
Flow rate in 2nd rinse =4.0gpm
=42,240gal/month
Parts Racked Vertically
Flow rate in 2nd rinse =2.4gpm
=25,265gal/month
Rinse Water Reduction
Reduction =16,975gal/month(based on % drag out reduction)
4) Process Solution Cost Savings:Nickel
Parts Racked Horizontally
Dragout =47gal/month
Cost =$348/month
Parts Racked Vertically
Dragout =28gal/month
Cost =$208/month
Cost Savings
Savings =$140/month
5) Rinse Water Use Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$147/month
Parts Racked Vertically
Water Use =25,265gal/month
Cost =$88/month
Cost Savings
Savings =$59/month(based on % drag out reduction)
6) WWTS Cost Savings
Parts Racked Horizontally
Water Use =42,240gal/month
Cost =$2,170/month
Parts Racked Vertically
Water Use =25,265gal/month
Cost =$1,298/month
Cost Savings
Savings =$872/month(based on % drag out reduction)
7) Summary Table
Tilting and Draining
NoneTilt and DrainDifference
Dragout Volume
for 5 racks (gal/rack)0.0130.008
per month (gal/month)46.627.940%
0.50.180%
Rinse Water Use (gal/month)42,24025,26540%
Chemical Costs ($/month)$348$208$140
Water Costs ($/month)$147$88$59
WWTS Costs ($/month)$2,170$1,298$872
Total Savings ($/month) =$1,071
(These are graph reference numbers below; do not alter!!)
No Tilting and DrainingTilting and Draining
Chemical Costs$348$208
Water Costs$147$88
WWTS Costs$2,170$1,298
Graph4a
0.000.00
19.008.00
35.0019.00
54.0031.00
70.0042.00
94.0054.00
&A
Page &P
No Tilting and DrainingTilting and Draining
Conductivity Increase (mS/cm)
Conductivity Increase (mS/cm)
Racks
Conductivity (mS/cm)
Tilting and Draining
Graph4b
348.25208.30
147.4288.18
2169.871297.87
&A
Page &P
No Tilting and Draining
Tilting and Draining
Cost per Month
Tilting and Draining
Summary Table
Demonstration Summary
Chemical Use SavingsWater Use SavingsWWTS SavingsTOTAL
Parts Racking$97$34$506$637
Drain Time$91$31$455$577
Spray Rinsing$87$40$589$716
Tilt and Drain$140$59$872$1,071
These are important referenced graphs below!! Do not modify!!!
Dragout
Original TechniqueModified Technique
Parts Racking55.842.8
Drain Time58.246.0
Spray Rinsing42.831.2
Tilt and Drain46.627.9
% Improvement
Tilt and Drain40%
Spray Rinsing27%
Drain Time21%
Parts Racking23%
Cost
97.1034.36505.74
91.1330.92455.10
86.7940.05589.44
139.9559.24872.00
Chemical Use Savings
Water Use Savings
WWTS Savings
Cost Savings
Cost Summary
Dragout
55.7742.77
58.1745.97
42.7731.15
46.6227.88
&A
Page &P
Original Technique
Modified Technique
Dragout (gal/month)
Dragout Summary
% Reduction
0.40
0.27
0.21
0.23
&A
Page &P
Percent Improvement
Dragout Reduction
36
Drain time should be increased but only with reasonable time standards. As mentioned earlier, conductivity can be used to decide between dragout reduction methods and how they are implemented. Based on this graph, drain times greatest impact on dragout is the 5 to 10 seconds
Dragout Reduction: Worker Practices
Withdrawal rateDrainage timeTiltingUse hang bars and other devices
36
Many metal finishing shops have manual operations or semi-manual operations. Worker practices are therefore important when completing a dragout reduction initiative.
Withdrawal rates, drainage time, tilting and hang bars can influence losses of plating solutions.
Impacts of Withdrawal Rate
The video demonstrated how the speed of withdrawal rates impact dragout rates. A faster withdrawal rate leaves a thicker film on part than a slow rate.
Dragout Reduction:Process Layout, Maintenance
Tank spacing and drain boardsTank sequenceDragout tanks (with or without sprays)Spray rinses
36
Process layout and maintenance can also influence dragout reduction. The video discussed proper tank spacing and drain boards.
The right tank sequence in important also, like including dragout tanks and spray rinsing.
Dragout Tanks
Single stage rinseRinse water flow rate = 2 gpmDragout rate = 0.25 gphCadmium discharge = 0.23 lb/day
Dragout tank followed by rinse tankRinse water flow rate = 0.6 gpmDragout rate = 0.20 gphCadmium discharge = 0.07 lb/day
Installing dragout tank that collect excess plating bath and returns to original bath reduces metal discharge by 30% per day. At the same time, rinse water flow rate was reduced by 30% also which yields water savings
Sprays: More than a Rinse!
Parts moved directly to rinse tank from plating bathDragout rate = 0.25 gphRinse water flow rate = 2 gpmChromium discharge = 2.2 lb/day
Parts rinsed with mist spray above plating tankDragout rate = 0.13 gphRinse water flow rate = 1 gpmChromium discharge = 1.1 lb/day
Spray rinsing, which we will go into more detail this afternoon can reduce metal discharge by more than 50% and reduce rinse water flow without installing a dragout tank. Sometimes both dragout tanks and spray rinse can be used it plating operations has space.
Dragout Reduction with Spray Rinse
Cost savings of a typical spray rinse system is 60%.
Conductivity Control Systems
This section focuses on how to utilize the relationship between conductivity and dragout to optimize rinse water usage. From discussion earlier conductivity and dragout are directly related and can be used to effectively measure dragout (increasing concentration of ions) in the subsequent rinse baths.
Keys to Identifying P2 Opportunities at Metal Finishing Facilities
Conductivity Controldoes the facility use conductivity measurement to manage their rinse system(s)?if they have a system, what type is it, how do they operate it, what are their results?if they do not have system do they know the relative costs and benefits of installing one?
Analyzer
The system brainReceives input from sensorDisplays conductivity readingDigital, analog, or noneSends output signal to solenoid valveKey features:Programmable set point Programmable deadband
These components are an example of a fully automated conductivity control system. There could be wide range of layouts and degree of automation utilized in implementing this approach. Including manually adjusting flows utilizing a continuous readout conductivity meter or even a hand held unit and control charting.
Conventional Sensor
The sensor has an anode and cathode which is placed in a solutionElectrical potential is measured between these electrodesProne to fouling$150-250
Problems with this system are caused because the cathode in the solution is going to plate with the metal ions in the solution. This requires constant cleaning & recalibration of the sensor.
Electrodeless Sensor
Uses two parallel torroidsNon-conductive casing (polypropylene or PVDF)No electrodes; no foulingCan measure full range of conductivity$435-635
Measures an induced current in the solution. This method avoids the fouling problems with conventional sensors.
Sensor Installation
Sensor placementHalfway down from top of water levelAway from stagnant areasAway from clean water inletIn final stage of multistage counterflow rinseGood circulation of rinse waterMechanical mixingDouble dipping parts
Keys to good control are representative measurement of the conductivity in the tank. Another item not on the list would be to have the sensor stationary and not in various positions over time. Good circulation of rinse water also is very helpful and can be achieved through mechanical mixing or double dipping of parts in the rinse tank.
Determining the Initial Set Point
Establishing the initial set point is very important for assuring that changing the rinse flows will not effect product quality. Product quality and conductivity need to measured carefully and measured together. The concept is the same as many other P2 opportunities, utilize the least amount of a raw material while maintaining product quality. The net result will be an increase in efficiency and a consistency in the product quality due to process control.
Rinse Water Use
40,000
80,000
120,000
160,000
5/6
5/28
6/17
7/15
8/5
8/26
9/16
10/7
10/28
11/18
Week
Weekly Rinse Water Use (gal.)
Installation
Note: No change in production occurred during the evaluation period.
This is the effect seen by establishing a set point and operational range for tank refill, and operating the rinse tanks with the controls in place. As you can see the effect is very dramatic and is typical for instituting controls.
Spray Rinse Systems and Design
As mentioned in the Drag-out portion of this mornings session, spring rinsing can reduce dragout significantly.
But spray rinsing has other benefits;
Less raw material wasted because of reduced dragout
Less contamination of process baths by dragin (Ill show an example of this process later)
Lower rinse water flow rates required in running rinses
More efficient, higher quality rinsing
Benefits of Reducing Rinse Water
Lower water bills and sewer feesWastewater treatment impactsLower treatment chemical costsHigher retention timeLess O&M requirementsDecreased sludge generation
Similar to dragout reduction, reducing rinse water can have to same WWTP benefits.
A efficient rinse water system can lower water bills and sewer fees.
Less water means lower treatment chemical costs and a higher retention time due to a lower flow rate.
In turn, Operational and maintenance costs and requirements are reduced
Techniques that Improve Rinse Efficiency
AgitationRack motionForced air and/or forced waterSpraysDouble dippingFlow Controls and Water QualityFlow restrictorsConductivity control systemsTap water vs. deionized water
39
Some basic techniques to improve rinse efficiency
Agitation
-rack motion-manual or automatic
-forced air and/or forced water- careful to use only enough air to blow excess dragout off part. To much can lead to flashing or oxidation of part. Usually air and water mix is better. Ill provide example later in this session
-sprays
-double dipping
Flow controls & water quality
-flow restrictors-must be used properly to determine most efficient flow
-conductivity control systems-Ron covered this
-tap water vs. deionized water-depends on product/customer specs and production process
Techniques that Improve Rinse Efficiency
Tank DesignSize (not bigger than necessary)Eliminate short-circuitingTank LayoutMultiple tanksCountercurrent rinses are extremely efficient 90% reduction compared to a single rinseMost old shops can not accommodate the larger footprint
40
Techniques continued
Tank Design
-size is important (a large tank does not mean better rinse efficiency)
-eliminating short-circuiting-improper mixing of rinse tank/stratification
Tank Layout
-multiple tanks-dragout tanks and rinse tanks
-Countercurrent or counterflow rinsing can often yield 90% reduction in rinse water compared to single rinse
-however, many old shops cannot accommodate major layout changes or the large tank footprint
Counter Current Rinse System
41
As I mentioned, counter current or counter flow is another rinse water reduction technique.
Here is an general diagram describing the process. The cleanest rinse and rinse water inlet is always in the last rinse tank. It then flows over or is pumped back to the first rinse tank.
Counterflow also Reduces Dragin
Single-stage zincate rinse Rinse water flow rate = 2 gpmDragin rate into bath = 0.50 gphZn buildup in EN bath = 6 ppm/day
Two-stage counterflow zincate rinse Rinse water flow rate = 1 gpmDragin rate into bath = 0.40 gphZn buildup in EN bath = 0.02 ppm/day
Example of counterflow rinsing reducing dragin
A zincate rinse before an electroless nickel bath. Before counterflow rinse,
Rinse water flwo rate was 2 gpm
Original zinc conc. In rinse was 415ppm
After two-stage counterflow zincate rinse,
Final rinse stage zinc conc.is 222ppm
Electroless bath dragin was 6.1 ppm of Zinc per day and now is 0.02 ppm
Thats is a 305% reduction!!!
Reactive Rinsing
47
Reactive Rinsing Example
172 Acid Bath Dumps/Year200 gallon bath$23k/year for bath makeupIn-Shop Measurements:Alkaline Rinse pH:12.15Acid Rinse pH:1.32Combination:1.77Estimated 50% Reduction in Acid Use/DumpsCapital: $1,250Payback:Spray Rinse Systems and Design
Spray rinsing might work well and save money and plating bath, but it must be set-up and properly design to accomplish any of these reductions
Keys to Identifying P2 Opportunities at Metal Finishing Facilities
Rinse Tank Optimization & Spray Rinsingare any measures in place to extend the life of the rinse baths, skimmers, agitation, sludge removal, water treatment?are spray rinses utilized, if so, where are they located, how are they operated and why?are rinse tanks utilizing counter current flow, are there flow restrictors or controls?is the quality of the rinse water monitored or measured?has the facility experimented with different rinse configurations, flows, or sprays?
Sprays Reduce Dragout by 58%
20.8 gallons of
dragout/month
50.0 gallons of
dragout/month
Number of Racks
Conductivity (S/cm)
58% Reduction
250
200
150
100
50
0
0 10 20 30 40 50 60
Spray Rinses Off
Spray Rinses On
Spray rinsing on Nickel line reduced dragout by 58%
50.0 gallons per month to 20.8 gallons
Air-Atomized Spray Guns
As mentioned in the beginning of this session, the correct spray rinse system and equipment is important. Using a garden hose spray gun compared to air-atomized spray gun can use over 36,000 gallon/yr more.
Air-Atomized Spray Guns
AIR-ATOMIZING SPRAY RINSING RESULTS
AnnualAnnual
ReductionSavings
Spray Rinse Water Use36,960 gal.$464
Wastewater Generation36,960 gal.$715*
Total Savings = $1,179/year
Total Cost = $636
Payback Period < 7 months
*Annual savings for wastewater generation is based on estimated treatment chemical use reduction.
These savings are significant with a short payback period
Sprays Over Heated Baths
_992259471.xls
Sheet: Chart4
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Sheet: Sheet15
Sheet: Sheet16
0.0
0.0
2.0
2.0
4.0
4.0
6.0
6.0
8.0
8.0
10.0
10.0
12.0
12.0
14.0
14.0
16.0
16.0
0.0
0.0
11.0
4.0
5.0
4.0
8.0
4.0
12.0
10.0
21.0
10.0
23.0
11.0
26.0
9.0
32.0
0.0
0.0
2.0
2.0
4.0
4.0
6.0
6.0
8.0
8.0
10.0
10.0
12.0
12.0
14.0
14.0
16.0
16.0
0.0
0.0
4.0
11.0
4.0
5.0
4.0
8.0
10.0
12.0
10.0
21.0
11.0
23.0
9.0
26.0
32.0
0.0
0.0
2.0
2.0
4.0
4.0
6.0
6.0
8.0
8.0
10.0
10.0
12.0
12.0
14.0
14.0
16.0
16.0
0.0
0.0
11.0
4.0
5.0
4.0
8.0
4.0
12.0
10.0
21.0
10.0
23.0
11.0
26.0
9.0
32.0
SPRAY GUN
WATER USE (gallons per day)
High-flow spray nozzle
297.0
Air-atomizing spray gun
176.0
0.0
0.0
You can see a 61% reduction in the conductivity slope and how bath life can be extended.
Sprays Over Heated Baths
FOG SPRAY RINSING RESULTS
AnnualAnnual
ReductionSavings
Black Dye Use43.2 lb$2,419
Wastewater Generation14,856 gal.$1,247*
Total Savings = $3,666
Total Cost = $355
Payback Period < 2 months
* Annual savings for wastewater generation includes $186 in process water purchases and $1,061 in wastewater treatment O&M.
Great payback of less than 2 months
Tools and Resources for Assistance
Available Tools
Metal Finishing P2 Videos1. DHWM Preserving the Legacy Series: The Metal Plating and Finishing Industries2. USEPA Pollution Prevention for Metal Platers: Drag-out ReductionAdvanced P2 Technical Assistance
- TECHSOLVE P2IRIS Metal Finishing http://www.techsolve.org/iamsorg/p2iris/metalfinish/default.html
U.S. EPA/NAMF/AESF
- Strategic Goals Program http://www.strategicgoals.org/
Good morning, welcome to the Metal Finishing Sector Pollution Prevention Workshop
Value of this training. This training should make you more comfortable in identifying potential pollution prevention opportunities at metal finishers and coaters that you inspect. We hope to give a broad but accurate overview of plating processes and situations that you may encounter. Each section will have some basic keys to look for when visiting a plating facility. We want you to be confident in suggesting options for facilities to pursue and know where to find resources and assistance should a facility be open to considering P2 opportunities.
9
This is a very basic input output diagram to begin to consider opportunities for reductions in raw materials and subsequent waste streams.
Basic metal finishing process usually incorporate these 3 major steps
Some type of cleaning and preparation step, in order to allow the work piece to accept a coating. The coating or Plating process where metal ions are attached to the surface by a bond Some sort of protective coating to seal the finish
Surface preparation will usually start with removal of fluids from machining and or shipping protective coatings. This step should be the beginning of the P2 focus at a facility. Carry over from the cleaning or preparation phase will impact the plating solution and possibly subsequent rinses.
Alkaline cleaning: oil, dirt, coating removal
Electropolishing: reverse plating process, remove thin coating of metal from part, shiny surface (from which the name is taken)
Oxide removal: acid stripping of rust also done for surface preparation, longer is pickling.
Electroplating is the electronic deposition of a metal ion on the surface of a negatively charged work piece.
Electroless plating is the same deposition process except current is not used, a solution of metal ions still deposits on the work piece.
Anodizing: this process is basically the same as electropolishing except the purpose is to form a thin oxide on the surface of the part.
Chromate Conversion Coating: this process uses chromic acid to form a thin gel like film of chromic oxide and aluminum oxide on the part surface. This is frequently used so that paint or adhesives will adhere to aluminum parts.
Phosphating: a thin layer of phosphate crystals on the metal surface, for coating adhesion.
Slide 17
Plating Line/Department Except for vapor degreasing, which normally is performed off-line, plating operations are normally incorporated into a sequence of tanks, called a "line."
A plating line may be designed to produce a single coating or a number of coatings. While not always the case, the process line contains tanks lined up in sequential order. Automated lines may or may not contain tanks in sequential order.
A zinc plating line may therefore consist of 13 tanks, each containing a chemical processing solution or rinse water, soak clean, electroclean, rinse, acid, rinse, zinc plate, rinse, bright dip, rinse, chromate, rinse, hot water rinse, and dry. If the line is for barrel plating, each tank may have one or more "stations," that is, places to put a barrel. A six-station zinc plating tank can plate six barrel-loads of parts at one time. To economize, some shops may have one cleaning line that services several plating lines. There also are tanks for rack stripping, stripping rejects, purifying contaminated solutions or holding solutions that are only sporadically used. The entire lineup of tanks and lines creates a "layout" of the shop, with parts entering the plating department from one direction, traveling through the process lines, and leaving the plating department.
Rinse water effluent receives metals loading, cleaners, etchants and often requires pH adjustment. Volume of the waste water is a key, along with any alternative chemistries for cleaning, coating, etc. Always ask if a process step is required by the customer, or if alternatives would be acceptable.
28
Least toxic chemicals, starting with coolants fluids or lubes if parts are machined, then cleaners, etchants, and plating solutions themselves. A key is to ask how solutions are prepared and maintained. (If they describe their process as a number of glugs, jugs, scoops, handfuls etc.) Take note, process chemistries should be carefully maintained. If they are proactive they will talk about extending the life of their baths and rinses. Be alert to fixed dump or batch replacement schedules. (like we dump that bath every Thursday) solution life is variable based on use, soil loading.
Dragout most easily managed due to ability to drain or rinse properly, covered in more detail in the drag-out control areas
Consequently, poor drainage and difficulty in rinsing make barrel plating a challenge.
Basically un-automated rack plating. Keys are agitation, withdrawal rate, hang time and tilting. Manual process changes must be addressed as a training/management issue. (Worker controlled) Can be potentially very effective if implemented properly.
Automated or Semi-automated plating could be either racks or barrels. Main features of automated plating both good or bad is consistent withdrawal rates, rinsing, agitation etc. Semi-automated with hoists has the same procedural constraints as manual plating (worker controlled) training issue.
Now that you have seen an introduction to dragout, we can discuss how to measure and understand it better. If you can measure dragout, you can identify material losses and wastes, and establish a baseline data point so you can measure improvement
Now lets look at the metal finishing diagram shown earlier during the Metal Finishing the Basics portion of our training.
Dragout from the process or plating bath has multiple impacts.
As shown in the video, dragout causes material losses. The material in this case is the process/plating chemicals. Plating chemical additions are more frequent because of these losses.
The dragout decreases rinse water quality which leads to an increase rinse water flow and use
The excess chemicals from dragout and increase rinse water flow send more rinse water to wastewater treatment
Increase wastewater generation has a direct correlation to wastewater treatment chemical use. This use increases because more gallons must be treated and there is a higher metal ion concentration from the dragout plating bath.
More chemicals and plating solution in the effluent produces more wastewater sludge and more disposal responsibilities including cost, paperwork, and liability.
Once a metal finishers is aware of dragout, they should measure it to establish baseline data and can measure improvements and reductions.
There are 3 methods of measurement;
Direct volume measurement (dragout volume from parts)
Metal concentration/conductivity in rinse tanks
WW contaminant concentration
Conductivity measurement is the easiest and most effective. Direct volume is time consuming and difficult to measure total volume and Wastewater concentration can be expensive because of lab testing. Also, with WW concentration, targeting a particular plating line or solution is difficult.
Calculating dragout volume in L/rack is possible. The estimated slope of the stagnant rinse tank is 1.5 mg/L/rack. That is delta C. We can assume that the rinse tank volume in 1000 L and the process bath metal concentration is around 70,000 mg/L. Dragout volume is about 21 mL/rack.
Measuring dragout with conductivity works because conductivity versus concentration is linear. This make measurement easy yet effective.
By measuring with conductivity, dragout costs can be estimated for particular parts. This can help when anylyzing what changes are most cost effective and/or save the most money.
Its may help a company make cost/benefit decisions;
Which will have the largest and most effective impact?
Lower Dragout or slower withdrawal rates
Lower dragout or longer hang time
Working training?
Incentive programs?
WWTS?
Recovery technologies to reclaim plating bath
Benchmarking is an important part of dragout measurement. A standard of measurement must to set to establish a reference point for future reductions and improvements.
Identifying and measuring dragout is the first step. From here, dragout reduction techniques can be applied.
You have a copy of this diagram in your manual.
It is important to look at the 4 ms that cause raw material loss through dragout
Methods, Man, Materials, and Machine
35
How parts are placed and positioned on a rack effects dragout rates.
Racks are made of metal and be receive the plating solution themselves as shown in the video. This leads to odd shape clusters that increase surface area for dragout to collect. Maintaining the racks are significant
The parts geometry themselves can attribute to dragout. Certain shaped parts like the ones on this slide and collect excess plating solution. They must be racked accordingly, for instance, with a different angle. Also, part overlap is critical so that the plating solution doesnt drip directly onto the next part below.
Finally, barrel rotation and hang time are important factors also. As seen in the video, a few extra seconds on hang time can reduce dragout significantly.
Barrel rotation also has impacts on dragout. 8 ppm/rack difference or nearly 20% reductions will be significant over a months and years production time.
36
Drain time should be increased but only with reasonable time standards. As mentioned earlier, conductivity can be used to decide between dragout reduction methods and how they are implemented. Based on this graph, drain times greatest impact on dragout is the 5 to 10 seconds
36
Many metal finishing shops have manual operations or semi-manual operations. Worker practices are therefore important when completing a dragout reduction initiative.
Withdrawal rates, drainage time, tilting and hang bars can influence losses of plating solutions.
The video demonstrated how the speed of withdrawal rates impact dragout rates. A faster withdrawal rate leaves a thicker film on part than a slow rate.
36
Process layout and maintenance can also influence dragout reduction. The video discussed proper tank spacing and drain boards.
The right tank sequence in important also, like including dragout tanks and spray rinsing.
Installing dragout tank that collect excess plating bath and returns to original bath reduces metal discharge by 30% per day. At the same time, rinse water flow rate was reduced by 30% also which yields water savings
Spray rinsing, which we will go into more detail this afternoon can reduce metal discharge by more than 50% and reduce rinse water flow without installing a dragout tank. Sometimes both dragout tanks and spray rinse can be used it plating operations has space.
Cost savings of a typical spray rinse system is 60%.
This section focuses on how to utilize the relationship between conductivity and dragout to optimize rinse water usage. From discussion earlier conductivity and dragout are directly related and can be used to effectively measure dragout (increasing concentration of ions) in the subsequent rinse baths.
These components are an example of a fully automated conductivity control system. There could be wide range of layouts and degree of automation utilized in implementing this approach. Including manually adjusting flows utilizing a continuous readout conductivity meter or even a hand held unit and control charting.
Problems with this system are caused because the cathode in the solution is going to plate with the metal ions in the solution. This requires constant cleaning & recalibration of the sensor.
Measures an induced current in the solution. This method avoids the fouling problems with conventional sensors.
Keys to good control are representative measurement of the conductivity in the tank. Another item not on the list would be to have the sensor stationary and not in various positions over time. Good circulation of rinse water also is very helpful and can be achieved through mechanical mixing or double dipping of parts in the rinse tank.
Establishing the initial set point is very important for assuring that changing the rinse flows will not effect product quality. Product quality and conductivity need to measured carefully and measured together. The concept is the same as many other P2 opportunities, utilize the least amount of a raw material while maintaining product quality. The net result will be an increase in efficiency and a consistency in the product quality due to process control.
This is the effect seen by establishing a set point and operational range for tank refill, and operating the rinse tanks with the controls in place. As you can see the effect is very dramatic and is typical for instituting controls.
As mentioned in the Drag-out portion of this mornings session, spring rinsing can reduce dragout significantly.
But spray rinsing has other benefits;
Less raw material wasted because of reduced dragout
Less contamination of process baths by dragin (Ill show an example of this process later)
Lower rinse water flow rates required in running rinses
More efficient, higher quality rinsing
Similar to dragout reduction, reducing rinse water can have to same WWTP benefits.
A efficient rinse water system can lower water bills and sewer fees.
Less water means lower treatment chemical costs and a higher retention time due to a lower flow rate.
In turn, Operational and maintenance costs and requirements are reduced
39
Some basic techniques to improve rinse efficiency
Agitation
-rack motion-manual or automatic
-forced air and/or forced water- careful to use only enough air to blow excess dragout off part. To much can lead to flashing or oxidation of part. Usually air and water mix is better. Ill provide example later in this session
-sprays
-double dipping
Flow controls & water quality
-flow restrictors-must be used properly to determine most efficient flow
-conductivity control systems-Ron covered this
-tap water vs. deionized water-depends on product/customer specs and production process
40
Techniques continued
Tank Design
-size is important (a large tank does not mean better rinse efficiency)
-eliminating short-circuiting-improper mixing of rinse tank/stratification
Tank Layout
-multiple tanks-dragout tanks and rinse tanks
-Countercurrent or counterflow rinsing can often yield 90% reduction in rinse water compared to single rinse
-however, many old shops cannot accommodate major layout changes or the large tank footprint
41
As I mentioned, counter current or counter flow is another rinse water reduction technique.
Here is an general diagram describing the process. The cleanest rinse and rinse water inlet is always in the last rinse tank. It then flows over or is pumped back to the first rinse tank.
Example of counterflow rinsing reducing dragin
A zincate rinse before an electroless nickel bath. Before counterflow rinse,
Rinse water flwo rate was 2 gpm
Original zinc conc. In rinse was 415ppm
After two-stage counterflow zincate rinse,
Final rinse stage zinc conc.is 222ppm
Electroless bath dragin was 6.1 ppm of Zinc per day and now is 0.02 ppm
Thats is a 305% reduction!!!
47
Spray rinsing might work well and save money and plating bath, but it must be set-up and properly design to accomplish any of these reductions
Spray rinsing on Nickel line reduced dragout by 58%
50.0 gallons per month to 20.8 gallons
As mentioned in the beginning of this session, the correct spray rinse system and equipment is important. Using a garden hose spray gun compared to air-atomized spray gun can use over 36,000 gallon/yr more.
These savings are significant with a short payback period
You can see a 61% reduction in the conductivity slope and how bath life can be extended.
Great payback of less than 2 months
Space
Constraints
Raw Material
Loss Through
Dragout
Parts
Process Baths Too Concentrated
Racking Angle
Established Concentration
Higher Than Necessary
High Evaporation
Rate
Worker Practices
Removal Rate
Too Fast
Over-add Chemicals
Inadequate Worker
Training
Habit
Costs
Space Constraints
Process Line Configuration
No Dragout Tanks
Old Design
Production Rate
Pressures
No Spray Rinses on
Process Tanks
Too Much Maintenance
Lack of Awareness
No Drainage Boards
Lack of
Awareness
Space Between Tanks
Old Layout
Drainage Boards
Not Maintained
Frequent Process
Changes
Rack Design
Parts Overlap
on Rack
Rack Design
Chemical Supplier
Recommendations
Worker Practices
and Assumptions
Temperature Too High
Part Configuration
and Surface Area
Part Design
Supplier Concern
About Dragout
No Statistical
Process Control
Inadequate Worker Training
Production Rate Pressures
Lack of Motivation
Drainage Time Too Short
800
600
400
200
0
1
2
3
4
5
6
7
8
Slope = 41 ppm/rack
Slope = 49 ppm/rack
Number of Barrels
Zinc (ppm)
Rotation Off
Rotation On
Drain Time
None5-SecondDifference
Dragout Volume
for 5 racks (gal/rack)0.0170.013
per month (gal/month)58.246.021%
Rinse Quality (
m
g/L)0.30.167%
Rinse Water Use (gal/month)42,24033,38121%
Chemical Costs ($/month)$434$343$91
Water Costs ($/month)$147$116$31
WWTS Costs ($/month)$2,170$1,715$455
Total Savings ($/month) = $577
0
1
2
3
4
5
01020304050
Drain Time (seconds)
Dragout (mL)
Barrel 1, Part 1
Barrel 1, Part 2
Barrel 2, Part 1
Barrel 2, Part 2
Wastewater
0.23 lbs Cd/day
Cadmium Bath
14,000 ppm Cd
Dragout
0.25 gph
Rinse
29 ppm Cd
Before
Rinsewater
2 gpm
Wastewater
0.07 lbs Cd/day
Cadmium Bath
14,000 ppm Cd
Dragout
0.2 gph
Dragout Tank
5,386 ppm Cd
After
Rinsewater
0.6 gpm
Rinse
29 ppm Cd
Wastewater
2.2 lbs chrome/day
Chromium Bath
130,000 ppm Cr
6+
Dragout
0.25 gph
Rinse
270 ppm Cr
6+
Before
Rinsewater
2 gpm
Wastewater
1.1 lbs chrome/day
Chromium Bath
130,000 ppm Cr
6+
Dragout
0.13 gph
Rinse
270 ppm Cr
6+
After
Rinsewater
1 gpm
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
Day 11
Day 12
Day 13
Day 14
Day 15
Date
Conductivity (
S)
Initial Set Point
Zincate Rinse
415 ppm Zn
Zn
Dragin
Electroless
Nickel Bath
6.1 ppm Zn
increase per day
Before
To EN
Rinse
Zincate
Dragout
0.5 gph
Zincate
Rinse
666 ppm Zn
Zn
Dragin
Electroless
Nickel Bath
0.02 ppm Zn
increase per day
After
To EN
Rinse
Zincate
Dragout
0.4 gph
Zincate
Rinse
2.22 ppm Zn
Zn
Dragin
Total water
use reduction:
36,960 gal/yr
0
50
100
150
200
250
300
350
Garden hose spray gun Air-atomized spray gun
Water use (gal/day)
AIR-ATOMIZING SPRAY RINSING
RESULTS
Annual
Annual
Reduction
Savings
Spray Rinse Water Use
36,960 gal.
$464
Wastewater Generation
36,960 gal.
$715*
Total Savings = $1,179/year
Total Cost = $636
Payback Period < 7 months
*Annual savings for wastewater generation is based on estimated
treatment chemical use reduction.
Slope = 1.85 uS/cm/rack
Slope =0.73 uS/cm/rack
0
5
10
15
20
25
30
35
0
5
10
15
20
Number of Racks Processed
Conductivity Increase (uS/cm)
Without Fog Spray
With Fog Spray
FOG SPRAY RINSING RESULTS
Annual
Annual
Reduction
Savings
Black Dye Use
43.2 lb
$2,419
Wastewater Generation
14,856 gal.
$1,247*
Total Savings = $3,666
Total Cost = $355
Payback Period < 2 months
*
Annual savings for wastewater generation includes $186 in
process water purchases and $1,061 in wastewater treatment O&M.