Merit Partnership Pollution Prevention Project for Metal Finishers

REDUCING Dragout WITH Spray Rinses

California Manufacturing Technology Center

JANUARY 1997

The Merit Partnership is a joint venture between U.S. Envi-ronmental Protection Agency (EPA) Region 9, state and localregulatory agencies, private sector industries, and communityrepresentatives. The partnership was created to promote pol-lution prevention (P2), identify P2 technology needs, and ac-celerate P2 technology transfer within various industries insouthern California. One of these industries is metal finish-ing, which is represented in the Merit Partnership by the MetalFinishing Association of Southern California (MFASC). To-gether, MFASC, EPA Region9, and the California Manufac-turing Technology Center (CMTC) established the Merit Part-nership P2 Project for Metal Finishers. This project involvesimplementing P2 techniques and technologies at metal finish-ing facilities in southern California and documenting andsharing results. Technical support for this project is providedby Tetra Tech EM Inc. (formerly PRC EnvironmentalMangement, Inc.). The project is funded by the Environmen-tal Technology Initiative and EPA Region 9 and is implemented,in part, through CMTC by the National Institute of Stan-dards and Technology.

This fact sheet summarizes the benefits of installing spray rinseson electroplating lines, including reduced dragout and betterrinsing; the components of spray rinses; and some consider-ations for designing them. In addition, this fact sheet de-scribes a spray rinse case study conducted at a decorative nickeland chrome electroplating facility in southern California.

WHY USE SPRAY RINSES?

Using spray nozzles as part of a rinse system can significantlyreduce (1) dragout of expensive and hazardous process chemi-

cals and (2) the amount of rinse water needed. When used onparts over plating and dragout tanks, spray rinses provide amethod to recover concentrated process chemicals for reuse.By reducing dragout, spray rinses allow immersion-type rinsetanks to operate at lower flow rates or even as static rinses.Also, spray rinses use rinse water more efficiently than stag-nant and running rinses. Spray rinse applications in electro-plating lines (both hand-operated and automatic conveyer andhoist systems) include use over plating tanks, dragout tanks,and rinse tanks. The ideal spray rinse application permitsdragout reduction and reuse and improves rinse performance.

CONES, FANS, AND MISTS

Nozzles are the key components of spray rinses and are com-mercially available with a wide range of flow rates and severalspray patterns. Common suppliers of nozzles are manufactur-ers of industrial nozzles and suppliers of plumbing and irriga-tion equipment. For applications over plating and dragouttanks where minimizing flow rate is critical, nozzles with flowrates ranging from 0.04 to 1.0 gallon per minute (gpm) areused in groups to provide coverage and are operated intermit-tently to minimize water use. Nozzles with flow rates rangingfrom 1.0 to 10 gpm are typically used for applications whereminimizing flow rate is not so critical. The two types of nozzles

available are hydraulic nozzles, which spray water only, andair-atomized nozzles, which use both water and air. Availablenozzle spray patterns include full cone, hollow cone, flat fan,and fine spray like mists and fogs. Hydraulic spray rinseswith full cone, flat fan, and fine spray patterns (see Figure 1)are adequate for most applications on electroplating lines. Air-atomized nozzles can be used where compressed air is avail-

Figure 1. Cone, Fan, and Fine SpraysBenefits of Spray Rinses

F Less raw material wasted because of reduced dragoutF Less contamination of process baths by draginF Lower rinse water flow rates required in running rinsesF More efficient, higher quality rinsingInstalling well designed spray rinses can have an immedi-ate and significant effect on your bottom line.

Tetra Tech EM Inc.

WATER SUPPLY

SWITCH

ON

OFF

FILTER

SPRAYNOZZLE

CHECK VALVE

Switches: Switches (operated manually or with timers) can beused to shut off flow when spray rinses are not needed. Usingswitches ensures that the resulting rinse solution is low involume, is highly concentrated, and is therefore easier to re-turn to the plating tank.

Check Valves: In spray rinses with nozzles that operate inter-mittently or on a timer, check valves offer two distinct advan-tages: (1) they prevent water in the supply line from draininginto the tank when the switch closes, and (2) they maintainline pressure so that the spray pattern develops quickly whenthe water is turned on. These advantages are significant for

spray rinses in-stalled over plat-ing tanks andfor stagnantrinse tankswhere overflowis a possibility.

CASE STUDY: ALL AMERICAN SPRAY RINSES

The Merit Partnership sponsored a P2 project that involvedinstalling and evaluating spray rinses at the All American Manu-facturing (All American) facility in Los Angeles, California.The All American facility performs job shop and captive shopwork, including both metal stamping and forming operations,and it electroplates decorative nickel and chrome onto plumb-ing fixtures. The facility covers about 20,000 square feet, ofwhich 5,000 square feet is dedicated to metal finishing. All

able to increase the rinsing effectiveness of the spray by gener-ating a mist or fog. Other nozzle specifications important todesigning spray rinses are the angle and length of the spraypattern, which determine the number and spacing of thenozzles. Specifying a nozzle spray angle can help to achievecomplete coverage or overlapping patterns from adjacentnozzles.

DESIGN CONSIDERATIONS FOR SPRAY RINSES

Components for spray rinses include filters, switches (electri-cal or mechanical) to turn the nozzles on and off, and checkvalves (see Figure 2).

Filters: Rust and dirt particles from aging metal supply linescan prevent check valves from opening and sealing properlyand can cause nozzle spray patterns to deteriorate. Adding afilter to the water supply line is necessary to prevent cloggingof the small orifices in check valves and nozzles.

Figure 2. Components of Spray Rinses

Pick the Best Switches for the Application

Lever: Mechanically switched on and off by passing equip-ment such as hoists, conveyors, and racks; well suited toautomated lines

Pressure Contact: A plastic-coated, pressure-sensitive stripswitch that can be used on hang bars; good for racks manu-ally placed on a hang bar over plating and dragout tanks

Trigger: Hand-held spray gun with trigger; allows focusedrinsing

Foot Pedal: Installed with sprays on hand-racked lines;ideal for brief rinses over a dragout tank while operatorholds racks

Determining Net Flow Rateof Spray Rinses Over Plating Tanks

To avoid overflow of plating tanks, the net flow rate of thespray rinses should not exceed the evaporation rate of theplating solution.

Net Flow Rate < Evaporation Rate

Net Flow Rate = (No. of nozzles) (nozzle flow rate) ( % of time nozzle sprays)

Evaporation Rate: Vari-ous plating handbooksprovide graphs and tablesfor evaporation rates as afunction of temperature.However, direct measure-ment of evaporation rateby recording volume ofmake up water added orthe increase in freeboardover time is preferable.

Source: Electroplating Engineer-ing Handbook, Durney, 1984

80 100 120 140 160 180 200 220

.01

.02

.04

.06

.08

.10

.20

.40

.60

GA

L./S

Q. F

T./H

R

TEMPERATURE F

Tips for Check Valves

F Buy check valves that allow adjust-ment of nozzle actuating pressure

F Use one check valve per nozzleF Place check valve close to nozzle

and rinse water drop into the tanks and overspray is mini-mized. The spray rinses on each tank turn on separately onceper cycle: the spray rinses over the plating tanks turn on as theracks are withdrawn from the tanks, and the spray rinse overthe nickel dragout tanks (see Figure 3) turns on as the racks arelowered into the tanks.

Chrome Plating Tank Spray Rinse: Six fine spray mistingnozzles are installed above a hang bar over the chrome platingtank (see Figure 4); one nozzle is used for each rack positionon the hang bar. A compressed air vibrator is also attached tothe hang bar in order to enhance droplet formation. The nozzlesare angled about 45 degrees toward the splash guard at the rearof the tank. The nozzles are actuated by two pressure-sensitivecontact switches installed along the top of the hang bar. Eachswitch controls three nozzles and is actuated by the weight ofthe racks on the hang bar.

Operation and Maintenance: Maintenance of the spray rinsesincludes periodically removing the nozzles from the nozzlebodies and washing away any obstructions from the nozzleinteriors with water or compressed air. The filters used at AllAmerican are canister-type filters with no fil-ter elements and needto be periodically un-screwed and rinsed.Before the filters wereinstalled, many of thecheck valves becameclogged and did notopen and shut quicklyand completely. Withthe filters in place,these problems havenot recurred.

CASE STUDYCOSTS

The total cost for allthree spray rinse appli-cations was $4,890. In-

American employs about 10 workers in the electroplating de-partment for one shift per day. The plating line consists oftwo parallel nickel plating lines with an automated hoist fol-lowed by a single chrome plating line that is first hand- andthen conveyor-operated. The rinse system for each line origi-nally consisted of an immersion-type dragout tank and a seriesof stagnant and running rinse tanks. The primary objective ofthe P2 project for All American was to reduce dragout lossand enhance dragout recovery by adding several spray rinsesto the existing rinse systems. By first reducing dragout, AllAmerican can reduce water use and consider chemical recov-ery technologies that move the operation toward its goal ofzero discharge.

Three spray rinses are installed at the facility: one over a pairof nickel plating tanks, one over a pair of empty nickel dragouttanks, and one over the chrome plating tank. Nozzle materialis selected based on the corrosiveness of each installation. Anadjustable check valve is installed immediately upstream ofeach nozzle to prevent draining of water and to maintain linepressure. The net flow rate from the spray rinses over thenickel plating tanks is selected so as not to exceed the evapora-

tion rate of the tanksand to minimizeevaporator use beforedragout is returned tothe plating tanks.

Nickel Plating LineSpray Rinses: Bothspray rinses on thenickel plating linesare actuated byswitches tripped bythe up-and-downmovement of thehoist. Each tankhas eight nozzlesmounted around thelip of the tank anddirected slightlydownward so that thecombined dragout

Three Spray Rinse Applications at All American

Nickel Plating Tanks (2) Nickel Dragout Tanks (2) Chrome Plating TankNozzles/Tank 8 8 6Nozzle Spray Pattern Flat Fan (Hydraulic) Flat Fan (Air-Atomized) Misting (Hydraulic)Nozzle Material Stainless Steel Brass PlasticFlow Rate/Nozzle 0.3 gpm 0.4 gpm 0.04 gpmNet Flow Rate/Tank 0.12 gpm 0.27 gpm 0.12 gpm

(8 nozzles at 0.3 gpm for (8 nozzles at 0.4 gpm for (6 nozzles at 0.04 gpm for3seconds per minute) 5seconds per minute) 30 seconds per minute)

Figure 4. Misting Nozzles over Chrome Plating Tank

Figure 3. Spray Rinses on Nickel Dragout Tank

$528

$315

$215

$115

$-

$100

$200

$300

$400

$500

$600

Nickel Solution Chrome SolutionMonthly Dragout Costs

Sprays On

Sprays Off

All American Spray Rinse Costs

NozzlesTwo Nickel Plating Tanks $800Two Nickel Dragout Tanks 480Chrome Plating Tank 60

Check Valves 100Piping 650Pressure Reducers and Filters 600Switches 600Installation 1,600

Total $4,890

Figure 5. Sprays Reduce Nickel Dragout by 58%

Spray Rinse ResultsWithout With MonthlySprays Sprays Savings

Nickel Solution Dragout 50.0 gal/mo 20.8 gal/mo $313Chrome Solution Dragout 63.1 gal/mo 23.0 gal/mo $200Rinse Water* 380,000 gal/mo 152,600 gal/mo $185

Total Cost Savings = $8,376/yearTotal Cost = $4,890

Payback Period = 0.6 year* Estimated based on dragout reduction

0

Figure 6. Monthly Cost Savings Due to Dragout Reduction

Data from the tests demonstrate that the addition of the sprayrinses to the existing rinsing scheme at the All American facil-ity dramatically reduced the dragout from both the nickel andchrome plating lines (see Figure 6). Based on the savings asso-ciated with recovery and reuse of the nickel and chrome plat-ing solutions and the corresponding rinse water reductionpossible, the payback period for the rinses installed is 0.6 year.Although All American does not treat its wastewater beforedischarge, facilities performing on-site treatment would experi-ence additional savings of the treatment chemical, sludge dis-posal, and operating costs associated with treatment systems.Industry average costs for treatment of wastewater from elec-troplating operations are about $12 per 1,000 gallons.

For more information on spray rinses, the Merit Partner-ship, or the All American case study, please contact thefollowing individuals:

Laura Bloch (EPA Region 9) at (415) 744-2279John Siemak (CMTC) at (310) 263-3097Dan Cunningham (MFASC) at (818) 986-8393John Norton (All American) at (213) 581-6293

Assistance for this fact sheet was provided byTetra Tech EM Inc.

Conductivity ExperimentNickel Rinse Tank

0

50

100

150

200

250

0 10 20 30 40 50 60No. of Racks

Con

duct

ivity

(

S/c

m)

250

200

150

100

50

00 10 20 30 40 50 60

20.8 gallons ofdragout/month

50.0 gallons ofdragout/month

Number of Racks

Con

duct

ivity

(S/

cm)

58% Reduction

Spray Rinses OffSpray Rinses On

stallation of the spray rinses was performed by All Americanstaff, and operation and maintenance are performed as part ofthe staffs daily inspection routine.

Nozzle costs vary widely (from $2 to $70 per nozzle) depend-ing on the material used and the supplier. Generally, indus-trial spray nozzle manufacturers provide higher quality at ahigher cost and offer nozzles made of a variety of materialswith precise spray patterns and flow rates; plumbing and irri-gation equipment suppliers provide less expensive, plasticnozzles and less selection of nozzle operating parameters.

CASE STUDY RESULTS

After installation of the spray rinses and several weeks of sys-tem shakedown and fine tuning, a series of tests were per-formed under controlled plating and production conditionswith and without the three spray rinses operating. As partswere plated, the conductivity (which can be related to the con-centration of plating solution) of the rinse water was mea-sured in a stagnant rinse tank immediately following the tankswith spray rinses.

During the tests, the spray rinses over the nickel plating anddragout tanks together reduced dragout from the nickel plat-ing lines by 58percent compared to dragout from the linesoperating with no spray rinses (see Figure 5). The spray rinseover the chrome plating tank reduced dragout by 64percentcompared to the system operating with no spray rinse.