CHAPTER 25AUTOMOTIVE INDUSTRY

The automotive and machinery industries segment, classified by SIC codes 3400to 3799, is composed of a wide variety of manufacturing operations, including (a)automotive (self-propelled) vehicles: farm implements, autos and trucks, con-struction equipment, and aircraft and aerospace; (b) machinery: appliances, elec-trical machinery, and fabricated metal products.

There are four basic operations in the manufacture of most of these products:casting (foundry operation, die casting, or investment casting), machining, stamp-ing and fabricating, and final assembly. Although water consumption is relativelymodest in each of these operations, water quality is important and aqueous wastesare quite concentrated.

Some plants may perform just one of the above operations, while others carryout the entire process from casting through assembly at a single integrated plant.Figure 25.1 shows the flow of material for the total operation of an automotiveplant.

FOUNDRY OPERA TIONS

In the foundry, parts such as crankshafts, engine blocks, and transmissions arecast. In a typical iron foundry, pig iron is purchased from a steel mill and meltedin a furnace called a cupola, similar in design to a blast furnace. The iron is mixedin the furnace with a charge of coke and a flux or slag-forming material whichmay be limestone or fluorspar. Air is blown into the furnace at the tuyeres, as inthe blast furnace, and the combustion of the coke melts the charge, with molteniron draining to the bottom and slag floating to the top.

The gases leaving the cupola are combustion products, basically CO2 with per-haps a small amount of CO, plus a small amount of SO2, if the coke was madefrom sulfur-bearing coal. When the charge is dumped into the burden, there issome breakup of the relatively weaker coke lumps, and there is an initial surge ofcoke fines into the exit combustion gases. There usually is iron oxide also brokenloose from the bars of pig iron, so the discharge from the cupola is high in sus-pended solids.

To avoid creating an air pollution problem, the foundry may install a baghousefor dry collection of the dust, or a wet scrubber. If the latter is installed, thisbecomes the principal use of the water in the foundry operation. A typical foundryoperation is shown in Figure 25.2.

Because the products of combustion are acidic, the pH of the scrubber wateris generally quite low. Figure 25.3 shows a pH chart taken from a recorder sam-

FIG. 25.1 Basic automotive manufacturing.

pling scrubber water. The effect of opening and closing the charging door is todilute the stack gases, which is apparent on the strip chart.

A second use of water in the foundry is for cooling the cupola shell. This isusually done by direct spraying of the steel shell with water through a circumfer-ential pipe at the top of the cupola. This water may be collected at the bottom ofthe cupola, pumped over a cooling tower and returned to the top of the cupola.Most foundries adjust pH and add a corrosion inhibitor to protect the cupolashell.

A third use for water is in the granulation of slag tapped from the cupola. Themolten slag collects in the granulation tank, and the slag grains are removed byflights up a ramp and discarded into a totebox.

FOUNDRY

BODYASSEMBLY

VEHICLEASSEMBLY

MISCELLANEOUSPARTS

ENGINE

GRINDING

COILSTEEL

STAMPING

CUSTOMERS

FIG. 25.2 Water circuit in a gray iron foundry with wet scrubbers.

October 15,1968 January 14,1969Drag tank influent Ventur i /scrubber eff luent

FIG. 25.3 Strip charts showing pH variations in Venturi scrubbereffluent.

Wetcop

Quenching

spray

Hotgases

Cooledgas

Venturiscrubber

Stack

Slurry from Venturi scrubber

Slurry from gas quenchingSlagquenchwater

SolidsSlag tap

Slag

Wastes f rom

Clar i f ier - th ickener

molding shop"

Over f low

Cupola

Coolingwater

Ducti le iron production

Ductilerun

Most foundries encounter dust problems in the preparation of sand molds andthe breakup of the sand from the finished casting, where the material is crushedfor return to the molding room. A variety of chemicals may be mixed with thesand to produce the green mold, which must be cured before molten metal ispoured into it. Phenolic compounds are sometimes used in preparing the mold,so phenol may be present in the foundry wastewater both from this source andalso from the coke charged to the cupola. Oils may also be used in the preparationof the mold, and these volatilize during the baking of the mold and must be col-lected by a wet scrubber. Depending on the operations, there may be individualwet scrubbers at the cupola, the sand mold, and the shakeout room, or wastewaterfrom these areas may be combined prior to treatment.

Table 25.1 shows the analysis of a foundry wastewater related to the installa-tion illustrated in Figure 25.2. The oil content was quite high, but there was noevidence of free oil in the sample. This is a common occurrence where the bulkof suspended solids consists of carbon and iron oxide, as in foundry operations.

TABLE 25.1 Analysis of a TypicalFoundry Wastewater

Constituent

Total dissolved solidsSuspended solidsExtractables (oil and grease)Phenols*PH

mg/L

7701900290

1.57.6

* Present in the coke and also in core binders.

After the treatment of this particular wastewater, the oil content was reduced toless than 50 mg/L, suspended solids to about 56 mg/L, and phenol to 0.5 mg/L.The collected solids were vacuum filtered for disposal, and the oil content of thedry cake was about 15%.

There is often some fluoride present in the wastewater, which may be intro-duced by volatilization into the cupola stack gas or may be dissolved from theslag in the granulation tank. Since most foundries discharge into a city sewerbefore the water eventually reaches a watercourse, the amount of fluoride is notusually so high as to require special treatment.

There is evaporation of the scrubber water, leading to concentration, so thatchemical treatment is usually required for control of scale and corrosion in therecirculating system, and special alloys are often required for the circuits of a mul-tiple-circuit washer where the pH may become very low.

MACHINING

Rough cast parts are sent to parts and accessories plants to be machined. Figure25.4 shows the typical operations in a plant that machines parts for and assemblescar engines. Major operations include machining, cleaning, engine testing (hydro-test), and waste treatment.

FIG. 25.4 Typical operations in an engine plant.

Rather than a single assembly line for the machining operation, a series ofsmall lines is set up for each part and department. Each department performs itsown particular machining operations on the subassemblies, and each of these mayrequire a specific type of machine coolant, varying from a water-base material toa heavy sulfur oil. These coolants provide lubricity and cooling to the metal andtool used to shape it. Many of these oils contain emulsifiers that readily createO/W emulsions when mixed with water.

Soluble oil coolants are usually maintained at 5 to 15% oil concentration andstored in central sumps. The oil is recirculated through screens or filters to themachine tool and back to the sump. At the machine the soluble oil absorbs heatand picks up metal fines and hydraulic oil from leaks. Plants will normally dumpthe entire coolant system periodically because of bacterial buildup or because theemulsion is no longer stable. It is good practice to add biocide to control bacterialactivity, but even this cannot extend coolant life indefinitely.

A recent development has been the introduction of synthetic and semisyn-thetic coolants. The synthetic coolants contain no oil, while the semisyntheticscontain some oil but less than soluble oil coolants. These have some advantagesover soluble oils on the machine; however, they are still in the developmentalstage.

5. READY FORFINALASSEMBLYINCAR

3. PAINTED(if appropriate)

2. CLEANED

1. MACHINED 4. ASSEMBLED

City water or clarified plant water is usually used to make up the coolants. Ifhigh hardness levels are found in the makeup water, soft water is sometimesadvantageous because calcium ions tend to destabilize the emulsions, especiallyif the coolant concentrates. Removing the calcium and magnesium extends thestability of the soluble oils.

Parts Cleaning

The other major operation in the machinery plant is cleaning. The parts must becleaned before and after machining to remove dirt, rust preventive, and coolant.Chemical cleaners are used, usually alkaline and detergent types. Anionic phos-phate cleaners had been used extensively in the past, but have been greatlyreduced. Nonionic surfactants have become quite popular. The cleaner usage issubstantial since the cleaners are continually depleted and fresh chemicals areneeded to maintain the strength necessary for effective performance.

In the machine shop, blowdown from the parts cleaners comprises roughly80% of the flow to the waste treatment plant. Because a primary function of thecleaner is to remove coolant, blowdown usually contains 500 to 4000 mg/L oil.These wastes are emulsions stabilized by the surfactants in the coolant and in thecleaners. Other flows to the waste plant include soluble oil dumps, other cleanerssuch as floor cleaners, cooling water from a variety of sources (such as air condi-tioning systems), boiler blowdown, hydraulic oil leaks and spills, and storm water.

Occasionally, changing from soluble oil to a synthetic coolant has caused prob-lems in the waste treatment plant when acid and alum were being used for emul-sion breaking. Organic emulsion breakers have proved more effective in remov-ing oil from the effluent under a wide variety of coolant selections. However,reduction of soluble BOD by alum or organic emulsion breakers is usually verylimited. BOD loadings to the waste plant may, in fact, increase since the synthet-ics usually have a higher BOD than soluble oils.

Another factor that can have an impact on the quality of the waste treatmentplant effluent is cleaner usage. Excessive cleaner usage, especially of certain strongnonionic cleaners, can increase dosages in the waste treatment plant or even makethe waste virtually untreatable. Volume and type of cleaner should be balancedagainst the impact on both the cost and quality of the waste treatment plantoperation.

TABLE 25.2 Raw Waste from MachiningOperations

Constituent

Hexane extractionP alkalinity (as CaCO3)Total alkalinity (as

CaCO3)Suspended solidsFe (total)TDSPHCa hardness (as CaCO3)Total hardness (as CaCO3)Total PO4

mg/L

4000424

708300

41500

10.420263.0

Table 25.2 shows a typical analysis of the untreated effluent from a machiningplant. Basically the effluent is an oil-in-water emulsion. This analysis does notinclude free or floating oils.

Machining plants use cooling water for air conditioning, powerhouse dieselgenerators and compressors, hydraulic oil coolers, and furnace cooling if the plantis involved in heat treatments, such as annealing.

Each plant, depending on what it manufactures, may have its own unique usesfor cooling water. For example, engine plants typically hydrotest the assembledengine on a dynamometer before shipment. A typical test system is shown in Fig-ure 25.5. On the tube side or closed side, the heat exchanger takes the place of aradiator. Soluble oil-type products are used on the closed side if the engine isgoing to be drained before shipment. These products lay down a film that pre-vents flash corrosion. If the engine is not going to be drained, either soluble oil orconventional corrosion inhibitors can be used, depending on the manufacturer'srestrictions.

A typical boiler plant generates an average of 2 million Ib/day of 150 lb/in2

steam, primarily for winter heat, but some steam is also used to heat variouscleaner baths, so there is a light boiler load in the summer. If the plant has a

(COMPUTEROPENSSOLENOID FORSETTiME)

FIG. 25.5 Cooling water circuit for hydrotesting finished engines.

COMPUTER

CHEMICALDRUM

CHEMICALPUMP

PRESSUREGAUGE

SOLENOID

ENGINE

(CLOSED SIDE)

HEATEXCHANGER

(OPENSIDE)DYNAMOMETER

COOLINGTOWER

RECIRCULATINGPUMP

FIG. 25.6 A large steam-operated forging hammer.The dies and sow block have been removed for rou-tine maintenance. (Courtesy of Forging IndustryAssociation.)

FIG. 25.7 The boiler house in an automotive plant is simple and reliable.

Continuousblowdown torecovery heatexchanger

Feedwater

Deaerator

Rawwater

Zeolites

Dea lka l i zersRece iver

Condensate

Feedpump

150 psi steam

forging operation, steam may also be used to drive the hammers (Figure 25.6).Zeolites seem to be the most common method of softening, with average feed-water hardness being 1 to 2 mg/L. Figure 25.7 is a diagram of a typical boilerplant.

Water-Washed Paint Spray Booths

Some machinery plants (such as engine plants) have small spray booths whereprimer is sprayed on parts. These small booths experience the same maintenanceproblems as larger ones, such as those used to paint car bodies, and they requirechemical treatment. They are not as important to production, so they are fre-quently poorly maintained.

Since spray booths are so widely used throughout the automotive andmachinery industries, a description is given here to illustrate the type of watertechnology required for successful operation. Goals of the water treatment pro-gram are to (1) keep the water circuit free of deposits, (2) make the paint over-

EXHAUSTFAN

WATER CURTAIN

ELIMINATOR

HEADERWITH SPRAYNOZZLES

DIRECTION OFPAINT SPRAY

WETWALL-

PAN

FIG. 25.8 Small parts paint spray booth.

FIG. 25.9 Automotive paint spray booth.

Fig. 25.10 Cross section of automobile paint spray booth.

EXHAUSTSTACK

EXHAUST FAN

AIR FILTERS

GRATING BACK SECTIONPANEL

WATER NOZZLE -SPRAY FORMSWATER CURTAIN

ELIMINATORS

BACK SECTIONPAN

ASSEMBLY LINECONVEYOR

spray collected in the water nonsticky and readily removable from the water, (3)minimize backsection deposits to prevent obstructing flow of paint-laden air fromthe booth, (4) minimize contaminants in the air discharged to the outside so itwill not create an air pollution problem, and (5) minimize booth maintenance.

Figure 25.8 illustrates a typical paint spray unit for small parts, such as wouldbe found in the machinery plants. The conveyor carrying the parts to be paintedpasses in front of the wet well, and the operator sprays paint on the parts as theypass by, with the excess or overspray being collected on the film of water flowingdown the wet wall. The water must be chemically conditioned so that the pigmentand the excess vehicle and solvent are killed and do not form a sticky mass thatwould be difficult to remove from the pan. Water is continually withdrawn andrecirculated to the spray header, which provides scrubbing of the discharge of ven-tilating air before water drains back down the wet wall.

The large paint spray booths used in the automobile assembly shops are illus-trated in Figures 25.9 and 25.10. Operators work inside these booths, applyingpaint to the car body. The floor of these units is grating supported above a waterbasin, and falling paint deposits on the water while other paint particles are car-ried by the air flow into the water curtain either on the wet walls or into the wallcavity, or back section, where additional sprays scrub the flow of air.

Detackifying Paint

Properly treated water will collect the pigment and organic components of thepaint and condition these so that they are not tacky, producing a sludge whichcan be readily handled without sticking to the scrapers or flights used for itsremoval. The material which carries up into the back section is scrubbed out andkilled by properly designed and treated water wash so that deposits do not formin this relatively constricted wall cavity. If the scrubber is not performing prop-erly, particles penetrate the water curtain, build deposits in the back sections, andgo out the stack as particulate emissions. In addition to the air pollution problem,extensive maintenance is required to remove the deposits in the back sections, onthe eliminators, on the fan blades, and in the basin below the grating to keep thebooth operating so that it provides safety to the operator and a clean discharge tothe outside air.

Paint spray booths are in some respects like an air washer, in that the spraywater may evaporate and cause concentration of dissolved solids, or water maybe condensed from the air and there may be a continual dilution of the spraywater. This means that a check on total dissolved solids, pH, and alkalinity isrequired periodically to keep the system under good control.

Recirculation volumes on washers of this type are high—about 10,000 gal/minfor a typical body spray booth and 500 to 1000 gal/min for a parts spray booth.The water retention time in the system is relatively low, perhaps only 2 to 3 min.The basin is usually dumped at the end of the shift. The actual water makeuprequirements are difficult to estimate because they depend on the evaporation rateand the frequency of dumping, which are unique for each installation.

STAMPING

In the stamping operation, the first step is to loosen mill scale from the metalsurface in preparation for stamping by passing the strip steel through a flex roller

(Figure 25.11). This flex roller bends and flexes the steel through a series of rollers.Wash oil is brushed on during the flexing operation to remove the mill scale anddirt.

The flexed steel is cut to size and then stamped to the desired shape by largehydraulic presses. Drawing oil is sprayed on the dies to aid in stamping.

The stamped part is further cut and trimmed to the precise size; and the draw-ing oil, cutting oil, and dirt are removed in a parts washer, creating an oily waste-water. The part may then be welded or primed depending on the manufacturingrequirements. The assembled part is then ready for shipment to the assemblyplant. Finished products from stamping and fabrication plants include doors,floor pans, trunks, hoods, and fenders.

The flows from stamping and fabrication are usually quite low (50,000 gal/day)and consist of oily wastes from the parts washers, cooling water blowdown, andblowdown from the spray booths. The wastewater contains 100 to 500 mg/L oiland can be effectively treated with O/W emulsion breakers. Occasionally, washoil, hydraulic oil, and drawing oil are dumped to the waste plant, but most plantstry to segregate these relatively clean oils from the wastewater for recovery or sale.

CUT INTO SHEETS

STAMPING

FLEX ROLLER

STEELCOILFROMSTEEL MILL

TRIMMINGSTAMPED PART

WELDING

CLEANING

ZINC-RICHPRIMING

TO BODY ASSEMBLY PLANT

FIG. 25.11 Fabricating and stamping.

FIG. 25.12 Heavy metals precipitation in a metal finishing shop using sulfide pre-cipitation. Freshly prepared iron sulfide slurry is normally fed to the neutralizedwaste at the precipitator inlet, but may be fed ahead of the filter where the natureof the waste better suits this alternative.

—> I Row or soft water-i ^ 1 ->- DI water

I 1 I 1 I 1 I 1 I 1 I 1 I 1 i 1I V T l Y l Y Y I Y l Y T I Y I Y l Y Y

Alkali Rinse Elect. Rinse Acid Rinse Copper Copper Rinse* cleaner (one or cleaner (one or pickle (one or f l a s h plates 2-4

more) more) more) cnt r f lo

^ V V XI ' ' 1I I

I l f tLoad Nickelwork plate

j~« ^ni iL__, ,__J

> i— Tap water—«- -*—i •— DI water 1 1 ]

Ii 1 I i i . iHot Rack Unload Hot Rinse Chrome Rinse Acid Rinse

rinse str ip work rinse 2-4 plate (oneor 2-4 -t—(dry) (dry) cntrf lo more) cntr f lo

A i A~~̂ i /* i i A i i A i * i i A i /K nl__J I 1 L - J J I I J I 1 1 _ _ J | L _ J L _ _ J J

FIG. 25.13 Flow sheet of a chrome-plating line, including cleaning step and three stagesof metal deposition.

Plating Wastes

Where plating of parts is a major operation, waste treatment plants are designedto remove heavy metals. Traditional treatments of reduction and pH adjustmentto remove the metal as its hydroxide are commonly used. A typical heavy metalremoval plant is shown in Figure 25.12. Destruction of cyanide may also berequired.

Equa l i za t i on andneu t ra l i za t i on tank

F i l t r a t e

Precipi tatorSludge cake

Dewater ing

F i l t ra te Fi l ter Finale f f l uen t

Recovery off i l ter backwash( A l t e r n a t e )

C l e a r w e l l -

PolymerIronsulfideAc id

Alka l i

Waste

Economics may justify heavy metal recovery, most frequently by an ionexchange operation. Nickel is easily reclaimed from rinse tanks following nickelplating on H-form cation resin, with the Ni-rich regenerant returned to the platingtank. Chromate is also recoverable, but not in a form useful in the platingoperation.

Plating is as much an art as a science. Parts to be plated require careful cleaningand rinsing, often with soft water to avoid spotting. The plating baths are preciselycontrolled and may require demineralized water makeup. A typical plating line isshown in Figure 25.13.

SOLDER& GRIND

BONDERIZE DRYER

BODY ASSEMBLY WELDING

PRIMING

OR ELPOOVEN

LEAKTEST

WINDOW&TRIM OVEN

COLORBOOTH

VEHICLE ASSEMBLYPOWER & RUNNING ASSEMBLY

ENGINE, TRANSMISSION, RADIATOR, CHASSIS,AXLES, WHEELS & TIRES, STEERING, SUSPENSION

WIRING & MISCELLANEOUSFRONT END ASSEMBLY

FRONT FENDERS, HOOD, GRILLE, BUMPERSMATING & FINAL ASSEMBLY

FINISHEDWASH& W A X

FINALTOUCHES

AUTOMOBILE

FIG. 25.14 Process flow in an automobile assembly plant.

Painting is increasingly important in the metal fabrication plants as the effortsto stop body corrosion increase. Zinc-rich primers are sprayed on the interiors ofdoors, fenders, and other areas that are enclosed after assembly to improve cor-rosion protection. This operation is carried out in the same type of spray boothas described earlier.

Utilities, such as steam and cooling water, are much the same in stamping andfabrication as described for the machining operation.

ASSEMBLYPLANTS

Figure 25.14 shows a typical flow diagram for an assembly plant. These plantsreceive all of the parts and subassemblies produced in supplier plants and assem-ble them into a finished car. Major operations include welding, bonderizing,painting, and assembly.

In the assembly plant, the sheet metal is welded to the frame and floor pan toconstruct the shell of the car. During the welding operation, the welder tips arecooled by recirculating water. The most common problem in this closed coolingsystem is fouling, plugging the tips with corrosion products. If the water flow isreduced by plugging, the tips may melt, causing a shutdown of the assembly line.Filtration and chemical treatment with soluble oil products and conventional cor-rosion inhibitors minimize this corrosion and plugging.

In the bonderizing step, a metal phosphate layer, such as zinc phosphate, isapplied to the metal surfaces to provide corrosion protection and a surface for thepaint finish. Figure 25.15 shows a typical phosphatizing operation consisting ofcleaning, rinsing, phosphating, rinsing, and sealing with chromic acid. After bon-derizing, many plants use a process to electrostatically deposit a primer coat ofpaint on the metal surface by dipping the electrically charged metal into a vat of

FIG. 25.15 Phosphating and electrocoating lines.

SIX-STAGESPRAY WASHER

CHEMICALMAKE UPTANK

RINSE

CLEANING

CONTROL PANEL

Dl RINSE

SEALER

RINSE

ZINCPHOSPHATE

GAS-FIREDBAKE OVEN

ELECTROCOATtNGTANK

TWO-STAGEPERMEATE

RINSE

water-base paint. The oppositely charged paint particles are attracted evenly tothe metal surface (see Figure 25.16). Makeup to this system is demineralized sothat the bath conductivity can be controlled.

In this process, the bath tends to heat up. The paint is cooled below 9O0F (320C)through a heat exchanger by either a chiller or open recirculating cooling towersystem. After the electrostatic dip, the painted car is baked in an oven to set thefinish. The exhaust gases from the oven pass through heat exchangers to recoverheat by warming the oven makeup air. These exchangers foul with paint residueand require frequent cleaning.

Periodically, concentrated rinse water from electrostatic coating is dumped tothe waste plant. These dumps can upset the waste plant by introducing waste thatis difficult to treat. It the pH of the paint is lowered to less than 4.0, gumballsform and plug the lines and pumps.

Most vehicle assembly plants have the type of wet spray booths described ear-lier. Their utility services are comparable to those found in the machining plants.

,CONVEYOR

CONNECTIOND-1 WATERMAKE UP

DIP TANK

D.C. POWERSOURCE

PAINTMIXINGTANKFILTER

HEAT EXCHANGER

COOLINGWATER

PUMPS

FIG. 25.16 Electrocoating process for automobile bodies.

There are two specific miscellaneous water uses in the assembly plant: (1) Theassembled car is passed through a spray to test for leaks. Fluorescent dye is putin the water so a black light will clearly reveal leaks. Wetting agents are also addedto make the test more severe and to prevent water spots. (2) The final process isa typical car wash operation. Various soaps are added to help clean the car.

Wastes from assembly plants are usually quite dilute. Typical contaminantsare paint solids, oil, BOD, suspended solids, zinc, chrome, and phosphate. Coag-ulants and O/W emulsion breakers work well on these waters. Water comes fromspray booths, stripping tanks, phosphatizing, wet sanding, car wash, coolingwater, water leak test, and various parts washers. Typical flows range from500,000to 1,000,000 gal/day.

Table 25.3 summarizes water uses in the major automotive manufacturingsteps.

TABLE 25.3 Summary of Water Uses

Cooling

Boilers

Cleaning

Spray boothsPlating

Foundry

Cupola wallsCupola wet capSlag granulatorComfortCompressorsFurnace walls

MakeupWet scrubbers

Machining

Engine testingOil coolersComfortCompressors

MakeupWet scrubbers

MakeupRinseMakeup

Fabricatingand stamping

StampingWelderComfortCompressors

MakeupWet scrubbersMakeupRinseMakeupMakeupRinse

Assembly

WelderELPOComfortCompressors

FuelInternalMakeupRinseMakeup