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Pretreatment system design for optimum end-use performance
SYSTEMS AND EQUIPMENT PRETREATMENT SYSTEM DESIGN FOR OPTIMUM END-USE PERFORMANCE by Tom Lincoln Cincinnati
/r~cfustrial Machinery,
Div. of Eagle Piche6
Cincinnati
A finishing system may have many possible arrangements, but only one is best suited to the user’s plant conditions and needs. Only after working closely with the user and suppliers are you able to determine the system best suited to your requirements. Finishing systems are comprised of washers, dry-off ovens, incinerators, pretreatment. electrocoating, spray booths, flowcoaters, dip tanks, cure ovens, conveyors, waste treatment, and air makeup. A complete paint finishing system consists of an integrally designed combination of equipment (or single compact machine) that conveys parts through the cleaning, pretreatment, paint application, and baking steps to deliver a finished part-ften without labor between loading and unloading. Systems can include makeup air equipment to replace exhausted air, loading and unloading devices, and other related equipment. A typical schematic is pictured in Fig. I.
DEFINING
PARAMETERS
Pretreatment can be accomplished in many different ways involving several technologies (see Table I). The optimum design for a family of parts evolves from understanding the following parameters and applying them with consistent design integrity: (1) quantity and configuration of parts: (2) material composition of parts; (3) desired material handling methods; (4) understanding soils and cleanliness desired; (5) facilities and utilities available; and (6) environmental considerations. Each of these parameters will influence the design of the system. Early involvement of competent representatives from chemical suppliers, equipment manufacturing companies, and paint companies will improve the design phase and enhance your objective. Once the parameters have been defined the design can begin.
Quantity and Configuration of Parts The production rate obviously determines the level of automation, capacity of the equipment, energy consumption, chemical usage, etc. Selection for today’s requirements may be inadequate for tomorrow’s needs and sizing the system too large can waste money. Long-term planning will help determine production rate, future designs, and available financial resources. 263
Table
1. Comparison
of Iron,
Zinc,
and
Manganese
Phosphating
Metal cnhmet\. furnitul-c, electrical and electronic enclosure\. and toys and other novcltie\.
Higher chemical ants than trorl, nlore sludge formation. higher maintenance cwt? than iron, more dtfficult to control than iron. Not used a\ a paint ha\c, higher temperature requirements. grcatw sludge formation.
264
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INDUSTRIAL
MACHINERY
P.O. Box 62027 ,Cincinnati, OH 45262 Pimne (513) 769-0700 • FAX (513) 769-0697 E.maih [email protected] Web Site: http://www.canwash.com Representative inquires welcome. Please call Tom Lincoln.
Circle 027 on reader information card Industrial Cleaning
by S. Spring
324 pages
$32.00
This book is the standard in the field of cleaning metal. A thorough understanding of the basics is provided so the finisher can deal with the problems as they arise. It is a straightforward work written in plain language and incorporates cleanliness evaluation, cleaner testing, and both general and special cleaning methods. A must for any finisher's bookshelf. Send Orders to: METAL FINISHING 660 White Plains Rd., Tarrytown, N Y 10591-5153 For faster service, call (914) 333-2578 or FAX your order to (914) 333-2570 All book ordersmttstbe prepaid.Pleaseinclude$5.00 shippingand handlingfor deliveryof each book via UPS in the U.S., $10.00 for each book shippedexpressto Canada;and $20.00 for each book shippedexpressto all other co,retries.
The proper analysis is essential. List all parts, their sizes, and annual production rate that you plan to process with the system. This will give you the yearly production requirements. Then, based on one, two, or three shifts, determine production time available. When comparing production requirements with production time available you can establish rate in feet per minute. The smallest, the largest, and the average part size must be defined in terms of dimensions. This allows equipment manufacturers to size the openings for washers (to minimize overspray), determine optimum drain length (minimize solution carryover), and size heaters, pumps, and fans. The overall weight of the part or batch of parts being conveyed must be known to calculate heat loss through the washer and ovens. Unusual shapes must be identified for early consideration. For example small, blind holes on surfaces could negate the power wash approach, whereas large, open or tlat surfaces that can drain are ideal. Small parts that can withstand tumbling can be ideal for a drum washer; baskets of parts that cannot be tumbled can be immersed and agitated. The same situation is true with paint application. Smooth, flat parts can be easily automated. while complex shapes may require additional. manual reinforcement for complete coverage.
Material Composition of Parts Knowing the base materials will allow compatibility waste treatment requirements, operating temperature, specifications.
with selected cleaners, subsequent method of handling, and process
Desired Material Handling Methods Selecting the appropriate material handling method should be done based on the principles of increasing productivity. The method selected must incorporate reliability, economy, flexibility, and ease of installation. For example an overhead monorail-type conveyor system is relatively low in cost but not very flexible, while a power-and-free system is very flexible but higher in cost.
Understanding Soils and Cleanliness Contaminants determine chemical selection and spray or immersion selection. and ancillary equipment for handling the effluent (chips, oil, or heavy metals) will impact the waste treatment stream. If the cleaning process is not defined it is important to get contaminated parts to the chemical and equipment suppliers and have the parts tested in a laboratory. While in the laboratory your suppliers can simulate conditions and test the different variables, Minimizing or avoiding contamination is the key to keeping your factory and parts clean. Know where your soils are coming from and why. This allows you to take steps to contain soils in the area where they occur. Effective and inexpensive means to check for clean parts are the “water-break-free surface test” and “white towel test.” If organic soil has been effectively removed a uniform sheeting of the rinsewater will occur as parts exit the last pretreatment stage. If the surface has beaded water standing you have not adequately removed organic soils. Inorganic soils can be checked by using a white towel after they have passed through the dry-off oven. If the towel is dirty you have not adequately removed the inorganic soils. More sophisticated is the millipore test. This test requires a vacuum pump, flask. funnel, filter papers, isopropyl alcohol. oven, and scale. This test can detect micron particle sire and weight in milligrams. 266
Facilities and Utilities Available A floor layout with height clearance is important for design considerations. Often. space constraints dictate-process times. Although it may not be the optimum process it may achieve acceptable results. Availability of electrical service, heating preference, and plant conditions (such as availability of truck dock, building door size, floor and roof construction, distance from unloading site to erection site, and whether there is a clear path) must also be considered.
Environmental Considerations Local, regional, and federal regulations are continually being added and changed. The recent Clean Air Act Amendments of 1990 established procedures for a national permit system for air pollutant emissions, as well as establishing a basis for more stringent controls on emissions from all manufacturing operations. Waste stream compliance ia forcing many manufacturing companies to invest in waste treatment plants. Understanding your local laws and knowing your process will determine your direction. If you are not familiar with either, outside help must be sought.
COMPONENT
DESIGN
Material Handling Selection of the material handling method varies directly with production volume and desired cleanliness. In general the monorail is the most economical, flexible, and reliable method of handling product, but it is not the ideal solution for all cases. If you handle product in batches/baskets a belt internal to the machine can provide an excellent and consistent means of transporting product through the washer. If your product can tolerate “bumping,” such as nuts or bolts, a drum machine is a cost-effective means of conveying high volumes with excellent results. There are also situations where combinations of belt and monorail are appropriate. Rather than having two machines you can easily assimilate dual lines into one washer. Conveyor systems are discussed in further detail in a separate section of this Guidebook. System size is a function of conveyor speed, which is actually based on part density rather than raw production rate. As an example, to determine the line speed for a given production shift divide the number of parts desired by the number of par& per rack times the rack spacing divided by the number of minutes available per shift.
Washers/Pretreatment The choice of a spray wand, three-stage, or five-stage machine is based on a number of variables: incoming soil loads, space available, results required, energy consumption, total initial cost, estimated total operating cost, production volume, size of part, etc. The initial cost of a five-stage machine (clean, rinse, phosphate, rinse, rinse) is somewhat higher than a three-stage type but operating economies and higher quality quickly offset the investment, The five-stage machine ensures longer chemical life. The high-pressure heated spray wand is an excellent choice for low-volume, hard-tohandle parts. This approach is a cost-effective technology with a great deal of flexibility and versatility. From experience and the recommendation of various chemical companies, to remove shop dirt and light machine oil a three-stage machine is adequate. The typical process would be a one-minute wash stage (heated), Dsecond rinse (ambient), and a 30.second rinse/inhibit (ambient or heated). If you have a more critical cleaning specification or phosphating requirement a five-stage 267
washer (heated),
with one-minute Dsecond rinse
Spray
versus
wash (heated), (ambient), and
30-second 30-second
rinse (ambient), one-minute rinse/inhibit (ambient) will
phosphate be required.
Immersion
In general, spray processing provides the most effective cleaning and rinsing capabilities owing to increased mechanical action, liquid impingement, and natural draining: however, for impingement of recessed or hidden surfaces of complex parts and assemblies. immersion processing is more appropriate. The addition of ultrasonics or agitation can enhance the impingement capability, but it is costly. When processing complex parts or heavily loaded baskets of parts a combination of immersion and spray stages is often required, Testing dirty parts in a laboratory will provide proper selection.
Sample
Three-Stage
The first a largest part
Washer
step in the design G/e of ?,‘b ft X
is to lay out the system (using IX in. X IX in.). The entrance
a conveyor speed of 1 fpm and profile should include a Sin.
Turnkey Finishing Systems Design • Engineering
• Fabrication
• Installation • Training • Service
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053 on reader information card
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clearance around the part. Thih will provide flexihility to process larger parts if required (see Fig. 2). A housing space of 1 ft on each side of tunnel openings allows for spray risers and piping. The cleanout section can he 2 to 2% ft: 3% ft from the floor to the bottom of the tunnel opening will provide enough apace to have the tank capacity to keep the pump-to-tank ratio around 3:l. The overall height of the machine is 7’S ft. but we need to allow another 3 ft minimum for ventilating ductwork. The machine length for a three-stage washer, allowing three minutes of drying, is shown in Fig. 3. You know that one minute in the wash stage is required and that the conveyor is traveling at 4 fpm, so you can size the wash stage at 4 ft. Similarly, rinse stages are 30 seconds: thus, they are each sized at 2 ft in length. Good design practice dictates that the approaches and exits should be two times the tunnel width: therefore, they should be 4 ft long. The drains should be three times the tunnel width, minimizing spraying and carryover contamination; therefore, they are 6 ft in length. Special consideration for drain lengths may be necessary for long parts or slow line speeds. The hot air blow-off will require three minutes of drying time, so size that at 12 ft. You also must have 1 ft between washer and hot air blow-off fan for ventilating. ENVIRONMENTAL
CONCERNS
Most washer systems require waste treatment of the effluent from the system prior to disposal to the sewer. In some cabes, where the potential discharge of cleaners and phosphates to the sewer are significant, a self-contained treatment system is required. Most municipal waste treatment authorities have a list of chemicals they can accept and in what concentx(ions. Check with the local authorities for additional information, or consultants are available to artist in your decision-making process. FIVE-STAGE A five-stage 270
monorail-type
fine
WASHERS
phoaphating
machine
is shown
in Fig. 4. Table
II
Conaldcrmg
Settling both
tank energy
and
pollutmn
problems,
Standard cust iron Mild steel
equpment
Pump Immersed heating
Mtld or stamlas Steel
N0.A5 Piping
new
procecws
mild steel
mild steel
JIIOW
luwcr
prucc\Gng
or Manganese
Phosphate
tn some
case?
1 I-gauge stainless steel or mild steel 14.gauge %Cnlers steel or 3/16 mild steel Stainless steel Stamless steel or extra heavy \tee1 Stainless steel Stainless steel or extra heavy steel Mild steel
160°F 60 Whirl-Jet IO
StURP No. 3 Phosphate
Zinc,
~empcramrc~
steel
Iron,
Standard cast tron Mild steel
Mild or stainless Steel
l/X-in.
l/&in
HCUSlllg
mild steel
l/4-m.
l/4-in.
mild steel
Room 30 V&et 15
Stqe No. 2 Rinse
for Five-Stage
145°F 60 Veekt IS
eel
Construction
Sragr No. I Wush
Monorail-Type
Destgn temperature Time cycle (wands) Type nozzle Nozzle pressure (psi) Mntennl.5 fir conwuction: Tank
Table II. Typical
mild steel
mild steel
No. 4
Standard
cast iron
Mild or stamless Steel
l/8-in.
l/4-in.
Room 30 VeeJet IO
Stale RiILX
Washer
ateel
or stainless
mild steel
mtld steel
Standtvd cast mm Mild steel
Mild StlXl
K-in.
l/4-in.
steel
145°F to assist drying 30 VeeJct IO
Stqe No. 5 Aud$ied Rinse
III. Typical
Belt-Type
Cuucldenng
Iron
1/4-m mdd rteel l/S-in. mild steel Mild or stainle9c steel Steel Iron Mtld steel
l/4& mild steel l/X-in. mild at‘1 Mild or uumle~r steel Steel Iron Mild steel
Phosphate
ROOlll 30 VceJet 15
Siuge No. 2 RUM
for Five-Stage
14SF 60 VeeJet I5
WlIdl
Srugr No. /
Construction
horh energ! rind p~,llut~n~~prohl~mr. ~wi ~~rucu~ccc allow tower processing icmprrarure\
Design temperature Time cycle (seconds) Type nozzle Nnrrle pressure (PSI) Materialsfor
Table
in wmr: caw
l/4-in. mild steel l/X-in. mild steel Mild or stainless steel Steel Iron Mild steel
160°F 60 Whlrl-Jet 10
Sfrcge No. 3 Pho.whate
Machine
ibin. mild steel l/&in. mild steel Mild or stainless steel Sled Iron Mild steel
l/4-in. mild steel l&in. mild steel Mild or stainlex steel Strel Iron Mild steel
l45’F to assist drying 30 VeeJet 10
Fig. 5. Five-stage
belt-@pe
iron phosphnting
machine
provides details for each stage. Table III provides phosphating system pictured in Fig. 5.
Fig. 6. Three-stage
drum-type
washer
with hlowwff
(,we TWle III for detuils)
similar
information
(see Table IVfor
for the five-stage
iron
details).
273
Fig. 7. Drum
washer
construction
detai1.s. DRUM-TYPE
Fig.
Fig. 6 depicts a typical three-stage 7. Table III gives further details
Table
IV. Typical
Design
temperature
Time cycle (seconds) Type nozzle Nozzle pressure (psi) Mutrriuls ,ji,r
Drum-Type
WASHERS
drum-type on drum-type
Construction
washer. Concentration systems.
for Three-Stage
Washer
145°F
Room
60
30
160°F to assist drying 10
VeeJet IO
VeeJet IO
Veelet I0
details
with
are shown
Blow-Off
~onmucrion.~ Tank Housing
IWin. l/Z-in.
NOZZICS
Mild or stainleah steel Steel Iron Mild steel
Piping Pump Immersed heating equipment Air heating equipment
mild steel mild steel
IWin. l&in.
mild steel mild steel
Mild or rtainless steel Steel IroIl Mdd steel
IWin. l&in.
mild steel mild steel
l/Z-in. mild qteel
Mild or stamle\s steel Steel Iron Mild steel Mild
steel
in
OVENS In former years there was a tendency to oversimplify oven problems. There was a widely held idea that an oven was ‘just a heated box” through which parts were passed to dry or bake a finish or tO evaporate and remove moisture or otherwise process by heat application. In more recent years the scientific aspects of heat engineering have come to be appreciated. True economy in operation matched by superior results can only be obtained by expert design based on sound engineering followed by quality manufacturing and conscientious installation. The ovens may be on the plant floor or elevated overhead. either inside the plant or outside, on the ground or on the roof. With the ovens elevated the factory floor may be used for manufacturing or storage. The oven panels should be tongue-and-groove, all-welded construction, fabricated of heavy-gauge sheet steel, with a minimum of through metal, which reduces the transmission of heat by conductance. To avoid “insulation sag,” which would leave an open space at the top of the wall panels, oven panels should be insulated with mineral wool batts 1/4 in. greater in thickness than the oven panels, Access doors should be fully insulated or of nonsagging construction and equipped with explosion latches. These doors should allow opening from inside or outside the oven. The relatively few ovens shown here are merely examples of the many types being built, each representing dozens and even hundreds of similar installations. Many special types are not shown because of limited use. For standard ovens, custom designs, and even economical prefabricated components it pays to consult true experts in heat engineering.
Direct
versus Indirect Heating Systems In a direct fuel-fired system the products of combustion are allowed to come into contact with the work; the combustion equipment can be located inside or outside the oven. Although gas is generally used with a direct fuel-fired system, modem processing of fuel oils, along with improved handling and firing equipment, has increased their use in this area. An indirect-fired system does not allow products of combustion to come into contact with the work. Electric and steam heating are common choices and fuel-fired equipment may be used in conjunction with a heat exchanger to separate the products of combustion from the oven atmosphere.
Fuels The brief outline that follows describes the most popular fuels being used today. You may want to investigate the possibility of using one as an alternative to back up your present system or as a supplement. Gas: This is generally considered a clean, convenient, and easy-to-use fuel. Work loads are commonly heated by the direct-fired method with no adverse effect from the products of combustion; however, because the availability and overall costs have changed it may be to your advantage to check the alternative fuels in your area. Oil: Many of the problems that once plagued the use of oil with direct-fired oven equipment have been eliminated, and indirect-fired systems are easily designed and installed when needed. In either case plan for a safe, convenient storage space. Steam: A very clean source that is simple, easy to control, and reliable for low-to-medium temperature operations, steam can be produced in a number of ways that are most economical. Electricity: This is a clean, simple, and efficient source of heat. High temperatures are easily obtained and heat recovery systems are available to economically reduce operating cost. Combination: Combination fuel systems are very popular with people who have been plagued by fuel price increases and shortages because they allow the ability to switch from one fuel to another without stopping production or adversely affecting the product. Recovery Recovery systems have recently become very important tO all users of energy. As fuel costs increase heat recovery systems become more practical. 275
Radiant: This is particularly applicable to flat parts and batches processed on the basis of part shape and size. It is a clean, high-energy source of heat where high surface temperatures are easily obtained in short periods of time. Although expensive to control it can provide shorter cure times and minimal floor space.
Features Knowledgeable plant operators want panels and the general construction to provide maximum strength and rigidity, minimum heat transfer or loss, and an attractive appearance. The panels should be filled with insulation of full thickness, formed in batts to resist sagging and settling that can leave uninsulated areas. Tongue-and-groove construction mates into a strong, neat joint. Ovens should be able to be readily disassembled and moved if necessary. A typical oven system is shown in Fig. 8. Air SYLIIS: Ovena can be provided with a variety of seals to prevent escape of heated air and fumes. The bottom entry oven, which must be elevated, has a natural lype of seal because the heated air rises into the upper, sealed portion of the oven. Exhaust-type seals. where conveyor opening\ into the oven are enclosed by a hood with an exhaust fan. are also available. In theory the most practical type of seal is the recirculating seal, which has been far from perfect in the past. Companies have invehted considerable time and money in this seal and they are now producing recirculating seals that allow adjustment to compensate for various oven temperature losses. By providing a recirculating fan with adjustable vents at least 80% of the normally escaping heat can be retained. Ovens can be designed as a high-velocity type or low-velocity type depending on the application. In most cases ovens are designed with both types in special zones to control paint popping, blistering, or in the case of a powder oven, dry powder blow-off. Low-velocity or “quiet” zones allow the coating to cure slowly, allowing solvents to evaporate before the surface film is set, which minimizes pops and blisters. Radiant and infrared ovens can fit into this category. 276
High-velocity zones allow direct impingement of the air to the work, which allows for quicker curing of the coating or evaporation of water. This air movement helps to obtain even temperatures throughout the oven as well. The air movement is induced by high-velocity nozzles designed to improve direct impingement of heated air on the work surface. Attempting to dry or cure a painted part too quickly is a notable cause of paint “skinning,” resulting in bubbles, blemishes, and powder blow-off. Rolling nir or high turnover rates: This induces an air movement that helps to obtain remarkably even temperatures. The air movement is induced by high-velocity nozzles that also prevent direct impingement of heated air on the work surface, a notable cause of “skin-drying,” resultant bubbles and blemishes, and powder blow-off. Burner size: When selecting burners for an oven concentrate on the total needs of the job at hand; then allow for a reserve capacity to handle higher work loads without expensive alterations. This provides the greatest overall economy and equipment flexibility because the burners are efficient throughout their operating ranges. Cnmhu~tiori chamber;\: Ovens are usually designed with the combustion chamber as an integral part of the unit, streamlining the appearance and eliminating the need for exterior ductwork. This compact arrangement also reduces power requirements connected with excessive ductwork, saving floor space as well. Di~pposahle filters: Intake air filters can minimize the intake of dust, which can cause finish tlaws. The filters should be arranged for quick and easy changing without use of tools. The best disposable filters to use are frameless, eliminating the usual cardboard frame as a possible fire hazard. Simple erection: Ovens should be constructed of prefabricated panels for easy erection. All components-panels, structurals, ductwork. wiring, and piping-should be keyed to assembly drawings and manufactured to fit easily, quickly, and precisely in the field. The purchaser can in many cases erect the oven with existing plant personnel under supervision for significant savings. For more complex ovens suppliers provide a complete service ranging from basic erection to complete turn-key jobs. Dry-Off Ovens The dry-off oven is usually a continuation of the washer. Drying metal pans with no “puddling” of water requires three to five minutes. depending on temperature. At 4 fpm you will need 12 to 20 ft of dry-off oven, excluding air seals. The next unit requiring the largest amount of floor space is the cure oven. Assume for design purposes that the paint you are using requires a 20.minute cure at 350°F. Again. conveyor speed is 4 fpm so you have to be in the oven at temperature for 80 ft of conveyor travel. The oven can be fabricated in practically any configuration, depending on the floor space available. It could be a single-pass oven (80 ft long) or a two-pass oven (40 ft long) or a four-pass oven (20 ft long). This you can determine from the floor space available. If floor space is a premium and the building height will allow it the oven can be hung from cross-beams supported from the floor or mounted on the roof. Available space usually dictates the position of the oven. The tunnel opening of the oven is normally the same dimensions as the washer except that usually 18 in. to 2 ft from the bottom of the tunnel opening to the floor is ample for ductwork. To sketch the oven layout you know that the maximum part width is 1 r/2 ft and that they are spaced on 24.in. centers. This indicates that a 3.ft.diameter wheel turn will permit clearance of parts on a turn, so the proposed oven is outlined as shown in Fig. 9. PAINTING
SYSTEMS
The major types of paint systems fall into five categories: conventional solvent water-reducible systems, high-solids systems, powder systems, and electrodeposition
systems, systems. 277
Fig.
9. Layout
for
curdbakr
own
sample
desip
Defining your criteria relative to operational characteristics, coating properties, initial capital expenditure, and operational costs will determine the paint system. A powder system and electrodeposition system have been included to demonstrate layout. The following arc component design considerations for an electrodeposition system. ELECTROCOAT
(ELECTRODEPOSITION)
PAINTING
Coating Thickness Control The main factors controlling film thickness are the applied voltage and the fihn resistance. Increasing the coating voltage or lowering the specific film resistance causes an increase in film thickness, You simply dial the desired coating thickness. The electrocoating process will continue until the organic film deposited provides an electrical insulating resistance, which prevents further current flow. When the coated parts are removed from the bath they are rinsed in permeate and deionized water to remove nondeposited paint particles. Tank
Design Electrocoat tanks are designed for an immersion time of 1 i/z to 2 minutes. It is possible to deposit approximately 1.0 mil organic coating in the first IS seconds: however, for heavier film deposits a longer time is required. 278
Tank equipment includes dual pumps with each pump prevent the setting of paint solids. Plate-and-frame heat exchangers are used with chiller temperature.
able to maintain units to maintain
the bath and proper
tank
Tank
Design is Vital In the design of the electrocoat tanks some of the most important items are circulation rate, circulation flow, and density of the paint. With the paint solids normally at X to 10% density a flow rate and pattern is determined to prevent settling. The flow rate in the average tank is accomplished by the use of headers with eductors. The flow pattern in the bottom of the tank is opposite that of the conveyor movement and with the conveyor at the top of the tank. The exit end of the tank is equipped with an overtlow weir tank designed to prevent foaming without dropping or aerating the paint. The recirculating pump suctions are also connected to this tank.
Filter
Systems Conventional filter systems are provided with approximately SO micron filter media to remove foreign debris that may enter the bath. An ultrafiltration system will be used to remove soluble salt and water carried into the bath from the cleaning process by the parts being coated. Ultrafiltration may also be used to recover paint solids from the postrinse so they may be returned to the bath. A virtually closed system exists when ultrafiltration is used to provide rinsewater in the place of deionized water. This arrangement will aid considerably in the prevention of water pollution.
SUMMARY Getting value from your finishing system involves a comprehensive review of your requirements and, as necessary, applying some or all of the many technologies available into your system design. Normally, one person or one company does not possess all resources to do this task. A good approach is to consult reputable suppliers and follow their recommendations. The best solution to your system design is one in which every selected supplier works as part of your team toward the common goal of a successful system installation, start-up, and operation.
Anodic
Coating Defects - Their Causes and Cures by A. W Brace 168 pages $150.00
This book provides guidelines and examples for troubleshooting defects in anodic coatings. Chapter one outlines an approach to identifying a defect. Here one finds a photo and description of each defect (for instance, fine pitting) with a remedy for curing it; a simple and straightforward approach to problem-solving. Send Orders to: METAL FINISHING, 660 White Plains Rd., Tarrytown, NY 10591-5153 For faster service, call (914) 333-2578 or FAX your order to (914) 333-2570 All book orders musr be prepaid. Please include $5.00 shipping and handling for delivery of each book via UPS in rhe U.S., 510.00 for each book shipped express COCanada; and $20.00 for each book shipped express 10 all orher coumies.
279
/r~cfustrial Machinery,
Div. of Eagle Piche6
Cincinnati
A finishing system may have many possible arrangements, but only one is best suited to the user’s plant conditions and needs. Only after working closely with the user and suppliers are you able to determine the system best suited to your requirements. Finishing systems are comprised of washers, dry-off ovens, incinerators, pretreatment. electrocoating, spray booths, flowcoaters, dip tanks, cure ovens, conveyors, waste treatment, and air makeup. A complete paint finishing system consists of an integrally designed combination of equipment (or single compact machine) that conveys parts through the cleaning, pretreatment, paint application, and baking steps to deliver a finished part-ften without labor between loading and unloading. Systems can include makeup air equipment to replace exhausted air, loading and unloading devices, and other related equipment. A typical schematic is pictured in Fig. I.
DEFINING
PARAMETERS
Pretreatment can be accomplished in many different ways involving several technologies (see Table I). The optimum design for a family of parts evolves from understanding the following parameters and applying them with consistent design integrity: (1) quantity and configuration of parts: (2) material composition of parts; (3) desired material handling methods; (4) understanding soils and cleanliness desired; (5) facilities and utilities available; and (6) environmental considerations. Each of these parameters will influence the design of the system. Early involvement of competent representatives from chemical suppliers, equipment manufacturing companies, and paint companies will improve the design phase and enhance your objective. Once the parameters have been defined the design can begin.
Quantity and Configuration of Parts The production rate obviously determines the level of automation, capacity of the equipment, energy consumption, chemical usage, etc. Selection for today’s requirements may be inadequate for tomorrow’s needs and sizing the system too large can waste money. Long-term planning will help determine production rate, future designs, and available financial resources. 263
Table
1. Comparison
of Iron,
Zinc,
and
Manganese
Phosphating
Metal cnhmet\. furnitul-c, electrical and electronic enclosure\. and toys and other novcltie\.
Higher chemical ants than trorl, nlore sludge formation. higher maintenance cwt? than iron, more dtfficult to control than iron. Not used a\ a paint ha\c, higher temperature requirements. grcatw sludge formation.
264
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INDUSTRIAL
MACHINERY
P.O. Box 62027 ,Cincinnati, OH 45262 Pimne (513) 769-0700 • FAX (513) 769-0697 E.maih [email protected] Web Site: http://www.canwash.com Representative inquires welcome. Please call Tom Lincoln.
Circle 027 on reader information card Industrial Cleaning
by S. Spring
324 pages
$32.00
This book is the standard in the field of cleaning metal. A thorough understanding of the basics is provided so the finisher can deal with the problems as they arise. It is a straightforward work written in plain language and incorporates cleanliness evaluation, cleaner testing, and both general and special cleaning methods. A must for any finisher's bookshelf. Send Orders to: METAL FINISHING 660 White Plains Rd., Tarrytown, N Y 10591-5153 For faster service, call (914) 333-2578 or FAX your order to (914) 333-2570 All book ordersmttstbe prepaid.Pleaseinclude$5.00 shippingand handlingfor deliveryof each book via UPS in the U.S., $10.00 for each book shippedexpressto Canada;and $20.00 for each book shippedexpressto all other co,retries.
The proper analysis is essential. List all parts, their sizes, and annual production rate that you plan to process with the system. This will give you the yearly production requirements. Then, based on one, two, or three shifts, determine production time available. When comparing production requirements with production time available you can establish rate in feet per minute. The smallest, the largest, and the average part size must be defined in terms of dimensions. This allows equipment manufacturers to size the openings for washers (to minimize overspray), determine optimum drain length (minimize solution carryover), and size heaters, pumps, and fans. The overall weight of the part or batch of parts being conveyed must be known to calculate heat loss through the washer and ovens. Unusual shapes must be identified for early consideration. For example small, blind holes on surfaces could negate the power wash approach, whereas large, open or tlat surfaces that can drain are ideal. Small parts that can withstand tumbling can be ideal for a drum washer; baskets of parts that cannot be tumbled can be immersed and agitated. The same situation is true with paint application. Smooth, flat parts can be easily automated. while complex shapes may require additional. manual reinforcement for complete coverage.
Material Composition of Parts Knowing the base materials will allow compatibility waste treatment requirements, operating temperature, specifications.
with selected cleaners, subsequent method of handling, and process
Desired Material Handling Methods Selecting the appropriate material handling method should be done based on the principles of increasing productivity. The method selected must incorporate reliability, economy, flexibility, and ease of installation. For example an overhead monorail-type conveyor system is relatively low in cost but not very flexible, while a power-and-free system is very flexible but higher in cost.
Understanding Soils and Cleanliness Contaminants determine chemical selection and spray or immersion selection. and ancillary equipment for handling the effluent (chips, oil, or heavy metals) will impact the waste treatment stream. If the cleaning process is not defined it is important to get contaminated parts to the chemical and equipment suppliers and have the parts tested in a laboratory. While in the laboratory your suppliers can simulate conditions and test the different variables, Minimizing or avoiding contamination is the key to keeping your factory and parts clean. Know where your soils are coming from and why. This allows you to take steps to contain soils in the area where they occur. Effective and inexpensive means to check for clean parts are the “water-break-free surface test” and “white towel test.” If organic soil has been effectively removed a uniform sheeting of the rinsewater will occur as parts exit the last pretreatment stage. If the surface has beaded water standing you have not adequately removed organic soils. Inorganic soils can be checked by using a white towel after they have passed through the dry-off oven. If the towel is dirty you have not adequately removed the inorganic soils. More sophisticated is the millipore test. This test requires a vacuum pump, flask. funnel, filter papers, isopropyl alcohol. oven, and scale. This test can detect micron particle sire and weight in milligrams. 266
Facilities and Utilities Available A floor layout with height clearance is important for design considerations. Often. space constraints dictate-process times. Although it may not be the optimum process it may achieve acceptable results. Availability of electrical service, heating preference, and plant conditions (such as availability of truck dock, building door size, floor and roof construction, distance from unloading site to erection site, and whether there is a clear path) must also be considered.
Environmental Considerations Local, regional, and federal regulations are continually being added and changed. The recent Clean Air Act Amendments of 1990 established procedures for a national permit system for air pollutant emissions, as well as establishing a basis for more stringent controls on emissions from all manufacturing operations. Waste stream compliance ia forcing many manufacturing companies to invest in waste treatment plants. Understanding your local laws and knowing your process will determine your direction. If you are not familiar with either, outside help must be sought.
COMPONENT
DESIGN
Material Handling Selection of the material handling method varies directly with production volume and desired cleanliness. In general the monorail is the most economical, flexible, and reliable method of handling product, but it is not the ideal solution for all cases. If you handle product in batches/baskets a belt internal to the machine can provide an excellent and consistent means of transporting product through the washer. If your product can tolerate “bumping,” such as nuts or bolts, a drum machine is a cost-effective means of conveying high volumes with excellent results. There are also situations where combinations of belt and monorail are appropriate. Rather than having two machines you can easily assimilate dual lines into one washer. Conveyor systems are discussed in further detail in a separate section of this Guidebook. System size is a function of conveyor speed, which is actually based on part density rather than raw production rate. As an example, to determine the line speed for a given production shift divide the number of parts desired by the number of par& per rack times the rack spacing divided by the number of minutes available per shift.
Washers/Pretreatment The choice of a spray wand, three-stage, or five-stage machine is based on a number of variables: incoming soil loads, space available, results required, energy consumption, total initial cost, estimated total operating cost, production volume, size of part, etc. The initial cost of a five-stage machine (clean, rinse, phosphate, rinse, rinse) is somewhat higher than a three-stage type but operating economies and higher quality quickly offset the investment, The five-stage machine ensures longer chemical life. The high-pressure heated spray wand is an excellent choice for low-volume, hard-tohandle parts. This approach is a cost-effective technology with a great deal of flexibility and versatility. From experience and the recommendation of various chemical companies, to remove shop dirt and light machine oil a three-stage machine is adequate. The typical process would be a one-minute wash stage (heated), Dsecond rinse (ambient), and a 30.second rinse/inhibit (ambient or heated). If you have a more critical cleaning specification or phosphating requirement a five-stage 267
washer (heated),
with one-minute Dsecond rinse
Spray
versus
wash (heated), (ambient), and
30-second 30-second
rinse (ambient), one-minute rinse/inhibit (ambient) will
phosphate be required.
Immersion
In general, spray processing provides the most effective cleaning and rinsing capabilities owing to increased mechanical action, liquid impingement, and natural draining: however, for impingement of recessed or hidden surfaces of complex parts and assemblies. immersion processing is more appropriate. The addition of ultrasonics or agitation can enhance the impingement capability, but it is costly. When processing complex parts or heavily loaded baskets of parts a combination of immersion and spray stages is often required, Testing dirty parts in a laboratory will provide proper selection.
Sample
Three-Stage
The first a largest part
Washer
step in the design G/e of ?,‘b ft X
is to lay out the system (using IX in. X IX in.). The entrance
a conveyor speed of 1 fpm and profile should include a Sin.
Turnkey Finishing Systems Design • Engineering
• Fabrication
• Installation • Training • Service
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053 on reader information card
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clearance around the part. Thih will provide flexihility to process larger parts if required (see Fig. 2). A housing space of 1 ft on each side of tunnel openings allows for spray risers and piping. The cleanout section can he 2 to 2% ft: 3% ft from the floor to the bottom of the tunnel opening will provide enough apace to have the tank capacity to keep the pump-to-tank ratio around 3:l. The overall height of the machine is 7’S ft. but we need to allow another 3 ft minimum for ventilating ductwork. The machine length for a three-stage washer, allowing three minutes of drying, is shown in Fig. 3. You know that one minute in the wash stage is required and that the conveyor is traveling at 4 fpm, so you can size the wash stage at 4 ft. Similarly, rinse stages are 30 seconds: thus, they are each sized at 2 ft in length. Good design practice dictates that the approaches and exits should be two times the tunnel width: therefore, they should be 4 ft long. The drains should be three times the tunnel width, minimizing spraying and carryover contamination; therefore, they are 6 ft in length. Special consideration for drain lengths may be necessary for long parts or slow line speeds. The hot air blow-off will require three minutes of drying time, so size that at 12 ft. You also must have 1 ft between washer and hot air blow-off fan for ventilating. ENVIRONMENTAL
CONCERNS
Most washer systems require waste treatment of the effluent from the system prior to disposal to the sewer. In some cabes, where the potential discharge of cleaners and phosphates to the sewer are significant, a self-contained treatment system is required. Most municipal waste treatment authorities have a list of chemicals they can accept and in what concentx(ions. Check with the local authorities for additional information, or consultants are available to artist in your decision-making process. FIVE-STAGE A five-stage 270
monorail-type
fine
WASHERS
phoaphating
machine
is shown
in Fig. 4. Table
II
Conaldcrmg
Settling both
tank energy
and
pollutmn
problems,
Standard cust iron Mild steel
equpment
Pump Immersed heating
Mtld or stamlas Steel
N0.A5 Piping
new
procecws
mild steel
mild steel
JIIOW
luwcr
prucc\Gng
or Manganese
Phosphate
tn some
case?
1 I-gauge stainless steel or mild steel 14.gauge %Cnlers steel or 3/16 mild steel Stainless steel Stamless steel or extra heavy \tee1 Stainless steel Stainless steel or extra heavy steel Mild steel
160°F 60 Whirl-Jet IO
StURP No. 3 Phosphate
Zinc,
~empcramrc~
steel
Iron,
Standard cast tron Mild steel
Mild or stainless Steel
l/X-in.
l/&in
HCUSlllg
mild steel
l/4-m.
l/4-in.
mild steel
Room 30 V&et 15
Stqe No. 2 Rinse
for Five-Stage
145°F 60 Veekt IS
eel
Construction
Sragr No. I Wush
Monorail-Type
Destgn temperature Time cycle (wands) Type nozzle Nozzle pressure (psi) Mntennl.5 fir conwuction: Tank
Table II. Typical
mild steel
mild steel
No. 4
Standard
cast iron
Mild or stamless Steel
l/8-in.
l/4-in.
Room 30 VeeJet IO
Stale RiILX
Washer
ateel
or stainless
mild steel
mtld steel
Standtvd cast mm Mild steel
Mild StlXl
K-in.
l/4-in.
steel
145°F to assist drying 30 VeeJct IO
Stqe No. 5 Aud$ied Rinse
III. Typical
Belt-Type
Cuucldenng
Iron
1/4-m mdd rteel l/S-in. mild steel Mild or stainle9c steel Steel Iron Mtld steel
l/4& mild steel l/X-in. mild at‘1 Mild or uumle~r steel Steel Iron Mild steel
Phosphate
ROOlll 30 VceJet 15
Siuge No. 2 RUM
for Five-Stage
14SF 60 VeeJet I5
WlIdl
Srugr No. /
Construction
horh energ! rind p~,llut~n~~prohl~mr. ~wi ~~rucu~ccc allow tower processing icmprrarure\
Design temperature Time cycle (seconds) Type nozzle Nnrrle pressure (PSI) Materialsfor
Table
in wmr: caw
l/4-in. mild steel l/X-in. mild steel Mild or stainless steel Steel Iron Mild steel
160°F 60 Whlrl-Jet 10
Sfrcge No. 3 Pho.whate
Machine
ibin. mild steel l/&in. mild steel Mild or stainless steel Sled Iron Mild steel
l/4-in. mild steel l&in. mild steel Mild or stainlex steel Strel Iron Mild steel
l45’F to assist drying 30 VeeJet 10
Fig. 5. Five-stage
belt-@pe
iron phosphnting
machine
provides details for each stage. Table III provides phosphating system pictured in Fig. 5.
Fig. 6. Three-stage
drum-type
washer
with hlowwff
(,we TWle III for detuils)
similar
information
(see Table IVfor
for the five-stage
iron
details).
273
Fig. 7. Drum
washer
construction
detai1.s. DRUM-TYPE
Fig.
Fig. 6 depicts a typical three-stage 7. Table III gives further details
Table
IV. Typical
Design
temperature
Time cycle (seconds) Type nozzle Nozzle pressure (psi) Mutrriuls ,ji,r
Drum-Type
WASHERS
drum-type on drum-type
Construction
washer. Concentration systems.
for Three-Stage
Washer
145°F
Room
60
30
160°F to assist drying 10
VeeJet IO
VeeJet IO
Veelet I0
details
with
are shown
Blow-Off
~onmucrion.~ Tank Housing
IWin. l/Z-in.
NOZZICS
Mild or stainleah steel Steel Iron Mild steel
Piping Pump Immersed heating equipment Air heating equipment
mild steel mild steel
IWin. l&in.
mild steel mild steel
Mild or rtainless steel Steel IroIl Mdd steel
IWin. l&in.
mild steel mild steel
l/Z-in. mild qteel
Mild or stamle\s steel Steel Iron Mild steel Mild
steel
in
OVENS In former years there was a tendency to oversimplify oven problems. There was a widely held idea that an oven was ‘just a heated box” through which parts were passed to dry or bake a finish or tO evaporate and remove moisture or otherwise process by heat application. In more recent years the scientific aspects of heat engineering have come to be appreciated. True economy in operation matched by superior results can only be obtained by expert design based on sound engineering followed by quality manufacturing and conscientious installation. The ovens may be on the plant floor or elevated overhead. either inside the plant or outside, on the ground or on the roof. With the ovens elevated the factory floor may be used for manufacturing or storage. The oven panels should be tongue-and-groove, all-welded construction, fabricated of heavy-gauge sheet steel, with a minimum of through metal, which reduces the transmission of heat by conductance. To avoid “insulation sag,” which would leave an open space at the top of the wall panels, oven panels should be insulated with mineral wool batts 1/4 in. greater in thickness than the oven panels, Access doors should be fully insulated or of nonsagging construction and equipped with explosion latches. These doors should allow opening from inside or outside the oven. The relatively few ovens shown here are merely examples of the many types being built, each representing dozens and even hundreds of similar installations. Many special types are not shown because of limited use. For standard ovens, custom designs, and even economical prefabricated components it pays to consult true experts in heat engineering.
Direct
versus Indirect Heating Systems In a direct fuel-fired system the products of combustion are allowed to come into contact with the work; the combustion equipment can be located inside or outside the oven. Although gas is generally used with a direct fuel-fired system, modem processing of fuel oils, along with improved handling and firing equipment, has increased their use in this area. An indirect-fired system does not allow products of combustion to come into contact with the work. Electric and steam heating are common choices and fuel-fired equipment may be used in conjunction with a heat exchanger to separate the products of combustion from the oven atmosphere.
Fuels The brief outline that follows describes the most popular fuels being used today. You may want to investigate the possibility of using one as an alternative to back up your present system or as a supplement. Gas: This is generally considered a clean, convenient, and easy-to-use fuel. Work loads are commonly heated by the direct-fired method with no adverse effect from the products of combustion; however, because the availability and overall costs have changed it may be to your advantage to check the alternative fuels in your area. Oil: Many of the problems that once plagued the use of oil with direct-fired oven equipment have been eliminated, and indirect-fired systems are easily designed and installed when needed. In either case plan for a safe, convenient storage space. Steam: A very clean source that is simple, easy to control, and reliable for low-to-medium temperature operations, steam can be produced in a number of ways that are most economical. Electricity: This is a clean, simple, and efficient source of heat. High temperatures are easily obtained and heat recovery systems are available to economically reduce operating cost. Combination: Combination fuel systems are very popular with people who have been plagued by fuel price increases and shortages because they allow the ability to switch from one fuel to another without stopping production or adversely affecting the product. Recovery Recovery systems have recently become very important tO all users of energy. As fuel costs increase heat recovery systems become more practical. 275
Radiant: This is particularly applicable to flat parts and batches processed on the basis of part shape and size. It is a clean, high-energy source of heat where high surface temperatures are easily obtained in short periods of time. Although expensive to control it can provide shorter cure times and minimal floor space.
Features Knowledgeable plant operators want panels and the general construction to provide maximum strength and rigidity, minimum heat transfer or loss, and an attractive appearance. The panels should be filled with insulation of full thickness, formed in batts to resist sagging and settling that can leave uninsulated areas. Tongue-and-groove construction mates into a strong, neat joint. Ovens should be able to be readily disassembled and moved if necessary. A typical oven system is shown in Fig. 8. Air SYLIIS: Ovena can be provided with a variety of seals to prevent escape of heated air and fumes. The bottom entry oven, which must be elevated, has a natural lype of seal because the heated air rises into the upper, sealed portion of the oven. Exhaust-type seals. where conveyor opening\ into the oven are enclosed by a hood with an exhaust fan. are also available. In theory the most practical type of seal is the recirculating seal, which has been far from perfect in the past. Companies have invehted considerable time and money in this seal and they are now producing recirculating seals that allow adjustment to compensate for various oven temperature losses. By providing a recirculating fan with adjustable vents at least 80% of the normally escaping heat can be retained. Ovens can be designed as a high-velocity type or low-velocity type depending on the application. In most cases ovens are designed with both types in special zones to control paint popping, blistering, or in the case of a powder oven, dry powder blow-off. Low-velocity or “quiet” zones allow the coating to cure slowly, allowing solvents to evaporate before the surface film is set, which minimizes pops and blisters. Radiant and infrared ovens can fit into this category. 276
High-velocity zones allow direct impingement of the air to the work, which allows for quicker curing of the coating or evaporation of water. This air movement helps to obtain even temperatures throughout the oven as well. The air movement is induced by high-velocity nozzles designed to improve direct impingement of heated air on the work surface. Attempting to dry or cure a painted part too quickly is a notable cause of paint “skinning,” resulting in bubbles, blemishes, and powder blow-off. Rolling nir or high turnover rates: This induces an air movement that helps to obtain remarkably even temperatures. The air movement is induced by high-velocity nozzles that also prevent direct impingement of heated air on the work surface, a notable cause of “skin-drying,” resultant bubbles and blemishes, and powder blow-off. Burner size: When selecting burners for an oven concentrate on the total needs of the job at hand; then allow for a reserve capacity to handle higher work loads without expensive alterations. This provides the greatest overall economy and equipment flexibility because the burners are efficient throughout their operating ranges. Cnmhu~tiori chamber;\: Ovens are usually designed with the combustion chamber as an integral part of the unit, streamlining the appearance and eliminating the need for exterior ductwork. This compact arrangement also reduces power requirements connected with excessive ductwork, saving floor space as well. Di~pposahle filters: Intake air filters can minimize the intake of dust, which can cause finish tlaws. The filters should be arranged for quick and easy changing without use of tools. The best disposable filters to use are frameless, eliminating the usual cardboard frame as a possible fire hazard. Simple erection: Ovens should be constructed of prefabricated panels for easy erection. All components-panels, structurals, ductwork. wiring, and piping-should be keyed to assembly drawings and manufactured to fit easily, quickly, and precisely in the field. The purchaser can in many cases erect the oven with existing plant personnel under supervision for significant savings. For more complex ovens suppliers provide a complete service ranging from basic erection to complete turn-key jobs. Dry-Off Ovens The dry-off oven is usually a continuation of the washer. Drying metal pans with no “puddling” of water requires three to five minutes. depending on temperature. At 4 fpm you will need 12 to 20 ft of dry-off oven, excluding air seals. The next unit requiring the largest amount of floor space is the cure oven. Assume for design purposes that the paint you are using requires a 20.minute cure at 350°F. Again. conveyor speed is 4 fpm so you have to be in the oven at temperature for 80 ft of conveyor travel. The oven can be fabricated in practically any configuration, depending on the floor space available. It could be a single-pass oven (80 ft long) or a two-pass oven (40 ft long) or a four-pass oven (20 ft long). This you can determine from the floor space available. If floor space is a premium and the building height will allow it the oven can be hung from cross-beams supported from the floor or mounted on the roof. Available space usually dictates the position of the oven. The tunnel opening of the oven is normally the same dimensions as the washer except that usually 18 in. to 2 ft from the bottom of the tunnel opening to the floor is ample for ductwork. To sketch the oven layout you know that the maximum part width is 1 r/2 ft and that they are spaced on 24.in. centers. This indicates that a 3.ft.diameter wheel turn will permit clearance of parts on a turn, so the proposed oven is outlined as shown in Fig. 9. PAINTING
SYSTEMS
The major types of paint systems fall into five categories: conventional solvent water-reducible systems, high-solids systems, powder systems, and electrodeposition
systems, systems. 277
Fig.
9. Layout
for
curdbakr
own
sample
desip
Defining your criteria relative to operational characteristics, coating properties, initial capital expenditure, and operational costs will determine the paint system. A powder system and electrodeposition system have been included to demonstrate layout. The following arc component design considerations for an electrodeposition system. ELECTROCOAT
(ELECTRODEPOSITION)
PAINTING
Coating Thickness Control The main factors controlling film thickness are the applied voltage and the fihn resistance. Increasing the coating voltage or lowering the specific film resistance causes an increase in film thickness, You simply dial the desired coating thickness. The electrocoating process will continue until the organic film deposited provides an electrical insulating resistance, which prevents further current flow. When the coated parts are removed from the bath they are rinsed in permeate and deionized water to remove nondeposited paint particles. Tank
Design Electrocoat tanks are designed for an immersion time of 1 i/z to 2 minutes. It is possible to deposit approximately 1.0 mil organic coating in the first IS seconds: however, for heavier film deposits a longer time is required. 278
Tank equipment includes dual pumps with each pump prevent the setting of paint solids. Plate-and-frame heat exchangers are used with chiller temperature.
able to maintain units to maintain
the bath and proper
tank
Tank
Design is Vital In the design of the electrocoat tanks some of the most important items are circulation rate, circulation flow, and density of the paint. With the paint solids normally at X to 10% density a flow rate and pattern is determined to prevent settling. The flow rate in the average tank is accomplished by the use of headers with eductors. The flow pattern in the bottom of the tank is opposite that of the conveyor movement and with the conveyor at the top of the tank. The exit end of the tank is equipped with an overtlow weir tank designed to prevent foaming without dropping or aerating the paint. The recirculating pump suctions are also connected to this tank.
Filter
Systems Conventional filter systems are provided with approximately SO micron filter media to remove foreign debris that may enter the bath. An ultrafiltration system will be used to remove soluble salt and water carried into the bath from the cleaning process by the parts being coated. Ultrafiltration may also be used to recover paint solids from the postrinse so they may be returned to the bath. A virtually closed system exists when ultrafiltration is used to provide rinsewater in the place of deionized water. This arrangement will aid considerably in the prevention of water pollution.
SUMMARY Getting value from your finishing system involves a comprehensive review of your requirements and, as necessary, applying some or all of the many technologies available into your system design. Normally, one person or one company does not possess all resources to do this task. A good approach is to consult reputable suppliers and follow their recommendations. The best solution to your system design is one in which every selected supplier works as part of your team toward the common goal of a successful system installation, start-up, and operation.
Anodic
Coating Defects - Their Causes and Cures by A. W Brace 168 pages $150.00
This book provides guidelines and examples for troubleshooting defects in anodic coatings. Chapter one outlines an approach to identifying a defect. Here one finds a photo and description of each defect (for instance, fine pitting) with a remedy for curing it; a simple and straightforward approach to problem-solving. Send Orders to: METAL FINISHING, 660 White Plains Rd., Tarrytown, NY 10591-5153 For faster service, call (914) 333-2578 or FAX your order to (914) 333-2570 All book orders musr be prepaid. Please include $5.00 shipping and handling for delivery of each book via UPS in rhe U.S., 510.00 for each book shipped express COCanada; and $20.00 for each book shipped express 10 all orher coumies.
279