- Email: [email protected]
Operation: Automation
TECHNlqLLY
speaong
BYARON LORENZ, WMV. INC.. SYLVAN LAKE. MICH., LOTHAR PEUKERT. WMV APPARATEBAU GMBH, AND TONY EVANS AND PETER SALMON. PALSURFACE TREATMENT SYSTEMS LTD.
al PCs that function as a Human Machine Interface (H MI). The HMIs can be located at the beginning or end of the line, and in one or more offices. PC-based software control is used to control elements of the process through a database containing parts and recipes (Figure 1). The recipes are customized to guarantee quality finishing is achieved by controlling the steps required for processing various parts. The PC control system can also automatically start-up and shut down elements of a system to save energy. Bath control can be achieved by automaticall y dosing chemistry to treatment baths based on time, square foot ofsu rface area or pounds of parts processed. Monitoring equipment can also be used to measure bath continuity that will control the addition of chemistry or the addition of fresh water to the bath. Monitoring treatment baths and automatically dosing chemicals will ensure the process is under control and finishing quality is maintained. Process in form ation can be archived in a database located on the PC or the processor's server. The archived
Operation: Automation The inherent benefits ofautomated dip-spin-tilt coating equipment when integrated with barrel plating, conversion coating and painting systems.
A
u to mating a finishing process can provide a host of ben efits ranging from increasing profits to a reduct ion in part damage. The specific benefits of installing a fully automated dip-spin-tilt coating or post-treatment system will be d iscu ssed in this paper. The term centrifuge-which will be used periodically-referenc es modules that sp in baskets of parts to accomplish various process steps. In its simplest form, automating a fin ishing line is the integration ofan automated fixed timeway hoist to transfer parts in a barrel, basket or fixtured on a rack through a series of tanks. For the purposes of this article, we will focus on fully automating bulk barrel plating, basket dip-spintilt post tr eatment and the painting of parts with zinc-rich paints using bulk dip-spin-tilt coating modules. One might describe a full y automated system as a black box. Parts are introduced into the syst em and are moved through all the required processes until the finishing process is complete. The only reason for an operator to in teract with parts after loading them into the lin e is to audit and in spect them to fulfill the processors quality control program. We will touch on many of the bene fits of a fully automated syst em. Financial just ifi cat io n, such as return on investment, is not addressed since it varies widely by company or even by country. Topics covered in this paper will be November 2008 1metalfinishing 114
discussed in the following order: computer controls and th e loading of bulk parts for plating and painting; pretreatment of parts prior to painting with centrifuge washing equipment; chromating, waxing, and seal ing parts using a dip-spin-tilt transfer hoist after plating, and dipspin-tilt coating with paint. PROCESS CONTROL AND LOADING PARTS
Dip-spin-tilt equipment can be integrated into either barrel plating lines or painting lines . A fully integrated line will allow operators to simply scan a bar code prior to introducing the parts into a line. The bar code scanner is connected to one of sever-
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www.metalfinishing.com
TECHNlqLLY speaong data can be queried at a later date to provide processing information to customers who need evidence that parts were processed within their control limits. The PC HMI references the part number and load weight for the batch of parts introduced into the finishing line. A part process recipe is assigned to the part. The recipe is created to optimize processing and can contain additional elements, such as: when and how often a basket needs to be washed; if the parts need to be handled gently; and inspection points in the line for quality checks. The HMI can be configured to alert the operator as to precisely which parts in the production queue are to be processed. The operator will load the bin or tray of parts into a bin or tray unloading system and start the job. A production ticket will be scanned to assure the correct part is being processed. It is standard practice that most parts are loaded into barrels or baskets based on weight. However, controlling the loading of parts into the barrel or baskets is often overlooked. Controlled loading ensures process integrity and optimizes finishing results. For example, if the part processing recipe calls for loading a dipspin-tilt coating basket with 500 pounds of parts, but only 20 pounds of parts are loaded into to the basket, the part may have less than the required coating weight applied to it since the part process recipe will treat the parts as though the basket is filled with 500 pounds of parts. The automated loading system should also handle bulk parts gently when necessary in order to prevent part damage. A properly designed loading and order entry system will ensure parts are treated properly. It will increase process control through the use of recipe-driven part processing and will lead to an increase in quality, allow for generation of process documentation, minimize the possibility of mixing parts and reduce part damage. www.metalfinishing.com
Vario-Cent-Unit-Con struction Conveyor
Dro lllng
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ZT
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Optional Accessories: De.Ull alion
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Figure 2: WMV washing recycling system.
,
Int ial loading was her A,B,C E
Tray to shot hlasl mac hines • F Belt 10 basket vib tray
I
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Clea n dry parts 10 the shol blast tray load er .
G Vib tray 10 bas ket
Shot blast mac hine to belt F Figure 3: WMV washing. blasting and coating line.
Operation
Present Equipment Total Drop Heights in mm
WMV Equipment Total Drop in Heights in mm
Wash
2998
1033
Blast
2871
1758
1st Basecoat
5766
1238
2nd Basecoat
5766
1200
Total millimeters Difference
17401 12172
5229
Figure 4: Comparison of total part drops using WMV equipment vs. other equipment.
November 2008 I metalfinishing I 15
TECHNlqLLY
speaong
CLEANING AND PRETREATMENT OF PARTS PRIOR TO PAINTING
Dip-spin-tilt equipment is often used to dean parts (Figure 2) as part ofa pretreatment cell when automating dip-spin-tilt coating lines. The cell typically will consist of centrifuges for deoiling, washing, rinsing, drying, batch shot blast equipment and the material handling to automatically transfer the parts through the cell. How the parts are treated in each of these modules is controlled by the part process recipe. Prior to washing the material, a basket of parts is placed into a deoiler, which spins oil off the parts prior to washing. (Reducing the amount oil that is introduced into the wash solution extends the life of the wash bath.) The recovered oil from captive wash systems in manufacturing or heat-treating facilities can be used to replenish lubricants or quench oils
Submerge
Spin Off
Figure 5: Dip-spin-tilt transfer hoist.
that are used in the upstream processes. After deoiling, the basket of parts is transferred through wash, rinse and drying centrifuge modules. Washing parts in a centrifuge basket begins by
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tilting the basket of parts and rotating it slowly while continuously feeding wash solution into the basket. The continuous flow of wash solution submerges the parts. (Submerging parts in washing solu-
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November 2008 I metalfinishing I 16
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TECHNlqLLY speaong
tio n and rotati ng the basket has the advantage of su bjecti n g the parts to che mical and mechanical cleaning.) After the was hing process is complete, the bask et of parts is spun to prevent was h solution from bein g dragged out in to the rinsing modu le. Rising modules operate similar to the wash modules and ag ain preven t th e d rag out of rinse wate r in to the d ryin g centrifuge by spin n in g the basket of parts prior to their transfer. The fin al pretreatment step s are drying and optionally shot blas ting the p arts. The cell layout is illustrated in Figure 3. One of the m ajo r advantages of automating the cell is gen tle part handling. A study done at Michigan Metal Coatings found that total part drops through the a utomated lo ading, washing, p ret reatment and coatin g process is one thi rd the di stance of decoupled proc esses (Figu re 4). Ad ditional b enefits are increased process contro l through recip e-d riven processin g; reduced use of was h che mistry; reduced use o f fresh wa ter; a reduction of water d ischarged t o the cities was tewater treat me nt system ; and the preven-
Reduce Waste Water Comparison of DSC Versus Barrel Treatment 1. Drag out of rinse water for each rinse using an efficient plating barrel Material M8x25 screws Charges per hour 16/hr Load weight per charge 176/lbs/charge Surface are per Ib 80 sq inllb Surface area per charge 97.77 sq ft/charge Capacity per hour 2,816lbs/hr Treated surface area per hr 1,564 sq ft/h r Drag out per sq ft of surface area treated .628 ozlsq ft Drag out per charge 61 ozlcharge Drage out per hour per rinse station 7.66 hr/rinse Rinse water sent to waster treatment to maintain the second rinse at a maximum concentration of 5 mg/I Chromium with the treatment bath maintained at 5 gil Chromium.
243 gallhr
2. Drag out rinse water for each rinse using a BS2000 Centrifuge System Material M8x25 screws Charges per hour 16/hr Load weight per charge 176 lbs Surface area per hour 80 sqinllb Surface area per charge 97.77 sq ft/char ge Capacity per hour 2,8161bs Treated surface area per hr 1,564 sq ft/hr Drag out per cu of surface area treated .125 ozlsq ft Drag out per charge 12.270zlcharge Drag out per hour per rinse station 1.53 gallhr/rinse Rinse water sent to waste treatment to maintain the second rinse at a maximum concentration of 5 mgll Chromium with the treatment bath maintained at 5 gil Chromium
48 gal/hr
3. Summary When utilizinga DSC hoist Transfer System versus a BarrelTreatment System, there is an 80% savings of rinse water and a 50% reduct ion of chrome sludge. The chemicals required to treat the rinse solutions when dumping the rinse tank are also reduced by 50%. Figure 6
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TECHNlqLLY
speaong
tion of m ixing parts due to the batch p roc essing of parts in centrifuge baskets .
cool load unload
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CHROMATING, WAXING AND SEALING PARTS USING A DIP-SPIN-TILT TRANSFER HOIST
Aft er pl ating, many parts require additional che mical processin g to en hance corrosion res istance, modify their frict ion coefficient, or provide coloration for part identification or appearance. High-strength st eels, for instance, may also require heat treatment to prevent defects caused by hydrogen em brit tlem en t. Until five years ago, most of these processes would have been performed in the barrel lin e, on multiple manual lin es, o r a co m bin atio n of the two. Due to the in cr eased chemical costs associated wit h non-hexavalent pass ivations, the difficulties of handling was tewater treatment from multipl e processes and the demand for
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Figure 7
in creased quality, processors that are required to provid e high-quality surface finishing have automated the post-plating processes. One of the most popular methods of automatin g the po st finish in g pro cess is to use a dip-spin-tilt transfer hoist to move baskets of parts through the post-finishing processes, reorient
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TECHNlqLLY speaong spin-tilt treatment baskets. To address this issue, parts are transferred through a water-filled funnel and basket. The water buffers the impact of parts while they are being transferred into the centrifuge basket. After parts are transferred to the basket, the solution is drained from the funnel and basket shuttle. When parts are transferred through water to the centrifuge basket, the plating line can typically be reduced by one rinse station since loading the parts to the centrifuge basket will function as a final rinse. Many parts that require high-quality, corrosion-resistant finishes have complex geometries. Some of the design elements that the parts may possess are cupped areas, blind holes, internal cavities, and recessed headed fasteners . These design elements make the part prone to head fill, excess puddling, and uneven coating.
Recessed headed fasteners can be particularly problematic since many are designed to be installed with automated torque angle fastening systems. Poor driver engagement due to head fill or improper application of friction modifiers will cause costly downtime for the final customer and, at worst, could tarnish the reputation of the finisher and the supplier of the post-plating chemistry. To increase the quality of postplating finishes, a DSC dip-spin-tilt transfer hoist can be used (Figure 5). Based on a part process recipe, the basket of parts can be dipped and tilted while rotating the basket filled with parts under solution. Tilting the basket up to a 60-degree angle assures parts are reoriented and solution turnover around the parts is maximized. Another option is to submerge the parts in solution and oscillate the basket up and down while the basket remains vertical or tilted. After the chemical treatment or rinsing is completed, the hoist
raises the basket above the treatment bath and spins it at a high rate of speed to centrifuge off excess solution. This can reduce drag out that would have been carried into the next process tank by up to 90%. To further reduce the drag out and increase coating uniformity of problematic parts, the basket can be tilted above the solution tank and again rotated to reorient parts. After the parts are reoriented, the basket is returned to a vertical position and again spun at a high rate of speed to further reduce drag out. All treatment parameters can be set in the part process recipe to ensure different parts are treated uniquely when necessary. The best recipe will optimize quality and productivity based on the final finishing quality that is required. Elements that can be specified in the part process recipe include: • basket or barrel loading weight • dipping time in solution • rotation speed under solution
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November 20081 metalflnishing 119
TECHNlqLLY
speaong
with the basket in either the vertical or tilted position • solution spin-off time and centrifuge RPM above the solution bath with the basket in either the vertical or tilted position • the number of repetitions desired if repeating a step further optimizes the process Careful planning of the process will reduce: the usage of chemicals;
fresh water; the amount of spent solution that will need to be sent to wastewater treatment; and the amount of effluent discharged from wastewater treatment-all increasing the quality of the fin ish . An internal study at WMV found the resu lt s illustrated (see Figure 6) can be achieved. Post treatment of plated parts may require that some parts be heat treated to prevent hydrogen embrittlement. Conveyor or batch ovens can be integrated into the automatic dip-
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November 2008 I metalfinishing I 20
spin-tilt, post-treatment cell to perform this step. If batch ovens are deployed, the heat treatment of parts can be scheduled in the part process recipe before, m idway through or at the en d of the processes that ar e required after plating. Batch ovens also allow finishers to bake parts at varying times to maximize the throughput and utilization of heattreatment equipment. One of the major benefits of using an automated dip-spin-tilt transfer hoist is increased finish quality due to part manipulation and process control based on specific part process recipes. Other benefits: reduced chemical usage; reduced consumption of fresh ware ; reduced work in process; reduced wastewater treatment; reduced effluent sent to public wastewater treatment facilities and precise documentation that parts requiring heat treatment have been heat treated. DIP-SPIN-TILT COATING WITH PAINT It is also possible to create a flexible , fully automated bulk d ip-spin-tilt coating operation. Fully automated systems tend to have aqueous cleaning and a shot blasting pretreatment cell or a phosphating line integrated to the coating line. (Either pretreatment method can be used for most paints.) Fully automated dip-spintilt coating facilities are typically designed to automatically coat parts with one to three coats of paint. Figure 7 shows an automated lin e that washes, shot blasts and coats parts. The overall process is monitored with a central computer system. The computer system will allow the fin isher to create recipes that set process parameters for the part being processed and store the actual processing data. The process recipe can have different parameters for pretreatment, coating, basket storage and curing of the paint. It is even more important to reorient parts with complex sh apes in a paint process vs. post finishing in a plating line. To ensure parts are reoriented, the basket they are lNINW.metalfinishing.com
TECHNlqLLY speal\.lng processed in should tilt at a minimum of 60 degrees. Parts that are very challenging to paint may need to have the basket tilt until it is horizontal to the ground and rotated to properly reorient parts prior to a final high-speed spin cycle to spin off paint via centrifuge. Paint booths can also allow the fin isher to process different paints. (Figure 7 demonstrates the elements that make up a flexible coating booth.) An independent basket is indexed into the paint booth, which allows automatic exchange of baskets to process different typ es of paint or different sizes of parts. The paint tank is on wheels to allow operators to easily change paints. The basket can tilt horizontal to the floor to maximize reorientation of pares , which is designed to prevent head fill or puddles in recesses. To assist in moving parts through
the system and prevent cros s-contamination, the parts should be batch processed in barrels, baskets or trays. All three of these methods allow different types of parts to get processed without stopping the process to create a gap in a machine before processing a new part. A fully automated coating line, when properly utilized, will: reduce paint usage; increase overall productivity ; and increase process control and part quality. Furthermore, it will also reduce tram p material contaminating batches of parts and reduce part damage by controlling falls. SUMMARY
Determining the level of automation that will benefit your facility should begin by taking inventory of the processes with which the parts are treated. In the case of plating plants that offer multiple servicessuch zinc plating, zinc alloy or zinc nickel-sa computer-controlled automated line may allow several
processes to run on a single line. Plants processing different paints might find it advantageous to feed multiple paint lines with one pretreatment line. In the event it is determined that economics do not justify a fully automated system when outfitting a plant, the lines should be planned and purchased to allow expansion and integration in the future. 810
The preceding article was co-authored byAron Lorenz of WMV, Inc., Sylvan Lake) Mich.; Lothar Peukert of WMV Apparatebau GmbH; and Tony Evans and Peter Salmon) PAL Surface Treatment Systems Ltd. For more information) please visit www.wmvusa.com.
ACKNOWLEDGEMENTS
Michigan Metal Coating Company contributed to the parts drop study referenced in this story.
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INWIN.metalfinishing.com
November 2008 I metalfinishing I21
speaong
BYARON LORENZ, WMV. INC.. SYLVAN LAKE. MICH., LOTHAR PEUKERT. WMV APPARATEBAU GMBH, AND TONY EVANS AND PETER SALMON. PALSURFACE TREATMENT SYSTEMS LTD.
al PCs that function as a Human Machine Interface (H MI). The HMIs can be located at the beginning or end of the line, and in one or more offices. PC-based software control is used to control elements of the process through a database containing parts and recipes (Figure 1). The recipes are customized to guarantee quality finishing is achieved by controlling the steps required for processing various parts. The PC control system can also automatically start-up and shut down elements of a system to save energy. Bath control can be achieved by automaticall y dosing chemistry to treatment baths based on time, square foot ofsu rface area or pounds of parts processed. Monitoring equipment can also be used to measure bath continuity that will control the addition of chemistry or the addition of fresh water to the bath. Monitoring treatment baths and automatically dosing chemicals will ensure the process is under control and finishing quality is maintained. Process in form ation can be archived in a database located on the PC or the processor's server. The archived
Operation: Automation The inherent benefits ofautomated dip-spin-tilt coating equipment when integrated with barrel plating, conversion coating and painting systems.
A
u to mating a finishing process can provide a host of ben efits ranging from increasing profits to a reduct ion in part damage. The specific benefits of installing a fully automated dip-spin-tilt coating or post-treatment system will be d iscu ssed in this paper. The term centrifuge-which will be used periodically-referenc es modules that sp in baskets of parts to accomplish various process steps. In its simplest form, automating a fin ishing line is the integration ofan automated fixed timeway hoist to transfer parts in a barrel, basket or fixtured on a rack through a series of tanks. For the purposes of this article, we will focus on fully automating bulk barrel plating, basket dip-spintilt post tr eatment and the painting of parts with zinc-rich paints using bulk dip-spin-tilt coating modules. One might describe a full y automated system as a black box. Parts are introduced into the syst em and are moved through all the required processes until the finishing process is complete. The only reason for an operator to in teract with parts after loading them into the lin e is to audit and in spect them to fulfill the processors quality control program. We will touch on many of the bene fits of a fully automated syst em. Financial just ifi cat io n, such as return on investment, is not addressed since it varies widely by company or even by country. Topics covered in this paper will be November 2008 1metalfinishing 114
discussed in the following order: computer controls and th e loading of bulk parts for plating and painting; pretreatment of parts prior to painting with centrifuge washing equipment; chromating, waxing, and seal ing parts using a dip-spin-tilt transfer hoist after plating, and dipspin-tilt coating with paint. PROCESS CONTROL AND LOADING PARTS
Dip-spin-tilt equipment can be integrated into either barrel plating lines or painting lines . A fully integrated line will allow operators to simply scan a bar code prior to introducing the parts into a line. The bar code scanner is connected to one of sever-
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;;;;
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Figure 1
www.metalfinishing.com
TECHNlqLLY speaong data can be queried at a later date to provide processing information to customers who need evidence that parts were processed within their control limits. The PC HMI references the part number and load weight for the batch of parts introduced into the finishing line. A part process recipe is assigned to the part. The recipe is created to optimize processing and can contain additional elements, such as: when and how often a basket needs to be washed; if the parts need to be handled gently; and inspection points in the line for quality checks. The HMI can be configured to alert the operator as to precisely which parts in the production queue are to be processed. The operator will load the bin or tray of parts into a bin or tray unloading system and start the job. A production ticket will be scanned to assure the correct part is being processed. It is standard practice that most parts are loaded into barrels or baskets based on weight. However, controlling the loading of parts into the barrel or baskets is often overlooked. Controlled loading ensures process integrity and optimizes finishing results. For example, if the part processing recipe calls for loading a dipspin-tilt coating basket with 500 pounds of parts, but only 20 pounds of parts are loaded into to the basket, the part may have less than the required coating weight applied to it since the part process recipe will treat the parts as though the basket is filled with 500 pounds of parts. The automated loading system should also handle bulk parts gently when necessary in order to prevent part damage. A properly designed loading and order entry system will ensure parts are treated properly. It will increase process control through the use of recipe-driven part processing and will lead to an increase in quality, allow for generation of process documentation, minimize the possibility of mixing parts and reduce part damage. www.metalfinishing.com
Vario-Cent-Unit-Con struction Conveyor
Dro lllng
Rlmlng (2·Casca de.)
Was blng& Spinning
Dryi ng
Unloading
ZT
.r : - - - F W
Optional Accessories: De.Ull alion
Collecling-Ta nk
Figure 2: WMV washing recycling system.
,
Int ial loading was her A,B,C E
Tray to shot hlasl mac hines • F Belt 10 basket vib tray
I
J)
Clea n dry parts 10 the shol blast tray load er .
G Vib tray 10 bas ket
Shot blast mac hine to belt F Figure 3: WMV washing. blasting and coating line.
Operation
Present Equipment Total Drop Heights in mm
WMV Equipment Total Drop in Heights in mm
Wash
2998
1033
Blast
2871
1758
1st Basecoat
5766
1238
2nd Basecoat
5766
1200
Total millimeters Difference
17401 12172
5229
Figure 4: Comparison of total part drops using WMV equipment vs. other equipment.
November 2008 I metalfinishing I 15
TECHNlqLLY
speaong
CLEANING AND PRETREATMENT OF PARTS PRIOR TO PAINTING
Dip-spin-tilt equipment is often used to dean parts (Figure 2) as part ofa pretreatment cell when automating dip-spin-tilt coating lines. The cell typically will consist of centrifuges for deoiling, washing, rinsing, drying, batch shot blast equipment and the material handling to automatically transfer the parts through the cell. How the parts are treated in each of these modules is controlled by the part process recipe. Prior to washing the material, a basket of parts is placed into a deoiler, which spins oil off the parts prior to washing. (Reducing the amount oil that is introduced into the wash solution extends the life of the wash bath.) The recovered oil from captive wash systems in manufacturing or heat-treating facilities can be used to replenish lubricants or quench oils
Submerge
Spin Off
Figure 5: Dip-spin-tilt transfer hoist.
that are used in the upstream processes. After deoiling, the basket of parts is transferred through wash, rinse and drying centrifuge modules. Washing parts in a centrifuge basket begins by
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tilting the basket of parts and rotating it slowly while continuously feeding wash solution into the basket. The continuous flow of wash solution submerges the parts. (Submerging parts in washing solu-
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tio n and rotati ng the basket has the advantage of su bjecti n g the parts to che mical and mechanical cleaning.) After the was hing process is complete, the bask et of parts is spun to prevent was h solution from bein g dragged out in to the rinsing modu le. Rising modules operate similar to the wash modules and ag ain preven t th e d rag out of rinse wate r in to the d ryin g centrifuge by spin n in g the basket of parts prior to their transfer. The fin al pretreatment step s are drying and optionally shot blas ting the p arts. The cell layout is illustrated in Figure 3. One of the m ajo r advantages of automating the cell is gen tle part handling. A study done at Michigan Metal Coatings found that total part drops through the a utomated lo ading, washing, p ret reatment and coatin g process is one thi rd the di stance of decoupled proc esses (Figu re 4). Ad ditional b enefits are increased process contro l through recip e-d riven processin g; reduced use of was h che mistry; reduced use o f fresh wa ter; a reduction of water d ischarged t o the cities was tewater treat me nt system ; and the preven-
Reduce Waste Water Comparison of DSC Versus Barrel Treatment 1. Drag out of rinse water for each rinse using an efficient plating barrel Material M8x25 screws Charges per hour 16/hr Load weight per charge 176/lbs/charge Surface are per Ib 80 sq inllb Surface area per charge 97.77 sq ft/charge Capacity per hour 2,816lbs/hr Treated surface area per hr 1,564 sq ft/h r Drag out per sq ft of surface area treated .628 ozlsq ft Drag out per charge 61 ozlcharge Drage out per hour per rinse station 7.66 hr/rinse Rinse water sent to waster treatment to maintain the second rinse at a maximum concentration of 5 mg/I Chromium with the treatment bath maintained at 5 gil Chromium.
243 gallhr
2. Drag out rinse water for each rinse using a BS2000 Centrifuge System Material M8x25 screws Charges per hour 16/hr Load weight per charge 176 lbs Surface area per hour 80 sqinllb Surface area per charge 97.77 sq ft/char ge Capacity per hour 2,8161bs Treated surface area per hr 1,564 sq ft/hr Drag out per cu of surface area treated .125 ozlsq ft Drag out per charge 12.270zlcharge Drag out per hour per rinse station 1.53 gallhr/rinse Rinse water sent to waste treatment to maintain the second rinse at a maximum concentration of 5 mgll Chromium with the treatment bath maintained at 5 gil Chromium
48 gal/hr
3. Summary When utilizinga DSC hoist Transfer System versus a BarrelTreatment System, there is an 80% savings of rinse water and a 50% reduct ion of chrome sludge. The chemicals required to treat the rinse solutions when dumping the rinse tank are also reduced by 50%. Figure 6
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tion of m ixing parts due to the batch p roc essing of parts in centrifuge baskets .
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CHROMATING, WAXING AND SEALING PARTS USING A DIP-SPIN-TILT TRANSFER HOIST
Aft er pl ating, many parts require additional che mical processin g to en hance corrosion res istance, modify their frict ion coefficient, or provide coloration for part identification or appearance. High-strength st eels, for instance, may also require heat treatment to prevent defects caused by hydrogen em brit tlem en t. Until five years ago, most of these processes would have been performed in the barrel lin e, on multiple manual lin es, o r a co m bin atio n of the two. Due to the in cr eased chemical costs associated wit h non-hexavalent pass ivations, the difficulties of handling was tewater treatment from multipl e processes and the demand for
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Figure 7
in creased quality, processors that are required to provid e high-quality surface finishing have automated the post-plating processes. One of the most popular methods of automatin g the po st finish in g pro cess is to use a dip-spin-tilt transfer hoist to move baskets of parts through the post-finishing processes, reorient
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TECHNlqLLY speaong spin-tilt treatment baskets. To address this issue, parts are transferred through a water-filled funnel and basket. The water buffers the impact of parts while they are being transferred into the centrifuge basket. After parts are transferred to the basket, the solution is drained from the funnel and basket shuttle. When parts are transferred through water to the centrifuge basket, the plating line can typically be reduced by one rinse station since loading the parts to the centrifuge basket will function as a final rinse. Many parts that require high-quality, corrosion-resistant finishes have complex geometries. Some of the design elements that the parts may possess are cupped areas, blind holes, internal cavities, and recessed headed fasteners . These design elements make the part prone to head fill, excess puddling, and uneven coating.
Recessed headed fasteners can be particularly problematic since many are designed to be installed with automated torque angle fastening systems. Poor driver engagement due to head fill or improper application of friction modifiers will cause costly downtime for the final customer and, at worst, could tarnish the reputation of the finisher and the supplier of the post-plating chemistry. To increase the quality of postplating finishes, a DSC dip-spin-tilt transfer hoist can be used (Figure 5). Based on a part process recipe, the basket of parts can be dipped and tilted while rotating the basket filled with parts under solution. Tilting the basket up to a 60-degree angle assures parts are reoriented and solution turnover around the parts is maximized. Another option is to submerge the parts in solution and oscillate the basket up and down while the basket remains vertical or tilted. After the chemical treatment or rinsing is completed, the hoist
raises the basket above the treatment bath and spins it at a high rate of speed to centrifuge off excess solution. This can reduce drag out that would have been carried into the next process tank by up to 90%. To further reduce the drag out and increase coating uniformity of problematic parts, the basket can be tilted above the solution tank and again rotated to reorient parts. After the parts are reoriented, the basket is returned to a vertical position and again spun at a high rate of speed to further reduce drag out. All treatment parameters can be set in the part process recipe to ensure different parts are treated uniquely when necessary. The best recipe will optimize quality and productivity based on the final finishing quality that is required. Elements that can be specified in the part process recipe include: • basket or barrel loading weight • dipping time in solution • rotation speed under solution
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with the basket in either the vertical or tilted position • solution spin-off time and centrifuge RPM above the solution bath with the basket in either the vertical or tilted position • the number of repetitions desired if repeating a step further optimizes the process Careful planning of the process will reduce: the usage of chemicals;
fresh water; the amount of spent solution that will need to be sent to wastewater treatment; and the amount of effluent discharged from wastewater treatment-all increasing the quality of the fin ish . An internal study at WMV found the resu lt s illustrated (see Figure 6) can be achieved. Post treatment of plated parts may require that some parts be heat treated to prevent hydrogen embrittlement. Conveyor or batch ovens can be integrated into the automatic dip-
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spin-tilt, post-treatment cell to perform this step. If batch ovens are deployed, the heat treatment of parts can be scheduled in the part process recipe before, m idway through or at the en d of the processes that ar e required after plating. Batch ovens also allow finishers to bake parts at varying times to maximize the throughput and utilization of heattreatment equipment. One of the major benefits of using an automated dip-spin-tilt transfer hoist is increased finish quality due to part manipulation and process control based on specific part process recipes. Other benefits: reduced chemical usage; reduced consumption of fresh ware ; reduced work in process; reduced wastewater treatment; reduced effluent sent to public wastewater treatment facilities and precise documentation that parts requiring heat treatment have been heat treated. DIP-SPIN-TILT COATING WITH PAINT It is also possible to create a flexible , fully automated bulk d ip-spin-tilt coating operation. Fully automated systems tend to have aqueous cleaning and a shot blasting pretreatment cell or a phosphating line integrated to the coating line. (Either pretreatment method can be used for most paints.) Fully automated dip-spintilt coating facilities are typically designed to automatically coat parts with one to three coats of paint. Figure 7 shows an automated lin e that washes, shot blasts and coats parts. The overall process is monitored with a central computer system. The computer system will allow the fin isher to create recipes that set process parameters for the part being processed and store the actual processing data. The process recipe can have different parameters for pretreatment, coating, basket storage and curing of the paint. It is even more important to reorient parts with complex sh apes in a paint process vs. post finishing in a plating line. To ensure parts are reoriented, the basket they are lNINW.metalfinishing.com
TECHNlqLLY speal\.lng processed in should tilt at a minimum of 60 degrees. Parts that are very challenging to paint may need to have the basket tilt until it is horizontal to the ground and rotated to properly reorient parts prior to a final high-speed spin cycle to spin off paint via centrifuge. Paint booths can also allow the fin isher to process different paints. (Figure 7 demonstrates the elements that make up a flexible coating booth.) An independent basket is indexed into the paint booth, which allows automatic exchange of baskets to process different typ es of paint or different sizes of parts. The paint tank is on wheels to allow operators to easily change paints. The basket can tilt horizontal to the floor to maximize reorientation of pares , which is designed to prevent head fill or puddles in recesses. To assist in moving parts through
the system and prevent cros s-contamination, the parts should be batch processed in barrels, baskets or trays. All three of these methods allow different types of parts to get processed without stopping the process to create a gap in a machine before processing a new part. A fully automated coating line, when properly utilized, will: reduce paint usage; increase overall productivity ; and increase process control and part quality. Furthermore, it will also reduce tram p material contaminating batches of parts and reduce part damage by controlling falls. SUMMARY
Determining the level of automation that will benefit your facility should begin by taking inventory of the processes with which the parts are treated. In the case of plating plants that offer multiple servicessuch zinc plating, zinc alloy or zinc nickel-sa computer-controlled automated line may allow several
processes to run on a single line. Plants processing different paints might find it advantageous to feed multiple paint lines with one pretreatment line. In the event it is determined that economics do not justify a fully automated system when outfitting a plant, the lines should be planned and purchased to allow expansion and integration in the future. 810
The preceding article was co-authored byAron Lorenz of WMV, Inc., Sylvan Lake) Mich.; Lothar Peukert of WMV Apparatebau GmbH; and Tony Evans and Peter Salmon) PAL Surface Treatment Systems Ltd. For more information) please visit www.wmvusa.com.
ACKNOWLEDGEMENTS
Michigan Metal Coating Company contributed to the parts drop study referenced in this story.
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