1 ALTERNATIVE RECOVERY METHODS FOR )

Size: px

Start display at page:

Download "1 ALTERNATIVE RECOVERY METHODS FOR )"

Olivia Payne
6 years ago
Views:

1 1 ALTERNATIVE RECOVERY METHODS FOR ) /, YOUR OVERSPRAYED POWDER: \ A COMPARATIVE ANALYSIS / David Has kins & Annessa Wyman Nordson Corporation Powder Coating '94 Proceedings 167

2 INTRODUCTION Recovery is defined as the process of removing non-deposited powder from the air. This powder can be collected and scrapped or it can be collected and conditioned for reuse. Powder coating has several characteristics that attract companies to consider it over conventional liquid spraying and other coating techniques. One of the most notable advantages is the ability to recover and even reuse such a high percentage of the oversprayed material that in most finishing methods would have to be discarded. Recovery is accomplished with either a cyclone or a cartridge filter collector. Collection systems must address several important requirements such as ease and time of installation and color change, minimal operational noise levels, safety approval for fire and explosion prevention, and containment of overspray to limit worker exposure to name a few. Powder recovery can be approached with two concepts, either a single booth or a multi booth set-up. In this paper we will discuss various recovery systems, some of the many ways they can be configured, and the major objectives that need to be considered when selecting the recovery method that is most appropriate for you. Keep in mind that each situation is different and must be analyzed on the merits of its own conditions and objectives. Depending on the number of colors, types of powders being sprayed, floor space, capital expense, and many other objectives, what works for one company might not work for another. 168 Powder Coating 94 Proceedings

3 SIZING A POWDER RECOVERY SYSTEM To properly size a powder recovery system consideration must be given to the following: - Total square footage of opening needed in the booth (Openings for parts to entedexit, gunslots, conveyor slot) - Number of powder guns needed (both automatic and manual) to obtain a given film build Gun mounting for automatic guns (fixed or moving) - Desired line speed Part configuration, height and temperature - Hook length measured from hang point to top of the part Example - A.B.C., Incorporated needs a powder booth. For the purpose of discussion we will make the following assumptions about their design specifications: - The parts will enter the powder booth at a temperature not to exceed 120" F Maximum part size = 18" deep x 48" H x 48" L Mil Thickness Mils on all surfaces Line Speed = 14 PM Automatic Guns = 10 (5 per side) Gun Mounting Device = vertical oscillators Manual Guns = 2 (some parts will require manual touch-up) Minimum Hook Length = 24" In properly sizing the collection system you must consider the canopy design. We will use a 6" clearance on all 4 sides of the parts giving an end opening dimension of 2.5' W x 5' H Powder Coating '94 Proceedings 169

4 To arrive at the total square footage of opening space needed, review this sample air containment calculation: Type # of Openines &EQQ&s End Opening 2.5' W x 5' H X 2 Manual Gun Openings 2.5'W x 3' H X sq. ft. 15 sq. ft. Auto Gun Slots 6" W x 5' H X 4-10 sq. ft. Conveyor Slot 4" W x 25' L X 1 = 8.25 sa. e sq. ft. Typically, booth fans are sized to yield an average air velocity of FPM across all openings. Therefore, for this model you would need sq. ft. x 120 FPM = 6,990 CFM of containment air to adequately contain the oversprayed powder in the booth, yet not draw the powder away from the part. In a detached collection system (Cyclone recovery or a combination cyclondcartridge reclaim system) the extraction rate of air from the booth hlfills a safety fbction and that volume must be adequate to maintain a safe ratio of air to powder mix. The booth must be sized to minimize any possibility of excessive concentrations of powder being suspended in air and causing a potentially hazardous situation.

5 This is true when a powder system contains components that could be considered tight enclosures such as ductwork, closed collectors, cyclones or any other structure that does not have a sufficient pressure relief opening area. Additional safety features (slide gates, explosion venting, etc.) must be more critically reviewed to provide relief of intend pressure. To determine the proper air flow in such a system the following calculation could be used for the ABC Inc. model: - Total f# of guns = 10 auto + 2 manual = 12 - Typical L.E.L. (Lowered Explosion Limit) of powder to be sprayed = 0.03 oz./ft - Typical maximum powder output per gun = 8.5 Oz./minute or 32 Ibs/hr. - Safety factor = 2 Formula Max outtut (oz\min\md X number of guns X safetv factor = safetv air required LEL Calculation 8.5 odmin x 12 mns x odft = 6,800CFM If the air containment figure is the higher of the two numbers use it in determining the size of powder booth air capacity. For our model we would design the booth capable of 6,990 CFM. Powder Coating 94 Proceedings 171

6 METHODS OF POWDER RECOVERY Once the recovery system is properly sized the next and more difficult decision of choosing the recovery method must be reached. For our discussion we will consider six methods of dealing with the oversprayed powder: - Non reclaim cartridge booth system (on line or batch system) - Cyclone recovery system - Reclaim cartridge booth system (1 booth) - Reclaim cartridge booth system (2 booth on-off line capabilities) - Combination cyclone and cartridge reclaimlnon reclaim system - Cyclone booth and cartridge reclaim booth /on-off line capability NON RECLAIM CARTRIDGE BOOTH SYSTEM Many people who make their first venture into powder coating do so using an off-line batch type booth. (figure 1). While a batch booth is considered flexible it also has its limitations. It is generally used in situations where production is in low volume or parts are very large. Floor mounted models allow for large parts to be rolled in on carts or carriers. 172 Powder Coating 94 Proceedings

7 Depending on the size of the parts to be coated, the operator may stand outside the booth or may walk in and around the parts as he coats it. Generally oversprayed powder is manually removed for disposal. Batch booths can also be used in larger systems as a sample booth. (FIGURE 1) For those needing higher production capacity but still spraying many low volume colors, an on-line non reclaim cartridge booth might be the answer. Normally these booths are set up with 2 to 4 manual operators depending on the line speed and part complexity (figure 2). Typically powder is pumped from round "quick clean" powder hoppers or directly from the supplier's container via a box unloader. As volume increases for a particular color, a reclaim module can be purchased for that color or colors.

8 Color change time can be as short as 5 minutes when using multiple feeders and booths with walls and roof designed with non-conductive materials such as polypropylene or polyethylene which minimize color contamination. First pass transfer efficiency is critical when considering any non-reclaim system because any powder that isn't attracted to the part through the electrostatic process is disposed of as "scrap". Therefore the profitability of the non-reclaim style finishing line depends greatly on keeping powder overspray to a minimum. Such the term "spray to waste" (the oversprayed powder is not recycled). Typically transfer efficiencies in such a system range between 35% - 70% depending again on line speed and part configuration. The addition of automatic guns on complex parts does allow higher production rates but may lower the 1 st pass efficiency. Floor space requirements are minimal on this type of system. (FIGURE 2)

9 CYCLONE RFCOV- Cyclone collection systems utilize a booths enclosure, extraction duct work, a cyclone separator, detached cartridge collector, exhauster and final filter housing (figure 3). The cyclone separator is located between the booth and the cartridge collector connected by ductwork. The cyclone separates the powder by creating a centrifugal force assisted by gravity to force particles out of the airstream where they are dropped to a reclaim canister to be manually removed or automatically pumped by to a feeder hopper. As the air stream, now containing only the fine powder particles, reaches the cone shaped neck of the cyclone it is forced up the center of the cyclone. From here the air is drawn by a blower motor through another section of ductwork to a cartridge filtration unit and then exhausted through a set of final filters into the powder room. Because of the high velocity of air entering the top of the cyclone (typically 3,500-4,200 FPM), certain powders are not reclaimed well in cyclones. (FIGURE 3) EXPLOSION EX P I.. 0 S I ON - VENT DUCT d I I I I I VENT DUCT BOOTH CYCLONE COLLECTOR FAN/SILENCER/ FINAL FILTERS (FIGURE 3)

10 The footprint required for a cyclone system is large when compared to a cartridge reclaim system. The most effective cyclone is one that is tall and slender, therefore room height must accommodate such a unit. Special consideration must be given to safety in a cyclone system because of the presence of "tight enclosures". Designed into the system should be an approved Fire Detection System, slide gate interrupt in the duct work between the cyclone and the cartridge house, explosion venting and relief duct work to an unoccupied area of the plant. This makes first pass transfer efficiency crucial. The higher percentage of material that adheres to the parts in the first pass, the smaller the percentage to be recycled and potentially lost in a cyclone system. Color change time between reclaimed colors can vary greatly. For a booth the size of our model discussed earlier, the time might range between 40 minutes to 1 hour. In addition to cleaning the booth enclosure and the guns, the lower 1/3 of the cyclone should be cleaned and the recovery canisters removed. Some powders may require special cleaning to the duct work such as glass beads as a scouring media or use of compressed air. 176 Powder Coating '94 Proceedings

11 The largest advantage to a cyclone system is its ability to recover multiple colors at a fairly high recovery rate within a single booth without the cost of multiple cartridge modules. RECLAIM CARTRIDGE BOOTH SYSTEM (1 BOOTH) Cartridge reclaim systems use dedicated color modules for each reclaimed powder (figure 4). During the coating process oversprayed powder is drawn by an exhaust fan to a set of cartridge filters or primary filters in the color module. Air used to contain and recover the oversprayed powder passes through these primary filters. The powder is separated from the air stream by the cartridge media. The air continues through the exhauster to a set of high efficiency final filters where the superfme particles are removed before the air is returned to the facility as clean air. The powder lefl on the cartridge media is discharged by a reversed pulse of compressed air blown down through the filters. For best cleaning no more than one filter should be pulsed at a time from a single air manifold. Cartridge filter orientation varies from horizontal to slant mounted to vertically mounted. For best cleaning, filters should not be stacked above each other. This ensures that powder drops into the collection area, and Powder Coating 94 Proceedings 177

12 not onto other cartridges. The advantage is for better operating efficiency and extended filter life. (FIGURE 4) Powder that is discharged from the filters is dropped into a reclaim fluid hopper where it is pumped back to the feeder hopper via a transfer pump. The standard cartridge filter media is made for cellulose fibers. For extended cartridge life and an enhanced powder discharge rate when pulsing, a polyester fiber is being used by some companies. System efficiency for a cartridge reclaim system generally ranges between 96% - 99%. This method of recovery is highly effective when recovering high volumes of powder at high production rates.

13 Color change time in a cartridge reclaim system will range between 30 to 45 minutes. This time can be minimized by use of non-conductive booth canopies such as rigid polypropylene and air flow enhancements through variable speed exhausted motors. Once the guns and booth are cleaned that color module can be disconnected, rolled away and the next module rolled in place. For ease of color change each module generally has it's own feeder hopper and powder feed hose (figure 5). As the number of reclaimable cuiors increases, the flexibility of the single booth cartridge system begins to fade due to increasing capital for more modules. Quite often colors can be grouped into major and minor categories with the minor colors being sprayed into a non reclaim module.

14 CLAIM SYSTEM ON/OFF LI- A two booth cartridge reclaim system presents a high degree of flexibility in many areas. Nearly all commercially available powders can be recovered and recycled in the 96% - 99% range. Floor space requirements can be kept within a reasonable range while maintaining a high degree of safety in operating the system. One of the most important advantages of a multibooth system is the ability to change colors within minutes. This is accomplished by rolling the one booth which color you have just finished painting, off line via floor tracks, and rolling the 2nd booth on line for the new color. The first booth which is now off line can be cleaned and prepared for a 3rd color by changing modules. Short run colors can be handled without interrupting production by acquiring a non-reclaim module to be used with either booth (figure 6 and 7) I I W

15 Parts are being painted green while the second booth is being readied for yellow. When the line gap arrives in the powder room the green booth is rolled oilline where it can be readied for the next color if necessary. The yellow booth is rolled on line to paint the next set of parts yellow.

16 This process can take place in just a matter of minutes depending on the length of the powder booths and the distance between them. For handling short runs of various color sometimes the most practical solution is a manual non-reclaim booth with the second booth handling the large volume colors operating with automatic guns and manual touch up if needed (figure 8) 1 U In this situation one short run color can be introduced almost immediately after the previous color. The time needed for this change over should allow the operator to purge the handgun with compressed air, disconnect and connect another powder feed hose and allow all atomized powder to be cleared from the booth and drawn into the collector. Non-conductive walls and roof panels aid in this process and minimize the chance of cross contamination. Multiple quick change feed hoppers or multiple powder box unloads also help.

17 BOOTH Another method of recycling powder is to combine two previously discussed methods into one booth. The combination booth integrates the cyclone recovering system along with the cartridge reclaim system. This system has a moderate to high degree of flexibility which can be further enhanced by adding a non-reclaim module for low volume scrap colors. When running high volume colors it is best to utilize the cartridge reclaim module or modules. For the multiple lower volume colors the module can be replaced with a section of extraction ductwork which carries the powder to the cyclone separator (figure 9) where it is returned to the feed hopper. (FIGURE 9)!! I i \ i t m i i i

18 The major advantage of a combination system is that it allows you to recover both major and minor colors at rates between 80% to 99% while avoiding the cost of additional color modules. Although the up front cost of this type system will be higher than a single color cartridge system, after the third or fourth reclaim color is added the advantage swings by to favor the "Combo" booth. You must also weigh the long term applied cost effect of recovering powder through a cyclone at the average rate of 85% vs. a cartridge system in the high 90% recovery rate. When considering a "Combo" system remember the added safety requirements of installing a cyclone booth. Color change time can vary between 20 minutes to 1 hour depending on the sequence of colors and the method of collection being utilized. One manufacturer builds a combination booth which gives the option of changing the cyclone recovery to cartridge non-recovery without removing any components of the system. this is accomplished by redirecting the exit flow of powder from the cyclone directly into the scrap module. A combination system can sometimes give the end user the security of knowing that whatever the color combination needs might be in the future he has a system that will handle it. At the same time he may limit his flexibility, due to color change time with a single booth system. 184 Powder Coating '94 Proceedings

19 CYCLONE BOOTH AND CARTRIDGE RECLAIM BOOTH WITH ON/OFF LINE CAPABILITIES Another solution to your coating needs might be to purchase a cyclone system and a cartridge reclaim system. For maximum color change flexibility, both booths should be able to roll odoff line. The cyclone booth will require a section of ductwork that can be detached or rolled away (figure 10). r REMOMABU DUCT SECllON 1 4-

20 This system allows for maximum color change possibilities with minimum color change time. Both reclaim and non-reclaim colors could be run in either booth. This allows you to meet J.1.T demands without sacrificing desired recovery rates on high volume colors. The price of such a system will be higher than others discussed, although normally cost justifiable for the high volume producer with a large number of colors to be reclaimed. As with any cyclone system, safety and room ceiling height requires special consideration. Also, the footprint of this two booth system will exceed that of a similarly sized 2 booth cartridge reclaim system. tkx&wqh Referring back to our model, let us assume ABC Inc. wants to start powder coating their product. Their customers vary in the color they desire, therefore we have numerous colors required all in small volume with many color changes per shift. The two most logical choices would be to purchase a non-reclaim cartridge system or a cyclone system. If the production requirements were low enough, an off line batch booth might also solve their coating needs. Powder Coating 94 Proceedings

21 On the surface the cyclone system would seem to make the most sense because of its ability to reclaim the numerous colors. Although color change time may cost more in lost production than the savings from recycling the powder. For someone just getting into powder coating, the capital cost of the equipment weighs heavily in the decision. In this case the non-reclaim cartridge system would be the most economical choice. SCENARIO #2 Now let us assume ABC's production needs are much higher with the number of colors \ reduced to a more reasonable number, say 4 to 6. All of these colors are nearly equal volumes. Color changes can be held to three per shift, but color change time must be minimal. A two booth ordoff line cartridge system would be a good choice in this scenario. Off line color changes would minimize production loss and add system flexibility. This two booth system would require less floor space than any other two booth set up. If initial capital outlay is a problem, purchase one booth with multiple modules but design the powder room to accept the second future booth. A cartridge reclaim powder booth will always provide the highest powder recovery rate of any system currently on the market. By design, the short, closed loop powder recovery path causes the least amount of damage to the recovered powder particles. This will Powder Coating '94 Proceedings 187

22 reduce rejects caused by changing film variance because the recovered powder and the virgin powder are very close in particle distribution. SCENARIO #3 For our final scenario let's consider A.B.C.'s color mix and production requirements consist of two major high volume colors and 8 to 10 lower volume colors, but still significant enough to merit reclaiming. One choice might be a combination booth with 2 reclaim modules for the high volume colors, with the rest of the powders being recovered through the cyclone. This allows A.B.C. to reclaim all powder with a moderate to high degree of flexibility. The floor space required would be more than a single booth cartridge system but less than a two booth system. The pricing would follow the same guideline. The major limitation with this type system would be loss of production due to color change time, which is basically true for any one booth system. Another choice would be to install one cyclone booth and one cartridge reclaim booth, both on roller bases. In system flexibility this set-up would be most beneficial for A.B.C., but would likely require the most floor space. Depending on the number of reclaim modules used in the two cartridge booth scenario, this system could be the most expensive. 188 Powder Coating '94 Proceedings

23 ~ Color Refer to the following chart for a comparison of all the discussed recovery methods and a list of set-up considerations. COMPARATIVE ANALYSIS OF VARIOUS RECOVERY SET-UPS Capital Equipmsnt Camidgc Booth * Floor Space Required Ceiling Ht of Powder Rwm Requirements System Efficiency 35.70% Time and Difficulty '5.20 Mi"$ * Far handguns one Booth >yolone Recovery systsm ~ % 40 - Mins - 1 Hour One Booth Two Booths Combination Camidgc Reclaim WMf Line Cyolone & system Capability Camidge Redaim Camidge Reclaim I Non Reolaim System Booth 2' 5 4 For up to 2 COl0,S I fl. 13A. ZOA % 96.99% Cyclone 80-92%. Camidge Rsclaim 96-99% Minutes 2-5Mins varies greatly. ' Calor change depending on done off line production sched. and whether COIOTS are to bc no limed 20 Mins - 1 hour %derate D s p I Lowest Degne 1 High Degne I Modcrate to High Cyclone Booth and Cartridge Reclaim Booth OniMfLine Capability 6 5 ZOfl. Cyclone 80.92%. Camidge Redaim 96-99% 2-5 Minutes 'Color change of line Highest Capability and Duchvork safety Built In NotNposssary Additional safeguards NeCeSSW Yes Not Necessary YCS Yes - but more oomplisatcd High Degree High De- Additional Safeguards NPOWUQ, NO NO YCS Yes -more camplioated for cyclone booth Additional safeguards 0" Cyolone system, High Degree on CamidgeBooth Yes 3 I that can be utilized All types iome Limirations All types All types Some Limitations All types, difficult powders should be run in oamidgs system - Line Speed 14 FPM - IO Auto & 2 Manual Guns Part opening 5' High change accomplished with a crew of 2 people L&eend 1 -Most Desirable 6 -Least Desirable Powder Coating '94 Proceedings 189

24 :O" It should be obvious that deciding which type powder system to purchase is not an easy decision. It will require extensive research to analyze current production requirements, customer needs and market trends, as well as looking to future requirements. When you approach this process in a logical and methodical matter you can be sure you will make the correct decision for your company. 190 Powder Coating '94 Proceedings

25 1.. About the Authors... David Haskins is a graduate of North Carolina State University with a Bachelor of Science Degree. He was Project and Research Engineer for several companies prior to joining the Nordson Corporation in 1980 as a Sales Engineer. Mr. Haskins currently resides in Atlanta, Georgia as a Regional Sales Manager for Nordson s Powder Systems Group. Annessa Wyman is an Inside SaledService Representative with Nordson Corporations Powder Systems Group located in Amherst, Ohio. She joined the company in Ms. Wyman is currently completing her B.A. in Business Administration at Baldwin-Wallace College in Ohio. Powder Coating 94 Proceedings 191

COLOR CHANGE SYSTEMS FOR POWDER COATING APPLICATIONS

COLOR CHANGE SYSTEMS FOR POWDER COATING APPLICATIONS Ken Kreeger Powder Systems Group Nordson Corporation Published by Nordson Corporation Introduction Color change is a critical issue most companies must