Volume 10 issue 5

What’s Happening at Missouri S&T:
(formerly UMR)

Short Course Dates

We will be offering "Basic Composition of Coatings"  September 23-27, 2013 (Fall 2013). The Basic Composition course is intended for new personnel in the coatings profession. It targets the components of coatings (resin, pigments, extenders, solvents and additives), testing and specifications, general formulation and manufacturing methods. Basic Composition is primarily a lecture course with several laboratory demonstrations.

We will be offering "Introduction to Paint Formulation"  October 21-25, 2013 (Fall 2013) . This course is intended to give the person a fundamental knowledge of how to approach a starting formulation and troubleshoot it. This course involves both lecture and laboratory work.

For more information see our web site at http://coatings.mst.edu and to register contact Catherine Hancock at cemv26@mst.edu or coatings@mst.edu or call 573-341-4419. **These courses are held on the Rolla Campus**

Online Short Course

We are offering "Introduction to the Coating Systems" online short course. This course is targeted for automotive and aviation type OEM companies. This self-paced seminar will cover the painting system from the composition of paints to the evaluation of the dry film.  The pigments, resin, solvents and additives will be discussed including their influence on the coatings performance.  Color measurement, surface profile, and other evaluation criteria will be related to composition.  The importance of surface preparation and other manufacturing criteria will show the system complexity and each step's importance.

We are offering "Surface Defects: Elimination from Human and Process Contaminants" online short course. This course addresses many of the issues in prevention and minimization of defects. The course covers the defects caused by the coatings process, as well as human issues, including personal care product causes. Several of the surface defects are discussed – from basic principles and real world automotive and aircraft examples. The highly practical approach of this course will greatly aid the personnel involved in the painting operation to reduce and systematically approach issues.

Employment Tab

      We have started an employment section for our students and companies. We have a full time job section, an intern / co-op section and a graduating and alumni students section . Please explore our section on employment on our web site. Anyone wanting to have job opening listed, please contact us at (573) 341-4419 or e-mail: svgwcc@mst.edu . You can also write to us at Missouri S&T Coatings Institute, BOM #2, 651 W. 13th St., Rolla, MO 65409-1020. Our web site is http://coatings.mst.edu

Technical Insights on coatings Science

Recycle of powder coating manufacturing reclaim and end user over spray

Sagar Vijay Gade, Graduate Research Asst., Missouri S&T

     The use of powder coatings have significantly increased in the past few decades. More and more industries have started using powder coatings to produce a high quality coatings with increasing production rates, cost cutting and making coatings more eco-friendly.  Commercial liquid coatings require the use of solvent and hence require venting, filtering and solvent recovery systems to control VOC emissions.¹ The powder coating industry has been attracting more attention since the coating composition is solvent-free, these coating are also efficient, durable, resistant to acid rain and UV rays as well as chip and scratch resistant.

     During the production and the application of powder coating materials, the over spray can be wasted if not recovered and recycled, but if recycled will add to the profit for the end user.  Recycling of powder coating overspray is done for the economy and to make these coatings more environment friendly.  In addition to overspray, the powder coating manufacturer can also have powder coatings with improper size or distribution which is an opportunity for reclamation.

Sources and recycling of powder coating

i. At manufacturing facility:

     Powder coating reclamation is coating powder having particle sizes or particle size distributions, which are not suitable for powder coating application. Electrostatic powder coatings for conventional application (film thickness - 50 microns) usually have particle size distribution in range of 10-75 microns, but particle size range between 10-50 microns guarantees good application properties. Recent thin film application (film thickness - 30 microns), a typical mean particle size would be in the range of 25-30 micron.

     A particle below 10 microns gives low electrostatic efficiency, poor flow characteristics while presence of courser particles gives coating of inferior appearance. Hence the powder coating material reclaim is formed, either in the form of particles with size below 10mm or coarser particles with size more than 60mm.

     In most manufacturers design, the recovery and recycle systems are integral part of the manufacturing unit.² During manufacturing, after premixing and extrusion, the subsequent grinding operation takes place in which material is ground to get preferable particle size in the range of 10-50 microns but still large quantity of material is below the required particle size. Cyclones are employed to remove particles less than 10 microns and sieving, using screen classifier, is done to remove courser particles which both can be termed as powder coating reclaim, which can be recycled by

1. Both, particle size less 10 microns and courser particles are recovered, re-agglomerated using precise controlled heated mixer. Here particles are soften allowing sintering to produce the powder coating agglomerates / pearls, which can be supplied alone or together with powder coating fresh material for extrusion.³
2. Both, particle size less 10 microns and courser particles are recovered and dispersed in water, and wet milled to average particle size of 3 microns to produce aqueous powder slurries. These slurries are stabilize using a low foaming nonionic surfactants and are applied similar to conventional water-based systems.³

ii.  At application facility:

     Powder coatings are applied by electrostatic spraying, tribochrage spraying and fluidized bed methods. Recycling systems coupled with the high transfer efficiency spray booth reduces recovered paint disposal and hence lowers both cost and environmental impact. ¹

     Though the range 10mm-50mm is desired in powder coating application, in spray booth particle size below 10mm gives dusting and particle size above 50mm are not attracted enough to reach the substrate from the spray gun due to their linear momentum. The powder particles that do not adhere to the substrate (overspray) are recovered as a dry powder. This powder is usually recycled by blending with virgin powder.⁴

     There are two general types of recovery and recycle systems: cartridge and cyclone. During the application, over spray, which is the powder coating, can be easily recycled using cartridge and cyclone assembly attached to spray booth. Since the powder coating is a dry powder, most powder coating overspray can be recovered and re-used. The unused powder reclaimed by a recovery unit is recirculating through the system after sieving to remove foreign particles such as hair or lint. ⁵

     Cyclones or cartridge filter modules used in the powder recovery systems can be dedicated to each color and are easily removable and replaceable when a color variation is desired.  With significant design improvements in spray booths and recovery systems, equipment manufacturers allow quick color changes with a minimal downtime and allow the recovery of a high percentage of the overspray, close to 100%. ⁵

     To avoid the installation cost of special spray booths for shorter runs, water washed spray booths have been suggested. The collected overspray is dispersed in the water in presence of a low foaming nonionic surfactant and flocculants and can be readily used as slurry coatings. ⁴

References