POWDER & BULK SOLIDS - Editorial-Technical Feature:
Dramatically Increasing Equipment Life and Batch Efficiency In Hi Speed Mixers/Blenders and their Tools using Thermal Sprayed Coatings

Overview
During the compound mixing process the additive materials that increase hardness, whiteness, extenders, and regrinds in the plastic, create excessive abrasion wear to the mixing tools and the vessel liner walls and metal entrapment in the compound. This wear condition reduces the performance of the Heat Mixers by decreasing shear and reducing the incorporation rate in pounds produced per batch and increasing cycle times. This problem is also experienced in Cool Mixers where proper distribution is key to effective temperature reductions and lower batch times. In today’s price sensitive production climate the need to provide longer wear life of these mixing components is very important. Thermal Spray Coatings are the key element to the success in longevity of blending equipment. The coatings are engineered to fit your compounding requirements.

Proper Geometry
All manufacturers utilize different designs of mixing tools. The tools have been tested to produce the rated performance in production output. The geometry they employ affects the formation of a viable vortex. It also provides proper Hi-Shear pressures to increase temperature at a recommended rate and proper incorporation of the additives and formation of the particle.

Wear
Beginning with the installation of a new set of mixing tools, contact with the compound starts the wear process. Depending on the type of material that is compounded the wear rates vary greatly. Typically the tips of the mixing tools are the first to go. This loss of parent material is very gradual but metal is being removed. The majority of stainless steel mixing tools, are not magnetic, therefore the use of magnets are not effective in the elimination of contamination in the compound. Even screens will not filter out all of the metal. That metal is carried in your compound particle and passes through the downstream equipment causing wear in them also. The thermal sprayed product particle size is much smaller in size and the wear rate very slow so that it is not noticeable. Mixing vessel liner walls are also being washed out and formation of holes is always a problem to the compounder.

Hardfacing is not the answer
Many manufacturers have attempted to utilize hardfacing techniques to provide an edge against wear. The problem with hardfacing mixing tools is they tend to increase parent material stress and also alter the design geometry of the tools. You have to heat the mixing tool to excessive temperatures to allow the hardfacing material to bond to the mixing tool creating a chemistry change in the substrate. If you have ever used this type of coating you will note excessive wash out behind the coating and chunks of material coming out of the compound when they break off.

Thermal Sprayed Coatings are not all the same
Proper selection of coating materials and their bond strengths are imperative. There are many types of equipment on the market today offering a wide variety of coating applications. Not all, thermal systems are capable of providing the quality of coatings required for your use. The proven method is the use of Plasma or Hi-Velocity Oxy Fuel sprayed coatings to provide the high energy and high bond strength required in high pressure shearing. This type of equipment is expensive and requires a high degree of experienced technical ability. Rigid inspection methods and part preparation are required for successful applications. The use of technician hand spraying is discouraged because of variations in application thickness, stand off distances, laminations, and heat checking can occur. Coating the entire surface prevents washout and metal loss. Proper polishing and balancing insures peak performance and extended use of your compounding equipment.

Longevity of Compound Equipment is proven with the use of Thermal Sprayed Coatings
We have examples of customers using 50% fill rates and experiencing 3-4 times the original equipment life using thermal sprayed coatings. The cost savings is multiplied in batch consistency, lower maintenance costs, lower capital equipment expenses, and limited down time. Also the fear of using fillers is eliminated. The benefits are too great to measure. Now you allow the coating to wear not the base material and your repair costs are reduced to only the coating replacement.