Plastics pellet manufacturer eliminates blend problems with uniquely designed rotary blender

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Courtesy of Munson Machinery Company, Inc.

Having no internal moving elements, blender achieves 100% discharge eliminating process problems.

To remain competitive in a widening world economy, manufacturers have to provide quality products at world market competitive prices. This has forced American manufacturers to rethink their approach to manufacturing. Particularly, rethink the cost effectiveness of their manufacturing strategies, and the production effectiveness of manufacturing equipment.

One such company, Diamond / Network Polymers, headquartered in Akron, Ohio, has positioned itself well to meet the demands of the global economy in both existing and emerging markets. Diamond / Network Polymers, through global affiliates, has developed leading-edge technology, manufacturing and supply capabilities benefiting their customers. 

Diamond / Network Polymers is one of the largest producers of ABA and ASA plastics as well as thermoplastics in the United States, offering a full line of these alloys. Diamond is known for its diversity of specialty color polymers, which are supplied for a wide variety of applications in the plastics industry — from automotive bumpers and dashboards, to cosmetic containers.

The Diamond process
Diamond produces plastic resin products utilizing several extrusion lines that each fill into individual Gaylord boxes. Upon completion of a color run it is critical that each box be blended together providing one, uniform homogenous blend of colors. Due to the nature of the polymer's final use, if the batch-to-batch color consistency is not uniform, the customer will be forced to reject the lot for quality issues. Therefore it is imperative that equipment used in the production process be capable of providing the quality end product the customer expects, without fault.

Diamond Polymers originally used a 300 cubic foot stainless steel ribbon blender to blend various streams of extruded pellets. This blender presented numerous quality control issues that needed to be addressed. First, the normal blending cycle produced poor blends. To achieve an acceptable homogenous blend of product required excess blending time. Additionally, the ribbon blender did not discharge 100% of batch materials and operators were forced to physically climb inside the mixing tub to manually clean out the mixer between each batch. Unless proper procedures are followed, physically entering a ribbon blender for cleaning can be extremely dangerous. Finally, batch contamination and blend rejection became a major concern.


Residual material causes problems
Common to all ribbon-style blenders is the clearance between the mixing agitator and the blender body. Because of this, mixed product cannot be fully discharged and leaves large heels of material after each batch. The residual 'heel' of material presented further quality control issues above and beyond the difficulty in cleaning. If 100% of the pellets were not discharged from the blender any remaining undetected pellets within the blender would contaminate the color recipe, the result of which is poor product quality and ultimately batch rejection. Material at this point has to be used as scrap or for black, which are worth significantly less money than the intended color pellets. Along with this problem, the mixer shaft seals buried under half of the batch are a constant contamination problem requiring careful cleaning. Frustrated with this poor record of performance, safety, and downtime, Diamond Polymers decided to research alternative machinery that could provide the results needed to efficiently and safely produce a quality end product. They tested with a shaft mounted rotary style mixer and were dissatisfied with the difficulty in cleaning and the large inaccessible seal. Also, this machine only allowed liquids to be sprayed in a very small area. Their search ultimately led them to Munson Machinery to look at, and test, the effectiveness of the 700-Series Rotary Batch Blender.

Diamond tests Munson blender
Diamond sent three representatives from management, engineering, and production to test the Munson Rotary Batch Blender. Of specific concern was the time needed to blend, blend quality, ease of access for cleaning, and, most importantly, the ability to fully discharge batch contents.

Successful testing
After testing the Munson rotary batch blender, the people of Diamond Polymers were pleased by the results and the Munson design. Lee Wilson, plant manager at Diamond Polymers made comment that the Munson equipment was unlike any other he had worked with in the past. 'The mixers and blenders I'm familiar with use rotating steel ribbon blades to mix materials. The Munson Rotary Batch Blender has been designed with a series of baffles that promote a homogenous blend of ingredients. With the ribbon blender we experienced considerable downtime for maintenance — ribbon blades would bend requiring repair and the associated time required to fully empty product, refill the mixing tub, and blend product was costly. The baffle system of the Munson provides a truly homogenous product blend that is completely discharged, requiring no between-batch maintenance.'

Unlike other blender styles
The Munson Rotary Batch Blender is unlike other blenders in that the vessel is smoothly rotating on massive trunnions at the inlet and discharge end of the machine. Unmatched mixing is achieved with the proprietary mixing flights which gently tumble and fold materials in a omnidirectional pattern. The tumbling action creates an ideal cascading bed of material for liquid spray applications. Batch times are typically in the 2-3 minute range seldom exceeding 3 minutes. Because the entire batch is in motion from the moment it enters the machine until the moment it is discharged, blends with minor additives as low as 1/100 % are accomplished this shortly.

Streamers are no longer a concern
A universal concern among manufacturers of custom colored pellets is the creation of 'steamers' or 'ribbons.' These are caused by friction between the blender wall and a rotating shaft compressing, smearing and elongating individual pellets. These deformed pellets, if shipped and used by Diamond's customer, may clog the customer's extrusion equipment during their manufacturing process causing unnecessary downtime and rejected product. Munson Machinery has found that the gentle tumbling nature of their machine, with no internal moving parts, is ideally suited for this process and does not create any unwanted 'streamers.'

During the processing of some product blends, Diamond is required to introduce a liquid into the blend cycle. Previously installed blenders, and others that had been tested, could not provide a uniform coating of the material or sprayed in a very narrow area and often over sprayed the material causing product build-up on the blender body.

The tumbling action of the Munson Rotary Batch Blender creates an ideal cascading bed of material for liquid spray applications. This cascading bed exposes the entire batch area to spray against. This method ensures no product is over saturated and no material build-up on the vessel's interior walls. After testing was completed Diamond Polymers was very happy with the results of the Munson Rotary Batch Blender. The company purchased a Munson Model 700-TSC-330-SS stainless steel 300 cubic foot blender. Since its installation blend qualities have dramatically increased, cycle times have been substantially reduced, and down-time has been eliminated between like batches. David Gschnell, Chemical Engineer at Diamond Polymers noted, 'In normal production the Munson provides a quick and clean mix of ingredients. It also provides us a much larger capacity and volume per batch than the old ribbon blender. Being nearly the same size as the old ribbon blender, the Munson will handle 11,000 lbs. compared to the 6,000 lbs. capacity we had before. For us this represents almost a 184% increase in production capabilities per batch with no scrap. The Munson also loads faster. The Munson will load 10,000 lbs. of material in half the time the ribbon blender would load 6,000. This represents a substantial increase in production time. With the old equipment we had problems discharging material. The Munson discharges 100% of the pellets, every time.'

Greg Gertz and Keith Williams, Blender/Packaging personnel, also noted the Munson blender, with its series of baffles and no internal moving parts, was safer to operate and maintain. 'The Munson, because it completely discharges all of the pellets, is easier to clean. We no longer have to deal with safety issues of climbing inside the tub. All we do is sometimes wash it down with a hose — from outside the tub.'

Throughout Diamond Polymers there is a total commitment to production quality that leads to quality end product. 'Innovation, dependable equipment like the Munson Rotary Batch Blender, help make quality a reality.'

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