Avoid blending blunders

Selecting the correct device is crucial to successfully handling solids. It must deal with discrete pieces that have physical size, electrical properties, frictional differences and surface characteristics that can change with the environment.

By Tom Blackwood, Healthsite Associates

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  • Don’t over-blend. Determine the correct blending time, speed and fill for each mixture and ensure that they’re used. Over-blending leads to attrition, heating and change in surface characteristics of the solids. If you must take samples during the blend, shut off the blender while the sample is analyzed. This is especially true if the sample size must be large to be representative. Return the sample to the blender before proceeding, if possible.
  • Use statistical methods to find hidden variables. Subtle changes in humidity, temperature and even the operator can influence blending. Emphasize using six-sigma methodology when developing the correct blending parameters (time, speed, etc.) for each type of blender.
  • Select the correct blender. While it may be easier, simpler and keep capital costs down to use one blender, as this article should’ve made clear, a single type of blender can’t handle all materials. Use Table 1 to find the most likely candidate based on the type of particulate solids being blended. However, keep in mind that this table only gives general patterns of behavior. It may be necessary to do flow testing to determine if the solids fluidize or have a strong tendency to segregate. If you don’t have the correct device, rely on a toll producer until you can afford one.
  • Consider clean-out. It’s not economical to have a blender for every product. So determine what cleaning between products will entail. Plows and ribbons are very difficult to clean and fluidized blenders may build up coating in hard-to-reach places. The more internals in the blender, the harder it will be to clean.
  • Test, test, test! This isn’t always the most practical suggestion due to the cost. Flow testing is an expensive proposition but can improve both the selection and operation of a blender. However, reserve it for high value or high volume products, especially when the blender choice is in doubt. A less expensive version of the testing scenario is to match the sample size to the packaging size and use statistical techniques to reproduce the correct operating conditions.
  • Make a solid start

    To select the best blender follow a systematic approach that considers where the blender fits in the process and the difficulty of the material. The amount of testing required can be a confusing issue. You can base some selections on similar materials being handled but other materials will require extensive and more expensive procedures. However, often there’s no single correct answer. Temper any expert opinions with an evaluation of overall process needs and potential problems. Ill-founded certainty is far worse than a realistic appreciation of the confusing issues.

    Tom Blackwood is director of technology for Healthsite Associates, St. Louis, Mo. E-mail him at trblac@att.net.

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