Coatings World - MAY 2017

Mobile processing system for product development with a powder hopper, induction hose and tube

Agglomerate-free mixing

By: Dr. Hans-Joachim Jacob, Process Engineering, Ystral Rick Isherwood, President, Powder Technologies, Inc.

Producing products that perform as expected is not an easy task when their manufacture requires mixing powders into liquids. The quality of the final product is highly influenced by the wetting and dispersing of the powders used in creating the product. Particularly good results are achieved with the Ystral Conti-TDS, which inducts the powder dust-free, disperses it under vacuum and distributes it homogeneously throughout the carrier liquid without any agglomerates remaining.

To have coatings achieve optimum coverage or glues provide proper adhesion, all powdery material used in its manufacture needs to be effectively dispersed. This can be difficult because powder particles have an enormous surface area requiring wetting and dispersing.

Indeed, these surfaces can quickly add
up to over 1 million feet² per pound of
powder. Consider: when powder is
mixed into liquids by conventional
means using stirrers, dissolvers,
injectors or inline blenders, the
particles come into contact
with the liquid as a dense,
bulk product. In these
set-ups, the liquid can only
wet a portion of the
particles due to
the mismatch of the large surface
area of the powder and the very
small surface area of the liquid.

Agglomerates are an inevitable
result leading to yet another obstacle
– trapped air between the powder
particles in the agglomerates.
This locked-in air cannot escape
and further hinders penetration of
the liquid.

To achieve the desired mixture, these partially wetted agglomerates have to be destroyed by long stirring or additional dispersing – something which is only rarely desirable. For example, in dispersions and lacquers, the additional stirring process stresses the binder and impacts quality, while with polymer or active ingredients, the product is heated up excessively and has to be cooled down again.

Also, these additional processes require time, energy and capacity in the vessel – increasing costs of production. The air in the product becomes detrimental to the dispersion of the agglomerates when the inline dispersing is carried out immediately after the powder has been added, either using the same or another machine. The air is actually finely dispersed and stabilized in the product.

The Ystral Conti-TDS totally avoids this problem by offering agglomerate-free wetting and dispersing. Due to its optimized and patented tool geometry, powder and liquid are immediately mixed and dispersed with maximum turbulence at the very first contact. Because powders have very different properties – in that they can attract liquids or repel them and they can swell, stick, thicken, be abrasive or sensitive to shear energy or even react with the liquid – the Conti-TDS can be easily adapted to specific conditions, and if necessary, equipped with several powder inlets to meet these challenges.

Consider the difference
with the Ystral Conti-TDS

· It offers a shear gradient that is about a thousandtimeshigherthan what is achieved withconventional mixing systems. Its complete mixing energy is applied in a tiny space resulting in very high energy density that is directly converted to wetting energy. Even particularly problematic products can be dispersed without any difficulty.

· It builds up a strong vacuum inside the wetting and dispersing zone and inducts powders directly from sacks, hoppers, big bagsor silosintoliquids. Particles of the powders are