In the adhesives and sealants industry, rotor/stators are used for particle size reduction of various solids. Rotor/stators are commonly used to "cut in" rubber solids and speed up the solution of these solids into various solvents. Sometimes the rotor/stator is used to disperse or break down an additive such as an accelerator or a pigment.
When your objective is an extremely fine "off-gage" dispersion, you are really talking about a sub-micron average particle size with narrow particle distribution. Generally, a media mill is required to achieve these results. In ultra-fine grinding, the rotor/stator is considered a pre-mixing device.
Preparing a good pre-mix for your pigment dispersions can present many problems, especially products with a low starting viscosity. Many times, this viscosity will increase substantially when the pigment agglomerates are broken down and properly dispersed. A traditional high-speed disperser blade is not very efficient in breaking down solids in low-viscosity dispersions because of the absence of hydraulic shear or viscous drag. Many people waste time and energy and put a lot of heat into the batch by trying to beat up a low-viscosity pre-mix to the point where it can be efficiently processed in a media mill.
So, if you have come to the conclusion that you need a rotor/stator, how do you know the type that is best suited for your application? Rotor/stator mixers can be classified in general terms with similar characteristics:
The second most common problem with rotor/stators is dealing with abrasive solid particles. Most rotor/stator devices operate at fairly close tolerances between the grinding surfaces and also contain shaft bushings that are submerged in the dispersion. A small change in clearances caused by routine wear can cause a dramatic drop-off in dispersion quality in some rotor/stator designs.
The VMS rotor/stator was designed with particle size reduction as the main objective but also with a high pumping capability for rapid circulation and blending of liquids for less stringent rotor/stator applications. As standard equipment, the VMS includes an adjustable down-thrust impeller for increased circulation and the ability to handle a wider viscosity range. An abrasive-resistant ceramic shaft coating is also standard to handle dispersions of pigments and other abrasive solids in suspension.
Which rotor/stator is best suited to your application? Consider the characteristics of your product such as temperature sensitivity and abrasive-solids content. Then test different types of rotor/stator devices to get the best combination of flow vs. shear that will produce the results you need for your product - whether the rotor/stator is used as a pre-mix device or to manufacture a finished product.
For additional information on the Vertical Max Shear rotor/stator mixer, contact Premier Mill, A Lightnin Company, One Birchmont Drive, Reading, PA 19606-3298; phone 610-779-9500; fax 610-779-9666; e-mail firstname.lastname@example.org; or visit the Web site www.premiermill.com. Or Circle No. 75.