The batching together of all the raw materials necessary for one mix of the product
formulation consisting in the main, of full bags (25Kg) of the bulk raw materials and
weighed small amounts to make up the pigments and the small amounts of material above
or below multiples of 25Kg. This material is pre-weighed and batched together ready for
loading into the mixer or mix container. With bulk storage of some of the large volume
materials the total amount may be weighed in with out batching the RM's, depending on
the size of mix(er). Pre-batching is a longer process for each mix but gives the opportunity
to double check each RM into the mixer or mix container so reducing the possibility of
errors in loading.
The physical input of the batch of weighed raw materials into the mixer or mixer container
ready for mixing. It is good practice to load some of the bulk raw material first, resin or
extender and then to add the small ingredients, pigments etc. and then the balance of the
bulk materials. This insures that the pigments will be evenly dispersed at the start of the
mixing sandwiched in the middle of the raw materials. Small amounts of pigment should be
added with the extraction turned down to prevent loss of these additions into the system.
When loading containers it is important that all fine materials are sandwiched so when the
container is inverted the fine materials are not exposed directly to the rotor blade seal.
Tumble mixers are available as fixed container for loading / blending / discharging the
material is loaded into the blender through a hinged doorway in the mixing chamber, these
chambers can be of differing geometry, fixed mixers are usually 'Y' or 'V' shape. The
chamber is pivoted on a central axis to allow material on rotation to be tumbled end over
end of the container. Sometimes fitted with a dispersion blade to aid mixing. The material
is discharged through a valve at the base of the mixing chamber.
The IBC type tumble blender allows the container this is usually rectangular with hinged
doorway for loading and bottom valve for discharge. The rotation on the diagonal axis
allows material to tumble diagonally corner to corner. The IBC tumble blender is used in
many production facilities for powder coatings manufacture.
With simple formulations tumble blending is successful but the mixing cycle time of (30-40
minutes) is generally over 100-200% longer than the using high speed shear blade mixer.
There can be problem's of segregation if incorrect or extended mixing times are used with
the range of particle size and shapes in the pre-mix.