Exploring the Benefits of Wet Milling
The size reduction of powder particles is an essential part of material processing. Reducing the particle size of materials after granulation, allows manufacturers to achieve a faster and more consistent drying process.
Here are some of the process advantages of wet milling pharmaceutical powders;
> During processing, any lumps are reduced to smaller particles with a narrow particle size distribution (PSD). This therefore increases the surface area of the product, to improve the evaporating process and thus, reduced the overall drying time.
> The process of wet milling prevents case hardening. This is an undesirable scenario where the surface on the outside of a lump or particle dries quicker than the inside and seals in unwanted moisture. Because case hardening is prevented in wet milling, this results in a more consistent drying process.
> As wet milling undertakes particle sizing sooner in the process, then final particle size reduction after drying does not need to be as aggressive. It also often means that the PSD is even more uniform, further improving powder flow and the quality of the final product.
> The method of wet milling is also ideal when an active pharmaceutical ingredient (API) or excipient is heat-sensitive and cannot be subjected to higher temperatures.
In conclusion, wet milling produces a uniform particle size in addition to increasing the surface area of a material. This leads to a quicker drying process and also benefits the quality of the finished product.
Uni-Mill (Under-Driven) for Wet Milling of Powders
Typically, the conical mill is positioned at the outlet of the high shear mixer / granulator. The material is discharged through the in-line mill and then vacuum transferred to a downstream container or process machine, such as drying equipment.
For wet milling applications, such as de-lumping wet mass granulation, the mill works best with a slotted or square hole screen. These screens have larger hole openings than is used for final particle sizing, allowing the material to pass through the mill quickly and prevents the build-up of product which might cause the equipment to become blocked.
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