Powder Mixer - How Do I Calculate the Mix Time Required.

Firstly if you are buying a new mixer, you have hopefully done your home work. Often our product we want to mix is not an Ideal mixture of particle sizes. With a wide variation in particle size it is more difficult to obtain the mix we require. Mixtures with the same or close particle sizes can produce a mix in the correct equipment often faster than a mixture with a wide particle size spread. ?

However we have a product to manufacture, so ensure you share you raw material data with the mixer suppliers.?

Trial Mix

Often suppliers will have a pilot mixer to carry out trials. You should use this opportunity. Ensure you plan and control the trial in your way. You can use the methodology below to measure mix times. Ensure you take lots of sample bottles and labels to the trial. One thing to remember, even when trials give good results on the installation of the mixer in your plant, you must repeat all the tests. Whatever the supplier tells you, only tests will prove if mixer has good scalability from a pilot machine.

Mix Time Assessment Procedure

I am providing you a simple but effective procedure, this does not stop you reading numerous information from quality Chemical Engineering books, this will offer even more insight to the challenges in mixing products.

Firstly batch size, all mixers have a minimum and maximum volume that they will mix efficiently. DO NOT be tempted to go outside these parameters as the mixer efficiency is greatly reduced.

Batch size organised and raw materials ready for loading. The Mixer supplier will have given you an expected time to achieve your mix. An example could be a Plough Shear Type mixer fitted with an interrupted ribbon and supported with High shear Mixers (Choppers). From your trials and the mixer manufacturer you are expected to achieve a mix in up to 3 minutes for the batch.

Load your raw materials in to the mixer with it running to even the load, once all loaded start the mix time and run for one minute. Stop the mixer. Open up the mixer doors and take 10 to 20 samples from different parts of the mixer. Label the samples.

Start the mixer and run for another minute, stop the mixer and repeat the sample procedure, ensure you label correctly.

Start the mixer and run for a further minute, stop the mixer and repeat the sample procedure, again ensure you label correctly.

Now it is time to test the three mix time samples. Below might be what you achieve after one minute.

Note many samples are giving results outside the QC limits. So clearly this is not acceptable. At 2 minutes maybe a slightly better result.

Now on to 3 Minutes:

Now we have all but one test result that is still on the boundary n specification. This would be a good result, we have a good Random Mix.

Now you must repeat with a new batch but complete a 3 minute mix time then a full sample testing as above. If the result is within the test specification boundaries you have your mix time. Mix times can be refined to lower the time especially across different products but follow the same procedure even with half minute intervals.

This was just a short introduction to finding the correct mix time for your product. If you require help on Mixer Choice and achieving the correct mix time on Installed equipment I am available to assist.