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The Inversina has many interesting qualities that other mixers cannot offer. This has led to the result that the Inversina is used in a vast variety of applications, where a high degree of homogeneity is important, the ingredients have to be treated gently, or where the mixing ingredients cannot be mixed in any other mixer.

The Inversina is the technical realization of the Oloid: the edges of the mixing container in a 50L model equipped with light fixtures and a time exposure camera makes this visible:

The challenge of building a mixer with the Paul-Schatz Principle caught the attention of Bioengineering AG, the Swiss Technology Firm that invented and still manufactures the Inversina. The idea was intriguing, but the task wasn’t easy: it took a team of engineers and mathematicians more than one year to derive the exact formulas and parameters that allowed for the Inversina to work. Finally, after many sleepless nights, the 2L model was born, followed by the 20L, the 50...350L Inversinas and the manual Inversina.

What are the optimal mixing parameters (fill volume, rounds-per-minute, mixing time)?

These parameters are highly process-specific and should be optimized individually for each application. These are our generic benchmark recommendations:

• Dry, light powder: Fill to ca 2/3 of total volume and check results after 3, 5, 10, 15, 25 minutes. RPM: 45-60 (manual / 2L Inversina), 20-30 (20L Inversina), 15-20 (50L Inversina and larger)
• Dry, heavy powder: Fill to ca 50% of total volume, mix ca twice as long and at half the RPM of light powder. Very heavy metallic powders, such as tungsten carbide: mix at 5-15rpm, for at least 15min and up to 4hrs.
• Liquids: Fill 95%, mix at max RPM. Final results can usually be obtained after just a few minutes.

To optimize mixing, we recommend changing one parameter at a time starting with RPM. Higher RPM does not always mean faster mixing– especially if mixing speed inhibits flow of ingredients in the mixing container. If you suspect you might be mixing too fast either decrease RPM or reduce fill volume.

What type of ingredients can the Inversina mix and why do you claim that it is better than other mixers, such as rigorous hand mixing, V-blenders or cone blenders?

The Inversina moves in a special figure-of-eight-3D rotating fashion developed by Paul Schatz. This effectively inverts the ingredients with every rotation.

This motion excels at homogenizing dry powders, liquids, powders + liquids, solids, and particles of different shape, size, or specific weight (such as pellets and fine powder, wet and dry powders, etc.) in any concentration – even if one of the ingredients makes up only a trace amount of the total volume.

In the vast majority of applications the Inversina substantially reduces mixing time and improves results (scattering of samples, reproducability, p values, etc) while providing a much more gentle mix. There are even some applications in which only the Inversina is capable of delivering satisfactory mixing results.

The Inversina can however not

• knead dough-like materials
• prevent caking in powder-liquid mixes if powders are not soluble
• cope with very viscous materials unless they have water-like flow properties (in other words olive oil is fine, ketchup will need lower rpm and will take longer, while tar is problematic)

How do I measure homogeneity?

In general a sample is obtained and compared to the theoretically perfect result of 100% uniform distribution, or the standard deviation is compared to an alternative method (other mixer, longer mixing time, lower rpm, etc). If the end-points are very critical, a formal scientific hypothesis and tests for robustness as well as stringend pass/fail criteria must be set up in advance. However, to just get a rough idea we can suggest the following basic testing procedures:

• If ingredients have different specific weight: Take sample of constant volume from various batches, obtain standard deviation to calculate confidence intervals, p values, etc.
• If ingredients have identical specific weight:
  - Visual test (if materials have same color use dye)
  - Use other properties to evaluate homogeneity of sample (works well if for example one ingredient is water-soluble, magnetic, flammable, etc – and the other is not!)
• Take very small volume sample and count particles

I mix very heavy powders. Can the Inversina cope with this weight?

All Inversinas are designed for heavy duty operations and can handle materials many times the density of water (such as Tungsten Carbide). Please check the corresponding models’ data sheet to observe maximum weight.

Why is max RPM smaller on larger mixers and how does it affect scale-up?

While nominal max RPM is smaller for larger Inversinas, the absolute speed at which ingredients are shaken in the container stays roughly the same or even increases with mixer size. Mixing in a 2L Inversina at 60rpm is approximately as fast as mixing in a 20L Inversina at 30rpm or a 50L at 20rpm, etc.

Scale-up is affected by a number of variables, including container shape, RPM, fill level, flow properties of ingredients, etc. In general we observe that with similiar container shape and similiar fill volume, the results of going from a few grams to 250L batches are very comparable.

How fast can we get it?

The manual and 2L Inversinas are kept on stock in the US and ship within 1-2 business days. Larger models are built-to-order and take from around 4 weeks (20L Inversina) up to ca 3 months (350L Inversina cGMP). Replacement parts are kept on stock.

How small of a container can be used in the flexible holder of the 2L / 20L Inversinas?

This depends on the exact shape of the container. Plastic or glass vials work fine even if they are just a few mL in volume, irregularly shaped container need a flat surface in the middle in order to be secured within the flexible rubber fixture. The mechanism of the flexible rubber fixture is demonstrated in our 2L Inversina video.

Can the Inversina be used as a ball mill?

Yes. This has been done several times. It has also been used to smooth / grind very hard materials. Please see our applications section for more info.

Are the supplied plastic bottles dishwasher / laboratory washer safe?

Due to the different temperatures and detergents used in the process this cannot be guaranteed. We recommend to try washing the bottles at a low temperature. Do not use any bottles which are deformed, molten or damaged in any other way.

What fuse protection should we use?

This depends on voltage and on the size and model of the mixer. Please see data sheets / manuals for further information. In general the Inversina requires quite little energy compared to other laboratory equipment – the 2L, 20L and 50L Inversina even just need a regular 110V outlet.

What containers can be used with the Manual Inversina?

The Manual Inversina comes with a 1.5L PET bottle, the 2L bottle with suitable rubber rings is optional. The brush insert can be used to fit smaller containers, such as vials.

What is the difference between cGMP and non-cGMP Inversinas?

20L Inversina: The cGMP model has a sealed frame for improved cleanability. All cGMP Inversinas come with IQ/OQ protocols and material certificates for product-wetted parts.