Agitators
Frequently asked questions

What is an agitator/mixer?

It is a mechanical piece of equipment used to fulfil a specific mixing or process task. These tasks could be anything from suspension of solids, to combining liquids or liquid-solids, for example. A basic mixer, in our instance, is made up of a motor, gearbox (unless a direct drive is used), coupling, shaft, hub(s) and blades. This is illustrated in the drawing on the right:

What is the difference between an impeller and a propeller?

Propellers and impellers both provide thrust – however, they do it in different ways. A propeller is a fan which propels a fluid by pushing against it. Basically, it converts rotational motion into linear motion. An impeller, on the other hand, is a rotor that produces a sucking force and makes up part of a pump.

What role does viscosity play in sizing a mixer?

Viscosity is a measure of a fluid’s resistance to flow. We measure flow regimes using Reynolds number which is a number designating the type of flow in a system.  There are three types of flow:

  • Laminar
  • Transitional
  • Turbulent

The higher your Reynolds number, the more turbulent the flow will be; and the smaller the number, the more laminar. For mixing, turbulent flow is the easiest form of a fluid regime to mix your product. The higher the viscosity, the lower your Reynolds number will be – inevitably leading to a more laminar flow. When we design an agitator for these conditions, we need to consider that the product will not mix as easily as lower viscosity fluids or fluids in the turbulent regime. In many instances, designs done in the laminar regime would require a different impeller, a larger impeller diameter or increased power to achieve the desired result.

Is there a difference in the mixer’s “performance” if the variables change or fluctuate in a solids suspension tank?

An agitator is a purpose-built piece of machinery designed specifically for the in-tank conditions. If these circumstances were to change, it is possible that your mixer performance will be affected. Examples of these changes are:

  • An increase in slurry density: This will increase your agitator’s power draw which will cause your agitator to overload. It will also increase the fluid forces of the agitator, possibly leading to a mechanical failure.
  • An increase in particle size: This will increase the settling rate of the solids. If the solids are left to settle, they will build up and eventually overload your agitator. The solid build up will either cause the agitator to trip on high power or can result in a mechanical failure due to the increased load being put on the mixer.
  • Changes in percentage solids: If your percentage solids increase, this will increase your density and lead to the same problem as explained in bullet 1. A decrease in percentage solids can increase your solids’ settling rate and result in settlement problems.
Are there preventative maintenance measures which can be taken to monitor the agitator during operation?

AFX can provide you with a solution for preventative maintenance. We can gear our agitators up with all necessary monitoring equipment including:

  • Vibration sensors
  • Oil pressure switches
  • Flow switches
  • Temperature switches

AFX can also provide an onsite maintenance service with agreed intervals to suit your schedule and budget. Our service personnel will look after your agitator’s wellbeing and increase its operational life.

How do I know which mixer I need?

If there is a new or replacement mixer that you require, and you know the details, please go to the “request a quote: spares page”. If, however, it is a new application, please go to the “request a quote: AMX agitators page”.

What do I need to know when requesting a quote for an agitator?

If you are not sure what will be required for us to quote you on a mixer, please go to the “request a quote: AMX agitators page” for a user-friendly questionnaire. An AFROMIX applications engineer will then process your requirement.

I am worried about the load and stresses of the agitator on the tank structure – what do you recommend as a solution?

We at AFX can provide you with a comprehensive mixer and structural solution. Our experts will design a suitable mixer for your unique application. We are then able to run a Finite Element Analysis on the structure with loads gathered from the agitator design. From there, AFX can advise you on how best to correct your structure or replace it.

Where are agitators/mixers used?

Mixers are used in almost every industry at some point.  Typical industries would be that of mining and minerals processing, pharmaceutical, food and beverage, pulp and paper, wastewater treatment, chemical, agricultural and petrochemical. AFX specifically focuses on fluid mixers for these industries – from your simple blending application to incredibly complex reactors. Our range of mixers caters for low, as well as very high, viscosity mixtures.

Are there portable agitators ideal for small blending applications?

Yes, indeed. AFX boasts a range of mixers that have been designed specifically for small tanks like Drum Mixers and IBC Tank Mixers, for example. These mixers are portable in the sense that they are easily removed and fitted to the next vessel. The good news is that we can supply lifting devices, electrical safety switches, pneumatic motors and stop-start controllers for these mixers, too.

I need assistance and advice on-site – are you able to provide this?

AFX can assist you on-site with installations, commissioning or general technical advice on problematic mixers. We have engineers and field service personnel who possess the necessary skills and expertise to meet your needs.

Are there mixers designed especially for the pharmaceutical and personal care industry?

Yes, there are. Depending on your application, we will have a solution. This solution could be anything from high polished stainless mixers, high viscosity mixers and biological reactors, for example. Contact us so that we can assist in providing a solution especially for you.

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