High viscosity mixing with Silverson Machines

Published: 20-Apr-2022

Mixing high viscosity products can sometimes be a challenging task. When processing viscous products such as slurries, creams, gels, mayonnaise or hair gel for example, a number of problems can prevent you from getting the product you want

While there are many designs of agitators and stirrer/scrapers capable of handling high viscosity products, the low shear nature of agitators limits their effectiveness to performing  simple tasks such as blending liquids of like viscosities, maintaining in-tank uniformity, and producing flow in a vessel to promote heat transfer from jacketed vessel walls. Where the product has to be processed in some way – liquids of differing viscosities are being blended, powders dispersed and hydrated, an emulsion or suspension formed, solids dissolved or disintegrated and so on, an agitator can take a long time to achieve the required results or, more often than not, is simply not capable. 

Silverson High Shear Rotor/Stator mixers are ideal for these types of applications and can cut mixing times by up to 90%, offering improved yield and product quality and greater batch-to-batch consistency. These advantages are further increased by the use of easily interchangeable workheads and screens which allow any one Silverson mixer to perform the duties that in the past may have required several different pieces of process equipment. Where the mixing is to be done in-tank, the high shear mixer would usually be working in conjunction with a stirrer scraper; the agitator maintaining movement and uniformity in the vessel and the high shear mixer forming the emulsion, or homogenising the contents etc.  

With some installations and larger volumes it is often preferable to mix in-line, by recirculating the product through a pipeline in which a high shear mixer is mounted. Traditionally with higher viscosity products this was something of a challenge. Rotor/Stator In-Line mixers have a high volume self-pumping capacity on lower viscosity products, but with the standard design the pumping capacity decreases above a certain viscosity level.  The solution used to be to add an auxiliary pump to the system, to ensure the mixer was continuously fed with product.  However, in addition to the cost factor of two pieces of equipment, matching the flow rate of the mixer with that of the pump could be something of a balancing act, as too low a capacity can starve the mixer of product, while too high a capacity will reduce dwell time in the mixer, reducing the amount of shear applied to the product. Faced with a requirement for a high shear mixer capable of processing higher volumes without the requirement for an additional pump, Silverson came up with a new design – the HV Series of In-Line mixers.

The HV In-Line has a unique and innovative ‘pumping rotor’ design which provides increased capacity when compared to standard In-Line mixers. The mixers are aeration-free and hygienic allowing them to be used for mixing in the cosmetics, pharmaceutical, food and chemical industries. 

It is the specially designed pumping rotor within the precision-machined workhead that forces liquid and solids into the rotor/stator assembly and ensures that the flow rate of the mixer is maintained as viscosity rises. 

Material is forced out through the holes in the stator and pumped back to the vessel as fresh material is drawn into the workhead, creating a circulatory pattern of mixing in which the entire contents of the vessel passes through the workhead, so no isolated mixing occurs. 

To further improve the capabilities of the HV In-Line, a range of workheads and screens are available. They offer great versatility by allowing the mixer to be adapted to perform a wide range of mixing operations including emulsifying, homogenising, dispersing, blending, particle size reduction and de-agglomeration. 

Silverson Machines have extensive knowledge and expertise in mixing high viscosity products and have been helping customers solve their mixing problems for over 70 years.  They have recently introduced a viscosity comparison guide in response to the number of enquiries for help with high viscosity mixtures. This guide will help customers quickly establish the viscosity of their mixes and in turn which Silverson mixer would be best for their application. 

If you would like help with your high viscosity application or would like to find out more about the HV In-Line mixer, please visit the Silverson website or email sales@silverson.co.uk.

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