High Shear Mixing FAQs
Q: How do I know if a Silverson mixer I buy through the Internet will work for my process/application?
A: Honestly, you don’t.
Many Silverson machines are customised to fit specific processing conditions, so they are not one-size-fits-all and may not work for another application. Another problem is used machines may no longer be in spec. Wear and tear increases the gap between the rotor and the stator, which decreases the efficiency of the machine.
“The problem with the second-hand market is customers don’t know what they’re buying,” explains Alan Pepper, head of manufacturing, Silverson Machines. “That’s the danger. Often when a customer calls us they subsequently find out the machine they’ve purchased is not suitable for their application.”
Q: Do you service second-hand Silverson equipment?
A: Yes, for an hourly rate (two-hour minimum) plus travel and expenses, a highly-trained Silverson engineer will perform service work on used Silverson equipment.
Q: When would you choose an In-Line mixer over a static mixer?
A: Static mixers are simple low shear devices which comprise a section of pipe fitted with baffles that divert and disrupt the flow of liquid as it is pumped through the pipeline. The baffles are most commonly a series of fixed elements in a helical configuration, which produce both radial and axial flow, ideal for heat transfer or blending liquids of like viscosity. As the name suggests, static mixers have no moving parts and need an auxiliary pump to generate the required flow through the pipeline.
Static mixers can be very effective for simple in-line blending tasks, such as liquid/liquid blending or dispersing gases into liquids, normally on a continuous basis. However they are generally not suitable for more demanding duties, for example blending liquids of widely different viscosity, creating fine emulsions or suspensions, disintegrating and dissolving solids, incorporating powders or where two materials react together on contact.
For these applications a high shear mixer is required. Silverson offers a range of high shear In-Line mixers with self-pumping capacities of up to 200,000 litres per hour; in most cases, a Silverson In-Line mixer can replace both the static mixer and the auxiliary feed pump, offering a dramatic improvement in product quality and process efficiency. Where a greater degree of particle or globule size reduction is required in a single pass, a Silverson In-Line mixer can be added to the line after a static mixer so that they work in conjunction with each other; the static mixer creates a coarse premix, which then passes into the In-Line mixer and is subjected to intense high shear, resulting in a homogeneous product with a fine particle or globule size.
Q: When would you choose an In-Line mixer over a Batch machine?
A: Silverson High Shear Batch mixers are ideal for volumes of up to 1,000 litres, depending on viscosity. While we do offer Batch machines for much larger capacities, in general beyond this point an In-Line mixer is often the most efficient and economical option. This is because the In-Line mixer’s energy is concentrated on the small volume within the mixing chamber at any given moment, rather than expended on circulating the entire contents of the vessel, as well as, the mixing task itself. Consequently a relatively small In-Line mixer can process a large batch.
Q: Single- or triple-stage In-Line Mixers; which is best?
A: The majority of products need to be recirculated through an In-Line mixer – whether single or multistage – to get the desired result. Our In-Lines self-pump at a far higher rate than triple-stage units, ultimately giving the same result in the same or less time. In addition the simple, robust construction of our mixers makes them easier to clean, easier to operate and easier to maintain.
Q: Is there a formula for scale-up?
A: There are theories and formulas put forward as the key to scale-up, but the mixing characteristics of high shear rotor/stator mixers are complex and no single rule can reliably be applied. Rotor tip speed, workhead design, power input, volume turnover, liquid rheology (characteristics of the liquid under shear) and viscosity all affect the end result. However, with more than 70 years’ experience in helping clients solve some of the most difficult mixing challenges, Silverson can offer expert advice and ensure you obtain the right mixer for your application.
Q: How can I mix without incorporating air?
A: The high shear mixing/shearing action of the Silverson rotor/stator workhead sets up a circulatory pattern of mixing that is all below the liquid surface, minimising aeration. For completely aeration-free mixing, a Silverson In-Line mixer, along with the pipework and vessel form a closed system, and the flooded suction provided by the self-pumping In-Line mixer cannot introduce air into the product.
Q: What particle size can I achieve with a Silverson High Shear mixer?
A: Many solids are supplied in premicronised form but reagglomerate when dispersed. A Silverson High Shear mixer will reduce these materials down to their original particle size. The degree of size reduction of other solids depends on their hardness, but typically, 5 to 10 microns can be achieved, or sometimes lower.
Q: What droplet/globule size can I achieve when forming an emulsion?
A: Silverson High Shear mixers will rapidly obtain stable emulsions of 2 to 5 microns, and it is possible to obtain a droplet size of 0.5 microns depending on the formulation.
Q: What is the difference between an In-Line mixer and a shear pump?
A: The clue is in the name! Silverson High Shear In-Line mixers are designed for the most demanding mixing duties – emulsifying, homogenising, disintegrating, solubilising, deagglomerating, powder/liquid blending and reaction acceleration – with the added advantage of having a high volume, self-pumping capacity. With a range of interchangeable workheads and stator screens, they offer unrivalled versatility and unmatched efficiency. By contrast, shear pumps are often a modified centrifugal pump with a limited shearing capacity, suitable for simple tasks. They don’t have the versatility or performance of a Silverson, and ironically, they frequently require an auxiliary pump.
Q: Where can I see a Silverson High Shear mixer in action?
A: Give us a call – one of our reps will be happy to arrange a site visit and bring a mixer in to try on your process. We also provide mixers for on-site trial and rental terms, as well as, operating a test facility where you can visit us and carry out production scale trials on your materials. Alternatively, go to our Trade Shows page, which gives details of where we will be exhibiting our range of high shear mixers.
Q: Are Silverson mixers 3-A approved?
A: Yes. Our Ultra Hygienic In-Lines have gained 3-A TPV (Third Party Verification) and are the only mixers in the world to be certified by both 3-A and the European Hygienic Engineering & Design Group or EHEDG, which is regarded as the most stringent hygienic standard in the world. Silverson's Ultramix and Flashblend Powder/Liquid mixers are also 3A TPV (Third Party Verification) approved.
Q: Does Silverson offer worldwide support?
A: Yes. We have offices in the U.K., the U.S., Europe and Japan, as well as a network of more than 60 associated companies, agents and distributors across the globe.
Q: Can Silverson offer mixers for sanitary duties?
A: We are the world leader in the design and manufacture of ultra hygienic mixing equipment and have pioneered many construction techniques, which we can apply across our range of products to provide the most hygienic mixing equipment on the market. We can supply mixers conforming to FDA and cGMP guidelines and produce the only mixers in the world certified by both 3-A TPV (Third Party Verification) and EHEDG, the European Hygienic Engineering and Design Group.
Q: I’m developing a new product – how can I be sure my mixing process is going to work?
A: At Silverson, our approach is “try before you buy.” Our reps will be happy to carry out laboratory scale trials at your site or you can visit us or send your materials in to our testing facility in Chesham, Buckinghamshire. These are available for clients to test their products on any of our mixers and discuss, in confidence, their process requirements. We also have a large fleet of laboratory and production scale rental machines available for client use. We will work with you to develop the best mixing process for your product and ensure that you can mix it right, first time, every time.
Q: We produce a number of different products: can I use a Silverson for more than one application?
A: The advantage of the Silverson approach to mixing is that any one machine can perform the duties that in the past may have required several different pieces of process equipment. Interchangeable workheads allow our mixers to mix, emulsify, homogenise, disintegrate, solubilise, reduce particle size and accelerate reactions. The simple, robust construction is designed for minimised maintenance and cleaning, and our Ultramix and In-Line ranges are designed for Cleaning-In-Place, ideal for applications where quick turnaround between batches is required.
Q: Why use a high shear mixer rather than a simple agitator?
A: Agitators can give satisfactory results for simple duties such as blending like-viscosity liquids, providing in-tank uniformity and promoting heat transfer in jacketed vessels. But if you need to blend liquids of differing viscosities, emulsify, homogenise, disintegrate, solubilise, disperse powders, reduce particle size or accelerate reactions, these tasks cannot readily be achieved with a low shear device. A Silverson High Shear mixer can do this and more, cutting your mixing time by up to 90 percent.
Q: How can I get rid of agglomerates in my mix?
A: When powders such as gums and thickeners are added to liquids they tend to agglomerate, and conventional agitators cannot readily break these lumps down. The easiest way to overcome this is to add a Silverson In-Line mixer to recirculate the product. The high shear action will rapidly disperse lumps and fisheyes to give a homogeneous end product, maximising yield. A Silverson In-Line mixer is easy to fit, easy to use and easy to clean.