The Mixing Science series produced by Silverson Machines uses animations to explain and demonstrate a range of mixing topics and terms such as Homogenisation and Emulsions.
The one of latest animation to be released in the series explains the pumping capacity of high shear In-Line mixers. When mixing continuously in larger batches, In-Line mixing is often the method chosen by manufacturers to get the best results; it also offers greater energy efficiency over in-tank mixers as the mixer’s effort is concentrated on the small volume in the mixing chamber rather than having to circulate the entire volume in the tank.
But although Silverson In-Line mixers are self-pumping, some people think that they will need a very powerful machine to recirculate the product back to the top of a large tank. The animation debunks this by explaining how a Silverson In-Line mixer can recirculate product in a large tank without the need for pumps or additional power.
Other videos in the series also focus on seals and sealant systems for Silverson In-Line mixers. One animation explains why some applications require single mechanical shaft seals, and why others require double mechanical seals on In-Line mixers. The mechanical shaft seal contains the mix in the body of the In-Line mixer where the rotating shaft passes through the body. For many applications, a single mechanical shaft seal is all that is required to prevent liquid from leaking out of the mixing chamber.
But mixing materials that are abrasive or sticky in nature can cause problems where a single mechanical seal is being used. Abrasive materials cause the seal faces to wear, and sticky substances can solidify between the seal faces when the mixer is switched off; this can cause the seal rings to seize and break when the mixer is restarted. To avoid this a double mechanical seal would be recommended.
A double mechanical shaft seal can be two single mechanical seals mounted in a chamber or a cartridge seal. The chamber between the seals needs to be flushed with sealant fluid which is compatible with the product being mixed and preferably non-flammable. The pressure inside the double seal chamber must be higher than that inside the mixer. This forces clean, lubricating liquid between the seal faces to cool and lubricate them and prevents any of the product from inside the mixer from getting onto the inboard seal faces.
If you are flushing the double seals with liquid other than mains water, for example, if you are using oil or glycerine, this is where a Thermosyphon system is often required, which is explained in another animation in the series.
Another animation in the series focuses on continuous powder/liquid mixing. Continuous addition and dispersion of powder is one of the most difficult mixing applications. It can be achieved if both the liquid and powder are metered into the powder/liquid mixer but there are significant difficulties to overcome. If the flow rate of the liquid is not sufficient, the powder/liquid mixer will not be able to absorb the powder at the required rate, and there is a limit to the percentage of powder that can be added in a single pass. If the percentage of powder being added is too low, the powder/liquid mixer can potentially incorporate air. And most importantly if there is even a momentary bridging of powder in the powder hopper, then liquid will pass through the mixer without any powder being added. Therefore, for most applications, adding powder into liquid continuously in a single pass is not a viable option.
A batch/recirculation system is normally recommended because it will overcome these problems and ensure a consistent, homogeneous product. The Silverson Flashmix is widely used to disperse powders into liquids, operating on a batch/recirculation basis. It works in a revolutionary way, unlike many powder/liquid mixers, which use vacuum to pull in powders, the Flashmix literally forces powder into the liquid stream. This not only allows it to disperse and hydrate large volumes of powders, it means it can be used at higher temperatures and with higher viscosity mixes.
Although we would recommend a batch/recirculation system rather than continuous dispersion, the animation details a number of ways to produce powder/liquid dispersions in order to continuously supply processes downstream.
Silverson also offer in-tank mixers and one animation details how to use and get the best results from these mixers. Other animations in the series include explanations of common mixing applications such as emulsions, homogenisation and deagglomeration. One of the most popular videos in the series, ‘What is Homogenisation?’ has almost 230,000 views on the Silverson YouTube channel. The ‘What is an Emulsion?’ animation is equally popular, with nearly 200,000 views.
For more information, or to watch the animations, visit the Silverson website or YouTube channel.
