Nothing to get agitated about

08-Sep-2004 - Last updated on 13-Mar-2017 at 11:52 GMT

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One of the key issues facing manufacturers is making the right choice of mixer for their processes. And there's certainly plenty of kit to choose from, as Bob Brooks discovers

"One thing which you do not do when seeking to specify mixing equipment is look in a catalogue," says Eddie McGee, technical manager at Ajax Equipment. "Every application is different."

And with batch blenders, continuous mixers and agitators vying for manufacturers' attention, picking the most cost effective and efficient is harder than ever.

That said, McGee is sold on the concept of continuous mixers, largely because they afford the operator greater control.

A new generation of continuous mixers for use with wet and dry multiple ingredients has sparked particular interest from among those struggling with the problem of combining friable constituents.

"Nuts, fruit, and cereals now can be mixed with foams, fudges, and viscous pastes to produce a free-flowing and homogeneous mixture -- the mixers are especially suited to the production of cereal bars and similar confections," says Ajax director Mark Waters.

Such mixers offer food manufacturers more versatility in the type and variety of recipes that they are able to process, allowing changes to be made at any point during production.

"You can see what is happening in continuous processing, so if something needs to be adjusted you can do it before it is too late. So often in batch processing the operator does not have the ability to make adjustments in situ which means that the quality of the mix can be difficult to check during the process leading to dispersion problems, over-mixing, etc," says McGee.

Continuous mixing plant also has the advantage of being smaller than that used for similar batch processing which means less power use. And they are easier to shut down and clean, which is particularly helpful for manufacturers processing a wide variety of different materials on the same line.

Ajax, which supplies twin shaft continuous mixers, has developed its own 'Lynflow' technology to build plant around the client's needs. Using paddle and ribbon screw geometry, Ajax claims that Lynflow allows efficient mixing with negligible damage to ingredients.

"The open form and geometry of the ribbon screw is designed to inhibit the build-up of sticky ingredients and allows ease of cleaning," Waters explains. "Alternatively, the paddle screw geometry can be used to provide more intensive mixing."

But when it comes to blending dry materials, the case for using continuous over batch machinery is not quite so obvious, according to Stewart Bryan at manufacturer Hosokawa Micron.

"Batch mixing usually is carried out in three stages: weighing/proportioning ingredients, blending, and discharge. In the continuous mixing process these three stages are simultaneous. In some cases it makes sense to use both methods. For example, where minor ingredients can be pre-mixed in a batch blender and the output treated as a single component for introduction alongside a major component in a continuous mixer."

While he agrees that continuous mixers are both labour- and space-saving, Bryan points out that fluctuations in feed are less easy to level out. This means component feeding accuracy has to be high and investment costs rise sharply with the number of components in the input.

"Continuous systems are also more sensitive to malfunction of components, and frequent calibration of feeding devices is required in order to preserve accuracy and consistent output," he says.

According to Chris Boone, of supplier John R Boone, technological advances are being pushed by demand for machines that are easy to operate and to clean while also using less power and operating shorter cycles.

He says many of his customers are seeking equipment that is capable of efficiently handling a variety of materials, including powders, pastes, and granules.

Hosokawa Micron is one of many manufacturers addressing the problem. It has developed units for high-grade food processing installations that require more exacting levels of cleanliness and minimal product retention.

"We are concentrating on designing mixers that incorporate frequency-controlled drive units, a high-speed rotor -- which provides intense mixing action -- and a selection of interchangeable mixing screws which enable adjustments to meet a range of process and product demands," says Bryan.

But while the batch versus continuous debate rages, some manufacturers have opted for a completely new technology.

Orthos (Engineering), for example, has introduced new agitator technology for gentle but thorough mixing of media of all viscosities in containers of any size or shape. According to sales manager Andrew Reynolds, agitators offer energy-saving and operational benefits, which are especially applicable to the food, dairy, and beverage industries since the action does not produce air bubbles. Agitator technology eliminates shear forces and heat production which, the company claims, reduces power consumption and removes the need for a wide selection of stirrers.

The 'secret' of the new technology is in the prolonged flow and turbulence created by the agitator with low circumferential speeds.

"Unlike conventional mixing devices, the technology does not produce turbulent flow at the edges, thus eliminating shearing action," explains Reynolds. "This, combined with the low rotational speed and short mixing time, means that media is not significantly heated -- optimal heat and cold transfer is guaranteed."

Orthos claims that energy savings of 30% can be achieved over conventional blade stirrers and that further cost savings result from the fact that only one agitator stage is required for large container volumes. "For example, a single impeller with three cones and a 1.8m diameter is sufficient to fully homogenise the contents of a 3m diameter, 15m3capacity container."

As budgets come under pressure some manufacturers are exploring second-hand equipment or looking to finance purchases through part-exchange arrangements with companies like Winkworth Machinery.

"Goods accepted in part-exchange become part of our stock of second-hand mixers and other process equipment," explains James Winkworth. "In addition, we work with customers to provide products and services tailored to their needs."

Winkworth has supplied a complete mini-processing line from its range of reconditioned stock to Reflex Nutrition, which manufactures sports nutritional products at its base in Hove, East Sussex. The company's most recent installation has been a Winkworth 3,000l U-trough mixer.

"We were offered a series of trials at Winkworth's test laboratories," explains James Phillips, md of Reflex. "In addition, the supplier took a second-hand dust extractor in part-payment of the deal."

Whatever type of mixer manufacturers opt for, they must be all too aware that results are not solely linked to the mixer alone, says Ajax's McGee. "In the long run, successful and efficient processing comes down to the quality of the machine, the quality of the ingredients and the interaction between the two." FM

Bakels invests in high-speed mixing

The first piece of equipment to be commissioned for Bakels' new £6.5m factory extension in Bicester, was a high-speed Silverson mixer.

The company, which supplies powdered and liquid bakery ingredients, says the new mixer will help with product quality and consistency and speed up the production process.

The company has seen rising demand for its liquid products, such as bread improvers and release agents, and has 12 more bays for future mixing lines to serve new customers in the confectionery, biscuit and dessert sectors.