Yaskawa solution delivers high precision in the food and pharmaceutical industry

Twin screw pumps are classic process pumps and have proven themselves in countless applications. Until now, however, they have been considered relatively unsuitable for precise metering tasks. That is about to change. Thanks to Yaskawa’s powerful drive technology, it is now possible to operate without slippage between the feed screws and the pump casing adversely affecting metering results. Dripping, for example when filling bags with viscous media, is reliably prevented. This new development is especially beneficial for users whose systems are cleaned on a regular basis, because the cleaning processes involved are much simpler compared to those of piston pumps. Cleaning is much more efficient and frequent product changes in the same filling system are no longer a challenge.

The German company Fristam Pumpen KG has developed into a globally recognised specialist in pumps for the widest variety of conveying tasks: from foodstuffs to cosmetics and pharmaceuticals to chemical applications. The company’s roots are in the dairy industry. No wonder, then, that these pump specialists focus so much on applications with strict hygiene requirements. The twin screw pumps of the FDS series are an excellent example.

They are made of high-quality stainless steel and are easy to clean. In addition, they are setting a multitude of new benchmarks in twin screw technology.

Increased efficiency during cleaning processes

The operation has been completely revised from scratch and known weak points have been eliminated. The design was continuously refined to optimise all aspects, including smoothness of operation, temperature stability, repair and maintenance. “In addition, through these improvements we have managed to significantly increase the added value for end users by providing drive systems that are perfectly matched to the pumps,” reports René Linck, Product Manager at Fristam. “The twin screw pumps are now also the ideal solution for dosing tasks with viscous or thixotropic media. At the same time, they can perform cleaning tasks in CIP processes at speeds of up to 3,600 revolutions per minute”. This means that no additional pump is required for cleaning processes. Compared to piston pumps, which until now have generally been the standard pumps for such dosing tasks, CIP processes run faster, especially since neither the pump nor the hoses, pipes or dosing nozzles need to be dismantled. “This is especially beneficial for systems that have to be cleaned at regular intervals.

for example, if you use the same dosing unit to fill bags with ketchup in one shift and mayonnaise or mustard in the next”.

A big challenge for the drive engineering

The challenge during development was to avoid dripping when filling the bags. Slippage between the screws and the inner wall of the housing is inherent in the design and cannot be avoided. A certain clearance must always be ensured so that the non-contact pump works properly and the surface of the screws and the housing are not damaged. For sealing compressor screws, for example, the gap is sealed with injection lubrication. In twin screw pumps, the conveyed medium performs this task itself. However, this results in the “slippage” described above. Depending on the viscosity of the medium, the volume conveyed differs with each revolution. Twin screw pumps offer an elegant solution to this problem: the sensitive but highly dynamic drive system prevents any dripping. For this purpose, the pump drive briefly runs backwards for a specific time at the end of the filling process, which ensures precise metering and a clean filling process.

This is a challenging task for the drive solution used, because each different type of media requires adapted acceleration, braking and return ramps. In addition to this, cycle times are short because the pumps fill up to 80 bags per minute. High dynamism is therefore essential. “In close cooperation with Yaskawa, our partner for many years, we succeeded in creating a drive solution perfectly adapted to these requirements,” reports Linck happily.

Power transmission from a single source

The driving force for the twin screw pumps is provided by Sigma 7 servo motors and suitable amplifiers. The fast-response AC servo drives feature high resolution (integrated 24-bit absolute encoder) and high dynamics, and are ideal for demanding positioning tasks. They are able to suppress machine vibrations and resonance frequencies automatically during operation. They are also designed for a long service life and operate at ambient temperatures between 0 and 55 °C without additional cooling. Thanks to their compact dimensions, they require only a small installation space and are easy to mount on dosing units that are commonly used on rotary tables in filling systems. There was also a wide variety to choose from during project planning.

The highly dynamic AC servo motors cover outputs from 50 W to 15 kW with supply voltages of 200 and 400 V, and are impressively quiet when in operation.

A compact Yaskawa control system from the VIPA SLIO series controls the servo drive for the dosing job. This system is easy to program in the TIA Portal environment and its modular design provides a good fit for the application. For convenient control of the dosing process, the Yaskawa controller was equipped with an intelligent HMI. Its 7-inch display not only enables menu-driven operation, but also allows you to visualise the status of the dosing unit. The combination of high quality components and the support of expert staff while tailoring solutions to specific requirements made Yaskawa the perfect partner. “We got a complete functional solution for our dosing unit from a single source,” says Linck.

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