Clean faster, produce more

Cleaning processes in manufacturing mean unproductive time. Especially with small batches, the availability of a mixer decreases. By selecting the right mixer types, cleaning time and thus production costs can be saved.

A large variety of products and the individual production of different premixes form part of today’s daily routine. Fast and easy cleaning of the mixing plant is essential. Due to increasing personnel costs and ever stricter environmental regulations worldwide, both the cleaning time and the use of cleaning agents and the disposal of drag losses are important criteria for investments in new mixing plants.

Container mixers are characterised in particular by their high flexibility and easy cleaning compared to static mixers. In the development of the new container mixer HENSCHEL-Mixer® CMQ, the focus was not only on the quality of mixing and dispersing but also on cleaning. The critical components were specifically optimized for this purpose.

In a container mixer, the materials to be mixed are pre-weighed and filled into the container (mixing bowl). Additional containers cleaned offline can be used for other recipes. The container is then moved to the mixer. The container is clamped, lifted to the mixing head and turned upside down in the mixing position. After completion of the mixing process itself, the container is swivelled downwards and released from the mixer. It is transported away from the mixer to a separate unloading station for emptying the mixture.

The new container mixer works with a wing-profile tool mounted on a flat, polished plate. Image: Zeppelin.

Thorough cleaning is essential

There are already various solutions on the market for automatic cleaning of the container, but if a recipe change is required, the parts of the mixer that come into contact with the product must also be cleaned very thoroughly. Contamination on the surrounding periphery must also be completely removed, as it may otherwise be carried over into the new batch when a new container is brought into position. Typical contaminated areas are the mixing tool, the mixing head, the mixer pedestal and the container guidance.

In order to ease the cleaning of the mixing tool, the tool should be easy to dismantle and free of sharp edges and shadows. In addition, the pressure on the wall and bottom created during mixing should be kept to a minimum so that there are no deposits in the mixer and there is no high increase in the material temperature.

Often mixers are equipped with slow-running tools which are combined with one or more high speed dispersion tools. In view of the cleaning aspect, the aim was to combine moving and dispersing in one tool. With the usual tools, the bottom clearance must be kept very small so that the material circulates evenly in the mixer in the form of a vortex. A large distance means that the material is no longer lifted sufficiently, resulting in an uneven distribution. Although a higher peripheral speed counteracts this, the result is a higher rise in temperature and deposits on the tool and mixing head.

These findings led to the development of a new wing-profile tool. The wing-shaped mixing arm together with the winglets, which have been used in aviation for many years to reduce air resistance, produces a very low mixing resistance. This reduced energy input limits the temperature rise to less than 2 K /min). This allows a higher tool speed (up to 20 m/s), which in turn increases dispersion. The high lift force created by the geometry of the wing allows a very large bottom clearance (up to 70 mm).

The shape and the polished surface of the mixing tool prevent deposits, which makes cleaning very easy. In addition, the mixing tool is very light (approx. 15 kg for a 1,000 litre mixer) so that it can be dismantled very quickly for thorough cleaning or replaced directly with a cleaned tool. The high bottom clearance also allows for easy cleaning between the tool and mixing head.

The conventional mixing head is usually trough-shaped. At the rim there is a seal where deposits can accumulate. Due to the high lifting forces, the normal mixing head can easily be replaced by a polished, flat plate. This allows for a very simple and fast cleaning of the mixing head. This combination achieves at least equivalent results compared to other container mixers equipped with homogenizing and dispersing tools.

The wing profile generates strong lifting forces. Image: Zeppelin.

Cleaning time from 5 to 15 minutes

Container mixers usually available on the market require a guide system mounted on the floor under the mixing head to ensure centring. When the container is moved away from the mixer at the end of the mixing process, some material always falls off the mixing head and mixing tool and contaminates the guide system.

Thanks to a well thought-out design of the container holder and clamping rotary holder, the container itself can easily be centred to the mixing plate. Since there is no guide system on the floor, it can be cleaned quickly and easily: even a scrubber-dryer can be moved on the floor underneath the mixer. The housing of energy chains and other electrical components makes it easy to clean the entire immediate surrounding of the container mixer. Cleaning times are thus reduced from 40 to 120 minutes to 5 to 15 minutes.

Sequence during operation of the container mixer. Image: Zeppelin.

Three-part design simplifies cleaning in the hot mixing process

If high dispersing capacities are required, there is no way around the hot mixing process in the high-speed mixer. Cleaning takes much longer with hot mixing than with cold mixing: the entire mixing container and the lid must be cleaned, the tool set (usually 3 to 4 tools) and the optional deflector must be removed in order to gain access to all corners and edges. But even here, new developments make it possible to significantly reduce cleaning times.

For example, the hydraulic lifting and turning of the lid simplifies access for thorough cleaning. The difficult-to-access material discharge cylinder common on conventional high-speed mixers has been modified to provide easy access to all areas of the mixer discharge, including the area behind the discharge plate. The hinge points are positioned so that connecting pipes no longer need to be separated for cleaning. A quick-release opening on the top of the outlet further simplifies cleaning. Safety limit switches prevent the mixer from starting during the discharging process.

To remove the mixing tool from mixers with a fixed mixing bowl, the operator must bend over the edge of the bowl. For large mixers, an operator must climb inside the mixing bowl. This is a time-consuming procedure that may require additional safety measures to protect the operator in the narrow bowl.

The new design gives the operator full access to the inside of the tank: the tank is designed as a two-part, fully sealed unit, in which the upper part of the tank can be lifted from the bottom shell and swivelled to the side. The mixer consists of a three-part, double jacketed mixing bowl, the hydraulic unit for lifting the upper part of the vessel and lifting and turning the lid, as well as the swing-away material discharge cylinder. Safety limit switches ensure safe operation.

Conclusion: The new design reduces the cleaning time from 30 to 180 minutes to 5 to 20 minutes. In productions where recipes are changed several times a day and cleaning is essential, high five-digit annual savings can be made.

 

The Author

Karl Hendrik Schluckebier is Sales and Process Manager at Zeppelin Systems BU Mixing.

For more information, please contact Paul Scott, UK Area Sales Manager at Zeppelin Systems.