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The solution for spilt milk: LinMot linear rotary motors and wing-cap closures

Category: Application report

200 million litres of milk and 60 million litres of cream. These impressive quantities of liquids are processed annually at Emmi’s Mittelland Molkerei AG in Suhr. Right in the center of it all: LinMot’s lifting rotary motors and Wing-Cap closures.

“Customer convenience” is the succinct answer Hans-Peter Steuri gives to the question of what prompted Emmi to use the Wing-Cap closure. The project manager at the Suhr site then takes us on a short journey through the history of Swiss packaging. “In the beginning, the design of the Tetra Pak packaging was rectangular, like a brick. In the 90s, this packaging was then replaced by the tubular bag.” However, the extremely economical and ecological packaging also had disadvantages: the bag was too susceptible to unwanted tears and also could not be resealed. So the company switched back to conventional packaging, but this time with a glued-on screw cap. After the first opening, an aluminium layer had to be torn away from the inside of the closure by means of a plastic ring. This solution required an effort, at the end of which a little of the liquid was often spilled due to the jerky removal of the aluminium cover. In order to be able to offer its customers the best possible packaging, Emmi needed a solution that could be resealed and opened easily and without the use of force. Also important: the drink must be pourable without spilling. The answer to these requirements: a wing-cap closure.


The closure with the “wings”. Wing-cap closures sealed with LinMot lift-and-turn motors also stand out visually from the crowd.


Reliable, precise and fast
The trick behind the Wing-Cap closure: the sealing disc is connected directly to the lid after the closure and thus opens easily and effortlessly when the Wing-Cap is opened for the first time. The decisive factor for an efficient and reliable closing process is the precise twisting on of the Wing-Cap closures. And it was precisely here that the renowned machine-building company Tetra Pak turned to linear rotary motors from LinMot.

The pre-filled carton packages are transported by conveyor belt to the Tetra Pak capper. There, a wing-cap closure is first placed on the packaging. The lids are then precisely sealed by a LinMot PR01 linear rotary motor, which contains two electromagnetic servo motors – a linear motor and a rotary motor – in just one housing. Thanks to its innovative mechanical design, this ready-to-use machine element is capable of implementing combined linear and rotary movements in the simplest possible way and, for example, of screwing on lids freely according to customer requirements. In Emmi’s case, the lid must be closed as follows: screwed shut at a 90⁰ angle with both “wings” aligned on a horizontal line. Of course, during the closing process, the LinMot stroke-rotation motors not only guarantee that the lid is rotated onto the thread sensitively and without damage, but they also find the correct start of the thread and, by combining linear and rotary motion, ensure that parameters such as linear position, angle of rotation, force as well as torque are always maintained throughout the entire process. This means that nothing stands in the way of a fully monitored closure, as is often required in connection with Industry 4.0 requirements. Once correctly screwed, the sealing coil then takes over the final work step.

This entire process is carried out in just 3 seconds in parallel by two stations at the same time. Weekly, production changes from 1-litre cartons to 0.5-litre cartons. The format changeover required for this is completed within fractions of a second on the part of the lifting and turning motors thanks to the simplest parameter adjustment of the movement profiles and can be carried out directly by the PLC.



Innovation that pays off
The machine developed by Tetra Pak has already been in use at Emmi for 3 years. During this time, there has not been a single failure of the linear rotary motors. This is despite seven-day production with three shifts each. Regular maintenance is sufficient to maintain a long-lasting, profitable production machine. Based on the positive experience, Emmi has been using another production line with an identical capper since March 2021.


The entire process at a glance. From placing the closures to positioning and sealing.


More sustainability for the future
When asked about innovations he would like to see in the future, Hans-Peter Steuri sees even more potential in one area in particular: sustainability. “Here we have already achieved a lot so far, but perhaps we can still save material.” Ultimately, the goal is for consumers to be able to close the recycling cycle properly. This is already possible today with Tetra Pak packaging. In Switzerland, there are about 100 collection points where beverage cartons can be returned. Future packaging should be even easier to recycle. Not only in Switzerland, but all over the world. And as soon as the requirement profile for the packaging of the future is clear, the motors from LinMot will be reliably on hand again.


Hans-Peter Steuri has been working as a project manager for Emmi Schweiz AG in Suhr for over 43 years. During this time, he has already witnessed a number of innovations in packaging technology. He has been perfectly satisfied with LinMot’s rotary hoist motors for 3 years.

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