For over 20 years now, the Treif Maschinenbau GmbH from Westerwald has been relying on plastic plain bearings in their machines, plants and systems for slicing food items. Installed in 1993 for the first time in a multi-tooth gripper, today virtually the complete range of lubrication- and maintenance-free products of the polymer specialist igus® are used. The technical demands are rising steadily.
"Our goal is to always integrate our suppliers early on in product developments", explains Dipl.-Ing. Rainer Hebisch from the Slicing business unit of Treif Maschinenbau GmbH in Oberlahr, Germany. "Thus we gain valuable time in designing our systems. "This is also what happened with the high-performance slicer; one of its technical features is a high-speed depositing system.
"There is a difference, whether meat or hard sausage is cut", clarifies Iris Henrich, who is responsible for public relations. "This is why each machine is tailored to the respective customer requirements. "Last year, the slicer, due to its capacity data and the associated increase in production, was awarded the "Success" Innovation Prize offered by the Ministry of Economic Affairs for Rhineland-Palatinate and the ISB (Investment and Economic Development Bank of Rhineland-Palatinate).
Used in these machines are corrosion-resistant drylin® linear bearings and
matching drylin® precision shafts. In total, the user gets a
long-lasting linear motion solution for a specific application, which allows,
among other things, high speeds and accelerations. The
maintenance-free and lubrication-free drylin® linear gliding elements are made of
the materials iglidur® J and iglidur® J200. Due to their wear and friction
properties they are suitable for most linear applications.
Designed for dry running, their applications are protected from contamination
by grease and oils, i.e. active lubrication.
In addition, plain bearings of the material series iglidur® J and iglidur® G display their strength in the high-performance slicing machines. They are robust, economical and universal. All machine elements made by igus® prove their capability in high-speed slicing and in depositing the sliced products.
The task was to supply the sliced products out of the slicing area to the
packaging machine without interrupting
the product flow. Handling is executed via the depositing system, a type of
fork that is shot into the production flow. 50 to 75 percent of the
available time is required by the slicing process. For auxiliary process times, such as
movement of the fork, the time cushion is reduced to a few
milliseconds. "When the fork is catapulted into the production flow, there are
incredible accelerations", explains Hebisch.
While finished, already-sliced packages directly underneath the knife are taken up and safely transported off, the machine keeps on slicing continuously. This enables a continuous product flow without empty slices, i.e. revolutions of the knife in which the product is not sliced. Up to six rows of product can be sliced simultaneously . Overall the advantages are clear: Fewer knife revolutions are necessary, the process is gentle on the product, work steps are dispensed with, and it is possible to slice at higher product temperatures. Also the cost for product refrigeration can be significantly reduced. The quality of the product increases, because through lightly freezing, the goods can change in taste, appearance and other sensory aspects.
When designing the machine, the task quickly became
defined. "No empty slices". Empty slices (revolutions of the knife in which
no product is sliced) cost capacity or increase the necessary RPM. Empty slices induce high dynamic loads in the product. The product
must be stopped and re-accelerated. Natural limits are imposed on acceleration
of "softer" / warmer sliced products,
in particular. To increase the strength of sliced products
they would have to be refrigerated. From the knife capacity and a chamber size
for inserting the products to be sliced of 450 x 130 mm, physical requirements
arise; and the machine elements must strictly ensure
these physical capacity data requirements are complied with. The acceleration values for catapulting the
fork, for example, can be as high as 25G. At the same time the slices
must be clean and absolutely uniform at all times.
"Due to the complex requirements profile, of the continuously fast motions, we have calculated a design. We then tested the plain bearings in question ourselves over months," recalls Hebisch, looking back. "In this process we also relied on the wear results and corresponding service life calculations provided by igus, so that overall we always felt like we had made the right decision. “
In addition, in the food industry there are strict hygiene regulations that must be complied with. Bevelled surfaces, the elimination of blind holes, lubricant-free lifting and slicing systems ensure hygienic design. Product contamination due to lubricants must not occur at any point when cleaning with water and the different cleaning media. In addition to chemical resistance and minimal moisture absorption, physiologically harmless materials are another crucial factor because for the most part they are in the product zone. And since the slicing machines can be in use up to six days a week, in some cases in three-shift operation, their service life must be in line with these requirements. The possibility of unscheduled maintenance should be excluded.
In the area of the depositing system for shooting in the product to be sliced and also in
the actual slicing machine itself, different lubricant-free
open and closed drylin® linear plain bearings, as well as iglidur® J plain bearings are
used. "The decision between linear bearings or plain bearings depends on the
requirements of the application relative to capacity, speed and
service life", points out Florian Berg, Technical Sales Consultant at
igus® GmbH. "In this environment the speed issue plays
the major role. " For this, precision shafts enhance the functionality.
Arguments for the liners of the drylin linear plain bearings are their easy handling and replaceability in day-to-day operation. They are clipped into the receptacle bore with positive locking. The liners are secured axially through a snap-ring groove and the anti-twist protection is enabled through engagement of the safety pin in the appropriate bore.
"Originally we expected that in the area of catapulting problems would occur", recalls Hebisch. But the problems occurred at a completely different point. " The toothed belts with which the fork is accelerated to 25G are synchronously driven and deflected. In the deflection, initially roller bearings were installed. They had to be sealed. The seal generated friction that acted negatively on the drives. Consequently roller bearings were dispensed with. Today in the linear feed of the sliced product holder, in combination with exterior soft stainless steel shafts that are chemically resistant and open, drylin® linear films are used.
In the area of the depositing fork, for the bearings the sliced product holder, in addition lubricant-free polymer bearings from the corrosion-resistant iglidur J series are used. They ensure the pivot motion of the drive towards the pneumatic cylinder. The material is resistant to weak acids, diluted alkalis, and many of the disinfectants that are used in the food industry. Thus the intensive cleaning of machines in the food industry is no problem for the polymer bearings.
Implementation of polymer technology extends even further: Soft stainless steel shafts and linear slide elements ensure the linear lift of the pre-gripper for feeding the sliced product. In the pivot bearing arrangement of the feed tower universal iglidur G polymer bearings are used. They are wear-resistant, insensitive to dust and contamination, and particularly economical. All materials that come into direct contact with food products are FDA-conformant and thus harmless over the long term.
"We view ourselves as pioneers and have been relying on plastic in our machines for more than 20 years", emphasises Hebisch. "And our experiences have been so positive that consistently choose igus materials. The consultation and design from igus are so good that there are failures or returns whatsoever on record. Kai Jakobsen-Urwald, Manager of Strategic Purchasing at Treif adds: "The slicing speeds have increased substantially in recent years. The lubricant-free polymer slide bearings easily handle this speed increase. Due to the many and diverse positive experiences they are being used with increasing frequency in our other business units. “
At the family-run enterprise Treif, everything revolves around the slicing
of food products. More than 400 employees around the world, develop
and produce equipment and systems. Customer-oriented solutions are planned and implemented
for trade, supermarkets, and industry, including
automated line solutions for slicing different products,
such as meat, sausage, cheese, bread, and baked goods.
To do this the company maintains four business units: "Dicing", dicing for sausage salads, or goulash, for example, "Portion Cutting", portioning or slicing of meat that contains bone and boneless meat, such as schnitzel or cutlets, "Slicing", slicing of sausage, ham, or cheese in thin slices, as well as "Bread Cutting", slicing of bread.