Dry running linear guides and bearings deliver high performance and long service life in wooden pallet production
Published: 29 August 2013 - Heather Ramsden
Aloysius Krenzer KG produces euro pallets and bespoke wooden pallets with a high degree of automation. When the company orders new systems it requests the equipment manufacturer uses drylin linear guides from igus for certain applications. These bearings have proven themselves in linear drives, which operate dynamically under high loads.
Aloysius Krenzer KG, which has headquarters in Germany, is one of the leading pallet producers in Europe. Founded in 1924, it is one of the few pallet manufacturers who controls the entire pallet production process from harvesting lumber, saw-cutting, fabrication, processing, and logistics with its own fleet. Three in-house sawmills supply the raw materials for the largely automated production lines. Several lines produce Krenzer's primary product – euro pallets in accordance with EN 13689-1 pursuant to EPAL quality criteria – and the company also produces chemical, glass and customer specific disposable and recyclable pallets. The manufacturing capabilities are continuously enhanced and the latest plant is characterised by its flexibility, as it is able to produce customer specific pallets in various dimensions with a high degree of automation.
The plant was developed and designed by a specialist for pallet production plants. However, the customer exerted considerable influence on the design. Owner-operator, Gregor Krenzer, who is responsible for engineering, said, "As the user of the machinery, we have extensive experience primarily with respect to the service life of the mechanical drive and handling components."
In this case, the design engineer has to account for the harsh environmental conditions, which include wood chips and dust with humidity and resin. In addition, many drives are highly dynamic. For exmaple, this applies to the units of the nailing station which nails down the stringer boards of the pallets.
The machine autonomously retrieves all required wood components from the magazines and nails them together. The stringer boards are positioned by servo drives and the precise guidance of the axes, which have diameters from 30 to 50 mm are carried out by igus drylin linear slide systems, which are proven as reliable in these conditions.
The operational demands on the systems are high. They carry out 50,000 strokes of 30 cm each per day in a dusty environment with alternating loads as the moving ends that are fastened to the axes move up and down when retrieving boards from the magazine. This is exacerbated by the continuous shock from the nailing operation.
The bearing selection is based on recommendations from Krenzer and the excellent experience gained with drylin linear guides.
"We also use drylin housing bearings and pillow block bearings in combination with hardened steel shafts. This is not the optimal pairing recommended by igus, but in our application this combination achieves a notably longer service life," continues Gregor.
Krenzer’s experience is that these linear guides have a service life of approximately three months. This appears to be fairly low at first glance, but considering 50,000 strokes are carried out every day for 90 days, the result is 4.5 million operating cycles, all with difficult operating conditions of dirt, fast movement and alternating loads. This is a substantially higher service life compared with other types of bearings, such as re-circulating ball bearing guides, that Krenzer has tested on other plants under similar conditions. Moreover, the igus guides operate maintenance-free under the most arduous operating conditions, and Krenzer is also very satisfied with the precision attained by the drylin systems.
The housing for the drylin gliding guides are manufactured from anodised aluminium and, thanks to their standard sizes, can be fitted easily using commercially available block carriages. The precise guidance of the axis at low friction is achieved with an igus iglidur J liner. This material consists of a wear-resistant high-performance dry running self lubricating polymer, which ensures very good sliding properties.
Krenzer also uses drylin systems for feeding and precisely positioning the stringer boards. This application uses two linear guides per station with two drylin bearings each. These dry-running bearings are also used by the other pallet production plants.
Gregor says, “At Krenzer we have our own machine building operation, which reconfigures existing plants or designs and builds individual components, such as guides. However, our experience has shown that we must carefully account for environmental conditions when selecting a bearing. For example, when a rack needs to be guided or travels are very long, we use other solutions. But with the frequent, dynamic movements in our handling and feeder units, our experience has shown that igus’ drylin linear guides have the longest service life."