Abrasive dust and grain husks are an extreme load for the components in impact hullers in the food industry. Sensitive recirculating ball bearing guides made of metal must therefore be lubricated and maintained regularly under these circumstances. In order to reduce downtime, minimise operating costs and also improve technology, designers at grain processing specialist Streckel & Schrader therefore turned to our plain bearings. This is because they are made of tribo-polymers and are self-lubricating and maintenance-free thanks to incorporated solid lubricants.
Machines for grains are Streckel & Schrader's specialty. Since its foundation, the company has focused on the design and continuous development of processes for processing grains and pulses. One of the new developments is the impact huller GG1. It is used in the food industry to hull oats, spelt, sunflower seeds and similar cereal products.
The impact huller GG1 uses the impaction method. In this process, the husk of the product is loosened by the impact against an impaction body. The machine uses a cylindrical impact ring on which the grain hits at the optimum angle and gently detaches itself from the core. To ensure that the product quantity is distributed homogeneously, an integrated adjustable quantity dosing system is used. Ring-shaped wear zones occur in the peeling ring due to the impact of the product. In order to distribute this wear evenly and increase the service life of the wear-resistant parts, the developers decided on an automatic control system.
Large amounts of abrasive dust and the resulting abrasion are special challenges for all components in the huller, including the bearings. This is because dust and dirt adhere to the bearing, which in practice can lead to poor, rough operation and damage and blockage of the bearing. The recirculating ball bearing guides used initially had to be regularly cleaned and re-lubricated with a lubricating oil approved for the food industry and maintained to ensure reliable and smooth operation. Therefore, a new and, above all, maintenance-free solution was needed.
When looking for an alternative solution, the designers came across our plastic plain bearings. A total of four drylin® R fixed flange bearings are used in the new centrifugal peeler on two drylin steel shafts. Thus, for the first time in the hulling mill, the use of a recirculating ball bearing guide could be avoided. The bearings contain a liner made of the tribo-polymer iglidur® A160. The material is highly resistant to media and meets the strict requirements of the FDA for hygiene and safety in the food industry. Due to its blue colour, the material is also visually detectable. Integrated channels in the liner ensure a self-cleaning effect of the bearing. Dirt and dust cannot adhere to the bearing. The soft and flexible liner also allows for greater manufacturing tolerances. By using base polymers, reinforcing fibres and solid lubricants, the iglidur sliding elements are not only lubrication-free, but also very wear-resistant.
Even during operation, the solutions in the centrifugal peeler showed a significant improvement over metallic recirculating ball bearing guides, as the plastic bearings have a larger contact area, and the iglidur material also absorbs the vibrations. In order for the impact ring to be adjustable in height, not only the bearings on the shafts are used. A dryspin® flange lead screw nut made of the iglidur R tribo-polymer additionally ensures a quiet and vibration-dampening adjustment on a trapezoidal lead screw. iglidur R has a very low coefficient of friction in dry running, good abrasion resistance and is very cost-effective. Quiet operation is very important, as resonances can be transmitted into the housing and affect the electronics. In addition, precise adjustment ensures uniform wear of the peeling ring.
Once the peeling ring is worn out, it can be easily replaced without tools, reducing machine downtime. The wear plates, as well as the bearings, can be easily replaced in a few steps after a high degree of use of the impact huller. "From the point of view of maintenance and costs, the new solution is significantly simpler and more economical than previous solutions on the market", says Streckel enthusiastically. So far, 25 GG1 impact hullers have been used on four continents. The company also wants to rely on the tribo-polymers for future projects in order to save on maintenance and also costs.