Mechanical and plant engineering
Hans Weber Maschinenfabrik GmbH has been synonymous with perfection in mechanical engineering for almost 100 years and provides customers from over 60 countries with impressive high-quality grinding and extrusion products. Over 20,000 machines are in use around the world. Most of their components are produced at the company’s headquarters in Kronach, Upper Franconia. For around 50 years, VEKA AG has been using Weber extruders to manufacture plastic profiles for windows and doors.
The two family-owned companies share not only a long-standing partnership, but also high standards of quality, innovation and reliability. These go hand in hand with future-oriented and sustainable action. This requires openness to change and to alternative ideas, especially in maintenance. Up to now, VEKA AG maintenance personnel have changed the gear oil on Weber extruders after 6,000 operating hours or one year. This means that they are always on the safe side, but if a large number of systems are in operation, the costs for the maintenance time and the purchase of the new oils increase. In order to reduce costs while saving fresh oil resources, the two companies began a joint field trial.
A Weber DS 11 twin-screw extruder
A mineral oil-based ISO-VG 460 industrial gear oil of type CLP was tested. It was installed in the transmission of a Weber DS11 twin-screw extruder. VEKA AG uses it to manufacture window profiles in Sendenhorst in Münsterland. It is here that the company’s headquarters and centre of excellence are located. In extrusion, thermoplastically deformable plastic is pressed through a shaping aperture under high pressure as a tough mass at a temperature of approx. 190°C. In a twin-screw extruder, two worm shafts are placed in a heated cylinder. These rotate by means of an upstream transmission and intertwine. They move the tempered raw material forwards. At the same time, the movement generates energy, which causes an additional temperature increase and causes the plastic to melt.
The performance of the transmission is not only essential for the melting process, it must also cope with high torques with relatively low axial spacing and withstand the axial forces from the extrusion process. This in turn results in the requirements for the industrial gear oil used. It should have a high pressure absorption capacity, excellent wear protection and very good resistance to ageing.
VEKA – first-class condition monitoring
From the outset, the industrial transmission oil was regularly monitored and all values and activities documented. The temperature of the gear oil is continuously checked. It should not exceed 65°C. To ensure the correct temperature at all times, VEKA AG employees regularly maintain the transmission's cooling system, among other things. They also check the bleed screws and their filters for cleanliness and functionality. This allows warm air to escape instead of forming condensate. And the clean filters prevent any impurities from entering the oil circuit.
40,000 operating hours – 28 oil analyses
The trial began at the end of 2014 and with it a long series of OELCHECK lubricant analyses. Since the ageing of the oil plays a decisive role in its use, all-inclusive analysis kits 2 are used with additional determination of AN/NZ. The AN (acid number) or NZ (neutralisation number) is a measure of the degree of oil acidification. By comparison with the fresh oil values, the AN allows conclusions to be drawn regarding the oxidation of the oil and the breakdown of oil additives, making it a valuable addition to infrared spectroscopy, which determines oxidation in A/cm. The oil samples are taken at regular intervals via a drain tap specially installed on the system. Data is recorded and transmitted to OELCHECK via a QR code and app. The laboratory reports are jointly reviewed by employees of VEKA AG and Hans Weber Maschinenfabrik GmbH.
To date, the gear oil has reached a running time of over 40,000 operating hours, which have now been monitored by 28 oil analyses. The current laboratory report shows: All values are still in the green range! Even the typical wear values for copper, tin and lead coming from the bearings or bearing cages are non-critical. Contaminant levels, such as from silicon, are minimal. The viscosity and oxidation, synonymous with oil ageing, and the AN/NZ value have not yet reached their limits. The gear oil condition as a whole allows further operation of the gear oil.
Conclusion: Condition-dependent oil changes
So far VEKA AG has replaced the gear oils of the extruders after 6,000 operating hours or one year. Assuming regular OELCHECK oil analyses, the oil changes are now carried out for all systems that are similar to the Weber DS 11 twin-screw extruder, depending on the oil condition. The trial continues, but its objective has already been achieved. Thanks to condition-dependent oil changes, the costs of fresh oil and labour have been reduced. OELCHECK lubricant analyses ensure the necessary safety of operation.