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Press Releases The Worm Gear Unit - A UK Industry Favourite
What is a worm gear? How to describe it? Well, it’s about as simple a gear unit as you can get – worm gears are typically, in their simplest form, a single reduction right-angled drive. With a worm gear, tooth contact is predominantly a sliding action as opposed to bevel tooth contact, where rolling action is predominant. The worm gear is an older design, but for ‘older’ also read ‘proven’ and ‘well established’. The worm gear unit has consistently proved its value through its reliable operation, high overload capacity, high ratio possibility in one stage, good damping and ultimately, smooth running. Flender’s own Cavex design was introduced to the world at the 1952 Hanover Fair, and by 1960 was being used in applications as diverse as conveyor drives, concrete mixers, cutting equipment and welding manipulators. Developed by Professor Niemann at Flender, the patented Cavex design features a unique concave (hollow) worm tooth profile working in conjunction with a convex (rounded) wormwheel tooth profile. This non-involute system using concave-convex tooth profiles can be given the general term ‘conformal gearing’. This special tooth form offers several advantages over conventional worm gearing, including improved efficiency, higher load bearing capacity, increased service life and lower heat generation, whilst retaining the smooth running characteristics associated with conventional worm gears. And it is these technological benefits that have ensured the lasting popularity of Cavex over a much longer time period than most gear unit designs. Compared with conventional worm gearing, the Flender Cavex conformal gearing system (using concave-convex tooth profiles) significantly increases the surface contact area and thus reduces the associated Hertzian stress. In addition to this technical benefit, the Cavex tooth form provides an improved oil film between the meshing flanks compared with conventional involute helicoid worm gearing. Tooth contact lines on the Cavex profile are curved and have a tendency to run at right angles to the sliding direction. Tooth contact lines associated with a conventional worm profile tend to run parallel to the sliding direction. The generation of an oil film between the tooth flanks is assisted when the sliding direction is at right angles to the contact line. The improved lubrication aspect associated with conformal gearing gives Cavex worm gear units the benefit of lower heat generation and improved efficiency. The accepted material combination for worm gears is a phosphor bronze wormwheel and a case-hardened and ground steel worm. With this combination, the limiting element based on permissible load for strength (bending stress), is nearly always the wormwheel. The use of a convex profile on the teeth of a Cavex wormwheel enables a wider root thickness to be achieved compared with conventional worm gearing; this provides greater security against tooth fracture and additional resilience to shock loads. Ongoing refinements Flender has undertaken a number of refining improvements to its concave-convex profile during the 50 years that Cavex has been in the market, including changing the angle of engagement, the radius of curvature and the tooth thickness. Changes have also been made to the housing, making it single piece wherever feasible for added strength, rigidity and noise reduction, and also a new fan system is providing more efficient cooling. Gear lubrication has also been improved over the same time period, and worm shaft diameters have been adapted according to centre distance/ratio to provide optimal balance. Finally, optimum addendum modification has been made possible by having a separate and dedicated cutting tool for each centre distance/ratio combination, which has brought about much higher power rating and performance levels. Development continues on Flender worm gear units, which are now achieving efficiencies comparable in some instances to bevel helical gear units in terms of energy costs, as well as lower noise emission levels resulting from improved contact ratios. Four additional sizes have been introduced by Flender in the last decade, with centre distances up to 630mm, responding to increasing demands for larger units, such as for pre-heaters, metro escalators, cement mills and wire drawing machines. Although it may appear to be a simple gear unit, the advanced technology of the Cavex worm gear unit has proved itself one of the most enduring – in an age where change is an all-too-regular occurrence. Further information on Flender’s Cavex gear units is available from Flender Power Transmission, telephone +44 (0)1274 657700, or e-mail info@siemens.com ENDS For further media information please contact Bridget Summers, Footprint, PO Box 4, Colton, Leeds LS15 8WX, UK. Tel: 0113 251 5697. Fax: 0113 251 5351. E-mail: bridget@fim.org.uk |
The worm gear unit has always been popular in the UK; more so than
in the rest of Continental Europe. Perhaps it’s because UK engineers just took to
its inherent simplicity and reliability over the years, but the fact is that the
worm gear is still popular in the UK market.