Worm gear technology given a new lease of life
Published: 05 May, 2016
During a recent visit to Renold Gears, PWE was shown some of the latest developments in worm gear technology by Rob Stanley, sales manager for open gears. Stanley looks at how modern innovations to one of the oldest forms of gearing technology have yielded benefits for manufacturers and users of precision machinery and equipment alike.
Despite the fact that worm gears are among the oldest type of gearing systems, modern worm gear sets produced using the latest CNC machines, inspection equipment, and materials technology are providing innovative, reliable, high performance solutions on a diverse and wide range of applications. They can be found on huge coal pulverisers at power generation plants, screw down mechanisms in steel mills, and they provide high precision solutions for machinery and equipment that requires the very highest levels of positional accuracy such as rotary tables and machine tools.
PWE: Renold Gears claims its worm gear sets have some ‘unique’ features. What is it exactly that makes your worm gears different to anyone else’s?
Stanley: Renold Gears manufacture worm gears using the renowned Renold-Holroyd tooth form. This is a unique version of the ZI helicoid involute tooth form. It has a leaving side contact pattern with an effective oil entry gap for increased lubrication, smoother running and optimum efficiency.
PWE: There’s a lot of investment in quality systems and procedures on site. Why is quality so important for this type of gearing technology in particular?
Stanley: Quality is absolutely paramount in the manufacture of worm gear sets, particularly for precision applications. For example, some machine tools using our gears are producing parts for the aerospace industry.
PWE: Can you be more specific? For instance, what quality standards apply to Renold’s precision worm gears?
Stanley: Renold manufacture to British Standard 721. Our precision worm gear sets exceed the highest standard class A, and, where required, they match and even surpass DIN 3962 grade 2. You basically can’t get better than that. Worm gear sets are graded according to the wheel which is always one below the worm, so grade 2 is literally the highest quality you can get.
PWE: So if quality and precision is so high and the Renold-Holroyd tooth form is so highly regarded is there anything new in the field and, if so, what are some of the latest developments?
Stanley: To improve the performance of our own gear hobbing machinery we developed the Precision Dual Lead Backlash Adjustable Wormgear Form. Now it’s known as the Renold DL series. Dual lead worm gears are the trusted solution for precision applications such as rotary tables, machine tool positioning systems and cutter drives.
PWE: What do you mean by dual lead worm gears?
Stanley: Dual lead, or duplex, worm gears are specialist gear sets that enable backlash to be adjusted to the required amount during the lifetime of the gears. They are manufactured with two leads, one short and the other long. The result is a worm thread that increases in thickness from one end to the other. If the worm is moved in an axial direction when in mesh with the worm wheel then the backlash can be adjusted between them to the desired amount.
(According to Stanley, the DL Series dual lead worm gear offers many advantages to the alternative split worm gear design. It provides a kinematically correct gear, that can run in either direction of rotation, and on which the backlash is infinitely adjustable from an acceptable maximum to near zero. To simplify the adjustment process the company recently designed and launched a high-precision dual-lead adjustment mechanism called Ren-Adjust.)
PWE: What are the benefits of this and how does it work?
Stanley: It permits precise adjustment without the need for additional machining operations whilst setting the backlash (i.e. grinding spacers used for controlling the worm’s axial position). The backlash is adjusted by simply removing a shrink disc allowing the worm shaft to move independently from the adjustment sleeve. By turning a precision screw the worm shaft is then moved axially, which adjusts the working backlash. Once the backlash is acceptable, the shrink disc is then re-applied.
PWE: What sort of specialist plant and equipment is required for the manufacture of high precision worm gears?
Stanley: We’ve got a wide range of gear hobbing machines with the very latest CNC technology and Klingenberg tooth measurement. Similarly, worm shaft production also takes place on CNC thread grinding machines with Klingenberg profile measurement. This reduces the need for off machine inspection and enables any deviations to be corrected during the production process.
Stanley concluded that this is supported with an in-house tool manufacturing facility enabling tools to be designed and manufactured to produce the Renold-Holroyd tooth form; although any tooth form can in fact be replicated.
For further information please visit: www.renold.com