The possibility to customize the components of worm gear reducers allows an optimization of their application
The Varvel Group, the Bologna-based specialists in power transmission, are committed to customization as a means of satisfying users’ needs. In the case of the company’s worm gearboxes, this customization begins with the choice of materials from which the gearbox is made. RS and RT Series worm gearboxes are superb examples of the versatility of Varvel products (but not the only, how you can read in the article System customization thanks to the modularity of gearboxes)
The search for the most suitable solution stimulated the study the possibilities for every circumstance, bringing great versatility in the range and starting to optimize the application of worm gear reducers. The constituent elements of these products are basically three:
- The casing,
- The worm shaft,
- The worm wheel.
The optimization of bronze in worm gearboxes
The worm wheel in particular is available in a number of variants, each made to suit the needs of specific applications. To optimize costs and avoid the unnecessary use of bronze (a precious and therefore high-cost metal), Varvel began long ago to produce worm wheels made from two components, with bronze used only where really needed. Varvel's standard worm wheel features a hub normally made from cast iron and a bronze sleeve bearing the teeth that mesh with the worm. This solution produces a customization of worm gearboxes that are suitable for most normal applications.
Cast iron hub to obtain greater resistance
In certain areas of industry, however, this standard hub in grey cast iron may not be able to achieve the level of performance required. Where greater mechanical strength is needed, Varvel offers worm wheels with a hub in spheroidal cast iron, an alloy that offers superior performance to grey cast iron and is therefore better suited to heavy-duty use. In applications in the food industry and in all areas associated with ship-building and the marine sector, cast iron hubs are unable to withstand the highly oxidizing operating environment. Food processing machines have to be washed with highly aggressive sanitizing solutions, and the atmosphere on or near the sea is too rich in chlorides. To avoid the problem of oxidation in these sectors, Varvel produces worm wheels with a stainless steel hub.
Nickel, normalized or hardened steel to resist to very violent impacts, very high loads and high stresses
For situations that demand greater mechanical strength, where spheroidal cast iron cannot be used, and for limited production series, Varvel also makes hubs in normalized or hardened and tempered steel. Worm wheel customization and adaptation options also extend to the bronze sleeve in which the teeth that mesh with the worm are cut. The normal material for this part is leaded bronze, an alloy that remains malleable throughout the fusion process and that therefore reduces production times while improving efficiency. Under normal conditions, leaded bronze gear sleeves satisfy the needs of most common applications. Here too, however, different circumstances may require customized and specific solutions. Variations in performance can be achieved by changing the bronze alloy from which the sleeve is made. Nickel bronze gear sleeves are used for higher torque transmission, to improve resistance to compression and impact and to combat corrosion. In applications involving larger worm wheels and wherever particularly high loads and stresses lead to violent impacts, aluminum bronze (also known as BRAL) sleeves can be used. Gear teeth made from this bronze alloy are less likely to break under the effect of sudden, violent impacts, and therefore guarantee less machine down-time for repairs and replacements.
Gearboxes with corrosion resistant materials are required for very oxidising environments
There are even some contexts in which composite worm wheels cannot be used and the only possible solution is to fit a single-piece worm gear. Under highly oxidizing conditions, for example, as in the food industry and marine applications mentioned above, the normal solution is to use a single-piece bronze worm wheel-certainly more expensive but also able to guarantee excellent corrosion resistance. This solution is ideal for dedicated production series and niche markets. A cheaper alternative, though one with certain limitations in terms of application, is to use single-piece cast iron worm wheels. These wheels can only be used in applications involving slow peripheral speeds of under 2.5 metres a second because the teeth mesh with steel and are therefore exposed to a higher risk of damage.
Customizations possible thanks to attention and awareness
This extensive range of solutions for worm gearboxes demonstrates the unrivaled versatility of Varvel products and explains their suitability for so many different applications. It also testifies to the amazing possibilities for customization that Varvel offers all customers, in line with a design philosophy aimed at developing the best possible solution for every need. An in-depth understanding of many different sectors allows Varvel to accurately interpret customers' requests and to respond with products that solve the specific problems while simultaneously improving the efficiency, operating costs and functionality of the machines in which they are installed.