The Varvel Group designs and produces gearboxes, gearmotors and speed variators for low- and medium-power fixed applications in numerous areas of industry. The company was created in 1955 in Bologna and today is an internationally renowned partner in the power transmission sector, exporting more than 70 per cent of its turnover. 

The skills it has developed over more than sixty years allow Varvel to meet the demands of the industrial world with both standard and customized solutions. A strong focus on innovation allows the company to support a constantly evolving market.

With a manufacturing output of 500,000 products every year, two foreign subsidiaries, and business partners in more than sixty countries worldwide, Varvel is a leading company in the gearbox and gearmotor industry, which is largely situated in northern Italy, and especially in the province of Bologna.

The gearbox sealing system

A critical aspect of the construction of gearboxes relates to the sealing of the casing using the side covers.

Gearbox casings often have an irregular shape because they are designed according to the shape of the gears and components they must contain. The sealing system is characterized by irregular bolt spacing, deformable structural parts, and low surface pressures.

The casings must ensure the containment of the fluid that surrounds the gears—oil, lubricant, and grease—over the entire life of the product; hence the importance of gaskets.

The paths taken by Varvel over the years to address this critical issue have evolved.

In the eighties and nineties, Varvel gearboxes used “pressed paper” gaskets.

Around the year 2000, in conjunction with a product range review, these gaskets were replaced with liquid sealants used specifically for cast iron and aluminum.

These products performed well but were limited in their use on an industrial level because they were subject to some requirements for correct assembly.

In 2013 Varvel decided to launch an improvement team, whose aim was to evaluate replacing the liquid seal with a solid seal in all worm gearboxes.

Over the course of six months, the working group analyzed and compared different solutions until it found a solid SLA gasket that was considered the best choice for that type of application.

Following the tests, the gasket was implemented on a wide range of Varvel products.

This gasket solved the problems related to the liquid sealant—the initial handling, polymerization, and settling time was eliminated, as was the greasiness in the lids that hinders polymerization.

The request

The SLA gaskets were made of a metal core and two layers of pressed graphite, one facing the case and one facing the lid. In situations where the gearbox is highly stressed; for example, when it is motorized with servomotors, the graphite layers may compress until they flake off and emerge from between the two seats like a strangulated hernia. With the increasing diffusion of the stepper and brushless motors, which are characterized by high rotation speeds and by very frequent start-stops, Varvel begun to look for alternative solutions to SLA gaskets, which led them to contact Vito Rimoldi.

The solution: seals made of novapress® 850

In response to Varvel's request, Vito Rimoldi proposed and manufactured a sampling of gaskets made from novapress® 850, a Frenzelit material that perfectly combines the positive properties of an elastomer gasket with the robustness of a fiber gasket.

novapress® 850 is, in fact, a material characterized by high adaptability and one hundred times higher tightness as compared to all traditional fiber gaskets.

Vito Rimoldi strongly believes in this solution—for years it has dedicated time and resources to analyzing the operating conditions in which the gaskets work inside transmission systems, including elements like the shape and roughness of flange surfaces, deformable structural parts, irregular bolt spacing, and low surface pressure, which are decisive for the choice of the most suitable material for achieving a good seal.

Seals made of novapress® 850 can compensate for the imperfections of the interface components and maintain the mechanical stability typical of fiber-reinforced seals even in the presence of medium-high temperatures.

The Vito Rimoldi gaskets have been tested on Varvel gearboxes.

After four months the gaskets showed no critical issues—there is no flaking and the gasket perfectly compensates for the rough crests and valleys of the carcasses and lid surfaces, both statically and, importantly, in a dynamic way.

The thickness is also suitable for the SLA gasket, so much so that no dimensional changes are necessary. This greatly facilitated the transition from the old gasket to the new one—finding a phase in-phase out with the same thickness, internal and external diameter, center distance, holes, etc., was a technical victory.

The implementation of Vito Rimoldi seals

Beginning in September 2021, Vito Rimoldi gaskets were installed in the Varvel RD, RT and RS series gearboxes. Today Varvel is carrying out even more selective tests on other gearbox series; in these tests, the seals are not showing any defects, which is further proof that they are a high-performing solution for that type of coupling.