Good vibrations with cushioned mountings

Under the Metalastik and Novibra brand names, the company’s rubber-to-metal bonded products are specified by major manufacturers around the world to attenuate noise and vibration in propulsion engines, generator sets, electronic cabinets, pumps, compressors and other auxiliary equipment.

Under the registered trademark of Metalastik, TI AVS is the originator of the Cushyfoot, Cushymount and Cushyfloat, products which it says have served the marine market for many years. TI AVS components are intended, wherever they are used, to contribute to the comfort and safety of passengers as well as quiet, efficient operation and, where required, shock protection of machinery. The range is includes the D, Super D and DX series of mounts, large rectangular mountings, Cushymount K and XK series and the family of Cushyfloat mountings. These products are all designed to meet the highest standards of reliability, vibration and acoustic efficiency as well as shock protection, all in accordance with NATO specifications, US MIL specifications, Lloyds Register of Shipping, Det Norske Veritas, and other marine approval authorities.

Among recent innovations is the Metalastik Cushymount XK mount designed for applications in medium-speed propulsion engines and marine generator sets. The mounting is designed for fail-safe operation, and to combine high levels of vibration isolation, at speeds down to 400rpm, with high deflection and load capacity – from 20kN to 120kN. It is claimed to withstand shock loads up to 180kN in all directions without deformation and a variant can be provided to handle shock forces up to 300kN.

The Cushymount XK is designed to provide optimal isolation in three directions (vertical, lateral and longitudinal) unlike conical mounts, which represent the current standard for isolating medium-speed diesel engines and which suffer from relatively high lateral stiffness. As a result, they offer relatively poor lateral isolation. The Trelleborg XK mount, on the other hand, features differing stiffness characteristics in the two horizontal planes. This offers the possibility of tuning the mounting system and optimising the desired natural frequencies. Symmetrical fixing holes in the base casting allow the unit to be rotated through 90° to change its performance characteristics, without additional drilling. There are options for a lockable jacking screw and height adjustment. The result, according to TIAVS, is a very stable mounting system with a high degree of vibration isolation and low levels of structure-borne noise.

The fail-safe element of Cushymount XK is an integral, cone-shaped buffer, which provides ‘soft touch’ limits to vertical and horizontal movement. In heavy weather, when the ship is rolling and pitching, the buffer limits the movement of the installation, providing a more comfortable solution than previous designs. There is a choice of fixed or variable buffer versions and a further practical refinement is the cut-out in the base casting, which allows the condition of the buffer to be simply checked.

TI AVS offers the XK mount in a standard range of three grades of rubber hardness, from 50 to 65 Shore hardness and it can also be supplied in different polymers for optimised dynamic performance. The captive rubber elements are housed within high-strength SG iron castings that serve to protect the mount against contamination and physical damage. The design is modular, and it is not necessary to replace the complete mountings when the rubber elements come to the end of their working life, which the company claims to be exceptionally long, offering a favourable total lifetime cost for the owner of the vessel.

For shipbuilders and engine manufacturers, an important feature of the design is the common footprint and wide range of capacities available within the Cushymount XK family. One illustration of this is its use by ABC Engines of Ghent, Belgium, which has carried out extensive testing of the Trelleborg XK Cushymounts and specifies them for use on their 12VDZC, 2750kW engines fitted in all types of vessels, including tugs, where operating conditions are notoriously heavy. Comment from owners and operators has been universally positive, with special mention made of the degree of comfort experienced at sea.

In reality, the range of applications is varied and includes diesel generator sets, marine chiller installations and pumps.

For all the qualities of an individual product or the comprehensive nature of the range, TIAVS believes that engineers will place a high priority on technical support and applications engineering. The company says it prides itself on having the most extensive catalogue of designs and rubber formulations in the industry, and alsot on its reservoir of experience and expertise. Development and applications engineering have been Trelleborg’s focus back to the company’s origins in 1937. TIAVS says it is always ready to work closely with the customer’s engineering team, studying applications on board and taking measurements in situ to ensure the optimum solution.

The other side of the equation is the manufacturing skillset to ensure that Trelleborg Metalastik and Novibra products not only meet specification in terms of isolation of vibration and structure-borne noise, but also give long, trouble-free service and proven whole-life cost benefits. All products are manufactured in the company’s own plants and supported from its global headquarters in Leicester, UK. In addition to manufacturing, this facility houses a technical centre containing the research and development unit. Production is primarily based in Leicester, with a engineering and sales support teams based in Europe, Asia and North America. The Trelleborg strategy is to make the company’s technology available on a local basis in all the world’s major marine markets.