ECONOMICAL, COMPACT AND SAFE - DISC PACK PRECISION COUPLINGS FOR THE MOST DIVERSE REQUIREMENTS

The basic requirement for the most accurate possible transmission of torque from the input to the output is the same. It applies both in pumps of refineries, in machining centres for tough machining operations and in highly sensitive use in test rigs that: Axial, lateral, and angular misalignments must be compensated for free of backlash and wear. Downtime should be avoided in the face of increasingly higher utilisation rates and torques. Here the custom design of clutches acquires special importance for the economic efficiency of machines and equipment.

Increasing demands on designers
Designers in general mechanical engineering are today confronted by an enormous variety of drive lines. So that the individual components are suitable for use for particular requirements, increasingly complex designs and calculations by the suppliers of components are necessary. This also applies for couplings: The engineering departments of the coupling manufacturers have to take into account in the design a complex patchwork of physical requirements with regard to torque, torsional rigidity, spring stiffness, moment of inertia, possible imbalance and freedom from backlash.

R+W presents newly developed disc pack precision couplings
R+W Antriebselemente GmbH has developed novel disc pack precision couplings, which it presents to international experts at the Hanover Trade Fair. The couplings developed with a view to high and increasingly specialized requirements meet the growing requirements reliably; they are torsionally stiff, temperature resistant and have a high power density with an almost unlimited service life, even under extreme operating conditions. Very low restoring forces in all three types of misalignment ensure low bearing temperature rises. Hardly any other kind of shaft coupling achieves comparable temperature resistance and power density. The manufacturer guarantees the latter in addition to the use of high-strength materials by FEM calculations and their subsequent verification in endurance tests on its own test rigs.

While these requirements are common to all the popular disc pack precision couplings, there are essential differences resulting in benefits in application. The disc pack precision couplings from R+W are usually of smaller build than comparable products on the market. The smaller size is beneficial right from the start. Among other things, designers need less space in the design of machinery and equipment.

Benefits by dispensing with set screws

The special screw fit contributes to improved safety, as well as to precise transmission of torque. While on the market set screws are used for the positive transmission of part of the nominal torque, the R+W couplings of the LP series are fitted with high-strength screws. This offers functional advantages over the use of set screws: The use of high-strength screws guarantees a high surface pressure and clamping force, which is essential for safety and contributes to the exact positioning of the assembly. Because of this design, unlike the use of set screws, the torque is transmitted only by friction - with the highest precision.

Disc packs made from high-strength spring steel: homogeneous alignment
A basis for a high level of torsional stiffness is homogeneous alignment of the disc packs inside the coupling. Each single disc is arranged offset at 60 degrees to the next during assembly. An optical characteristic on each disc facilitates accurate assembly according to this principle. In this way, the rolling direction of the steel used in the design exerts no negative influence on the torsional rigidity of the disc pack precision couplings. The disc packs are made of a specially developed spring steel. The material is tailored to the needs of the application. It has very high tensile strength and is at the same time very flexible, to deal with the different forces - for optimal torque transmission and high torsional stiffness.

A characteristic of the LP disc pack precision couplings with benefits for designers is that they are delivered in fully assembled condition. Users need not worry about assembling the couplings, there is no need to tighten any screws or similar. This saves time and reduces any possible sources of error by users and thus contributes to greater efficiency in operation.

Transmission of torques of up to 20,000 Nm
The LP series is available in four different models for nominal torques between 350 nm and 20,000 Nm. They have been specially designed for the different requirements of users in different industries.
Within each of the individual models, there are six series, graded according to specifications. The disc pack precision couplings are equipped consistently with six-hole discs, with diameters of between 18 and 140 millimetres (depending on the series), and uniform angular offset of 0.7 degrees per disk pack. Bearing loads and vibrations are minimized thanks to their special design.

Models for different applications


The LP1 model has a single flex design, provides an extremely high level of torsional stiffness and is ideally suited for use under extreme loads on test rigs. The coupling consists of two high-precision coupling hubs made of high-strength steel. These are connected with the disk pack by bushings and high-strength screws, clamping screws (DIN 916) ensure axial fixation. The bushings are also made of high-strength steel, screws and nuts have the quality 12.9. The measuring shaft can be installed unsupported in the case of the LP1 for quick and easy use. Applications are for example mixers, agitators, immersion pumps or fans.

The LP2 model with keyway mounting, in which the torque transmission is based on positive engagement, is in contrast to the LP1 of double flex design, with two disk packs and variable spacer tubes, which are connected by bushings and screws with the disk packs. For a substantial saving of time and effort, the fully assembled coupling can for example be installed to connect the motor and worm gear without displacing the two components to be connected. The spacer of the coupling is removable for increased flexibility. The LP2 with its high displacement capability with low restoring forces was developed especially for the demanding requirements in certain areas of mechanical and plant engineering. Manufacturers of paper and printing machines also benefit from their properties as well as certain applications in material handling (e.g. conveyor belts or lifts). The couplings are also used in the steel industry in punching machines or presses as well as in the construction of generators or mill drives.

In comparison to this, the LP3 model requires no keyway mounting, but a backlash-free, frictionally engaged conical clamping ring for mounting on the shaft. This ensures with a fixed stop a high level of safety as the conical ring sits tightly against the hub. The coupling is also of double flex design and has spacer tubes like the LP2.
The LPA is a special model in the LP series. It is designed for the special requirements of the American Petroleum Institute (API). This association represents the interests of the American oil and gas industry. The API defines the standards for materials and technologies that may be used in the petroleum industry. The LPA is designed with two safety loops and meets these high requirements on operational reliability, for example when used in refineries for the connection between motor and pump in process pumps, water pumps, compressors or turbines. The coupling can be mounted radially, hence no displacement of the plant is necessary. The LPA also consists of two precision machined coupling hubs and spacer tubes, which are connected with the disk pack by bushings and high-strength screws.

Summary

Disc pack precision couplings of the LP series from R+W guarantee precise torque transmission - torsionally stiff, backlash-free and maintenance-free. The homogeneous alignment of the of the high-strength spring steel disks compensates for high misalignment with low restoring forces. Their special design facilitates easy and quick installation by the user, for instance in the paper and printing machine industry, materials handling, the steel industry and the construction of generators or mill drives.
With a view to future trends and rising requirements, R+W has a separate development department for new developments and special solutions in response to customer inquiries. All products are extensively tested and optimised on its own static and dynamic test benches. These enable tests at up to 75,000 Nm torque or vibration of up to 30 Hz.

Author: Dirk Hasenstab

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