How High-tech Materials Save Up To 60% In Weight On Couplings

2023 Author : Hannah Pearcy | [email protected] . Last modified: 2023-05-24 11:12

When it comes to the sensible use of energy and resources, it has long been clear to the aerospace industry, but also to the automotive industry: The goal must be to reduce masses in order to increase speed or save energy. But this also applies to production machines such as industrial robots, machine tools or hand-held machines: Here, too, reducing the mass can conserve resources or increase performance

With its safety couplings, R + W also follows the trend in general mechanical and plant engineering to produce ever higher quality with constant precision at ever lower costs. Lightweight construction also plays an important role in this context: lower moments of inertia due to the selection of new high-tech materials in combination with new types of coatings result in an enormous reduction in weight while increasing the release torque.

Frank Kronmüller, managing director, R + W Antriebselemente GmbH

Construction completely covered

The compact SL coupling series from R + W works absolutely free of play thanks to the tried-and-tested spring-loaded ball locking principle. In collaboration with universities, the developers of the coupling manufacturer have rethought the series from scratch within just two years. R + W did not limit itself to further development or optimization, but designed, constructed and manufactured a completely new series. This was the only way to achieve the goal of reducing 50% of the weight.

The SL coupling series is made from high-tech materials combined with a unique coating. This reduces the weight by up to 60% compared to the standard series. A clutch for torque limitation of up to 160 Nm only has a dead weight of 370 g and a moment of inertia of 0.8 × 10 ^-3 kg m ² .

The series comprises four sizes. Starting at 10 Nm to 700 Nm, torques can be safely limited. In addition to the choice of materials, the weight reduction was also achieved by compressing the individual components - without affecting the durability or accuracy. The safety couplings in the lightweight design of the SL series can achieve cycle times of up to 10,000 disengagements or more. The use of new disc springs specially developed for R + W in combination with a further development of the ball locking principle leads to an increase in torque of up to 40%.

Additional information at a glance: The advantages of lightweight constructions

• Energy saving processes
• low manufacturing costs
• less use of materials

Added value can be generated especially in dynamic applications such as the implementation of greater acceleration while increasing precision.

A leading manufacturer of aircraft and aviation equipment is one of the users of the new couplingswho was looking for a safety coupling for an intelligent lifting device in mobile cabins for transport and service work. The goal: to reduce the moments of inertia with a compact design. Depending on the aircraft type, the release torque should be integrated between 40 and 135 Nm with a maximum total length of 30 mm and a maximum total weight of 200 g in a scissor lift table in a confined space. The company chose the lightweight safety coupling from R + W. The coupling of the SLP series 30 was adapted to other customer requirements: with overload protection in a sealed design, protected from liquid media and dirt, can be used in any weather.

Dead weight only 200 g

In this application too, the use of high-tech materials was able to reduce the weight by up to 60%. For example, with a torque limitation of up to 135 Nm, the SLP 30 only has a dead weight of 200 g and a mass moment of inertia of 0.1 × 10 ^-3 kg m ² . Due to the special toothing of the base body and mounting flange, the safety coupling reacts in the millisecond range with a repeat accuracy of ± 5%.

Industrial clutch for electric cars

Even those who drive an electric car can come into situations that force them to brake hard. However, the braking energy that is released brings a high moment to the transmission - higher than it would be able to cope with. A safety clutch therefore ensures its protection.

Mechanically switching safety clutches actually protect systems and machines in the event of a collision or incorrect operation. But the clutches can do more - with adjustments, they can also be used in electric vehicles . For a pilot project, the engineers at R + W also developed a mechanical safety coupling for this application. It is located between the two drive shafts on the gearbox and the brakes. In the event of full braking, the force generated is distributed to the brakes in different ways. Since the braking energy has a higher torque than the gearbox allows, the gearbox must be protected against the back torque of the brakes.

The instructions of the client it was a mechanical safety clutch with a maximum weight of 1.5 kg min for an overload of more than 600 Nm at 1100 ^-1 to develop. This could be achieved with the TÜV-certified model series SLN of the 300 series. It separates the input and output side in the millisecond range. The safety clutch works so that the backlash is guaranteed. The SL series is made of alloys - new for coupling technology - in combination with coatings. A clutch for a torque limitation of 600 Nm, as it could be used in an electric vehicle, has a dead weight of 1.5 kg and a mass moment of inertia of 3 × 10 kg m ² .

In addition to the choice of materials, the developers also achieved weight reduction by compressing the individual components without negatively affecting the durability or accuracy. These safety clutches in lightweight construction can realize cycle times of up to 10,000 disengagements or more.

The use of disc springs specially developed for R + W - they have a special characteristic curve - in combination with an optimization of the ball detent mechanism led to a torque increase of up to 50% , precise torque limitation and short switching times.

User meeting mechatronic drive technology

The focus of the user meeting mechatronic drive technology is on the mechanical components of gears, clutches and brakes as well as their design, dimensioning and interaction in the overall mechatronic system.

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Wear minimized

The clutch only begins to move after the set disengagement torque has been exceeded. The balls leave their conical counterbores and the torque flow is interrupted. The spring force decreases towards zero. Back and forth movements of the ball in their countersinks in the limit range of the set disengagement torque are not possible. Clutch wear during operation below the disengagement torque is avoided. The reduced spring force during the switching process and the light switching ring reduce the forces and wear during the switching process to a minimum.

The international space station ISS is one of the largest technology projects of modern times. Since 2000, between two and three astronauts have been researching key topics such as life sciences or materials science. German scientists are specifically studying the human balance system, basic physics (plasma research) and radiation biology issues.

The regression of the bones and muscles of the astronauts during the stay of up to 6 months is a known fact, because weightlessness changes the human body. Aerospace physicians also know that when you stay in space for a longer period of time, the defense against infection decreases, that the sugar balance changes, and that bones and muscles recede due to less stress.

Train safely on the ISS

In order to avoid muscle regression, a special training device was developed by the ESA and OHB system. Similar to a rowing bench, special muscle parts of the astronauts can be trained. A special version of the R + W safety coupling SK1 made of stainless steel in a weight-optimized and sealed version serves as a protective function in this training device. As an overload unit in an angle-synchronous design, the sensitive load unit is protected if the astronaut's force is applied too much. The re-engagement after 360 ° enables the exact position of the rudder bench. After a 15-day flight time, the maintenance-free training device was permanently integrated in the space station and has since been used by the respective crew to build muscle.

The structure of the special safety coupling differs from the standard construction in many areas of the coupling. The coupling manufacturer met the requirement for a "light" and specially sealed safety component by reducing the weight of the existing safety coupling series and many years of experience in the field of vacuum applications.

The selection of special materials and the compression of the components used were decisive for the reduction in weight - of course without any impact on durability or accuracy.

Special sealing prevents grease from escaping

Overload components that are based on the ball detent principle require a lubricant. This prevents corrosion of the components in continuous use or excessive stress on the components in the event of an overload (disengagement of the coupling). Due to the residual friction of the disc spring, the clutch heats up during repeated disengagement processes, which leads to a lower viscosity of the grease. Excess grease or lubricant escapes.

Exactly this behavior had to be avoided with the safety clutch in space. Special seals on all parts and components of the coupling including an extended switching ring hermetically seal the grease in the coupling. The eventual leakage of the unnecessary grease after repeated disengagement is avoided.

Furthermore, the ESA demands that all materials used are approved for the space industry. The components of the safety coupling had to be tested in advance, especially in the area of the highly stressed mechanical components. After the successful TÜV inspection of the R + W safety couplings for standard applications, an internal inspection was carried out according to similar criteria. A final documentation or listing of all components met the high requirements of the space industry. R + W therefore develops, designs and manufactures safety components not only “for” the space industry but for “real” use in space. This shows the know-how and professionalism of the manufacturer for unusual requirements.

The sum of the changes in the ball locking principle and the use of new materials enabled R + W to develop the series of backlash-free Torqlight SL safety couplings. This provides a light, compact safety coupling with a high power density. (ud)