Hydraulic shrink discs on gearbox shafts
There is enormous cost pressure in all branches of industry – and that includes mechanical engineering. The aim is to reduce production costs, keep maintenance costs low – which can be achieved, for example, by saving time in the assembly process – and ensure a long service life. That is why demands for greater efficiency have also increased in drive technology and in the development and design of gearboxes: Frictional losses must be reduced and moving masses minimized.
STRONG CONNECTION
It creates a secure connection between components, allowing high torques to be transmitted reliably, movements to be executed precisely, and thus ensuring the functionality of an entire system. The shrink disc is therefore a solution that is used across a wide range of industries and applications. Among other things, gearboxes, hydraulic motors, and electric motors are equipped with shrink discs.
Shrink discs create a force-fit connection between the shaft and hub: the surfaces are pressed together so tightly that strong static friction is created and the parts cannot slip. The force-fit connection is usually backlash-free, which ensures high precision in power transmission. It can not only absorb high forces, but also reliably withstand fluctuating loads, load peaks, and load changes.
EASY ASSEMBLY AND DISASSEMBLY
Another advantage of the force-fit connection is that its parts are not permanently joined together, for example by welding, but can be easily separated again. Simplified assembly and disassembly reduces maintenance requirements. At the same time, this increases the service life of the shaft and the connection, as no components are damaged during separation.
This is not the case with form-fit connections, such as plug-in systems or keyways: they require mechanical intervention, and use weakens the connection. Power is transmitted here by the geometry of the components, for example by interlocking teeth, keyways, or bolts. A form-fit connection requires uniform loading due to the existing play. Another disadvantage is the lower degree of efficiency, which requires a larger shaft and thus more material.
Shrink discs, on the other hand, allow the use of smaller shafts and therefore require less material. Their force-fit connection also allows the components and shafts to have a cylindrical shape, which is less costly to manufacture than interlocking with grooves.
Mechanical and hydraulic shrink discs
In the case of the mechanical shrink disc, the force required to connect the shaft and hub is applied via a screw connection; in the case of the hydraulic disc, it is applied by means of oil pressure.
The main difference is the speed at which they are tightened and loosened, which is many times faster in the case of hydraulic shrink discs. If quick assembly and disassembly is necessary, hydraulic shrink discs can be used to reduce downtime and save up to 95 percent of the assembly time compared to mechanical shrink discs. If you think of wind turbines, the shafts and gearboxes used here require shrink discs with an inner diameter of up to one meter. With a mechanical system, up to two working shifts are needed to clamp these very large shrink discs.
A hydraulic system needs only a few minutes for a shrink disc of the same size. Accordingly, mechanical shrink discs are generally used in applications that run constantly and over long periods of time, with the shrink disc being tightened perhaps two or three times and only loosened in the event of damage, over a service life of up to three decades. A hydraulic shrink disc, on the other hand, is ideal for industrial applications where a system standstill would be particularly expensive and installation and removal must be carried out quickly – for example in production lines, conveyor systems or the paper industry.
There are other special features of hydraulically tensioned shrink discs: the SHS PA series from TAS Schäfer GmbH, a leading manufacturer of frictionally engaged shaft-hub connections, can be opened and closed with a lower pressure – 200 bar – for example, while 300 to 400 bar, or sometimes even several thousand bar, are required for others.
The shrink discs are compact and consist of simple parts, and their design is easy to understand, enabling operators to carry out maintenance and repairs themselves: the bayonet system allows for quick locking and unlocking without any additional tools. In addition, the inner ring can be adapted to different sizes. The robustness combined with wear resistance and reliable performance minimizes the risk of failures, damage to other components and thus downtime. This allows industrial gearboxes to work safely and efficiently – even under extreme conditions.
The functionality and design of hydraulic shrink discs have changed little in recent decades. However, further development is moving in the direction of smaller, lighter and more powerful hydraulic shrink discs that are easier to handle and can be clamped and released more quickly. In the case of TAS Schäfer, the goal is to develop a more cost-effective hydraulic shrink disc to replace mechanical ones.
There are two designs for shrink discs: two-part and three-part. In the former, two parts with cones are pushed onto each other – the pressure for the connection is created by pushing them on. In the three-part system, two cones are arranged against each other, with an inner conical ring and two outer rings, which are moved towards each other. The three-part system has technical advantages: larger cone angles can be used with the same bolt force, which means that the system cannot clamp and jam itself. In addition, a larger amount of play can be bridged in the overall system. The three-part approach is often used in systems with highly loaded gearboxes, such as in wind turbines or in conveyor technology.
Mechanical and hydraulic shrink discs can be built with both approaches: In the latter, the force-transmitting friction surfaces are separated from the hydraulic system, thus preventing oil from coming into contact with these surfaces. This is essential because oil would reduce static friction, which would have a negative effect on the stability and performance of the connection between the shaft and hub. In contrast, there is the oil press fit, a type of connection in which oil is pressed into the connection point. However, the resulting lower friction coefficient on the contacting surfaces means a disadvantage in power transmission. In contrast, shrink disc connections are always dry and grease-free; this is accompanied by a higher friction coefficient and thus greater load transmission at the same pressure.
It is not always easy for companies to choose the right product for their requirements, as many factors have to be considered. That is why it makes sense to seek technical advice in order to find the solution that is technically and cost-effectively suitable.
An experienced partner can determine the best possible option for the respective requirements and, ideally, also manufacture it if needed. It is therefore important that the partner has the technical know-how and a high level of consulting expertise, has its own design department and can develop products itself.
Hydraulic shrink discs are a future-oriented solution for connecting shafts and hubs in transmissions. Their ability to transmit high torques precisely and without loss makes them an indispensable element in modern drive technology. Thanks to their compact design, easy handling and quick assembly and disassembly, they not only offer efficiency advantages but also reduce maintenance and life cycle costs.
Further development of this technology aims to make hydraulic shrink discs even lighter, more robust and cost-effective, while innovative coatings could simultaneously increase the coefficient of friction. This would also make it possible to realize smaller, more resource-efficient systems. Particularly in applications where downtime is expensive, such as wind turbines or industrial production lines, hydraulic shrink discs set the standard in terms of performance, reliability and sustainability.
Overall, the combination of technical innovation and material optimization remains crucial to meeting the demands of modern industrial applications and paving the way for even more efficient drive systems.
Dieser Artikel ist erschienen auf antriebstechnik.de 01/2025