With the Torque ball bushings effect Dr. Tretter Special machine elements in the portfolio, which have already proven themselves in demanding applications. Also known as slot shaft guides, they can transmit and support torques - each with simultaneous translation - even in confined spaces. The system can be set free of play via the ball size and the rigidity can be increased by means of a corresponding preload. This is a big advantage compared to normal ball bushings. Now the supplier increases the flexibility for designers with further versions of this series.
Torque ball bushings, also called groove shaft guides, can transmit and support torques - each with simultaneous translation. During transmission, these elements fulfill the function of a splined shaft. Due to the ball rolling element no stick-slip effect occurs. In addition, the ball runs in ground grooves and thus allows higher loads than conventional round guides. The translational movement and reversing operation are smooth. If this ball bush is used as a torque support, it takes on the task of a profile rail guide or of two parallel round guides. Just like ball bushings, it is also suitable as a load-bearing construction element that can be easily connected to the surrounding structure and installed. Depending on the application, the user can order prestressed elements.
Construction of surrounding parts simplifiedA variant of this drive element is the torque Flanschkugelbuchse. Depending on the size, it has a flattened or a round flange. The wall thicknesses and ball diameters are optimized to allow a compact design. Through the flange, the fitter can easily install the socket. This also simplifies the construction of the surrounding parts. Another variant is the rotary torque ball bushing. In her, the outer ring is rotatably mounted. It can simultaneously record linear and rotational movements and thus offers a space and weight-saving solution for many handling and automation tasks. The combination of grooved shaft and rotating nut also reduces the number of components significantly compared to a conventional system. This combination also reduces the diameter of the case, making it lighter and easier to assemble.
From multi-axis system to PCB assemblyTretter has now added further types to the series. These include the newly developed SSP AM compact torque ball bushings. These are currently available in sizes 4 and 5. New in the "AM" version is the outer deflection cap. In addition, the outer diameter and length of the nut are smaller than in the standard version SSP. With size 4, the torque support is no longer a keyway but by a reduction. It is suitable, for example, for use in multi-axis systems. They can still be installed in systems for PCB assembly. On request, the torque ball bushings are also available in stainless steel.
The specialist has also expanded the range of rotary torque ball bushings with types SPB and SPB-KP. Type SPB combines slot shaft guidance and angular contact ball bearings in X arrangement. Radial and axial loads and moments can thus be transmitted in a balanced ratio. This gives designers a suitable solution for high-speed rotary applications. The SPR version, on the other hand, is equipped with cross rollers located directly on the outer cylinder of the slot shaft guide. It is thus more compact and lighter, yet very stiff. A typical application is, for example, the pivotal movement between two positions in tool changers.
Short-stroke torque ball bushings - the slightly different versionDesigners can now access the new short-stroke torque ball bushings. These are designed as high-precision linear bearings with very low friction. They differ fundamentally from the other versions of the torque ball bushings, in which the balls rotate in the nut. As a result, it is possible to implement any desired length of stroke. The short-stroke torque ball bushings, however, have a cage with recesses in which the balls lie. Thus, no ball circulation takes place, but the cage moves in the linear motion in the mother. By this principle, the maximum possible stroke is limited to twice the travel of the cage in the mother. This design allows for about 20% more compact mother. In the standard version, this variant also has no end seals, because the movements should be smooth and usually low-friction. In dirty environments, therefore, bellows and / or protective covers are provided. Since all parts of the short-stroke torque ball bushings are made of stainless steel, they work well even at operating temperatures from -20 ° to + 140 ° C.
Use in coating and varnishing plantIn particular special machine builders rely on torque ball bushings with their special characteristics. This includes a manufacturer of automated coating and varnishing equipment, which is used for the functional and decorative coating of standard parts or for the interior coating of metal packaging such as tubes, cans or beverage bottles. If the aluminum component is deep-drawn and, for example, shaped into a tube, provided with a threaded ring and trimming, these systems receive it with vacuum drums and push it into chuck. These are up to a speed of up to 3000 min-1 accelerated. Subsequently, spray guns equipped with a nozzle extension move inside the components and paint them from the inside. The smallest tubes are on the order of about 9 mm. In order for the paint to be distributed cleanly, a precise movement is required. Even the smallest vibrations in the machine can deflect the lances from their exact position.
In order to immediately absorb the paint mist or the powder that is released during the coating process, an extraction system is located in each machine. The bigger her cross section, the more efficient she works. However, the cross-section can not be chosen arbitrarily large. Because in the space is located next to the suction a large warehouse in which sits the rail guide, which is responsible for the lifting movement of the injection unit. In order to minimize the installation space, the designers had to change the type of guidance of the spray technique. At this time, linear guides were installed. Ball bushings were not an alternative because they did not deliver the required performance. The developers opted for the torque ball bushings: The higher stiffness of the guide, for example, has a special effect on the accuracy and the swivel behavior. Because of the masses, which are moved during the lifting of the injection unit, the machine comes easily to vibrate. The wall thicknesses and ball diameters of the torque ball bushings are optimized to allow a compact design. Through the flange, the socket can be easily mounted. With all these advantages, they can withstand the same loads and are just as powerful as rail guides.
Use in feeding and handling systemTorque ball bushings are also used by a manufacturer of automated feeding and handling systems that safely and cost-effectively position and check tools, workpieces, assemblies or raw materials between defined process steps in a cycle-time optimized process. High demands were placed on a loading system that stacks camshafts and feeds them via a gripping system to a grinding machine. If the workpieces come to the loading system via a belt, a lift-stroke conveyor or a stacking cell, they are aligned and then checked for their contours. A quick-change gripper technology takes a blank and places it in the feeder unit, which transports it to the grinder. At the same time, it removes a finished part.
A challenge for the automation specialists was to realize a very short cycle time when feeding the workpieces. For this purpose, the carriage, which moves on the waves, compact and weight-optimized to be built. Two shafts, each with a torque ball bushing, are now installed in the machines. These are designed so performance-oriented and high-quality that ready-to-use standard elements are used. Because there are no drives on the slide with this solution, very few cables are required. Without the torque ball bushings would have a huge structure with energy guides and electrical cables are carried, which takes up a lot of space and is heavy. This makes the whole system faster, lighter and more compact. The workpiece change times could significantly shorten the design engineers.
Picture above: Torque ball bushes in the painting machine: More compact than rail guides, but just as strong and powerful.