Engineers have explored many ways to make shaft-hub connections over the years and this present article explores the evolution to the hydraulic type that is now considered by many to be the state of the art.
Today three types of shaft-hub connection are commonly used by machine builders, namely keyways, mechanical connections and hydraulic clamps. We will consider each type in turn.
A keyway connection consists of a slot cut in a shaft component, receiving part of a key that also engages with an equivalent slot on a mating hub component, thereby locking the two parts together.
While keyways are cheap to produce and well standardised, disadvantages include:
Mechanical clamping connections consist of two sleeves with tapered surfaces that are pressed against each other along the shaft. Many screws with a high tightening torque are used to hold it together. When mounted the two sleeves deform into contact with the bore of the hub and the surface of the shaft. This technique is used in rough applications where surfaces finish and tolerances are variable.
While this standard connection is suitable for transmitting high radial loads, bending torque and can withstand temperature variations, disadvantages include:
Hydraulic clamping connections enable effortless mounting, adjustment, easy reach and a well-balanced design. The technique is a problem-solver for critical applications. ETP hydraulic clamping connections are beneficial for working with tight tolerances, resulting in superior runout.
French scientist Blaise Pascal devised the maxim of pressure propagation in liquids during the 17th century. The principle refers to pressure changes in a liquid within a confined container where pressure transmits evenly throughout the liquid. When applying pressure at one point of the liquid, an even pressure change occurs throughout the whole container (see below).
ETP hub-shaft connections are guided by Pascal's principle. The products consist of hardened double-walled steel sleeves that are welded together to create a hollow chamber; this chamber is filled with a hydraulic pressure medium.
By using the ETP principle, a hydraulic shaft-hub connection offers a number of advantages compared to the alternatives:
Available through Abssac, this is a truly innovative product. All ETP products consist of a double-walled hardened steel (in some cases stainless steel) sleeve, filled with a pressure medium. Within the connection flange there are one or more screws and a piston with seals for the pressure setting. When the pressure screw is tightened an even and moderately high surface pressure is created against the shaft and hub, causing the locking effect. The self-contained product allows the clamping procedure to be repeated many times. Whether the hubs are to be removed or repositioned, mounting and dismantling takes only a few seconds. The hydraulic principle gives immediate advantages for today's machine builders.
Follow the link for more information about ETP hydraulic shaft-hub locking bushes from Abssac.