IMPROVED DESIGN FOR AN IMPELLER KEY GROOVE (02-Nov-2009)

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IMPROVED DESIGN FOR AN IMPELLER KEY GROOVE

BACKGROUND

    The present invention relates generally to a groove or keyway machined on an impeller and more specifically, to an improved design of the key for transmitting torque between a shaft and an impeller in a centrifugal compressor.

    An impeller key is generally a square or rectangular piece of metal located in the groove underneath the impeller hub and the shaft. The function of a key is firstly to provide a positive lock to prevent any angular displacement between the impeller and the shaft, and secondly to transmit input power from the shaft into the impeller. A groove is a longitudinal slot or notch usually milled into the outside of a cylindrical machine shaft, or into the inside hole of a pulley or gear, all of which indentations are intended to accept a small rectangular metal key or semi-circular bit of metal. This provides one way of locking pulleys, gears, impellers and other parts to shafts so as to prevent relative angular movement. The groove usually has rounded ends. Therefore, a square key does not fill up all the spaces in the groove - the rounded ends will remain void. This void creates some unbalance on the rotor that may result in excessive vibration as well as excessive stresses especially at high speed.

    There exist various conventional techniques, such as rectangular-shape and rounded shape key grooves. The key groove machined on the impeller represents an intensification factor for stresses. For some compressors due to the shape of the groove, this may lead to stress at the key groove location higher than material strength causing machine failure due to concentration of stresses.

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    Accordingly, there exists a need in the art for a new and improved design for the key and groove for effective transmission of the torque between a shaft and impeller in a centrifugal compressor.

BRIEF DESCRIPTION OF DRAWINGS

    Figure 1 illustrates a diagram of an improved design for an impeller key according to the present invention.

    Figure 2 illustrates a diagram for the groove on the impeller according to the present invention.

    Figure 3 illustrates a diagram for the impeller groove on the shaft according to the present invention.

DETAILED DESCRIPTION

    Figure 1 illustrates a diagram of an improved design for an impeller key according to the present invention. The cross sectional view of the impeller key showing the width of the key (L), height of the elliptical half (H) and height of the rectangular half (h). It further illustrates the longitudinal view of the key showing the length (A) and fillet radius (r).

    Due to geometric discontinuities in a material, such as a groove, the stresses in the locality get...