Generation of Wheel-Blast Shot Velocity

Author:  David Kirk
Source:  The Shot Peener magazine, Volume 21 / Issue 2, Spring 2007
Doc ID:  2007045
Year of Publication:  2007
Abstract:  
INTRODUCTION Shot velocity is of primary importance because it governs the kinetic energy of the impacting shot and hence the peening intensity. Wheel-blast shot acceleration is much more energy-efficient than air-blast shot acceleration - which accounts for its continued appeal. A variety of wheel types have evolved but the mechanics involved are generally similar. Normally, blades attached to a rotating wheel throw shot at components. Shot velocity is achieved in two stages: accelerator drum and throwing blades. Particles are fed into peripheral slots formed between the accelerator and a stationary control cage. Centrifugal force keeps the particles pressed into the slots as the accelerator drum rotates. At this stage the shot particles have the rotational velocity of the drum. When a slot reaches the outlet slot in the control cage some shot particles escape onto a throwing blade for the second stage of acceleration, see fig. 1. This article is an account of the mechanics involved in generating the final shot velocity. Equations are presented that allow estimates to be made of the thrown shot velocity, direction and angular range when leaving the wheel. These equations accommodate the variations in wheel speed and diameter, blade length, number of blades and control cage that occur with different wheel designs. It is shown that the radial velocity is a large percentage of the tangential velocity. The ratio of radial/tangential velocity determines the direction of individual thrown shot particles.