SWDM40 OPERATION & MAINTENANCE MANUAL
7. KELLY AND DRILLING TOOLS
7.1 KELLY
7.1.1 Introduction of Kelly
Telescopic Kelly is to lift or lower the drill bit, drill and dump by the extension and retraction of
itself. This way reduces assistant working time and improves drilling efficiency. It mainly
consists of two to six sections, including following structure: junction pin shaft, spring seat,
cushion spring, outlet pan, outer arc plate, drive sleeve, outer key bar, steel pipe, O-ring,
positioning ring, shock absorbing parts, center flange, triangle plate, top end flange and flat
head. For a machine-lock kelly, pressure table and inclined plate are included. (as following
figure)
During drilling, Kelly delivers swing torque and axial pressure to the drill bit.
Kelly bear the compound stress, such as pull, press, twist and bend. According to different axial
pressure and structure features, there are two kinds of Kelly, machine-lock Kelly and friction
Kelly.
Friction Kelly delivers swing torque by outer key and inner spline. When key is pressed tightly
on the side to deliver swing torque, the friction is transmitted to crowd cylinder or crowd winch
via the pressure enforced by Rotary drive. The characteristics of friction kelly is that simple
structure, easy operation and less strength transmission, besides, it’s one more section than the
machine-lock kelly, and deeper drilling.
Machine-lock Kelly meets for the requirements of large torque and large axial pressure. It can
deliver strong axial pressure via crowd steps. It features in more suitable for drilling into hard
layer comparing with friction Kelly. Meanwhile, the more sections the harder operation and the
higher requirements for the operator.
The Kelly rotation and downward pressing of rotary drilling rig is driven by inner spline, which
is adopted quick-change technology with patent, besides, its material is matched with the
pressurized block. The Rotary drive inner spline and kelly have long service life, thus, low cost.
Sections among Kelly deliver torque and axial pressure via inner and outer spline by layers.
Each section of machine-lock Kelly has 3 to 5 pressure steps, for which position in the hole, the
operator should remember, in this case, improving the working efficiency.
Below figure is the illustration of shape and parts of normal machine-lock Kelly.
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