(57) Drilling apparatus is coated on selected surfaces with PTFE.
In the drawing is shown an example of the application of the invention to a core barrel
assembly.
An outer core barrel l0 and an inner core barrel ll are shown which are normally in
sections.
At the lower end of the outer core barrel there is attached a core catcher sub l3.
At the lower end of the inner barrel ll is attached an inner barrel breaker sub l4
and below that a core catcher l5. A core bit l6 is attached to the lower end of the
outer barrel.
Parts are shown coated with PTFE by thick lines, e.g. the inner surface l8 of the
inner barrel ll, the outer surface l9 of the inner barrel and the inner surface 20
of the outer barrel l0.
The outer surface 2l of outer barrel l0 may also be coated for example, and the surface
22 of the drill bit, the inner surface 23 of the core catcher and the inner surface
24 of the inner barrel breaker sub.
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