Due
to the harsh working environment, the hollow hexagonal tapered drill rod often
has various failure modes during drilling. When these failure modes appear,
understanding the common positions of the drill rod failure in advance can
help us to analyze the specific problems. Let's learn together today.
The
common positions of the drill rod failure
mainly refer to the damage or fracture at the shank end, the root of the shank
collar, the middle of the shank collar, the front of the shank collar, the rod,
the taper section, etc. The different failure
forms and reasons are as follows.
1.
Fracture at the shank end
There
are two failure forms of shank end. One is that due to the low hardness of the
shank end, under the impact of the rock drill piston, it is easy to cause the
end upsetting phenomenon. The other is that under the high-frequency impact of
the rock drill, local caving occurs at the end of the shank end.
2.
Fracture at the root of the shank collar
The positions
where the root of the shank collar starts to break are on its transition arc. The fracture plane is very
uneven, and there is a relatively smooth crack development area at the corner
or around the corner. However, the ratio of the total area of this area to the
whole fracture area is very small, and the brittle fracture area is very large.
3.
Fracture in the middle of the shank collar
The
fracture in the middle of the shank collar generally occurs in the place where
the cross-section of the flushing hole changes suddenly, commonly known as the
"bell mouth". This "bell mouth" has two shapes: one is due
to the expansion of the diameter of the flushing hole in the middle of the
shank collar during the process of forging the shank collar, and the
unreasonable design of the forging die or insufficient machining allowance.
When the swollen inner hole continues to be subjected to the axial extrusion
force at the shank collar, a "bell mouth"-shaped flushing hole is
formed. The other is to insert a forging needle into the flushing hole when
forging the shank collar to prevent the flushing hole in the middle of the
shank collar from being blocked due to metal forging deformation. The diameter
of the flushing hole will shrink when the metal expands, forming another shape
of a "flare" under the push of the needle.
4.
Fracture at the front part of the shank collar
Fracture
often occurs mostly
on the front edge of the transition arc between the shank collar and the rod.
Most cracks occur on the outer surface and most of them are on hexagonal edges
and corners.
5.
Fracture of the rod
During
the drilling process of the drill rod, the rod may break, but most fractures
occur at 20-400mm in front of the shank collar. Some cracks on the fracture
surface arise from the outer surface, and the fatigue arc zone expands from the
outside to the inside, forming an external fatigue fracture. Some cracks occur
on the inner surface of the rod, and the fatigue arc zone expands from the
inside to the outside, resulting in internal fatigue fracture.
6. Broken taper
section
The
taper section often breaks at its smaller end due to its production process and
technology. You
can roughly analyze the force characteristics of the drill rod and the cause of
failure based on
your understanding of the common positions of the drill rod failure, and different
fracture shapes. It is not only conducive to the improvement of process
technology and other aspects but also to prolonging the service life of the
drill rod.
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