13
Care & maintenance
The service life and performance of DTH hammers depends to a
large extent on good operating practice and regular maintenance.
The following recommen dations should be observed:
• Make sure that the compressed air is always clean and dry.
• Always blow clean the air hoses before connecting them to the rig.
• Make sure that the drill pipes are stored properly in the pipe rack,
or stacked on trestles in such a way that dirt cannot enter the pipes.
• Fit thread guards to the ends of the drill pipes whenever practica
-
ble. Keep the threads and the insides of the pipes clean.
• Always cover the “open” thread end of the drill pipe during
pipe-jointing operations. The ingress of dirt into the drill string will
cause blockages and/or seizure in the hammer, which can result in
breakdown.
• Check regularly that the dosage of lubricating oil into the operat
-
ing air is sufficient. Check that the lubricating-oil tank on the rig is
filled with oil of the correct type and quality. See “Recommended
lubricants”.
• Check the wear on the driver chuck and hammer cylinder regularly.
The diameter of the driver chuck must never be less than that of
the hammer cylinder. The service life of the hammer cylinder can
be prolonged by always fitting a driver chuck with a greater outside
diameter than that of the hammer cylinder. When the components
are approaching their minimum permissible diameters, frequent in
-
spection is necessary. Alternatively, change the compon ents in good
time – it makes good economic sense.
N�B� When the hammer cylinder is replaced, the driver chuck should
be replaced at the same time (see “Wear limits”).
A general overhaul of the hammer should be carried out at suit
-
able intervals, depending on the operating conditions and empiri-
cal statistics. The abrasiveness of the rock will have a considerable
effect on the rate of wear, and will affect the overhauling intervals
accordingly.
Lubrication
Lubricating oil is vital for the satisfactory
operation of DTH hammers. Apart from
regular checking of the oil level in the
lubricating-oil tank, always make sure that
there is oil in the compressed air. This can be
checked whenever the rotation unit is free, i.e.
disconnected from the drill string.
Simply place a plank over the drill-steel sup
-
port and blow operating air on to the plank.
After a few moments, the surface of the plank
should become oily, which confirms that lu-
bricant is being carried to the ham mer in the
operating air.
The importance of ad equate lubrication of the hammer cannot be
over-emphasized. Poor lubri cation will accelerate wear and ultimate
-
ly result in breakdown. The effective lubrication of the DTH hammer
is not always a straight-forward matter, owing to wide variations
in operating conditions, e.g. extreme temperature differentials
between the hammer and the lub -ricator, water or foaming concen-
trate added to the operating air, etc.
Different lubricants have different properties. Mineral oils have the
best lubricating properties and are preferable in most cases. Min
-
eral-base oils have good adhesion properties and are produced in
different viscosity and temperature- range grades.
Since mineral oils have good resistance to water, they are suit
-
able for use even when comparatively large volumes of water are
injected into the operating air. In this case, however, the dosage
must be increased.
Glycol-based lubricants, such as Atlas Copco Air Oil, are water
soluble, and must not be mixed with mineral oils. They are used
primarily to prevent freezing, and should be used only when
there is a minimal water content in the operating air. Glycol-based
lubricants are used extensively in water-well drilling for reasons of
water hygiene. If there is a lot of condensation in the drill string,
which is often the case in long drill strings, then lubrication may
become unsatisfactory because dilution seriously affects the func
-
tion of glycol-base lubricants.
Other lubricants worth mentioning are the so-called “edible” oils,
which consist of vegetable oils, synthetic lubricants of the ester
type, or a mixture between these two. Edible oils can be mixed
with mineral oils, have good lubricating properties and are non-
toxic.
Lubricators
Both plunger-pump and nozzle-type lubrication systems are avail-
able.
The plunger pump is relatively insensitive to the viscosity of the
lubricant and gives a more reliable dosage compared with the
nozzle-type lubricator. This is of major importance when the ambi
-
ent temperature is low.
About 1 ml of oil per m
3
of operating air consumed should be the
minimum dosage for bench drilling. As a rule, higher dosages are
needed in water-well drilling.
Normal lubrication dosage
COP 32 0,2–0,4 l/hr
COP 42 0,3–0,5 l/hr
In case of water injection, increase dosage by 0,1–0,2 l/hr.
N�B� The distribution of lubricating oil through the compressed air
system generally takes place in the form of so-called “wall flow”.
If the air system has been shut off for a long period of time, it can
take quite some time for the lubricant to reach the hammer. In
such cases, a small amount of oil must be poured directly into the
hammer or air hose before drilling.
Choice of lubricating oil
For COP down-the-hole hammers it is recommended to use Atlas
Copco COP oil. When choosing between other types of lubricants,
the oil should have:
• Suitable viscosity
Ambient temp�°C(°F) Viscosity grade
–20 to +15 (-4 to +59 ISO VG 46-100
+15 to 35 (59 to 95) ISO VG 100-150
> +35 (95) ISO VG 150-220
• Good adhesion properties
• High film strength
• Corrosion inhibitors
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