Mincon Rockdrills 6DH360 Operation & Service Manual Download Page 7

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Mincon Rockdrills – “The Driller’s Choice”

Page 7

3. Trouble Shooting

Problem

Possible cause

Remedy

Low penetration
and high pressure

Chuck shoulder length worn too
much

Measure chuck shoulder length against discard length and
discard if necessary as air is restricted on the upstroke of the
piston

Exhaust tube not fitted properly

Check exhaust tube dimensions on spec sheet

Contamination in hammer

Open hammer and clean the obstruction

Too much water injection

Reduce level of water in flow

Rough or erratic
operation

Too much feed pressure

Set the feed pressure until the rotation starts to bind. Then back
off the feed pressure until the rotation runs smoothly

Shoulder length of the chuck has
worn too much

Measure the chuck shoulder against the discard length and
discard if necessary as air is restricted to the upstroke of the drill

Rotation speed too slow

Drill bit peripheral rotation speed of 12 – 15” per second (300-
380mm). Place chalk mark on drill rod and check the advance
revolution. If greater than ½” (12mm) per revolution increase
rotation until the advance per revolution is a maximum of
between 3/8” – ½” (10-12mm)

Worn bit exhaust tube or piston
bore

Measure bit exhaust tube and piston bore Vs specification and
replace either if necessary. Leakage in this area will reduce the
piston upstroke force

Worn bit bearing (some models
only)

Replace bit bearing if outside discard limit

Too much water injection

Reduce level of water injection

Low penetration /
Low pressure

Worn drill clearances

Inspect piston, inner cylinder, wearsleeve, air distributor probe
and bearing against discard measurements as outlined in repair
section 2.2 and discard as necessary

Lack of oil

Ensure there is an oil film coming from bit spline and bit parts.
(Place cardboard under bit to check)

Drill running off
bottom

Worn piston

Measure the large end of the piston for wear. If air leaks past
this area it can cause the piston to cycle when off bottom

Too much water injection

Reduce water injection flow

Exhaust tube
breaking

Damaged tubes

Ensure that the bit / chuck and wearsleeve are aligned properly
when changing the bit. Alternatively ensure the bit exhaust is of
correct diameter and is fitted properly

Chuck I/D is worn

Replace chuck.

Bearing I/D is worn.

Replace bearing.

Erosion of exhaust tube

The water strikes the exhaust tube in the piston strike position
when using in the drill. Reduce the flow of water

PART FAILURE

Problem

Possible cause

Remedy

Cracked
wearsleeve

Abuse of wearsleeve

Avoid welding, heating or torque wrenching in the wrong place
as outlined in section 1.4. Note also section 1.6

Worn wearsleeve

Casing has worn beyond the discard point. Measure casing
O/D approx. 3” from chuck end and backhead end and replace
if necessary

Corrosion

Ensure a pH neutral water, well filtered and free from
contaminants is used in the drill. Corrosion usually accelerates
from the threaded area or any undercut area. Coat with
corrosion protector if there is any danger of corrosion

Cracked backhead
body

Bogged Drill requiring lots of fighting
to recover the drill

If such danger is imminent use a dig out sub

Piston cracked
through large
diameter

Lack of lubrication causes micro-
cracks leading to breakage

Check lubricator and ensure oil film on the bit splines and slow
holes

Drill badly bogged which can cause
wearsleeve to distort (causing
functional heat and cracks)

Flood tool with water when bogged

Feeding hard through voids on
broken ground can cause
wearsleeve to distort causing heat
and cracks

Use light feed and ensure the hole is kept clean and
consolidated. Use foam or mud if necessary

Using wrench over wrong area
causes wearsleeve to distort

Use wrench only in the
Area indicated in spec 1.4