Summary
This
project was the first stage of a research program which has as its primary
aim the introduction and development of condition based monitoring (CBM)
maintenance practices into underground coal mining operations. The project
was conducted by BHP Research in collaboration with BHP Steel, Appin
Colliery and BHP Engineering.
Condition
based monitoring is an activity in which selected parameters associated
with machinery operation are observed, so that the machinery can be
more effectively maintained, to provide increased machine reliability
and a reduction in the loss of production due to unscheduled machinery
breakdown. It has been widely accepted by maintenance personnel as the
most effective maintenance strategy and is being increasingly utilised
in many industries worldwide.
Introducing
CBM to the coal face is seen to be an extension of existing CBM practices
into a difficult environment. Unfortunately, the lack of intrinsically
safe (IS) sensors, systems and data communications networks has meant
that CBM has been applied to a limited extent in hazardous zones in
underground coal mines.
This
situation is beginning to change with the certification of data collectors
and other condition monitoring equipment. Demonstration of the effectiveness
of CBM at the face is one way of ensuring the continuing development
of equipment for IS applications.
Project
Objectives
Broadly,
the aim of this first stage project was to examine the ways in which
monitoring the condition of underground mining equipment can lead to
more effective maintenance practices and to increased machine reliability
and availability. Machine reliability/availability is one of the major
limits to increasing the productivity of underground coal mines. Improved
maintenance practices should therefore lead to improved productivity.
The
aim of this project was covered by a set of specific objectives. These
objectives were to:
Provide
the scope and evaluate the requirements for effective on-line CBM of
underground mining equipment.
Identify
and prioritise mining equipment for which CBM will provide a major benefit,
and outline the resources required to facilitate such monitoring.
Demonstrate
the viability of CBM by adapting existing IS instrumentation to the
monitoring of mining equipment located in hazardous areas underground.
Determine
the system specifications of a dedicated IS monitoring system and data
communications protocol, which could be developed at a later stage of
the research program.
Conclusions
The
results of the survey indicated that there was an awareness of condition
monitoring and that it was generally viewed in a positive light. By
way of example, the average (unweighted) response of those responding
to whether there was sufficient industry support for CBM was on the
scale of 1 to 5 (a 5 indicating that the respondees believe that there
is very good support available). A figure of 3.5 suggests that there
is potential for suppliers of CBM equipment and expertise to expand
their services to the industry.
Maintenance
engineers confidence / expectation in CBM rated 4.0 (5 being high confidence).
Maintenance personnel rated the cost effectiveness of CBM as 4.1, the
safety effectiveness as 3.6 and other contributions of CBM as 3.9. Ratings
of management in these three categories were 3.5, 3.6 and 4.1 respectively.
The
level of implementation of CBM ranged from virtually non-existent to
fully net-worked on-line monitoring systems. The most widely use CBM
method was oil analysis, with 25 out of 29 mines indicating that oil
analysis was used. Sixteen respondees indicated that they used vibration
analysis (four respondees gave no reply), twelve respondees that they
monitored the mechanical condition/wear of major components (six respondees
giving no reply) and six respondees that electronic equipment was monitored
(ten respondees giving no reply).
Other
CBM techniques used by individual mines included motor current signature
analysis and face equipment monitoring. Some of the reasons given for
not using one or more CBM techniques were the high cost and the poor
availability of intrinsically safe sensors and systems.
In
Longwall mines, 14 out of 20 respondees indicated that shearers were
considered to be highly critical (a rating of 5 out of 5). For all mines
surveyed, 21 out of 29 rated continuous miners as highly critical and
20 out of 27 rated belt drives as highly critical. In addition, individual
respondees identified a wide range of equipment which caused continuing
maintenance problems at their mines, the most numerous of which was
various problems with conveyor belts.
Unscheduled
maintenance was experienced by 26 of the respondees (the other three
did not reply). Seventeen of the 26 provided a figure for unscheduled
maintenance as a percentage of all maintenance costs.
These
figures ranged from 2% to 50%, with an average of 16% (production weighted).
Five of these mines also provided the cost of their maintenance budget
as a percentage of total costs. For those five mines, unscheduled maintenance
accounted for approximately 6.2% (production weighted) of the total
costs.
The
wide range in the percentage of unscheduled maintenance suggests that
different mines use different criteria for estimating unscheduled maintenance.
One possible reason for this wide range could be that the cost of lost
production resulting from in-service equipment failure has not been
included in the cost of unscheduled maintenance. In some mines this
can amount to almost $90,000 per shift. The inclusion of the cost of
lost production in unscheduled maintenance costs would significantly
increase the 6.2% estimated above.
Overall,
the results of the survey show that CBM has been adopted by some within
the industry who believe that CBM can improve mine productivity. However,
there are others who believe that the benefits of CBM are not sufficient
to warrant the necessary expenditure. This belief is less prevalent
in mines where a high rate of production is supported by a high degree
of mechanisation. For example, all longwall mines carry out some form
of CBM.
Trial
Results
Three
successful trials were held at Appin Colliery on 25 November 1993 and
on 8 June and 5 July 1994. The results of the first trial showed that
the AFC maingate drive gearbox had suspected bearing faults and that
the crusher had suspected alignment problems. The alignment of the crusher
was a known fault and was due to the loss of some pick boxes.
A
change-out of the Appin longwall took place in December / January 1994.
Crusher pick boxes and coupling rubbers were replaced. As a consequence
of the monitoring results, the maingate drive gearbox was overhauled.
A second trial indicated that the bearing faults were still evident
and that there was evidence of 'knocking' in the gearbox, possibly due
to wear of the first gearset.
Other
results from this trial showed that the left and right hand cutter heads
of the shearer may be developing faults, possibly related to gear meshing.
The levels of the suspected faults were moderate and low, respectively.
Of the five longwall components monitored, only the shearer was monitored
in the final trial.
In
this trial, conducted with an IS data collector, the fault in the left
hand cutter head was confirmed but the suspected low level fault in
the right hand cutter head was no longer evident. The possible fault
in the AFC maingate drive gearbox remains to be confirmed.
The
project objective of conducting monitoring trials of CBM was completed
with the final trial on 5 July 1994. However further monitoring at Appin
Colliery has been scheduled for 250,000 tonnes of coal to be extracted
from the longwall. In addition other pieces of equipment such as auxiliary
fans are to be monitored on a monthly basis. The benefit of monitored
face equipment in the hazardous zone has been clearly demonstrated