Maintenance of Bucket Elevator (Case of the Cement Plant of El Malabiod, Algeria) - Juniper publishers
Journal of Insights in Mining Science & Technology
Abstract
The most important objective of this work is to examine the
failures of the Bucket Elevator based on the cost of the parts. We use a both
methods, Pareto Analysis and Ishikawa diagram, to predict areas of parts
affected by breakdowns. The hexagonal head bolts and the square head bolts
represent 74.92% of the total cost of the changed parts. We consider, in
perspective, to review the design of elevator and apply the recommendations of
the manufacturer to increase the lifespan of the lift and improve its
reliability.
Keywords : Bucket Elevator; Pareto diagram; Faillure; Cost;
Ishikawa diagram
Introduction
The primary concern of a company is the
improvement of the safety, the maintenance and the availability of its
equipment, due to their direct influences on the smooth running of the tasks,
the respect of the deadlines and the increase of production. Condition
monitoring in mining industry is not as well developed as it is in other
branches (i.e. power engineering, oil industry etc). One of the reasons is that
mine is the specific kind of company with harsh environment and dissipation of
assets in wide area. There are a lot of different mechanical systems in a
lignite mine but one of the most important is a transportation system [1].
According to the study reported by Mobley, from 15% to 40% (average 28%) of
total production cost is attributed to maintenance activities in the factory
[2]. The complexity of maintenance in modern mining systems is based on the
combination and use of various resources and the characteristics of the dynamic
environment in which they exist. Maintenance is usually categorized into
preventive, corrective, and predictive types [3]. In NF EN 13306 standard
maintenance is defined as: “the assembly of all administrative and management
technical actions during the life cycle of an asset, intended to maintain or
restore it in a state which in, it can perform a required function.
Face to the development and competition
to competitiveness, which drives the search for quality and above ail; cost
reduction, maintenance has become one of the strategic functions in the company
[4]. The Italian economist Vilfredo Pareto (1848-1923) observed in 19th century
Italy that 20% of the population owned 80% of the usable land [5]. Pareto chart
has been used to evaluate mining equipment failure frequency. A Pareto chart is
a tool which enables factors influencing a phenomenon to be organized. By means
of this graphic picture it is possible to present both relative and absolute
distribution of the types of errors, problems and their causes. The detection
and exclusion or reduction of the problems inherent in the Bucket elevator
machine using a continuous process improvement tool will be significantly
valuable in the argument of reduced machine down time, minimized repetitive
stops, and diminished cost of replacing spare parts and productivity increase.
The principle of this paper is to analyze the functioning of strategic
equipment (elevator machine), considered the most essential machines in the
cement plant of El Malabiod, Algeria. Its damage causes the stopping of the
production chain. The cost of lost production and maintenance caused by this
blockage is very high. In this context, the Pareto chart is undoubtedly a real
optimization tool maintenance cost. The present paper will characterize the
maintenance of buckets elevator type 250 by the root cause analysis methodology
based on the combination of Pareto Analysis and Ishikawa diagram. The Pareto
analysis is used to identify the major causes while the cause-effect
relationships are illustrated by a Fishbone diagram.
History of bucket elevators
Bucket elevators are the most efficient
means of elevating free flowing granular materials and most materials even some
sticky materials. Bucket elevators of the centrifugal discharge are normally
used, and most are of belt type. Friable materials are best handled in
continuous bucket elevators that operate at low speeds. The continuous buckets
are discharged by gravity on the back of the preceding bucket while passing
over the head pulley, thus reducing breakage caused by the centrifugal force discharge
of a centrifugal elevator. Bucket elevators usually require the least amount of
horsepower for vertical conveying of any conveying system. The bucket elevator
has been in used in the USA for many over a century. In addition, for the most
part the same basic design has been followed. Leonardo da Vinci in the 1400’s
believed art was the chief instrument of man’s search for knowledge. The
ancestors of the modern-day bucket elevator first appeared at these devices
were predominantly used for elevating water by the use of pots attached to an
endless rope. It is believed that the water used for the famous Hanging Gardens
of Semiramus was brought up to a height of 300 feet by this means. A remarkable
achievement, having regard to the fact that modern elevators rarely work to
heights greater than 150 feet. Since this time, the bucket elevator has gone
through a period of evolution. There was a flourish of activity in elevator
design and patents between 1850 and 1930. Since that time there has been very
little new work or mathematically supported designs developed. As Leonardo da
Vinic said, “Art is never finished, only abandoned”, this can be said for the
design of bucket elevators, development has been abandoned [6].
Practical Use of a Pareto Chart for Evaluating Bucket
Elevator Failure Frequency
In the mining industry a Pareto chart is
used to monitor and control mining machines (a cutter-loader, chain conveyor,
belt conveyor, crushers as well as power supply and control equipment) which
are an important element of the mining process. It is important to evaluate
these machines’ failure frequency and reliability as well as to find which of
the discovered causes responsible for the high failure rate may be eliminated in
the first place [7].
Using one of the important quality management tools a
Pareto chart. A Pareto chart has been constructed according to the following
steps:
a) Data on the type of failures of the Bucket elevator
type 250 has been collected.
b) Spare parts have been assigned to particular
failures with costs.
c) Cumulative percentage values have been calculated
(Cost of the different replacement parts of the elevator with their cumulative
percentage)
Description of the the bucket elevator
The bucket
elevator has the advantages of big conveying capacity, high hoisting height,
stable and reliable operation and long service life. Performance and parameter
are in accordance with JB3926-85 Vertical Bucket Elevator, which is consistent
with the international and foreign advanced standards and the towing circle
chain is in accordance with MT36-80 High-Strength Circle Chain for Mine. The
machine is applicable for conveying the power, grain and block materials, such
as coal, cement, block, sand, clay and ore. The bucket elevator can convey
materials with high temperature when armed with special circle chain structure
(Figure 1). The bucket takes the materials from the storage silo below, follows
the conveyor to the top, around the top wheel and then turns to the bottom, and
pours material into the acceptance trough at the end. The conveyor which drives
the belt bucket elevator is always the rubber belt, it is installed in the
drive roller at the top or bottom and in the changing roller at both sides. But
for the type 250 chain bucket elevator, it is always to install two parallel
drive chains, with chain wheel torque and that of change to upper or lower.
Generally, the bucket elevator is equipped with the hull to prevent floating
dust.
Application of the pareto method
In Table 1, we present the cost of the
various replacement parts of the elevator with their percentage. We present the
Pareto diagram in Figure 2.
Interpretation of pareto chart
Zone A: Parts number 1, 2 & 3 (hex bolt, 10-link chain
strand, full hex head bolt and M36x80 square bolt respectively) account for
74.92% of the total cost of the parts changed. It should be noted that this
zone (A) is the most important one that must be given priority.
Zone B: In this area the maintenance actions on the parts, 5, 6, 7.11
represent 21.35% of the total cost of the faulty parts. By analyzing the
historical file, it is noted that the causes of these failures are related to a
design error, and zone (B) has lower costs compared to the first zone.
Zone C: Contains 50% of the number of rooms, and it represents
only 3.73% of total cost, we contend that it is the smallest zone compared to
the first two zones.
Ishikawa diagram (Figure 3)
Cause-and-effect
diagrams or Ishikawa diagrams (Fish bone diagram) is one of the seven basic
tools of quality, which is used to identify potential factors causing an
overall effect. This technique helps the users to identify the top causes that
need to be addressed to resolve the 80% of the problems. Once the major causes
are identified, tools like the Ishikawa diagram or Fish-bone diagram can be
used to illustrate the root causes of the problems. Then efforts can be made to
remove the major obstacles in order to develop a more sustainable process [8].
To try to surpass this problem is to know all the causes that may give rise to
know ‘’ the five M: Machine, Materials, Methods, Manpower and Milieu, to deduce
the causes (Table 2).
Interpretation
of ishikawa diagram:
According to Ishikawa diagram, we may
hire the following:
Material: Inappropriate quality of replacement parts and
lubricant quality are the most factors affecting the profitability of the
machine.
Environment: The dusty environment is the major factor that
increases downtime.
Manpower: The lack of training and qualification of workforce are
major problems it is necessary to resolve.
Machines: The machines are typically used in reduced condition
(poor lubrication, improper adjustment).
Method: The absence of information on the state of the machine
and the ineptitude of the corrective maintenance makes the task of maintenance
personnel difficult.
Proposition
To provide solutions that improve maintenance and
increase the lifespan of the equipment (elevator) we propose the application of
the maintenance range based on the manufacturer’s recommendations with the aim
of:
a) Eliminate air and material leaks.
b) Cleaning of the installations, and their
surroundings.
c) Operate the
hoists on elevators before the long stop (or replace them)
d) Return to service of emergency stops for carriers
e) Infrared bar control before long stop or inspection
of busbar during stop
f) Rehabilitation of the protection of rotating
installations
g) Cleaning the workplace.
Conclusion
The failures problems of buckets
elevator in cement plant of El Malabiod are analyzed. Pareto chart and Cause
and- Effect Diagram are used to identify and evaluate different defects and
causes for these failures responsible for breakdowns of buckets elevator.
According to the Pareto analysis Parts (hex bolt, 10-link chain strand, full
hex head bolt and M36x80 square bolt respectively) account for 74.92% of the
total cost of the replacement parts. It should be noted that this part is the
most important that must be given priority.
According to the root cause, the
preventive maintenance action is recommended to reduce defects in order to
minimize the replacement of parts.
Acknowledgement
The authors wish
to register their heartfelt gratitude to all management staff and workers of
cement plant of El Malabiod (Algeria) for supporting us with necessary
technical information and giving feedback about the failure modes for drilling
machine.
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