Maintenance of Construction equipment 1

Introduction

Maintenance can be defined as an activity carried out for any equipment to ensure its reliability to perform its expected functions. Maintenance is also defined as any activity carried out on an asset in order to ensure that the asset continues to perform its expected functions, or to repair any equipment that has failed to operate properly, or to keep the equipment in running condition, or to bring it back to its favorable operating condition. Over the years, many new strategies have been applied as a maintenance strategy which is intended to overcome or eliminate the problems related to equipment breakdown.

OBJECTIVES AND GOALS

Maintenance objectives fall into two categories: the primary objective and the secondary objective. The primary or basic objective of maintenance is to repair and upkeep production equipment to make sure that it is kept in a safe and well operating condition so that production targets can be obtained on time, in the budget, and in good quality as per the planning. The secondary objective of maintenance is to carry out approved maintenance and repair tasks to the extent that such maintenance tasks do not minimize the planned operating hours per year upon which the equipment’s hourly rental rates are anticipated. Objectives aid to ensure that the intended maintenance work can be carried out effectively and efficiently. The basic objectives of a well-planned maintenance policy are as follows:

• Reduce work cost
• Eliminate unnecessary maintenance
• Reduce overall maintenance cost
• Reduce repair parts inventory
• Extend the service life of construction equipment
• Increase productivity
• Reduce lost production caused by failure during normal shift
• Increase overall profit generated by equipment

Types of maintenance programs

Generally, there are two major types of maintenance: unscheduled maintenance and planned or preventive maintenance.

Unscheduled maintenance is carried out to get the construction equipment that breaks down during the scheduled shift back to its normal operating condition. The main aim of this type of maintenance is to reduce equipment downtime after failure. This type of maintenance is also called non-predictable maintenance as they are not predictable. As a result, it is a daunting task to implement a balanced or rational unscheduled maintenance program or policy. The equipment manager must compromise on the cost of idle time for mechanics on the job waiting to repair a piece of equipment versus the cost of an idle crew waiting for the mechanics to arrive at the construction site. This type of maintenance is normally called ‘‘reactive maintenance’’ since the manager has to respond to unscheduled maintenance requirements, trying to bring the tools, repair parts, and expertise together in a fashion which will get the broken machine up and run as quickly as possible. The substitute to regularly reacting to unpredictable equipment failure is to reduce them by implementing a sound and well-planned preventive maintenance program on the job site.

The fundamental objective of preventive maintenance (PM) is to reduce unplanned equipment failure by spending a regular period of time to inspecting the equipment and making sure that minor problems are solved before they lead to major failures. It specifically involves timely inspection, lubrication, and replacement of worn parts, oil, filters as well as other equipment engine fluids. It is done with the purpose of extending the life of the engine parts by minimizing wear, reducing cases of equipment breakdown, and hence increasing the overall productivity of the equipment and associated teams by maximizing equipment availability. The term predictive maintenance has been used more recently to describe this type of approach to maintenance. Predictive maintenance attempts to schedule maintenance tasks based on the past performance of engine parts so that parts are replaced just before they fail or begin to adversely influence the performance of the engine. It is expected that the future performance will be similar to past performance. It must be considered that the main goal of preventive and predictive maintenance is to minimize the time and money spent on this type of maintenance i.e. unscheduled maintenance.

1.Reactive Maintenance

Reactive maintenance is normally the “run it till it fails” mode of maintenance. No actions or efforts are taken to carry the maintenance of the equipment as the designer primarily intended to ensure the design life is utilized. Recent studies of 2000 show that this is still the predominant mode of maintenance in the United States. The referenced study shows the average maintenance program as follows:

• Reactive – more than 55%
• Preventive – 31%
• Predictive – 12%
• Others – 2%

More than 55% of maintenance resources and activities of an average facility seems to be still reactive.

Advantages

• Less staff.
• Low cost.

Disadvantages

• Increased labor cost, especially if overtime is needed.
• Increased cost due to unplanned downtime of equipment.
• The cost involved with repair or replacement of equipment.
• Inefficient use of staff resources.
• Possible secondary equipment or process damage from equipment failure.

2.Preventive Maintenance

Basic philosophy

• Schedule maintenance activities at predetermined time intervals.
• Repair or replace damaged equipment before obvious problems occur.

Preventive maintenance is defined as follows: Actions are taken on a time- or machine-run-based schedule that detects, prevent, or lessen the degradation of a component or system with the purpose of sustaining or extending its useful or service life through controlling degradation to an acceptable level.

Advantages

• Flexibility allows for the adjustment of maintenance periodicity.
• Cost effective in many capital-intensive processes.
• Energy savings.
• Reduced equipment or process failure.
• Increased component life cycle.
• Estimated 12 – 18% cost savings over reactive maintenance program.

Disadvantages

• Labor intensive.
• Catastrophic failures still likely to occur.
• Potential for incidental damage to components in conducting unneeded maintenance.
• Includes performance of unneeded maintenance.

3. Predictive maintenance

Basic philosophy

• Schedule maintenance actions at predetermined time intervals.
• Repair or replace damaged equipment before noticeable problems occur.

Predictive maintenance is defined as follows: Measurements that help to detect the onset of system degradation (lower functional state), hence allowing causal stressors to be eliminated or controlled before any significant deterioration in the component physical state. Results show current and future functional capability.

Fundamentally, predictive maintenance differs from preventive maintenance on the basis that maintenance is done according to the actual condition of the machine rather than on some preset schedule. Preventive maintenance is time-based. Tasks such as changing lubricant are done on the basis of time, like calendar time or equipment run time. For example, oil in the vehicles is changed every 10,000 to 20,000 Km. traveled. This is effectively basing the oil change needs according to equipment run time. The actual condition and performance capability of the oil is not considered. It is changed because it is on the schedule. This methodology would be same as the preventive maintenance task. If on the other hand, the operator of the car discounted the vehicle run time and had the oil analyzed at some periodicity to find out its actual condition and lubrication properties, he/she may be able to extend the oil change time until the vehicle had traveled 40,000 km. This is the basic difference between predictive and preventive maintenance, whereby predictive maintenance is the required maintenance task based on quantified material/equipment conditions.

Advantages

• Allows for preemptive corrective actions.
• Increased component operational life/availability.
• Decrease in costs for parts and labor.
• Decrease in equipment or process downtime.
• Better product quality.
• Improved worker morale.
• Improved worker and environmental safety.
• Estimated 8% to 12% cost savings over preventive maintenance program.
• Energy savings.

Disadvantages

• Increased investment in staff training.
• Savings potential not readily seen by management.
• Increased investment in diagnostic equipment.

References

1. Technical book, “Construction Machinery Training”, Instate, Imlambad
2. Harris, F. and McCaffer, “Management of Construction Equipment”, Macmillan Education Ltd. London, UK.
3. Erich J. Schulz, “Diesel Equipment I and II”, Mcgraw-Hill book co.
4. Frank Harries, Ronald McCaffer, “Construction of Plant Excavating and Material Handling”, Granda Publishing.
5. SAE Handbook Volume 4
6. “Caterpillar performance Handbook”, Edition 33, Caterpillar Inc, Peoria, Illinois, USA.