Open Pit Mine Planning and Design, Two Volume Set & CD-ROM Pack, Third Edition, 3rd Edition

CHAPTER 13

Machine availability and utilization

13.1 INTRODUCTION

Today the basic method of equipment scheduling in the surface mining industry is to deter-

mine the equipment required to maintain the desired tonnage and to then schedule only the

required equipment to do the job. In the event of a breakdown, production is maintained by

the crew picking up another machine on standby or just out of repair. In order to properly

schedule and size the overall equipment fleet, knowledge of a number of factors dealing with

machine availability and utilization are needed. In this regard, one or more of the following

terms are used:

• availability

• operational availability

• mechanical availability

• physical availability

• utilization

• use of availability

• working efficiency

• job efficiency

• operating efficiency

• effective utilization

The calculation of useful hours or minutes is accomplished by applying these factors to

various periods of time. Time expressions such as

• scheduled hours

• annual hours

• total hours

• working hours

• shift hours

• operating hours

• efficiency hours

may be used. Unfortunately there is little consistency with which most of these terms are

used and their values calculated in the mining industry today. ‘Availability’ to one mining

company may not have the same meaning to another mining company or to a supplier of

mining equipment. In this section, the authors have attempted to provide a consistent set

of definitions and formulate an overall logical framework for these important concepts.

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A number of different information sources have been drawn upon in this effort and some

new terms have been applied. It is hoped that confusion will be reduced rather than increased

with this approach.

13.2 TIME FLOW

A simple flow sheet showing the distribution of total hours for equipment at a mining

operation is shown in Figure 13.1.

The definition of the terms is given in Table 13.1.

The time flow sheet in Figure 13.1 can be represented as a series of nodes (Figure 13.2)

at which the flows are split into basically productive and non-productive streams from a

production viewpoint.

The ratio of the productive flow out of a node to the total flow into the node can be

considered an ‘efficiency ratio’ or a ‘node efficiency’. The total time flow to any given point

can then be determined by multiplying the flow in by the efficiencies of the nodes in between.

Node 1:

operational availability =

up-time

total time

(13.1)

Node 1*:

mechanical availability =

working hours

working hours + downtime

(13.2)

Figure 13.1. Total hour distribution with respect to mining machinery. Source unknown.