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Today we’re going to start a series on operational indicators, crucial tools for optimizing the efficiency and structure of mining operations. Using these indicators helps to identify and mitigate bottlenecks, failures and low productivity, positively impacting the organization’s economic results.
Let’s start by exploring indicators related to hours. In this blogpost, we’ll understand the basic concepts and equations, as well as a practical example to illustrate their application.
CONCEPT AND EQUATIONS:
The indicators will be presented considering mine and dispatch equipment, not employees.
BASIC DEFINITIONS:
Calendar hours (CH): correspond to the 24 hours of the day for each piece of equipment;
Inactive hours (IH): intervals that are not scheduled for the work shift schedule;
Scheduled hours (SH): represent the hours defined by the work shift schedule, using the following equation:
Maintenance hours (MH): refers to the hours in which the equipment is under maintenance.
Available hours (AH): hours in which the equipment is available for use in operation.
For the above equation (eq3) we refer to the available hours as the scheduled hours when the equipment has not undergone any type of maintenance during the period analyzed.
Operational stoppages (HOS): these are the hours when the equipment is at a stoppage linked to the operation of the equipment. E.g. shift change, refueling, among others.
Hours worked (HW): these are the hours when the equipment is operating. When the equipment is not working on its main activity, these hours are considered to be auxiliary hours worked.
In addition, we can cover the basic concepts of AA (Asset Availability), MU (Machine Utilization) and OE (Operating Efficiency) in this article, remembering that there will be other times when we will cover these three indicators in more detail.
Asset Availability (AA): the asset availability of mining equipment refers to the ability of this equipment to be operational and ready for use when needed. It is one of the main maintenance performance indicators, along with Mean Time Between Failure (MTBF) and Mean Time to Repair (MTTR). For today, we’re only going to look at the equation that takes into account the concept of hours that we covered earlier.
Machine Utilization (MU): machine utilization is the indicator that reflects the efficiency of the operation in terms of the use of the assets available for operation.
Operating efficiency (OE): indicator that represents the percentage of hours the equipment has operated in relation to the total hours scheduled for it.
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“When scheduled to operate, reach the highest possible AA;
When available for operation, achieve the highest possible MU;
When operating, achieve the highest possible productivity.”
EXAMPLE IN HOURS:
For this example, we will consider an operation with three pieces of equipment.
CH = 3 ∗ 24h
CH = 72h
Considering that in this three-day period there were 24 hours of inactive hours, we have:
IH = 24h
If observed in equation (1), SH will be the difference between CH and IH. Ps.: If IH=0, SH = CH. This calculation gives us the total expected operating time of the equipment according to the work shift schedule, excluding periods of unplanned downtime.
SH = 72 h-24h
SH = 48h
For maintenance hours (MH), we will take into account that two pieces of equipment underwent preventive maintenance for 1 hour each and one piece of equipment had a leak in the hydraulic system and had to undergo corrective maintenance for 3 hours:
MH = 2 ∗ 1h + 3h
MH = 5h
There are two variations of the AH equation (2 and 2.1). Note that equation 2.1 requires MH to be 0. In this scenario, we will opt to use equation 2, which gives us the value of AH through the difference between SH and MH ≠ 0.
AH = 48h – 5h
AH = 43h
We will take into account some operational stops such as: 3 hours of shift change, 5.5 hours of meals (lunch, snack and dinner), 1 hour of refueling and 3.5 hours of infrastructure services.
HOS = 3h + 5.5h + 1h + 3.5h
HOS = 13h
The HW calculation, like other calculations, offers two equation options (3 and 3.1). For our example, we could opt for both, as neither equation requires solving more equations to find the result. In this case, we’ll choose to use equation 3.
Both equations provide a measure of the time the equipment is actually in operation, taking into account different aspects such as scheduled stops and downtime.
HW = 43h – 13h
HW = 30h
This equation calculates the percentage of the total available time that the mining equipment was actually in operation. The higher the value resulting from the equation, the greater the asset availability of the equipment, which is essential for maintaining the efficiency and productivity of the mining operation.
AA (%) = (43/48) *100
AA = 89.58%
This equation calculates the percentage of the total time available that was actually used to operate the equipment. The higher the value resulting from the equation, the more efficiently the available assets were used. For example, if the MU is 80%, this means that the equipment was used effectively for 80% of the time available for operation.
MU (%) = (30/43) ∗ 100
MU = 69.78%
Both OE equations (6 and 6.1) provide a measure of the equipment’s performance in relation to the time scheduled for operation. A higher Operating Efficiency indicates more efficient operation of the equipment in relation to the time available.
OE = 89.58% ∗ 69.78%
OE = 62.50%
As we apply the formulas to different examples, we can get a better grasp of these concepts. A process with good operational indicators will evaluate the main unproductive maintenance activities that will impact the OA, for example, high waiting times and waiting for tools, delays in starting activities, idle times, lack of parts in good time, etc. In the same vein, processes with good indicators will certainly look for the most recurrent operational downtime codes and assign targets to them so that we have an optimized MU.
PRACTICAL EXAMPLE:
Let’s use a practical example to memorize all this?
Analyzing the process of a mine, an analyst observed a fleet of 5 trucks (I, II, III, IV and V) and the following events over a period of 7 days of operation:
- The mine operated 24 hours a day in 8-hour shifts;
- 36 hours of maintenance on truck I to repair the gearbox;
- 23.33 hours spent changing shifts;
- 15h of maintenance on truck IV to repair its suspension;
- 73.5 hours spent on meals, including lunch at 12pm and dinner at 7pm;
- 3 hours of maintenance on each of trucks II, III and V to fix the headlights;
- 8.75 hours spent refueling;
- 32.08 hours spent waiting for an excavator that was without an operator;
- 15.17 hours spent waiting for the crusher to stop;
Question: How do we calculate the AA, MU and OE of this equipment?
Answer: For 7 days of operation and 5 pieces of equipment, we have:
CH = 7 ∗ 5 ∗ 24
CH = 840h
IH = 0 (ran 24h)
SH = CH
Total hours of maintenance:
MH = 36h + 3h + 3h + 15h + 3h
MH = 60h
AH = 840 – 60
AH = 780h
Total operational downtime:
HOS = 23.33h (SHIFT CHENGE) + 73.5h (MEAL) + 8.75h (REFUELLING) + 32.08h (WAITING FOR EXCAVATOR) + 15.17h (CRUSHER STOPPED)
HOS = 152.83h
HW = 780 – 152.83
HW= 627.17h
With all the Hours values calculated, we can finally obtain the AA, MU and OE of the equipment.
AA (%) = (780/840) ∗ 100
AA (%) = 92.86%
MU (%) = (627.17/780) ∗ 100
MU (%) = 80.41%
OE (%) = 92.86% ∗ 80.41%
OE (%) = 74.66%
As mentioned in the first example, let’s demonstrate in practice how a single different value can change the values of AA, MU and OE significantly?
For example, in the practical example above, what would the new AA, MU and OE values be if we hadn’t carried out the 36-hour maintenance on truck I, i.e. if we had only carried out the 3-hour headlight maintenance similar to trucks II, III and VE?
Answer: The values for CH, SH and IH would not change, however, we would have to redo the calculations for MH, AH and HW.
MH = 3h (I) + 3h (II) + 3h (III) + 15h (IV) + 3h(V)
MH = 27h (↓)
AH = 840 – 27
AH = 813h (⭡)
HW = 813 – 152.83
HW = 660.17h (⭡)
AA (%) = (813/840) ∗ 100
AA (%) = 96.79% (⭡)
MU (%) = (660.17/813) ∗ 100
UF= MU (%) = 81.20% (⭡)
OE (%) = 96.79% ∗ 81.20%
OE (%) = 78.59% (⭡)
By choosing to maintain truck A’s headlights instead of a more complex intervention, we saw a 45% reduction in maintenance time (MH), which consequently resulted in an increase in the values of the indicators directly related to AA, MU and OE.
- HW = 4.05% increase
- HOS = No change
- HW = 5% increase
- AA = 4.1% increase
- MU = 1% increase
- OE = 5% increase
Did you like this content? Share it on your social networks! And, remember, this was just the first operational indicator presented. Stay tuned, because there are many more to come!
