This article was written by Emerson Carlos Assunção Sanches, whose passing occurred on September 27, 2024. The publication of this work represents a posthumous tribute to a brilliant professional, mentor, and friend who contributed immensely to the success of FanTR from its inception.
A mechanical engineer and master in Mechatronics from UFBa, Emerson had extensive experience in Rotating Equipment Maintenance since 1978 and Reliability Engineering since 2009. Trained in Reliability Engineering at Reliasoft/Compass, he applied his expertise in major industries such as Cement Plants and Mining, and served as a professor at Cimatec, teaching undergraduate and graduate courses. His dedication and excellence have left a legacy that will continue to inspire professionals in the field.
1. INTRODUCTION
The secondary fans used in underground mines are fundamental elements in the operation and progress of underground mining. They are critical pieces of equipment and require continuous operational campaigns, without failures and delivering the required air flow and pressure.
This equipment is usually installed at the top of the gallery, making it difficult for the maintenance staff - mechanics, lubricators and predictive inspectors - to access it and carry out their work to keep the equipment running. (Figure 1)
Figure 1 - FanTR fan installed on the roof of the mine
Because of this difficulty, coupled with the maintenance strategy of some mines, this equipment is run to failure, and as a result, some components are damaged to a degree that cannot be recovered, causing longer downtime and high costs.
While other mines have taken the decision to carry out scheduled overhaul programs, Preventive Maintenance, removing equipment before it fails and replacing it with recovered and tested equipment. This policy reduces operational downtime and the cost of repairing removed equipment.
There are mines that have adopted mechanical condition monitoring of the fan and included an automatic lubrication system for the fan's electric motor bearings.
In these cases, the fan delivers greater availability, but at the same time is removed at the right time, avoiding further damage to its components, and with a replacement schedule adjusted to the operating condition. Repair costs and operational downtime are minimized.
This article, focused on Equipment and Systems Reliability, aims to help the operations and maintenance teams of mines that fall into the last two cases discussed in the previous paragraph and to motivate those that fall into the first case to review their current strategy.
2. THE SECONDARY FAN
FanTR axial fans used in secondary ventilation in mining are generally made up of the following basic components, shown in Figure 2:
- Rolling set:
- Electric motor;
- Central hub (fixed to the axle of the ME);
- Disc / ring (attached to the central hub);
- Fasteners, screws and nuts (central hub, disk and ring, split blades);
- Split bearings
- Aluminum split bearing (bearing type rotors);
- Shovel, made of fiberglass composite material, coated on the leading edge with stainless steel tape;
- Spinner (if available).
- Static set:
- Metal housing;
- Noise attenuator;
- Fasteners, screws and nuts;
Figure 2 - Typical fan assembly
Tipos de Rotores
FanTR includes vibration and temperature sensing in these fans, as well as a grease injection system, when the customer does not refuse.
3. THE PROPOSAL
3.1 The fan's working regime and environment.
Over the years, when visiting mining companies located in Bahia and Sergipe, where we provide technical support, we have encountered some of the working regimes of these fans, as well as some of the operating environment conditions with their own characteristics.
We list these conditions below:
- Continuous operation 24 hours x 7 days;
- Operation continues from Monday to Saturday, with no operation on Sunday.
Note: No mines were found that adopt a defined operational campaign, the period agreed between operations, maintenance and the commercial area, to make the mine's equipment available for preventive maintenance. During this period, the Mine or the area in front of the Mine does not produce.
Regarding the working environment of the secondary fans, moisture / water droplets, particulates in suspension from detonations and the operation of the mine's larva front and combustion gases are found. These elements affect the service life of the fan components, especially the blades.
We have also identified some conditions associated with truck traffic and handling of the fan, which damage the fan structure, but we understand that as these are random occurrences and associated with the Mine process, we will not address them in this article and they can be dealt with in the Human Reliability environment.
3.2 Fault occurrences and critical components
Over the years of monitoring assemblies, maintenance, inspections and failure analyses, it has become clear that some secondary fan components are more critical than others when it comes to failure.
We have identified:
- The electric motor bearings;
- The blades;
- Noise attenuators;
- Carbon steel fasteners;
- Housing elements;
Considering these components of the secondary fans, a useful life estimate was made for each of them, which is shown in Table 1.
4. MAINTENANCE / INSPECTION PLAN
4.1 Reliability Recommendation
What we want in terms of reliability is for the secondary fan not to fail during the planned campaign period, affecting the production schedule and increasing maintenance costs.
To this end, the inspection and maintenance record database becomes the basis for establishing the periodicity and scope of the intervention.
In the absence of such a database, inspections of critical components such as fasteners, shovel bodies, bearings and the general condition of the casing must be carried out between campaigns, during scheduled or general shutdowns, in order to assess the level of degradation of each component and thus define the new inspection/intervention periodicity.
4.2 Maintenance / Inspection Plan (Table 1);
The recommendations contained in the Maintenance / Inspection Plans are Scheduled Inspection activities, taking advantage of Preventive interventions and condition monitoring activities, within the Predictive concept.
Table 1: Recommendations for assembly, maintenance and inspection
Components
|
Task description
|
Frequency
|
Central hub
|
- Preparation of the machining and assembly procedure for the end of the gearbox's parallel and bevel shafts (seating > 80%)
|
When assembling new cubes
|
Lower and upper discs
|
- Carry out documented / photographic visual inspection of the surface of the discs / ring in the areas where the blades and central hub are attached
|
Scheduled Maintenance Shutdown (limit 03 years of campaign)
|
Fasteners: screws, nuts and washers
|
- Drawing up assembly procedures / using the recommendations in the equipment manual; training staff
|
During assembly of new rotor/blades.
|
- Inspection / Replacement of screws, nuts and washers
|
Scheduled Maintenance Shutdown (up to 03 years of operation)
|
Split bearings
|
- Documented visual inspection: checking the state of corrosion and integrity.
|
Scheduled Maintenance Shutdown (up to 03 years of operation)
|
Shovel (with stainless steel banded edge)
|
- Documented visual inspection: in the areas of the neck, spade body and attachment of the leading edge stainless steel strip
|
Scheduled Maintenance Inspection (up to 02 years of operation)
|
Complete rolling set
|
- Monitored inspection: vibration monitoring on the VT housing (field collection < 7.0 mm/s)
|
30 / 45 days.
|
|
4.3 LUBRICATION PLAN;
Considering that the fan does not have an automatic lubrication system, you should follow the recommendations on the electric motor plate, see Figure 3, which shows the bearing, the amount of grease in grams, the type of grease and the relubrication time, considering the electric motor in continuous operation.
Table 2 shows the recommendations for each ventilator TAG;
Figure 3: Typical ME board for axial fans.
Tabela 2: Dados de lubrificação dos mancais de rolamentos dos ME
Modelo do Ventilador |
TJFD13026200cv4P – dupla ponta de eixo – duplo rotor: |
Aplicação |
TAG |
Pot - CV |
RPM |
Rolamentos |
Qte Graxa-grs |
Período - hs |
Tipo de Graxa |
Secundário |
|
200 |
1790 |
6319 C3 |
45 |
12.000 |
Mobil Polirex EM |
6319 C3 |
45 |
- ESTIMATIVA DE SUBSTITUIÇÃO DE COMPONENTES
As informações contidas na Tabela 3, devem ser consideradas para efeitos de recomendação de sobressalentes de componentes deste tipo de Ventilador.
Tabela 3: Estimativa de vida útil dos componentes:
Components
|
U.V. estimate
|
Central hub
|
20 years
|
Lower and Upper Discs (Upper Ring)
|
12 / 15 years
|
Fasteners: screws, nuts and washers
|
03 / 04 years
|
Split bearings
|
08 / 10 years
|
Shovel (with stainless steel banded edge)
|
*NOTE
|
Housing
|
10 / 15 years
|
Noise attenuators
|
08 / 10 years
|
|
*Note: The durability of the blades depends a lot on the conditions of the Mine, considering:
- Level / type of suspended solid;
- Humidity level in the room;
- Proximity of operation to detonation zones.
It is therefore recommended to have a spare set of secondary fan blades in stock, as these are components that are supplied in around 45 / 60 days.
The other components, the central hub, lower disk, upper ring and split bearings, have a long service life and require inspection when scheduled.
6. SUGGESTIONS FOR IMPROVEMENT
At the beginning of this article, it was mentioned that many mines have adopted fan condition monitoring by installing bluetooth sensors in the bearings of electric motors. These sensors capture and transmit vibration in 03 directions and the temperature of the installed location, maintaining storage for a certain period. The system that picks up these signals can be cell phones and tablets, positioned at distances of less than 10 meters from the sensor site.
FanTR understanding that these secondary fans can have advances, not only in the performance of the equipment, has been working with customers to insert the fan in the demand control of the front of the Mine, in an automated way, and with this adjust energy consumption for the operating point of the Mine gallery.
7. FINAL CONSIDERATIONS
The need to run secondary fans for longer periods of time, reducing maintenance costs and electricity consumption, has led mines to implement maintenance strategies suited to their campaigns and modern monitoring and control systems, adjusting this equipment to the mine's operating conditions.