Understanding the Cost of Underground Conveyor Systems

While there are other ways of bringing material to the surface, nothing beats an underground conveyor. A custom-engineered conveyor system is fast, safe, and reliable. It doesn’t emit any fumes, can be installed in ways that leave passageways clear for workers and provides the lowest cost per ton moved.

An underground conveyor is different from those used on the surface, particularly since many underground conveyors are hung from the mine roof.  Here we’ll review the components included in a complete system and provide some ballpark cost estimates.

UNDERGROUND CONVEYOR SYSTEM REQUIREMENTS 

The underground areas of a mining operation are an extraordinarily challenging environment. High temperatures, dust, cramped conditions, and poor illumination are all typical and can take a toll on motors, bearings, reducers, and belts. For long-lasting and reliable operation, equipment used underground must be up to the task.

Fire is a particularly serious hazard underground. For this reason, MSHA regulations address methods of fire prevention. This includes the components used in conveyor systems and especially conveyor belt materials. Many conveyor belts used underground must comply with MSHA Part 14 regulations for fire resistance.  However, depending on the underground gas classification, another MSHA specification may be required.

ELEMENTS OF AN UNDERGROUND CONVEYOR SYSTEM 

A typical underground conveyor brings coal, salt, copper, potash or other material from where it’s extracted to the surface. In many mines, this involves a substantial change in elevation which places additional loads on the system.

Once at the surface, the material is typically transferred to an overland(surface) transfer or stacker conveyor. This means there’s a rock box or transfer chute at the discharge end of the belt.

Details depend on the specific application, but most underground conveyor systems include the following:

• Structure — The framework that supports the belt on idler rollers.
• Drive unit — This comprises the motor(s), reducers, fluid couplings, and drive pulley that moves the belt. Drive units are typical of the alignment-free design as this minimizes wear, maximizes reliability, and reduces maintenance costs.
• Starter — The system that manages how electrical power is supplied to the motors.
• Rock box or Transfer Chute — Used at the discharge end of the belt to direct material onto the lower belt, ideally in the belt center.
• Tail section — Where the material is loaded onto the belt. May have a rock box design and include dust containment features.
• Conveyor Belt Drive — Wraps around the drive pulleys and connects the drive units in order to provide torque to the conveyor system for material extraction.
• Take-up unit — This keeps the belt under tension, minimizes sag on the return side, and accounts for permanent stretch in the belt.

FACTORS INFLUENCING UNDERGROUND CONVEYOR SYSTEM COST 

An underground conveyor is inherently more expensive than one designed for overland or surface use. This stems from the need for fire-resistant materials and dust protection. However, the structure can be less complex than that used outside as the passageway floor or roof can provide mounting points. 

Here’s a look at these points and others that affect system cost:

• Capacity required — Expressed in tons per hour (tph), when combined with a knowledge of material density this determines the width, speed, and strength of the conveyor belt. It’s also the major determinant of motor power requirements.
• Vertical rise — The higher the material needs raising to bring it out of the mine, the greater the load on the motor.
• Material characteristics — Density and tph determine the volume of material to be moved, but properties like abrasiveness, sharp edges, and whether wet or dry influence conveyor belt and component selection. 
• Structure installation — In mine passageways, structure can be mounted to the floor or roof.  Roof mounting frees up space for workers, vehicles, and equipment.
• Belt speed — Determines reducer ratio and torque requirement at the drive unit.
• Belt width — A wider belt is always more expensive.
• Distance — This determines belt length and quantity of structure needed.
• Discharge system — When the belt reaches the surface it usually discharges material onto another conveyor. This might be via a rock box or transfer chute.

STRUCTURE COST

Structure can be floor or roof mounted. Good quality structure incorporates CEMA standard idler rollers and is powder-coated for corrosion protection. Structure is priced per foot and can range from as low as $40.00 per foot to $150.00 per foot depending on required belt width, CEMA rating, shell thickness, and structural support requirements.  The higher the CEMA rating and wider the belt width, the higher the cost.

ALIGNMENT-FREE DRIVE COST 

This is made up of a motor or motors plus couplings and reducers. It also requires a motor starter.

Motors can be pricey: figure about $25,000 for 300 hp.

Several types of starter are available. VFDs offer the greatest energy savings and control but are higher cost, approximately $50,000-$60,000 for a pair of 300 hp motors. Complex motor control systems will also need a control panel at an additional $20,000.

Across-the-line starters are the least expensive option but use more power and impose higher loads and more wear on the system. These would cost $15,000-$20,000. In between VFDs and across-the-line starters are soft starters. These reduce wear but provide little in the way of energy savings.

CONVEYOR BELT COST

The belt is one of the more expensive elements of a conveyor system, especially in underground applications where fire resistance is oftentimes mandatory. Cost depends on belt width, (mining belts usually range from 36-60”), strength (expressed in pounds per inch of belt width (PIW), and the number of plies.

Depending on these variables, an underground conveyor belt costs between $25-$100/ft.

DISCHARGE UNIT/ROCK BOX/TRANSFER CHUTE 

The cost of this depends on capacity, height, and design characteristics. A simple rock box could be in the region of $5,000-$15,000 while a more complex transfer chute might be $15,000-$30,000.

TRANSPORT AND DELIVERY COSTS 

The cost of moving underground conveyor systems from our factory in Oakwood, VA depends on distance. For budgeting purposes, use $5,000-$10,000.

TOTAL PACKAGE COST 

While an underground conveyor system may have higher up-front costs than alternative methods of bringing material out of a mine, lower energy, and maintenance costs plus improved safety and avoidance of fumes quickly make it the most economical.

The cost of a complete system depends on the individual application. However, to give an indication, consider a system with a capacity of 300 tph and a belt 30” wide moving at 450 feet per minute over 1,000 feet. Here the total cost, including alignment-free drive, takeup unit, tail section, starter, structure, and belt would probably be in the range of $275,000-$400,000.

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