Working in tight spaces

Belt conveyors for underground mining have to have a more compact design than those for overland conveyors, adapted as they are to the limited space available underground. The tight space restraints also makes servicing underground conveyors more difficult. When classical multi-pulley drives are used, service is complicated, while load balancing problems can also appear.

As a result, the drives used underground are necessarily smaller than those used above ground. This article will provide an overview of such small drives and their potential application.

Overview

The drum motor

In this type of drive, the drum casing also serves as the housing for a gear unit and a motor that are placed inside the drum. The torque is transferred to the drive construction by fixing the drum axis end with pivots at both ends. The supply voltage is introduced into the drum through the axis.

The power of such a drive is limited to several dozen kilowatts due to the following factors:

• A geared motor is rigidly connected without a flexible or hydraulic coupling.
• There may be a problem with dissipation of heat from the drum.
• The possibility of reaching a suitable torque is limited.

The construction of the drum motor type of drive is satisfactory, when it is operating as it should; however, it is not convenient when performing scheduled inspections, repairs and emergency repairs, because the whole drum has to be dismantled. In underground mines, this brings difficulties related to the limited space available. The whole drum must be ejected to the side of the conveyor, requiring the belt to be detensioned, while suitable space must be available for the operation of the required tools. Alternatively, the drum can be pulled upwards and rotated within the dimension of the conveyor, but this requires the belt to be cut.

Another disadvantage of placing the motor and the gear inside the drum is the large quantity of lubricant required within the casing, as the gear usually has an open construction and the oil simultaneously lubricates the cogwheels, low-speed coupling and the drum bearing on the axis. This causes problems with sealing the unit, as well as the need to remove all lubricants each time the gear or motor is repaired.

The drive with a gear coupled with the drum

The construction of this drive includes a two-stage cylindrical drive gear, where the second-stage wheel is set on the drive drum shaft in the side wall of the drive. The gear unit housing is bolted to the side wall, comprising the remaining gear wheels. High-speed coupling, brake and motor are all located under the conveyor belt. In the classic gear with a two-stage helical drive, the motor is positioned to run perpendicularly to the axis of the conveyor. In the case of high-power drives, the motor can protrude beyond the width dimension of the drive casing. In such a case, a conical attachment on the first gear level is installed. The motor remains under the belt, but parallel to the axis of the conveyor.

The fundamental problem in the operation of such a drive comes in ensuring a high stiffness of the drive casing, so that there is no skewing of the drive drum with respect to the gear housing. Even the slightest skewing causes an unfavourable change in the geometry of gearing on the last gear level, reducing the durability of the gearing at this level.

Drive drum with an internally mounted motor and gear

A 1992 article entitled ‘Kleinbauende Antriebe für Gurtfoerdereranlagen’ presented a construction of the miniaturised drive for the conveyor belt. This solution is based on two mounting sleeves positioned on either side of the drum and secured in a fixed casing located outside the drum. The drum casing has been placed on the outer cylindrical surfaces of the sleeves. In one sleeve, a drive motor is arranged and in the second one there is a gear. The motor and gear are separately set in their respective mounting sleeves, so that dismantling is easy. The drive is equipped with a coupling placed inside the drum, between the motor and the gear, and a brake is installed on the motor shaft or on the gear shaft protruding outside the drum. The proposal for the internally installed drum eliminates some of the disadvantages of previous solutions in compact drives. The main advantage of this drive is its smaller dimensions and the possibility of dismantling the motor and gear without loosening the belt. Unfortunately, the basic disadvantage is also related to the dimensions. In order to remove the motor and the gear, considerable width must be ensured. As the motor or the gear must be dismantled crosswise to the axis of the conveyor, one of these units must be dismantled together with the coupling mounted on it. A significant problem is also monitoring the coupling condition, its cooling and filling or refilling of the liquid to the appropriate filling level.

FCD 315 compact drive

The FCD 315 compact drive was created as part of the efforts of conveyor designers to obtain a device to meet the demands of users to provide high power in haulings of high-performance walls, as well as in beam stage galleries, without having to use substantial cross-section areas of the housing.

The FCD 315 conveyor drive has a drive drum in the form of the drum casing mounted on two fixed sleeves. The drive unit placed inside that casing, consisting of a motor, a gear and a coupling. It is characterised by the fact that the coupling is positioned on the outer side of the motor and is connected to the input shaft of the gear by means of the transmission shaft placed in and through the motor hollow shaft. This provides easy access to all of the trains, after removing the covers, and ensures the possibility of de-coupling the gear with the motor and replacing the brake disk without having to remove the motor.

In order to ensure easy introduction of a new product into operation, it was assumed that its design should be compatible enough with existing designs. For this reason, the FCD 315 drive has been built into the casing, which is compatible with the dimensions of conventional drives.

As the drive drum does not have to be mounted in the stiff casings, a mounting unit can be used, using a handle that can be mounted in a suitable manner, thus creating applications that guarantee implementation of the drive basic tasks, including dimensions minimisation.

This is an excerpt from an article that was first published in World Coal November 2016. To register and receive your free trial of the magazine, click here.