Lec12 - Mechanical Handling - Belt Conveyors II - F2023.pdf

Mining Optimization Laboratory Materials Handling ENGR 3307 - Fall 2023 Lec12 - Mechanical Handling - Belt Conveyors II Dr. Ahlam Maremi Bharti School of Engineering Laurentian University F215B Email: [email protected] 1 Components of Belt Conveyors • Features of belt conveyors: 1. 2. 3. 4....

Mining Optimization Laboratory Materials Handling ENGR 3307 - Fall 2023 Lec12 - Mechanical Handling - Belt Conveyors II Dr. Ahlam Maremi Bharti School of Engineering Laurentian University F215B Email: [email protected] 1 Components of Belt Conveyors • Features of belt conveyors: 1. 2. 3. 4. 5. 6. 2 Ahlam Maremi Belt construction Idlers Drive arrangements The power unit Loading and discharge arrangements Belt cleaners 2 Mining Optimization Laboratory Drive Arrangements 3 • On a basic belt conveyor, the belt runs between two terminal cylindrical drums, one of which is powered. • The end of the conveyor where the transported material is loaded is a tail end or feed end, • The other end, from which the load is discharged, as the head end. 3 Drive Arrangements • The drive arrangement supplies the torque (rotating force) to create the necessary motion for the pulley to move the conveyor belt. • It consists of several components but is primarily considered as the motor and reducer. • It may be at either end of the conveyor: – It is better to drive the head end drum as this will involve the smallest amount of belt being subjected to the maximum tension. 4 Ahlam Maremi 4 Mining Optimization Laboratory 5 Drive Arrangements • The drive could be at an intermediate point on the return strand of the belt close to the head end. • Where the conveyor is operating downhill, the drive should be at the tail end (feed), or a separate driven pulley on the return strand fitted as close as possible to the tail end. Tail end Head end The drive close to the head end Head end Tail end The drive Centre drive 5 Drive Arrangements • Factors that effect the efficiency of the conveyor drive: – The difference in tension between the tight side and the slack side of the belt, – The friction between the belt and the drive drum, – The angle of wrap, or arc of contact, of the belt to the drum. • The power that can be transmitted from the driving drum to the belt is limited by the point at which the belt begins to slip. 6 Ahlam Maremi 6 Mining Optimization Laboratory 7 Drive Arrangements • To increase the power: – Increase the coefficient of friction (by applying a rubber lagging to the surface of the drum), – Increase the angle of wrap by snubbing the drum, – Provide a multiple drive. Rubber lagging 7 Drive Arrangements - Some Common Types • With the plain drive, the angle of wrap is limited to 180°. • The snubbed drive has larger angle of wrap (up to 240°) it brings the carrying and return strands of the belt closer together. • With a tandem drive, two drums are geared together and driven by a single motor, – This arrangement gives an angle of wrap almost double that of a single drum. 8 Ahlam Maremi 8 Mining Optimization Laboratory 9 Drive Arrangements - Some Common Types • With a dual drive, this arrangement gives an angle of wrap almost double that of a single drum, – The two drums are separately motorized. • A drawback to both arrangements (c & d) is that one of the driving drums will be in contact with the carrying (dirty) side of the belt. • Using bend and snubbing pulleys (e.), we can reverse the belt so that only the clean side is in contact with the two driving drums. Bend pulley Snubbing pulley 9 The Power Unit • When selecting the driving motor and power transmission, there are several factors to be considered: – – – – Single-speed or multi-speed requirements, Type of electrical power supply, Environmental conditions, The starting characteristic. • A long and fully loaded conveyor may require a considerable time to accelerate to its normal running speed, • The power unit should normally be capable of providing a constant torque during the whole of this period. 10 Ahlam Maremi 10 Mining Optimization Laboratory The Power Unit - The Electric Motor • Squirrel cage induction motor: – It is very common to be used for belt conveyors, – It is a high-speed machine, – It will not start under a heavy load, – Speed reduction mechanism is essential. 11 • Compound DC motor: – It used where starting conditions are severe, – It is used for constant speed, – Speed reduction mechanism might be needed. 11 12 The Power Unit • Speed control device is used to change the speed characteristics of the motive unit to suit the conveyor. – It allows some flexibility in the selection of the electric motor. • There are two types: – Fluid couplings: Fluid couplings • They are available based on variable-speed operation; • They are considered as a pump and a turbine, fitted in the same casing, with the output fluid from the pump being used to drive the turbine. • It is cheap. – Eddy-current couplings: • It is an electromagnetic device, • It allows a measure of control over the acceleration of the conveyor belt. • It is expensive Eddy-current couplings 12 Ahlam Maremi Mining Optimization Laboratory Loading and Discharge Arrangements 13 • Loading of a bulk material on to a belt conveyor is usually: – From a hopper by direct gravity discharge, or – From a preceding conveyor or feeder. 13 Loading and Discharge Arrangements • The loading system should provide: – A steady flow of product to the belt, and – Distribute it uniformly about the centerline of the belt • This is to ensure that the optimum loading level is achieved without problems of spillage or dust generation. 14 Ahlam Maremi 14 Mining Optimization Laboratory Loading and Discharge Arrangements 15 • The product should flow on to the belt in the direction of travel and with the same forward velocity to minimize acceleration losses and abrasion of the belt surface. • Usually, the use of some kind of transfer chute would be involved to avoid the product falling vertically on to a moving belt. 15 Loading and Discharge Arrangements • The design of a chute must be undertaken with some care to avoid build-up of product on the sides and bottom of the chute (and possible complete blockage). • Skirt plates are generally fitted at the outlet from the chute to confine the product towards the centre of the belt and minimize spillage. • Skirt plates would extend along the belt beyond the feed point, – The distance between them being normally about two-thirds (2/3 W) of the width of the belt. 16 Ahlam Maremi 16 Mining Optimization Laboratory Loading and Discharge Arrangements 17 • The most straightforward approach to discharging product from a belt conveyor is simply to throw it over the head-end drum. • We have to carefully design the discharge chute so that erosive wear of the front plate of the chute. • Where conveyed product is to be discharged at one or more points before the head-end drum there are basically two methods that can be employed: Discharge chute 17 Loading and Discharge Arrangements • To use a plough at each desired discharge point. – The belt is flattened at the desired discharge point so the plough blade will direct the conveyed product into a chute at one side of the belt. – Use of a V-shaped plough allows the product to be discharged simultaneously to chutes on each side of the belt. • If a single variable discharge point is specified, a tripper car can be used, – It raises the belt towards a discharge chute directing the product to one side of the conveyor or the other. V-shaped plough Over the end drum 18 Ahlam Maremi With a plough With a tripper car 18 Mining Optimization Laboratory Belt Cleaners 19 • Belt-cleaning devices are very important for belt conveyors, • When transporting bulk materials that have any tendency to stick to the surface of the belt, it is essential to use some kind of cleaning technique at the head end to minimize the buildup of material on snub pulleys and return idlers. – Any build-up can cause: • Sharp particles to be pressed into the belt cover • The belt to run off-center, – Both of which can drastically shorten the life of the belt. • It is necessary to ensure that any product spilt on to the clean side of the belt is removed before it enters the tail pulley and becomes trapped between the belt and the pulley. 19 Belt Cleaners • Various types of cleaner are available such as: – Rotary brushes or – Scraper blades of steel or rubber • We have to ensure that the cleaner is effective without causing damage to the belt, and • That excessive build-up of cleared particles does not occur on the brush or scraper and so reduce its efficiency. 20 Ahlam Maremi 20 Mining Optimization Laboratory 21 Belt Cleaners • An effective cleaning method for sticky materials is by: – A water spray to soften and loosen the material sticking to the belt, – Followed by rubber wiper blades to plough the material off. • However, this technique presents the considerable problem of subsequently disposing of the wastewater and it is therefore rarely used except on high-speed conveyors. 21 The Bulk Solid to be Transported • The design of a belt conveyor depends on the bulk solid to be transported. • The conveying rate of the bulk materials depends on its bulk density and the height to which it can be piled on the belt, – The bulk density is the mass of the material divided by its total volume (particles and voids). • Knowing the bulk density allows the conveying rate (in tonnes/hour) to be calculated from the belt speed and the average cross-sectional area of the conveyed material as stacked on the moving belt. C = a  v C is the conveying rate v is the speed of the belt conveyor a is the average crosssectional area of material 22 Ahlam Maremi  is bulk density 22 Mining Optimization Laboratory The Bulk Solid to be Transported 23 • Repose angle influences the height of material piled on a conveyor belt, • The movement of the belt causes the heap to slip and flow out slightly, • A surcharge angle is defined as the angle to the horizontal which the surface of the material assumes while at rest on a moving conveyor belt. Cross-section of a typical troughed belt conveyor showing angle of surcharge of material on the belt. 23 The Bulk Solid to be Transported 24 • The surcharge angle, for most materials, is 5° to 15° – It is less than the repose angle. • The table presents details bulk densities, angles of repose and angles of surcharge for a selection of familiar bulk solids. 24 Ahlam Maremi Mining Optimization Laboratory The Bulk Solid to be Transported 25 • There are other properties of the conveyed product that should be considered including: – – – – – Moisture content, Dustiness, Cohesiveness and adhesiveness, Abrasiveness, Chemical corrosiveness. • The most important property is the lump size of the material, – Lump size has a direct effect on the speed of the belt and the belt width. – Most manufacturers of belt conveyors use an empirical relationship between the width of the belt and the size of lumps to be handled. 25 The Bulk Solid to be Transported • The usual practice is to allow a maximum lump size of: – One-fifth (1/5) of the belt width for surcharge angles of 20° – One-tenth (1/10) of the belt width for surcharge angles up to 30° • Larger lumps can be handled if the conveyed material contains a high percentage of fines (around 90%). 26 Ahlam Maremi 26 Mining Optimization Laboratory Learning Outcomes 27 • By the end of this lectures, you have learned about: – – – – – Drive arrangements The power unit Loading and discharge arrangements Belt cleaners The bulk solid to be transported – Will continue the discussion about the speed of the belt 27 Don’t Forget! • • – • • • • 28 Ahlam Maremi 28 Check your D2L regularly Review additional resources available on D2L Final report due Monday, November 6th, 2023, before Midnight. Quiz 2, Nov 7th – Tutorial time - 3:00 PM– Lec10 to Lec14 Final report due Monday, Nov 6th Presentations: Groups 1, 2 and 3 - Tue. Nov 14th Final Exam Dec 9th at 2:00 PM