Designing belt conveyors – the main quality criteria
The key to a successfully-operating production line is setting up a correctly-designed Material Handling System (MHS). Installing high-quality material handling system can lead to significant gains in productivity. Designing a Material Handling System for specific operating conditions should only be done in accordance with the industry standards for designing belt conveyors, factoring in the specific requirements applied to the individual components of the conveyors. Let's take a closer look at the principle components of conveyors.
The support structures and rollers. When fragmented abrasive goods are delivered, the conveyor flight loading area should be equipped with cushioning rollers (rubberised, bunch type, etc) with elastic support sections (ropes, springs), and sliding supports.
The brackets used for mounting the position angle of the side-rollers shall be adjustable, particularly in junctions of grooved and flat belt sections.
The quality the belt mounted on the conveyor needs to meet the requirements of GOST 20-76. Specifically, belts up to 650 mm in width should have no more than 2% width tolerance; belts over 650 mm should have width tolerance no greater than 1.5%. The design thickness of the carrying-side conveyor cover for 1.2R and 2R belt types with synthetic fibre base should be at least 4.5 mm, while the bottom conveyor cover design thickness should be at least 2 mm. The thickness deviation should not exceed 10%. The longitudinal misalignment of the belt edge surface over a distance of 20 metres should not exceed 5% of the belt width. Newly-installed belt surfaces must not include any folds, cracks, blister-holes, or mechanical damage.
Elongation of the fabric-ply belt warp at rated load, amounting 10% of the belt tensile strength for the distance specified, should not exceed: for belts with warp & weft of composite fibres – 3.5%; with warp & weft of polyamide fibres – 3.0-4.0%; with warp of polyester fibres and weft of polyamide fibres – 2.0%.
It is necessary to carry out rating of the belt consumption in specific terms based on the service life calendar calculation.
Drive, take-ups and automation. The drives should be assembled using separate unified unit assemblies of correct power-rating; they should be compact; they should enable smooth start of the conveyor at full capacity, with stepped speed control (for different types of load flow). The conveyors must be fitted with stop controls, to be used if the belt is inadvertently snagged if the belt continues moving after the drive is disconnected.
The equipment of powerful conveyors should include an auxiliary drive for powering the belt at motion speeds of 0.5 metres per second. A control unit is designed for uniform distribution of the load between the drive drums.
The drive drums are fitted with ceramic rubber liners, and in some cases clamp mechanisms assist in providing the traction power required.
Automation equipment should provide for automated operation control and the protection of each conveyor. There should be automatic control of the conveyor line in the specified mode, safety alarms and system interlock with system overload protection equipment. Conveyors which cover long distances are turned on according to load traffic.
Centering equipment. Conveyors should include roller units which are adjustable laterally and vertically, and provide for centering the belt in the event that it deviates from the centerline of the conveyor. It is recommended to use a mobile (rotating) roller arrangement, in which rotation only occurs if the belt is misaligned. Once the belt has been returned to the correct position, the centering roller returns to its usual position. In this kind of operation centering rollers with a vertical rotation axis and deflector rollers should be used.
If required, the conveyor can be fitted with a helical surface roller, which makes centring of the belt possible. Increased capacity conveyors are fitted with centralising rollers or a mechanism with drive and displacement sensors. This provides for the automatic regulation of the mode of the centralising rollers and belt in any given mode.
Conveyor flights which a curved in plan view are fitted with roller carriages installed at an angle to the vertical plane, in order to prevent any snagging or separation of the belt from the line roller carriages. In some circumstances a provision can be made to regulate the position of the drive drum, and also the drum cowling using belt centering elements.
Conveyors need to be fitted with belt offset sensors, included into the conveyor drive control circuit or connected to centering device operation control circuit.
Loading machinery. In order to reduce wear of the belt, the loading machinery should provide for: reduced fall height of the raw materials onto the belt; making the load flow to move at the speed close to that of the belt in terms of the speed value and direction; sizing of the load flow for heaping up; specified capacity with minimal sticking; adjustability and controllability ofl the load outflow mode; separating oversize and extraneous items in the load (by length, or metallic items); control of the outlet clogging; dust reduction.
Mechanisms for controlling failure, integrity, continuity or slippage of the belts. Conveyors must include control of the thrpough destruction of the belts, and give warning of longitudinal splitting. Furthermore, any external or internal damages to the belts must be controlled so that timely repairs of damaged sections could be made, and avoiding breakdowns which could arise from a belt splitting. Conveyors set up at an inclination angle exceeding 10 degrees can be fitted with belt catchers.
Equipment for cleaning and reversing the belts, removing outspill. All conveyors which are involved in transporting bulk cargoes should be fitted with cleaning machinery. When transporting extremely highly sticky cargoes conveyors can be fitted with an idle-speed disk or a spiral roller. If the company has a slurry facility, appropriate use can be made of mechanical cleaners with a hydraulic spray, which provides for high-level cleaning of the belts and disposal of the removed material and pulp.
If the conveyors are required to work for extended periods at very low temperatures, to prevent loads from freezing to the belts it is suggested to use liquid solvents which reduce freezing, along with drying the belts and drums to improve their cleaning.
On conveyors which are longer than 80 x B (where B is the belt-width) reversible belts should be used, to avoid dirtying the roller on the return strand. When doing so the belt needs to be vulcanised, and on the reverse-use section there should be a mechanism to clear the spillage.
Dust-clearing mechanism. When transporting bulk materials with a tendency to produce intensive dust, measures should to be taken to prevent the spread of air-born dust. The loading areas should be hermetically sealed and fitted with apparatus for spraying and aspiration. It may sometimes be advisable to deploy dust suppression foams and solutions. It is essential to aim for a compact layout of the crushing, screening and tranbsferring equipment, to reduce the amount of crumbling of the particle load during the processing and handling operations.
Design and manufacture of conveyor systems by the Samara Strommashina plant.
The Strommashina plant in Samara offers its services for high-skilled design of conveyor systems and equipment. Our extensive experience over many years has included almost every kind of manufacturing system. From 1942 onwards, the Strommashina has been providing high-quality manufacturing machinery to the mining, quarrying, and chemical industries; for road and highway construction; and in the metallurgical and energy fields. The experience the company has acquired, along with its powerful manufacturing base and the development and introduction of its own innovatively-developed technologies enable the Strommashina corporation to offer top-quality equipment at highly competitive prices. Alongside with its mainstream range of manufacturing machinery, Strommashina can price and install material handling systems, and complete production lines in 'turnkey' setups. When you order a conveyor design solution from the Strommashina, you know that you've made the right choice for successful business!