Material handling operations present unique challenges.
Regardless of whether you’re handling scrap or finished components, you need to think about several points to select the right equipment for your particular application. You have many equipment choices today to move, elevate, and distribute material. If you’re considering a belt, vibratory, or a magnetic conveyor, it’s a challenge to select the most efficient conveyor for a particular application. To make the best choice, it’s imperative that you consider all operating parameters. Be prepared that the conveyor system you choose will need to be designed or modified to meet your specific material handling requirements.
Conveyor pulleys will always be the core manufacturing function of Bosworth
Making the right choice
In a rugged environment such as a working mine, it is even more critical that you make the right choice.
Mechanical engineering and fabricator Bosworth, located in Alrode, South Gauteng, is one of South Africa’s largest manufacturers of conveyor pulleys. Managing Director Gary Howell explains why.
Conveyor pulley design
“There are many elements to consider during the design of a conveyor pulley. The most important however is the design of the shafts. Other elements that need to be considered are the pulley diameter, the shell, the hubs and the locking elements.”
“There are three main factors that influence shaft design. Bending from the tensions on the conveyor belt and torsion from the drive unit and deflection. The shaft therefore needs to be designed considering all three of these elements.”
“For the design of the shaft, based on bending and torsion, a maximum stress is used. This stress varies according to the material that is used for the shaft or according to the maximum stress allowed by the end user. Typical allowable stresses, for the most commonly used shaft material, are 43MPa for BS970 070M20 (EN3), 55MPa for BS970 080M40 (EN8) and 83MPa for BS970 709M40 (EN19).”
In a rugged environment such as a working mine, it is even more critical that you make the right choice of conveyor pulley
“The industry uses additional safety factors for shaft design such as load factor (Kb = 1.5 to 1.75) and torque factor (Kt = 1.25 to 1.4), resultant forces and what we call moments. To calculate the shaft size from these, the Guest (equivalent bending) and Rankine (equivalent torsion) formulas also need to be considered.”
“For the above, formulas are taken to be equal since the allowable direct stress is a fatigue case and the shear stress is not. The third calculation determines free shaft deflection limit. This limit ensures that there is no excessive deflection of the shaft at the point where the bearings and the locking elements are fitted. The industry standard is 0.0015 rad to 0.0017 rad maximum allowable deflection.”
“There are various factors influencing the pulley diameter. The pulley diameter is mainly determined by the conveyor belt class, but the required shaft diameter also influences the diameter. A golden rule for the pulleys diameter is that it should be at least three times the diameter of the shaft.”
“There are two main types of pulleys i.e. the turbine pulley and the T-Bottom pulley. In both these types of pulleys the shaft is removable for easy maintenance.”
“The turbine pulley is well suited for low to medium duty applications with a hub designed to allow for flexing, thus preventing high stresses on the locking assemblies or welds.”
Bosworth Managing Director Gary Howell
The new Faccin 4-roll plate roller supplied by Talmac Machine Tools
“The T-Bottom pulley is normally used for heavy duty applications with shaft diameters of 200mm and bigger. The main feature of this construction is a face welded pulley and thus the shell to hub weld is moved out of the highly stressed area at the end plate.”
“You also have to take into account pulley crowning, both full and strip crowning, and lagging. Various types of lagging can be applied to the pulley i.e. rubber lagging, flameproof (neoprene) lagging or ceramic lagging.”
Bosworth is a 105-employee company that was founded in 1943 by the late Walter Bosworth to manufacture components and products for the agricultural industry. The company has seen some ownership changes but has been part of the Hudaco Industries Limited Group since the 1990s.
Bosworth started manufacturing pulleys in the 1960s and says it was the first company in South Africa to manufacture fabricated pulleys and has been instrumental in developing conveyor pulleys to the currently popular designs that are used worldwide.
“Over the years, Bosworth has manufactured conveyor pulleys that were exported throughout Africa and the rest of the world. All Bosworth pulleys are purpose-designed by the company’s own design team through the use of the latest design software – SolidWorks – and manufacturing technology that is available. We are capable of designing and manufacturing conveyor pulleys to cater for any application. We are also able to produce FEA’s for any pulley and we are continuously striving to improve on current designs as well as developing new designs and standards.”
“We operate from two facilities in Alrode. The 8 000m² facility in Juyn/Vereeniging Road concentrates on manufacturing the pulleys and the 3 000m² facility in Bosworth Street is where all our fabrication and wear lining processes take place.”
Plate rolling is not like working a press brake, where there is a single bend and one direction of inertia. A plate roll involves multiple forces and directions of inertia as the forming takes place
The shells of the pulleys are normally between 8mm and 60mm thick but the majority that Bosworth manufacture are in the 30mm range and an OD of up to 1 250mm. The new Faccin plate roller now enables Bosworth to cold roll plates of up to 45mm thick
“To manufacture pulleys like we do there is a fair amount of IP and know-how involved and for this reason we have tried to incorporate most of the processes inhouse. This includes plate rolling, welding, hot-rolling, heat treatment, normalising, stress relieving after welding, machining and rubber-lining.”
“Wherever possible we also use suppliers within the Hudaco Industries Group. For example, sister company Ambro Steel will supply us with pre machined shafts and we do the final machining.”
“Bosworth did invest in its own open-die forging equipment to produce the hubs for the pulleys because at the time it proved difficult to procure them. But, with time, pulley design changed and forged hubs were no longer specified. As a result, most forging done by Bosworth was for the open market and not for pulley production. This has however changed as we focused more on the pulley manufacturing and we have now closed the forging section.”
“The hubs, or end disks as they are referred to, are now cut from plate.”
New Faccin 4-roll plate roller
“One of the biggest operations in pulley manufacture is the plate rolling. Although dramatic advances in machine technology have largely decreased dependency on seasoned machine operators, plate rolling still requires a lot of skill. A few metal fabricators are lucky enough to have a talented roll operator on staff. These experienced operators have comprehensive knowledge about materials and rolling practices, which enables them to control this extremely dynamic fabricating process.”
Shells that have been processed on the Faccin 4-roll plate roller
Welding of a conveyor pulley shell
“Plate rolling is not like working a press brake, where there is a single bend and one direction of inertia. A plate roll involves multiple forces and directions of inertia as the forming takes place.”
“Aside from a skilled operator, the machine you choose is equally imperative for effective plate rolling. We have just invested in a new Faccin 4-roll plate roller, supplied by Talmac Machine Tools. The majority of our plate rolling is done for own use but we do offer plate rolling of between 3mm and 80mm thick plate depending on the width and diameter of the required rolling, to other fabricators. The shells of the pulleys are normally between 8mm and 60mm thick but the majority that we manufacture are in the 30mm range and an OD of up to 1 250mm. Our new plate roller now enables us to cold roll plates of up to 45mm thick.”
“We used to cut our own plate but because of the wastage we now have this delivered cut-to-size. When you are consuming 250 tons of plate a month you have got to make sure that your scrap dealer is not making more money out of the material than you are.”
Plenty to consider
“Plate rolling is an art when compared to some other fabricating processes, but having the right equipment and accessories for the job can help even a new operator turn out quality rolled parts after a few days of training. The new Faccin 4-roll plate roller, which was installed earlier this year, has allowed us to bend a plate in one operation whereas with our older machines we had to perform a number of operations.”
Large Thailand order
“We are currently busy with an order to supply 89 fully assembled pulleys to a power station in Thailand. We began work on this project in March 2019 and we have to finish by October 2019. In total the project will consume 1 016 tons of metal.”
Through the use of top hat furnaces, Bosworth’s heat treatment facilities offer stress relieving up to 4m in length, normalising up to 4.5m in length, annealing up to 4.5m in length, oil quench and temper up to 2m in length and water quench and temper up to 2m in length. All these services are supported by straightening facilities and machining if required
The hubs for the pulleys are now machined
“Other projects where we have supplied pulleys to include most of the power stations in South Africa, the Richards Bay coal terminal, numerous mining operations around South Africa, a power station and a cement plant in Taiwan and other projects in Peru and other South American countries, as well as in India, Bulgaria, Mozambique, Mali, Botswana, Israel, Indonesia, Vietnam, Australia and Qatar.”
“Our aim over the years has been to supply as many of the mechanical products that the project requires and not just the pulleys. As a result, we now manufacture our own idlers and rollers to SANS 1313 or any other international standard, if required. The sealing arrangement for the idlers is made up of a 3-piece triple labyrinth seal, protected by a LDPE dust flinger. The bearings are therefore sealed for life. The conveyor rollers are manufactured in steel and plastic with typical tube diameters of 102, 127 and 152mm industry standards.”
“Although we don’t manufacture the conveyor belts through our sister companies we are able to source all that is needed.”
“One building of our facility in Bosworth Street is entirely dedicated to fabrication work. There we have the capability of doing small to medium size general fabrication like conveyor chutes and pipework. But we are not limited to this type of work. One of our specialities in this department is manufacturing industrial mixer impellers.”
Wear linings and rubber sheeting
“Our products operate in some very harsh conditions and have to endure huge pressures, while at the same time reduce downtime because of mechanical failure. It is an industry standard to use wear linings or rubber sheeting on pulleys. They prevent wear and tear, increase the grip for better tension and can operate as a self-cleaning system for the conveyor belting, which extends the life expectancy of the shell. In most instances the linings, which are also referred to as laggings, helps to reduce spillage and corrosion.”
A conveyor pulley shell that has been fitted with Rexline rubber linings for wear resistance
Bosworth has a machine shop that makes use of various CNC machines
“This is a relatively new side to the business but an important one as we are now able to supply conveyor pulleys that have been completely manufactured and assembled by ourselves. We are an authorised distributor of Rexline rubber products and apply the rubber with the Linabond adhesive, a brand name specially formulated for the Rexline rubber linings.”
“Having this product available to us has also opened up other areas of industry where wear linings are required, for us to pursue, and not just conveyor pulleys. The extra spin-off is that we are also attracting additional fabrication work. The wear lining operation is situated alongside the fabrication facility in Bosworth Street.”
Bosworth will do the final machining of shafts, an important component of the conveyor pulleys
Conveyor pulleys in the assembly and inspection bay
“We also have the capabilities to supply and install a wide range of alumina wear resistant tiles for wear protection of chutes, pipes, underpans, cyclones and tanks to name a few.”
Other services that Bosworth offers include the refurbishment of all makes of pulleys, plate rolling plates with thicknesses ranging from 6mm to 80mm, with lengths of up to 3 000mm depending on the plate thickness, MIG and sub-arc welding and re-rolling. The range of cylinders that can be rolled include special thick-walled pipes, cylinders, hydraulic rams, winch and pulley drums, cones, special purpose cylindrical segments curved plates, tanks and silos and road rollers.
Through the use of top hat furnaces, Bosworth’s heat treatment facilities offer stress relieving up to 4m in length, normalising up to 4.5m in length, annealing up to 4.5m in length, oil quench and temper up to 2m in length and water quench and temper up to 2m in length. All these services are supported by straightening facilities and machining if required.
Wear linings is a relatively new side of Bosworth’s business
The fabrication department in Bosworth Street has the capability to manufacture chutes, cyclones and tanks
The company also has ISO 9001:2008, ISO 14000 and ISO 18000 certification in place as well as health and safety approval.
“Conveyor pulleys will always be the core manufacturing function of Bosworth. We can manufacture conveyor pulleys for all types of industry with turbine and T-bottom type conveyor pulleys taking up the majority of our capacity. Turbine type pulleys are mainly used for light duty applications, whereas T-bottom pulleys are commonly used for heavy duty applications.”
“We will never turn away a client and, if we can add value in the manufacturing process, we will.”
For further details contact Bosworth on TEL: 011 864 1643 or visit www.bosworth.co.za