Direct drive motors, both mechanical and electrical, are used where a steady load or fixed speed is required. But for applications such as the car — which relies on a power transmission system based on gears, linkages and a clutch — a more complex solution is needed.
Without some kind of gearing system the rotational speeds required to move a car at any speed beyond the average for London traffic would be so high as to be inefficient and would probably shake an average SUV apart in a matter of months.
Even if an internal combustion engine could be manufactured to produce a suitable output — a typical engine runs at between 600 rpm and 7,000 rpm — the car’s wheels typically revolve at around 0-1800 rpm.
The same problems apply to industrial applications where large forces need to be transmitted.
South Africa-based David Brown Engineering, for example, has received an order from F L Smidth Minerals to supply a gear weighing some 65 tonnes as part of a contract for Armenia. The gear is so big it will have to be transported in four sections to the republic.
The steel industry needs to move huge pieces of metal around and, subsequently, many of the motors driving these moving ingots and billets require transmission systems to operate effectively. One such installation is that provided by Siemens Flender at Corus’ Clydebridge works, which makes specialist, high-strength steels. It has upgraded its machinery with the installation of a series of Siemens drives and Flender gear units on systems for moving steel between furnaces and processing units such as rolling mills.
Previously motors without a gearing mechanism were installed but the units proved unreliable — and in heavy industry, downtime is very expensive. Jim Cossar, Corus manufacturing manager, said: ‘Speed matching was becoming an increasing problem for the roller tables conveying steel from the furnaces.’
This upgrade has contributed to a claimed 30 per cent increase in throughput and ‘significantly’ improved efficiency. Production improvements such as these have led to the plant trebling output over the last two years.
Also for the steel industry, Renold Gears has produced its heaviest pair of wormwheel gearboxes at Milnrow near Rochdale. Weighing in at some 25 tonnes, they are destined for installation at an Asian steel mill as part of a mechanism used to reform recently cast steel billets into thinner sections.
Screw-down units are designed to apply sufficient force to squeeze steel into the required section widths — the units are manufactured as pairs and transmit loads from massive 220kW motors with a reduction ratio of 21.5:1, meaning they have to withstand enormous static torques of up to 53,000Nm.
Materials handling also uses power transmission technology at a materials recovery facility operated by Nordic Recycling in Tilbury, Essex. Ken Mills Engineering (KME) built an advanced materials handling system for the plant, which uses more than 50 gearboxes supplied by Oxfordshire-based Nord Drivesystems, to enable the extraction of different recyclable materials.
The facility incorporates a number of screening stages and automatic balers linked by a sophisticated conveyor system over several hundred metres. The system is driven by the 50-plus Nord SK9000 gearboxes, which employ helical bevel gears to offer a claimed efficiency of over 95 per cent — which leads to significant savings as the plant typically runs for about 16 hours a day.
These gears were chosen as they can provide a right-angle connection necessary for the conveyor system. They were also deemed to be extremely reliable, which is essential as the plant has a nominal capacity of recycling 25 tonnes of material an hour.
It is not only heavy industry that needs power transmission devices. Watching a football match at Wembley Stadium no longer means getting wet if it rains, thanks to a system of sliding roof panels driven by Brevini Power Transmission gear units.
The gearing system needed to be a low-speed, high-torque design, and able to move panels weighing up to 330 tonnes at about 30mm/sec. Thirty-four Brevini planetary gear units were chosen for the job due to their efficiency, small size and high reduction ratio. They move the panels in place to keep the spectators completely covered within 15 minutes and it is a major addition to comfort at the new stadium.
The importance of power transmission was also the focus of a recent BBC TV Top Gear programme. In one of the team’s recent stunts they arranged a race between a G-Wiz automatic electrical vehicle and the Ford Shelby Mustang GT.
Of course the G-Wiz had to have a touch of upgrading to make a race of it, and with the help of refinements such as four huge electric motors driving the rear wheels via a custom transmission system consisting of drive belts and pulleys developed by Brammer UK, the Lynch Motor Company and Exeter University, the team upped the car’s top speed considerably from the production version’s 40mph (65kph).
In the end it did beat the Mustang, showing what can be done with a bit of attention to the power transmission mechanism.
To ensure power transmission systems run in the most cost-efficient way a wide range of gear technology is available in many types and sizes. Colin Carter reports.