A STUDY by an assistant professor of Motilal Nehru National Institute of Technology (MNNIT) has found that majority of tractor-trolley accidents taking place in the city as well as in the state are due to their faulty designs.
The study found that lack of knowledge of the iron-smiths who use empirical design rules to connect the tractors to the trolleys are leading to their overturning and causing death and injuries to thousands every year.
"After the study we can confidently say that incidences of tractor-trolley overturning related accidents can be checked by creating technological awareness in the society. We found that tractor-trolleys are mostly produced as non-standard items by local iron smiths using empirical design rules for all tractors though different tractors have different power and speed capabilities," said Dr HS Goyal, assistant professor in the Mechanical Engineering Department of MNNIT.
Citing examples, Dr Goyal said that the maximum speed limit of various models of tractors differs significantly. "For example for a particular tractor brand the speed can vary from 26 Km/hr to 34 Km/hr depending on the engine power capacity which itself varies between 30 to 60 HP," he said.
Dr Goyal said that the trolley is attached with the tractor using a simple joint that allows pull and push to be transferred to the trolley and in the process causes fretting fatigue at the point of contact.
{{/usCountry}}Dr Goyal said that the trolley is attached with the tractor using a simple joint that allows pull and push to be transferred to the trolley and in the process causes fretting fatigue at the point of contact.
{{/usCountry}}"Along with the push and pull, at the time of turning on a curved path or during use of steering by the driver of the tractor, the connecting bolt has to allow relative movement between different contact points and that demands tough control on design and manufacturing of joints," he pointed out.
Dr Goyal said that the best design of a tractor-trolley and tractor connector should follow the mechanism as used in army truck–trailer combinations. "In that case, the connector allows only the push and pulls while the torsion and sliding is taken care by separate members," he said.
Dr Goyal said that coupling required for transmitting driving thrust from tractor to trolley should allow perfect rolling of trolley wheels on turn as far as possible and ensure that misalignment on the rolling wheels due to variation on the road surface positions at a particular moment of time automatically gets accommodated by the tractor-trolley connector.
He said that the trolley connector should also be able to transfer the push or pull from the tractor and the twisting on turns should not result into the fretting wear of the hook joint bolt or the excessive torsion load on the connector.
He said that it should be remembered that human loaded trolley behaves differently as compared to brick loaded trolley.
"A tractor with higher power and speed capability becomes more dangerous with the tractor trolley from the stability point of view. A tractor trolley loaded with bricks behaves differently as compared to the situation when loaded with 25 humans. Though the load on trolley gets reduced when loaded with humans, the centre of gravity of the trolley rises as compared to the trolley loaded with bricks," he said.
Dr Goyal said that a trolley loaded with humans will result in less load on tractor engine and in turn the possibility of more speed and more chances of instability.
"Hence a tractor driver experienced with driving a brick loaded tractor trolley will have to take extra care when driving a human loaded trolley and more control on speed, steering and brake is desired for safety against overturning.
The speed of a high speed tractor has to be controlled by proper selection of low speed gears," he added.
After examining and studying the recent accident involving overturning of the tractor-trolley on October 7, 2006 at Sangam, where one person died and two dozen villagers got injured, Dr Goyal found that it was the result of a brittle fracture of tractor-trolley main connector coupling.
"The shaft along with hook joint could not sustain the excessive torsion load. In the recent incident, a new tractor was attached with an old trolley and the connector bolt also was new with very little free play," he pointed out.
Dr Goyal said that a well lubricated surface of the bolt and hinge point and a fairly loose connection between them allows a safe turning of the tractor with respect to trolley resulting into reduced torsion stressing of the main connector.
"The simple suggestion will be that for a tractor-trolley, a well lubricated and loose joint with tractor allowing a scope for misalignment adjustment and easy turning be used. It is advisable that people ensure lubrication of connector joints on those points where metal to metal contact occurs and also see to it that the connecting bolt allows sufficient clearance with the eye where it has been attached," he said.
Similarly, Dr Goyal said, as a human loaded trolley requires tough driving skills and more control on speed as compared to brick loaded trolley, a new driver on an unknown tractor attached with trolley carrying passengers should be avoided.