An evaluation carried out on driveshafts sold in Brazil shows that we are still far from having very safe products that meet all safety requirements.
One of the main ways to mechanically drive agricultural implements, transmitting power (torque and rotation) at an angle to the agricultural implements is through the cardan shaft. This connects the agricultural tractor's power take-off shaft (TDP) to the implement's power input connection (CEP).
The cardan shaft basically consists of two universal joints joined by two tubular shafts. Transmission takes place through the so-called “universal joint”, or cardanic joint, made up of two terminals (also called forks or sleeves) coupled to each of the trees (of the tractor and the implement) joined by a crosshead.
It is a power transmission system that has expanded the application of the tractor in agriculture, however, it is still one of the main sources of risk and accidents in agricultural work, as the use of the cardan protector, doesn't always run on the field. When existing, It is common to find it with some part broken or cracked, causing it to lose its protective function. The cardan protector consists of protective cones at each end of the cardan shaft, a protective cover along the telescopic tube, retention devices and pictograms.
So that security of agricultural machines or components, in particular the cardan shaft, is achieved, there must be actions and commitment from the government, manufacturers and users, each in their field of activity.
In this sense, Brazilian legislation through regulatory standards (item 31.12.22 of NR 12 and Annex XI of NR 31) imposes that “o cardan shaft must have adequate protection, and must be in perfect condition throughout its entire length, fixed to the power take-off of the machine (or tractor) from the crosshead to the coupling of the implement or equipment”. The same regulations (Annex XI, item 11 of NR 12 and item 31.12.35 of NR 31) also require that “a protection must be installed on the tractors’ power take-off (TDP) that covers the top and sides”.
Agricultural machinery manufacturers are expected to comply with legislation and technical standard requirements. Figure 1 generally represents the necessary mechanical protections, complemented by adequate and durable safety signs (instructions and use of pictograms). Serve to alert the operator and others of the risk of personal injury during normal and service operation, as exemplified in figure 2.
The ISO 5673-1:2005 standard establishes safety and manufacturing requirements for the agricultural tractor power take-off shaft and the power input connection of implements. Figure 3 illustrates one of the safety requirements of this standard for protecting universal joints on the tractor side.
According to the ABNT NBR ISO 4254-1(2015) standard, the CEP protection must be constructed and fixed to the implement so that, together with the PTO cardan shaft protection, it covers the shaft on all sides up to the first housing. of fixed bearings of the machine, at the same time allowing the connection and articulation of the PTO cardan shaft. Furthermore, the straight overlap of the power take-off cardan shaft (TDP) protection with the power input connection protection (CEP) cannot be less than 50 mm (Figure 4).
Users are responsible for following the manufacturers' technical recommendations, exercising good operating practices, such as: dressing safely to avoid trapping clothing or footwear, maintaining the PTO protections, keeping the cardan shaft protection in place , turn off the PTO and stop the engine before getting off the tractor, never pass or jump over the moving cardan shaft and follow the recommended maintenance intervals.
Several accidents are reported in the virtual media and technical literature by inappropriate use of this equipment and the absence of the protector. Contributing to this is the fact that coupling and uncoupling are done manually and the lack of use of the cardan shaft protector. In the first case, the tractor x TDP connection and disconnection operation is mentioned, which is carried out manually in a reduced space between the tractor and the implement, which exposes the operator to conditions of fatigue and discomfort. In this case, the operator must lift and correctly place the cardan shaft in place and push it until locking occurs. The development of automatic devices can reduce this manual intervention.
In the second case, the absence of the cardan shaft protector, When this is in operation, it can cause clothes or hair to get tangled around the axis, turning the person, who is immediately pulled by it. The body is rotated around the cardan axis and amputation of arms and legs, scalping, spinal cord injuries, other injuries or even death may occur.
A database analyzed by Purdue University (USA), with records of accidents related to cardan transmissions that occurred from 1970 to 2004, sought to identify those involving people under 18 years of age. In this study, 22,0% of cases with a known age were identified in this age range. Cases of limb amputation (almost 50% occurrence), spinal injuries and bone fractures have been reported in accidents involving worm shafts, elevators and grain conveyors.
Research in central Italy demonstrated the precarious conditions of the cardan protectors in use, where only the youngest ones, up to 2 years old, were in adequate condition, while the others were in precarious conditions, with restriction devices missing in 72% of the cardan shafts and legible pictograms in only 39% of cases; in the others, safety signs were damaged or lost.
To analyze the conditions of cardan protectors in use in Brazil, the Engineering and Automation Center/IAC sought to characterize such equipment on several agricultural properties in the State of São Paulo. 112 examples of cardan shafts were sampled in nine municipalities in São Paulo. The information was collected using a form specially developed for this purpose.
For each of the protectors found, the brand and model of the protector was characterized, as well as the presence and condition of the protective devices, the maintenance and storage method, and the difficulties during assembly and disassembly. The following components of the protector were analyzed: protective cones, telescopic tube protection, retention device and pictograms.
Of the 112 tractor-implement sets analyzed, 77 had a device characterized as “protection” of the cardan shaft. In this research, the cone, tube, retention device and safety signs were observed to identify the condition (integrity, damage, absence) of each part. Graphs 01 to 05 summarize these results.
The low percentage of “intact” condition points to the poor quality of the protector material, confirmed by claims from users who say that some protectors last less than six months and that this does not encourage them to replace them when damaged. On the other hand, it was observed that users also do not maintain good storage conditions for the equipment when not in use. They also complain about the difficulty in lubricating the crossheads and the difficulty in coupling and uncoupling the cardan-protector assembly on the tractor.
Of the components analyzed, the cones and the tube showed the most damage (63,6 and 71,4%, respectively). The most common damages to cones are cracks, cuts and dents. Even binding with wire and improvisation with plastic containers were found. Some tubes were incomplete, cut, and loose on the cardan shaft.
In the case of retention devices (chain) and pictograms, absence (50,6 and 53,2%, respectively) is the most critical situation. Improvisations made with wire were also found. to the retention device.
Improving the quality of this component must necessarily involve carrying out resistance and durability tests. However, the absence of specialized laboratories, that can provide assistance to interested manufacturers, makes action in this regard difficult. A good start would be to improve the characteristics of the plastic material that makes it possible to increase resistance to ultraviolet rays. This alone will mean an important gain, as it will increase the useful life of cones and tubes. And there are already laboratories for this assessment, such as the Textile Technology Laboratory, at the Technological Research Institute.
Ila Maria Corrêa, Cláudio Alves Moreira, Sergio Roberto Filipini, Roberto da Cunha Mello, Pedro Sérgio Pontes, CEA/IAC
Article published in issue 159 of Cultivar Máquinas.
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