Efficiency in vertical transport

With low installation cost and high levels of safety, rack elevators are struggling for space in handling loads and persons at high speeds

 

In complex areas such as construction, petrochemical, hydroelectric, steel and offshore, large projects normally need to transport loads and persons vertically, lifting them from the ground or from another surface to high points. And rack elevators, machines for vertical transport that use gears to handle heavy loads at considerable speeds are one of the best options to carry out this work.

This equipment is on average 2 to 3 m long and 1.1 to 1.5 m wide. It may transport up to 2 t at a speed of 40 meters per minute. This means that this machine has a high driving force and may transport tools, materials and persons safely and efficiently. Most of the existing models are equipped with features such as metallic tower made with carbon-steel tubes, cabin closed  with metallic mesh (side and top), articulated or guillotine door, internal ladder for access to the top, non-slipping floor and electric operating system.

Equipment motion is carried out by a circular structure with teeth (called pinion), that turns on a surface with symmetric pins (called rack). They are simple and easy-to-assemble parts that may be easily transported due to their compact size and low weight.

Inside the works, this type of machine may be installed in the façade or in the shaft of the elevator that will be definitely installed in the building. To prevent accidents, the equipment has type-parachute safety brakes that are automatically activated when the downwards speed exceeds the normal in 15 percent. In addition, some models have other safety devices such as a system that allows its motion only when the doors are completely closed, ensuring the integrity of everything that is being transported in its interior.

Another system—using electric locks—is actuated when the maximum load capacity of the elevator is exceeded, blocking its motion. This ensures that the machine will not be forced and the motion upwards will be carried out with no accidents.

SAFETY

According to the engineer Dirceu José Ramos, director from Metax in Brazil, there are other important items in the list of safety devices of these machines. Among them there is a system that allows the doors and gates to open only with the elevator leveled, as well as shock absorbers of nominal speed in the base. “In addition, there are models with the top module without rack to prevent cabin traction if it surpasses the final stop limits”, says him. “There are also mechanisms that prevent that the cabin may surpass the last top or bottom stop and others that prevent that it maywould accidentally detach from the tower.”

Still talking about safety, the Project Manager of the Grupo Orguel, João Neves Junior, remembers another feature that ensures safety in rack elevators: automation. “All components communicate with each other. This puts their logic configuration in the Category 3 of safety”, explains the engineer, talking about the standard which establishes that the safety-related command parts have to be configured in a way that just one error in one of these parts does not cause the loss of its functions.

Thus, each occurrence of error is identified during the next call of the safety function or even before it. “This does not mean that all errors will be identified”, points the executive from Orguel, which controls the brand Mecan. “Therefore, an accumulation of non-found errors may cause a non-intentional output signal and a dangerous situation in the machine. For this reason, this category allows a better monitoring of the entire system in a way to match the safety requirements.”

But elevators using steel wire ropes are much more dangerous. That is why its use is forbidden in Brazil from a long time ago. In spite of that, this type of equipment is still being used in the country. Ramos estimates in 20 percent of the existing total the quantity of these machines that is still being used.

For Paulo Carvalho, technical director from Locabens, it is complicated to carry out such estimation. “In the capitals, their use is practically ending, but it is hard to talk about what happens in the country’s inland”, says him, agreeing with Neves Júnior, who also traces a profile of the industry. “To have an idea, some surveys estimated approximately six thousand machines of this type operating in 2013. In other words, there was a significant potential to be replaced by rack elevators”, says him. “But currently this percent is much lower than the sales of the past. With the new requirements of the standards, traditional elevators with steel wire ropes became technically and commercially unfeasible due to the adaptations required by the standards. Therefore, as time goes by, the natural trend is of significant reduction in the sales of these obsolete machines in worksites.”

 

 
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