03 June 2020

Spotlight-Esquire Machines

Tower Hoist Innovation



Founded in the year 1975 Esquire Machines Pvt Ltd has carved a niche for itself in the field of manufacturing, selling & servicing of Concrete Mixers, Man & Material handling equipment and other construction equipment. The company has a wide portfolio of products which are indigenously developed and manufactured in house.Today Esquire Machines has established an enviable network and strong reputation in India, Middle East, Africa and Sri Lanka. An ISO 9001: 2008 company, it is rated “SE 1B” by NSIC CRISIL and recognized as a Government Recognized Export House. Today it reaches out to customers all over the world through a network of dealers and distributors.



Esquire Machines Tower Hoist EMTH: Use of Brake Motor, Positive Free Fall Locking and Bucket Door Closing



Background Information

Due to high rise buildings coming up in Metro and all other modern cities across India, the construction industry continues to face the challenge of transporting the men and material in vertical direction quickly and efficiently. The Builder Hoist or Tower Hoist is one of the economical solution to meet the demand of material transportation in vertical direction. The Builder Hoist is known to industry for more than several decades. The Builder Hoist is easy to erect, transportable and provides a fast economic means for transporting concrete, bricks and any other compact building material.



Builder Hoist

The Builder Hoist consists of three main elements:

Tower structure made out of angles

Rope winch with prime mover and

Moving Platform supported by Rope and Pulleys

In the traditional designs, the prime mover power is generally provided by either by Diesel Engine or Electric Motor. The Winch Drum is rotated at reduced speed by means of Chain sprocket, or belt reduction drive.

When the rope winds on the winch the bucket goes up guided on the tower. To hold the bucket in place at the top delivery point, a manual brake is applied on the wheel of the winch. Generally the engine drive can not rotate in reverse direction, hence the lowering of the bucket is done by releasing the brake on the winch drum, and the bucket due to self weight falls under the gravity force. Just near the ground, the operator applies the brake and stops the bucket. Sometimes the bucket may fall with a force on the ground and to absorb that shock, there is flexible tyre / rubber pieces which are kept at the bottom.



Solution offered by Esquire Machines Tower Hoist

To put the over travel concern to rest, and to prevent the dangerous high speed gravity fall of the bucket during downward travel, Esquire Machines has developed a safe concept of controlling the winch drum by a positively engaged coupling, and gearbox transmission. In this design the prime mover used is motor equipped with brake mounted on the fan side of the motor. The brake is fail safe arrangement and in case of power failure the brake immediately engages and stops the bucket travel.

Since electric motor with forward and reverse contactor control panel is used, the motor can rotate at constant speed in both the directions in a controlled way offering the controlled downward travel of the bucket, not under free fall condition of gravity.

To prevent over travel at the top destination of the bucket and bottom point, a limit switch is mounted both at the top point and bottom point where the operator wants to stop the bucket. During traveling the cam mounted on the bucket actuates the limit switch and cuts off the supply to relay in the panel, which releases the motor power circuit contactor, and stopping supply of motor. As soon as the supply to motor is cut off, the brake coil de energizes and the brake is applied on winch, immediately stopping the bucket at precise point. Thus use of brake motor and limit switches protects the winch from over travel.



Positive Locking arrangement in case of Free Fall

For all rope driven products, there is always hazard of rope snapping either due to wear of the rope, overloading, or snapping due to entangling of rope in some other parts of building. In case of tower hoist the bucket travels in a earmarked area of base frame, and generally protective scaffolding enclosure is used surrounding the bucket travel region, hence un authorized, or accidental entry of operating persons is avoided directly below the bucket travel area.

Never the less, in case of rope snaps with filled bucket, the bucket travels with a free fall, and although bucket does not disengage from tower, still the hazard of accident, breakage remains. Also if filled bucket falls, then in that case the materials carried in bucket will spill over and fly near the buket area and can result into injury of surrounding people. Also such a free fall can damage the bucket platform beyond repairs sometimes.

There are some solution exists in this regards, in which the pulley mounted on bucket is spring loaded. So in case of sudden loss of rope tension, the spring returns the pulley to extended position. The movement of this spring is used to actuate a friction induced cam arrangement which grips the tower.

In practical cases, however this arrangement is a complete failure, since most of the cases, due to wear and misalignment of tower, the gap between locking roller and tower angle varies a lot. Moreover grease is applied on the working surfaces of the tower which results in loss of friction and this arrangement of eccentric cam generally is a failure.

Here Esquire Machines have extended the concept of movement of spring, and the same movement is magnified by leverage to actuate a locking lever. In case of rope snap and free fall of the bucket, the lever actuates and the extended hook portion comes in the path of cross supports of tower. In case of this actuation, the lever latches on the next cross angle on the mast, and the free fall downwards motion of the hoist is prevented.



Limit switch to on the bucket door

In case of Esquire Hoist to prevent the mistake of accidentally starting the hoist before, the material is fully unloaded, or before the door is closed, limit switches are provided at both the bucket doors. So when the lift stops and the bucket door is opened, the limit switch contact opens the supply to control circuit of motor On Contactor, thus even if accidentally the On button is pushed before both the doors are fully closed, the winch does not start. Winch can only start when both the bucket doors are fully closed.

This arrangement also prevents the accidental opening of the latch of the door. Even if the door opens accidentally the winch immediately stops giving indication of opened door.



Advantage with Tower Hoist made by Esquire Machines

Electric motor driven positive drive of the winch drum through gear box. No uncontrolled downward “free fall” movement of bucket

  • Brake motor with push button control, keeping operator engaged and vigilant while the bucket moves
  • In case of loss of wire rope tension due to breakage or slippage from the fixed hook, the mechanical lock prevents free fall of the bucket preventing accident
  • Top and bottom limit switches prevent over travel and disengagement of the bucket.
  • Limit switches on the bucket prevent accidental start of the winch when bucket doors are in open condition.



Safety concerns of conventional Builder Hoist

Since the engine and electric motor does not rotate in opposite direction while downward travel of the bucket, the safe operation of the hoist depends on skill of operator. In fact in very tall installations the top of the mast is not visible to the operator, and generally a marking strip is tied to the point on the rope at which the operator remains vigilant, and stops the hoist at the marked point on the wound winch rope. Hence both in upward travel and downward travel of bucket, there is an over-travel hazard which is present.

In traditional hoists, while the material is being unloaded from the bucket, the bucket door is opened and the construction workmen remove the materials. During this time, the operator at bottom of the building does not have means of knowing if the material is completely unloaded or not, before starting of the winch for downward travel. In case the hoist is started before unloading there is a chance of material falling from the bucket, or bucket door being left open in downward travel of the bucket.



For more details contact:

Website: www.esquiremachines.com

Email: getintouch@esquiremachines.com

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