Question

The figure 3 represents the construction hoist used to handle material handling in construction sites Figure 3: Construction Hoist

a) Explain the working principle of construction hoist and its application.

b) Identify the mechanism used for construction hoist.

c) Identify the driving link and generate the kinematic diagram.

d) How the vibration on the machine is managed during operation?

Answer 1

A) A hoist is a device that is used to lift or lower the load attached to it by the means of a lift wheelor drum. The lifting of the load is done by the rope or wire that is looped around the wheel orthe drum. The wheel or the drum may use electricity for its operation or in some cases it mayalso be manually operated. Along with the drum and the wire, another integral part of the hoistis the lifting medium that is used. The different lifting mediums that are used are chain, fiber orwire rope. A hook is also available where the load is attached.One of the most commonly used type of hoist worldwide is the Chain Hoist. The type that iscommonly used is electrically operated. In this type of hoist, the chain is used as the liftingmedium. Here there is a closed chain that forms a loop which ultimately lifts the load. A pulleyis also attached with the hoist to lift the load. Numerous small and large pulleys are found inthe chain hoist.For raising the load, the chain has to be pulled. When pulled, the large pulley draws in morechain than what is required by the smaller side facilitating the beginning of the liftingprocedure.

The different areas of application of chain hoist comprises of industries mostlymanufacturing ones and construction sites.The working of the chain hoist can be understood from the following points:

• It uses gears to multiply the force.

• A chain hoist when operated by hand requires an operator to pull the light loop chain on the side.

• This turns a gear mechanism inside to turn the chain pulley.

• When this pulley turns, it raises the heavy chain which usually has a hook on the end.

• By pulling the light chain loop, the manual hoist is actually able to increase the force that is being applied by the heavy chain.

• This is caused by the gear ratios inside the manual chain hoist.

• The mechanical work done by the operator is the same as the work done by the heavy lifting chainThe procedure specified can also be automated by using the electrically operated Chain Hoist.Thus it simplifies lot of load lifting work.

Nowadays, there are machines to accomplish various tasks. This is very true for lifting a heavy load. Youcan find cranes and chain hoists to help you in accomplishing the job of lifting heavy goods. One nolonger needs human beings to carry out this work.A chain hoist performs the task of lifting a heavy weight by the means of hard and strong chains. Achain block consists of a tackle and an endless chain. This chain block is used to lift heavy goods from anoverhead track. It is mainly used in workshops. Chain hoists can also have a lever to operate the hoist. Itmay also have a loop of operating chain that one can pull through the block (known traditionally as achain fall). This activates the block to take up the main lifting chain.There is one more category of chain hoists known as electric chain hoists. It can help you carry heavyloads from one place to the other with just the push of a button. They prove to be cost efficient in thelong run. You need not spend money behind professionals to operate this equipment. It can be easilyoperated by an amateur.Many more types of chain hoists exist in the market. They are classified on the basis of the amount ofload they can lift. They can also be classified on the basis of the speed they operate. Therefore, researchand analysis is recommended before you purchase one for your premise. You also need to take care thatyou buy a quality product from a reliable dealer.Spending money on chain hoists is a wise investment. You can save on labor cost and time. They willalso ensure that you obtain maximum productivity for low costs. They will see to it that your premiseremains safe from fatal accidents. They are recommended in every premise.

B)  

The mechanism which is used for raising and lowering heavy loads to the desire height by using comparatively small effort is called as hoist mechanism.
It is mostly operated with a system of pulley and gears (either manually or mechanically) using power electric supply or fuel.

Hoist mechanism

Hoist mechanism Uses

• Hoist mechanism is particularly used at construction work for loading and unloading of materials.
• Frequently, it is used for lighting of materials in bulk quantities at various sites. e.g. dams, multi-storeyed building, bridges, docs etc

Hoist mechanism is used in following hosting machine –

• Various types of cranes.
• Weston differential pulley blocks.
• Screw jack or hydraulic jack.
• It is also used in Shovel
• C)
• D)

  When it comes to hydraulic systems, excessive vibration is a common issue. Although it’s not always a hydraulic issue, but normally a mechanical one, the design of a hydraulics system comprises of many mechanical parts and components which can also need to be considered.

  For example, there are cylinders that may not be moving in a linear fashion, pumps and motors rotating at speed and even the oil itself can all contribute to a mechanical imbalance that could result in vibration.

  As a maintainer of a hydraulic system, it will be down to you to discover what’s causing this issue and to remedy it.

• Here is our approach for taking steps to remedy any vibration issue in your hydraulic system:

  1.       Check whether the vibration is originating from the pump. It could be that the flexible coupling is not balanced. If the alignment is not correct, then realign the drive shafts.

  2.       In a case like this you’ll need to either align, repair or replace it. If this is not the case, check the pump mounting for issues.   Also check whether there is air in the system. If there aren’t issues with these areas, then you may need to remove the pump and examine it.

  3.       Other areas to check are the pipework. Check whether there is adequate support for it. If there isn’t then you may need to install clamps or tighten the ones already in place.

  4.       Sometimes the vibration is occurring because the unit needs to be adjusted.

  One of the patterns of thought that all of us as engineers can be affected by is doing our best in resolving an issue to give an immediate result. However, there are also longer-term consequences that should be considered with any resolution. Although replacing a pump may well fix something, having a design that makes it almost impossible to remove that pump can cause serious problems. Although the designers may have manufactured the unit without any issues relating to this, once the other components are added to the machine, repairing, maintaining and replacing that pump can cause a lot of stress. Sometimes it’s almost impossible to reach the malfunctioning unit due to the positioning of other components.

  One of the best practices of any maintenance staff should be to communicate any issues with management. Management need to review any issues and suggestions for resolution so that future equipment purchases can be made with these issues in mind.