Facilitator's Question

What are the constraints and limitations of crane for material handling? Explain.

There are different constraints and limitations when using cranes for material handling, depending on the models of crane used.

Here are some constraints and limitations of most cranes:

- Cost
The costs of setting up cranes in warehouses are very expensive. Therefore, the company has to make a solid decision whether cranes are needed for their operations. Any wrong decision made might have a great impact on the company.

- Not able to move a heavy flow of volume like conveyor does.
Cranes are only able to move goods one at a time, discontinuously. As compared to conveyors which move goods continuously. This could slow down operation time and affect the total production of the company.

- Space utility.
With the usage of cranes in warehouses, the space utilized will not be exactly 100%. This is because certain cranes need some space to move, like the radius from the pivot to the material. This will definitely decrease the storage space in the warehouse. Therefore, the warehouse might be better off not using cranes, increasing space utiization for the goods.

- Stability of crane.
For the crane to be stable, the maximum lifting capacity of the crane has to be taken into serious consideration. Failure to comply may result in the crane tipping over, due to over-lifting. Serious accidents may occur if the crane tips over.

- Need for certification.
As cranes accidents can be very fatal and dangerous, and not everyone is able to operate cranes well, finding a skilled and experienced crane operator may be a concern. In some regions, the crane operators licence may be needed, hence companies have toeither hires certified operators or send their employees to be trained and certified.

- Regular checks required.
Regular checks need to be conducted on the cranes to ensure that the equipments are in good working condition, which would mean machine downtime, affecting operations unless company has another machine to stand-by for such cases. Any malfunctioning parts will need to be replaced immediately, without further delay. Failure to do so, might have undesirable consequences in future.

4) Stacker Cranes

Lastly, stacker cranes are similar to bridge cranes. However, instead of using hoists, it uses a mast with forks or platform to handle unit loads. Stacker cranes are considered “fork trucks on a rail” due to its look.

These cranes are usually used for storing and retrieving unit loads in storage racks, especially in high-rise applications in which the racks are more than 50 feet high.

The crane can be either controlled remotely or by an operator in a cab on the mast.

Below are some pictures of stacker cranes:


1) Operator-controlled




2) Remotely-controlled

3) Bridge Cranes

Thirdly, bridge cranes are named as such because the hoist is attached to the “bridge”. The “bridge” is then mounted onto tracks that are located on opposite walls of the warehouse facility.
An “overhead” bridge crane is better suited for transporting heavier loads, whereas an “underhung” bridge crane is more suitable to carry lighter loads.

An “underhung” bridge crane has an advantage, whereby it can transfer loads and interface with other material handling equipments, such as monorail systems. In this way, goods can be transferred without wasting too much manpower’s effort.

Below are pictures of bridge cranes:

1) Underhung Bridge Crane



2) Overhead Bridge Crane

2) Jib Cranes

The second most commonly used cranes in the industry are jib cranes.

A jib crane operates like an arm in a work area where it can function as a manipulator to position the respective goods.

A hoist is attached to the arm for lifting. The hoist can move along the arm, to lift the goods from one place to another. The arm can be mounted onto the wall or to the floor as support, and it can rotate 360°.

The pictures below are some examples of jib cranes:

1) Gantry Crane

There are various types of gantry cranes, such as single leg, double leg and mobile cranes. Gantry cranes are used to cover a smaller work area. The heights of the cranes are also adjustable, depending on the model of the crane. The weight that can be lifted by each crane will also depend on the crane model.

For single and double leg cranes, the legs of the cranes are in a fixed position and it is secured tightly onto the floor.

For mobile gantry cranes, they are self-supporting and travel directly on the floor. The cranes are operated by power drives, which act as wheels. In this way, these cranes can be moved from one location to another easily.

The 4 pictures below shows the different types of gantry cranes available:

1) Single Leg (fixed)



2) Double Leg (fixed)




3) Double Leg (Mobile)




4) Power drives for mobile gantry cranes

Cranes

General Characteristics of Cranes:

• Used to move loads over variable (horizontal and vertical) paths within a restricted area.
• Used when there is insufficient (or intermittent) flow volume such that the use of a conveyor cannot be justified.
• Provide more flexibility in movement than conveyors.
• Provide less flexibility in movement than industrial trucks.
• Loads handled are more varied with respect to their shape and weight than those handled by a conveyor.
• Most cranes utilize hoists for vertical movement, although manipulators can be used if precise positioning of the load is required.
  

There are various types of cranes being used in the logistics industry. For our project, we are focusing on 4 types of cranes, which are:

1) Gantry Cranes;

2) Jib Cranes;

3) Bridge Cranes;

4) Stacker Cranes.

The types of cranes and their uses will be explained further in the following entries on cranes.

All of our information on cranes are sourced from these websites:

Cited from:
http://www.ise.ncsu.edu/kay/mhetax/TransEq/Crane/index.htm

http://www.lkgoodwin.com/cgi-bin/quikstore.cgi?category=Cranes_-_All_Types

Pallet Jacks (Extra information...)

After further research, we have found that pallet jacks are considered one of the major industrial trucks used to move materials over variable paths, with no restrictions on the area covered by the movement. 2

Below are additional information on Industrial trucks: 2
- Used to move materials over variable (horizontal) paths with no restrictions on the area covered (i.e., unrestricted area)
- Provide vertical movement if the truck has lifting capabilities
- Used when there is insufficient (or intermittent) flow volume such that the use of a conveyor cannot be justified
- Provide more flexibility in movement than conveyors and cranes
- Not licensed to travel on public roads—"commercial trucks" are licensed to travel on public roads

Pallet jacks are also used for external distribution operations, where 1 or 2 pallet jacks are usually kept in the trucks that are used for distribution of materials. 3

While pallet jacks are common equipment used in Distribution Centres, there are still limitations. Here are some points to note when deciding on pallet jack usage.

Restrictions: 1
- Reversible pallets cannot be used.
- Double-faced non-reversible pallets cannot have deckboards where the front wheels extend to the floor, and enables only two-way entry into a four-way notched-stringer pallet because the forks cannot be inserted into the notches
- Operate only on one level. 4

Advantages: 4
- Excel at picking bulky or full case items.
- Can travel fast (twice the speed of a person) and can carry a large load.
- Can add an extra long fork and carry two pallets at once.
- Very versatile and can pick order, load trucks, or transport pallets from one place to another.
- Equipment ranges from manual jacks to powered equipment that the operator rides.

In conclusion to our pallet jack posts, we can see that there is a big variety of pallet jacks in the market nowadays due to the constantly changing and improving technology.

Instead of the traditional manual pallet jacks, customers can now choose from multiple catergories under pallet truck types. One example taken from LK Goodwin Co. 5 would be classifying pallet trucks under,

1. Hand Propelled Pallet Trucks

2. High Lift and Tilting Pallet Trucks

3. Special Purposes Pallet Trucks

For more information, we hope that the sources stated will be able to help. Other wise, leave us a message and we'll get back ASAP.

Sources:

1-http://www.ise.ncsu.edu/kay/mhetax/TransEq/IndusTr/index.htm#Pallet%20jack
2-http://www.ise.ncsu.edu/kay/mhetax/TransEq/IndusTr/index.htm#Pallet%20jack
3- Temasek Business School, Diploma in Logistics and Operations Management, Transport Management, AY2007/2008, April Semester, Students’ Note, Lecture 11
4- http://www.2wmc.com/Companion/KnowledgeVehicles.html
5-http://www.lkgoodwin.com/cgi-bin/quikstore.cgi?category=Pallet_Trucks_-_All_Types