Overhead Crane Purchase Guide for New Buyers

 overhead crane in use

Overhead crane overview

An overhead crane also known as bridge crane, overhead travelling crane, or industrial crane is a material handling machine which lifts, lowers, and transport a load horizontally. Typically, an overhead crane involves a hook-and-line mechanism that moves along a horizontal beam which moves on a runway beam, the supporting structure.
Overhead canes are heavy duty material handling equipment with high lifting capacities for transporting load. Overhead crane travel is directed by an operator, either manually or with a wired pendant station or wireless controls. Typically, overhead crane is used for the multi-directional movement of materials to help manufacturing, storing, loading or unloading works inside a facility or outside in a yard, or at a railway, or shipping port, and other application environments.

Overhead crane components

Generally, the overhead crane is consisted of three main parts, the crane bridge, the hoist or trolley, and the runway. The crane bridge is the part which traverses across the runway. The hoist or trolley is the lifting mechanism which traverses across the crane bridge and lifts vertically.
The runway is tied to the building structure. Besides, there are other parts are involved, showing in the following diagram for your reference.

Double Girder Overhead Crane componets drawing

Basic crane terminology

Crane capacity: The maximum weight the overhead crane is required to handle.
Crane span: The horizontal distance between the rails of runway on which the crane travels.
Lift or hook height:The distance from the floor to the crane hook, which determines the height of the runway from the floor and is subjected to the clear inside height of the building.
Bridge, trolley and lift speeds: The rate at which the bridge or trolley runs or at which the hoist lifts. Dual speeds are available.
Crane bridge: The main travelling structure of overhead crane which is consisted of two end trucks and one or two bridged girders varying with the type of the crane.
End trucks: The end trucks is located on both sides of the span. The end trucks house the wheels on which the crane runs.
Bridge girder(s)：Bridge girder is the principal horizontal beam of the crane bridge which is supported by the end trucks. The bridge girder of the crane is meat to support the trolley.
Trolley hoist: The trolley hoist is consisted of hoist and the trolley frame. According to the lifting requirements, one or more hoist can be installed, which can be supplied on the same trolley or on separate trolleys.
Trolley: The trolley takes the hoist across the bay along bridge girder(s) traversing the span.
Hoist: Hoist is mounted to the trolley and is the main lifting equipment together with the crane hook or other lifting attachment.

Overhead crane configuration

Overhead crane mainly have two configurations: Top running overhead cranes and under running overhead cranes.

Top running overhead cranes

The top running overhead crane or bridge crane refers to the crane which has the bridge travel on the top of rails mounted on a runway beam supported by either the building columns or columns specifically engineered for the crane. The top running overhead crane or bridge crane is the most common crane configuration with the feature that the crane loads are transmitted to the supporting columns or free standing structure and with the advantage of minimum head room and maximum height of lift.

Top running overhead crane 

Classification of top running overhead cranes

Top running overhead cranes can be further classified into single girder, double girder, and box girder overhead crane or bridge crane in terms of girder types.
single girder overhead crane or bridge crane is consisted of two end trucks, trolley hoist unit and a single bridge girder, on the bottom flange of which the trolley runs on.
Single girder overhead crane designed for your application can be cost-effective. Single girder overhead crane has lower wheel loads so that it will save on new support structures and it will also allow you to add more lifting capabilities to your runway structure without upgrading.
Double girder overhead crane or bridge crane is consisted of two end trucks, trolley hoist unit and two bridge girders, on the top of which located the rails on which the trolley runs.
Double girder overhead crane provides better hook height for the hoist of the double girder overhead crane is mounted on top of the bridge rather than underneath.
Box girder overhead crane or bridge crane is a crane equipped on a girder formed by multiple walls in the shape of enclosed tube, rather than on an I-beam or H-beam.
Box girder overhead crane is used for heavy duty material handling with the feature of extremely rigidity and durability.

Under running overhead cranes

Under-running or under-hung overhead crane or bridge crane has the end trucks ride on the bottom flange of the runway, which is usually suspended from the roof, with no need of extra floor columns for the support of the runway. The under-running or under-hung overhead crane has the advantage of taking no floor space and saving cost for supporting system. Moreover, an under-running or under-hung overhead crane can be applied to the sloped ceilings or multiple crane systems.

Under running overhead crane

Classification of under-running or under-hang overhead crane

In terms of crane girder, the under-running or under-hang overhead cranes can be grouped into single girder, double girder and box girder overhead cranes.
Single girder under running overhead crane provides you a cost effective material handling solution for it can save new support structure because of its reduced wheel loads, which also makes it possible to add more lifting capabilities without upgradation.
Double girder under running overhead crane is usually used for handling loads over 25 tons, which is usually provided with a complete material handling solution. Double Girder Cranes provides a higher lifting height for the crane hook travels between the beams, comparing with that of the single girder overhead crane.

Overhead crane comparison -top running Vs. under running

To choose the top running or under running overhead crane is mainly determined by two factors:

• Capacity: Even though the under running overhead crane can be up to 25 ton capacity, the practical limit is more like 15 tons.
• Support structure: Under running overhead crane can be suspended directly from the overhead steel for the lighter duty crane. Top running overhead cranes needs a bracket off the building support steel (up to 10 tons capacity) or independent columns for larger capacities.

Top running overhead crane configuration is best used when headroom is an issue. Double girder top running configuration is the most space efficient one. Whereas when the headroom is not an issue a top or under running configuration can be either single girder or double girder.

Overhead crane application

Overhead crane or bridge crane can be applied for material handling in various situations and industries, such as, Automotive, Beverage, Chemicals, Commercial printing, Manufacturing, Newspaper, Paper, Steel and warehousing and distribution, etc.

• Assembly: Overhead cranes are used to move the products through production processes.
• Transportation: Overhead cranes are used to transport the finished products onto open trailers or other vehicles.
• Staging: Holding work-in-process for additional production processes.
• Storage: Overhead crane also can be used to transport heavy item into or out of the storage area.
• Warehousing: Heavy items can be moved with overhead cranes to and from docks.

Overhead cane advantages

Overhead crane are most applied material handling equipment for the following advantages:

• Adaptable: Due to overhead crane cane be operated on any plant floor surface and also because they can be modified to accommodate changing needs, overhead cranes provide high adaptability.
• Customizable: Customized overhead cranes are available. The below hook attachments, riggings, and other special material handling tool to deal with the variety of loads.
• Comfortableness: The design of overhead cranes takes the comfortableness of crane operators into consideration, which would improve the efficiency and safety in the working area.
• Efficiency: Overhead cranes lift loads up and over obstacles with high efficiency without navigating back and forth through aisles.
• Load control: Radio remote control, pendant pushbutton control, and driver’s cabin control are also at your choice for your overhead cranes.
• Lower maintenance costs: Adopting with advanced technologies and offered in a variety of usage of capacity ratings, overhead cranes need less maintenance comparing with other lifting equipment.
• Positioning: The overhead cranes can place the loads to an exact location with high precision.
• Reduce labor cost: A set of single overhead crane can replace many forklifts and cover a large work area.
• Lower damage to loads: With soft start features, wide selection of speed options, and a variety of handling tools or riggings, the loads can be safely handled.
• Safety: Varity of safety measures are installed on overhead cranes to ensure the safety of your lifting equipment, crane operator and loads, etc.
• Higher lifting height: Overhead cranes can provide you a higher lifting height with higher efficiency.

Overhead crane controls

Overhead crane control 

Overhead crane control controls your crane safety and reliability. Flexible and reliable control for overhead crane are very important. Usually, the following controls are frequently used on overhead cranes.

• Pendant control: The pendant overhead control can give the crane operator precise control over the motion of the crane. According to the different functions, the pendant control has different configurations. The pendant control could be either suspended from the Trolley Hoist, which requires the crane operator to walk with and beside the load or on a separate sliding track system allowing the operator to move independently of the load.
• VFD: A pendant overhead crane control can also be used in conjunction with a Variable Frequency Drive, which controls the motion for smooth acceleration and deceleration by varying the frequency of motors. The VFD controls could be highly customized.
• Radio control: The radio control for overhead crane is just like the pendant control except the operator uses a radio frequency instead of pendant. The radio control has higher safety feature and also provide the operator a wider range of operating motions that a pendant.
• Power supply: The electrical power supply in the building should be matched with the designed rate of overhead crane.
• Electrical cabin: The electrical components of overhead crane could be placed and protected in the control cabin.
• Safety: The safety of the overhead crane is ensured by protection against accidental contact, electrical shock, enclosed equipment, and indoor protection against dirt, dust, oil and water, and, etc.

Overhead crane runways

Overhead crane runway

• The runway of overhead cranes refers to the rails, beams and columns on which the crane operates.
• The crane rails is where the end trucks travel, and is fixed on the runway beam,
• The runway beam is supported on the columns of top running overhead crane or from the roof structure of under running overhead crane.
• During the design of crane runway system, the existing building columns can be taken advantages. By then, it is important to provide the down shop center to center spacing between them.
• And also, the conductors are mounted to the runway beam, which supply power to the overhead crane.

How to choose your overhead crane

Generally the lifting capacity of the overhead cranes decides the types of crane girders: single, double and box girder. The single girder overhead is designed for handling loads of about 20 tons and the double girder and box girder overhead crane can be used to handling materials above 20 tons.

To choose the right material handling solution is critical. Therefore the customized or tailored overhead are manufactured. However, how to find out the best type of overhead crane for your application? The most suitable overhead crane should be selected out based on the specific application conditions and your building dimensions if the building has been constructed. The following tips is given for your reference to find your best cranes.

• Load capacity: The maximum weight of your loads should not exceed the rated lifting capacity of your crane.
• Crane span: The span or width of the crane system is important to decide the size of the overhead crane.
• Working frequency: The operational frequency of your crane will be used to define the crane classification needed for your application.
• Supporting systems: Usually, the overhead crane is supported by runway structures, attached to workshop building or the overhead crane could be supported on a free standing runway set up specifically for the crane.
• In order to give you a better understanding of what should be considered on choose an overhead crane, the top running double girder overhead crane are taken for an example for your references

1. Crane lifting capacity   2. Lifting height of crane. 3. Runways height.  4. Clearance required. 5. Building width.

6. Crane span. 7. Building height. 8. Runway size and length. 9. Hook approach & end approach 10. Hoist speed

11. Bridge gravel speed 12. Trolley travel speed. 13. Electrical requirements. 14. Control requirements.
 

 Overhead crane maintenance

Overhead crane maintenace

As there many parts of the bridge crane, for different technical characteristics of the various components, in the actual work they will generally be maintained into periodic check in weeks.

• Check the nut, cotter pins, positioning plate on the brakes whether it is complete, lose or not, lever and spring is free of cracks, pin bolts on the wheel and the brake washer is loose cushion, or complete; if it is reliable when the brake is open. The opening of the movable tiles should be less than 1.0mm and the distance across the gap between the brake drum should be equal, each axle pin may not have stuck phenomenon.
• Checking the rope on the winding drum and the pulley is normal or not, is there any phenomenons such as jumping from slot, channeling, knotting, twisting and so on. Whether rope plate bolts are tightened and has a double nut locking device or not.
• Checking the installation of the safety switch and limit switch are accurate, flexible and reliable, especially the rise limit is reliable.
• Checking all lubrication points is in a good condition.
• Check if it is lost or shortage of the fastening screws on coupling closures of the lifting mechanism.
• Checking the track to confirm that no foreign body to obstruct running of the overhead crane.
• If there is any abnormal noise on the transmission of the overhead crane.