How to Specify an Overhead Bridge Crane

Specifying and getting the correct overhead bridge crane for your application requires upfront work but getting the right piece of material handling equipment for your facility will be worth the effort. Often putting a bridge crane into your new or existing building is an afterthought in the overall scope of work. Following is a list of questions to present to your architect, or crane sales person.

1. What type of crane do I need? If you are not familiar with the type of cranes below is a short list of the types. Each has their own advantages and disadvantages.

a. Workstation crane system. These type of cranes are typically used for lighter weights 2 tons and under although they are usually used in applications of 1 ton and under. Advantages include lightweight, pre-engineered, and relatively inexpensive. Disadvantages include limited capacities.

b. Top running single and double girder. These cranes are used in heavier applications. In a single girder application the trolley hoist runs on the bottom flange of the bridge beam. Advantages include reduced cost versus double girder and lighter wheel loading thus reducing building and/or runway costs. Disadvantages include less hook height possible, not as durable and trolley is in a suspended position versus running on top of bridge beams (on heavy applications premature beam wear has been noted).

For truly heavy duty designs then a double girder design should be considered. The trolley rides on top of two bridge beams on ASCE rail. This is a superior design for heavy applications such as steel service centers, concrete facilities, foundries, and aerospace to name a few. Advantages include superior durability and more options available such as walkways and cabs. Disadvantages include heavier wheel loads and cost.

c. Under running single and double girder design. Under running cranes are normally thought of as lighter duty than top running cranes. This is due to all of the running surfaces for the crane and trolley hoist are on the bottom flange of the beams and premature wear can occur with heavy duty cycles. Advantages include better hook coverage and it can be designed to hang from your building structure on new buildings. Disadvantages include typically lighter duty cycle.

d. Gantry Cranes. Gantry cranes can solve numerous issues when you are limited in building structure. They can be provided in numerous configurations and can run on one runway with the opposite end running on the floor, or be completely independent of your building. Some require special track or ASCE rail, and some can run on the floor trackless. Configurations include single girder and double girder.

Advantages include being independent from building structure in some configurations with disadvantages including moving legs on your shop floor, and not as mobile or fast as a crane on two runways.

2. What is the duty cycle of my crane? The duty cycle of your crane is as important as the type of crane you choose. CMAA has service classifications as follows:

Class A-standby or infrequent service

Class B-Light service

Class C-Moderate service

Class D-Heavy service

Class E-Severe service

Class F-Continuous severe service

Refer to CMAA Definitions of crane service class and load cycles as shown in Table 2.8-1 of CMAA Specification #70, Revised 1994 and Table 2.6-1 CMAA Specification #74, Revised 1994.

Numerous factors go into determining the correct crane class including weight of load, number of payloads at average load, how many lifts per hour, per shift, per day, travel distances of the hoist, trolley and bridge, speed required for each movement.

3. What type of power and control will my application require? Cranes can be provided as manual, air or electric powered. Cranes can also be a combination of manual and electric or manual and air. Depending on what you are lifting and what is available in your plant will help determine what you need.

Typically air is used in explosive environments or severe duty cycle applications at lighter capacities. Electric control is the most common and can be provided with simple single or two speed controls or precise variable frequency controls with control ratios up to 1000 to 1.

4. How will I control my crane? Cranes are generally controlled from a cab, pendant push button station or radio control. Depending on how you are going to use the crane will determine what type of control is best for your application.

5. Is there anything unusual about my application such as a special environment? If you have a special application such as molten metal, explosive environment, high heat, or some other special consideration then special care needs to take place in choosing your bridge crane.

Make sure and have a qualified crane professional help in specifying the correct bridge crane per applicable requirements.

These items will help you get started with choosing the

right piece of equipment for your facility. Using the above guideline as well as consulting with industry professionals will lead you to purchasing the proper bridge crane.