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Bridge Cranes

Types of Overhead Bridge Cranes


Single girder crane: An overhead traveling crane that utilizes a single bridge beam attached to the two runway/end trucks. This bridge beam or single girder supports a lifting mechanism or hoist that "runs" on the bottom flange of the bridge beam.

Double girder crane: An overhead traveling bridge crane that utilizes two bridge beams set atop the runway (end) trucks. Generally this type of crane utilizes a top running trolley hoist which moves along the top of the two bridge beams on its own set of trucks/trolley wheels. The hook from the hoist "falls" between the two bridge beams. Headroom under the crane is increased by utilizing this hoist/crane configuration.

Top running crane: An electric overhead traveling crane having the end trucks supported on rails attached to the top of the crane runways.

Under running crane: An electric overhead traveling crane having the end trucks supported on track attached to the bottom flanges of the beam; or supported on bottom flanges of beams. These beams make up the crane runway.

Top Running Single Girder Crane
  • Capacity: ½-15 tons
  • Span: 10’-60’
  • Hoist & Trolley operates on the lower flange of the bridge beam.
  • End Trucks operate on the top of crane rail.
 
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Under Running Single Girder Crane
  • Capacity: ½-15 tons
  • Span: 10’-60’
  • Hoist & Trolley operates on the lower flange of the bridge beam.
  • End Trucks operate on the lower flange of the runway beam.
 
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Top Running Monobox
  • Capacity: 3-15 tons
  • Span: 55’-100’+
  • Hoist & Trolley operates on the lower flange of the Monobox Bridge.
  • End Trucks operate on the top of crane rail.
 
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Top Running Double Girder Crane
  • Capacity: 5 tons and Up
  • Span: 10’-100’+
  • Hoist & Trolley operate on top of double girder bridge.
  • End Trucks operate on top of crane rail.
 
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Top Running Double Box Girder
  • Capacity: 5 tons and Up
  • Span: 50’-100’+
  • Hoist & Trolley operate on top of double girder bridge.
  • End Trucks operate on top of crane rail.
 
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Types of Runways

A Runway is the assembly of rails, girders, brackets and framework on which the crane operates. The crane type will dictate whether the end trucks ride on the top of the runway rail or on the bottom flange of the runway beam. The runway design and ASCE rail size utilized will determine the feasibility of adding future cranes and costs associated for increasing the capacity of an existing runway. Runways should be installed per CMAA runway specifications and tolerances.

Runways that are not installed per CMAA runway specifications or are misaligned due to wear and tear may cause premature wheel wear and other crane & component issues. An engineered runway survey is recommended, if you have abnormal wheel wear, bridge skewing, loud scraping sounds or other indications of a potential runway problem. Below is a brief description of types of runways and components.

Runway System using Sister Columns & Tied Back to Building
  • Building is able to support lateral loads from runway system.
  • Our standard tieback is a bolted flexible tieback design vs. rigid tiebacks.
  • Flexible tiebacks allow the tie back to flex.
  • The runway deflects and vibrates as the crane travels.
  • Rigid tieback welds are put under repeated fatigue loading.
  • The bolted flexible tieback is highly recommended for larger capacity systems.
  • Longitudinal bracing is STANDARD on all of Ace|Gaffey Crane systems.
 
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Runway on Haunches
  • Haunches or Secondary Columns mount directly on building columns.
  • Building design must be able to support crane loadings.
 
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Free Standing Runway System
  • Used if building cannot support any loading and footers may be required.
  • Requires more steel to fabricate vs. a system that can be tied back.
  • Ace|Gaffey uses Moment Columns vs. A Frame Columns.
  • Moment Columns use the foundation to support and stabilize the system.
  • No bracing is needed, more steel in the column than a system tied to building.
  • A-Frame columns may be less expensive, but take up more space.
  • Longitudinal bracing is STANDARD on all Ace|Gaffey Crane systems.
 
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Moment Columns
  • Footer takes lateral and longitudinal loads imposed on the system.
  • Takes up minimal floor space.
  • Larger footer design.
  • Increases the cost of the system, but the best choice for columns.
 
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Ceiling Mounted
  • Mounted to building trusses or other support structure.
  • Longitudinal bracing required on both sides.
  • Lateral bracing required-one side only.
  • Building and roof truss design may limit options.
 
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Rail
  • Hot rolled steel the crane travels on.
  • Subject to very high stresses.
  • Rail size may vary depending system capacity.
  • Attachment options: J Bolts, Weld on and Bolt on Clips.
 
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End Trucks

End Trucks ride on the runway rail and move the bridge crane. There are two main designs:

Fixed Axle
  • A fixed axle has an exposed gear on the wheel.
  • Requires maintenance to keep the exposed gear lubricated.
  • Fixed axle end trucks are class C Duty cycle.
 
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Rotating Axle
  • A rotating axle’s wheel is directly driven by the motor through a gear box.
  • Requires less maintenance.
  • Rotating axle end trucks are class D duty cycle.
  • Minimum of 10,000 hours of wheel bearing life.
 
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Electrification Types

The vast majority of hoists and cranes are powered by electricity. Electrification components of hoist and crane systems are relatively simple in application. There are two circuits in most hoist electrification systems: Power and Control. The power circuit provides the energy to lift loads and run other motors. The control circuitry activates the devices that turn the main motors on and off. The control circuit operates at lower voltage and current than the power or primary circuit.


Rigid Bar

Uses:

  • Any length
  • Moderate to Expensive
  • Can handle multiple hoists
  • Can negotiate curves.

Potential Concerns:

  • Voltage drop on long runs
  • Requires hangers every five (5) feet
  • Collectors & bar require replacement over time
 
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Festoon

Uses:

  • Medium length (under 100’)
  • Moderately expensive
  • Very little maintenance

Potential Concerns:

  • Long runs put stress on cable
  • Large cable requires heavy duty track and trolleys
  • Can handle two hoists maximum on one track
  • Requires hangers every five (5) feet
 
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Cable Reel

Uses:

  • Short length (under 50’)
  • Relatively inexpensive
  • Only a reel hangar is required.

Potential Concerns:

  • Limited on length
  • Cable sag
  • Reel spring can pull manual trolleys
  • Must have slip ring for 360 degree rotation.
 
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Controls and Variable Frequency Drives (VFD's)

Pendant Control Stations

Ace|Gaffey offers a large variety of pendant stations. 2, 4, 6, 8, 10 and 12 button pendant stations are in stock and usually ship the same day. Pendant Control Stations can be wired into the hoist, trolley or bridge. They are an economical solution for operating a crane, but most customers prefer a Radio Remote Control system for crane operator safety reasons. Pendant Control Stations can be installed on a crane system as a secondary control option, when a Radio Remote Control is installed.

 
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Radio Remote Controls

Ace|Gaffey offers and stocks a variety of Radio (wireless) Controls. Radio Remote controls should always be considered, because they allow the operator freedom from the load. A Radio Remote Control system is 2 transmitters, 1 charger unit and a receiver unit. An audible or visual warning device must be installed on a traveling bridge crane, if a Radio Remote crane control system is installed. The reliability of Radio Remote Controls has increased over the years and the cost associated has decreased.

 
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Variable Frequency Drives

A Variable Frequency Drive (VFD) system controls the rotational speed of an alternating current electric motor. VFD’s enable the crane operator to better control the load with softer starts and programmable controlled acceleration and deceleration. A VFD allows the operator to perform precision placement and lifting of the load.

 
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Powered Hoists - Chain

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Suspensions

Hook, Push or Motor Driven Trolley

Standard Options

Lift Changes, Lift (Trolley) Speed, Two Speed Control, Voltage, Chain Container, Beam Size for Trolleys.

Custom Options - Mechanical

Epoxy Paint, Spark Resistance, Corrosion Resistance, Weatherproofing, Food Grade Lubrication, Mechanical Overload Protection, Stainless Steel Chain, Stainless Steel or Bronze Trolley Wheels, Trolley Safety Lugs (Drop Stops), Curved Track Operation.

Custom Options - Electrical

Explosion Proof, Special Control Enclosures, Mainline Disconnect, Branch Circuit Fusing, Thermal Overload Relays.

Powered Hoists - Wire Rope

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Suspension Type

Trolley Only - Push, Hand Geared or Motor Driven

Standard Options

Lift Changes - Different Drum Sizes, Lift (Trolley) Speed, Two Speed Control, Voltage, Beam Size for Trolleys.

Custom Options - Mechanical

Curved Track Operation, Epoxy Paint, Spark Resistance, Corrosion Resistance, Weatherproofing, Food Grade Lubrication, Mechanical Overload Protection, Stainless Steel Wire Rope, Stainless Steel Trolley Wheels, Trolley Safety Lugs (Drop Stops).

Custom Options - Electrical

Explosion Proof, Special Control Enclosures, Mainline Disconnect, Branch Circuit Fusing,Thermal Overload Relays, NEMA Rated Contactors, Variable Frequency Drive Control, Inching Control, Electronic Overload Protection, Motor Heaters, Additional Limit Switches.

Buyer Tips for Bridge Cranes

Select the proper equipment for the application:
Choosing the lowest price crane bid without understanding the variances in equipment quoted, may result in additional long term maintenance costs to you. Prior to compiling specifications for RFQ submittal, here are some basic points to consider:

1. What type of “Service” will the overhead crane be used for?
2. What is the “Frequency” or how often will the bridge crane be used?
3. What “Speed” of the bridge, trolley and hoist is necessary to match production efforts?
4. Does the buyers’ budget match the specifications desired?

Why do minor changes in the length, width or height of a system impact the overall cost?
Steel comes in standard lengths: Beams: 30’, 40’, 50’ & 60’ Angle: 20’ & 40’ Tube Steel: 40’ & 48’ Adding another foot of lift or increasing the length of just one bay, could change the design and cost.

Example:

Original System:

 

6 Columns = 3 @30’

30ft x 26lbs/ft. x $.75 lb. = $585 x 3

4 Beams= 2 @40’

40ft x 67lbs/ft. x $.75 lb. =$2010 x 2

 

Total Cost = $5,775.00

Modified System:

 

6 Columns = 3@40’

40ft x 26lbs/ft. x.75 lb. =$780 x 3

2 Beams = 1@50’

50ft x 77lbs/ft. x.75 lb. =$2,887.50

2 Beams =1@40’

40ft x 67lbs/ft. x.75 lb. =$2,010.00

 

Total Cost = $7,237.500

Additional Buyer Considerations:

1. What are the long term maintenance costs associated with less expensive crane systems and components?
2. Are replacement motors and other parts readily available from multiple suppliers or just one?
3. Does the crane provider meet your company’s minimum liability insurance requirements?
4. Does the crane provider adhere to all CMAA manufacturing guidelines and specifications?
5. Does the crane provider have engineering and manufacturing capabilities or do they outsource these services?
6. Are the replacement components readily available, to eliminate potential long lead times and increased costs?
7. Does the crane provider have their own installation team or do they outsource installation?
8. Not having a qualified crane company install the runway? Make sure the runway is installed to meet the CMAA runway tolerance specifications. An improperly installed runway will either delay installation of the bridge crane or create future problems and add additional costs.
9. Are you considering whether or not you will be able to increase the capacity of the crane or add a 2nd bridge in the future? If so, verify if the runway beam size and rail quoted is adequate for future upgrades.


Crane Duty Cycle Chart


CMAA Class

Description

Explanation

Class A

Standby or Infrequent Service

This class normally includes installation and maintenance cranes. This equipment usually operates at slow speeds for precise handling with long idle periods between lifts. Maximum capacity lifts are sometimes required.

 

Class B

Light Service

This class of crane is used in repair shops, light assembly operations, service buildings, light warehousing, etc. Service requirement is light and speeds are slow. Loads vary from none to occasional full capacity. Lifts per hour would range from 2 to 5, and average 10 feet per lift.

 

Class C

Moderate Service

In terms of numbers, most cranes are built to meet Class C service requirements. This service covers cranes that may be used in machine shops or paper mill machine rooms. In this type of service, the crane will handle loads that average 50% of the rated capacity with 5 to 10 lifts per hour averaging 15 feet. Not over 50% of the loads at rated capacity.

 

Class D

Heavy Service

This service covers cranes which may be used in heavy machine shops, foundries, fabricating plants, steel warehouses, container yards, lumber mills, etc., and standard duty bucket and magnet operations where heavy duty production is required. In this type of service, loads approaching 50 percent of the rated capacity will be handled constantly during the working period. High speeds are desirable for this type of service with 10 to 20 lifts per hour averaging 15 feet, not over 65 percent of the lifts at rated capacity.

 

Class E

Severe Service

This type of service is reserved for top riding bridge and gantry type multiple girder electric overhead travelling cranes and requires a crane capable of handling loads approaching rated capacity throughout its life. Applications may include magnet, bucket, magnet/bucket combination cranes for scrap yards, cement mills, lumber mills, fertilizer plants, container handling, etc.,with 20 or more lifts per hour at or near the rated capacity.

 

Class F

Continuous Severe Service

This type of service is reserved for top riding bridge and gantry type multiple girder electric overhead travelling cranes and requires a crane capable of handling loads approaching rated capacity throughout its life. Applications may include custom designed specialty cranes essential to performing the critical work tasks affecting the total production facility. These cranes must provide the highest reliability, with special attention to ease of maintenance features.