Author Archive for: Justin Bolduc

 

Mechanical Principles

 

There are three major considerations in the design of cranes. First, the crane must be able to lift the weight of the load; second, the crane must not topple; third, the crane must not rupture.

Cranes illustrate the use of one or more simple machines to create mechanical advantage:

The Lever:

  •  A balance crane contains a horizontal beam pivoted about a point called the fulcrum. The principle of the lever allows a heavy load attached to the shorter end of the beam to be lifted by a smaller force applied in the opposite direction to the longer end of the beam. The ratio of the load’s weight to the applied force is equal to the ratio of the lengths of the longer arm and the shorter arm, and is called the mechanical advantage.

The Pulley:

  •  A jib crane contains a tilted strut that supports a fixed pulley block. Cables are wrapped multiple times round the fixed block and round another block attached to the load. When the free end of the cable is pulled by hand or by a winding machine, the pulley system delivers a force to the load that is equal to the applied force multiplied by the number of lengths of cable passing between the two blocks. This number is the mechanical advantage.

The Hydraulic Cylinder:

  • This can be used directly to lift the load or indirectly to move the jib or beam that carries another lifting device.
  • Cranes, like all machines, obey the principle of conservation of energy. This means that the energy delivered to the load cannot exceed the energy put into the machine. For example, if a pulley system multiplies the applied force by ten, then the load moves only one tenth as far as the applied force. Since energy is proportional to force multiplied by distance, the output energy is kept roughly equal to the input energy (in practice slightly less, because some energy is lost to friction and other inefficiencies).
  • The same principle can operate in reverse. In case of some problem, the combination of heavy load and great height can accelerate small objects to tremendous speed. Such projectiles can result in severe damage to nearby structures and people. Cranes can also get in chain reactions; the rupture of one crane may in turn take out nearby cranes. Cranes need to be watched carefully.

 

Basic Crane History

  • A crane, also known as a bridge crane or overhead crane, is a type of machine used for lifting. Cranes are generally equipped with a winder (also called a wire rope drum), wire ropes or chains and sheaves, that can be used both to lift and lower materials and to move them horizontally. It uses one or more simple machines like a hoist to create mechanical advantage and thus move loads beyond the normal capability of a human. Cranes are commonly employed in the transport industry for the loading and unloading of freight, in the construction industry for the movement of materials and in the manufacturing industry for the assembling of heavy equipment.
  • The first construction cranes were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys. These cranes were used for the construction of tall buildings. Larger cranes were later developed, employing the use of human tread wheels, permitting the lifting of heavier weights. In the High Middle Ages, harbor cranes were introduced to load and unload ships and assist with their construction – some were built into stone towers for extra strength and stability. The earliest cranes were constructed from wood, but cast iron and steel took over with the coming of the Industrial Revolution.
  • For many centuries, power was supplied by the physical exertion of men or animals, although hoists in watermills and windmills could be driven by the harnessed natural power. The first ‘mechanical’ power was provided by steam engines, the earliest steam crane being introduced in the 18th or 19th century, with many remaining in use well into the late 20th century. Modern cranes usually use internal combustion engines or electric motors and hydraulic systems to provide a much greater lifting capability than was previously possible, although manual cranes are still utilized where the provision of power would be uneconomic.
  • Cranes exist in an enormous variety of forms – each tailored to a specific use. Sizes range from the smallest jib cranes, used inside workshops, to the tallest tower cranes, used for constructing high buildings. For a while, mini – cranes are also used for constructing high buildings, in order to facilitate constructions by reaching tight spaces. Finally, we can find larger floating cranes, generally used to build oil rigs and salvage sunken ships.

 

Overhead Cranes in New Buildings

Industrial buildings, as well as some other building types, require large clear spans and heavy loadings. It is generally conceded that a tapered web-rigid frame is one of the most economical types of framing for the loads and spans normally encountered in crane buildings. When conditions beyond the normal are encountered, a truss frame may be more appropriate.

The building manufacturer should be given the opportunity of recommending the building type and support system to be used for the cranes.

Top-running Cranes

Runway beams for top-running cranes located within the building may be supported by brackets attached to the building frame columns, by separate columns located inside and in line with the building frame columns, or by stepped. When crane aisles extend outside the building, A-frames are commonly used to support the runway beams.

Brackets on the building columns are commonly used to support the runway beams for cranes up to 10-ton capacity. However, cranes with up to 20-ton capacity may be supported in this manner depending on the type, span, and service classification of the crane.

For cranes of more than 20-ton capacity, it may be more economical to support the runway beams with separate support columns. However, the columns for buildings having high eave heights and/or large wind and snow loads may support heavier cranes without substantial weight penalty.

Runway beams for cranes with capacity of 20 tons or less, but with bridge spans greater than 50 feet, may also be more economically supported by separate columns.

Underhung Bridge Cranes

Runway beams are supported by hangers or brackets attached to the rafter of the building frame. The location of the support hanger can materially affect the design, shape and economy of the building frame.

It is usually more economical to purchase a crane with a bridge span approaching the building width. This places the crane end trucks near the building columns. The savings in the building support framing will normally exceed the extra bridge cost. This savings can be substantial in long buildings with a large number of frames.

Underhung Monorail Cranes

Runway beams for underhung monorail cranes are supported similar to runway beams for an underhung bridge crane.

Crane loads and other crane data varies between crane manufacturers. These variations can affect the design and economy of a crane building. Significant economics may be achieved if the crane manufacturer is selected prior to the design of the building. This provides the building manufacturer with specific crane data for design of the crane building. For crane loading information, please consult us.

 

Preventative Maintenence

Why does Crane-Tec recommend performing a preventive maintenance service on a quarterly basis?

  • Many crane owners have inspections performed on an annual basis. This is an OSHA requirement. What many companies don’t know is OSHA also requires that the crane must be maintained on a scheduled basis, complete with dated records based upon the manufactures criteria. The maintenance can be performed in house or by a third party and the schedule is based on the duty cycle of the equipment along with following the manufacturer’s requirements.
  • Aside from the mandatory requirements listed and their costs, there may be additional costs involved by doing only an annual inspection. Historically, cranes with only an annual inspection/preventive maintenance service incur more break downs than cranes serviced quarterly. Small problems or adjustments normally taken care of during a quarterly inspection/preventive maintenance service have become bigger problems by the time the annual inspection/preventive maintenance service is due. Deficiencies found on an annual inspection/preventive maintenance service may be multiplied vs. cranes being inspected and maintained quarterly.
  • When breakdowns do occur, production time is lost and repair costs rise. If one was to look at two identical cranes of the same age, running at the same duty cycle and one unit maintained quarterly, the other maintained annually; you would find that the equipment maintained annually would cost more in higher operating costs, with lost time and expensive repair bills.

Benefits of Performing a Quarterly Inspection/Preventive Maintenance Service

  • 1) Lower your costs on repairs, including expediting costs and airfreight bills when purchasing replacement parts.
  • 2) Decrease your equipment down time due to breakdowns.
  • 3) Allows you, the Crane Owner and Crane Service Company to schedule repairs around your production.
  • 4) Provides you and your staff advanced notice of equipment condition for future and existing budget requirements.
  • 5) The above cost savings alone can be enough to allow for future upgrades or equipment replacement.

Are you proactive or reactive when it comes to maintaining your overhead cranes and hoists? Why take a chance, let a qualified Crane –Tec specialist recommend the correct program for your operation.

 

What Is an Overhead Bridge Crane?

According to the United States Department of Labor’s Occupational Safety and Health Administration, “Overhead crane” means a crane with a movable bridge carrying a movable or fixed hoisting mechanism and traveling on an overhead fixed runway structure. These devices are widely used in many industrial environments where large and heavy items require moving from one location to another.

Function

Overhead bridge cranes have long been used in factories and warehouses to hoist and move heavy objects, often in small or cramped areas that may not allow for proper and safe maneuvering of forklift trucks. An overhead bridge crane can remedy this situation by providing an effective manner to hoist and move heavy loads that require significant power capability. It can readily meet numerous requirements that are sometimes performed by other types of equipment.

Types

Overhead bridge cranes can be divided into two groups: top-running bridge cranes and under-running bridge cranes. The primary distinction is the manner in which the end trucks are attached to the crane. Top-running overhead bridge cranes have the end trucks supported on rails attached to the top of the crane runway, while under-running bridge cranes have the end trucks supported on tracks attached to the bottom flanges of the beams.

Benefits

The benefits of an overheard bridge crane, whether top-running or under-running, are fairly numerous and can be significant solutions to alternative methods such as forklifts and elevators. A major benefit is that overhead bridge cranes are considerably less expensive than other options. They are also of a relatively simple design, lending to ease of operation and can be ordered as kits and installed on-site by the purchaser. They are designed so that in case of failure, they lock their load in place and prevent it from falling.

Shortcomings of Overhead Bridge Cranes

The primary–and possibly only–drawback to having an overhead bridge crane is that they are not very mobile. However, even this situation can be remedied by installing a track network to extend the range of the crane. This added expense still allows an overhead bridge crane to be a more economical choice than a forklift. The fact that an overhead bridge crane can actually reduce or even eliminate the need for forklifts or freight elevators is also a considerable benefit.

Considerations

When pondering the need to acquire equipment that allows for the safe and efficient relocating of heavy objects as is required in warehouse environments and the like, an overhead bridge crane is a candidate for serious consideration. They are readily available to be shipped in kit form, can be configured to meet just about any application requirements and are safe when properly installed and operated. They are very suitable for small spaces and require less electricity to operate.

For any help in deciding your crane needs please contact us at Crane-Tec 800-755-6378 or www.crane-tec.com.

 

Overhead Crane Classification

Determine the proper CMAA classification for your crane:

Having been in the crane industry for more than 30 years, I have noticed that a reoccurring  problem I encounter on a daily basis is the determination of the CMAA classification of a particular crane. The problem lies in the broad wording used in the classification charts as well as an end user, builder and even some crane sales persons I have encountered just making a determination without even looking at the specification charts and true application.
The proper determination is crucial to the correct crane being specified for each application. In the current state of our industry, this is becoming even more critical as crane manufactures are engineering all their components to much tighter specifications in order to be cost competitive. Today,components are no longer being over built and almost everything is built to the specification required. Thus the proper classification is extremely important in today’s crane world.
I came across this simple way to determine the specification necessary years ago and still implementing this strategy today. While in some of the higher specifications further examination may be necessary but this will get you pretty close in almost any situation. It is based on a points system and pretty self explanatory. You go through each area and make the proper number selection and then add them all up and use the matrix to determine your classification. The key here is to be honest in the application, there is no use in cutting corners as you might as well just be pulling it out of the sky again!

1. Operating Factor

  • The first factor is the operating factor. How often will the crane be used? Is it for stand-by or maintenance service? Is it for 2,000 hours per year or less, which is the one shift operation, 4,000 hours per year, which is the 2 shift operation, or the 6,000 hours per year, which is the three shift operation
  • POINTS
  • Stand-By or Maintenance 5
  • 2000 Hours/Year or less (1 Shift) 8
  • 4000 Hours/Year or less (2 Shifts) 15
  • 6000 Hours/Year or less (3 Shifts) 25

 

2. Relative Load Factor

  • The next factor to consider is the relative load factor. How does the average lifted load compare to the rated capacity of the crane?
  • Several loads per week at rated capacity 5
  • Several loads per day at rated capacity 15
  • (Majority of loads less than 50% of rated capacity)
  • Several loads per day at rated capacity 25
  • (Majority of loads greater than 50% of rated capacity)
  • Frequent capacity loads per day 35
  • (Majority of loads greater than 50% of rated capacity)

3. Load Impact Factor

  • The load impact factor considers the relative severity of the cranes operation. Is the service low and smooth as in a powerhouse operation? Will the crane be subject to the high impact forces inherent in magnet/bucket service found in steel mills or cement mills? Or does the service fall somewhere in between?
  • Stand-by, Maintenance, Powerhouse 5
  • Warehouse, Machine Shop, Assembly Shop 8
  • Foundry, Hot Metal 15
  • Bucket, Magnet, Grapple 25

4. Relative loss factor (Downtime)

  • The relative loss factor is a measure of the importance of the crane to your operation. If the crane is down for unscheduled maintenance, what is the effect; an inconvenience, a slowdown of operations, or a plant shutdown?
  • Low value on downtime (Inconvenience) 5
  • Medium value on downtime (Slowdown of operation) 15
  • High value on down time (Plant shutdown) 25

5. Ambient Temperature and Environmental Factor

  • Are the ambient temperatures extremely high or low? Or is there a combination of these conditions affecting the crane? The A and E factor considers where the crane is located. Is the environment normal, corrosive or highly contaminated?
  • Normal Indoor or Outdoor Service 5
  • Corrosive, Highly Contaminated Area, or Temperature Extremes 10
  • Corrosive and Highly Contaminated Area 15

6. Maintenance Factor

  • The last factor to consider is the Maintenance factor. While a true preventive maintenance program is ideal, it is very seldom the case.
  • Preventive Maintenance Program 5
  • Normal Maintenance Handled by Maintenance Department but
  • Reactionary other than Lube and minor adjustments 15
  • No In-House Maintenance Capabilities 25
  • This is where you need to add up your points and see where you fall in the matrix key.
  • 0 to 40 Points = CMAA Class “A” and “B”
  • 41 to 65 Points= CMAA Class “C”
  • 66 to 85 Points= CMAA Class “D”
  • 86 to 115 Points= CMAA Class “E”
  • 116 to 150 Points= CMAA Class “F”

I have found over the years there are two areas overlooked or misunderstood the most when determining the classification, the relative loss factor and the Maintenance Factor. If you use this and understand it, it will save you time and possibly money in the future by specifying the correct crane for the application.

 

 

Top Running Overhead Crane Runway Systems

 

Runway Beams:

  • Runway beams and columns for top-running bridge crane applications may be provided by the building supplier or the crane supplier. The design of these beams takes into account the vertical impact of the crane, the lateral force resulting from the effect of moving crane trolleys and longitudinal force from moving cranes. Typical sections include mill shapes and welded built-up plate sections. Support Columns-The columns can be part of the building columns, Independent tie back columns, or an independent column. For new construction the runway system is designed as part of the building. For use in an existing building you have two options.
  • 1) Independent tie back columns that use the building structure to take the horizontal load of the runway system.
  • 2) Independent columns that are freestanding on the foundation or floor, that take the horizontal and vertical loads.

Runway Rail:

  • Runway Rail should be installed in such a manner so that wear to the crane, runway beam supports and the rail itself will be minimized. Rails should be arranged so that joints on opposite runway beams for the crane will be staggered with respect to each other and with respect to the wheel base of the crane. Rail joints should not coincide with runway beam splices. Runway rails should be ordered in standard lengths with one short piece on each side to complete a run. The short piece should not be less than 10′ long. Rail ends will normally be furnished saw cut only, unless otherwise specified by the buyer. Rail ends will normally be furnished with standard drilling for commercial rails splices, unless otherwise specified by the buyer.
  • Common methods of fastening rails to runway beams are hook bolts, bolted clamps, welded stud clamps and welded clamps with a pad. Crane rails should not be painted as this may cause the wheels to slip, resulting in skewing of the bridge and columns.

 

Overhead Crane Alternatives

Jib Cranes and Gantry Cranes are good alternatives to an overhead crane where a small area is being covered and light loads are being lifted:

The Jib Crane:

  • The Jib crane is a type of crane that has a rotating horizontal boom attached to a fixed support. A standard trolley equipped with electric or hand-geared chain hoist normally operates on the lower flange of the jib crane boom.
  • Jib cranes may be appropriate for servicing machinery located outside of the coverage of an overhead crane, or for assembly lines where jib boom areas can overlap for staged operations.
  • Jib cranes may be floor mounted or supported by the building frame. Floor mounted jib cranes are generally preferred. Jib cranes which must be supported by the building frame may be mounted directly to the building column or mounted to a supplemental column.
  • The floor-mounted jib crane requires no top braces or supports of any kind from the building structure. The jib boom will rotate through a full 360 degrees. Under ordinary conditions, these base-mounted jib cranes can be anchored directly to a properly-designed reinforced concrete floor or separate foundations.
  • The column-mounted jib crane is generally mounted on a building column. The boom rotation is limited to approximately 200 degrees.
  • The application of a column-mounted jib crane requires that the building column, column base anchorage and bracing be designed to account for the special loads imposed by the jib crane. This will usually increase the building column size.

The Gantry Crane:

  • Gantry cranes are adapted to applications where overhead runways would be very long and costly to furnish. They are also appropriate where overhead runways would interfere with handling operations, storage space, or service areas.
  • Single-leg gantry cranes are used in those installations where it is convenient to have one end of the bridge supported on an overhead runway rail and the other end supported on a gantry leg. This design can then utilize adjacent building framing to support the overhead runway rail. This application requires that the building framing, column base anchorage and bracing be designed to account for the special loads imposed by the gantry crane.

 

Overhead Crane Types

In planning a crane building, and in selecting overhead cranes, it is important to consider future operations that may increase loading and service requirements in addition to present operations. Be certain to plan for both crane building and cranes to satisfactorily meet the increased service conditions that may arise in the future. This planning effort will minimize the possibility of overloading or of placing the structure in a more severe classification than intended.

There are many types of cranes in use today to meet material handling requirements.The types described here include those cranes currently being supplied by major crane manufacturers support of these crane types usually affects the design of the building in which the crane is installed.

Top Running Cranes

Top-running bridge cranes are characterized by bridge end trucks bearing on top rails attached to the runway beams. Top-running bridge cranes are generally used for more severe applications with heavier loads and high service classifications. They are generally applicable when one crane isle extends the full width of a building aisle, and they are frequently used where high travel speeds are required. In comparison to underhung cranes, top-running cranes usually provide greater hook height and clearance below crane girder.
Top-running bridge cranes may be single girder, double girder, or box girder. Single girder cranes are generally used on shorter spans and lower capacities or service classifications. The trolley of a single girder crane is suspended from the girder. Cranes are normally operated by a pendant pushbutton station suspended from an independent track or radio remote.

Double girder cranes

Double girder cranes are generally used on moderate spans and higher capacities or service classifications. The trolley of a double girder crane usually bears on rails attached to the upper flange of the crane girders. Low headroom double girder cranes are available that are designed to produce maximum clearance beneath the bridge.

Box girder cranes are generally used on larger spans and high capacities or service classifications. The trolley bears on rails attached to the upper flange of the crane girders. Box girder cranes are normally operated from a pendant pushbutton station suspended from an independent track or a radio remote.

Underhung bridge cranes

Underhung bridge cranes are characterized by the bridge end trucks being suspended from the lower flange of the runway beam. Underhung bridge cranes are generally used for less severe applications with lighter loads and lower service classifications. They are frequently used where multiple crane aisles are required in a building aisle,where the crane aisle is only a portion of the building aisle, and when materials must be transferred between building aisles. In comparison to top running cranes, underhung cranes usually provide greater hook cover, clearance beneth the runway beam, and clearance for overhead obstructions.

Underhung bridge cranes may be single or double girder with the trolley suspended from the lower flange of the girder or girders. The power source of the hoist, trolley, or bridge may be hand geared or electric. Electric powered cranes are normally operated by a pendant pushbutton station suspended from the hoist.

  • GENERAL RANGE OF CRANE TYPES
  • Crane Type Power Source Description Span or Reach Capacity
  • Underhung 1. Hand Geared Single Girder 10’ to 50’ Spans ½ to 10 Tons
  • 2. Electric Single Girder 10’ to 60’ Spans 1 to 10 Tons
  • Top-Running 1. Hand Geared Single Girder 10’ to 50’ Spans ½ to 10 Tons
  • 2. Electric Single Girder 10′ to 60′ Spans ½ to 10 Tons
  • 3. Electric Double Girder 20′ to 60′ Spans 5 to 25 Tons
  • 4. Electric
  • Box Girder
  • Pendant-Operated
  • 4-Wheel End Truck 20′ to 100′ Spans
  • 5 to 25 Tons
  • 5. Electric
  • Box Girder
  • Radio Controlled
  • 4-Wheel End Truck 50′ to 100′ Spans
  • Up to 60 Tons
  • 6. Electric Box Girder
  • Radio Controlled
  • 8-Wheel End Trucks 50′ to 100′ Spans Up to 100 Tons
  • Jib Cranes 1. Hand Geared or Electric Floor-Mounted
  • 280 to 360 8′ to 20′ Reach
  • ¼ to 5 Tons
  • 2. Hand Geared or Electric Column-Mounted
  • 180 8′ to 20′ Reach ¼ to 5 Tons