Requirements and taboos for wheel pressure calculation and wheel selection of bridge cranes

The wheel pressure of the bridge crane is the vertical pressure of the wheels on the track. The calculation of the strength of the components of the crane operating mechanism and the metal structure mainly depends on the maximum wheel pressure of the crane. At the same time, it also provides the basis for the design of the wheel device and the original data for the design of the track support structure. The minimum wheel pressure is mainly used to check the wheel slip when the operating mechanism starts and brakes.

The calculation of the wheel pressure of the bridge crane is to calculate the total pressure of the fulcrum. The calculation of wheel pressure is divided into the calculation of wheel pressure under moving load and the calculation of wheel pressure under statically indeterminate structure.

Approximate solution of wheel pressure under statically indeterminate structure

The four-point supporting structure adopted by the bridge crane is super statically indeterminate. The distribution of the supporting reaction force is not only related to the load, but also to the structural rigidity of the frame, the foundation rigidity, the manufacturing and installation accuracy of the frame structure, and the elasticity of the track. Factors such as flatness are related, but it is time-consuming to calculate the influence of these factors on the supporting reaction force, and it is difficult to estimate the unevenness of the track. Therefore, the calculation of wheel pressure under statically indeterminate structures generally adopts an approximate solution, and the difference between the approximate solution and the exact solution has not yet been studied.

Example analysis:

1. Known: Lifting weight: Q=20 tons, span: L=22.5 meters, number of cart wheels: 4, total crane weight (including trolley) = 32.5 tons:

Trolley weight: G=7.5 tons, spreader weight: 0.5 tons, the minimum distance from the center line of the hook to the center line of the end beam L1=1.5 meters (the limit position of the hook)

Second, the calculation process

•  The maximum wheel pressure of the cart (full load) Pmax=(32500-7500)/4+(20000+500+7500)*(22.5-1.5)/2*22.5=19317kg
•  The minimum wheel pressure of the cart (full load) Pmin=(32500-7500)/4+(20000+500+7500)*1.5/2*22.5?=7183kg
•  The maximum wheel pressure of the cart (no load) Pmax=(32500-7500)/4+(500+7500)*(22.5-1.5)/2*22.5?=9983kg
•  The minimum wheel pressure of the cart (no load) Pmin=(32500-7500)/4+(500+7500)*1.5/2*22.5?=6517kg

So the maximum wheel pressure Pmax=19317, the minimum wheel pressure Pmin=6517kg

There are many classifications of the wheels of bridge cranes, which can be classified according to usage, according to whether there is a wheel flange, according to the wheel tread, and according to the contact with the top of the track.

When choosing a crane wheel, it is necessary to choose according to the regulations, so how to choose? There are a few tips for your reference when choosing:

1) The longer the track of the cart, the worse the linearity, and the easier it is to " gnaw the road ". Therefore, the width of the wheel tread should be wider than the width of the track.

• The width of the wheel tread of the conical cart should be 30-40mm wider than the top surface of the track.
• The width of the wheel tread of the cylindrical cart should be 25-35mm wider than the top surface of the track.
• The width of the wheel tread of the cylindrical trolley should be 15-20mm wider than the top surface of the track.
•  The unilateral clearance of a single-rim wheel is 5-10mm.

2) To prevent the crane from derailing , the height of the wheel rim should be: 25-30mm for double-rim wheels; 20-25mm for single-rim wheels.

3) The driving wheel of the centralized drive large-span crane generally adopts conical wheels, and the passive wheel adopts cylindrical wheels, which can automatically adjust the deflection of the crane during operation to a certain extent to prevent the crane from tilting.

4) In order to reduce the wear of the wheel rim and prolong the service life of the wheel, the method of matching the wheel without rim and the horizontal guide wheel can be used, and the running of the wheel rim is replaced by the rim guided operation, which can make the sliding friction between the rim and the side of the track. , It becomes the rolling friction between the horizontal wheel and the side of the track, which reduces the running resistance and improves the life of the wheel.

5) Conical wheels are generally used on the running mechanism of two driving wheels and two passive wheels.

6) The size of the wheel diameter depends on the wheel pressure (the pressure of the wheel on the track), and the wheel pressure is limited by the load-bearing capacity of the track foundation. When a crane runs on rails supported by sleepers, its allowable wheel pressure is generally 100-120kN; when it runs directly on a track supported by concrete foundations or steel structures, its allowable wheel pressure can reach 600kN.

When the lifting weight is slightly larger, the wheel diameter can be increased to reduce the wheel pressure.

When the lifting weight is large, the wheel diameter is usually increased to reduce the wheel pressure. In order to make the wheel pressure of each wheel evenly distributed, a balanced (balanced) beam type supporting device is adopted.

For large cranes with a particularly large number of wheels, in order to shorten the length of the wheel arrangement, double-track rails can be used.

7) The wheel pressure of the two active wheels of the trolley operating mechanism is slightly greater than the wheel pressure of the two passive wheels.

At the same time, pay attention to the following taboos when selecting bridge crane wheels:

1.  The large end of the wheel diameter of the conical wheel cannot be placed on the outside of the track.
2.  The taper of the wheel tread is related to the radius of the arc at the top of the track. The use of conical wheels cannot be equipped with a track with no curvature on the top of the track.
3.  The wheels should be free from jamming and deformation.
4.  The gap between the wheel sweeping plate and the top surface of the track should not be greater than 10mm.
5.  The wheels must not have defects that affect the performance, cracks and repair welding.
6.  The relative wear of the two driving wheel diameters should not exceed 3/1000 of the diameter.
7.  When the operating mechanism is started or braked, the driving wheel generally should not slip.
8.  The fixing bolts of the wheel angular bearing box must have anti-loosening measures.