How To Buy Cranes For Steel Structure Workshops?
Apr 13, 2023
How To Buy Cranes For Steel Structure Workshops?
At present, steel structure workshops are widely used in factory construction. Due to its short construction period, simple construction process, and low cost, steel structure workshops are always preferred except for some special occasions.
Different from the inspection of cranes installed in reinforced concrete workshops, there are several issues that need attention in the inspection of cranes in steel structure workshops.
1. Large vibration, loud noise, easy to loose connection
Due to the poor vibration and sound absorption effect of steel structure workshops, large vibration and noise will be generated when the crane is running, especially when the cart is running.
At present, the commonly used vibration reduction method is to insert rubber inclined gaskets between the crane cart rail and the rail bearing beam. These rubber gaskets can absorb vibration and noise, and at the same time adjust the level of the cart track.
However, this structure reduces the coupling stiffness between the cart track and the rail bearing beam. When the crane cart is running, the intermittent compression and rebound of the rubber gasket will cause the connection of the cart track (such as the track joint plate, hook bolts, etc.) to loosen more easily.
During the inspection, it was found several times that the connecting bolts between the rails of the carts were loose or the bolts of the track hooks were loose. Therefore, it is recommended to take the following measures during track installation:
(1) Strictly control the height of the rubber gasket. When the height difference of the rail bearing beam is large, the iron gasket should be used for leveling first, and the rubber gasket should be placed at last;
(2) Use a larger pre-tightening force on the hook bolts to compress the rubber gasket to increase the connection stiffness. At the same time, a torque wrench should be used to evenly distribute the pre-tightening force between the track fixing bolts;
(3) More reliable anti-loosening measures such as double nuts are adopted.
2. Lateral stiffness and instability of the rail bearing beam
The rail-bearing beams of steel structure factory buildings mostly use self-made section steel with "I"-shaped bearing surfaces. The following methods are commonly used to fix the rail-bearing beams: the rail-bearing beams are erected on the steel column corbels, and the lower edge plates of the beams are connected to the corbels with bolts. The upper edge plate of the beam is connected with the column through the connecting plate.
When the trolley of the crane is running or the hanging object swings longitudinally along the main beam, it applies a laterally changing load to the rail bearing beam through the large wheels;
At this time, if the lateral rigidity of the supporting rail beam is not enough and severe vibration occurs, or the supporting rail beam is not fixed firmly and becomes unstable, it will have an adverse effect on the safe operation of the crane.
For some long-span rail girders, when the crane is in the middle span of the rail girder, the starting and braking of the empty trolley will cause the rail girder to generate large lateral vibrations.
The current crane inspection regulations do not have clear standard requirements and corresponding inspection methods for the lateral stiffness of the rail bearing beam, making it difficult to judge during inspection.
It is suggested that the simple starting and braking trolley under no load, rated load and 1.1 times the rated load can be used to verify the lateral stiffness of the rail beam during the inspection.
3. Measurement of crane girder stiffness
Judgment of main girder stiffness Traditionally, the level method is commonly used to hang a scale at the mid-span of the main girder, and a pre-tightened weight is hung under the scale, and the level is used to measure the readings of the corresponding tape of the main girder under no-load and mid-span rated load respectively, and calculate The elastic deflection value of the main beam is used to determine whether the stiffness of the main beam is qualified.
In fact, the readings of the main girder under the rated load include not only the actual elastic deformation of the main girder, but also the deformation of the supporting rail beam, the assembly gap of the cart wheel, the assembly gap of the trolley, the deformation of the cart track and trolley track, and the deformation of the hoisting wire rope. wait.
For the crane installed in the concrete structure factory building, the elastic deformation of the main girder is much larger than the other items mentioned above, and the assembly gap and track deformation can be ignored; but for the crane in the steel structure factory building, the rail bearing beam is in Under the wheel pressure of the rated load, there will be a large elastic deflection (measured about 2-3mm), which will be added to the measured value of the deformation of the main girder of the crane, resulting in a large error.
Therefore, when the value measured by the traditional method is close to or exceeds the critical value S/800 (S is the span of the crane), especially for the occasion of installing a small-span crane on the large-span rail beam, the influence of the elastic deflection of the rail beam should be considered .
The following method can be used to test again to verify: hang three scales on the inner side of the two end beams of the crane and the middle span of the main beam respectively, pre-tighten them with heavy objects, and use a level to measure the load of the crane under no-load and rated load respectively. Then calculate the actual elastic deflection value of the main girder under rated load.
The above method reflects the deformation of the rail girder and the deformation of the cart wheel in the numerical change of the end beam scale, basically eliminates the influence of the deformation of the rail girder on the determination of the stiffness of the main girder, and has high accuracy.
