Abstract: With the large-scale realization of modern industrial production, industrial production plants of all sizes have sprung up everywhere. Bridge cranes for lifting and transportation in industrial production have been widely used in indoor and outdoor industrial and mining enterprises, steel and chemical industries, railway transportation, ports and docks, and logistics turnover. How to choose a bridge crane to reduce the cost of industrial production plants is actually worth serious discussion.
Keywords: industrial production plant overhead crane cost
With the large-scale realization of modern industrial production, industrial production plants of all sizes have sprung up everywhere. Bridge cranes for lifting and transportation in industrial production have been widely used in indoor and outdoor industrial and mining enterprises, steel and chemical industries, railway transportation, ports and docks, and logistics turnover.
Bridge cranes are lifting equipment that are horizontally mounted above workshops, warehouses, and material yards for material handling. Because its two ends are located on tall concrete columns or metal brackets, it is shaped like a bridge, so it is called a bridge crane. The bridge of the bridge crane runs longitudinally along the tracks laid on the elevated platforms on both sides, and can make full use of the space under the bridge to lift materials without being hindered by ground equipment. Bridge cranes are the most widely used and largest type of lifting machinery, and their application forms are shown in the figure.
The general practice of owners to build factories and purchase bridge cranes is as follows: after getting the project, the owner first communicates with the factory design institute and provides the relevant requirements to the factory design institute. Then the designers of the factory design institute are fully responsible for designing the factory buildings required by the owner. In the design process of the factory design institute, some bridge crane parameters are inevitably needed. At this time, the designers of the factory design institute will use the traditional national standard bridge crane parameters, and basically verify them according to the extreme values. When the factory building design is basically completed or even the construction begins, the owner begins to consider purchasing bridge cranes.
In fact, this process does have some problems. The problem lies in the bridge crane parameters based on the designers of the factory design institute. Because the current bridge crane companies are constantly developing more reasonable and more economical bridge cranes, gradually replacing the traditional rough and clumsy bridge crane design form, in addition, the owner's specific use requirements are not reflected in the design of the bridge crane. Due to the existence of this series of factors, the design of the factory building is conservative and wasteful.
Here we will focus on the factors that affect the cost of the factory building by the bridge crane.
The maximum wheel pressure of bridge crane will have a great impact on the design and cost of factory buildings, and it is also a crucial link related to safety.
At present, the design process of factory buildings is that the designers of the factory design institute calculate the maximum wheel pressure of bridge crane according to the lifting weight and deadweight of the bridge crane, and the engineers who design the factory buildings generally use the maximum wheel pressure of bridge crane as the main design load of crane beam, factory building column and foundation. Although the engineers of the factory design institute also hope that the wheel pressure applied to the crane beam track is smaller, the designers always tend to be conservative in design, and often calculate the maximum wheel pressure of bridge crane according to the maximum rated load of the bridge crane trolley and the position closest to the end of the main beam. At this time, the wheel pressure may be very large. In fact, most bridge cranes do not generally run to the limit position when lifting the maximum rated load. Indeed, once the wheel pressure is given, even if the cost of the factory building is high, the owner can only meet the requirements. In the past, designers had almost no discussion on how to determine the wheel pressure of bridge cranes and whether it was reasonable, and they all took it for granted. In fact, there is room for discussion on this issue. As long as the wheel pressure of bridge cranes is reasonably controlled, the cost of factory buildings can be greatly reduced, and the normal operation of bridge cranes can still be guaranteed.
The most obvious example is the bridge crane used to hoist the generator stator in a thermal power plant. Since the installation position of the generator stator is often located near the central axis of the factory building, the trolley does not need to be transferred to the extreme position far away from the central axis and cannot be moved. If the maximum wheel pressure of the bridge crane calculated when the trolley is in the extreme position is actually much higher than the actual wheel pressure, the factory building designed and built according to this wheel pressure will cause unnecessary waste due to excessive surplus strength.
Taking steel structure factory buildings as an example, most of the investment is in the steel consumption of main components such as steel columns, crane beams, roof beams, and foundations. The greater the wheel pressure of the crane, the greater the steel consumption of the factory building and the higher the cost; on the contrary, the less steel consumption and the lower the cost. According to past experience, for every 10% increase in the maximum wheel pressure of the bridge crane, the cost of the crane beam, column and foundation of the factory building will increase by 5% to 7%. If the actual wheel pressure is 100kN less than the designed wheel pressure, the cost of the factory building can even save millions of yuan.
For example, the original 100t×30m bridge crane in the heavy workshop of a machine tool factory had to be replaced with a 125t×30m due to insufficient lifting capacity. The maximum wheel pressure that the crane beam of the factory building can withstand is 480 kN, and the maximum wheel pressure calculated by the traditional calculation method after the bridge crane was replaced is 580 kN, which exceeds the maximum bearing capacity of the original crane beam and factory building column. Since the method of reducing the maximum wheel pressure of the bridge crane was not adopted, the crane beam and column of this workshop had to be dismantled and reinforced, and then reinstalled, with a loss of more than 3 million yuan. This example is similar to the above-mentioned thermal power plant example. Although the user requires the bridge crane to be able to lift a load of 125t, it only needs to lift heavy objects within a certain range in the span. If a small number of large equipment that needs to be repaired is arranged near the middle of the span of the plant during design, light and small objects can be hoisted near the span end limit. In this way, it is not necessary to calculate the wheel pressure based on hoisting 125t to the limit position.
The above example shows that the actual maximum wheel pressure of the bridge crane is not as large as it is usually calculated. In other words, according to the existing bridge crane design habits, the maximum wheel pressure of the bridge crane will be greatly overestimated, thereby increasing the cost of the plant and causing unnecessary waste.
The size of the bridge crane's own height H3 and the maximum distance of the hook rising H5 are relatively intuitive factors that affect the cost of the factory building. The height of the factory building H1 is generally determined according to the following formula:
H1 = H2 + H3 + H4
H2 = H5 + H6
In the formula:
H1——the elevation of the lower chord of the roof truss
H2——the elevation of the bridge crane rail top
H3——the height of the bridge crane itself (including the trolley)
H4——the upper clearance between the bridge crane and the factory building
H5——the maximum distance of the bridge crane hook rising
H6——the maximum height of the product or equipment produced (including the height of the hoisting rope)
The Chinese national standard GB/T-14405 "General Bridge Crane" 4.2.7 clearly stipulates that the gap size between the bridge crane and the factory building should generally meet the upper clearance of not less than 100mm, that is, H4 in the figure is basically a fixed value. Since the lifting height of the hook is determined by the largest product or equipment produced by the owner's factory, it is basically calculated according to the actual size, so H6 in the figure is basically fixed. H3 and H5 are generally determined by the design and manufacturing process of the bridge crane itself. These two factors are also the determining factors of the factory building height.
The layout of bridge cranes will also affect the cost of the plant. For example, if a small number of large equipment that needs to be repaired is arranged near the middle of the plant span during design, and light and small objects are hoisted near the end of the span, then the actual maximum wheel pressure of the bridge crane can be reduced, thereby reducing the requirements for the structural strength of the plant and reducing the cost.
Different types of bridge cranes (such as ordinary bridge cranes, metallurgical special bridge cranes, etc.) and different specifications of bridge cranes (such as lifting weight, span, working speed, etc.) have different effects on the cost of the plant. Generally speaking, the larger the lifting weight and the larger the span of the bridge crane, the higher the requirements for the plant structure, and the cost increases accordingly.
In addition to the factors of the bridge crane itself, the design and construction quality of the plant will also affect the cost. Reasonable plant design can reduce construction costs and improve efficiency; while strict construction quality control can reduce rework and maintenance costs.
In recent years, foreign light and novel bridge cranes have gradually entered the Chinese market. At the same time, domestic bridge crane companies are also constantly developing more reasonable and economical bridge cranes. These bridge crane products have the advantages of excellent design, high hook lifting height, and low maximum wheel pressure. They can directly reduce the steel consumption of factory building steel beams, thereby saving the cost of factory building. We recommend that owners of factory buildings contact the factory design institute and bridge crane designers, and truly reflect their actual needs and actual usage to the designers. I believe that they will design products that truly belong to you, allowing you to directly lead your many competitors at the starting line.
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