According to the stability, component strength, safety and practical application of forklift, this paper discusses the allowable lifting capacity of forklift equipped with accessories and the extended overload protection of forklift.
Key words: forklift accessories lifting capacity overload protection
Forklift is designed according to standard fork and rated lifting capacity. Because the accessories are configured after the forklift is made, and the weight is generally larger than the original forklift, and the load center is also different, resulting in the change of the center of gravity of the whole forklift system. In order to ensure the safe and reliable operation of the forklift, the allowable lifting capacity of the forklift after the configuration of accessories shall be re determined without changing the structure of the forklift and various safety indicators. At present, the types of forklift accessories are increasing. It is of great significance to correctly determine the allowable lifting capacity of forklift after configuring accessories to ensure the safe use of forklift and make full use of the lifting capacity of forklift.
1. Determine the allowable lifting capacity according to the stability principle
The load of forklift before and after changing accessories shall not exceed the allowable value, that is, the maximum load moment of each part shall remain unchanged. At this time, the allowable lifting capacity after using accessories can be determined through stability calculation. Based on the center of the front wheel of the forklift, make the torque of the rated lifting capacity of the forklift and the weight of the removed standard fork to the center of the front axle equal to the torque of the new allowable lifting capacity and the weight of the replaced accessories to the same center. Available:
Where Q - rated lifting capacity
SC -- load center distance
A - fork weight
GC - fork weight
GCx - weight of new accessories
SBC -- the horizontal distance from the center of gravity of the new genus to the vertical front surface
Sbx -- the horizontal distance from the center of gravity of the new accessory to the front surface of the fork
Z - horizontal distance from the rear surface of the vertical section of the fork to the front axle
SCX -- the horizontal distance from the specified load center of the new accessory to the front surface of the vertical section of the original fork
QX -- allowable lifting capacity when configuring accessories
According to formula (1-2), the forklift is allowed to lift after it is equipped with accessories.
When the forklift works under this allowable lifting capacity, it will not damage the performance of the whole machine, which is the same as when the standard fork is used. This method can be used as the basic principle for determining the allowable lifting capacity after the forklift is equipped with accessories.
2. Determine the allowable lifting capacity according to the bearing principle of components
If the new load center distance (SC-2) can be determined by the new load center distance in the first formula: SC-2. If the load center distance decreases and SCX is less than SC, the new allowable lifting capacity obtained by equation (1-2) may be greater than the original rated lifting capacity. This situation is absolutely not allowed in the actual operation of forklift. Because the allowable safety factors of hydraulic systems such as gantry components, lifting chain, lifting hydraulic cylinder, bearing part of drive axle and multi-way valve should not be changed. In the overall design of forklift, all components only constitute the safety guarantee of forklift under rated load. Therefore, under this condition, the new allowable lifting capacity can be determined according to the principle that the load of forklift and components should be equal before and after the configuration of accessories. The following formula can be obtained:
In the above formula, QY refers to the new allowable lifting capacity of forklift equipped with accessories determined by this principle.
The forklift can still maintain its original performance under this allowable lifting capacity. This method determines the necessary principle of allowable lifting capacity after configuring accessories for the forklift.
3 comprehensive analysis
According to formula (1-2) and formula (2-2), the relationship graph of Q, QX, QY and SC, SCX can be roughly drawn. Q curve is the load curve under the original use of fork; QX is the new allowable load curve of forklift equipped with accessories calculated according to formula (1-2); QY is the new allowable load curve calculated according to formula (2-2).
The shaded part below the intersection of each curve is the safe area, that is, the allowable load range of the rear forklift.
According to the graph, the following situations can be obtained:
(1) When SCX > SC, formula (1-2) is used to calculate the new allowable lifting capacity, which is the most restrictive, because the QX value is the smallest and the safety factor is the best.
(2) When SCX > SC, formula (2-2) is used to calculate the new allowable lifting capacity, which is the most restrictive, because the QY value obtained has the best insurance value for the operation of the forklift and will not cause damage to the forklift.
(3) When SCX is close to SC, due to the great influence of fork self weight GC and accessory self weight gCx, it can be calculated by formula (1-2) and formula (2-2) respectively, and then take the small value as the allowable lifting weight.
4 overload protection of forklift under different load center distance
From the above analysis, it can be seen that when the center of gravity of the same goods is at different positions in the length direction of the fork, the impact on the bearing capacity of the forklift is different. When the weight of the goods is unknown, there is a risk of overload when lifting with a forklift. The following is divided into three cases.
It is assumed that the weight of the goods is greater than the rated lifting capacity of the forklift.
(1) The horizontal distance between the center of gravity of the goods and the vertical surface of the fork is less than the load center distance of the forklift.
At this time, according to formula (2-2), the lifting capacity of the forklift is: Q1 = q = QY (2) the horizontal distance between the center of gravity of the goods and the front surface of the vertical section of the forklift is close to or similar to the load center distance of the forklift.
At this time, SCX = SC, according to formula (1-2) and formula (2-2), the lifting capacity of the forklift is: Q2 = q = QX (3) the horizontal distance between the center of gravity of the goods and the front surface of the vertical section of the fork is greater than the load center distance of the forklift.
At this time, SCX > SC, according to formula (1-2), the lifting capacity of the forklift is: Q3 = QX, which is strictly limited in the safety operation regulations of the forklift. It is not allowed to forcibly lift the known overweight goods at the position exceeding the load center distance. Only in this way can the forklift get effective overload protection.
