Strength calculation of expansion bolts for air conditioner outdoor units

Strength Calculation of Expansion Bolts for Air-Conditioning Outdoor Units of Luoyang Industrial College, Zhang Lihong, Yang Xiaofeng 21. Department of Mechanical Engineering, Luoyang Industrial College, Luoyang, Henan 471003, China; 2 Department of Public Affairs of Xiamen Xianglu Dr. Textile Fiber Co., Ltd., Xiamen 3626, Fujian The choice of the size of the expansion bolt provides a theoretical basis. With the improvement of people's living standards, air conditioners have increasingly entered the lives of ordinary people. More split air conditioners used by households consist of two parts, an indoor unit and an outdoor unit. According to the installation requirements of the air conditioner, the outdoor unit should have a suitable space. However, most of the buildings currently have no reserved space, and the installation of the outdoor unit is generally in the form of fixing brackets with expansion bolts. The choice of expansion bolts directly affects the quality of the outdoor unit installation. As a non-standard part, the force form of the expansion bolt is different from that of the ordinary bolt and the hinged hole bolt. The following is a simple analysis of the working principle of the force analysis and strength calculation.

1 Working principle of expansion bolts Expansion bolts are non-standard parts. The composition of the expansion bolts consists of bolts, nut washers and expansion sleeves. When installing the expansion bolts, first punch holes in the wall and then drive the entire bolts. Then screw the nut to move the bolt rod and the expansion sleeve relative to each other. The expansion sleeve is stationary because of friction with the wall, so the bolt rod is screwed outward. During the outward movement, the bolt head has a larger head support and an expansion sleeve to receive an axial load between the expansion sleeve and the wall. The lateral load is mainly balanced by the shearing force of the expansion bolt.

2 Analysis of the force of the expansion bolts The installation of the air conditioner outdoor unit 2, I know that the total weight of the air conditioner is the distance from the center of gravity to the wall. The lateral spacing of the bolts is 3, and the longitudinal spacing is 21.

8 brackets face up bracket left view 2.1 bolt force analysis of the bolt group force analysis based on the following assumptions that the bolt is an elastic body, its deformation is within the elastic range; each bolt has the same pre-tightening force; The piece is a rigid body, and the joint surface remains flat after being loaded. The force is reduced to the joint surface centroid, and the force of the bolt group is the lateral load of the bolt group. The overturning moment of the bolt group is the single bolt caused by the lateral load of 22.2 single bolt. The shear force is known as 1. The expansion bolt mainly balances the external load by the shearing force of the bolt and the friction between the expansion sleeve and the wall of the joint. Regardless of the influence of the preload force, it is assumed that each bolt evenly distributes the external load, and the lateral load 3 of the single bolt is the axial force 4 on the single bolt caused by the 2 overturning moment, and the overturning moment acts on the longitudinal symmetry plane passing through the 1 axis. Inside. Assuming that the bracket is rigid and the wall is elastic, under the action of the bracket, the bracket has a tendency to rotate around the joint axis of symmetry. The bolt above the shaft is pulled, the axial pulling force is increased, the wall below the shaft is pressed, the bolt is relaxed, and the axial pulling force is reduced.

It is known from the deformation coordination condition that the bolt working tension condition is proportional to the distance between the bolt and the shaft. The bolt farthest from the axis above the 1 axis is subjected to the maximum working tension, that is, the shear strength condition bolt rod and hole. The extrusion strength condition of the wall is determined by Equations 8 and 10. The theoretical size of the bolt rod can be calculated, and then the larger of the rods can be taken and rounded to determine the size of the expansion bolt.

3.2 Calculating the strength of the axial load due to the axial load compensation. There is no mature theoretical formula because it does not rely on the preload to balance the axial force, but mainly depends on the expansion sleeve and the wall. Friction to balance the axial force. In addition, the main load of the air-conditioning bracket expansion bolt is the lateral load, and the axial load is very small. The commonly used expansion bolt 2 father 0 can withstand 2, 30 and 4 after being expanded in the concrete wall. Axial force 2. Therefore, under normal circumstances, the expansion bolt bolt is pulled on site 2 to verify it.

3 Calculation of the strength of the expansion bolt 3.1 The strength calculation of the transverse load is considered. The shear strength and the extrusion strength are mainly considered in the design.

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