Large tonnage fork and its detecting device National Construction Machinery Quality Supervision and Inspection Center Chen Baoqiang I. Preface <br> As a major component of forklifts, forks are increasingly attracting attention to their quality. Especially after the forklift is included in the special equipment, it puts forward higher requirements on the manufacture and inspection of the fork: the performance of the fork should meet the requirements of GB/T5182-1996 "Technical Requirements and Tests for Forklift Fork". At the same time, the export of forklift trucks to the European Union must be carried out with “CE†safety certification. The EU's forklift-related coordination standards also stipulate that the forks must meet the requirements of the ISO2330:1995 standard. The two standards are mainly the same, and the test method of the large-tonnage fork (single fork weight is not less than 5000Kg) is similar.
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The detection device of domestic large-tonnage forks is almost zero, which brings great inconvenience to the inspection of forklift special equipment and forklift export. The author develops the fork detection device below 4000 Kg and the large tonnage according to the standard requirements. The inspection device for the fork was studied and the overall design was proposed.
Second, the preliminary design of the test device <br> According to GB/T5182-1996 "Forklift fork technical requirements and test" and ISO2330: 1995 standard requirements, fork samples must be subjected to yield test.
For a single fork with a rated lifting capacity of 5000 Kg (including 5000 Kg), the test load FT is three times its rated lifting weight C;
Single fork with rated lifting capacity greater than 5000 Kg, test load FT=G×R
Where G is the rated lifting weight coefficient R=3-0.08 (Q-10), and R≥2.5
experiment procedure:
The fork must be fixed in the same way as it is on the forklift and equipped with a length gauge for measuring permanent deformation.
The yield test must be loaded twice without impact, and the appropriate time interval should be maintained between the two loads, which can be set to 10 minutes, and each loading time is maintained for 30 seconds. The loading position is from the front surface dimension D of the vertical section of the fork (see Figure 1). When the single rated lifting weight is less than 5500 Kg, D is the load center distance. When the single rated lifting capacity is greater than 5000 (including 5500) Kg, D is the specified value of the forklift manufacturer. 
figure 1
Third, the detection device composition and test principle :
According to the requirements of the standard, the schematic diagram of the fork detection device of 5000Kg or more is shown in Figure 2.
1 . The test device mainly includes: a loading device, a fork positioning device, a load display device, a hydraulic system, a measuring device, and the like.
2 . Test principle:
2.1 The fork positioning fork is fixed on the fork frame (the large tonnage fork is generally sleeve type), the fork frame should have a simple structure and the carrying capacity is 100 tons. The pin shaft jacket on the fork frame should have different specifications to suit the forks of different tonnages. The lower positioning block of the fork frame should also be determined according to the specifications of the fork. Different thickness dimensions should be determined. The forks should be solid and reliable, without deflection. The upper surface of the fork should be level.
2.2 The fork frame is installed on the slide rail, and the front and rear positions of the fork and the fork frame are adjusted by the moving cylinder at the tail to determine the load center distance or load loading position of the fork, and the fastening bolt is locked after the position is determined.
2.3 The loading device consists of a spherical pressure sensor, a frame, a load display device and a hydraulic station that load the cylinder and the head of the cylinder rod. The hydraulic station should provide 20MP pressure, the hydraulic cylinder output pressure is not less than 80 tons, the head spherical pressure sensor range should also reach 80 tons, and the display accuracy is guaranteed to be 0.1. The hydraulic cylinder is the first choice for the servo cylinder, which ensures that the cylinder can be moved slightly during loading and the load is stable.
Load monitor loading device hydraulic station moving cylinder moving rail and fork carriage fork and pressure sensor 
figure 2
2.4 Dimensional measurement after unloading, the side end of the fork is equipped with a length measuring device, which is measured once before loading (the position is selected at the fork tip, and the measuring tool should be parallel with the fork when measuring), and the measurement is performed after loading for 30 seconds. Repeat the above operation after 10 minutes, and check if the fork is permanently deformed after loading twice.
Fourth, the detection device design plan determination and requirements:
At present, the largest tonnage forklift in China is 45 tons. Therefore, the carrying capacity of the testing device should be no less than 45/2 × 3 = 67.5 tons, which can be selected as 80 tons. The brackets, forks and forks of the relevant cylinders shall be moved and the fixing bolts shall be checked for strength to meet the loading strength requirements. Since the detecting device as a whole is in a static load state during loading, a small safety factor can be selected during design.
Requirements of the hydraulic station: The hydraulic station can ensure that the output force of the cylinder rod is stable after loading, that is, the output pressure of the hydraulic system is stable, so the servo cylinder and the hydraulic system should match. At the same time, when the fork is required to be elastically deformed, the cylinder can follow the movement to ensure that the output pressure of the cylinder is constant. The hydraulic station should have a fine adjustment function.
The spherical pressure sensor has a self-aligning function to ensure that the pressure is applied to a point while the load is vertically loaded on the upper surface of the fork.
The digital load display instrument monitors the loading condition of the test device. The installation position should be near the hydraulic station. The test load is kept stable by the manual hydraulic valve.
The fork frame rail can be processed into a dovetail type. When the load position is adjusted, the fork frame and the fork are linearly moved, and the fixing bolts are evenly distributed and the positioning is reliable. Since the longitudinal adjustment resistance is small, the cylinder selection cylinder diameter can be small.
Design and manufacture of large-tonnage fork detection device, expanding the detection range of fork test, filling the gap of domestic large-tonnage fork detection device, adding testing equipment for parts inspection in large-tonnage fork type test, to meet forklift products Export inspection provides the protection of experimental equipment.
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