Reason analysis and repair of the broken ear plate of imported concrete pump arm

The sustained and rapid development of the global and domestic economy has led to a rapid increase of capital construction. A series of concrete regulations and laws have been promulgated in the country to promote the continuous improvement of the proportion of commercial concrete used in various places and provide a good market environment for the development of commodity concrete pumping machinery. The concrete pump truck is flexible in movement and easy to use. The cloth boom has three functions of luffing, twisting and turning. The pipeline is laid along the boom, and the concrete pouring position can be arbitrarily changed within the range of the boom without temporary laying on site Pipeline; saving auxiliary time, improve efficiency, pumping large volume, high pouring quality, is more and more by construction units and rental companies of all ages. However, due to the unique structure of concrete pump, the pursuit of construction efficiency and other reasons, pump parts damaged. The following for my company for a customer repair a 37m imported from abroad to buy concrete pump, the damage analysis and repair program, the first is to repair the pump to continue to put into use, the second is to give our design and Manufacturing to provide some experience and learn from, to avoid similar damage, to improve product quality, extend the service life, safety and reliability purposes. 1 concrete pump truck breakage of the specific parts and appearance features According to the vehicle and the site of the fault site inspection, fracture (cracking) has the following characteristics: (1) two arm rear articulation point of the side of the ear plate completely broken, the vast majority Of the crack marks show the old crack (the end of the boom section - the joints of each arm with the head of the previous arm, the head of the arm section - the connection end of each arm and the tail section of the next section.) (2 ) The other side of the two-arm arm, ears completely distorted, big curved connecting rod, a small curved connecting rod and two arm due to the end of the ear plate rupture caused by an arm head ear plate local extrusion deformation. Except for the deformation of the arm of one arm, the others are new cracks due to the rupture of the ear plate on the tail side of the two-arm; (3) the flaw to be measured , Such as the deformation of the boom and cylinder, connecting rod damage. 2 concrete pump truck fracture formation and expansion analysis of two arm rear side of the ear plate rupture site and shape as shown in Figure 1, (a), (b), (c) is the tear off the ears removed from the various sides Photo. According to the location and shape of the fracture, most of the cracks at the fracture are old cracks. It can be inferred that the first microcracks, microcracks after a certain period of alternating stress cycle macroscopic cracks, and finally due to crack growth, extending the base material caused by a sudden fracture. As for the formation of cracks, there are the following reasons: (1) weld and the base metal is not fusion, defects appear in the welding defects, especially the pump truck plate using high-strength steel, can be clearly seen from the fracture surface (2) From abroad and domestic design point of view, pump boom, especially with the turntable connected to the first few sections of the arm generally use high-strength steel plate, high-strength steel to ensure the yield strength , Some indicators such as ductility, ductility, solderability decreased, especially in the thermal stress zone formed by welding, causing the strength of the weld and the surrounding area to reduce; (3) the construction of concrete pump truck caused by the particularity of the structure of. Concrete pump truck in the construction of the role, the deployment of fabric arm, the fabric boom, leg hydraulic cylinder lock, the entire fabric arm system to form a cantilever structure. And the concrete pump truck boom with R-shaped structure, after the two arm there are three or four arm, of which three arm also used bending structure, two arm but also bear a certain torsional load. At the same time, concrete pump truck at work, the two pumping hydraulic cylinders alternating cycle of action, which will continue to pressure delivery of concrete pouring position. Due to the alternating action of two pumping cylinders, the concrete pump truck is subjected to a forced impact with a certain frequency. In the pumping cylinder under the impact of the cloth arm vibration amplification, so the cloth arm to withstand the alternating load, causing fatigue damage. (4) The pin shaft and the copper sleeve wear and tear cause the impact force of the tail end of the cloth arm. When the test is found, there are three pin shafts and the six copper sleeves are worn, and the abrasion degrees of the two pins and the copper sleeves in the same group are inconsistent. Two-arm root sleeve at the stress concentration. According to the previous 37 m similar to the qualitative analysis of the arm of the root of the truck, the force diagram and I-Deas finite element analysis of the results shown in Figure 2, you can see the underside of the sleeve has obvious stress concentration (blue display section). The high-strength plate as a jib plate has good toughness and plasticity, the initial crack tip in the high stress concentration zone and the residual force of the local small-scale yield. In this case, the alternating loads act to gradually expand the tiny cracks. (6) The concrete pump truck basically works in the open air environment, which causes oxidation corrosion due to the long-term erosion of rainwater and hydrogen sulfide and other corrosive media in the air , Local strength decreased; (7) construction environment. Our country's concrete construction machinery construction tasks are heavy, the working environment is poor; do not attach importance to equipment maintenance; lack of training of hand, quality is not high. Such as our country's concrete pump rental company, a month pumping 8 thousand to more than 10,000 square is normal, one-year pumping capacity of 10 to 130,000 square. Correspondingly, foreign 8 hours a day, do not just work overtime, the use of personnel training well, high quality, know how to use, maintain, maintain a pump 3-5 years abroad pumping 100,000 square. Basically it is used in our country for one year, which is equivalent to the foreign use for more than three years. Under such a big construction intensity, the maintenance and repair work of the hands and maintenance personnel is much worse. The pump truck for the European import pump, at design time, according to Europe and the United States operating conditions in China to consider the intensity of construction, conditions. In this way, it is not surprising that this concrete pump truck was shipped more than three years ago (the sign shows that it was delivered to the factory by the factory in June 2002), which is equivalent to local fatigue cracking after more than 10 years of overseas use. (8) Failure to detect early And take measures. As a result of this highly integrated concrete pump truck equipment, local cracks and fatigue cracks can not be completely avoided, Europe 500 hours to maintain as a system, but our country did not do well in this area, and sometimes even with the maintenance, Such as the oil between the pin and the copper sleeve are not carried out, not to mention the overall maintenance. Sometimes a little crack is not terrible, after a small repair or strengthening on it, if not found, or found not timely measures to crack will be enlarged