Once the pump truck problems will bring a lot of inconvenience to the construction. Taking a 37m imported concrete pump truck purchased from Italy as an example, we observed the characteristics of the broken part of the boom and analyzed the causes of the damage, and implemented the rehabilitation plan on the basis of the analysis. According to the on-site inspection of the vehicle and the fracture site, it is not difficult to find that the site of fracture (cracking) has the following characteristics: the lateral ear at the hinge point of the two-arm end is completely broken, and the vast majority Of the crack marks show the old crack (the end of the arm: each arm with the arm of the previous section of the connection end; arm section head: each arm and the next section of the tail end of the arm connection. The same below) two arm The other side of the tail of the ear plate completely distorted, big curved connecting rod, a small curved connecting rod and the ear arm caused by the rupture of the two-arm rupture caused by an arm head ear plate local extrusion deformation. In addition to a section of the head of the arm deformation, the rest are new cracks, due to the two arm end of the ear caused by rupture. As the two arm root side of the ear plate rupture caused by the naked eye is difficult to detect, you need to measure the defects, such as the deformation of the boom and cylinder, connecting rod damage. 2 fracture formation and expansion analysis According to the fracture site and shape, the fracture of the cracks are mostly 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, extension caused by a sudden rupture of the base metal. As for the formation of cracks, there are the following reasons: (1) the weld and the base metal is not fusion, this defect is more common in welding defects, especially the pump truck plate using high strength steel, it can be clearly seen from the fracture surface (2) From the perspective of foreign and domestic design, the boom of the pump truck, especially the plates of the first few sections connected with the turntable, generally adopt high-strength steel plates. When the high-strength steel plates ensure the yield strength, Some indicators such as plasticity, ductility, solderability decreased, especially in the welding of the thermal stress zone, causing the weld and the surrounding area to reduce the intensity; (3) concrete pump truck construction, fabric arm deployment , Each section cloth 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, there are three or four arm after the two arm, of which three arm also adopts the bending structure, but also bear some torsion load two arm. 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. Under the impact of the pumping cylinder, the vibration of the cloth arm has an amplification effect, so the cloth arm withstands the alternating load action and causes the fatigue damage. (4) The wear of the pin shaft and the copper sleeve causes the impact force of the tail of the cloth arm. There are three pins, six copper sleeve has worn, and the same group of two pins, copper sleeve wear degree of inconsistency; (5) two-arm root sleeve stress concentration. According to the previous 37m similar to the qualitative analysis of the root of the arm, the bottom of the sleeve has obvious stress concentration. 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, alternating loads act to gradually expand the tiny cracks. (6) The pump truck basically works in an open air environment and causes oxidation corrosion due to the long-term erosion of rainwater and hydrogen sulfide and other corrosive media in the air, Local strength decline; (7) Our country's concrete construction machinery heavy construction tasks, poor working environment; do not attach importance to equipment maintenance; lack of training of hands, the quality is not high. Such as our country's concrete pump rental company, a month pumping 8 thousand to more than 10,000 square are normal, one-year pump capacity of at least 10 to 130,000. 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 before the pump only 10 million. 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 has been shipped for nearly 4 years (the sign is shown for delivery to the factory in June 2002) that is equivalent to local fatigue cracking after more than 10 years of overseas use; (8) Highly integrated equipment, local cracks and fatigue cracks can not be completely avoided. In Europe, 500 hours of maintenance are taken as a system. Our country has not done well in this respect. Sometimes it is even followed by maintenance such as pin shafts and copper Oil between the sets have not been carried out, not to mention the overall maintenance. Sometimes a little crack is not terrible, after a minor repair or strengthening can be, if not found, or found to be not timely measures to crack will expand, and finally may lead to structural damage, and even lead to accidents. The damage to the pump truck illustrates the problem. 3 Boom fault repair method According to the accident analysis, concluded that the boom repair method first boom of the first, two, three, four (from the turntable up) hanging. Detection of the various components, focusing on checking one or two arm damage and two arm cylinder damage. After examination, the results are as follows: turntable, chassis, three or four arm, each arm fuel tank intact; one or two arm connection pin, copper sleeve, three or four arm connection pin, copper sleeve, On the turntable connected to the copper sleeve has been damaged, to be measured manufacturing; in addition to a small arm of the head bent by the two arm deformation, the other deformation is small, does not affect the assembly performance and use; two arm root side of the ear plate Has been completely cracked, the other side of the contralateral ear plate due to cracking and serious distortion; connected to one or two arm of the large curved connecting rod and the straight rod is also due to the two arm lugs fracture. As the non-domestic truck pump truck, there is no drawings and measurement data, so before the repair, the need for the following measurements: (1) one or two arm connection pin, copper sleeve size, three or four arm connection pin, The size of the copper sleeve, the size of the arm and the copper sleeve connected to the turntable; (2) repair the big curved connecting rod and the large straight connecting rod, measure the partial dimensions after restoration, and the remaining dimensions as the connecting dimensions The size of the hinge point needs to be deduced from the parts connected with it; (3) the head size of one arm (to the position of two-arm cylinder support); (4) the retractable size, stroke and ear-ring thickness ; (5) repair of the two-leg root ear plate repair, after the welding part of the size of the restoration measure, the remaining dimensions, such as the connection with the size of an arm needs to be calculated from the arm connected to it; Arm, two, three arm limit size, used to check whether the repaired arm can be a reasonable limit. Draw the measurement results, but also need to link mechanism analysis to determine the shape and size. As a result of the two arm of the ear plate rupture caused by the two arm root, a large curved connecting rod and a large straight rod deformation and a slight distortion of the head arm, the measurement of the size of the deformation due to parts inconsistent with the original, Therefore, it should be used as a diagram to fine-tune the shape and size of the measured large bends, large straight bends and two-arm roots to ensure that both opening and retraction are in place without interference. After finishing the above work, we must carry out the process specification. Before welding, paint and stains should be polished clean, preheating before welding, heating the flame before and after the request around the move, the metal evenly heated to prevent local overheating; all welding are high strength welding rod, or carbon dioxide gas shielded welding, with high strength Welding wire, such as the use of high-strength welding rod, the electrode should be dried before welding; All welds after welding should be detailed inspection, there should be no cracks, undercuts, porosity and other welding defects; The above operations generally have high strength welding experience weld.