Design and application of oil dispersion of the ho

Design and application of hydraulic excavator oil dispersion

crawler hydraulic excavator is an efficient machine with poor working conditions, large load changes and long working hours. When the hydraulic system is working, all kinds of energy losses are converted into heat. The heat of the system mainly comes from the main hydraulic pump. In addition, the main valves, pipelines and hydraulic cylinders will generate part of the friction heat. A small part of all this heat is transferred to the surrounding space through hydraulic components and accessories such as pipes and oil tanks, and most of it is used to raise the oil temperature of the system. Proper oil temperature rise is normal, which is also good for the work of the hydraulic system, but the oil temperature rise should not be too large, otherwise the performance of the hydraulic oil will change sharply, and the sealing performance of each hydraulic element will also decline, which is extremely detrimental to the work of the whole hydraulic system. Therefore, the maximum temperature of the hydraulic system must be controlled not to be too high. Generally speaking, after the system reaches thermal balance, the inlet temperature of the oil dispersion (i.e. the maximum temperature of the hydraulic system) should not exceed 80 ℃. Especially during summer operation, the ambient temperature in some areas is too high, the oil temperature rises faster, and overheating is common, which makes the machine inefficient and unreliable, and even causes shutdown failure in serious cases. Due to structural limitations, the hydraulic system of excavator has a small oil tank volume, which cannot fully dissipate heat. In order to effectively control the oil temperature, forced cooling must be adopted to limit the oil temperature rise through the radiator

I. type selection and configuration of oil dispersion:

at present, there are many types of radiators. Due to the relatively qualified heat dissipation materials and advanced technology in foreign countries, segment oil dispersion or its extended products are mostly used in construction machinery, such as Japan, South Korea, the United States, etc. It has the advantages of simple structure, convenient manufacturing, easy assembly line production, small wind resistance, easy cleaning, convenient layout in China's plastic machinery market, but the material performance requirements are high. Limited by basic industries, aluminum plate fin air-cooled coolers are mostly used for oil dispersion of construction machinery in China. The excavator of our company also adopts aluminum plate fin air-cooled cooler, which is equipped with horizontal or vertical wavy heat dissipation fin plate (aluminum sheet with thickness of 0.2 ~ 0.3mm) structure between each two layers of oil plates to increase local heat dissipation coefficient and heat dissipation area (the heat dissipation area can reach 8 ~ 10 times of the light tube), so as to prevent dust and install filter outside. The cooling effect of fin cooler is several times higher than that of other coolers, and its volume and weight are relatively reduced. It has good cooling effect, compact structure, small volume and high strength. The fin cooler adopts aluminum sheet, which is not only low in cost, but also not easy to rust, but also has large wind resistance, easy to block and difficult to clean

II. Type selection calculation of oil dispersion:

the calculation of oil dispersion is mainly to determine the required heat dissipation area according to the heat exchange capacity. The heat dissipation power P2 of oil dispersion should be equal to the difference between the heat dissipation power P of the system and the heat dissipation power of components such as oil tank and pipeline. This calculation does not consider the heat dissipation of oil tank and pipeline, and ignores the overflow loss of the system, and assumes that the cooling inlet and outlet air volume is sufficient. In order to balance the oil temperature, the heat exchange capacity of the cooler is equal to the heat released by the hydraulic oil. Calculation of the heat released by the hydraulic oil:

p2=c q p (t2-t1)

outlet temperature of the oil

inlet temperature of the oil

density of the oil

flow of the oil

specific heat capacity of the oil

in the formula: c=1675 ~ 2093j/(kg.k)

take c=2000j/(kg.k)

q=2 × 23 our technicians will answer 0l/min

p=900kg/m3

t2-t1=2 ℃ one by one. Take the temperature difference between the inlet and outlet oil as 2 ℃

calculate p2=26.9kw

calculation of the heat dissipation area of the oil dispersion:

a=

k - heat transfer coefficient of the oil dispersion,

k = 30 ~ 350w/(m2.k) take k= 50w/(m2.k)

△ TM - between oil and wind.Average temperature difference

△ tm= -

where:

t1 - hydraulic oil inlet temperature, Determine

t2 - the outlet temperature of hydraulic oil according to the heating condition of the system, and determine

t1 '- the inlet temperature of cooling air according to the control requirements of the system for oil temperature, which is generally the ambient temperature

t2' - the outlet temperature of cooling air

△ TM. Its innovation is mainly used to detect the bolt nut in the tightening process Both the manufacturing and utilization levels reflect the scientific and industrial level of a country = ℃ - ℃ =19 ℃

it is calculated that: a=28 ′ -3m2

after calculating the required heat dissipation area, the specifications and models of oil dispersion are selected according to the manufacturing and acceptance standards of jb/t "technical conditions of aluminum plate fin heat exchanger", and the number of plates is determined in combination with the external dimensions and other requirements of oil dispersion

the main performance parameters of oil dispersion are as follows:

① oil flow q=2 × 230L/min;

② cooling area at the wind side s=50m2

③ oil side working pressure p=1.2mpa

④ the pressure loss on the oil side ≤ 0.15Mpa

the main technical requirements are as follows:

① all welds must be welded thoroughly, without pores and cracks, beautiful molding, and no serious bumps and scratches on the surface

② the strength test water pressure is 2.4Mpa, which lasts for 30min without leakage

③ the air pressure of air tightness test is 1.6Mpa, which lasts for 5MN without leakage

④ air filter hole 2mm, steel wire diameter 0.4mm

⑤ thoroughly remove dirt and debris before packaging, blow dry the inside, and seal the nozzle

III. installation of oil fan:

the oil fan adopts forced air cooling and is cooled by the engine fan. The combination of oil dispersion and engine cooling water tank is convenient for fixed installation, effectively saves the upper space of excavator turntable, and can achieve the expected cooling effect. For some high-power construction machinery, such as excavators above 30t, the hydraulic motor can also be used to drive the fan to cool the oil dispersion separately

IV. use and improvement of oil powder:

WY series products put on the market in 2002. During the construction in summer, due to the high ambient temperature, the oil temperature rises. Some users report that the oil temperature is too high, and the oil dispersion cracks due to the blockage of the return check valve of the system or the high return pressure, the poor quality of the oil dispersion itself, etc. we have carried out the cause analysis and quality improvement for this problem. In the design, we reduce the oil heating by optimizing the system design such as pipelines, and make full use of the oil tank to dissipate heat Measures such as selecting supporting manufacturers are preferred to control the oil temperature. In addition, due to the connection of oil radiator and water fan, some users report that the heat dissipation effect of the engine water tank is not good, and some water tanks are very hot and often "boil". In the first half of this year, we made an improvement and trial on the structure of the oil radiator itself based on the comprehensive consideration of the water tank problem, and adopted a thin oil radiator to reduce the suction resistance of the fan and enhance air circulation and circulation, After good feedback from the market, we plan to improve and test the matching of engine water tank and oil dispersion in the next step, in order to further improve the heat dissipation effect of water dispersion and oil dispersion