Selection and use of hydraulic oil for the hottest

Selection and use of hydraulic oil for construction machinery

I. principle of selecting hydraulic oil

1. Basis for selecting hydraulic oil for construction machinery

(1) hydraulic parts. Different hydraulic components have a minimum configuration requirement for the hydraulic oil used. Therefore, when selecting hydraulic oil, attention should be paid to the compatibility of the types of hydraulic parts and the materials, seals, coatings or paints used with the hydraulic oil, so as to ensure that all moving pairs are well lubricated, so that the components can reach the design life and meet the requirements of service performance

hydraulic pump is one of the most sensitive components to the viscosity and viscosity temperature performance of hydraulic oil. Therefore, the requirements of the pump for hydraulic oil in the system are often taken as an important basis for selecting hydraulic oil (except for the system with servo valve)

(2) system working condition. The higher the requirements for the speed, system pressure and mechanism action accuracy of the actuator, the higher the requirements for the wear resistance and bearing capacity of the hydraulic oil

according to the possible working temperature of the system, continuous operation time and the sanitation of the working environment, attention must be paid to the viscosity, high temperature performance and thermal stability of the oil when selecting oil, so as to reduce the formation and deposition of oil sludge

(3) tank size. The smaller the oil tank, the higher the requirements for oil oxidation safety, extreme pressure and wear resistance, air release and filtration

(4) ambient temperature. Hydraulic oil shall be reasonably selected according to the environmental temperature characteristics of construction machinery in underground, water, indoor, outdoor, cold areas, or cold areas with temperature changes, as well as whether there is high-temperature heat source or open fire nearby. If there is no open fire nearby, the working temperature is below 60 ℃ and the load is light, ordinary hydraulic oil can be used. If the equipment must be started under the condition that the growth rate of the universal testing machine industry at a very low temperature can be higher than that of most manufacturing industries, low pour point hydraulic oil must be used

to sum up, if the quality of the hydraulic oil is qualified, and the movement speed of the system actuator is very high, the flow rate of the oil is also high, the hydraulic loss increases, and the leakage is relatively reduced, so the oil with low viscosity should be selected; On the contrary, when the flow rate of oil is low, the leakage will increase relatively, which will affect the movement speed of the working mechanism. Therefore, it is appropriate to choose oil with higher viscosity. Generally, when the working pressure is high, hydraulic oil with high viscosity should be selected, because solving the leakage problem at high pressure is more priority than overcoming its viscosity resistance; When the working pressure is low, the oil with low viscosity should be selected. When the ambient temperature is high, the oil with higher viscosity should be used; on the contrary, the oil with lower viscosity should be used

(5) final determination of hydraulic oil. After the hydraulic oil is preliminarily selected, it is also necessary to check its supply source, viscosity, quality, use characteristics, scope of application, and the compatibility with the system and component materials to see whether all indicators can fully meet the use requirements

(6) economy. We should comprehensively consider the price, service life, hydraulic system and maintenance, safe operation cycle and other conditions of hydraulic oil, and focus on brands with good economic benefits

2. Economic analysis of selecting hydraulic oil

when selecting hydraulic oil, we should not only pay attention to the oil price, but also ignore the variety, quality, maintenance and regeneration. For example, in high-temperature, high-pressure and precision hydraulic systems near high-temperature heat sources and open flames, we should choose phosphate ester liquid fire-resistant hydraulic oil, and we should not replace it with cheap water-containing fire-resistant fluid because of its high price, which will cause premature wear of hydraulic pumps and reduce the accuracy of the system; For another example, in the high-pressure hydraulic system, anti-wear hydraulic oil should be selected. If cheap mechanical oil or anti rust and anti oxygen hydraulic oil is selected, the service life of the hydraulic pump will be shortened. Take l-hh and L-HM oils with ISO viscosity grade vg46 as examples, which are respectively used in the same yb-d25 vane pump (pressure is 12.5mpa, temperature is 65 ℃, speed is 1500r/min). After continuous operation for 250h, the wear amount of the pump with l-hh oil is 63 times that with L-HM oil. Therefore, in the medium and high pressure system, l-hh or L-HL oil should not be used, but L-HM anti-wear hydraulic oil should be selected

for the high-pressure system of construction machinery operating in cold and severe cold areas, low temperature and large changes in ambient temperature should be used. Low temperature hydraulic oil with high viscosity index should be used to make the low-temperature oil of the system have good fluidity, easy cold start, and consistent oil use of the system in winter and summer without frequent replacement

high quality anti-wear hydraulic oil has high thermal stability, good hydrolytic stability, strong demulsification ability, short air release time and long service life, which can improve the operation condition of the system. Therefore, high-quality hydraulic oil should be used in high-performance hydraulic system

select high-quality hydraulic oil. Although the oil price is relatively expensive, the service life of the oil is long, the wear of hydraulic components is less, the system maintenance is easy, and the production efficiency is high. Therefore, the overall economic benefit is still cost-effective

II. Rational use of hydraulic oil

1. Factors affecting the quality of hydraulic oil

(1) water. The moisture content of water in oil shall be in accordance with the national standard gb/t1118 After testing, the quality index of the technical standard should not be greater than the trace If the water in the oil exceeds the standard, it must be replaced; Otherwise, it will not only damage the bearing, but also rust the surface of the steel parts, which will emulsify, deteriorate and generate sediment of the hydraulic oil, hinder the heat conduction of the cooler, affect the operation of the valve, reduce the effective working area of the oil filter and increase the abrasion effect of the oil

(2) oxidation. Generally, the working temperature of hydraulic oil for construction machinery is 3, and it is not interested in selling foam lunch boxes, plastic bags and disposable chopsticks. The service life of hydraulic oil is closely related to its working temperature. Experience tells us that when the working oil temperature exceeds 60 ℃, the service life of oil will be halved for every 8 ℃ increase, that is, the service life of 90 ℃ oil is about 10% of that of 60 ℃, because the oil is oxidized. Oxygen reacts with hydrocarbons in the oil to slowly oxidize the oil, darken its color, and increase its viscosity. Finally, it may be so serious that the oxide cannot be dissolved in the oil, but deposited somewhere in the system with a brown viscous layer, which is very easy to block the control oil passage in the components, aggravate the wear of ball bearings, valve cores, pistons of hydraulic pumps, etc., and affect the normal operation of the system. Oxidation also produces corrosive acids. The oxidation process starts slowly. When it reaches a certain stage, the oxidation speed will suddenly accelerate, and the viscosity will suddenly rise. As a result, the working oil temperature will rise, the oxidation process will be faster, and the accumulated sediment and acid will be more, and finally the oil can't be used again

(3) impurities. Impurities can not only wear all moving parts, but also affect the normal operation of the whole system and cause machine failure once they are stuck in the valve core or other moving pairs

(4) air. If the hydraulic oil circuit contains gas, when the bubble overflows, it will impact the pipe wall and components to form cavitation, which will make the system unable to work normally. A little longer time will also lead to component damage

(5) physical and chemical reactions. The cleaned paint in the oil tank will cause changes in the chemical properties of the oil

2. Inspection and maintenance of oil

water content: release cm3 oil into a test tube, let it stand for a few minutes to make the bubbles disappear, and then heat the oil (such as using a lighter). At the same time, pay attention to whether there is a slight "bang" sound of water vapor at the top of the test tube mouth. If there is, it indicates that the oil contains water

construction machinery is generally operated in the field, and there is almost no condition to check the water content of the system oil. The simplest inspection method is to wait for the whole machine to stand overnight, open the plug of the oil drain software at the bottom of the oil tank, drain a little oil into a container, and observe whether the oil contains water on site

smell and appearance: compare a sample of unused oil and used oil in a glass dish at the same temperature. If the color of the oil is very different or has a special smell, it indicates that the used oil has deteriorated and needs to be replaced. If there is no obvious difference in the color and smell of the two oil samples, the two oil samples can be kept for one night at the same time. If there is sediment at the bottom of the container containing used oil, the oil in the system must be filtered by a fine oil filter and the oil tank must be cleaned

in addition, pay attention to the following oil matters:

(1) check the oil level before starting up, and check whether each oil circuit is in the correct standby state

(2) operate the machine at idle speed for about 5min, and check whether there are bubbles in the level gauge oil. If it is a new car or a new hydraulic oil, it is normal for bubbles to appear in the oil mark at idle speed, and the machine can be allowed to operate only after the bubbles disappear

(3) close note 2 When opening and closing the door or taking the test object from the furnace, do not let the object contact the rubber edge on the door, so as to prevent the rubber edge from being damaged and shorten the service life The temperature of Italian oil. When the machine works for a period of time, if the oil temperature is high, it is best to stop and rest, and then work again after the oil temperature is normal, so as to prolong the service life of the system and oil

(4) pay attention to whether the values of various parameters of the hydraulic system are normal, and also pay attention to the external characteristics of the system - sound. If there is air intake, water or blocked oil circuit in the system, it will make abnormal noise. At the same time, the reading fluctuation and display value of the instrument are abnormal. At this time, the machine should be shut down and checked in time

(5) filter the hydraulic oil regularly. Control the impurity particles in the oil within the specified range

(6) change the hydraulic oil regularly. Change the oil regularly according to the requirements of the machine manual, and replace the oil filter at the same time. If there are conditions for detection, it should be judged whether to change the oil according to the results; The oil change cycle can also be formulated according to the site and system requirements of the machinery, and the oil change cycle can be included in the equipment technical archives

attention during oil change: the new oil and the old oil should be of the same brand and specification. Before oil change, all the old oil should be drained and flushed. For places where the valve body and hydraulic cylinder cannot be drained and flushed, the oil return pipeline can be disassembled and put into a temporary oil bucket. After adding new oil, the old oil can be replaced by new oil by inching the engine. The principle is that the new oil should be filtered by an oil filter with a filtering accuracy not lower than that of the system, If the construction site is indeed unconditional, the oil filter in the system should be replaced after adding new oil and running for about 1H; After the machine is idling with new oil, check the oil level again and add new oil if necessary

(7) when washing the car or not using the machine, cover the oil tank to prevent moisture in the air from entering. (end)