Archive for February, 2017

The significance and method of hydraulic system flushing

First, the significance of hydraulic system cleaning
From the use of point of view, the hydraulic system is the first condition of the normal work of the internal system must be clean. Contamination of the hydraulic system is unavoidable before new equipment can be operated or after a major overhaul has occurred. It is possible to introduce contaminants into the system during installation of the hose, pipe and fittings. Even if the new oil will also contain some unexpected pollutants straightening machine. Measures must be taken to filter out the contaminants as soon as possible, otherwise malfunctions may occur shortly after the equipment is put into operation, and early failures are often severe and some components such as pumps and motors can potentially be fatal.
The purpose of system flushing is to eliminate or minimize the early failure of the equipment. The goal of flushing is to improve the cleanliness of the fluid and to maintain the cleanliness of the system fluid within the tolerances of the critical hydraulic components within the system to ensure the reliability of the hydraulic system and the service life of the components

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Second, the cycle flushing device
Circulating flushing devices generally use a separate high-flow high-pressure flushing device or the system of the pump station for the operation of the pipeline cycle flushing operations. According to the parameters of the metallurgical hydraulic system, the flow rate of the high pressure pump (31.5MPa) is configured to 250 liters / min. The flow rate of the high-pressure flushing device is not less than 1000 liters / min. Min, 160 l / min, 100 l / min, 63 l / min and low pressure pump (2.5 MPa) 400-600 liters / min can constitute different rinse pressure \ flow needs.
The output tubing interface of the recirculation unit should allow both the flush pump output flow and the rinse circuit to be flushed simultaneously, as well as to flush multiple independent flushing circuits simultaneously.
Using the working pump station of the system copper busbar bending machine itself is more and more widely applied and recognized. The working pipeline pumping system piping flushing is a reliable and fast way to achieve the quality of flushing and has more advantages, Specific performance in saving precious time schedule, saving a lot of temporary piping materials, can use the work of the pumping station itself, the formal electrical protection and system cooling cycle, the internal loop filter makes the system better and faster flushing effect.
Third, the cycle of washing steps
Cycle is generally divided into the hydraulic pump station to control the main valve pipe frame flushing and control valve rack to the oil tank and oil motor branch pipeline rinse. In accordance with the requirements of the pipeline flushing accuracy is divided into the middle of the pipeline and the rough rinse of all the pipeline rinse.
Hydraulic pump station to control the main pipeline flushing circuit is relatively simple, only the end of the main channel will be connected.
Control valve rack to the oil tank and oil motor branch of the pipeline is relatively more complex. Sometimes need to make a lot of temporary flushing piping to form a flushing circuit, then pay attention to the previously mentioned series and parallel washing should consider some of the factors.
Hydraulic system flushing, can be carried out as follows:
Before the installation of the sensing element (such as servo valves, etc.), the pipe and the pollutant insensitive components are assembled and the end of the pipe sealed tightly.
Replace the sensing element with a jumper wire, connect the hydraulic circuit and pressurize with water to achieve the specified cleanliness.
The selected flushing circuit should skip the sensing element and minimize flow resistance. Flushing should be avoided when the dirty oil has been rinse through the pipeline, for more complex systems, select the loop from the main branch to the main pipeline, and then separated from the main road and then flush the main channel, the flushing circuit Back to the oil on the road, the installation of oil filter or filter, the initial washing more impurities, the general use of 80 mesh filter, wash later switch to more than 150 mesh filter.
In order to improve the flushing effect, the process of washing the pump to intermittent movement is better, the intermittent time is generally 10 to 30 minutes, can be detected in this intermittent time flushing effect. In the flushing process, in order to facilitate the pipe wall attached to the fall off, you can use a wooden Dished Head Punching Machine stick or rubber hammer and other non-metallic hammer gently percussion pipe, continuous or intermittent percussion.
The choice of flushing medium is usually the actual use of hydraulic oil or test oil. Avoid the use of alcohol, steam, etc., to prevent corrosion of hydraulic components, pipes, fuel tanks and seals and so on.
Rinse the amount of the general working capacity of the tank to 60% to 70% is appropriate, not too long rinse time, usually 2 to 4 hours, in exceptional circumstances no more than 10 hours. Flushing effect to the loop filter pollution-free impurities as the standard. Rinse the hydraulic oil after the need to go through quality testing to determine whether to continue to use.
Flushing process should also note:
(1) the fuel tank to be closed to reduce the particles in the air into the tank the opportunity to air;
(2) phase tank with flushing oil should be used when the filter with the fuel car to filter out the barrels of oil pollutants;
(3) to replace the filter to suspend the washing pump, be careful not to bring impurities;
(4) to emptying and sewage to be carried out regularly to ensure that the system is full, and timely discharge of gases and pollutants.
(5) in the pre-washing, oil evaporation is very important in the flushing tank should have steam escape the window.
(6) After washing out the flushing oil, pipelines should pay attention to protection before use, so as not to enter the system of pollutants.
Fourth, the parameters of the cycle flushing
To get a good flush quality selection cycle flushing pressure and flow is a very important guarantee. Generally 30-40 units of the hydraulic system circuit flushing accuracy for the NAS7 level when the flushing time is often 10-15 days for the hydraulic servo system when the required accuracy of the flushing time for the  drilling machine NAS5 level even longer. For those projects with relatively short construction period, it is urgent to accelerate the flushing progress of the hydraulic system and shorten the flushing time. It can be said that it is the late construction of a very difficult problem.
To achieve the desired flushing effect, the Reynolds number at the time of flushing must be around 4000 (we know the critical Reynolds number Re (L) = 2200-2300 for a smooth round-walled pipe). Engineering practice tells us after pickling pipe carbon steel pipe flushing cycle of each unit circuit 3-4 hours after the test oil sample cleanliness basically reached NAS6-7 level, when the washing circuit short oil sample cleanliness even to NAS4 -5. We know that the Reynolds number is related to the size of the pipe, the velocity of the medium in the pipe, and the kinematic viscosity of the medium. Reynolds number of the formula
Re = υ × ρ × D – 2 ⁢ δ × 10 – 3 / λ * 10 – 6
In the formula:
Re ——————– – Reynolds number for pipeline flushing;
Υ ——————– is the flow rate in pipe flushing, in meters per second;
Ρ ——————– is the density of the medium during pipeline flushing, ρ = 910 for hydraulic oil;
Λ ——————– for the pipeline when the media’s kinematic viscosity, with oil temperature changes, the unit is Shi;
Δ ——————– for the pipe wall thickness, the unit is mm
D ——————— is the diameter of the pipe, in millimeters.
The pressure loss along the cell flushing circuit with diameters above DN50 is very small and the pressure loss of the unit circuit for rinsing a pipe length of 100 meters will not exceed 10 bar. And a pressure loss of more than 150 bar for a piping unit circuit that flushes one hundred meters of DN10 or DN15.
The above is when the use of 46 # hydraulic oil (40Co viscosity value) when flushing data, but the general ambient temperature, such as the ambient temperature is 25Co, 46 ​​# hydraulic oil viscosity of 105Cst, so the pressure along the rinse The loss is greater. Normal flushing oil washing oil temperature required in the 40Co — 60Co between the following gives the oil temperature at 50Co when some of the flushing data, the same diameter metal punching equipment of the flow is only about 60% of the original, the pressure loss along the way only The front 30% – 40%.
Recommended flushing circuit flow selection According to the data in the table above, at the beginning of the initial flushing process, the Reynolds number is less than 4000 because the normal flushing temperature has not been reached. However, after a period of time, the oil temperature will gradually increase, Of the pressure will be a corresponding decline in the normal washing temperature to reach about 3-4 hours after the sampling test was flushing the unit circuit cleanliness can meet or exceed the system requirements for cleaning the next unit circuit flushing.
Fifth, summary
After the assembly of the system washed into the new hydraulic system is absolutely necessary, any lucky to give up cleaning will bring fatal damage to the equipment beveling machine. After a strict rinse, you can reduce and avoid system debugging and early operation of the fault, shorten the debugging cycle of the system to reduce unnecessary losses. However, the system’s pollution control is an ongoing process, not once and for all, during the operation of the system but also regularly detect the oil state, and control of pollutants to ensure that the system allows cleanliness within the allowable range.