1. Main Performance Parameters of Vacuum Generator
(1) Air consumption: refers to the flow rate qv1 from the nozzle.
(2) Inhalation flow rate: refers to the air flow qv2 inhaled from the suction port. When the suction port is open to the atmosphere, the maximum inhalation flow rate is called the maximum inhalation flow qv2max.
(3) Inhalation port pressure: recorded as Pv. When the suction port is completely closed (such as suction cup sucking workpiece), that is, when the suction flow is zero, the pressure in the suction port is the lowest, recorded as Pvmin.
(4) Suction response time: Suction response time is an important parameter to show the performance of the vacuum generator. It refers to the time from the opening of the reversing valve to the attainment of a necessary vacuum degree in the system loop.
2.2. Main factors affecting the performance of vacuum generator
The performance of the vacuum generator is related to the minimum diameter of the nozzle, the shape of the shrinkage and diffusion tube, the diameter, the corresponding position and the pressure of the gas source. Figure 2 shows the relationship between suction inlet pressure, suction flow rate, air consumption and supply pressure of a vacuum generator. The graph shows that when the supply pressure reaches a certain value, the pressure at the suction inlet is lower, and then the suction flow reaches its maximum. When the supply pressure continues to increase, the pressure at the suction inlet increases, and then the suction flow increases. The quantity decreases.
(1) Characteristic analysis of maximum inhalation flow qv2max: The ideal qv2max characteristic of vacuum generator requires that qv2max be at the maximum value in the range of common supply pressure (P01=0.4-0.5MPa), and the change of qv2max is gentle with P01.
(2) Characteristic analysis of pressure Pv at suction port: The ideal PV characteristic of vacuum generator requires that in the range of common supply pressure (P01=0.4-0.5 MPa), Pv is at the minimum, and the change of Pv1 is gentle.
(3) Under the condition that the noise of the suction port is completely closed, the relationship between the pressure Pv at the suction port and the suction flow rate is shown in Figure 3. In order to obtain an ideal matching relationship between the pressure at the suction port and the suction flow rate, a multi-stage vacuum generator can be designed and assembled in series.
(4) The length of the diffuser should ensure the full development of all kinds of wave systems at the nozzle outlet, so that the approximate uniform flow can be obtained at the outlet section of the diffuser pipeline. However, the friction loss of the pipe wall increases when the pipe is too long. In order to reduce energy loss, an expansion section with an expansion angle of 6 8 can be added to the outlet of the straight diffuser pipe with an expansion angle of 6 - 8.
(5) The adsorption response time is related to the volume of the adsorption chamber (including the diffusion chamber, the adsorption pipeline, the suction cup or the airtight chamber), and the leakage of the adsorption surface is related to the pressure at the suction port. For certain pressure requirements at the suction port, the smaller the volume of the suction chamber, the shorter the response time; if the pressure at the suction port is higher, the adsorption volume is smaller, and the surface leakage is smaller, the suction response time is shorter; if the adsorption volume is larger and the suction speed is faster, the nozzle diameter of the vacuum generator should be larger.
Vacuum generator should reduce its gas consumption (L/min) on the premise of meeting the requirements of use. The gas consumption is related to the supply pressure of compressed air. The greater the pressure, the greater the gas consumption of vacuum generator. Therefore, the relationship between supply pressure and air consumption should be paid attention to when determining the pressure duty hours at the suction port. The pressure at the suction port produced by the generator ranges from 20 kPa to 10 kPa. At this time, the pressure at the suction port will no longer decrease, but the gas consumption will increase. Therefore, to reduce the pressure at the suction port should be considered in terms of controlling the flow rate.
_Sometimes, due to the shape or material of the workpiece, it is difficult to obtain a lower pressure at the suction port, and the pressure at the suction port rises due to the suction edge or the suction of air through the workpiece. In this case, it is necessary to select the size of the vacuum generator correctly so that it can compensate for the pressure at the suction port caused by leakage. Rise. Because it is difficult to know the effective cross-section area at the time of leakage, a simple test can be used to determine the pressure rise at the suction port caused by leakage. Since it is difficult to know the effective cross-section area at the time of leakage, the leakage rate can be determined by a simple test. The test circuit consists of workpiece, vacuum generator, suction cup and vacuum meter. It consists of the display reading of the vacuum meter and the performance curve of the vacuum generator. It is easy to know the leakage rate.
When considering leakage, the characteristic curve of the vacuum generator is very important to determine the vacuum generator correctly. Leakage is sometimes inevitable. When there is leakage, the method to determine the size of the vacuum generator is as follows: add nominal suction flow and leakage flow to find out the size of the vacuum generator.