Vacuum generator is a new, efficient, clean and economical vacuum component using compressed air source to generate negative pressure. Vacuum generator has the advantages of small size, high vacuum, convenient installation and maintenance, good reliability and so on. It is widely used in industrial automation, machinery, electronics and robotics and other fields. In industrial automation machines, vacuum adsorption devices are used in the upper boxes and top covers of the box machinery, the carton forming of the packing machines, the delivery and delivery of labels in the packing machine, and the labeling and supply of labels in the labeling machines. In this kind of machinery, a common characteristic is that the required vacuum flow rate is small, the vacuum requirement is not high, and most of them are intermittent. The use of conventional vacuum pumps to provide a vacuum source is not only complicated in mechanical structure, but also affects the reliability and efficiency of the machine due to the long vacuum response time. The vacuum generator and sucker with adsorption, can be a variety of material handling, especially suitable for the adsorption of fragile, soft, thin non iron nonmetallic materials or spherical objects, a There is nothing comparable to this advantage, plays an increasingly important role in automatic production.
2. The structure and performance analysis of the vacuum generator
2.1. The structure of the vacuum generator
The vacuum generator consists of 3 parts: the nozzle, the adsorption chamber and the diffusion chamber. The principle of the vacuum generator is to use jet nozzle to jet air at high speed, and form a jet at the outlet of nozzle to produce entrainment flow. Under the action of suction, the air around the nozzle outlet is sucked continuously, so that the pressure in the adsorption chamber drops below atmospheric pressure, forming a certain degree of vacuum.
From fluid mechanics, the continuity equation for incompressible air is:
In the formula, the section area of A1 and A2- pipes is m2, and the velocity of flow of V1 and v2- is m/s.
The upper section shows that the cross section increases, the flow velocity decreases, the cross section decreases, and the flow velocity increases.
For horizontal pipes, the Bernouri equation of incompressible air is
P1+1/2 P v12=P2+1/2, P V22
P1, P2- A1, A2 section of the corresponding pressure, type Pa; V1, v2- A1, A2 section of the corresponding velocity, m/s; P - air density, kg/m2. From the upper model, the flow rate increases and the pressure decreases. When v2>>v1, P1>>P2. When the V2 increases to a certain value, the P2 will be less than one atmospheric pressure, which will produce negative pressure. Therefore, the negative pressure can be obtained by increasing the flow velocity and the suction is generated.
2.2. Performance analysis of vacuum generator
(1) the main performance parameters of the vacuum generator
Air consumption: the amount of flow that flows out of a nozzle;
Vacuum flow: refers to the air flow from the adsorption port;
Vacuum: the difference between the absolute pressure of the atmosphere and the vacuum. When the suction port is completely closed, that is, when the amount of exhaust is zero, the vacuum of the cavity is called the maximum vacuum;
Adsorption response time: the adsorption response time is an important parameter to indicate the performance of the vacuum generator. It is the time required to reach a necessary vacuum from the reversing valve to the system circuit.
(2) the main factors affecting the performance of vacuum generator
The minimum pass performance of vacuum generator and nozzle diameter, nozzle diameter, receiving tube entrance shape and size, diffusion chamber volume, the nozzle and the receiving tube of the relative position and size of the air pressure.
The adsorption response time is related to the volume of the adsorption chamber (including diffusion chambers, adsorption pipes and suction cups, or the volume of the closed chamber, etc.). Usually the equation is:
T= (V/c) 1/a
The t- adsorption response time, s, V-, total suction capacity, L, c- tightness coefficient are related to the tightness of the sucker and the adsorbate; the response coefficient of the a- vacuum generator.
For a certain vacuum requirement, if the volume of the adsorption chamber is smaller, the response time is shorter; the greater the contact surface tightness is, the shorter the adsorption response time is.
(3) selection of vacuum generator
Vacuum generator selection should first according to the conditions of adsorption surface structure, surface status estimation of suction vacuum flow, according to the size minimum through the vacuum generator nozzle suction vacuum flow path; if the adsorption volume, and the adsorption speed and nozzle diameter should be minimum through some. The vacuum generator should be selected to meet the operation requirements under the premise should try to reduce its air consumption, gas consumption and compressed air of the working pressure, the greater the pressure is, the larger the gas consumption, but does not increase the degree of vacuum, so the hour determine the vacuum value, should pay attention to the relationship between the improved system working pressure and gas consumption.
3. Application of vacuum generator in automatic labeling machine
In the packaging machinery, plastic bags, cartons and labels and other light books for the supply and packaging, usually vacuum suction device.
The vacuum generator is a compact and economical vacuum component. It can be used in the place of positive pressure air source, which can greatly simplify the vacuum circuit. The utility model has the advantages of reducing the manufacturing cost of the machine, improving the reliability of the machine, and realizing the high-speed and automation of the machine, and has wide application prospect.
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