How to remove air from a can
Remove the air of their cans in various ways, one of them: IR-eksgaustirovanie. For infrared exhaust, electric emitters of the type KI-220-1000 are most suitable. They are tubular quartz incandescent lamps connected to an alternating electric current network of 220 V. The lamp is mounted in a quartz tube, on the axis of which is a tungsten spiral, which is the glowing body. The maximum radiation of such a lamp falls at a wavelength of about 1 micron. It is this region of the short-wave infrared spectrum that has the greatest penetrating power, which, however, does not exceed a few millimeters. Interacting with the material of the product, the infrared flux is converted to heat. By concentrating in a small volume of the surface layer a high energy density of the order of 60 kW / m2, it is possible in a very short time to raise the temperature of the material to high values close to 100 ° C.
Scheme of irradiation of cans with canned infrared rays during a heat recovery. IR emitters are located at the level of free space on both sides. Since the glass passes the infrared rays well in the short-wave part of the spectrum, the radiation easily penetrates into the jar, and the surface layer undergoes direct heating. To obtain a directed flux of radiant energy, the lamps are positioned at the focus of parabolic reflectors of anodized aluminum. With this arrangement, the surface layer of the product and the metal lid are heated at the same time.
The jars to be exhasted are covered with lids and sent to the exhauster conveyor passing through the tunnel along which the IR emitters are located along the sides. In the area of infrared radiation, banks with the product are exhausted for 20-60 s. Upon exiting the tunnel, the banks enter the conveyor of the sealing machine and immediately become sealed.
Mechanical exhausting consists in suctioning air from the can with the help of a vacuum pump.This process is carried out on vacuum-sealing machines, in the chamber of which, preceding the process of sealing, a vacuum is created.
It is necessary, however, to say that mechanical exhaustion can be used in relation to the limited name of canned fruits and vegetables, due to the phenomenon of so-called vacuum expansion. This phenomenon lies in the fact that the fruits, getting into a rarefied atmosphere, increase in volume due to the expansion of air in the intercellular spaces of plant tissue. The increase in the volume of fruits leads to the outflow of a certain amount of the liquid part of the canned food from the can.
It turned out that different fruits and vegetables expand in different ways, falling into a rarefied atmosphere, apparently due to different air content in the intercellular spaces, different elasticity of cell walls, etc. Therefore, to observe the desired ratio of canned components between the solid and liquid part and prevent losses pouring it is necessary to limit the amount of vacuum that the vacuum pump allows to create, a value of about 400 mm Hg. Thus, in some cases, the natural properties of the preserved raw materials limit the efficiency of mechanical exhaust by 50% (400/750 • 100).
Thus, taking into account this coefficient, it turns out that on average, with the help of mechanical ekshauustirovaniya fruit and vegetable canned food can create a vacuum in the bank to the beginning of sterilization, in fact, only in the range of 150-200 mm Hg. Art., i.e., the degree of exhaustation does not exceed 20-25%. True, it should be noted that the phenomena of vacuum expansion and vacuum absorption can be weakened by blanching plant raw materials before packing, that is, by removing a part of the air from the fruit before packing them in a container.
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