Vacuum Water Absorption Technology

The application of vacuum water absorption in printing and dyeing is mainly after water washing, before drying, and when the woven fabric comes out of the alkali reduction steamer, the residual lye is sucked out to reduce the burden of washing; as a vacuum chemical recovery device. This article focuses on vacuum dehydration. 1 How It Works To understand vacuum dehydration, it is first necessary to understand how water is present in fabrics. Water exists in fabrics in two ways: bound water and unbound water. The bound water is water that chemically combines with the fibers. It cannot be removed by vacuum. Instead, it needs heat to destroy the chemical bonds and the water can be released from the fabric. The non-bonded water is not chemically bonded to the fibers, but the surface tension is not Attached very firmly to the fabric, the moisture is removed from the fibers and the yarn gap as the air is drawn through the fabric. This is how vacuum suction works.

There are mainly two types of suction ports used when the fabric is dehydrated.

The fabric vacuum dehydration suction port indicates that all the vacuum suction devices at home and abroad are composed of the vacuum chestnut pipe-suction port and attachments.

The advantage of slot-type suction mouth is that the size of the suction mouth can be controlled by adjusting the positions of the left and right plates according to different fabrics and different vehicle speeds to achieve the best process effect. The herringbone slot suction structure is simple, and the fabric tension during operation can be significantly lower than the slot suction. The suction effect and the tension of the fabric as it passes through the mouth have a greater influence. According to actual measurement, when the polyester fabric tension is 80~90g/cm, the suction effect of the slit type suction mouth is the best; and when the tension of the same fabric is 20~30g/cm, the herringbone groove suction mouth has the best suction effect.

The dehydration process of the fabric by the vacuum pump can be regarded as: the air on one side of the fabric is under one air pressure, and the other side is in a certain degree of vacuum due to the work of the vacuum pump. Because of the pressure difference between the air on both sides of the fabric, the air will be worn. Pass through the fabric to remove moisture from the fibers. When the fabric is deflected and the exposed suction mouth is not sealed in time, the gas will enter the pipe from the exposed suction port because the resistance of the exposed suction port is less than the suction port covered by the fabric. Since the pumping speed of the vacuum pump is small, the air sucked from the exposed suction mouth will inevitably lead to a drop in the degree of vacuum in the suction pipe, so that the pressure difference across the fabric gas is reduced, resulting in a decrease in the suction capacity. On the other hand, due to the large amount of air entering the pipeline from the exposed suction, the pipeline resistance loss will inevitably increase. The formula is as follows: S - local resistance loss factor; V-air flow rate; Q-fan flow; - leakage area.

When the AP is increased to balance the resistance loss AP' with the air penetrating the fabric, the gas is again sucked into the pipe from the fabric cover. Because the Q value of the vacuum pump is small, when the A leakage port is slightly larger, it is difficult for the AP to reach equilibrium with the AP', so that the air is continuously exposed to the suction inlet and the suction port covered by the fabric does not reach the suction effect.

When using a vacuum pump to absorb water, its motor power is large, the domestic minimum is 15kW, the imported equipment is not less than llkW, and the noise is large during the T: operation process. If noise reduction is needed, an additional noise suppression device is needed to ensure the suction process. The degree of vacuum in the fabric requires a relatively high centering of the fabric. If the gap is not tightly closed, the suction capacity will be reduced. Therefore, complicated fabric centering devices must be provided.

According to the above reasons, when designing a vacuum suction device, our factory uses a high-pressure centrifugal fan instead of a vacuum pump.

When the centrifugal fan is used for dehydration, its working principle is also to achieve dehydration by creating a pressure difference between the two sides of the fabric. However, the centrifugal fan is used to make the gas gain energy by rotating the impeller blades. When the gas gets enough energy to overcome its resistance, the gas can be sent to a high place or a distant place. At this time, because the gas in the impeller center is sent away, a pressure difference will be generated between the air inlet and the impeller center. Because the high-pressure fan flow rate Q is 55.2m3/min is large enough, the leakage when the fabric is deflected will not be aspiration. This has a big effect, so that the discharge of the gas from the exposed suction pipe into the pipe will be quickly equilibrated with the air resistance AP' through the fabric, and the air will then pass through the fabric to carry away the water. In view of the above analysis, Our factory designed a vacuum suction device for a high-pressure centrifugal fan of a motor. See the suction capacity of the vacuum suction device and the vacuum pump suction device produced by the US TVE Company. The results are shown in the following table.

Table vacuum pump dehydration and high-pressure fan dehydration after the comparison of moisture content Variety vacuum pump dehydration after the moisture content, high-pressure fan dehydration moisture content, pure polyester-cotton cotton from the above table comparison data can be seen, both the suction effect is basically similar, The high pressure fan costs less than the vacuum pump. Therefore, replacing the vacuum pump with a high-pressure fan in the vacuum suction device has very significant economic benefits. The vacuum suction device of the high pressure centrifugal fan has been used in the alkali reduction combined machine and the padding and shaping combined machine manufactured by our factory. The user has a good response to the device, and it is believed that its performance is reliable and the structure is simple. At present, the vacuum suction of the high pressure fan is used. The device has the disadvantage of being unable to control the moisture content of the fabric in accordance with the process requirements. Vacuum pumps, on the other hand, can be controlled by adjusting their degree of vacuum, ie increasing the leakage. Therefore, our factory is considering to use the frequency converter to control the motor that drives the high pressure blower, and control the flow rate of the air inlet to control the moisture content of the fabric by controlling the rotation speed of the motor.

Whether it is a vacuum pump or a vacuum suction device of a high-pressure fan, the moisture content of the fabric after passing through the device is much lower than that after the rolling mill. For example, the cotton/cotton fabrics have a rolling allowance of 75%, and the moisture content after smoking is about 25%, thereby greatly reducing the energy consumption during drying or setting, and at the same time increasing the vehicle speed and achieving the purpose of increasing the productivity. Therefore, vacuum water absorption will be more and more widely applied to printing and dyeing.

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