As early as the early 1970s, screw compressors were manufactured and applied in China. At that time, the defects in manufacturing precision and service life, to some extent, contained the breadth and depth of its development. Until the reform and opening up, foreign advanced bearings, seals, control instruments, etc. have been introduced or joint venture production, and the design and manufacturing technology of screw compressors have been introduced by foreign advanced equipment, management concepts or joint venture production, and have developed rapidly. , gradually entered the fields of petroleum refining, coal chemical, fine chemicals and so on.
2 Overview of screw air compressor
The screw air compressor is a single-stage twin-screw compressor with oil injection. It adopts high-efficiency pulley (or shaft) transmission to drive the main body to rotate for air compression. The main combustion chamber is cooled and lubricated by injection, and the air discharged from the compression chamber is compressed. The oil mixed with the oil is separated by coarse and fine separation, and the oil in the compressed air is separated to finally obtain clean compressed air.
The twin-screw air compressor has excellent reliability, light weight, low vibration, low noise, convenient operation, less wearing parts and high operating efficiency.
3 screw compressor principle introduction
The screw compressor cylinder is provided with a pair of intermeshing helical male and female rotors, and both rotors have several concave teeth, and the two rotate in opposite directions. The gap between the rotor and between the casing and the rotor is only 5-10 filaments. The main rotor (also known as the male rotor or the convex rotor) is driven by the engine or electric motor (mostly driven by a motor), and the other rotor (also called The female rotor or the female rotor is driven by the oil film formed by the main rotor by injection or by the synchronous gears of the main rotor end and the concave rotor end. The length and diameter of the rotor determine the compressor displacement (flow) and exhaust pressure. The longer the rotor, the higher the pressure; the larger the rotor diameter, the greater the flow.
The spiral rotor groove is filled with gas as it passes through the suction port. When the rotor rotates, the rotor groove is closed by the casing wall to form a compression chamber. When the rotor groove is closed, the lubricating oil is sprayed into the compression chamber to seal. Cooling and lubrication. When the rotor rotates to compress the lubricant + gas (referred to as the oil and gas mixture), the volume of the compression chamber is reduced, and the oil and gas mixture is compressed toward the exhaust port. As the compression chamber passes through the exhaust port, the oil and gas mixture is discharged from the compressor to complete an aspiration-compression-exhaustion process. Each rotor of the screw machine is supported by an antifriction bearing that is held by an end cap near the end of the shaft. The intake end is supported by a roller bearing, and the exhaust end is supported by a bearing which is usually a discharge end supported by a pair of tapered roller rollers, that is, a thrust bearing, resisting axial thrust, and receiving radial load, and Provides the minimum clearance required for axial operation.
The working cycle can be divided into three processes of inhalation, compression and exhaust. As the rotor rotates, each pair of intermeshing teeth successively complete the same duty cycle.
4 advantages of screw compressor
(1) The screw compressor is the same as the piston compressor and belongs to a positive displacement compressor. The screw air compressor has the following advantages in terms of the effect of use.
(2) High reliability. The screw compressor has few parts and no wearing parts, so it runs reliably and has a long service life. The interval between overhauls can reach 4 to 80,000 hours.
(3) Convenient operation and maintenance. The screw compressor has a high degree of automation, and the operator does not have to undergo long-term professional training to achieve unattended operation.
(4) The power balance is good. The screw compressor has no unbalanced inertia force, and the machine can work smoothly at high speed, which can realize no-base operation. It is especially suitable for mobile compressors. It is small in size, light in weight and small in floor space.
(5) Strong adaptability. The screw compressor has the characteristics of forced air transmission. The volume flow is almost independent of the exhaust pressure, and it can maintain high efficiency in a wide range. It can be applied to various working conditions without any change in the structure of the compressor.
5 screw compressor has problems
In the past, reciprocating compressors were more aware than other types of compressors, and screw compressors were not easy to adopt. Now there are significant improvements in the installation, commissioning, maintenance and repair technical capabilities, management capabilities, and cultural level of screw compressors. There are fewer wearing parts for screw compressors, long operating cycles, and resistance to liquids and gases. Dust, tar-resistant, large gas transmission and small unit size have a full understanding, they hope to use screw compressors in some special process sections.
(1) In order to meet the requirements of low pressure and atmospheric volume, it is bound to increase the capacity of the cylinder. At present, the diameter of the first-stage cylinder has been broken to record 1.5m, and often requires two or even three parallel connections. The problems brought are as follows.
1 requires large-scale processing equipment for each component to increase manufacturing costs; 2 affected by the column spacing of the compressor, the maintenance space becomes narrow and difficult to maintain; 3 the process of giving a conventional pressurized cylinder liner due to too large cylinder bore Bringing the challenge, if there is no cylinder liner, once the mirror wears out (this is inevitable), you can only replace the entire cylinder block! The economic loss is quite large; the four large cylinders must use the atmospheric valve, install and replace the atmospheric valve, just like lifting the barbell piece, the labor intensity of the worker is quite large; 5 with a large piston body, it is bound to increase the friction of the support ring. Accelerate the damage of the support ring.
(2) Air valve, piston ring is a wearing part, especially when the gas contains coal tar, dust and other harmful substances, its life is greatly shortened, and the shutdown rate is increased.
(3) The large-scale piston machine and its inherent overturning moment require the construction of a large-scale workshop and a deep foundation.
(4) The water content in the body is high, and it is easy to cause a liquid impact accident if it is not noticed.
(5) To reduce the pulsation of the airflow, a large buffer is required.
(6) The spare parts of the plug-in spare parts are mixed, the quantity is large, and the service life is short. It is required to have a spare parts warehouse and professional management personnel, and occupy more inventory funds.
It is this change that was first reflected in the air screw compressor. The reciprocating air compressor that was relished in the user's mouth a decade ago is no longer being lifted, but instead is an air screw compressor. This demand has greatly stimulated the manufacturers of air screw compressors. In addition to foreign famous manufacturers who have seized the beach heads, there are no fewer than one hundred new domestic manufacturers. Many of them use foreign air screw compressors. The head is assembled in China.
6 gas screw compressor manufacturing process characteristics
Compared with the rapid development of the air screw compressor manufacturing industry, the relative calm of the process gas screw compressor manufacturing industry is due to its higher threshold.
(1) The gas screw compressor is a non-standard product, and the single-piece small batch is basically a pattern of one machine. It was decided that it needed a strong design team. Not only the design workload is large, but also requires "professional". It involves machine, electricity, control, container, pipeline, structural parts and so on. Although some aspects can be resolved through "outside", they are often constrained by "delivery time." (2) Like the gas screw, you can buy a screw head to assemble outside. According to different process gas parameters, choose the rotor diameter and material, speed, sealing, etc., when developing new models, you need professional Rotor milling cutter designer. (3 compressors need to be processed compared with reciprocating compressors, although much less, but also very specific. Need several different rotor diameter range, more different specifications (at least one set of products) Positioning to determine its specific specifications) Rotor machining CNC milling machine, this milling machine is expensive and has a single function. In addition to machining the rotor, other functions are not available. Others, such as housing processing equipment can be considered externally.
7 Conclusion
In view of the increasing market acceptance and acceptance of screw compressors; in view of the market demand and huge economic benefits of screw compressors; and in view of the challenges of the continuous updating of screw compressor design and production technology, in China, the process gas screw is promoted. A good time for the development of compressors has arrived. The pattern of focusing on a few productions will certainly be broken, which will surely bring new impetus to the development and promotion of the technology and production level of our country's process screw compressors.
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