Talking about screw compressor

Talking about screw compressor

It has become an inevitable trend to use highly reliable screw compressors to replace piston compressors with many wearing parts and poor reliability. Japan's screw compressors accounted for only 27% in 1976, and rose to 85% in 1985; the current market share of screw compressors in western developed countries is about 80%, and it maintains an upward trend. Screw compressor has the advantages of simple structure, small size, no wearing parts, reliable work, long life, simple maintenance and so on. There are two types of screw compressors: twin screw and single screw.

　　 One, twin screw compressor

　　 The two screws of a twin-screw compressor are actually a pair of helical gears, whose tooth profile has a significant impact on energy consumption. In addition to satisfying the conjugation condition and ease of processing, the tooth profile must have good axial and lateral air tightness and a larger volume (in order to obtain a larger displacement) and a larger exhaust port (in order to reduce the airflow speed )Wait. The tooth profile is mainly composed of cycloid and arc. The improvement of the tooth profile has roughly gone through three generations (Figure 1). The first generation is symmetrical. The second generation is an asymmetric type represented by the X type. The third-generation tooth profile is characterized by bringing the potential of symmetrical and asymmetrical tooth profile parameters and material strength close to the limit. The most prominent of these is the 5:6 star tooth from Kaiser, Germany, which breaks the traditional 4:6 The gear ratio is about 10% more energy-efficient than the second-generation tooth profile.

figure 1

　　 Although my country has made great progress in the research of tooth profile, it still relies on introduction. In 1983, Wuxi Compressor Factory introduced Atlas Company’s X profile to produce LGD series oil-injected compressors; in 1994, it introduced α profile from Kobelco to produce AL series dry compressors. Liuzhou and Italy jointly introduced star gears to produce LU series oil-injected compressors. Some domestic twin-screw compressor parameters are shown in Table 1.

Table 1 Parameters of some domestic twin-screw compressors

Production Plant Type 　

Number Volume Flow

m3/min working pressure

MPa Motor power

kW cooling water l/min noise

dB(A) Dimensions (L×W×

Height)mm weight

kg

No

Tin AL132X 20.1 0.7 132 183 78±6 1950×1300×1540 2600

ZL150X 22.18 160 208 78±6 2700

AL180X 29.37 185 258 77±6

2350×1550×1850

3700

AL220X 34.85 220 308 78±6 4200

LGD-317-X 3.4 0.7 22 ≤16.7 70±3 1450×835×1075 900

LGⅡ12B-6/7-D 6.36 45

≤60

73±3

2450×1100×1250 1100

LGⅡF12B-3/7-D 3.4 30

Wind cooling

73±3 2300×1100×1250 1050

LGⅡF12-7/7-D 7.32 55 73±3 2450×1100×1600 1200

Willow

State LU710-22A 3.4 0.7 22 Air cooling 75±3 1050×950×1498 550

LU910-37A 6.1 37 77±3 1450×1050×1640 720

LU910-75A 12.2 75 80±3 1700×1250×1960 1200

LU1000-132A 22 132 82±3 2280×1200×1770 2800

LU2000-160A 30 160 82±3 3150×2000×2100 4000

LU2000-250A 43.2 250 82±3 3150×2000×2100 5000

　　 The life of screw compressors is mainly limited by bearings. Foreign twin screw compressors use specific bearings and can run for 30,000 hours for overhaul. Sullair claimed that their products were overhauled for 100,000 hours.

　　 Two, single screw (worm) compressor

　　The screw of the single screw compressor (Figure 2) meshes with two star wheels at the same time, which not only doubles the displacement but also makes the screw force fully balanced, thus has a series of advantages:

1. Screw 　 2. Star wheel 　 3. Spindle

4. Exhaust port 　 5. Suction cavity 　 6. Body

figure 2

　　① The screw has no bending deformation, less vibration and low noise. ② It can work under high pressure. For example, the single-screw process compressor developed by the American Dresser Rand (D.r) in the late 1980s can reach 6.16MPa under the condition of one-stage compression. ③The meshing pair can work in a small gap to reduce leakage, and the clearance volume is zero, so the volumetric efficiency is high and the energy consumption is low. At present, single-screw and twin-screw compressors have equivalent energy consumption indicators for oil-injected compressors. In oil-free compressors, due to the significant reduction in viscous shear loss, the energy-saving advantages are obvious: the large oil-free compressors in the 1990s The performance of the screw chiller has fully reached or surpassed the z* energy-saving turbo chiller, becoming a modern z* best refrigeration compressor; the American Grimeyer*Schmidt company claimed that their water spray list The screw compressor, even under the condition of one-stage compression, saves 20% energy than a two-stage twin-screw compressor (also saves a compressor and its floor space, reduces maintenance costs and improves reliability). ④Because the bearing force is small and the bearing size is not as restricted as the twin screw, the life of the standard ball bearing can reach 50,000 hours, and the tapered roller bearing is 100,000 hours. The "maintenance-free" time of the whole machine is also For 50,000 to 100,000 hours. The performance comparison of single screw compressor, piston compressor and twin screw compressor is shown in Table 2 and Table 3. Although single-screw compressors came out later than twin-screw compressors, they have a strong upward trend due to their excellent performance. At present, single-screw compressors and twin-screw compressors are equally divided in the international market.

Table 2 Comparison of low-pressure air compressors (extracted from U.S. Navy data)

Item Piston compressor Single screw compressor

Characteristic Exhaust pressure MPa 0.875 0.875

Exhaust volume　m3/min 5.66 5.66

Specific power　kW/(m3.min-1) 7.11 6.32

Volume　m3 3.96 2.40

Weight　kg 1687 1497

Number of moving parts 60 3



Reliability index Average repair time　h 3.0 0.8

z*Overhaul time　h 7.0 3.38

Average preventive maintenance time 　h/month 1.5 0.02

z*Maximum preventive maintenance time　h/month 2.5 0.04

Mean failure cycle　h 6000 7239

Table 3 Comparison of single-screw and twin-screw compressors (taken from the data of CP company in the United States)

Comparison items Single screw compressor Twin screw compressor

Balance of forces 　The force is fully balanced, the life of each bearing component is long, and the machine life is long. 　The force is unbalanced, and the life of the bearing and the machine is affected.

Noise level

　 quieter operation

　 10～15dB(A) higher than single screw

Maintainability

　Can be repaired on site

Requires skilled workers or manufacturer to maintain

Operating temperature 　

The operating temperature is low, the oil temperature is low, and the parts have a long life. 　

The exhaust temperature is 16℃ higher than that of a single screw Transmission mode 　

Direct transmission, no gear 　With gear transmission power loss and failure

Friction situation 　

Small friction, high efficiency, low operating cost 　High efficiency, high operating cost 　　 Japan's Mitsui Company is a famous manufacturer of single screw compressors in the world, and its early products are shown in Table 4. In recent years, new products have increased the displacement under the same motor power, and changed the split body to an integral type, realizing computer single control or group control. The process compressor produced by D.r company j* is shown in Table 5.

　　 Domestic development of single screw compressors began in 1975. The tooth profile of the star wheel has a significant impact on the life of the meshing pair. Domestic experts believe that the tooth surface of the star wheel is the envelope surface of the screw (Figure 3) and can only be processed with a hob; there are two meshing lines between the envelope surface and the screw. For more than 20 years, the manufacturing technology of the hob has not been solved, and the envelope surface can only be approximated by the profiling method, and the processing accuracy is low. We use a digital model to study the hobbing process of the meshing pair and find that the tooth surface of the star wheel can be composed of an envelope surface and a characteristic surface. In addition to the two meshing lines on the envelope surface, there are also characteristic surfaces between the tooth surfaces. The other meshing line, the characteristic surface is also called the third meshing area, that is, there are three meshing lines between the tooth surfaces. Due to the existence of the third meshing zone, the actual working tooth surface of the star wheel is 5 times larger than the envelope surface, which reduces the load on the unit meshing line and increases the life of the meshing pair by more than 6 times under the same accuracy conditions. This is not only a major breakthrough in meshing theory, the research method is also advanced and accurate than foreign test methods, and it successfully solves the high-precision machining technology of this three-mesh area tooth profile under mass production conditions (including star wheel tool ), so it has practical value.

image 3 Table 4 　 Main parameters of Mitsui single screw compressor Model Volume flow

m3/min working pressure

MPa Motor power

kW speed

r/min Cooling method Dimensions (length×width×height)

mm total weight

kg

Z-085A

Z-086A 1.0 0.7 7.5 3100 air cooling

1050×750×1075

315

Z-115A

Z-116A 1.5 11 4400 1050×750×1075 330

Z-155A

Z-156A 2.0

15

　 　 　 ZM19 2.6 0.7 18.5 2950 water cooling

1320×940×1440

590

ZM22 3.2 22 3550 1320×940×1440 590

ZM30 4.6 30 2950 1410×1100×1610 765

ZM37 5.6 37 3550 1410×1100×1610 765

PZM45-W5 7.0 45 2950 2000×1040×1820 1600

PZM55-W6 8.5 55 3550 2000×1040×1820 1600

PZM60-W5 10.0 60 2950 2100×1160×1950 2350

PZM75-W5 12.0 75 2950

2100×1160×1950

2350

Table 5

　 Parameter of single screw compressor for TVC process of D.r.

Displacement

　m3/min

(3600r/min) Single-stage double-stage

Xu 　 use 　　 large 　 work 　 work 　 pressure 　 force 2.49MPa 3.85MPa 6.16MPa 2.49MPa 6.16MP

4.047 —— —— TVC15HP —— ——

6.34 —— TVC17 TVC17HP —— ——

8.46 TVC19 TVC19D TVC19HP —— ——

12.14 TVC22 TVC22D —— TVC2215 TVC2215HP

16.22 TVC24 TVC24D —— TVC2417 TVC2417HP

23.6 TVC27 TVC27D —— TVC2719 TVC2719HP

31.05 TVC30 TVC30D —— —— ——

Theoretically, the star wheel has three teeth participating in the meshing at the same time, and each tooth has three meshing lines. To achieve three-tooth and three-line meshing, the screw and the star must be machined with a high-precision special machine tool. The number of teeth of the star: the number of screw heads is It is quite difficult to ensure that the transmission chain error is less than or equal to 15" (arc seconds) under the condition of 11:6. We have successfully developed a special machine tool that can meet the above-mentioned processing requirements. The meshing pair with three meshing areas is processed by this machine It is used for 3m3/min single screw air compressor. It has been tested by the National Compressor Quality Supervision and Inspection Center and other units. It is proved that the volumetric efficiency is 5% higher than that of similar foreign products, the operating time is 5 times longer than the foreign acceptance standard, and no displacement drop is found. .

　　The auxiliary system of single and twin screw compressors is the same, and the difference lies in the main engine. As mentioned above, the life of the screw compressor main engine depends on the bearing. The main engine overhaul is mainly to replace the bearing. The overhaul period of the domestic twin screw main engine is about 25,000 hours. The screw compressor has a complete control system and protection system, which can run automatically without being on duty, and some have achieved computer control, with fewer circuit faults. Since screw compressors are not allowed to reverse, some compressors are equipped with anti-reverse devices in the circuit. When the compressor fails to run after connecting to the power supply, it may be that the phase of the power supply is wrong, just change any two-phase connectors in the three-phase power supply. Because single-screw compressors have low vibration, do not need a good foundation and fixation, and can move the working place at will, most single-screw compressors are equipped with anti-reversal devices, while twin-screw compressors often need to test the phase of the power supply when installing! In the air system, the cooler, oil filter and air filter should be inspected or cleaned usually every three months or 500 hours of operation. The oil and oil filter should be changed every year or 1000 hours of operation. When the pressure drop of the oil-air separator filter element exceeds 0.1MPa, it should be replaced. In addition, the failed seals (seal ring, O-ring, etc.) need to be replaced in time.