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Air compressor main engine overhaul must pay atten

Screw air compressor is widely used. Regular maintenance and maintenance of air compressor is the premise to ensure its normal operation.

The main engine is the core part of the air compressor, which is in high-speed operation for a long time. It is similar to most running machines. After running for a certain period of time or years, it must undergo preventive overhaul, and the overhaul period is usually between 30000 ~ 40000h (4 ~ 5 years). Most mainframe overhauls will choose to return to the factory for overhauls or to be repaired by qualified maintenance companies.

Air compressor main engine overhaul must pay attention to several key issues

First, screw main engine overhaul timing

After a period of operation, the screw host will have the following problems:

1. Increased clearance

(1) The distance between the Yin and Yang rotors of the main engine increases. The direct consequence is that the compressor leakage in the process of compression (i.e. back leakage) increases, and the volume of compressed air discharged from the machine becomes smaller. Reflected in the efficiency of the compression efficiency of the compressor is reduced. 

The gap between the Yin and Yang rotor and the rear cover and the bearing increases, mainly affects the sealing and compression efficiency of the compressor, and has a great impact on the service life of the Yin and Yang rotor, because many mechanical failures are caused by the clearance between the bearing and the spindle.

2. Wear increases

As we all know, as long as the machinery is in operation there is wear, under normal circumstances because of lubrication fluid lubrication, wear will reduce a lot, but long-term high-speed operation, wear is slowly increasing.

Take Sweden SKF bearings as an example: under nearly impossible conditions (such as long-term idling, clean enough lubrication fluid, good enough cooling system, and the use of environmental temperature, humidity, etc.), it can only be guaranteed for a few years. As far as the compressor host is concerned, there are wear and tear of other parts in addition to bearings. If minor wear does not take correct preventive measures, it is easy to lead to wear and tear, causing damage and wear of other main components.

3. Deformation of components

The main air compressor is the core compression component of the compressor. Its internal components are in the environment of high temperature and high pressure for a long time, coupled with the high-speed operation. For a long time, the phenomenon of component deformation is bound to exist. At the same time, the cause of deformation and the use of environmental factors, and the air compressor of the use of the general environment will have dust and impurities in the air, after these small solid material into the machine, accumulate over a long period if form larger solid block, it may cause rotor deformation of Yin and Yang, clearance increases, serious can lead to a host.

4. Damage of components

In the main part of the air compressor, the main vulnerable parts are: all kinds of gaskets, sealing rings, shaft oil seals, etc., especially the shaft oil seals, in the environment of high temperature, high pressure, and high-speed operation for a long time, the service life ratio is greatly shortened. The direct consequence of the damage is the compressor oil leakage, if not found in time, it will cause the Yin and Yang rotor and bearing due to lack of lubrication and burn out. 

Conventional air compressor overhaul is to a large extent the maintenance of bearings and rotating parts, mainly is to replace the corresponding bearings and seals, and the compressor head overhaul can also achieve the effect of close to the new machine. Of course, the premise of maintenance is that the compressor itself is fault-free, the rotor and the inner cavity of the casing have no obvious wear.

Therefore, it is of great guiding significance to understand the selection of compressor bearing for compressor overhaul.

Air compressor main engine overhaul must pay attention to several key issues

Second, compressor bearing selection

The main factors that should be considered in the selection of bearings: various structure types of bearings due to different structural characteristics, can adapt to different use conditions, designers can choose according to their own needs. Usually, the following main factors should be considered when choosing bearings:

Load is the most important basis for choosing bearings. Usually, bearings should be selected according to the size, direction and nature of the load.

(1) load size: under normal circumstances, roller bearings because of the line contact, bearing capacity is large, suitable for bearing large load; Ball bearing is suitable for light and medium load because it is point contact and has small bearing capacity.

(2) load direction: because the compressor head bearing is under the combined action of radial load and axial load, angular contact ball bearings or tapered roller bearings are generally selected, and the axial load capacity of these two bearings is improved with the increase of contact Angle. If the radial load is large and the axial load is small, the deep groove ball bearing and the cylindrical roller bearing with the inner and outer rings are also available. If the axial load is large and the radial load is small, the thrust angular contact ball bearing and thrust tapered roller bearing can be selected.

③ Load nature: when there is impact load, roller bearings should be selected.

Because of the interaction force between the Yin and Yang rotors and the reaction force of compressed gas on the rotor, the bearing of the compressor needs to bear radial and axial loads at the same time. In addition, at the start moment of the air compressor, the starting rotation is up to 3692N·m, so roller bearings should be selected. In addition, the factors to be considered include axial swimming performance, high-speed performance, self-aligning performance, allowable installation space, installation and disassembly convenience, etc.

To sum up, the compressor head bearing selection: the high-pressure end adopts tapered roller bearings as thrust bearings, and the low-pressure end adopts cylindrical roller bearings with inner rings with flanges as support bearings.

Three, compressor head disassembly

1. Disintegration process and steps

(1) Equipment preparation, including special support, pull, jack, hand tools (spanner, copper bar, hammer, pliers, etc.), measuring instruments (vernier caliper, depth ruler, lead wire, etc.), oxygen acetylene, bearing heaters, lifting equipment, etc.

(2) Remove the low pressure end cover shell (bearing seat) and the high pressure end cover.

③ Key data measurement before disintegration:

• The clearance at the low pressure end (the clearance between the end faces of the Yin and Yang rotors and the front housing) shall be measured with a feeler;

• The clearance at the high pressure end (clearance between the end faces of the Yin and Yang rotors and the end faces of the rear housing) is measured with a feeler;

• The clearance of the rotor bearing of the high pressure end is measured by the pressure lead wire method.

(4) Remove the spindle drive gear, key and sleeve by surface heating.

(5) Disassemble and pull out the main engine housing and the low pressure end bearing of the Yin and Yang rotor and its gland.

⑥ Remove and pull out the high pressure end housing (bearing seat), Yin and Yang rotor bearing and its gland, inner ring gasket.

Clean up and check the damage of spindle, rotor, bearing and inner shell.

Damaged components repair processing.

2. Data measurement records before disintegration

Screw and screw side clearance is before and after assembly shall ensure that the technical parameters, when the gap size has been considered the host before and after high temperature runtime screw and the expansion of the transverse deformation, at the same time compression screw radial load and axial load shall be borne by host positioning bearing, began to run screw without axial displacement. However, after a certain period of operation, the main engine bearing will inevitably wear, resulting in the increase of axial and radial movement of the screw, which will change the clearance between the screw and the screw, between the screw and the housing of the main engine as well as the front and rear end faces. Therefore, these assembly gaps should ensure the normal operation of the host for a long time.

3. Reloading process and steps

(1) The Yin and Yang rotors are lifted and fixed after meshing, and the exhaust end housing is covered.

② Put the gasket of the inner ring of the bearing, heat the bearing, and install the bearing gland and lock bolt.

(3) After lifting the housing, the Yin and Yang rotors are free to fall, and the total clearance at the exhaust end is measured.

(4) If the total clearance at the exhaust end is not qualified, re-assemble the bearing and adjust the number of inner ring gaskets until the clearance is in the required value.

(5) Install the exhaust cover cover, adjust the bearing clearance at the exhaust end of the Yin and Yang rotor through the thickness of the cover gasket, and the exhaust clearance during operation is the difference between the total clearance at the exhaust end and the bearing clearance.

(6) Install the rotor housing of the main engine in turn, the Yin and Yang rotor bearing and the cover at the intake end.

⑦ Adjust the intake gap by the intake end cover gasket thickness.

The sleeve is heated and installed on the spindle (installation in the end), and the drive gear key is installed, and the gear is heated and heated.

Install the gear gland and lock bolt, apply thread fastening adhesive on the lock bolt, and tighten the bolt.

Attending attention should be paid to the tightening strength of bearing gland bolts and bolts of the host machine during reloading.

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Air compressor main engine overhaul must pay attention to several key issues

Four, conclusion

The head of screw air compressor belongs to high precision parts, especially the Yin and Yang rotors. The machining accuracy is quite high, and the installation requirements are naturally very high. Users must be very careful to achieve satisfactory overhaul results.

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