6-20 Explain the overhaul process card and quality standard examples of micro-oil screw air compressors.

Answer: See Sheet 6-3 for the overhaul process card and quality standard examples of micro-oil screw air compressors.

 Sheet 6-3     Screw air compressor main engine overhaul    process card

Process 0: Preparation before maintenance

1.Understand the existing defects of the equipment and do a good  job of pre-repair appraisal

2.Prepare the wearing parts that need to be replaced and the tools for maintenance, lifting and cleaning

3.Apply for maintenance work tickets

Process 1: Disassembly

1. Contact the thermal engineer to calibrate each instrument and remove the instrument connected to the main body

      2. Drain the lubricating oil in the oil pool of the machine body

3. Remove the air filter

4. Remove the intake valve

5. Remove the cooling water pipe, oil pipe, measuring point and other pipe fittings

6. Remove the flywheel protection cover or flywheel V-belt

7. Remove the motor anchor bolts

8. Use a hoist to lift the machine body, remove the machine body  anchor bolts, and lift out the machine body

The following work is carried out in a clean maintenance area:

(1) Turn the rotor, check the appearance and wear of the main and auxiliary rotors, and measure the axial and radial clearance      between the main and auxiliary rotors and the machine body

(2) Remove the pair of wheels

(3) Remove the inlet end cover.Some models have a speed-increasing gear mechanism. In this case, the gearbox should be removed.

(4) Remove the outlet cover and prepare to inspect and remove the bearings.

(5) Remove the inlet bearing seat.

(6) Install a hydraulic puller at the outlet to separate the main and auxiliary rotors from the outlet bearings. Apply force slowly during the removal process and rotate the rotors.

(7) Remove the main and auxiliary rotors in turn.

(8) Remove the main and auxiliary rotors and the inner or outer   rings of the bearings in various parts of the machine body.

Process 2: Inspection and repair stage

1. Cleaning of parts

1.1 The removed parts should be cleaned in kerosene or carbon     deposit cleaning agent to remove the carbon deposits and rust on  them.

1.2 Clean and dredge the machine body and oil pipeline

1.3 Clean and dredge the cooling water pipe and cylinder cooling  water chamber

2. Inspection of main and auxiliary rotors

2.1 Check the surface wear of the main and auxiliary rotors, and  check whether there is shedding, grooves, nodules, cracks. Under  normal circumstances, the main and auxiliary rotors are not worn. Different surface conditions reflect the working conditions of th air compressor, such as bearing wear, foreign matter in the       machine body, and rotor rust due to long-term shutdown.

2.2 Grind the surface defects of the rotor, first use a shaped    file or a special-shaped file to smooth it,then use #500 sandpaperto polish it

2.3 If the air compressor is not overhauled in time or foreign    objects enter the body, the rotor will be seriously damaged and   cannot be repaired

3. Body inspection

Check the body wear and tear, whether there are cracks,rust scars, burrs, notches, grooves, etc. If there are such phenomena, repair them

4. Inspection of the gearbox

4.1 Check whether the fitting marks of the main and auxiliary     gears meet the requirements

4.2 Check the wear of the main and auxiliary gears. If there are  cracks or broken teeth, new gears should be replaced

5. Inspection of bearings

The screw air compressor has a small matching clearance and strictrequirements on bearings. All bearings must be replaced during    overhaul or fault repair. Bearings must use original accessories  or bearings of the same model

6. Inspection of shaft seals

Overhaul of screw air compressors requires replacement of new     shaft seals. The shaft seal replacement process is simple, but anynegligence during assembly will cause oil leakage during          operation. Shaft seal spare parts require the use of original     accessories

The following work should be done before assembly:

(1) The compressor host and auxiliary equipment should be cleaned and all cleaning agents or moisture should be removed. Carefully  check the rotor, bearing, gear, and cylinder for damage and other defects, and strictly prevent impurities from entering the workingchamber.

(2) The cylinder and rotor of the compressor should be tested for tightness according to the pressure specified in the equipment    technical documents.

The assembly of the cylinder, rotor, and gear should meet the     following requirements.

The longitudinal and transverse unevenness of the cylinder should not exceed 0.05/1000, and the inclination should be in the same   direction. It can be measured on the cylinder center plane or in  the bearing hole.

Process 3: Assembly

1. After the air compressor is repaired normally and the spare    parts are ready, the air compressor can be reinstalled. During theinstallation process, be careful to prevent foreign objects from falling into the air compressor body.

2. Install the main and auxiliary rotors of the air compressor in turn. It can be installed horizontally or vertically.

3. Install the inlet bearing seat, and pay attention to applying  the sealant evenly and not too thick. After installation, measure the total axial clearance of the rotor

4. The axial positioning piece is installed at the outlet bearing position of the main and auxiliary rotors. Check that the         positioning piece is not worn. If the radial clearance of the     shaft is normal before disassembling the air compressor, the      positioning piece can be directly reinstalled

5. Install the bearings in the original position.Install the inletand outlet bearings one after another. Control the heating        temperature to 90~120℃ when installing the bearings. When        installing the bearings, pay attention to installing one bearing  and cooling it before installing the other bearing

6. Lock the bearing positioning nut

7. Install the outlet elastic gasket and the outlet bearing end   cover. Measure the inlet axial clearance of the main and auxiliaryrotors and the body

8. Measure the radial clearance between the main and auxiliary    rotors of the air compressor and the body. Normal clearance       indicates that the above steps are installed normally. For air    compressors with abnormal rotation, you can use red lead powder toapply it and check whether there is friction in the meshing of themain and auxiliary rotors

9. Reinstall the gearbox bearings and large and small gears. When reinstalling the gearbox, pay attention to applying the sealant   evenly and not too thick

10. Reinstall the air compressor shaft seal. Pay attention to     applying lubricating oil during reinstallation to ensure smooth   installation. Apply a small amount of sealant to the moving and   static parts of the shaft seal

11. Reinstall the wheels, and the main engine is installed

Quality standards

1. Method for measuring the fit clearance of the air compressor

The fit clearance of the main engine of the air compressor        includes the radial fit clearance between the outer circle of the main and auxiliary rotors (screws) and the wall of the body      (cylinder); the axial clearance between the two end surfaces of   the main and auxiliary rotors (screws) and the side wall of the   cylinder. The axial clearance has two gaps at the outlet and inlet

The radial clearance between the main and auxiliary rotors and thebody is measured from the air compressor inlet using a feeler     gauge

The axial clearance at the outlet = the total axial clearance of  the rotor minus the axial clearance at the inlet. The total axial clearance of the rotor can be measured during the installation of the air compressor. After the main and auxiliary rotors and the   inlet bearing end cover are installed, the main and auxiliary     rotors are pushed back and forth axially, and the dial indicator  is used to measure

The axial clearance at the inlet of the main and auxiliary rotors and the body is measured from the air compressor inlet using a    feeler gauge. When measuring, the body is after the air compressorbearing is installed and the outlet elastic gasket and end cover  are pre-installed

The meshing clearance between the main and auxiliary rotors      (screws) is positioned by bearings,and red lead powder can be usedto check whether there is friction

2. Quality standards for air compressor matching clearance

The radial clearance between the main and auxiliary rotors and the body is 0.1mm, generally not more than 0.1mm

The axial clearance at the outlet is 0.10~0.2mm

The axial clearance at the inlet is 0.4~0.7mm

3. Adjustment method of rotor axial clearance

After measuring the axial clearance of the air compressor rotor,  if the axial clearance needs to be adjusted, a gasket is added to the outlet positioning piece accordingly. Generally, if the       positioning piece is not obviously worn, it does not need to be   adjusted. In addition, if the bearing is not installed in place or the locking force is insufficient after the bearing is installed, the axial clearance at the inlet will be too small. At this time, use a copper rod to tighten the bearing or lock nut to adjust it normally.

4. After the cylinder and rotor are aligned and leveled, the      anchor bolts should be tightened symmetrically and evenly; and a  level should be placed on the center plane of the cylinder and on the rotor journal to check the unevenness of the cylinder and     rotor; when aligning the unit, the axis of the motor shaft (or    speed increaser shaft) should be used as the reference, and the   different axis degrees should not exceed the provisions of the    equipment technical documents. If there is no provision, the      radial displacement of the different axis degrees should not      exceed 0.05mm

5. Gearbox

The gear surface should be free of cracks, erosion, etc., and the tooth surface contact requires a close fit of 70% along the tooth length. The meshing clearance of the gear is 0.2~0.3mm. If it     exceeds 0.50mm, it should be replaced.

6. Shaft bending measurement

When overhauling some faulty air compressors, the shaft bending   should be measured. The measurement should be carried out before  and after the air compressor is disassembled. The measurement     method is to directly position the bearing on the body. The       qualified standard for shaft bending is 0.03mm

Process 4: Trial run

1. During the trial run, the pressure and current of the air      compressor should be within the allowable range without large     fluctuations, and the vibration of each part should not exceed    0.10mm

2. The bearing temperature should not exceed 80℃, and the oil    temperature should not exceed 60℃

3. The shaft seal has no oil seepage or oil leakage

4. The overhauled screw air compressor often has large vibration (about 0.1mm) during the trial run. Since the elastic gasket at   the outlet of the air compressor has automatic adjustment and     compensation functions, the clearance between the rotors is       adjusted appropriately after a period of operation, and the       vibration is automatically eliminated

5. Termination of work ticket