Refurbishment process of the pumping unit in a volumetric screw compressor of the ‘oil free’ type
A refurbishment process for a volumetric screw compressor of the ‘oil-free’ type, which comprises a male rotor and a female rotor, is described. The process comprises visually checking the wear condition of the rotors, treating their surface for removing the previous coating, and applying a new coating on the surface. The composition of the coating applied on the surface of the rotors consists of the following materials: Material Amount (g) Polytetrafluoroethylene 750 ÷ 850 (954G 303 C Teflon, DuPont) Amorphous graphite powder 300 ÷ 400 Thinner for spray cleaning apparatuses 200 ÷ 270 (8595 thinner, DuPont) Methyl ethyl ketone (MEK) 170 ÷ 220 Cellosolve acetate coating additive 200 ÷ 300 (Syn Fac 800 resin).
1. A new coating for a refurbishment process of an oil-free volumetric screw compressor comprising a pumping unit with an outer body and an inner chamber comprising a first and a second seat adapted to accommodate respective male and female rotors provided with respective reversing helical screws meshing each other, said process comprising gradually disassembling the components of the compressor up to extraction of a rotor at a time from the respective seats of the chamber, visually checking the wear condition of the rotors, treating the rotor surface to remove the previous coating, applying said new coating on the surface of the rotors, repeating the operations of treating and applying a coating on the outer body of the pumping unit, inserting and then extracting one rotor at a time into the respective seat and checking for lack of interference, reassembling the pumping unit by meshing and inserting the two rotors inside the seats with further checking for lack of interference, reassembling the remaining components of the compressor,
wherein said new coating consists of a mixture of the following materials:
Material
Amount (g)
Polytetrafluoroethylene
750-850
Amorphous graphite
300-400
powder
Thinner for spray
200-70
cleaning apparatuses
Methyl ethyl ketone
170-220
Cellosolve acetate
200-300
coating additive.
2. The new coating according to claim 1 for a process as defined above, wherein said treatment of the rotor surface comprises a sandblasting process adapted to increase roughness and promote wettability, a degreasing process by means of a thinner, and finally a drying process adapted to evaporate the thinner in appropriate ovens.
3. The new coating according to claim 2 for a process as defined above, wherein fine grain corundum is used in said sandblasting process.
4. The new coating according to claim 1 , wherein it is applied by means of a dry compressed air gun adapted to spray the coating on the rotors, the rotors with coating are pre-cured in appropriate ovens, the quality and thickness of the paint coating is checked by means of an appropriate ultrasound instrument, the rotors inside the ovens are cured by means of a temperature ramp up and cooled at uniform temperature for an optimal paint coating quality.
5. The new coating according to claim 1 , wherein its formulation is a mixture of the following materials:
Material
Amount (g)
Polytetrafluoroethylene
800
Amorphous graphite
360
powder
Thinner for spray
240
cleaning apparatuses
Methyl ethyl ketone
195
(MEK)
Cellosolve acetate
240
coating additive.
6. The new coating according to claim 1 , wherein said materials are mixed for about four hours using a low speed gear system.
7. A coating for refurbishing an oil-free a-volumetric screw compressor, wherein the coating consists of a mixture of the following materials:
Material
Amount (g)
Polytetrafluoroethylene
750-850
Amorphous graphite powder
300-400
Thinner for spray cleaning
200-270
apparatuses
Methyl ethyl ketone
170-220
Cellosolve acetate coating additive
200-300.
8. The coating according to claim 7 , wherein the coating is a mixture of the following materials:
Material
Amount (g)
Polytetrafluoroethylene
800
Amorphous graphite powder
360
Thinner for spray cleaning
240
apparatuses
Methyl ethyl ketone
195
Cellosolve acetate coating additive
240.
9. A refurbishment process of an oil-free volumetric screw compressor, said compressor comprising a pumping unit with an outer body and an inner chamber, comprising a first and a second seat adapted to accommodate respective male and female rotors provided with respective reversing helical screws meshing each other, said process comprising gradually disassembling the components of the compressor up to extraction of a rotor at a time from the respective seats of the chamber, visually checking the wear condition of the rotors, treating the rotor surface to remove the previous coating, applying a new coating on the surface of the rotors, repeating the operations of treating and applying a coating on the outer body of the pumping unit, inserting and then extracting one rotor at a time into the respective seat and checking for lack of interference, reassembling the pumping unit by meshing and inserting the two rotors inside the seats with further checking for lack of interference, reassembling the remaining components of the compressor,
said process being wherein the composition of the coating applied on the surface of the rotors consists of a mixture of the following materials:
Amount
Material
(g)
Polytetrafluoroethylene
750-850
Amorphous graphite powder
300-400
Thinner for spray cleaning
200-270
apparatuses
Methyl ethyl ketone
170-220
Cellosolve acetate coating
200-300
additive.
10. The process according to claim 9 , wherein said treatment of the surface of the rotors comprises a sandblasting process adapted to increase roughness and promote wettability, a degreasing process by means of a thinner, and finally a drying process adapted to evaporate the thinner in appropriate ovens.
11. The process according to claim 10 , wherein fine grain corundum is used in said sandblasting process.
12. The process according to claim 9 , wherein applying the coating comprises painting by means of a dry compressed air gun adapted to spray the coating on the rotors, pre-curing the rotors with coating in appropriate ovens, checking the quality and thickness of the paint coating by means of an appropriate ultrasound instrument, curing the rotors inside the ovens by means of a temperature ramp up and cooling the rotors at uniform temperature for an optimal paint coating quality.
13. The process according to claim 9 , wherein the formulation of said coating applied on the surface of the helical screws is a mixture of the following materials:
Material
Amount (g)
Polytetrafluoroethylene
800
Amorphous graphite
360
powder
Thinner for spray
240
cleaning apparatuses
Methyl ethyl ketone
195
Cellosolve acetate
240
coating additive.
14. The process according to claim 9 , wherein said materials are mixed for about four hours using a low speed gear system.