Claims
- 1. In a rotor for a rotary screw machine having helical lobes and intermediate grooves forming the working surface of the rotor, the rotor being axially limited by two radial end surfaces and having a core with a coating on at least said working surface, said coating comprising at least one layer of substantially uniform thickness and being made of plastic,
- the improvement wherein:
- said core includes a shaft of a first material and a rotor body of a second material mounted on said shaft, and the coefficient of thermal expansion of said plastic is 1 to 3 times as great as that of said second material, and the coefficient of thermal expansion of said second material is 1 to 6 times as great as that of said first material.
- 2. A rotor according to claim 1 in which said second material is a plastics material.
- 3. A rotor according to claim 2 in which said second material is a polyetherimide.
- 4. A rotor according to claim 2 in which said plastics material is reinforced with fibers.
- 5. A rotor according to claim 2 in which said second material is a polyetherimide which is reinforced with fibers.
- 6. A rotor according to claim 5 in which said fibers are glass fibers and the amount of said fibers corresponds to 10 to 40% by weight of said second material.
- 7. A rotor according to any one of claims 2 to 6 in which said second material is porous.
- 8. A rotor according to claim 1 in which said second material is a metal.
- 9. A rotor according to any one of claims 1 to 6 or 8 in which said plastic coating consists of one layer polyetherimide.
- 10. A rotor according to claim 9 in which said polyetherimide contains 0 to 40% by weight of reinforcing fibers.
- 11. A rotor according to any of claims 1 to 6 or 8 in which said coating also is applied on at least one of said end surfaces of said rotor.
- 12. A rotor according to claim 11 in which said coating also is applied on at least one of said end surfaces of said rotor.
- 13. In a rotary screw machine having a housing provided with a rotor therein, the rotor having helical lobes and intermediate grooves forming the working surface of the rotor, the rotor being axially limited by two radial end surfaces and having a core with a coating on at least said working surface, said coating comprising at least one layer of substantially uniform thickness and being made of plastic,
- the improvement wherein:
- said core includes a shaft of a first material and a rotor body of a second material mounted on said shaft, and the coefficient of thermal expansion of said plastic is 1 to 3 times as great as that of said second material, and the coefficient of thermal expansion of said second material is 1 to 6 times as great as that of said first material.
- 14. In a rotor for a rotary screw machine having helical lobes and intermediate grooves forming the working surface of the rotor, the rotor being axially limited by two radial end surfaces and having a core with a coating on at least said working surface, said coating being of substantially uniform thickness and being made of plastic,
- the improvement wherein:
- said core includes a shaft of a first material and a rotor body of a second material mounted on said shaft,
- said plastics coating consists of two layers,
- the coefficient of thermal expansion of said plastic is 1 to 3 times as great as that of said second material, and
- the coefficient of thermal expansion of said second material is 1 to 6 times as great as that of said first material.
- 15. A rotor according to claim 14, in which said second material is metal.
- 16. A rotor according to claim 14, in which said second material is a plastics material.
- 17. A rotor according to claim 16, in which said second material is a polyetherimide.
- 18. A rotor according to claim 16, in which said plastics material is reinformed with fibers.
- 19. A rotor according to claim 16, in which said second material is a polyetherimide which is reinforced with fibers.
- 20. A rotor according to claim 19 in which said fibers are glass fibers and the amount of said fibers corresponds to 10 to 40% by weight of said second material.
- 21. A rotor according to any one of claims 14 to 15 in which each of said coating layers is made of polyetherimide containing 0 to 40% by weight of reinforcing fibers.
- 22. In a rotary screw machine having a housing provided with a rotor therein, the rotor having helical lobes and intermediate grooves forming the working surface of the rotor, the rotor being axially limited by two radial end surfaces and having a core with a coating on at least said working surface, said coating being of substantially uniform thickness and being made of plastic,
- the improvement wherein:
- said core includes a shaft of a first material and a rotor body of a second material mounted on said shaft,
- said plastics coating consists of two layers,
- the coefficient of thermal expansion of said plastic is 1 to 3 times as great as that of said second material, and
- the coefficient of thermal expansion of said second material is 1 to 6 times as great as that of said first material.
- 23. A rotary screw machine according to claim 22, in which each of said coating layers is made of polyetherimide containing 0 to 40% by weight of reinforcing fibers.
Priority Claims (2)
| Number |
Date |
Country |
Kind |
| 8603720 |
Sep 1986 |
SEX |
|
| PCT/SE87/00397 |
Sep 1987 |
WOX |
|
BACKGROUND OF THE INVENTION
This Patent Application is a continuation-in-part of U.S. Pat. application No. 07/314,119, filed Feb. 1, 1989, now abandoned.
The present invention relates to a rotor for a rotary screw machine having helical lobes and intermediate grooves forming the working surface of the rotor, the rotor being axially limited by two radial end surfaces and having a core with a coating on at least said working surface, said coating being at least one layer of substantially uniform thickness and being made of plastic.
Screw rotors are normally manufactured by machine cutting of solid metal blanks. Having a complicated geometry, the screw rotors require high manufacturing precision, and the amount of material to be cut away is very large. In combination these drawbacks result in long manufacturing times and high costs.
Consequent)y, it has long been desired to produce screw rotors in a simpler fashion and With less stringent requirements on precision and accuracy, in order to enable the rotors to be manufactured in very large quantities at reasonable costs.
Endeavours have been made as early as in 1953 to therefore produce the rotors from plastic, as evident from U.S. Pat. No. 2,868,442. This document thus discloses a male rotor for a rotary screw compressor of the Lysholm type, in which the rotor is made of a plastic surrounding a metal core. The core consists onlY of the rotor shaft and the rotor holds a large quantity of plastic. To make a rotor with a large plastic body having varying thickness entails drawbacks of different kinds. Large and varying shrinking results in bad accuracy to size. Such a rotor therefore is appropriate only for small rotor dimensions.
In order to achieve improved strength in a rotor consisting of a plastic surrounding a metal core it is further known to reinforce the plastic with metal. U.S. Pat. No. 3,918,838 discloses a female rotor molded from plastic around a metal shaft whereby the plastic is reinforced by a skeleton having radial metal discs substantially corresponding to the external shape of the rotor. Since the plastic also in this case reaches the rotor shaft the difficulties with varying shrinking remain, in partiCular if such a construction would be used for the male rotor having a larger amount of material.
Attempts also have been made to make a rotor of a metal core substantially corresponding to the external shape of the rotor and coat the rotor with a thin plastic layer. An example of this type is disclosed in GB 1,306,352. The metal core in this case is made integral with the shaft. With regard to the material required for the rotor shaft the manufacture of the rotor body implies a moulding procedure, whereby considerable unevennesses will occur on the external surface thereof. This complicates the moulding of the plastic layer around the metal core since the unevennesses creates constrictions in the narrow space between the rotor body and the surrounding mould which obstruct a uniform distribution of the plastic in said space. The unevennesses also create unbalanced centrifugal forces in the rotor, in particular at high rpm. These problems could be avoided by milling or grinding the working surface of the rotor body before applying the plastic layer although the manufacturing costs thereby would be increased.
In spite of the achievements in this field--to eliminate the need for machine cutting of the rotors by making them partly of plastic--a satisfactory solution has up to now not been attained, neither through the above mentioned examples nor through other similar constructions.
The object of the present invention thus is to attain a rotor for a rotary screw machine which does not require any machine cutting for creating correct intermeshing lobes and grooves and which does not have the drawbacks entailing earlier attempts to attain this.
This has according to one aspect of the invention been achieved in that the core of a rotor of the introductionally specified kind includes a shaft of a first material and a rotor body of a second material mounted on said shaft, 1.0 to 3.0 times as great as that of said second material, and the coefficient of thermal expansion of said second material is 1.0 to 6.0 times as great as that of said first material.
The invention also relates to an appropriate application of the rotor in a rotary screw machine.
The invention is further explained in the following detailed description of preferred embodiments of the invention and with reference to the accompanying drawings.
US Referenced Citations (8)
Foreign Referenced Citations (1)
| Number |
Date |
Country |
| 2409554 |
Sep 1975 |
DEX |
Non-Patent Literature Citations (1)
| Entry |
| The Polymer Handbook (3rd Edition), J. Brandrup, E. H. Immergut, Wiley-Interscience Publication, 1989, p. V36. |
Continuation in Parts (1)
|
Number |
Date |
Country |
| Parent |
314119 |
Feb 1989 |
|
Patent Grant
5011389
