Rotary expansible chamber devices – Non-metallic working member – cylinder or partition – Resilient
Patent
1986-11-10
1988-08-02
Vrablik, John J.
Rotary expansible chamber devices
Non-metallic working member, cylinder or partition
Resilient
418201, F03C 208, F04C 1816
Patent
active
047611243
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a screw-type rotary machine intended for the compression or expansion of an elastic fluid and comprising at least two rotors, a male rotor and a female rotor, provided with helically extending lands and grooves, of which rotors at least one is comprised substantially of a plastics material located preferably on a metal shaft or core.
Screw rotors are normally manufactured by machine cutting solid metal blanks. The screw rotors have a complicated geometric form, which demands a high degree of accuracy in manufacture. In addition, the amount of material cut-away during manufacture is very considerable. In combination, these drawbacks result in long manufacturing times and high costs.
Consequently, it has long been desired to produce the rotors of such machines 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 produce the rotors from plastics, as evident from the U.S. Pat. No. 2,868,442. Because of the limited strength properties of plastics materials, however, it has been necessary to manufacture the female rotor from metal, since the lands of the female rotor are relatively narrow, and to utilize the advantageous elastic properties of plastics in the male rotor, which remains shape stable even when made predominantly from plastic. It is necessary to machine the plastic rotor finely and with precision, however, in order to obtain the desired accuracy in shape and configuration, and this has been the case also in connection with attempts to produce moulded female rotors from plastics. An unavoidable complication is, however, that the rotor during the solidification process is subjected to a dimensional deviation.
Due to the fact that a dismountable mould is impossible to use here, it would be thinkable to screw the solidified rotor out of an integral mould after removal of a removable end-wall of the mould. This method is not applicable without problems, however, because the rotor becomes firmly jammed in the mould due to the dimensional deviation occurring during the solidification process.
Another substitute for metal in the present context are the ceramic materials, as disclosed in the German Patent Specification Serial No. 1,426,771, which when taken in combination with a plastics male rotor in accordance with the aforesaid U.S. patent, can afford some improvement.
As will be seen from U.K. Patent Specification Serial No. 1,276,348, endeavours have been made to coat or line steel rotors with a plastics material, in order to protect the rotors against corrosion. Although plastics materials have a certain degree of elasticity or resiliency, they are sufficiently hard to resist deformation as a result of the pressure exerted by the working medium. This solution affords a certain amount of improvement with regard to function, but does nothing to alleviate the complicated manufacturing procedures required, or to lessen the time taken to effect these procedures. In addition it is difficult to achieve satisfactory bonding of the plastics coating or lining to the steel substrate.
The object of the present invention is therefore to provide a screw-type rotor machine of the aforesaid kind, with which the rotors thereof can be manufactured quickly and cheaply, in a manner which enables the rotors to be produced in large number at a low labour input. This object has been achieved in accordance with the invention in that the rotor which is made at least predominantly of a plastics material is the female rotor, which is injection moulded from a plastics material having a modulus of elasticity of at most 25,000 N/mm.sup.2, and in that the thickness of the lands of the female rotor is so adapted in respect of said modulus of elasticity that the lands are able to spring away, be deflected resiliently, when clashing contact occurs with the other rotor, as a result of dimensional deviations caused by hardening or so
REFERENCES:
patent: 2868442 (1959-01-01), Nilsson
patent: 3015283 (1962-01-01), Knipp
patent: 4490102 (1984-12-01), Carre et al.
Sjolin Ulf
Timuska Karlis
Svenska Rotor Maskiner Aktiebolag
Vrablik John J.
Walnoha Leonard P.
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