Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Patent
1999-02-11
2000-12-12
Denion, Thomas
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
418151, 418 94, F01C 116
Patent
active
061589969
DESCRIPTION:
BRIEF SUMMARY
The invention concerns measures for balancing a screw rotor set in an axially parallel arrangement engaging in opposite directions in the external axes and with wrap angles of at least 720.degree. in a single-thread construction.
The centre of gravity centreline distance, end face and wrap angle thereby determine the extent of static and dynamic unbalance which occurs in screws with single-thread profiles.
In publication Sho 62 (1987)-291486 by the firm Taiko of Japan, a method is described for screw balancing: static balancing is firstly achieved by setting the screw length to integral multiples of pitch. Cavities on both sides of the end face of the screw, which are hollow or filled with light material, provide dynamic balancing.
This method of balancing is not feasible where special materials are required which cannot be cast. With unusual profile geometries as well, this method has its limits, as firstly the wall thickness of the screws cannot be reduced freely for reasons of stability, and on the other hand too large an axial elongation of the balancing cavities due to the spiral form entails substantial production problems; filling the cavities with light material exacerbates this problem.
In Swiss patent application 3487/95 by Busch S. A., Switzerland, another method of screw balancing is described: the screw length (=2W.sub.2) is greater by integral multiples of pitch 1 than 11/2 times the pitch (2W.sub.2 =5.multidot.1/2, 7.multidot.1/2, 9.multidot.1/2, etc.)
To compensate the remaining static and dynamic unbalance, modifications are made to the inlet side on external passive screw components and/or one or more balancing cavities on the end faces and/or external additional masses.
This method offers on the one hand the option of using special materials or enables on the other hand a reduction in balancing cavities, thereby achieving an increase in stability of form.
The use of screw rotors for pumping certain media and the reduction in temperature sought on the screw end on the outlet side require small, smooth, cavity-free screw surfaces, which deflect dirt and are easy to clean. The requirements for a reduction in costs of maintenance, assembly, spare parts stocks and for small, compact pumps run counter to the use of external additional masses.
The invention is based on the task of defining measures to balance single-thread screws with cavity-free smooth surfaces without using external additional masses.
This task is resolved for a screw rotor set for screw pumps in an axially parallel arrangement engaging in opposite directions in the external axes and with wrap angles of at least 720.degree. in a single-thread construction, and with smooth plane-parallel rotor end faces, by each screw rotor consisting of several individual parts fixed rigidly together with a common axis of rotation, optionally eccentric centre of gravity positions and optionally different material densities; the individual parts inside the rotor form a cavity sealed off from the pump chamber, the balancing cavity; adjustment of the material density and the geometry of the individual parts inside the rotor cause static balancing and affect dynamic unbalance, and dynamic balancing is achieved with little effect on static unbalance by calculated determination of the screw length/pitch ratio=a at values which are somewhat smaller than uneven multiples of 1/2.
Configuration options in the context of the specified screw geometry lie in the choice of number, shape and material of the individual rotor parts and in the configuration of the balancing cavity 3, as described in the characteristic subsidiary claims.
Increased production costs are offset by the following advantages obtained with the invention: chemical and mechanical stresses. shafts.
The invention is explained in more detail with the examples of construction shown in the Figures:
The figures show:
FIG. 1: A screw rotor set with pilot gearing for a screw pump in single-thread construction as per the invention composed of individual parts with eccentric interior mass concent
REFERENCES:
patent: 2266820 (1941-12-01), Smith
patent: 2441771 (1948-05-01), Lysholm
Ateliers Busch S.A.
Browning Clifford W.
Denion Thomas
Trieu Theresa
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