Machine element or mechanism – Gearing – Directly cooperating gears
Reexamination Certificate
1999-02-25
2002-01-01
Fenstermacher, David (Department: 3682)
Machine element or mechanism
Gearing
Directly cooperating gears
C074S431000, C074S434000
Reexamination Certificate
active
06334369
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a toothed wheel unit with external toothing, preferably for heavy machinery gears and/or rapidly moving gears like turbomachinery gears, comprising a toothing carrier with an external toothing provided on a circumferential surface and a bearing journal or connection portion in at least one axial end region of the toothing carrier, joined with the toothing carrier.
Toothed wheel units of this type of interest are e. g. used in spur gears, as shown in BHS catalogue “BHS-Stirnradgetriebe, einstufig, für hochtourige Anlagen” (BHS spur gears, single stage, for high-speed installations) with masthead H-3/1-87.
In such gears, preferably the large spur toothed wheels have dimensions with diameters from e.g. 500 mm up to 1250 mm. Simultaneously the axial width of the large toothed wheels can be in the range of 200 to 600 mm in the case of spur toothing and single helical toothing, and in the range of 250 to 700 mm in the case of double helical toothing.
It is known to produce such toothed wheel units in full shaft construction. Full shaft construction means that a plate body is produced integrally with a shaft, the shaft projecting over the end surfaces of the plate body and serving for bearing. This full shaft construction has advantages. The stress due to the centrifugal force and the difference in heat between the toothing region and the central region is small. Furthermore, due to the massive construction, small variations in shape (constant volume) result e.g. in the case of stress by centrifugal forces.
However, the full shaft construction also presents some disadvantages. In order to illustrate these disadvantages, the way of producing such toothed wheel units in full shaft construction has to be outlined in brief. At first, a cast steel part is produced, which comprises the shaft and the plate body in integral construction. This case steel part is then forged and after that subjected to a metal cutting treatment, in order to define the final dimensions and preferably to provide the toothing. To reduce the casting and forging stresses and to optimize the texture of the material, various heat treatments are executed in between. Subsequently, carbonization is performed at approx. 900° C. and after that it is hardened (case hardening).
The thus produced hardening strains can amount to considerable values, especially in case of larger parts, and cause problems.
Further problems are to a considerable degree due to the process of casting, in which a so-called segregation zone forms in the central region of the shaft and the plate body, in which impurities of the steel alloy and perturbations of the texture structure are present in high concentrations.
When the finished toothed wheel unit is finally commissioned, additional centrifugal force stresses and operation heat stresses occur, especially during rapid starting operation. These stresses can lead to uncontrollable stress conditions in the segregation zone.
In order to eliminate the negative effects of the segregation zone, which are the larger, the larger the volume of the entire toothed wheel unit is, it has already been thought of going over to a hollow shaft structure, preferably by reboring the segregation zone so that the aggregation of bad material in the interior of the shaft is removed. However, this reboring of the shaft has not allowed to solve all the problems. On the one hand, the stresses occurring due to the centrifugal force and the temperature differences are increased with respect to the full shaft structure so that the material can give way, when centrifugal forces occur in the region of the inner diameter, and thus, additional possibilities for the deformation of the plate body occur. On the other hand, the concentration of impurities and perturbations of the texture structure known as segregation persists in the regions adjacent to the bore. Furthermore, hardening strains cannot be excluded, because the hardening process is insufficient in the region of the bore.
Toothed wheel units have also been considered in which the plate body is shrunk on the shaft. The application of this structure is limited, because a disengagement of the plate body from its connection with the shaft body cannot safely be avoided due to high centrifugal force and heat loads. The tendency, therefore, still goes to an integral structure.
SUMMARY OF THE INVENTION
It is an object of the invention to construct a toothed wheel unit of the generic type in such a way that strain conditions, which are difficult to control, especially hardening strain conditions, are avoided or minimized.
To achieve the object it is proposed according to the invention that the toothing carrier is either provided with a toothing carrier casing, whose inner diameter is larger than the diameter of the bearing journal or the connection portion, or/and with a plurality of toothing carrier plates following each other in axial direction and joined with each other.
With the construction according to the invention, segregation zones can be avoided to a large extent or completely, as the concentration of material over a large volume hardly accessible to heat treatments from the outside is avoided. With the construction according to the invention, all volume regions of the components, i.e. the toothing carrier casing, the bearing journals, the connection portions and the toothing carrier plates, are relatively thin-walled so that, on the one hand, in contrast to large volume work pieces, they do not present comparable problems caused by the segregation zone and, on the other hand, external treatments act more homogeneously onto all volume regions.
It may happen that with the toothed wheel units according to the invention, individual components or regions of components are exposed to higher stresses than with the known toothed wheel units of the full shaft construction and the hollow shaft construction. However, it has turned out that the occurring stress distributions are easier to calculate, in particular because elements like tubular body plates lead to two-dimensional, possibly even linear stress conditions and cubically oriented radial stress profiles are avoided.
In the case of a tubular toothing carrier casing, the stress problem reduces to the problem of a thin-walled tube, a wall thickness of 150 to 200 mm being possible, when the toothing diameter is 900 mm and more. In case of smaller toothing diameters, the wall thickness is reduced corresponding to the ratio of the toothing diameters. This thin-walled tube is shorter than the length of the shaft in case of a full shaft construction. Due to the thinness of the wall, an almost uniform heat treatment of all volume regions can be expected on case hardening. Forging is also rendered easier and more favourable in view of the avoidance of stress conditions, inasmuch as the toothing carrier casing can be rolled in a ring-roll mill.
In case of the second alternative of the proposition according to the invention (toothing carrier plates), similarly favourable conditions result in view of the forging and the hardening in case of a corresponding dimensioning of the respective plate thickness.
At first, the possibilities of development of the first alternative (toothing carrier casing) will now be treated. The toothing carrier casing can be joined at at least one end, preferably at both ends, to a end plate, in the central region of which the bearing journal or the connection portion is arranged . If end plates with one respective bearing journal or other connection portion are mounted on both ends, the same possibilites as to the bearing of the toothed wheel unit result as with the known full shaft constructions or hollow shaft constructions. Compared to the size of the entire toothed wheel unit, the end plates with bearing journals or other connection portions have a relatively small volume so that the problems on casting, forging and hardening and during operation due to centrifugal force and temperature stresses can be avoided.
Besides the two-plates-solution, one em
Baker & Botts L.L.P.
BHS Cincinnati Getriebetechnik GmbH
Fenstermacher David
LandOfFree
Toothed wheel unit with external toothing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Toothed wheel unit with external toothing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Toothed wheel unit with external toothing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2844623