METHOD FOR STRENGTHENING A GEAR WHEEL, AND A GEAR WHEEL

Abstract: A method for strengthening a gear wheel (1) is described. Each tooth (2) is fixed like a theoretical beam between two extreme points in that two strengthening wheels (3, 4), shaped on their respective insides in accordance with the gear wheel teeth (2), are placed around the gear wheel. To achieve a best possible shrink fit, the toothed rim of the gear wheel (1) is envisaged stretched out to a corresponding larger circle, shrink fits being selected for this circle. Similar considerations are made for the ring.

Description: METHOD FORSTRENGTHENINGAGEARWHEEL,ANDA GEARWHEEL The invention relates to a method for strengthening a gear wheel. The invention also relates to a gear wheel thus strengthened. Gear wheels in cranes and lifting devices are highly stressed components. Experience has shown that, for example, driving gear wheels in jack-up systems for jack-up offshore platforms, driving gear wheels interacting with vertical toothed racks, have a surprisingly short useful life. Their useful life is notably shorter than that ofthe interacting toothed racks, which is due to the fact that the gear wheel teeth are quite naturally exposed to a greater number of alternating loads than the teeth ofthe rack. Studies have shown that the teeth of driving gear wheels in large structures are exposed to motions that ultimately cause fracture in the root ofthe tooth. It is an object ofthe invention to provide a method and an apparatus for strengthening gear wheels, particularly, but not exclusively, large driving gear wheels that are used in cranes and lifting devices. Based on the acknowledgement ofthe fact that the teeth are subject to breakage as a consequence ofthe alternating motions in the tooth itself, most notably in the roots of the teeth, it is proposed according to the invention to fix each individual tooth in the gear wheel in the direction of circumference in order thereby to counteract the said tooth motions during operations, i.e., that each individual tooth will be like a theoretical beam fixed at both ends. According to the invention, a method is therefore proposed for strengthening a gear wheel, characterised in that each tooth is fixed like a theoretical beam between two extreme points, in that two strengthening rings, each shaped on its inside in conformity with the gear wheel teeth, are placed around the gear wheel. It is especially advantageous if the rings are secured around the gear wheel in such manner that the rings will be firmly shrunk onto the gear wheel with a material- technical tensile/compressive strength within 80% ofthe 0.2% elastic elongation range ofthe material (steel). According to the invention, a gear wheel is also proposed that is characterised in that each tooth is fixed like a theoretical beam between two extreme points, in that around each gear wheel there are fixed two strengthening rings, each shaped on its inside in conformity with the gear wheel teeth. It is especially advantageous if the strengthening rings are shrunk on in such manner that the rings will remain firmly shrunk onto the gear wheel with a material-technical tensile/compressive strength within 80% ofthe 0.2% elastic elongation range ofthe material (steel). Each individual strengthening ring is designed in principle like an internal ring gear having teeth intended for engagement in the tooth pockets ofthe gear wheel, with clearance towards the base ofthe teeth ofthe gear wheel or clearance towards the base ofthe teeth of both gear wheel and ring. The invention can be carried out in a particularly advantageous way by envisaging the toothed rim ofthe driving gear stretched out to a correspondingly larger circle, shrink fits being chosen for this circle in accordance with the ISO tables of limits and fits, and by making similar considerations for the ring. The invention will now be described in more detail with reference to the drawing, wherein: Fig. 1 shows a gear wheel viewed looking towards the teeth; Fig. 2 is a side view of a gear wheel; Fig. 3 is a section taken from Fig. 1 ; Fig. 4 is a section taken from Fig. 2; Fig. 5 is a section of a gear wheel and ring in the area where they are secured together; and Fig. 6 is another section of a gear wheel and ring in an area where they are secured together. The gear wheel 1 shown in Figs. 1 and 2 has a plurality of teeth 2 around its circumference. At each end side ofthe gear wheel 1 there is shrink-fitted a strengthening ring 3 and 4 respectively. Each ring 3, 4 is made in the form of an internal gear wheel with teeth 5. The teeth are shaped to fit with the teeth 2 on the gear wheel 1, see in particular Fig. 4. As can be seen from Fig. 1 and from the section in Fig. 3, each tooth 2 on the gear wheel 1 will be fixed like a beam between the two strengthening rings 3 and 4, and the rings 3, 4 will counteract motions of each individual tooth 2 in the direction of circumference when the teeth are subjected to forces in interaction with another set of teeth on a gear wheel or a toothed rack (not shown). As shown in Fig. 4, a clearance 6, 7 is provided between the tooth crest and the tooth base on/in the gear wheel and ring. This ensures a best possible flank contact between the teeth 2 and 5 as well as a reduction in the stress of radial forces, see also Figs. 5 and 6. In Fig. 6 there is a clearance 8 only between ring-tooth crest and ring-tooth base. In order to achieve the best possible effect, each individual strengthening ring 3, 4 is fitted on/around the gear wheel 1 by producing/utilising a tensile force within 80% of the permanent elongation limit ofthe material (steel). This is achieved by suitable sizing of each individual ring prior to fitting. It is particularly expedient if, in this connection, it is possible to envisage the toothed rim stretched out to its correspondingly larger circle, shrink fits for this circle being selected in accordance with the ISO tables of limits and fits. Similar considerations are made for the strengthening rings. The invention permits a reduction in the danger of fatigue fractures without the need to increase the size, and consequently the material consumption.

Claims: P a t e n t c l a i m s 1. A method for strengthening a gear wheel (1), characterised in that each tooth (2) is fixed like a theoretical beam between two extreme points in that two strengthening wheels (3, 4), each shaped on its inside in conformity with the gear wheel teeth (2), are placed around the gear wheel. 2. A method according to claim 1, characterised in that the strengthening rings (3, 4) are secured around the gear wheel (1) in such manner that the strengthening rings (3, 4) will be firmly shrunk onto the gear wheel (1) with a material-technical tensile/compressive strength within 80% ofthe 0.2% elastic elongation range ofthe material (steel). 3. A method according to claim 2, characterised in that during the sizing process the toothed rim ofthe driving gear (1) is envisaged stretched out to a correspondingly larger circle, shrink fits being selected for this circle in accordance with the ISO tables of limits and fits, and that similar considerations are made for each strengthening ring (3, 4). 4. A gear wheel (1), characterised in that each tooth (2) is fixed like a theoretical beam between two extreme points in that two strengthening rings (3, 4), shaped on their insides in conformity with the gear wheel teeth (2), are fitted around the gear wheel. 5. A gear wheel according to claim 4, characterised in that the strengthening rings (3, 4) are shrink-fitted in such manner that the strengthening rings (3, 4) will be firmly shrunk onto the gear wheel (1) with a material -technical tensile/compressive strength within 80% ofthe 0.2% elastic elongation range ofthe material (steel).

Inventors: EILERTSEN BJOERN, EILERTSEN, BJOERN
Applicants: EILERTSEN BJOERN, ENG & DRILLING MACHINERY AS, EILERTSEN, BJOERN, ENGINEERING & DRILLING MACHINERY AS
Application year: 2000
Main classification: F16H
IPC codes: F16H55