CONTROL OF LOADING CAPACITY OF REDUCTION GEARS FOR MARINE APPLICATIONS

The aim of this paper is to analyse the calculation criteria and procedures for checking reduction gear load capacity, i.e. the capacity of a gear mesh to transmit fully and safely a given torque, without causing failures such as "pitting" and "scuffing" or, even, breaking of the teeth, these being the most usual damages which gear teeth are likely to undergo. To summarize, the above listed damages are due to an excessive tangential stress transmitted, i.e. to an excessive load on the teeth. Since the tangential force or the load are functions of the maximum transmitted torque, it is necessary, to prevent such failures from occurring, to check down to a pre-determined value, for a given couple of gears, the value of such moment. A theoretical analysis of the stresses actually taking place in reduction gears is quite difficult. It is a case, in fact, of a machinery component where a state of tridimensional stress with local concentrations effects, occurs because of a more or less pulsating load, leading back therefore to fatigue phenomena, and where a thorough surface finish, an accurate working, an effective teeth meshing, the pressure angle, the peripheral speed, the pinion deformation due to combined bending and torsion effects, the pre-tensions in the case of shrunk rims, etc. play a more or less important part affecting the results of experimental tests. This phenomenon is even more complicated in marine applications, because of the hull deformations and of the particular securing arrangements which make alignments less accurate. This explains why the criteria followed by various authors and by different manufacturers are often dissimilar and some times contradictory. In view of the above, a checking of gear load capacity may be grounded on simplified calculation theories, adopting coefficients conveniently selected on the basis of experimental results. Usually, such a checking is carried out taking into consideration the Hertz pressure and the bending stress. It should be noted that, for non-surface-hardened gear teeth if the Hertz pressure checking criterion is satisfied; the one in respect of bending is generally also satisfied, the former being the most critical for non-hardened teeth. Experience shows, in fact, these kind of teeth to be liable to pitting and scuffing damages rather more than to tooth breaking, unless flaws of the material exist, such as, for instance, the peculiar circumferential segregations. As for hardened teeth (case-hardened or nitrided), which withstand high surface pressures, the bending strength becomes more relevant and a verification in this respect is therefore impervative. The report sets forth the theory and ideas that dictate the present R.I.N.A. rules for checking gear load capacity against Hertz pressure and bending of teeth. They are quite in line with those followed by the ISO/TC60/GT6 Committee.

• Corporate Authors:

  Registro Italiano Navale

  20 Via Vente Settembre
  Genoa,   Italy 
• Authors:
  • Selvaggi, M
• Publication Date: 1972-5

Media Info

• Features: Appendices; References;
• Pagination: 38 p.
• Serial:
  • Issue Number: 49

Subject/Index Terms

• TRT Terms: Gear teeth; Gears; Pitting; Reduction gears; Stresses
• Old TRIS Terms: Gear pitting; Gear tooth loading; Gear tooth stress
• Subject Areas: Marine Transportation; Vehicles and Equipment;

Filing Info

• Accession Number: 00050808
• Record Type: Publication
• Source Agency: Registro Italiano Navale
• Report/Paper Numbers: Tech Bul
• Files: TRIS
• Created Date: Jan 24 1974 12:00AM