Tham khảo tài liệu 'manual gearbox design part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 96 Manual Gearbox Design Figure cont. Strength of teeth When determining the dimensions of bevel gears the strength of the teeth must be checked so as to ensure that the power can safely be transmitted when operating at maximum load. By calculating the beam strength of the teeth the allowable power-transmitting capacity of the gear will be well within the safe limit as the beam strength of the teeth is the more important consideration for hardened gears. It must however not be forgotten that many other factors which cannot be considered in the formulae for the beam strength of the teeth have an influence on the gear tooth strength. For example the type of lubricant and method of lubrication whether the shafts on which the gears run are rigidly supported the elasticity of the full gear train the Crown wheel and pinion designs 97 tooth surface finish on both the face and flanks together with the relative sliding motion between the mating faces - all have great influence upon the strength and ultimately the overall performance of the gear train. The determination of the beam strength of the gear teeth using the Lewis formulae is calculated as follows 6 PbB aB- j7mn -b-y 72 o V For bevel gears which run at higher speeds - above 33 ft s - and which need a lot of attention to detail both in design and manufacture the factor 6 6 v can be replaced by 10 10 V when calculating the dynamic load capacity of the gear drive where the factors in the formula are as follows ƠB static breaking strength kg cm2 - the static breaking strength for 5 ECN 55 is 12000kg cm2. The static breaking strength for other steels varies in proportion of their Brinell hardness to the Brinell hardness of . the Brinell hardness of equals 200-235 6 1 6 K speed factor 10 I 10 kJ K circumferential speed at the mean cone length derived from the following formula r liA im s 60000 m s 73 mn normal module b facewidth y tooth profile factor depending upon the equivalent number
