Shigeru Hoyashita

Remarkable effects of running-in upon surface durability of steel and bronze

Abstract The authors have shown that, in order to obtain a pitting limit higher than 0.5 times the Brinell hardness, the nearly full elastohydrodynamic lubricating (ehl) oil film must be formed at an early stage of loaded running. However, it was almost impossible to obtain a full ehl oil film without running-in at Hertzian stresses higher than 1000 MPa in the case of metal rollers made from two representative materials, ie a low hardness steel and a phosphor bronze. The progress of running-in was affected deleteriously by a few small protrusions on the harder surface with different hardness combinations, or a hard spot with nominally equal hardness combinations (rolling pairs). This paper demonstrates how and why the few protrusions or the hard spot occupying an area less than 0.2% of the total contact surface can prevent the completion of running-in, ie the formation of the full ehl oil film. The reduction in the rate of running-in can cause pitting due to the accumulation of the fatigue damage before emergence of the beneficial effect of running-in

Appreciable increase in pitting limit of steel and bronze

Abstract The influences of lubrication and slide/roll ratio on the pitting limits of metal rollers, made from two representative materials, a steel and a phosphor bronze with hardness 180 and 150 HB respectively, have been studied using high performance testing machines designed by the authors. The pitting limit of both materials was appreciably greater in full ehl conditions than when much metallic contact occurred. With 180 HB steel, the highest pitting limit (0.74 times the Brinell hardness) was uninfluenced by the amount of sliding in the contact, provided nearly full ehl conditions were achieved within 0.5 × 10 6 revolutions. With phosphor bronze, a pitting limit of 0.71 times the Brinell hardness could be achieved in pure rolling conditions, but only 0.58 times the Brinell hardness when sliding was introduced. This is shown to be due to difficulties of running-in with the phosphor bronze rollers

Effects of Surface Roughness and Spin Motion on Surface Durability and Traction Coefficient.

The durability (pitting limit) of through-hardened steel rollers (about 500 HB) whose surfaces have Rmax ranging from 0.2 to 6μm is examined using a rolling contact fatigue testing machine. Then, the torque of a driving shaft and duration of full EHL conditions between two rollers are measured during running. The greater the surface roughness is, the larger the traction coefficient, and the smaller the surface durability. When a pair of tapered rollers is used, a spin motion is induced. However a surfacc durability is not markably decrcased. If a pit might occur on a pair of rollers, it has occurred on the contact surface with minus sliding ratio of a following roller. The effective traction coefficient between rollers with a spin motion is calculated from those obtained in the absence of the spin motion.

Calculation Method of Cutting-Edge Profile of Globoidal Worm-Shaped Tool for Finishing Helical Gear.

In this paper, exact calculation methods for cutting-edge profiles of two kinds of globoidal worm-shaped tools for finishing a helical gear with an arbitrary tooth profile are proposed. One is a globoidal worm-shaped tool which is in line contact simultaneously with many teeth of a helical gear finished by it. The other whose cutting-edge profile is the same in all sections including the tool axis, is in point contact with the helical gear to be generated. The latter can finish many kinds of gears with different numbers of teeth or helix angles. By substituting zero for the number of threads, these methods are applicable to a form-grinding wheel.

Effects of tooth heights on noise and vibration of mirrorlike ground gears.

Spur gears with profile contact ratios ranging from 1.62 to 2.15 were mirrorlike finished to an accuracy of JIS 0 class using a CNC gear grinder designed and made by the authors. Elastic deformations of teeth and the resulting rotational errors of test gears were calculated, and then the amount and the starting point of profile modifications were decided by considering both the total elastic deformation and the pitch errors of the gears. In the case of non-modified gears, running noise and vibration could be decreased when the profile contact ratio was made greater than two. They could be decreased further when a proper modification was given to the gears. Experimental results suggested that the proper amount of modification is a little greater than the elastic deformation at the tooth tip when the proposed load (full load) is assumed to be applied at a point, where the modification start, which is a little higher than the pitch point.

New release ports applicable to high-pressure gear pumps and their effectiveness.

The authors introduced two kinds of new pressure-release ports for improving the performance of gear pumps with involute profiles. High-pressure gear pumps as well as low pressure ones were used for verifying the effectiveness of the new release ports. In the case of the low-pressure pumps, the total efficiency of the pump with the new release ports was higher by about 10% when compared with the one having conventional release ports. However, when the improved conventional release ports, which were found in a gear pump currently available on the market, were used, the increase reduced from 10% to about 4% at a delivery pressure of about 700 kPa. Running noise and vibration of the gear pumps with the new release ports were appreciably smaller than those of the one with the conventional release ports. In the case of the high-pressure gear pumps, the increase in the total efficiency was about 5% at a delivery pressure of about 10 MPa. The reason for the improvement in the total efficiency was clearly explained by the maximum pressure measured in the semienclosed tooth space between two mating gears of the gear pumps with different release ports.

Design, Manufacture and Performance of Internal Gear Pumps : 1st Report, Non-Involute Type Pumps for Easy Manufacture

For easy manufacture of internal gear pumps, an internal gear with a convex tooth profile and an external gear, of which tooth-top edge contacts with the convex profile, are used for the gear pumps. Gearing theory of these gears and the theoretical delivery of the internal gear pumps with these gears are clarified. The prominent characteristic found in the gear pumps is that the theoretical torque caused by delivery pressure is zero for the external gear (idler). In practice, a small value of the resistance torque appears on the idler due to viscous friction, etc. It is shown that the resistance torque has no detrimental effects on the tooth surface up to a delivery pressure of about 2 MPa in the present experiments because the Hertzian contact pressure is less than the allowable contact stress of a low hardness steel when the tooth-top edge is rounded to a radius of about 0.5 mm. Six kinds of gear pumps were designed and made by the authors, and almost all characteristics of these gear pumps were clarified by experiments with the support of the theoretical results obtained in the present investigation.