Kayra Ermutlu-030060081 (7th Week)

Svetozarov's Variator

This variator was developed in Russia and is known as the spheroid with swivelling discs variator too. The trans mission ratio is changed by tilting the dics about their axes, and the instantaneous valur is given by the relation ship: i=r1*Ψ/r2

The spheroids are made of hardened steel (HRC 60-65) and the discs of tekstolite. This variator has the following characteristics: Rv(max)=8, N(max)=25kW, v(max)=20 m/s, η=0.85

(Metha N.K., Machine Tool Design and Numerical Control, pg.116, Kayra Ermutlu)

Wulfel-Kopp Variator

Wulfel-Kopp variator uses two spheres as drive elements. The driving shaft which is mouthed with a conical driver, drives the sphere which transmits power to another conical member, mouthed on the driven shaft. The spheres are mouthed on seperate shafts, to enable tilting them when required. The tilt of the sphere shafts determines the contact radii r1 and r2 on the sphere. Other factors contributing to the transmission ratio (i), are the contact diameters d1 and d2, on the driving and driven shaft cones.

(Joshi P.H., Machine Tools Handbook: Design and Operation, pg.253, Kayra Ermutlu)

Bevel Gear

Bevel gears are most commonly used for power transmission through shafts with intersecting axes. Bevel gears are analogous to friction-cone drive when the conical surface of one cone drives the conical surface of the other cone by friction, with teeth provided on the cones for positive drive.

The pitch surface of a bevel gear is truncated cone. When two bevel gears mate, their respective pitch cones contact along a common tangent. When expanded, pitch cones meet at a common pitch called apex.Shaft center lines of gears also intersect at the apex.

While a bevel gear is in motion, every point on a bevel gear remains at a constant distance from the apex. The back of the bevel gear is also made conical, and so this cone is known as back cone, and it is tangent to a theoretical sphere at the pitch diameter.The thickness of the tooth varies from the inner edge to the outer edge (large end). Tooth data of a bevel gear always refer to the large end.

(Jindal U.C., Machine Design, pg. 687, Kayra Ermutlu)

Snap-fit

In all types of joints, a protruding part of one component, such as a hook, stud, or bead, is briefly deflected during the joining operation, and it is made to catch in a depression (undercut) in the mating component. This method of assembly is uniquely suited to thermoplastic materials due to their flexibility, high elongation, and ability to be molded into complex shapes. However, snap-fit joints cannot carry a load in excess of the force necessary to make or break the snap-fit. Snap-fit assemblies are usually employedto attachlids or covers that are meant to be disassembled or that will be lightly loaded. The design should be such that, after assembly, the joint will return to a stress-free condition.

(Harper C.A., Handbook of Plastics, Elastomers, and Composites, pg.547, Kayra Ermutlu)