Worm Gear Sets
Printable Documentation [pdf]

Advanced production methods combined with years of experience have made Framo-Morat's name a byword for quality in worm gears.

Our catalog gear sets come in a wide range of center distances and transmission ratings and are usually available direct from stock. Other center distances and transmission ratings can be designed and produced at our factory.

The gear sets are normally right-handed, but can be produced left-handed on request.

Materials

The worms are case-hardened steel; the bore and worm flanks are ground.

Standard worm gears are made from VL22, a copper-zinc alloy with aluminium, silicon and manganese additives. 

Phenolic worm gears available for some sizes

Made from phenolic resin and ultra-fine cotton fabric, phenolic (Hgw 2083) is a moulded laminate with very good mechanical properties.  Worm gears made from Hgw 2083 can only be used at around 40% of the torque loading recommended for bronze gears.

Self-locking

Self-locking is affected by the lead angle, the roughness of the flanks, the sliding speed, the lubricant and increases in temperature.

Self-locking can be dynamic or static. Dynamic self-locking: lead angle up to 3° with grease lubricant; lead angle up to 2.5° with synthetic oil lubricants.

Static self-locking: lead angle from 3° to 5° with grease lubricant; lead angle from 2.5° to 4.5° with synthetic oil lubricants. No self-locking facility is available for lead angles over 4.5° or 5°.

Jarring and vibration can prevent gears from self-locking. Self-locking can also be adversely affected if sliding conditions are particularly good. This can be caused by a number of factors relating to the lubricant, sliding speed and loading. For this reason we are unable to assume any warranty obligations for self-locking.

Installing the worm gear

	The reference surface tolerances will determine the lateral positioning of the worm gears. The lateral tolerance “c” must not exceed 0.15 mm for any centre distance.
	Turn gear wheel in direction of arrow	Correct marking	Turn gear wheel in direction of arrow

You can tell whether the worm gear is in the correct axial position by checking the position of the tooth contact pattern when the gear wheel is installed. If possible the tooth contact pattern should be towards the run-out side. When the gear is turned in the other direction (reverse operation) the tooth contact pattern should be towards the centre.

Efficiency

The efficiency of the gear set generally depends on the following parameters:

• Lead angle of the worm
• Sliding speed
• Lubricant
• Surface quality
• Installation conditions

The larger the centre distance, the greater the degree of efficiency. Sliding bearings are often used with gears with smaller centre distances to save space and reduce costs. The sliding bearings have higher coefficients of friction, which can have a considerable effect on the overall efficiency of the gear. Efficiency data can be obtained from the manufacturer or our catalogue.

Helical gearing

A helical gearing is a spur-type gearing which is inclined at the same angle as the lead angle of the worm. As the contact pattern is linear, a lower torque than that of a worm-type gearing is transmitted and the service life is reduced.

Lubricant table (extract)

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