Worm Gear Sets
Printable Documentation [pdf]

Advanced production methods combined with years of experience in manufacturing gears and providing customers with sound advice have made Framo®’s worm gear sets a byword for quality.

Over the last few decades Framo gear sets have won appreciable market shares both in Germany and abroad. As well as stocking moderate quantities of catalogue gear sets (made to Framo standards), we also make custom-designed gear sets to order.

Our catalogue gear sets come in a wide range of center distances and transmission ratings and are usually available direct from stock.

Other centre distances and transmission ratings can be calculated and produced at our factory, although it is not always possible to use existing gear cutting tools.

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

Materials

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

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

Plastic worm gears

Owing to their poor thermal conductivity, plastic worm gears are only suitable for low sliding speeds of <1.5 m/s and medium tooth flank loading. The worm must be hardened and must have ground flanks.

Plastic worm gears have around 60% of the torque capacity of comparable bronze worm gears (this applies for use with mineral grease).

Phenolic worm gears

Made from phenolic resin and ultra-fine cotton fabric, phenolic (Hgw 2083) is a moulded laminate offering 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.

Bronze worm gears

Cu Sn 12 DIN 1705 Relatively soft material with good wear resistance: suitable for high sliding speeds.

Cu Sn 12 Ni DIN 1705 Relatively soft material with very high wear resistance: suitable for very high sliding speeds.

CuAl10Fe3Mn2 DIN 17665 / 17672 Relatively hard anti-friction materials for high loads and relatively low rotational speeds.

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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