Worm drives (or worm equipment sets) are right angled drives and so are used in screw jacks where in fact the input shaft is at right angles to the lifting screw. Other types of right angle drives are bevel gears, and hypoid gears. Worm drives fulfill the requirements of many systems and offer a compact method of decreasing rate whilst increasing torque and so are therefore ideal for use in systems utilising e.g. lifting equipment where a high gear ratio implies it could be driven by a small motor.
A worm drive consist of a worm wheel and worm gear also referred to as worm screw or just worm. The worm steering wheel is similar in appearance to a spur gear the worm equipment is in the form of a screw generally with a flank angle of 20°. The worm gear screw can be solitary start or have multiple starts depending on the reduction ratio of the apparatus set. The worm includes a relatively few threads on a small size and the worm steering wheel a sizable number of teeth on a large diameter. This combination offers a wide selection of equipment ratios typically from 4:1 to 300:1.
The low efficiency of a worm drive lends itself to applications that require intermittent rather than continuous use. The worm get inefficiency originates from the sliding contact between your teeth. Appropriate and adequate lubrication must be applied to dissipate the heat produced and reduce the wear price. For extended life the worm equipment it created from a case hardened steel with a ground finish and the worm wheel is often created from bronze or cast iron. Other material combinations are used where suitable and in light duty applications contemporary nonmetallic materials are deployed.
Worm Gear Assembly
Multi-Start Threads and Self-Locking
Often a screw system (such as for example that found in a screw jack) is required never to ‘back-drive’ when the holding force is eliminated and an axial load is applied. An individual start multi start worm gear thread is often used in these situations as the shallower helix position causes better friction between threads and is usually sufficient to prevent slippage. Such something is said to be self-locking. This assumes a statically loaded system with little if any vibration as this may cause the friction angle to be conquer and the combination to untighten. In systems that are at the mercy of vibration a locking mechanism or brake is advised to prevent back-drive.
If self-locking isn’t a requirement of a system but a greater acceleration of translation is a multi begin thread can be utilized. This implies that multiple thread forms are manufactured on the screw shaft.
Single Start Thread: A single helical thread formed around a screw body. For every 360° revolution of the screw, the form offers advanced axially by the pitch of 1 thread. This has the same worth as the pitch. In the case of an individual start thread, lead and pitch are equal.
Double Start Thread: Two thread forms. During 360° revolution the forms progress axially by the combined pitch of two threads. Lead is usually 2x the pitch.
Triple Start Thread: Three thread forms. During 360° revolution the forms advance axially by the mixed pitch of three threads. Lead is normally 3x the pitch.
Single Begin Thread, Double Begin Thread, Triple Start Thread
A multi start thread has a steeper helix angle which results in less friction between your threads and for that reason such a system is less inclined to be self-locking. It comes after a steeper helix permits quicker translation along the threads i.e. something utilising a multi start thread could be tightened in fewer rotations than one using a single start thread.
Worms are the driving equipment in a worm and worm equipment set. EFFICIENCY of worm equipment drives is dependent to a large extent on the helix angle of the worm. Multiple thread worms and gears with higher helix position prove 25% to 50% better than solitary thread worms. The mesh or engagement of worms with worm gears generates a sliding action causing considerable friction and greater loss of efficiency beyond other styles of gearing. The use of hardened and surface worm swith bronze worm gears raises performance, but we’ll make them out of virtually any materials you specify. The amount of threads on a worm and the number of tooth on a worm gear will determine the ratio of your established. Ratios are determined by dividing the number of teeth in the gear by the number of threads. Typically the amount of threads on a worm are 1,2, and 4, but 3, 5, and 6 are out there as well. To determine how many threads are on your worm just look at it from the best where the threads begin and count the number of starts.
Incorporating various multi start threaded worm shafts in to Ever-Power screw jacks increases the linear output rate range we are able to offer.