The worm gear system consists of two components - the wheel and the worm itself. It is necessary in order to receive rotation and transfer it between the intersecting shafts (from one to the second), while reducing the speed and number of revolutions. The wheel works in conjunction with a worm, which can have left or right threads, as well as single or multiple threads.
Basic data
A worm is a threaded screw that transmits its rotation to a screw wheel with arc-shaped teeth, causing it to rotate.
The teeth and threads of the screw are in the hitch. The axes of the shafts of the worm wheel intersect at right angles, the screws intersect in the same plane and are mutually perpendicular.
The self-braking capability only allows movement from the worm to the wheel, otherwise braking may start and stall.
The helical screw is a worm cutter that is used in the worm wheel. Such cutters have different classifications (according to processing, quantityvisits, etc.).
Varieties
Classification of worm gears is divided into two types: globoid gear worm wheels and spur gears. The globoid version requires concentrated precision manufacturing and increased attention to cooling, and when worn, it reacts very subtly to the displacement of the screw along the axis. The cylindrical view has circular cylinders on the surfaces of the wheel and the worm (initial and index).
Worm threads can have a trapezoidal thread in axial section (the most popular type is Archimedes), the same profile, but in normal section (convolute), involute (with a similarly named thread in axial section) or with a concave profile for maximum contact with the wheel.
Pros and cons
Benefits include:
- quiet and smooth running due to the special hitch;
- reliable performance;
- small size and compact design;
- possibility of reduction (obtaining large gear ratios) using one stage;
- self-braking or stopper, no possible backstop;
- easy to use and make worm wheels;
- low cost compared to other gearboxes (helical).
As for spur gearboxes, with which worm designs are often compared, their advantages include high efficiency, hardly perceptible heating and little backlash of the output shaft. They are just as reliable and have a highoperability, there is no independent stopper.
Flaws
The main disadvantages of the worm wheel include reduced power and restrictions on its transmission, a decrease in efficiency, as a result of which it is impossible to transfer heavy loads. Also, for the manufacture of some parts, strict adherence to accuracy is necessary, the use of expensive and rare materials, special lubricants, and in case of rapid wear or jamming, quality adjustments are important. The disadvantages can include an increase in the temperature of the housing and heating at the clutch site, an increase in the backlash of the output shaft when the gearbox wears out.
Occasionally it becomes necessary to reverse the output shaft without having to start the gearbox. In this situation, locking, which is considered an advantage of this type, becomes its disadvantage. Despite all the existing flaws in the form of increased heat generation and lack of power transfer, this transmission option is used in cases where there are no significant shock-type loads. This is a budget and relatively cheap option, which is used in mechanical engineering, mixers, conveyors and conveyors.
Worm gears are compared with cylindrical ones, which also have a number of disadvantages. They have a low gear ratio using one step.
Scope of application
Worm gears are used as a gearbox in order to reduce the number of revolutions. Such an elementused for cars and other vehicles, in various machine tools and cranes, machines, when lifting loads.
The use of worm gear wheels is relevant in cases where, at low cost, it is required to reduce rotation and accelerate torque. The worm in each of these options sets the movement, the wheel reacts.
Product design
As you know, a worm wheel is a transmission consisting of two links: driven and driven, which work in a coupling. The main one is a worm in the form of a screw, which sets the movement to the second element - the helical gear. It is on its teeth that the turns on the screw slide. All together this is a gear-screw system. Most often, worm wheels are composite, this affects the cost, lowering it.
The worm is the master, and most often the postback is not feasible because
this may cause the gearbox to brake. Worm teeth are longitudinally circular coils.
Archimedean screws are the most common type of worm in mechanical engineering. This option is in demand and easy to manufacture.
The standard options for worm wheels in mechanical engineering include bimetallic, shrouded and bolted designs. The first is often found in mass production.
Materials used
Specialized anti-friction materials are used for the manufacture of the worm wheel, which prevent sticking and sticking, promote long-term operation and wear resistance, affectcoefficient of friction, reducing and reducing it.
If all materials are chosen correctly, the efficiency increases, and friction does not cause additional costs.
Various materials and alloys are used for the links: for the screw - steel, paying special attention to the grade of the material and its hardening. Most often, the screw is one-piece, joint with the shaft. Attached options are periodically found.
In the manufacture of the wheel, bronze is used, as well as alloys of tin and nickel, aluminum and iron. It is possible to use cast iron, brass for the ring gear. Often the wheel has a steel or cast iron hub. The wheels are cast using the centrifugal method.
Shapes and views
The screws are divided into left and right, depending on the location and direction of the turns. In the first case, the screw is unscrewed by moving clockwise. In the second case, moving in the same direction, the screw is screwed in. These changes can be seen when tracking movement from the end of the propeller.
The screw can have one or many turns (ridges), which, depending on the number, are placed on a helix located on the dividing cylinder. This characterizes the number of turns of the screw. The worm can be located above, below or to the side of the wheel, thus changing the shape of the transmission.
The worm wheel shaft can be horizontal or vertical.
Surface and profile may also varyscrew threads, while several transmission options are possible, each of which has its own cutting method (with a convolute, involute, Archimedean screw).
In addition, worm wheels may differ depending on the shape of the surface of the screw on which its thread is formed (cylindrical or globoid screw). In the second case, the transmission has a higher efficiency, but is not easy to create and release, a distinctive feature of the formation is the arc of a circle. In the first version, the distinguishing feature is a straight line that forms a dividing surface.
The worm wheel is the main part of the worm gear, which includes the wheel and the screw. These two links are a worm pair that interacts with each other according to the screw principle. Gearboxes are made on its basis. The product has a low efficiency, but is easy to manufacture and use.
We examined what a worm wheel is, highlighted the main advantages and disadvantages, indicated the production materials and scope.
