Articulated joint: types and purpose
If electricity, for example, began to be used relatively recently, then mechanics has been accompanying humanity for thousands of years. Ancient knowledge in this area is not inferior to the knowledge of modernity, although, of course, the technologies of our days have changed in many ways. But the elementary laws of kinematics that underlie all mechanical processes are still relevant today. As well as relevant communication centers and transmission between mechanical elements. One of such knots is the hinge.
What is a hinge
A hinge is a pair of kinematic, one element of which makes a rotational movement, turning relative to the second element. The simplest and most widely used hinge is the door hinge. A distinctive feature of a swivel, which is used in mechanics, is the ability of the structural parts, united by it, to make an angular displacement. In the hinges there is no transfer of bending moment between parts of the structure.
In the diagrams and technical drawings, the hinge connection is depicted in the form of a circle small in diameter. This circle can combine two or more structural elements, sometimes adjoining only one.
If the image of the beam superimposed image of the hinge, then the beam has a composite structure, assembled on the hinges. If the hinge is only adjacent to it in the diagram, then such a beam is integral, with a hinge connected to it.
Types of swivel joints
If with the help of a hinge no more than two elements are combined, then such a connection is called a simple hinge. A complex hinge involves the interaction of three or more elements in a single node.
What is a hinge fixed? The system, where the rod can be rotated around the hinge axis, but the hinge pinning point itself remains fixed. Moving are such connections where the axis rotates on the hinge, and the point of attachment of the hinge can move along the guide.
All hinges are classified according to a possible way of displacing the parts to be connected relative to each other. They are:
- Cylindrical rotation. This design of the hinge involves the implementation of angular motion relative to the axis common to both links.
- Ball turning.Angular movement is possible around a common point.
- Cardan type. A complex joint is a hinge, which consists of cylindrical hinges intersected by axes at a right angle (cross). They are consistently combined in combination with the forks of the driving and driven shaft.
- Equal angular velocities (CV). The design is difficult to transfer thrust and the simultaneous implementation of rotational movements with the support of the same torque between the drive and driven shaft.
Rigid joints are represented by elastic half-cardan joints. This is a mechanism where the torque from the leading to the driven shaft, having a different angle, is carried out by the deformation of the link connecting them. The elastic link is made of rubber with possible reinforcement.
An example of such an elastic element is Guibo coupling. It has the form of a hexagonal element in which metal inserts are vulcanized. The clutch is pre-compressed. This design is characterized by good smoothing of oscillations in torsion, as well as knocking of the structure. Allows articulation of shafts with an angle of up to 8 degrees of divergence and movement of the axis up to 12 mm in both directions. The main objective of such a mechanism is to compensate for inaccuracies during installation.
The disadvantages of the site include increased noise in the work, difficulty in manufacturing and a limited service life.
Where applicable swivel
It is possible to apply a joint in practice in accordance with its degree of freedom. A complex hinge can have up to six degrees of freedom in a knot. Three degrees fall on movement, and three on turn. The more degrees of freedom, the more interesting the hinge for the modeling process.
A simple cylindrical hinge is common in household and industrial engineering: all types of door joints, plumbing elements (rotary mixers), tools such as pliers, scissors, any where flat parts are displaced, etc.
The spherical (ball) joint is used in the automotive industry in a running gear, in remote controls, in mechanical engineering and robotics.
Cardan (Hook's hinge) in the transmission of rotational motion from the engine to the rear-wheel drive of the car, from the power take-off shaft to the attachments in special equipment, wherever the gear goes between the angled shafts.
Movable articulated joints of the CV-joint type are installed in front-wheel-drive cars.
Caring for the hinge knot
Hinges are elements that are subject to mechanical stress. They undergo friction loads. Due to the fact that in the modern design of the hinges used bearing units, friction is significantly reduced. But in the process of producing a lubricant, wear increases. Therefore, the hinge connection requires constant lubrication.
In complex joints (automobile CV joints), where open bearing units are used, dirt and dust are a destructive factor. They act as an abrasive and cause rapid metal wear. In such systems, protective covers are used (anthers) that protect the entire hinge as a whole. Caring for such nodes consists in the timely replacement of the anthers, since the rubber tends to collapse, lubrication of the joints will also be required.
Lubricants used for swivels
- Based on lithium. Reliable greases with high conservation characteristics. Reduce the load on the nodal connections up to ten times. They neutralize dust and are compatible with almost all polymeric materials for anthers.The disadvantage is that they have low anticorrosion protection and destroy some plastics.
- Based on molybdenum disulfide. Lubricants long service up to one hundred thousand mileage. Excellent lubricating and anti-corrosion properties. Do not destroy plastics. The disadvantage is that when moisture gets in, the lubricant loses its properties.
- Based on barium. Good lubricants with the virtues of lithium and molybdenum disulfide. Also, they are not afraid of moisture. The disadvantage is destruction at low temperatures and high price.
Do not forget that among the great variety of mechanical structures with different hinge connections and methods of kinematic transmission, the main mechanism is still a human apparatus. Which, by the way, contains 187 natural hinges, called joints. Therefore, in a timely manner taking care of technology and prolonging its life, a person allows her to ease the burden on our body - after all, you see, there is nothing to replace it with.