Mechanical engineering: design, production, analysis, working and improvement of technical objects with moving parts

LINKING IN TECHNICAL OBJECTS A link holds two or more parts of the same technical object together. In mechanics, a component is a part or fluid that performs a mechanical function.

Linking is the mechanical function performed by any component that connects different parts of a technical object. Every link displays four basic characteristics: 1.direct or indirect, 2.rigid or flexible, 3.removable or non-removable, and 4.complete or partial.

There are six possibilities of independent motion: three translational motions and three rotational motions, in relation to the three axes commonly used to define dimensions (x, y and z). The degrees of freedom are the set of independent movements that are possible for a given part in a technical object.

GUIDING CONTROLS Guiding is the mechanical function performed by any component that controls the motion of one or more moving parts. A guiding component or control is a component whose mechanical function is to guide the motion of moving parts.

There are three main forms of guiding: 1. Translational guiding ensures the straight translational motion of a moving part. 2. Rotational guiding ensures the rotational motion of a moving part. 3. Helical guiding ensures the translational motion of a moving part while it rotates about the same axis.

Adhesion is the phenomenon by which two surfaces tend to remain in contact with each other without slipping. The strength of adhesion between two surfaces depends mainly on five factors: 1.the nature of the materials in contact, 2.the presence of a lubricant, 3.temperature, 4.the state of the surfaces in contact, 5.the perpendicular force exerted by one surface on another.

In mechanics, friction is a force that resists the slipping of one moving part over another. Lubrication is the mechanical function performed by any component that reduces friction between two parts.

Motion Transmission Systems In some technical objects motion is transferred from one part to another. The most common types of motion transmission systems are: a.Gear trains b.Chain and sprocket systems c.Worm and worm gear systems d.Friction gear systems e.Belt and pulley systems.

Each mechanical system has a component the activates the motion (driver) and a component that transfers the motion to another part (driven). Some systems may even have an intermediate component(s). The direction of rotation of the components depends on the type of system and the placement of the components.

Speed change A speed change in the rotation of the gears will occur when using components of different sizes. When connecting smaller components with larger ones, the smaller one will have a greater rotational speed.

When using a gear with teeth the rotational speed is inversely proportional to the teeth number ratio(s). When using a smooth gear, the rotational speed is inversely proportional to the diameter of the gears.

Ex. Find the rotational speed of the driven pulley below.

Ex. Find the rotational speed of the larger gear if the smaller one is at 20 rpm.