Types of Machines, Components, and Detachable and Permanent Connections
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A machine is a device that performs mechanical movements to convert energy, materials, and information. Based on their primary purpose, machines are divided into three types:
- energy machines,
- working machines,
- information machines.
What are energy machines?
Energy machines are designed to convert any kind of energy into mechanical energy, and they are called engines. Energy machines include electric motors, internal combustion engines, turbines, and steam engines.
How do working machines differ?
Working machines are divided into technological and transport machines. Technological machines transform the material being processed (raw material), changing its shape, properties, state, and position. Material here is the object being processed, which may be in a solid, liquid, or gaseous state. The transformation of material in these machines lies in changing its form, properties, state, and position.
In transport machines the material is the object being moved, and its transformation consists only of a change in position. Transport machines include automobiles, locomotives, hoists, conveyors, transporters, and similar equipment.
What do information machines do?
Information machines are designed to process information — for example, counting and computing machines. A set of machines connected in sequence and intended to carry out a defined technological process forms a production line. All machines share common assemblies: a frame (bed), a drive, transmission mechanisms, and working parts.
Machine frames are usually cast from cast iron. In the meat and dairy industries, the working parts and machine components that come into contact with the product are made from stainless steel, bronze followed by tinning, or food-grade aluminium, as well as other materials whose use in contact with food products is permitted by the State Sanitary Inspection. In manufacturing food-industry equipment, polymers and plastics are increasingly used.
The machine drive is provided by alternating-current electric motors that have a defined power and shaft rotation speed. The rotation speed of an electric motor does not always match the speed required for the normal operation of the equipment. To provide the necessary rotation speed of a machine's working part, reduction gears as well as belt, chain, and gear drives are used.
Machines, apparatus, and aggregates: what is the difference?
Alongside machines, engineering uses apparatus — devices in which no conversion of energy from one form to another takes place. Heat exchangers are an example of such apparatus.
An aggregate is a mechanical combination of several machines working together as a complex. For instance, a drying-and-grinding aggregate, intended for drying and finely grinding skimmed milk and buttermilk, consists of a dryer and a crusher technologically linked to each other.
Mechanization is the full or partial replacement of manual operations by machines and mechanisms. Automation of production is the stage of machine production characterized by freeing people from directly performing production-control functions and transferring those functions to technical means — automatic devices and systems.
Systems of machines in which individual machines are arranged in the sequence of the technological processes, with the product passed from one machine to the next, are called flow-mechanized lines. A flow line made up of machines and automatic units connected to one another by inter-operation transport mechanisms is called an automatic line.
How are machine parts joined together?
Any machine consists of separate parts — gears, shafts, pulleys, bearings, and so on. All these parts are called components. Each component is usually made from a single piece of metal or some other material.
Components are produced by casting, forging, stamping, welding, or by machining blanks on the appropriate machine tools (lathes, milling machines, planing machines, and so on). Each component has a definite purpose and name.
By purpose, parts are distinguished as connecting parts, parts for rotary motion, coupling parts, transmission parts, crank-and-connecting-rod mechanism parts, and others. Connecting parts are intended to join the separate parts of a machine together. These can be either detachable or permanent joints.
Detachable joints allow parts to be separated from one another without damaging the points of connection. The most widely used connecting parts in detachable joints are bolted and pin connections (Fig. 1) and connections made with a wedge.
Permanent joints are those in which the parts can be separated only after the joint is destroyed. 
Figure 1 — Detachable joints: a – bolted; 1 – nut; 2 – bolt; b – pin; 1 – pin head; 2 – pin rod; 3 – cotter pin.
Permanent joints include welded joints and joints made with rivets. Parts are welded by simultaneously heating them and a metal rod to a high temperature. The rod, melting, fuses with the partially melted parts of the joint, forming a weld seam and connecting the parts being welded.
Joining parts by welding is faster than using rivets, and the welded joint itself has a number of advantages over the riveted joint, which is why the latter method is now applied less often.
Which parts create rotary motion?
A large group of parts is intended to create rotary motion in machines, including:
- shafts,
- axles,
- supports,
- bearings,
- keys.
Shafts are intended to transmit rotary motion, while axles only support the rotating parts of a mechanism; for this reason axles work only in bending, whereas shafts work in both bending and torsion. Shafts may be either straight or crankshafts (for example, in the engines of tractors, automobiles, and other machines).
The parts of a shaft by which it rests on bearings are called journals (support sections). The parts that support shafts are called bearings (sliding or rolling).
A sliding bearing (Fig. 2, a) consists of a housing, a liner, shims, and bolts. In sliding bearings, 5 to 10 times more work is lost to friction than in rolling bearings. Lubricating sliding bearings also requires more lubricant, and their maintenance is more complicated than that of rolling bearings.
Rolling bearings can be ball bearings (Fig. 2, b) or roller bearings. Depending on their purpose, ball bearings can in turn be radial, thrust, angular-contact, and so on, while roller bearings can have cylindrical (Fig. 2, c) or tapered rollers (Fig. 2, d).
Keys are intended to fix pulleys, gears, couplings, and other parts onto shafts. There are several designs of keys. Most often, parallel (prismatic) keys are used. A parallel key is a rectangular bar, part of which fits into a slot in the part and part into a groove in the shaft, thus fastening the part to the shaft. 
How do mechanisms and transmissions work?
Transmission mechanisms are used to transfer rotary motion from one machine shaft to another. The shaft from which the rotary motion is transmitted is called the driving shaft, and the shaft to which this motion is transmitted is called the driven shaft.
Transmissions can be belt, gear, worm, chain, articulated, and friction types. Transmissions of all these kinds are widely used in agricultural machine-building. A belt transmission (Fig. 3) consists of pulleys fixed by keys on the shafts and a flexible belt that wraps around the pulleys. The ratio of the rotation speed (n1) of the driving pulley to the rotation speed (n2) of the driven pulley is called the transmission ratio, that is, i = n1/n2.
If pulleys are connected by a belt, they have the same circumferential speed at their surfaces, and the product of the diameter (D1) of the driving pulley and its rotation speed (n1) equals the product of the diameter (D2) of the driven pulley and its rotation speed (n2), that is, D1n1 = D2n2. Using this relationship, you can always determine one unknown value if the other three are known.
Belt transmissions come in two kinds — with a flat belt or a V-belt. In a V-belt transmission (Fig. 3, d) the cross-section of the belt is a trapezoid. Such a transmission has one belt or several, with a separate groove on the pulley for each one. 
V-belt transmissions are used when the distance between pulleys is comparatively small, while flat-belt transmissions are used when this distance is large (when transmitting motion from engines to stationary machines). Flat-belt transmissions can be open, when both pulleys rotate in the same direction (Fig. 3, a), and crossed, when the pulleys rotate in opposite directions (Fig. 3, b).
Half-crossed transmissions (Fig. 3, c) are used to transmit motion between shafts set at a 90° angle to one another.
A chain transmission (Fig. 3, e) is intended to transmit rotary motion between parallel shafts. A single chain can wrap around and drive several sprockets mounted on different shafts. However, such transmissions can work properly only when all the sprockets lie in the same plane. Agricultural machines widely use two types of chain transmissions — with roller and barrel (bushing) chains.
Gear transmissions consist of two gear wheels fixed on shafts. Rotary motion and load in gear transmissions are transferred through the meshing of teeth arranged on the rim of the wheel. In gear transmissions, the wheels can be cylindrical (Fig. 4, a, b) and conical (Fig. 4, c).
Cylindrical gears transmit rotary motion between parallel shafts, while conical gears transmit it between shafts set at an angle to one another. 
The transmission ratio of a gear transmission is the ratio of the number of teeth of the driving wheel to the number of teeth of the driven wheel.
A worm transmission (Fig. 4, d) — a type of gear transmission — is intended to transmit rotary motion between shafts set at a right angle. A worm transmission can provide transmission ratios over a wide range (from 5 to 300) and consists of an endless screw (worm) and a worm wheel. If the worm is the driving element and the wheel the driven one, the transmission slows down the rotary motion; conversely, if the wheel is driving and the worm driven, the transmission accelerates it. 
A cardan, or universal-joint, transmission is used to transmit rotary motion between shafts of which the driven one is, as it were, a continuation of the driving one but set at an angle that may change slightly (for example, in transmitting motion from the gearbox shaft to the driving pinion of an automobile's rear axle, or from a tractor's power take-off shaft to the working parts of a feed distributor).
Flexible shafts are used when rotary motion has to be transmitted to a shaft that constantly changes its position by a fairly significant amount — for example, transmitting rotary motion from a stationary electric motor to the shaft of a shearing machine, whose position constantly changes during operation. A flexible shaft consists of a core and a casing (armour). The core is twisted from several layers of thin wire and inserted into the casing, which has the form of a flexible tube.
What types of mechanisms convert motion?
Mechanisms are the parts of machines intended to produce or transform movements. Mechanisms can be crank-and-connecting-rod, eccentric, cam, planetary, ratchet, and others.
A crank-and-connecting-rod mechanism is intended to convert rotary motion into reciprocating motion or vice versa. Figure 5 shows the crank-and-connecting-rod mechanism of an internal combustion engine. In it, the rectilinear reciprocating motion of piston 1 is converted into the rotary motion of crankshaft 4.
An eccentric mechanism is often used where, in crank-and-connecting-rod mechanisms, the role of the crankshaft is played by an eccentric — a disc with a pin set at a certain distance from the disc's centre of rotation.
A cam mechanism converts the rotary motion of a shaft into the reciprocating or reciprocating-rotary motion of a follower that rests on the cam.
A ratchet mechanism (Fig. 6) converts the continuous rotary motion of the driving shaft into the intermittent motion of the driven shaft. A ratchet mechanism works as follows. The ratchet wheel 1 is firmly mounted on the shaft that is to rotate intermittently. The pawl 2 sits freely on an axle mounted on lever 4 and is pressed against the ratchet wheel by spring 3. Lever 4 is hinged to lever 5, the other end of which is also hinged to an eccentric that rotates continuously about axle 7. As the eccentric rotates, lever 4 performs an oscillating movement. 
When the lever moves counterclockwise, the pawl engages a tooth of the ratchet wheel and turns it through a certain angle. When the lever moves in the opposite direction, the pawl slips over the teeth of the ratchet without rotating it. In this way the intermittent rotary motion of ratchet wheel 1, and with it the driven shaft, is achieved. Ratchet mechanisms are widely used in tractor feed distributors to drive the unloading conveyor.
A planetary mechanism is a gear transmission in which the wheels rotate not only about their own axis but also about the axis of the central wheel.
A differential mechanism is a planetary mechanism in which the resulting motion equals the difference or the sum of the motions of which it is composed. This mechanism is widely used in automobiles and tractors and allows the driving wheels of an automobile or tractor to rotate at different speeds. This is needed when turning, when the outer wheel travels a greater distance because it moves along a curve of larger radius, and when driving over an uneven road, where the paths of the two wheels are also unequal (one wheel rolls, for example, along a level stretch of road, while the other rolls along a curved one).
