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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Mill. History of invention and production
Directory / The history of technology, technology, objects around us The first tools for grinding grain into flour were a stone mortar and pestle. Some step forward in comparison with them was the method of grinding grain instead of crushing. People very soon became convinced that grinding flour turns out much better.
However, it was also extremely tedious work. The big improvement was the transition from moving the grater back and forth to rotation. The pestle was replaced by a flat stone that moved across a flat stone dish. It was already easy to move from a stone that grinds grain to a millstone, that is, to make one stone slide while rotating on another. Grain was gradually poured into the hole in the middle of the upper stone of the millstone, fell into the space between the upper and lower stones and was ground into flour.
This hand mill was most widely used in ancient Greece and Rome. Its design is very simple. The basis of the mill was a stone, convex in the middle. At its top was an iron pin. The second, rotating stone had two bell-shaped recesses connected by a hole. Outwardly, it resembled an hourglass and was empty inside. This stone was planted on the base. An iron strip was inserted into the hole. When the mill rotated, the grain, falling between the stones, was ground. Flour was collected at the base of the lower stone. Such mills were of various sizes: from small ones, like modern coffee grinders, to large ones, which were driven by two slaves or a donkey. With the invention of the hand mill, the process of grinding grain was facilitated, but still remained a laborious and difficult task. It is no coincidence that it was in the flour milling business that the first machine in history arose that worked without the use of the muscular strength of a person or animal. This is a water mill. But first, the ancient masters had to invent a water engine. The ancient water-motors apparently developed from the watering machines of the Chadufons, with the help of which they raised water from the river to irrigate the banks. Chadufon was a series of scoops that were mounted on the rim of a large wheel with a horizontal axis. When the wheel was turned, the lower scoops sank into the water of the river, then rose to the top of the wheel and overturned into the chute. At first, such wheels were rotated by hand, but where there is little water, and it runs quickly along a steep channel, the wheel began to be equipped with special blades. Under the pressure of the current, the wheel rotated and drew water itself. The result was a simple automatic pump that does not require the presence of a person for its operation.
The invention of the water wheel was of great importance for the history of technology. For the first time, a person has at his disposal a reliable, versatile and very easy to manufacture engine. It soon became apparent that the movement created by the water wheel could be used not only to pump water, but also for other needs, such as grinding grain. In flat areas, the speed of the flow of rivers is small in order to turn the wheel with the force of the impact of the jet. To create the necessary pressure, they began to dam the river, artificially raise the water level and direct the jet along the chute onto the wheel blades.
However, the invention of the engine immediately gave rise to another problem: how to transfer the movement from the water wheel to the device that should perform useful work for humans? For these purposes, a special transmission mechanism was needed, which could not only transmit, but also transform rotational motion. Solving this problem, the ancient mechanics again turned to the idea of the wheel. The simplest wheel drive works as follows. Imagine two wheels with parallel axes of rotation, which are in close contact with their rims. If now one of the wheels begins to rotate (it is called the driver), then due to the friction between the rims, the other (slave) will also begin to rotate. Moreover, the paths traversed by the points lying on their rims are equal. This is true for all wheel diameters. Therefore, a larger wheel will make, in comparison with the smaller one associated with it, as many times fewer revolutions as its diameter exceeds the diameter of the latter. If we divide the diameter of one wheel by the diameter of the other, we get a number that is called the gear ratio of this wheel drive. Imagine a two-wheel transmission in which the diameter of one wheel is twice the diameter of the other. If the larger wheel is driven, we can use this gear to double the speed, but at the same time, the torque will decrease by half. This combination of wheels will be convenient when it is important to get a higher speed at the exit than at the entrance. If, on the contrary, the smaller wheel is driven, we will lose output in speed, but the torque of this gear will double. This gear is useful where you want to "strengthen the movement" (for example, when lifting weights). Thus, using a system of two wheels of different diameters, it is possible not only to transmit, but also to transform the movement. In real practice, gear wheels with a smooth rim are almost never used, since the couplings between them are not rigid enough, and the wheels slip. This drawback can be eliminated if gear wheels are used instead of smooth wheels. The first wheel gears appeared about two thousand years ago, but they became widespread much later. The fact is that cutting teeth requires great precision. In order for the second wheel to rotate evenly, without jerks and stops, with uniform rotation of one wheel, the teeth must be given a special shape, in which the mutual movement of the wheels would be as if they were moving over each other without slipping, then the teeth of one wheel would fall into hollows of the other. If the gap between the teeth of the wheels is too large, they will hit each other and quickly break off. If the gap is too small, the teeth cut into each other and crumble. The calculation and manufacture of gears was a difficult task for ancient mechanics, but they already appreciated their convenience. After all, various combinations of gears, as well as their connection with some other gears, provided enormous opportunities for transforming movement.
For example, after connecting a gear wheel to a screw, a worm gear was obtained that transmits rotation from one plane to another. Using bevel wheels, it is possible to transmit rotation at any angle to the plane of the drive wheel. By connecting the wheel to the toothed ruler, it is possible to convert rotational motion into translational, and vice versa, and by attaching a connecting rod to the wheel, a reciprocating motion is obtained. To calculate gears, they usually take the ratio not of the diameters of the wheels, but the ratio of the number of teeth of the driving and driven wheels. Often several wheels are used in the transmission. In this case, the gear ratio of the entire transmission will be equal to the product of the gear ratios of the individual pairs.
When all the difficulties associated with obtaining and transforming movement were successfully overcome, a water mill appeared. For the first time, its detailed structure was described by the ancient Roman mechanic and architect Vitruvius. The mill in the ancient era had three main components interconnected into a single device: 1) a motor mechanism in the form of a vertical wheel with blades rotated by water; 2) a transmission mechanism or transmission in the form of a second vertical gear; the second gear rotated the third horizontal gear - the pinion; 3) an actuator in the form of millstones, upper and lower, and the upper millstone was mounted on a vertical gear shaft, with the help of which it was set in motion. Grain poured from a funnel-shaped bucket over the top millstone.
The creation of a water mill is considered an important milestone in the history of technology. It became the first machine to be used in production, a kind of pinnacle reached by ancient mechanics, and the starting point for the technical search for Renaissance mechanics. Her invention was the first timid step towards machine production. Author: Ryzhov K.V.
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