Types of heat transfer: thermal conductivity, convection, radiation. space
Subject: Physics and Astronomy
Class: 8 rus
Subject: Thermal conduction, convection, radiation.
Lesson type: Combined
Purpose of the lesson:
Educational: introduce the concept of heat transfer, types of heat transfer, explain that heat transfer with any type of heat transfer always goes in one direction; which depends on internal structure The thermal conductivity of different substances (solid, liquid and gaseous) is different, so a black surface is the best emitter and the best absorber of energy.
Developmental: develop cognitive interest in the subject.
Educational: to develop a sense of responsibility, the ability to competently and clearly express one’s thoughts, be able to behave and work in a team
Intersubject communication: chemistry, mathematics
Visual aids: 21-30 drawings, thermal conductivity table
Technical means training: ___________________________________________________
_______________________________________________________________________
Lesson structure
1. ABOUTlesson organization(2 minutes.)
Greeting students
Checking student attendance and class readiness for class.
2. Homework survey (15 min) Topic: Internal energy. Ways to change internal energy.
3. Explanation of new material. (15 minutes)
A method of changing internal energy in which particles of a more heated body, having greater kinetic energy, upon contact with a less heated body, transfer energy directly to the particles of a less heated body is calledheat transfer There are three methods of heat transfer: thermal conductivity, convection and radiation.
These types of heat transfer have their own characteristics, however, heat transfer with each of them always goes in the same direction: from a more heated body to a less heated one . In this case, the internal energy of a hotter body decreases, and that of a colder body increases.
The phenomenon of energy transfer from a more heated part of the body to a less heated one or from a more heated body to a less heated one through direct contact or intermediate bodies is calledthermal conductivity.
In a solid body, particles are constantly in oscillatory motion, but do not change their equilibrium state. As the temperature of a body increases when it is heated, the molecules begin to vibrate more intensely, as their kinetic energy increases. Part of this increased energy is gradually transferred from one particle to another, i.e. from one part of the body to neighboring parts of the body, etc. But not all solids transfer energy equally. Among them there are so-called insulators, in which the mechanism of thermal conduction occurs quite slowly. These include asbestos, cardboard, paper, felt, granite, wood, glass and a number of other solids. Medb and silver have greater thermal conductivity. They are good heat conductors.
Liquids have low thermal conductivity. When a liquid is heated, internal energy is transferred from a more heated region to a less heated one during collisions of molecules and partly due to diffusion: faster molecules penetrate into a less heated region.
In gases, especially rarefied ones, the molecules are located at fairly large distances from each other, so their thermal conductivity is even less than that of liquids.
The perfect insulator is vacuum , because it lacks particles to transfer internal energy.
Depending on the internal state The thermal conductivity of different substances (solid, liquid and gaseous) is different.
Thermal conductivity depends on the nature of energy transfer in a substance and is not related to the movement of the substance itself in the body.
It is known that the thermal conductivity of water is low, and when the upper layer of water is heated, the lower layer remains cold. Air is an even worse conductor of heat than water.
Convection - is a heat transfer process in which energy is transferred by jets of liquid or gas. Convection in Latin means"mixing". Convection does not exist in solids and does not occur in a vacuum.
Widely used in everyday life and technology, covection is natural or free .
When liquids or gases are mixed with a pump or stirrer to uniformly mix them, convection is called forced.
A heat sink is a device that is a flat cylindrical container made of metal, one side of which is black and the other shiny. There is air inside it, which, when heated, can expand and escape out through the hole.
In the case when heat is transferred from a heated body to a heat sink using heat rays invisible to the eye, the type of heat transfer is calledradiation or radiant heat transfer
Absorption called the process of converting radiation energy into internal energy of the body
Radiation (or radiant heat transfer) is the process of transferring energy from one body to another using electromagnetic waves.
The higher the body temperature, the higher the radiation intensity. The transfer of energy by radiation does not require a medium: heat rays can also propagate through a vacuum.
Black surface-best emitter and best absorber, followed by rough, white and polished surfaces.
Good energy absorbers are good energy emitters, and bad energy absorbers are bad energy emitters.
4. Consolidation:(10 min) Self-test questions, assignments and exercises
specific tasks: 1) Comparison of the thermal conductivity of metal and glass, water and air, 2) Observation of convection in a living room.
6. Assessment of student knowledge. (1 min)
Basic literature: Physics and astronomy grade 8
Additional reading: N. D. Bytko “Physics” parts 1 and 2
THERMAL CONDUCTIVITY IN Aluminum and glass pan poured the same capacity hot water. Which pan will heat up faster to the temperature of the water poured into it? Aluminum conducts heat faster than glass, so aluminum pan will heat up faster to the temperature of the water poured into it
CONVECTION In industrial refrigerators, air is cooled using pipes through which cooled liquid flows. Where should these pipes be located: at the top or bottom of the room? To cool the room, the pipes through which the cooled liquid flows must be located at the top. Hot air, in contact with cold pipes, will cool and fall down under the influence of the Archimedes force.
Type of heat transfer Features of heat transfer Figure Thermal conductivity Requires a certain time Substance does not move Atomic-molecular energy transfer Convection Substance is transferred by jets Observed in liquid and gas Natural, forced Warm up, cold down Radiation Radiated by all heated bodies Carried out in a complete vacuum Emitted, reflected, absorbed
Heat transfer is a spontaneous irreversible process of energy transfer from more heated bodies or parts of the body to less heated ones. Heat transfer is a way of changing the internal energy of a body or system of bodies. Heat transfer determines and accompanies processes in nature, technology and everyday life. There are three types of heat transfer: conduction, convection and radiation.
10/22/16 03:50:35 PM
Types of Heat Transfer
Physics 8th grade.
© Microsoft Corporation 2007. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the United States and/or other countries.
The information contained in this document is for illustrative purposes only and does not reflect the views of Microsoft Corporation at the time this presentation was written. Because Microsoft is sensitive to changing market conditions, Microsoft does not guarantee or assume any responsibility for the accuracy of the information provided subsequent to this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED, OR STATUTORY, WITH RESPECT TO THE INFORMATION IN THIS PRESENTATION.
THERMAL CONDUCTIVITY
transfer of energy from more heated areas of the body to less heated ones due to thermal movement and interaction of microparticles (atoms, molecules, ions, etc.), which leads to equalization of body temperature.
Various materials have different thermal conductivities
Copper Steel
THERMAL CONDUCTION IN HOUSEHOLD
Good thermal conductivity
Poor thermal conductivity
CONVECTION
This is the transfer of energy by jets of liquid or gas. During convection, matter is transferred.
CONVECTION CAN BE:
NATURAL
ARTIFICIAL
(FORCED)
Convection in everyday life
Home heating
Home cooling
In both thermal conductivity and convection, one of the conditions for energy transfer is the presence of matter. But how is the heat of the Sun transferred to us on Earth? space– vacuum, i.e. there is no substance there, or it is in very sparse condition?
Therefore, there is some other way to transfer energy
RADIATION
Radiation is the process of emitting and propagating energy in the form of waves and particles.
All bodies around us emit heat to one degree or another.
sunlight
A night vision device allows you to capture the weakest thermal radiation and convert it into an image
Light (mirror) surfaces – reflect thermal radiation
This way you can reduce heat loss or direct heat to the right place
Dark surfaces absorb thermal radiation
Solar collector - a device for collecting thermal energy from the Sun (solar installation) transferred by visible light and near infrared radiation. Unlike solar panels directly producing electricity, solar collector produces heating of the coolant material.
- Why are beautifully designed heating radiators not placed in the room near the ceiling?
- Why on a hot sunny summer day do we wear light and light clothes, cover our heads with a light hat, Panama hat, etc.?
- Why do scissors feel cooler to the touch than a pencil?
1. There are three types of heat transfer: conduction, convection and radiation.
Thermal conductivity can be observed in the following experiment. If you attach several nails to a metal rod using wax (Fig. 68), fix one end of the rod in a tripod, and heat the other on an alcohol lamp, then after a while the nails will begin to fall off the rod: first the nail that is closest to the alcohol lamp will fall off, then next, etc.
This happens because as the temperature rises, the wax begins to melt. Since the studs did not fall off simultaneously, but gradually, we can conclude that the temperature of the rod increased gradually. Consequently, the internal energy of the rod gradually increased and was transferred from one end to the other.
2. The transfer of energy by thermal conduction can be explained from the point of view of the internal structure of a substance. The molecules of the end of the rod closest to the alcohol lamp receive energy from it, their energy increases, they begin to vibrate more intensely and transfer part of their energy to neighboring particles, causing them to vibrate faster. They, in turn, transfer energy to their neighbors, and the process of energy transfer spreads throughout the entire rod. An increase in the kinetic energy of the particles leads to an increase in the temperature of the rod.
It is important that during thermal conduction there is no movement of matter; energy is transferred from one body to another or from one part of the body to another.
The process of transferring energy from one body to another or from one part of a body to another due to the thermal movement of particles is called thermal conductivity.
3. Different substances have different thermal conductivities. If you put a piece of ice at the bottom of a test tube filled with water and place its upper end over the flame of an alcohol lamp, then after a while the water in the upper part of the test tube will boil, but the ice will not melt. Consequently, water, like all liquids, has poor thermal conductivity.
Gases have even poorer thermal conductivity. Let's take a test tube containing nothing but air, and place it over the flame of an alcohol lamp. A finger placed in a test tube will not feel any heat. Consequently, air and other gases have poor thermal conductivity.
Metals are good conductors of heat, while highly rarefied gases are the worst. This is explained by the peculiarities of their structure. Molecules of gases are located at distances from each other that are greater than molecules of solids, and collide much less frequently. Therefore, the transfer of energy from one molecules to others in gases does not occur as intensely as in solids. The thermal conductivity of a liquid is intermediate between the thermal conductivity of gases and solids.
4. As is known, gases and liquids conduct heat poorly. At the same time from batteries steam heating the air heats up. This occurs due to a type of thermal conductivity such as convection.
If you carefully lower a crystal of potassium permanganate through a tube into the bottom of a flask with water and heat the flask from below so that the flame touches it in the place where the crystal lies, you can see colored streams of water rising from the bottom of the flask. Having reached upper layers water, these streams will begin to descend.
This phenomenon is explained as follows. The bottom layer of water is heated by the flame of an alcohol lamp. When water heats up, it expands, its volume increases, and its density decreases accordingly. This layer of water is acted upon by the Archimedean force, which pushes the heated layer of liquid upward. Its place is taken by a cold layer of water that has descended, which, in turn, heats up and moves upward, etc. Consequently, energy in this case is transferred by rising fluid flows (Fig. 69).
Heat transfer occurs in gases in a similar way. If a pinwheel made of paper is placed over a heat source (Fig. 70), the pinwheel will begin to rotate. This happens because the heated, less dense layers of air rise upward under the action of the buoyant force, and the colder ones move down and take their place, which leads to the rotation of the turntable.
The heat transfer that occurs in this experiment and in the experiment depicted in Figures 69, 70 is called convection.
Convection is a type of heat transfer in which energy is transferred through layers of liquid or gas.
Convection is associated with the transfer of matter, so it can only occur in liquids and gases; Convection does not occur in solids.
5. The third type of heat transfer is radiation. If you bring your hand to the coil of an electric stove plugged in, to a burning light bulb, to a heated iron, to a radiator, etc., you can clearly feel the heat.
If you fix a metal box (heat sink), one side of which is shiny and the other black, in a tripod, connect the box with a pressure gauge, and then pour boiling water into a vessel with one surface white and the other black, then turn the vessel towards the black side the heat sink first with the white side and then with the black side, you will notice that the liquid level in the pressure gauge elbow connected to the heat sink will decrease. At the same time, it will decrease more strongly when the vessel faces the heat sink with its black side (Fig. 71).
A decrease in the liquid level in the pressure gauge occurs because the air in the heat sink expands, this is possible when the air is heated. Therefore, the air receives from the vessel with hot water energy, heats up and expands. Since air has poor thermal conductivity and convection does not occur in this case, because the tile and the heat sink are located at the same level, then it remains to be recognized that the vessel with hot water emits energy.
Experience also shows that black surface the vessel emits more energy than the white one. This is evidenced by a different level of liquid in the pressure gauge elbow connected to the heat sink.
A black surface not only emits more energy, but also absorbs more. This can also be proven experimentally by bringing a plugged-in electric stove first to the shiny side of the heat receiver, and then to the black one. In the second case, the liquid in the pressure gauge elbow connected to the heat sink will drop lower than in the first.
Thus, black bodies absorb and emit energy well, while white or shiny bodies emit and absorb it poorly. They reflect energy well. Therefore, it is understandable why people wear light-colored clothes in the summer, and why they prefer to paint houses in the south white.
By radiation, energy is transferred from the Sun to the Earth. Since the space between the Sun and the Earth is a vacuum (the height of the Earth's atmosphere is much less distance from it to the Sun), then energy cannot be transferred either by convection or by thermal conduction. Thus, the transfer of energy by radiation does not require the presence of any medium; this heat transfer can also be carried out in a vacuum.
Part 1
1. In solids, heat transfer can occur by
1) convection
2) radiation and convection
3) thermal conductivity
4) convection and thermal conductivity
2. Heat transfer by convection can occur
1) only in gases
2) only in liquids
3) only in gases and liquids
4) in gases, liquids and solids
3. How can heat transfer be carried out between bodies separated by airless space?
1) only using thermal conductivity
2) only using convection
3) only using radiation
4) in all three ways
4. Due to what types of heat transfer does water in reservoirs heat up on a clear summer day?
1) only thermal conductivity
2) convection only
4) convection and thermal conductivity
5. What type of heat transfer is not accompanied by the transfer of matter?
1) only thermal conductivity
2) convection only
3) radiation only
4) only thermal conductivity and radiation
6. Which type(s) of heat transfer is accompanied by the transfer of matter?
1) only thermal conductivity
2) convection and thermal conductivity
3) radiation and thermal conductivity
4) convection only
7. The table shows the values of the coefficient that characterizes the rate of thermal conductivity of a substance for some building materials.
In conditions cold winter least additional insulation with equal wall thickness requires a house made of
1) aerated concrete
2) reinforced concrete
3) sand-lime brick
4) wood
8. Metal and plastic mugs of equal capacity standing on the table were simultaneously filled with hot water of the same temperature. In which mug will the water cool faster?
1) in metal
2) in plastic
3) simultaneously
4) the rate of cooling of water depends on its temperature
9. An open vessel is filled with water. Which figure correctly shows the direction of convection flows with the given heating scheme?
10. Water of equal mass was heated to the same temperature and poured into two pans, which were closed with lids and placed in a cold place. The pans are exactly the same, except for the color of the outer surface: one of them is black, the other is shiny. What will happen to the temperature of the water in the pans after some time until the water has cooled completely?
1) The water temperature will not change in either pan.
2) The temperature of the water will drop in both pans by the same number of degrees.
3) The temperature of the water in the shiny pan will be lower than in the black one.
4) The temperature of the water in the black pan will be lower than in the shiny one.
11. The teacher conducted the following experiment. A hot tile (1) was placed opposite a hollow cylindrical closed box(2), connected by a rubber tube to the U-shaped pressure gauge elbow (3). Initially, the fluid in the knees was at the same level. After some time, the fluid levels in the pressure gauge changed (see figure).
Select two statements from the proposed list that correspond to the results of the experimental observations. Indicate their numbers.
1) The transfer of energy from the tile to the box was carried out mainly due to radiation.
2) The transfer of energy from the tile to the box was carried out mainly due to convection.
3) During the process of energy transfer, the air pressure in the box increased.
4) Black surfaces matte color Compared to light, shiny surfaces, they absorb energy better.
5) The difference in liquid levels in the pressure gauge elbows depends on the temperature of the tile.
12. From the list of statements below, select two correct ones and write their numbers in the table.
1) The internal energy of a body can only be changed during the process of heat transfer.
2) The internal energy of a body is equal to the sum of the kinetic energy of movement of the molecules of the body and the potential energy of their interaction.
3) During the process of thermal conduction, energy is transferred from one part of the body to another.
4) Heating of the air in the room from steam heating batteries occurs mainly due to radiation.
5) Glass has better thermal conductivity than metal.
Answers
Types of heat transfer (thermal conduction, convection, thermal radiation).
Thermal conductivity is the process of transferring internal energy from more heated parts of the body (or bodies) to less heated parts (or bodies), carried out by chaotically moving particles of the body (atoms, molecules, electrons, etc.). Such heat exchange can occur in any body with a non-uniform temperature distribution, but the mechanism of heat transfer will depend on the state of aggregation of the substance.
The ability of a substance to conduct heat is characterized by its thermal conductivity coefficient (thermal conductivity). Numerically, this characteristic is equal to the amount of heat passing through a material with an area of 1 m² per unit of time (second) with a unit temperature gradient.
In steady state, the energy flux density transmitted through thermal conductivity is proportional to the temperature gradient:
where is the heat flux density vector - the amount of energy passing per unit time through a unit area perpendicular to each axis, - coefficient of thermal conductivity(specific thermal conductivity), - temperature. The minus on the right side shows that the heat flow is directed opposite to the vector grad T (that is, in the direction of a rapid decrease in temperature). This expression is known as law of thermal conductivity Fourier .
Convection is the spread of heat caused by the movement of macroscopic elements of the environment. Volumes of liquid or gas moving from an area with higher temperature to an area with a lower temperature, they transfer heat with them. Convective transport is usually accompanied by thermal conduction.
Convective transfer can occur as a result of free or forced movement of the coolant. Free movement occurs when fluid particles in different parts of the system are under the influence of mass forces of varying magnitude, i.e. when the field of mass forces is not uniform.
Forced movement occurs under the influence of external surface forces. The pressure difference under which the coolant moves is created using pumps, ejectors, and other devices.
Heat transfer by radiation (radiation heat transfer) consists of the emission of radiation energy by a body, its distribution in the space between bodies and its absorption by other bodies. In the process of emission, the internal energy of the radiating body is converted into the energy of electromagnetic waves, which propagate in all directions. Bodies located in the path of propagation of radiation energy absorb part of the electromagnetic waves incident on them, and thus the radiation energy is converted into the internal energy of the absorbing body.
1. Surface treatment of bodies of rotation: grinding.
Grinding– the process of processing all kinds of surfaces on appropriate equipment using abrasive tools. Accuracy up to 6th grade. Ra=0.16…..0.32 µm
Types of grinding Quality Ra (µm)
Roughing 8-9 2.5-5
Preliminary 6-9 1.2-2.5
Final 5-6 0.2-1.2
Thin -- 0.25-0.1
Tools: grinding and abrasive wheels.
Grinding methods:
Cylindrical grinding machines.
A) Grinding with longitudinal feed
The table with the workpiece performs a reciprocating motion (longitudinal feed), the workpiece performs a circular feed; circle – the main cutting movement and cross feed.
B) Plunge grinding
The circle performs the main cutting movements and transverse feed (plunging), the workpiece carries out a circular feed.
Advantages of longitudinal grinding:
Can process surfaces longer than 50 mm;
More accurate;
Uniform wear of the circle;
Use soft wheels that do not require frequent editing;
Minimal heat generation.
Advantages of plunge grinding:
Great productivity;
Possibility of multi-tool adjustment;
Simultaneous grinding of the neck and end.
Disadvantages of plunge grinding:
Can process surfaces up to 50 mm long;
Uneven wheel wear;
Frequent wheel adjustments are necessary;
Large heat generation;
Machines with increased power and rigidity.
Centerless grinding
A) with radial feed – used for processing short parts;
B) with axial feed;
The axis of the circle is set at an angle to the axis of the workpiece, due to this we obtain an axial feed. Used for processing long, smooth shafts.
Grinding is a technological method of processing metals that allows obtaining surfaces on parts High Quality with high dimensional accuracy.
Grinding is carried out using grinding wheels, which are cut with abrasive grains made of minerals and superhard materials that have a random shape and relative position.
A special feature is that each grain, like a cutting tooth, cuts off a small layer of metal, resulting in a scratch of limited length and a small cross-sectional area remaining on the surface of the part.
In the manufacture of machine parts and devices, grinding is used for final finishing, making it possible to obtain surfaces with dimensional accuracy of 6-7 grades with a roughness of Ra = 0.08..0.32 microns.
Types of grinding: external round, internal round, flat, face.
2. The concept of an algorithm. Its structure.
An algorithm is an ordered set of rules that determines the content and order of actions on certain objects, the strict implementation of which leads to the solution of any problem from the class of problems under consideration in a finite number of steps.
Basic Algorithm Structures is a specific set of blocks and standard methods connecting them to perform typical sequences of actions.
The main structures include the following:
o linear
o branching
o cyclic
Linear are called algorithms in which actions are carried out sequentially one after another. The standard block diagram of the linear algorithm is given below: 
Branching out is an algorithm in which an action is performed along one of the possible branches of solving a problem, depending on the fulfillment of conditions. Unlike linear algorithms, in which commands are executed sequentially one after another, branching algorithms include a condition, depending on the fulfillment or non-fulfillment of which one or another sequence of commands (actions) is executed.
As a condition in a branching algorithm, any statement understandable to the executor can be used, which can be observed (be true) or not be observed (be false). Such a statement can be expressed either in words or in a formula. Thus, the branching algorithm consists of a condition and two sequences of commands.
Depending on whether the sequence of commands is in both branches of the problem solution or only in one, the branching algorithms are divided into complete and incomplete (reduced).
The standard block diagrams of a branching algorithm are given below: 
Cyclic is an algorithm in which some part of the operations (loop body - a sequence of commands) is performed repeatedly. However, the word “repeatedly” does not mean “indefinitely.” The organization of loops, which never leads to a stop in the execution of the algorithm, is a violation of the requirement of its effectiveness - obtaining a result in a finite number of steps.
Before the loop operation, operations are carried out to assign initial values to those objects that are used in the body of the loop. The cycle includes the following basic structures:
o condition check block
o a block called the body of the loop
There are three types of loops:
Loop with precondition
Loop with postcondition
Loop with a parameter (a type of loop with a precondition)
If the loop body is located after the conditions have been checked, it may happen that under certain conditions the loop body will not be executed even once. This type of loop organization, controlled by a precondition, is called loop with precondition.
Another possible case is that the body of the loop is executed at least once and will be repeated until the condition becomes false. This organization of the cycle, when its body is located before checking the condition, is called loop with postcondition.
Loop with parameter is a type of loop with a precondition. Feature of this type cycle is that it has a parameter, the initial value of which is specified in the cycle header, where the condition for continuing the cycle and the law for changing the cycle parameter are also specified. The operating mechanism is completely consistent with a cycle with a precondition, except that after executing the body of the cycle, the parameter is changed according to the specified law and only then the condition is checked.
Standard block diagrams of cyclic algorithms are given below: 
Question 1. Analysis of fuel supply units in the DLA
Question 2. Hole processing: drilling, boring, countersinking, reaming.
Question 3. Types, sections, sections in mechanical engineering drawing
1. Analysis of fuel supply units in DLA
Scheme liquid rocket engines(LPRE) differ mainly in feed systems fuel. In liquid rocket engines of any design fuel pressure before combustion chamber there must be more pressure in the chamber, otherwise it will be impossible to supply components fuel through injectors. There are two fuel supply systems - repressive And pump house. The first is simpler and is used mainly in engines of relatively small rockets, the second - in engines of long-range rockets.
PUMP FUEL SUPPLY SYSTEM- (liquid rocket engine) - a set of mechanisms or devices that ensure the supply of fuel components from tanks to the chamber of a liquid rocket engine using pumps. At pumping system fuel supply can be reduced total weight power plant than with a displacement fuel supply system.
With displacement feeding, fuel components are supplied to the combustion chamber using compressed air. gas, coming through gearbox into fuel tanks. The reducer ensures constant pressure in the fuel tanks and a uniform supply of fuel to the combustion chamber. In this case, high pressure is established in the rocket tanks, so they must be strong enough. This increases the weight of the structure, this increases the weight of the structure, which is a disadvantage of all positive displacement fuel delivery systems.
2. Hole processing: drilling, boring, countersinking,
deployment.
Drilling get holes in solid material. For shallow holes, standard drills with a diameter of 0.30...80 mm are used. There are two methods of drilling: 1) the drill rotates (machines of drilling and boring groups); 2) the workpiece rotates (lathe group machines). Processing of holes with a diameter of up to 25...40 mm is carried out with spiral drills in one pass, when processing holes large diameters(up to 80 mm) - in two or more transitions by drilling and reaming or other methods. To drill holes with a diameter of over 80 mm, drills or drilling heads of special designs are used. When processing deep holes (L/D > 10), it is difficult to ensure the direction of the hole axis relative to its inner cylindrical surface. How longer length holes, the greater the tool withdrawal. To combat drill drift or bending of the hole axis, following methods: − use of small feeds, careful sharpening of the drill; − use of preliminary drilling (centering); − drilling with the direction of a twist drill using a drill sleeve; − drilling a rotating workpiece with a non-rotating or rotating drill. This is the most radical way eliminating drill drift, as conditions are created for self-centering of the drill; − drilling with special drills with a rotating or stationary workpiece. Special drills include: - semicircular - a type of single-sided cutting gun drills that are used for processing workpieces made of materials that produce brittle chips (brass, bronze, cast iron); − gun - single-sided cutting with external coolant outlet and internal outlet (ejector) with hard alloy plates (soldered or non-grindable with mechanical fastening), designed for high-performance drilling; − trepanning (ring) drills (Fig. 38, d) for drilling holes with a diameter of 80 mm or more, up to 50 mm in length; They cut out a ring surface in solid metal, and the surface remaining after such drilling inner part in the shape of a cylinder can be used as a blank for the manufacture of other parts. Countersinking holes – pre-treatment of cast, stamped or drilled holes for subsequent reaming, boring or broaching. When processing holes according to the 13th...11th quality, countersinking can be the final operation. Countersinking is used to process cylindrical recesses (for screw heads, valve sockets, etc.), end and other surfaces. The cutting tool for countersinking is a countersink. Countersinks are made in one piece with a number of teeth of 3...8 or more, with a diameter of 3...40 mm; mounted with a diameter of 32...100 mm and prefabricated adjustable with a diameter of 40...120 mm. Countersinking is a productive method: it increases the accuracy of pre-machined holes, and partially corrects the curvature of the axis after drilling. To increase the processing accuracy, devices with conductor bushings are used. Countersinking is used to process through and blind holes. Countersinks correct, but do not completely eliminate the axis of the hole, the achieved roughness Ra = 12.5...6.3 µm. Deployment holes – finishing of holes with an accuracy of 7th grade. By reaming, holes of the same diameters are processed as during countersinking. Reamers are designed to remove small allowances. They are different from countersinks a large number(6...14) teeth. Unrolling achieves high accuracy of the diametrical dimensions of the mold, as well as low surface roughness. It should be noted that the processed hole is slightly larger in diameter than the diameter of the reamer itself. This breakdown can be 0.005...0.08 mm. To obtain 7th quality holes, double deployment is used; IT6 – threefold, for final unfolding the allowance is left 0.05 mm or less. Boring The main holes (which determine the design of the part) are made on: horizontal boring, jig boring, radial drilling, rotary and aggregate machines, multi-purpose machining centers, as well as in some cases on lathes. There are two main methods of boring: boring, in which the workpiece rotates (on turning group machines), and boring, in which the tool rotates (on boring group machines). Typical operations for lathes are boring a single hole and boring coaxial holes using the universal method and cutter (cutters ).Drilling- one of the most common methods for producing cylindrical blind and through holes in solid material When the accuracy requirements do not go beyond 11-12 quality. The drilling process occurs with two combined movements: rotation of the drill or part around the axis of the hole (main movement) and translational movement of the drill along the axis (feed movement).
When working on drilling machine the drill makes both movements, the workpiece is fixed motionless on the machine table. When working on lathes and turret machines, as well as on automatic lathes, the part rotates, and the drill makes translational movement along the axis.
1. front surface - a helical surface along which chips flow.
2. rear surface - the surface facing the cutting surface.
3. cutting edge - a line formed by the intersection of the front and rear surfaces.
4. ribbon - a narrow strip on the cylindrical surface of the drill, located along the axis. Provides direction to the drill.
5. transverse edge - a line formed as a result of the intersection of both rear surfaces
2φ from 90-2400; ω up to 300, γ-rake angle (smaller towards the center, increases towards the periphery)
Countersinking - processing of pre-made holes to give them a more correct geometric shape, increasing accuracy and reducing roughness. Multi-blade cutting tool– a countersink, which has a more rigid working part, is missing! the number of teeth is at least three (Fig. 19.3.d).
Deployment – final processing cylindrical or conical hole by reaming in order to obtain high accuracy and low roughness. Reamers are a multi-blade tool that cuts off very thin layers from the surface being processed (Fig. 19.3.e).
Holes are bored on lathes when drilling, reaming or countersinking do not provide the required accuracy of the hole dimensions, as well as the cleanliness of the machined surface, or when there is no drill or countersink of the required diameter.
When boring holes on lathes, you can get a hole no higher than 4-3 accuracy class and a finished surface finish of 3-4 for roughing and 5-7 for finishing.
Boring cutters and their installation. The holes are bored on lathes using boring cutters (Fig. 118). Depending on the type of hole being bored, they are distinguished: boring cutters for through holes (Fig. 118, a) and boring cutters for blind holes (Fig. 118, b). These cutters differ from each other in the main angle φ. When boring through holes(Fig. 118, a) main angle φ=60°. If a blind hole with a shoulder of 90° is bored, then the main angle in the lead is φ=90° (Fig. 118, b) and the cutter works as a thrust-through one or φ=95° (Fig. 118, c) - the cutter works with longitudinal feed as a thrust feed, and then with a transverse feed as a scoring feed.
2. Types, sections, sections in mechanical engineering drawing
Kinds
4. The views in the drawing are arranged as follows:
5. Location of views
6. If the views are not located along the projection connection, then they must be indicated by the arrow.
7. Specifying views outside the projection connection
Cuts
9. Sections indicate what is located behind the cutting plane.
10. In the drawing, views can be combined with sections. As a boundary between the view and the section, it can
11. Only a dashed line or a wavy line should be used.
13. Cuts
Sections
15. Sections depict what is in the cutting plane.
16. If the section breaks up into several parts, then a section should be used instead of a section.
17. Sectional image not in drawing
The image of the visible part of the surface of an object facing the observer is called view.
GOST 2.305-68 establishes the following name main views obtained on the main projection planes (see Fig. 165): 7 - front view ( main view); 2 - top view; 3 - left view; 4 - right view; 5 - bottom view; b - rear view. In practice, three types are more widely used: front view, top view and left view.
The main views are usually located in a projection relationship with each other. In this case, there is no need to write the name of the types on the drawing.
If any view is displaced relative to the main image, its projection connection with the main view is broken, then an inscription of type “A” is made over this view (Fig. 166).
An image of an object mentally dissected by one or more planes is called with a cut. Mental dissection of an object relates only to this cut and does not entail changes in other images of the same object. The section shows what is obtained in the secant plane and what is located behind it.
Sections are used to depict the internal surfaces of an object in order to avoid large quantity dashed lines that can overlap each other if the internal structure of the object is complex and make it difficult to read the drawing.
To make a cut, you need to: mentally draw a cutting plane in the right place on the object (Fig. 173, a); mentally discard part of the object located between the observer and the cutting plane (Fig. 173, b), project the remaining part of the object onto the corresponding projection plane, make the image either in place of the corresponding type, or on the free field of the drawing (Fig. 173, c); flat figure, lying in the secant plane, shade; if necessary, give a designation of the section.
Rice. 173 Making a cut
Depending on the number of cutting planes, cuts are divided into simple - with one cutting plane, complex - with several cutting planes.
Depending on the position of the cutting plane relative to the horizontal projection plane, the sections are divided into:
horizontal- the secant plane is parallel to the horizontal projection plane;
vertical- the secant plane is perpendicular to the horizontal projection plane;
inclined- the secant plane makes an angle with the horizontal projection plane that is different from a right angle.
A vertical section is called frontal if the cutting plane is parallel to the frontal plane of projections, and profile if the cutting plane is parallel to the profile plane of projections.
Complex cuts can be stepped if the cutting planes are parallel to each other, and broken if the cutting planes intersect with each other.
The cuts are called longitudinal if the cutting planes are directed along the length or height of the object, or transverse if the cutting planes are directed perpendicular to the length or height of the object.
Local cuts serve to reveal the internal structure of an object in a separate limited place. The local section is highlighted in the view by a solid wavy thin line.
The position of the cutting plane is indicated by an open section line. The starting and ending strokes of the section line should not intersect the contour of the corresponding image. On the initial and final strokes you need to put arrows indicating the direction of view (Fig. 174). Arrows should be applied at a distance of 2...3 mm from the outer end of the stroke. In case of a complex section, strokes of an open section line are also drawn at the bends of the section line.
Rice. 174 Arrows indicating the direction of view
Near the arrows indicating the direction of view from outside the angle formed by the arrow and the stroke of the section line is marked on a horizontal line capital letters Russian alphabet (Fig. 174). Letter designations are assigned in alphabetical order without repetitions and without gaps, with the exception of letters I, O, X, b, ы, b .
The cut itself must be marked with an inscription like “A - A” (always two letters, separated by a dash).
If the secant plane coincides with the plane of symmetry of the object, and the section is made in place of the corresponding view in the projection connection and is not divided by any other image, then for horizontal, vertical and profile sections it is not necessary to mark the position of the secant plane and the section does not need to be accompanied by an inscription. In Fig. 173 frontal section is not marked.
Simple oblique cuts and complex cuts are always designated.