Tools used when aligning shafts of electrical machines

The simplest linear measurements when aligning the shafts of electrical machines are made using steel rulers with divisions and folding meters. Accurate measurements of lengths, diameters and gaps are performed using multidimensional, precise measuring instrument: calipers, micrometers, clamps with a reading device, micrometric bore gauges and plate probes.

Calipers

Vernier calipers (Figure 1) measure the outer and inner diameters, as well as the length of parts up to 4000 mm in size. In addition, certain types of calipers can measure depths, distances of external and internal ledges, and also carry out marking work. Vernier calipers come in a variety of types, models, measuring ranges, and levels of measurement accuracy. The measurement accuracy can be from ±0.01 to 0.1 mm.

There are mechanical and electronic or digital calipers. Mechanical calipers have two types of reading devices - a frame with a vernier or a dial indicator. Instead of a frame, a digital caliper has a digital reading device in which the measured values ​​are displayed in the form of numbers on a liquid crystal display.

The simplest caliper, which allows you to measure diameters and lengths, consists of a rod 1 , with a measuring scale printed on it, on which the measuring jaws are fixed 2 . A movable frame moves along the rod 3 with vernier 5 . The frame is tightened on the rod using a clamp 4 . The caliper has a micrometric feed 6 framework.

Figure 1. Vernier caliper design

How to measure with a caliper? Before starting measurements (for example, the diameter of the end of the shaft), it is necessary to loosen the screw, release the rod and move the outer measuring jaw until both jaws lightly clamp the shaft. Then, using a micrometric feed screw, the frame with the vernier is brought in and the latter is secured with a clamp. Whole millimeters are counted by divisions on the rod, and fractions of a millimeter by the vernier.

To get acquainted with the designs of other types of calipers and study in more detail the methods of making measurements with calipers, watch video 1.

Video 1. Measuring with a caliper

Micrometer

Micrometers (Figure 2) are used to measure the outer diameters (for example, the diameter of the end of the shaft) and the length of parts up to 2000 mm in size. The measurement accuracy can be from ±0.001 to 0.01 mm.

Figure 2. Micrometer structure

Readings of whole and half millimeters are made on stem divisions 7 , and fractions of a millimeter - on the vernier applied on the drum 5 .

Before starting to work with the micrometer, unscrew the locking screw. 3 and lock washer 8 on the bracket 1 and move your heel 2 until the zero divisions of the drum and stem coincide (when the measuring surfaces of the heel and the micrometer screw come into contact 4 ). After this, the locking screw is screwed back in and the heel is secured.

To measure, the part must be lightly clamped with the measuring surfaces of the micrometer. To do this, rotate the micrometer screw using a ratchet. 6 until the last one slips.

In video 2 you can clearly see how to use a micrometer.

Video 2. Micrometer measurement

Staples with a reading device (Figure 3) are designed for measuring the outer diameters and lengths of parts up to 1000 mm in size.

Figure 3. Design of a bracket with a reading device

The bracket consists of a flat semicircular body 3 , in which the movable 1 and adjustable 5 heels, as well as an indicator reading device attached to the movable heel 2 with divisions. The bracket is equipped with heat-insulating linings 4 , preventing the influence of the heat of the measurer’s hands on the accuracy of the measurement results.

The accuracy of measurements with staples ranges from ±0.002 to 0.01 mm.

Micrometric bore gauges (Figure 4) are used to measure internal diameters (for example, the diameter of the hole in the hub of a coupling half) or the distance between surfaces. Bore gauges are produced with measurement limits from 50 - 75 mm to 400 - 10000 mm.

Figure 4. Micrometric bore gauge device

Bore gauges with measurement limits of 1250 - 4000 mm and more have two heads: micrometric and micrometric with indicator.

The micrometer bore gauge consists of a tube 2 connected to extension cords 3 and attached to the last measuring tip 4 . Inside the second end of the tube there is a stem (not visible in Figure 4) of a micrometer head. 1 , on which the latter drum rotates smoothly. The measuring surfaces of the micrometer head and the measuring tip of the bore gauge are made of hard alloy. There are divisions on the stem and drum of the micrometer head.

After the bore gauge is installed in the working position and the measuring surfaces of its micrometer head and measuring tip are in contact with the surfaces of the hole in the half-coupling hub, it is necessary to align the zero line on the micrometer head drum with the longitudinal line on its stem. When measuring the diameter of the hole in the hub of the coupling half, the bore gauge must be installed at a right angle to the axis of the hole, since even if it is slightly inclined, the measurements will be incorrect.

Plate feelers (Figure 5) are used to measure the gaps between the planes of the coupling halves of centered shafts, as well as between the cone of the indicator rod (or the centering bracket pin) and the rim of the coupling half. Such a dipstick 1 consists of calibrated plates 2 thickness from 0.02 to 1 mm. The length of the plates in the probes can be 100 or 200 mm. Styli with 100 mm long inserts are supplied in four sets only, from 9 to 17 inserts in each set. Styli with 200 mm long plates are supplied as separate plates.

Figure 5. Plate probe design

The probe plates should enter the gap to a depth of no more than 20 mm, not freely, but with some friction, which should be approximately the same for all measurements.

Instruments used for aligning shafts of electrical machines

In addition to the listed tools, when aligning the shafts of electrical machines, indicators, levels, vibrometers, vibrographs, as well as a number of devices are used.

Indicator

Indicators are used to measure the runout of centered shafts, the runout of connecting coupling halves, as well as to check the correctness of the shape of the above-mentioned parts of electrical machines. The indicator (Figure 6) is a simple device consisting of the indicator itself 1 with measuring rod 2 , secured with a holder 3 on the counter 4 , which is mounted on a tripod 5 .

Figure 6. Indicator design

To make a measurement (for example, shaft runout), the indicator is installed on a stationary support that does not experience vibration, and the measuring rod is perpendicular to the shaft axis and lightly pressed on the surface being tested. The design of the indicator is based on the use of gearing, which converts the translational movement of the measuring rod into the rotational movement of the indicator needle. Indicators are manufactured with measurement limits of 0 - 2; 0 - 3; 0 - 5 and 0 - 10 mm and the reading accuracy of the main indicator scale is 0.01 mm.

Level

Levels are used when aligning the shaft lines of connected machines, as well as to check the horizontalness of foundation slabs during the installation of electrical machines and the mechanisms they operate. For these purposes, the following levels are used: frame, with a micrometric screw of the “Geologorazvedka” type and hydrostatic.

Frame levels are available with sides measuring 200 × 200 mm and 300 × 300 mm and with division values ​​from 0.02 to 0.3 mm. The division price refers to the angle of inclination of the ampoule or the amount of rise in millimeters per 1 m, corresponding to the movement of the bubble by one division.

The working surfaces of the level are flat; There are prismatic recesses on the bottom, top and one of the side surfaces.

The "Geological exploration" type level with a micrometric screw is shown in Figure 7. Top part it is a cylindrical glass ampoule enclosed in a metal cylinder with a cutout. On one side the cylinder is pivotally connected to the level body; on the other side there is a micrometric screw with a dividing head, the rotation of which causes the end of the cylinder with the ampoule to rise or fall. The division value is 0.1/1000 mm, that is, one division corresponds to a rise of 0.1 mm per 1 m.

Figure 7. Appearance"Geologorazvedka" type level with micrometric screw

To determine the slope of any surface, the bubble in the ampoule is brought to the zero position by rotating the micrometer screw, after which the slope value is determined by reading on the micrometer head. To check the correctness of the readings obtained, rotate the level 180°.

Vibrometers (Figure 8) are designed to measure the vibration amplitude of electrical machines or their individual parts and its direction. The vibration amplitude should be understood as the amount of movement of the controlled surface of the machine (for example, the surface of the coupling half) from one extreme position through the equilibrium position to the other extreme position. The vibrometer consists of a frame 1 , massive prism 2 suspended from the frame by springs 3 , built into the indicator prism 4 , resting his button 5 in the ring 6 , fastened to frame, screws 7 locking the prism and handle 8 for carrying the vibrometer. The indicator rotates freely around its axis, so that the button can occupy any radial position. This makes it possible to check not only the amplitude of vibrations, but also its direction. To attach the device to a vibrating surface, there is a threaded hole in the lower part of the frame. The use of a massive prism is caused by its property, due to inertia, being elastically suspended, to remain practically motionless when the device body oscillates; in this case, the movement of the body relative to the stationary mass is measured with an indicator.

Figure 8. Vibrometer design

Vibration should be measured in three directions; vertical axial (along the axis of the machine) and transverse (in the horizontal plane perpendicular to the axis of the machine).

When measuring vibrations from 0.05 to 6 mm in electrical machines with a rated speed of more than 750 rpm, hand-held vibrographs VR-1 should be used.

The VR-1 vibrograph (Figure 9) consists of a transmitting lever mechanism, a device for moving the tape and a timer.

On axis 1 (Figure 9, A) there is a pin 2 touching a vibrating surface. Axle with hinge 3 connected with a steel pen 4 , which can rotate around the axis of the handle 5 . Spring 6 , the tension of which can be adjusted, is designed to obtain proper contact between the pin and the vibrating surface. The vibration curve is recorded with the tip of a pen scratching on paper tape. 7 covered with a layer of wax. The belt moves at a certain speed using a spring-wound clock mechanism. The timer makes a mark on the tape every second, which makes it possible to determine the frequency of vibrations.

Figure 9. Vibrograph device

The general view of the vibrograph is shown in Figure 9. b. Axis 1 with pin placed in guide tube 8 . A screw is used to adjust the spring tension 9 . The lever is used to turn on and off the movement of the tape and timer. The spring of the clock mechanism is wound with a handle 5 . The movement of the vibrograph pen is observed through a hatch in the housing. The device is equipped with a lever magnifier for recording vibrations, which is put on the guide tube and allows you to enlarge recordings by 2 and 6 times.

Devices used for aligning shafts of electrical machines

Also used for shaft alignment special devices: centering brackets, devices for centering with electromagnetic clamp and indicators, devices for centering machines with an intermediate shaft, devices for grinding the shaft, for rotating the shafts, for lifting the shaft to a small height, stops against axial displacement of the shaft, universal three-jaw pullers for coupling halves and other. The design of individual types of centering brackets is discussed below. The design and operating principle of the remaining devices will be discussed in detail in the articles “Preparation for shaft alignment” and “Aligning shafts of electrical machines”.

Centering brackets are made immediately before installation or repair of electrical machines. In some cases, this is done without preliminary calculation, which should be considered a serious omission, since the right choice The design of the brackets largely depends on the accuracy of alignment.

Table 3 shows the main dimensions by which, knowing the length of the bracket, you can select the cross-section (height h and width b).

Table 3

Main dimensions of centering brackets

Figure 10 shows individual designs centering brackets. The bracket shown in Figure 10 is A, used in cases of large distances between coupling halves. Its area cross section must provide sufficient rigidity to prevent the end of the bracket from moving during the alignment process.

In the case when there is no special cut hole on the rim of the coupling half for screwing in the bolt securing the bracket to the coupling half, the bracket shown in Figure 10 is used, b. This bracket is secured with a pin installed in the hole for the coupling half bolt.

Also widely used are brackets attached to the rim of the coupling half (Figure 10, V).

Figure 10. Centering bracket designs.
A- for large distances between coupling halves; b- secured with a pin installed in the hole for the coupling half bolt; V- fixed on the rim of the coupling half

In the USSR, brigade sets of special tools were used for the installation of medium and large electrical machines.

Each of these sets includes the following tools, devices and devices, including those necessary for shaft alignment: micrometer type MK, measurement limit 0 - 25 mm, measurement accuracy 0.01 mm (GOST 6507-90); set of micrometric bore gauges, measurement limits 50 - 600 mm (GOST 10-88); set of probes type I 1 - 100, 5 - 100 and type II 7 - 200 (GOST 882-75); a set of wrenches measuring 8 - 36 mm (GOST 2906-80); set of conical reamers Ø 13 - 27 (GOST 10082-71); set of indicator brackets type C, 300 - 800; gross indicator type I, measurement accuracy up to 0.01 mm; "Geological exploration" type level with a micrometric screw, with a division value of 0.1 / 1000 mm; frame level unregulated; hydrostatic level; wedge probe; wrench with replaceable heads for large nuts; a set of tools for a fitter; electric roller, pneumatic bush hammer, device for drilling holes in coupling halves; device for turning shafts; device for shaft alignment with electromagnetic clamp and indicators; device for centering machines with an intermediate shaft; rolling bearing puller (with bracket and clamp); three-jaw universal puller; wedge jack with a lifting capacity of 50 t; hydraulic jack with a lifting capacity of 100 t; vibrometer with a division value of 0.01 mm; centrifugal manual tachometer type IO-10; set of plumb lines; set of slings; prism 100 - 150 mm long (GOST 5641-88).

In addition, rigging mechanisms are used to align the shafts of electric machines: hoists and blocks, as well as rigging equipment: steel and hemp ropes, thimbles and clamps.

Materials used when aligning shafts of electrical machines

In the process of aligning the shafts of electrical machines, a number of materials are also consumed. The latter include: kerosene and gasoline - for cleaning the journals and ends of the shafts and the landing part of the coupling halves from preservative anti-corrosion lubricant; in addition, kerosene is used to dilute GOI paste; clean calico and gauze - for wiping the specified parts of machines; colored chalk or colored pencils - for making marks on the coupling halves; notebooks - for recording measurement results; burlap as a protective covering; clean rags; wiping ends; harsh threads, twisted twine; felt and felt - for grinding the shaft journals; presspan, leather, chalk, GOI paste - for polishing shaft journals; white spirit, xylene - for removing anti-corrosion coating on shaft journals; ethyl alcohol - for wiping the shaft journals.

Installation and Troubleshooting plumbing system can only be performed when the pipe parameters are known. It happens that they are difficult to reach, but measurements need to be taken. How to measure in this case? For these purposes, various tools are used: calipers, tape measures, sensors, etc. Using them is not so difficult, but measurements must be taken correctly.

Outer and inner diameter

Most often, this design parameter is measured in inches, which are easily converted into centimeters (the value is multiplied by 2.54). First of all, you need to decide what needs to be measured: the inner diameter of the pipe or the outer diameter. Products used for water and gas supply are usually measured by internal diameter. This is due to the fact that this indicator defines constructs.

The outer diameter may be different meanings depending on the wall thickness (the mechanical strength of the entire product depends on it). According to GOST 355-52, each subsequent pipe diameter differs from the previous best throughput(by 50%). The permeability of a structure is often called the conditional (nominal) diameter. In this case, the indicator usually differs from the internal diameter (by 1-10 mm). This important parameter is considered the main characteristic of the product, which is taken into account during the design and installation process.

We measure with a caliper

This high-precision instrument measures parameters various designs. How to measure the diameter of a pipe with a caliper? To do this, you need to spread its jaws, insert the product into them and bring them together so that they are pressed against the surface. When closing, the jaws must be parallel to the cross-sectional plane of the pipe, otherwise the measurement will be incorrect. The internal diameter is also measured with a caliper. With him reverse side There are sponges that are placed inside the structure and spread until they abut the walls.

Sometimes it is necessary to measure the diameter of an installed pipe that is too large. In this case, you can measure the chord with a tool and calculate the diameter mathematically. We spread its lips to the maximum distance and apply it to the pipe. The resulting indicator is the length of the chord. To calculate, you will also need to measure the height of the device’s jaws. The diameter is calculated using the formula:

If the jaws are too long, then you can place some kind of part (a block, etc.). Then the height will be calculated using the formula:

We measure with a ruler and tape measure

If the cross section is visible on the pipe, then the diameter can be measured with a regular ruler. We apply it to the cut area so that the scale runs exactly in the center. Take the distance between the right points(for inner or outer diameter). Distance between extreme points will be the outer diameter. If needed inner size, then you can find out the thickness of the walls and subtract them from the resulting figure.

Everything is clear with a ruler, but how to measure the diameter of a pipe with a tape measure? This tool is suitable for solid and large structures, which are difficult to get to. We wrap the product so that the tape with the scale fits tightly, and find the place where it intersects. The resulting figure is To get the diameter, divide it by (3.14).

Copy method

If you don’t have any tools at hand, but have a camera, then you can use the copying method. How to correctly measure the diameter of a pipe? For this:
- take an object with known dimensions (for example, a brick);

We lay it on the pipe, along its length or next to the cut;
- photograph this area so that you can evaluate the difference in size;
- carry out calculations based on photographs;
- based on the data obtained, we estimate the actual dimensions (it is important to take into account the scale).

We measure with a micrometer

High-precision measurements (up to 0.01) of the pipe can be made using a micrometer. It should be noted that they are convenient for measuring small products. The tool is a bracket equipped with a support heel and a stem with a high-precision thread (for screwing in a microscrew). On the stem you can see a scale with millimeters and their hundredths. This equipment allows you to obtain more accurate indicators.

How to measure the diameter of a pipe with a micrometer? We place the structure between the end of the screw and the heel. We begin to rotate the ratchet handle until it clicks three times. First, we look at the lower scale of the stem, showing the number of whole millimeters. We check for the presence of the risk, which is on the right. If it is not visible, we take readings from the drum. If there is a risk, add 0.5 mm to the resulting number. Measurements on the drum are determined relative to the line on the stem between the scales.

Laser sensors

Modern laser sensors have been created to take dimensions from pipes (and not only). Their advantages: lack of contact with the surface, the ability to use on different structures (hot, sticky), durability and speed of obtaining results. How to measure the diameter of a pipe with such sensors? There are several measurement methods.

With laser triangulation, the beam from the sensor creates a spot on the surface of the structure. Behind the laser is a camera scanner that sees it under different angles. Using these indicators, the digital processor calculates the distance between the sensor and the product.

We measure the diameter using the shading method. IN in this case the sensor serves as an emitter and a receiver, but they are located in different housings. Inside it, the laser beam is reflected from a rotating mirror, bends around the measurement area and creates a virtual strip of light. Inside the device, a moving beam passes through a special diode, which measures the duration of shading (corresponds to the size of the object).

Another option is the principle of light section. The sensor is equipped with a laser, camera and electronic circuitry. The laser creates a line perpendicular to the product, and the camera is positioned at a certain angle to it. Any curvature causes the laser line to deform, which is what pushes the sensors away when calculating dimensions.

It was described above how to measure the diameter of a pipe. But it is important to know that some structures have curvature (maximum 1.5 mm per 1 m of length). In this case we talk about their ovality. This parameter is determined by the formula: the difference between the large and small diameters is divided by the nominal one. Allowable ovality: no more than 1% for pipes with a wall up to 20 mm, no more than 0.8% - with a wall more than 20 mm. This parameter is very important because it affects performance characteristics designs.

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Determining the outer and inner diameter of a pipe using available tools

One of the skills required for high-quality and quick replacement of pipes at home is accurately determining their diameter using available tools.

Before making measurements, you should understand in what units they are made. It is generally accepted that the diameter of pipes is always measured in inches (1 inch = 2.54 cm).

Whether it's problems with the plumbing or plumbing in the bathroom or problems with the water supply in the kitchen, knowing how to determine the diameter of a pipe using available tools will come in handy.

Of course, there are special tools for measuring, such as a ruler-circometer, laser meter, etc. But everything can be much simpler.

Before making measurements, you should understand in what units they are made. It is generally accepted that such values ​​are always measured in inches (1 inch = 2.54 cm), and the standard size, for example, of steel products is most often 1 or 0.5 inches. By the way, the diameters of plastic, steel and metal-plastic parts vary.

The next step is to select the measured value. External - more important, because it is on it that the threads are installed and threaded connections. This diameter directly depends on the thickness of the pipe walls. The dimensions of the wall thickness are determined by the difference between the external and internal diameters of a given pipe.

Taking words to action

In order to correctly measure both diameters, you should take into account the features of all measurement methods, because each of them is suitable for different conditions.

One method is to measure the circumference of the piece by wrapping it with a measuring tape or tape measure. Then the resulting value must be divided by Pi (3.14).

We will need:

• ruler;
• calipers;
• tape measure (measurement tape).

If access to an area of ​​the part is not difficult and it can be measured before installation, then the most in a simple way will use a ruler or tape measure. The outer diameter is determined by placing a ruler over the widest part of the pipe and counting from the first outer point on the scale to the last.

There may be cases where measurements are already indicated in inches (imported deliveries). To convert to centimeters, the size is multiplied by 2.54, and to convert back to inches - by 0.398.

There is another way to determine the internal diameter if the pipe is directly accessible. The walls are measured along the cut using a caliper or ruler, and then the resulting reading is subtracted from the measurements of the outer diameter and multiplied by 2.

What if there is no direct access to the required area? One method is to measure the circumference of the piece by wrapping it with a measuring tape or tape measure. Then the resulting value must be divided by Pi (3.14). This way we can find out the outer diameter of the pipe. This method Also suitable if the length of a caliper or ruler is not enough.

There is a method for determining the outer diameter that excludes all sorts of calculations, but only for those parts for which it is no more than 15 cm. To do this, you will need to measure the readings using only a caliper, on the scale of which the correct results are measured.

One of the most extraordinary ways is to compare the values ​​of a pipe with some object, take photographs and further recognize the measurements. Take a ruler or any object whose length is already known in advance (a coin) and bring it to the area to be measured, then take a picture. Further scaling on the computer will help determine the exact dimensions of the outer diameter. This method is ideal if it is impossible or extremely difficult to get close to the area being measured.

A bore gauge is a measuring tool that is designed to obtain data on the distance between two surfaces, as well as determine the internal diameter of various parts. On average, the measurement accuracy of this device is 0.01 mm. A bore gauge for measuring cylinder diameter consists of replaceable gauge rods, which are extensions, and a head. The head itself consists of the following parts:

• Replaceable tip;
• Locking device;
• Stem;
• Cap;
• Drum;
• Micrometer screw

Thanks to the presence of replaceable tips, you can increase the measuring range. For those devices with a measurement accuracy of 0.01 mm, the current GOST is 868-82, and for devices with a division value of 0.001 or 0.002 mm - 9244-75.

The advantages of bore gauges are their fairly high measurement accuracy, both for private and industrial applications. The cost of the device is also not high. The main thing is that the advantages of all are preserved here mechanical devices, which includes durability. At the same time, they require special care and special conditions storage When a device breaks down, repairs are often very complicated and it is easier to replace the device with a new one than to repair it. During some measurements, deformations may remain on soft parts if there is strong pressure. When it comes to measuring cylinders, difficulties arise in places where there are windows.

What types of bore gauges can be used to measure the diameter of a cylinder?

Bore gauges are often used to measure the diameter of a cylinder. Micrometers are not suitable for this operation, so specialists use these types of devices. The measurement of cylinders with a bore gauge is carried out in two perpendicular planes and four zones. The most popular types of bore gauges are suitable for this.

The indicator type of device is more suitable for those cylinders whose diameter is relatively small. They can work with sizes from 6 mm and larger. It is easy to use, but uses a relative measurement method, so the device has two scales. Although it can work with small values, its error is higher than that of other types of these devices.

photo: indicator bore gauge for measuring cylinder diameter

A micrometric bore gauge uses an absolute measurement method, which, at the same division price as the indicator type, gives a significantly smaller error. The measurement limit here ranges from 50 to 4000 mm, which depends on the specific model. People often use two instruments to get more accurate data.

Selecting a bore gauge for measuring cylinder diameter

To measure a cylinder with a bore gauge, you need to select the device itself correctly. The accuracy of the result, as well as ease of use, will directly depend on this. First of all, you need to decide suitable sizes, since the micrometric and indicator types have too large a spread in the minimum limit. If you need to work with parts with a diameter of up to 5 cm, then an indicator bore gauge is suitable, if larger, a micrometric one.

Next, you need to decide which replacement caliber rods should be included in the kit. They expand and contract the operating range of the instrument, so that to obtain correct data you need to have a wide supply of replacement parts. The higher the accuracy class, the smaller the error, so modern high-precision devices allow you to obtain the most accurate data for further work.

Naturally, the device must pass verification, be free of damage and comply with accepted GOST standards. If possible, specialists carry out measurements using several devices simultaneously.

How to use a bore gauge - the principle of measuring cylinder diameter

Before using the bore gauge for cylinders, you must make sure that all its arrows are in the zero position. If this is not the case, then they can be adjusted using special screws responsible for the position of the arrows. The difficulty in measuring a cylinder lies in the fact that it is not always possible to fix the device so that it stands level and exactly corresponds to the required horizontal line.

photo: measuring the cylinder diameter with a bore gauge

The part is measured in at least four different places, preferably at the same distance from each other. This helps determine the product's taper and internal deformations. Another difficulty is the impossibility of measuring the diameter in those places where the cylinder windows are located. When the instrument reaches them, it simply falls inside. In four-stroke engines, where there are no windows in the cylinders, such problems do not arise and the bore gauge can perform all the necessary functions. Otherwise, the use of additional measuring instruments may be required. You can also measure dimensions in close proximity to windows.

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Bore gauge for measuring cylinder diameter: Video

Practical work No. 5.

Measurement and control of external diameters (2 hours)

Goals:

To study the means and methods for measuring outer diameters when processing external cylindrical surfaces on a rotary lathe.

Equipment: rotary lathe, part, cams, hollow prismatic pads, cutters, vernier calipers.

Exercise.

1. Study methods for measuring and controlling outer diameters when processing outer cylindrical surfaces on a rotary lathe.

2. Learn measuring techniques for rough turning.

3. Learn measuring techniques for finishing.

4. Learn indirect measurement techniques large sizes.

5. Learn measurement techniques when using overhead instruments.

Report on the implementation of practical work.

1. Write down what measurements are taken during rough turning and what is the accuracy of these measurements.

2. Write down what tools are used for measurements during finishing in conditions of single and small-scale production, in conditions of serial and mass production. In what cases is each tool used?

3. Write down how turning is distinguished by the nature of processing and what parameters of surface roughness and processing accuracy correspond to them.

4. Write down the basic technological techniques for increasing productivity and for more fully utilizing the useful effective power of the machine.

5. Write down what indirect measurements are, what and how they are performed.

6. Write down the main types of defects when processing external cylindrical surfaces and measures to prevent them.

7. Draw a sketch of the workpiece.

8. Specify the type of workpiece (rolled, forged, casting), material of the workpiece.

9. Write it down technological sequence transitions when processing an outer cylindrical surface, the tool used, cutting modes (depth of cut per pass, faceplate rotation speed n, feed S, cutting speed, main time T o for surgery).

Control questions

1. What means and methods of measurement used for roughing and finishing?

2. List the rules for using calipers.

3. How to measure external cylindrical surfaces with micrometers and indicator clamps?

4. In what cases are limit gauges used?

5. Name the methods and means of indirect measurement of large diameters.

THEORETICAL INFORMATION

MEANS AND METHODS OF MEASUREMENT OF OUTER DIAMETERS

The choice of means and methods for measuring external cylindrical surfaces is made depending on their size and the required measurement accuracy.

Rough turning measurements

Rough measurements of diameters during rough turning of external surfaces with a diameter of up to 500 m: m are made using calipers and rulers. The caliper is set to the size being measured by light blows from the outside or inside one of its legs touches the workpiece or other object. When measuring, the calipers must be held strictly perpendicular to the axis of the part being measured. After taking the size from the part, the caliper is carefully applied to the measuring ruler so that one of its jaws rests against the end of the ruler, and the other is placed on the ruler, and at the end of this jaw the diameter size is measured from the divisions of the ruler. When measuring diameter with a ruler, it must be positioned so that its edge passes through the center of the part. The measurement accuracy with calipers and a ruler is 0.2-0.5 mm (14-16th accuracy grade).

Finishing measurements

Measurement of precise cylindrical surfaces in conditions of single and small-scale production is carried out using calipers, micrometers and indicator clamps, and in conditions of serial and mass production - using limit gauges.

Vernier calipers are used to measure outer diameters and lengths using the method of directly assessing the size using a scale and vernier. Calipers type ШЦ-III with measuring ranges (mm):

250-630; 320-1000; 500-1600; 800-2000; 1500-3000; 2000-4000

Vernier reading 0.1 mm. It is recommended to measure the diameter in two mutually perpendicular directions I – I and II – II (Fig. 8.16). When measuring, a stationary jaw is placed on a cylindrical surface and, with a slight rocking of the caliper in the horizontal plane, a micrometer screw is used to move the movable jaw until it lightly touches the surface being measured. In this position, the movable jaw is fixed and the resulting diameter size is measured along the vernier. When taking measurements, it is necessary to ensure that the caliper is in the correct position so that the measuring surfaces of the jaws are in precise contact with the outer cylindrical surface along its generatrices. Limit errors of measurement (µm) with calipers for size intervals (mm):

Over 500 to 1000 – 210

» 1000 » 1600 – 270

» 1600 » 2000 – 270

» 2000 » 2500 – 300

» 2500 » 3150 – 380

» 3150 » 4000 – 470

Arc micrometers and indicator clamps are used to measure diameters up to 3000 mm, and linear micrometers are used for outer diameters at the end of the part and lengths. Micrometers can be equipped with a micrometer head and a replaceable heel (Fig. 8.17, a) or a micrometer head and indicator. Indicating linear brackets (Fig. 8.17, b) are used to measure the diameter at the end of a part and lengths up to 6 m in size.

Before each measurement, micrometers with an adjustable heel and indicator micrometers and brackets must be set to the size of the part being measured - nominal (one of the maximum or average). When adjusting the size, the micrometer head and indicator must be set to zero, and the indicator must be set after two or three turns of the arrow. The installation is carried out using an installation gauge, a certified bore gauge or plane-parallel end length gauges, preferably near the part being measured. The pre-micrometer or clamp and the established measure must be kept next to the part on cast iron stove, the machine bed or on the part itself for some time. The temperature in the workshop should be within 20 ± 8 °C. During installation, the micrometer (bracket) and the installation gauge must be supported by the heat-insulating pads. In order to reduce the influence of deformation of the bracket due to its own weight, during the installation process the micrometer (bracket) is placed in the same position as when measuring products with it. The bracket should be moved or lowered onto the measure depending on whether it will be in a horizontal or vertical position when measuring the part. Two controllers are involved in the installation process: one of them presses the heel of the bracket to the surface of the installation measure, and the other rocks the bracket in two directions by its second end, finds the return point on the indicator scale and aligns it with it zero mark scales. When checking the zero setting of a micrometer with an adjustable heel without an indicator, the correct position of the micrometer relative to the setting standard is determined by feeling.

When measuring with micrometers and clamps on the scale of a micrometer head or indicator, the deviations of the part being measured from the size to which the micrometer or clamp is installed (from the size of the setting standard) are determined. Before measuring, the part must be kept in a room with a stable temperature for at least 24 hours; measurements must be taken immediately after setting the micrometer to size. Sizes up to 1000 mm are measured by one controller, and sizes over 1000 mm are measured by two controllers. One of the controllers presses the heel of the clamp to the surface of the part, and the second brings the measuring surface of the micrometer head to the part, and then slightly turns the bracket in the diametrical and axial planes and, adjusting its size by turning the drum of the micrometer head, finds it by feel, and if there is an indicator - on his scale largest size in the diametrical and smallest in the axial planes.

When measuring exact dimensions it is necessary to take into account additional errors, such as errors of the setting standard, reading on scales, errors from elastic deformations, etc., data on which are given in specialized literature. For example, the errors in installing staples by size are given in table. 8.11.

Table 8.11

Errors in the process of installing staples to size

In conditions of serial and mass production, clamp gauges called limit gauges are used to measure outer diameters, since they do not control the actual dimensions of the part, but establish that the actual size of the part is within the specified size tolerance. Limit gauges-staples consist of two parts: pass-through (PR) and non-pass-through (NOT). The dimensions of the flow and non-pass parts must correspond to the maximum dimensions of the measured diameter. The distance between the measuring surfaces of the pass side of the PR (Fig. 8.17, c) is equal to the largest maximum diameter size, and the size between the measuring surfaces of the non-pass side is NOT equal to the smallest diameter of the part. When checking dimensions, the through dimensions must pass freely through the part under the influence of its own gravity or a set load. In this case, it is necessary to prevent skewing and jamming of the gauges by correctly aligning the measuring jaws with surfaces of the controlled diameter.

Before starting the inspection, the part being inspected must be kept in a room with a stable temperature for at least 24 hours, and the working gauges next to the part must be kept at metal plate, the machine bed or on the part itself until the temperatures of the part and calibers are equalized.

Caliber holding time before control for the controlled size (mm): up to 1000 1.52; up to 2500 – 2.5; up to 3500 – 4 hours.

When checking, the gauges should be held by the heat-insulating pads.

Indirect measurements of large sizes

By indirect measurements we mean measurements in which the desired value of a quantity is found on the basis of a known relationship between this quantity and the quantities subjected to direct measurements. Indirect measurements are used mainly for measuring dimensions from 2 to 30 m, and their accuracy is usually less than that of direct measurements, so they are used when direct measurements are impossible or difficult. The following methods of indirect measurements are distinguished: 1) from additional bases; 2) girding method; 3) according to the elements of the circle.

Dimensions from additional bases are measured both on the machine and outside the machines. Additional bases are divided into hard (workpiece surfaces, machine parts, special columns, etc.), elastic (stretched string) and light. The first ones are most widely used, where bore gauges, tape measures, measuring tapes, and special devices are used as measuring instruments from additional bases.

In Fig. 8.18a shows a diagram for measuring the outer diameter of a part from an additional measuring base in the form of a machine stand.

The outer diameter of the part D (mm) is determined by the formula

D= 2 (l 1 + d/2 – l 2) ,

where d is the diameter of the auxiliary mandrel installed in the center of the faceplate, mm; 1 1 - distance from the auxiliary measuring base to the mandrel, measured before installing the workpiece on the faceplate, mm; 1 2 – distance from the auxiliary measuring base to the outer surface, measured with a pin, mm.

When measuring, the additional base should be located at a distance of 500-1000 mm from the outer surface greatest detail, which can be machined.

An additional elastic base consists of one or two strings with a diameter of 0.5-1 mm, tensioned with a force of 100-150 N. Measurement at the distance to the string is carried out using a sensitive element, which must be equipped with electrical or electronic contacts.

The light beam created by the light source is used as an additional light base. The measuring device is equipped with a photocell and moves along the axis of the part being measured. When the beam axis shifts, the electronic circuit of the device generates a signal, which, after amplification, is fed to the motor, which performs the corresponding movement. The system is used for automatic control maintaining dimensions and cylindricity when turning large parts.

Measurement errors from additional bases depend on the dimensions of the part, temperature conditions measurements and other factors. Data are given in specialized literature.

The essence of the girding method is to determine the outer diameter D (mm) of the part based on the results of measuring the circumference L (mm) with a tape measure or metal tape. When measured with a tape measure D - L/φπ – t, where π = 3.1416; t – thickness of the tape measure, mm.

The diagram for measuring the circumference by girding with a tape measure is shown in Fig. 8.18, b. When measuring, the tape measure is pulled onto the surface being measured with a certain force of 20-60 N, created by weights 1 and 4 using blocks 2 and 3. The maximum errors for measuring parts using the girdle method are given in Table. 8.12.

Table 8.12

Maximum errors in measuring the outer diameters of parts using the girding method using a tape measure

Surface-mounted devices