What are the commonly used measuring devices in the steel pipe production workshop?
Classification of measuring instruments
Table of Contents
- 1 Classification of measuring instruments
- 2 Technical performance index of measuring instruments
- 3 Selection of measuring tools
Measuring instrument is a kind of instrument with fixed shape to reproduce or provide one or more known values. According to different uses, measuring tools can be divided into the following categories:
Single value measuring tool
A measuring tool that can only reflect a single value. It can be used to calibrate and adjust other measuring instruments or as a standard quantity to directly compare with the measured, such as gauge block, angle gauge block, etc.
Multi value measuring tools
It can reflect a group of measuring tools of the same kind. It can also be used to calibrate and adjust other measuring instruments or compare them directly with the measured ones, such as linear ruler.
Special measuring tools
A gauge specially used to test a specific parameter. The common ones are: smooth limit gauge for testing smooth cylindrical hole or shaft, thread gauge for judging the qualification of internal thread or external thread, inspection template for judging the qualification of surface profile of complex shape, functional gauge for inspecting assembly accuracy by simulating assembly trafficability, etc.
General measuring tools
In our country, the measuring instrument with simple structure is called general measuring tool. Such as vernier caliper, outside micrometer, dial indicator, etc.
Technical performance index of measuring instruments
Nominal value of measuring tool
A quantity marked on a measuring tool to indicate its characteristics or guide its use. Such as the size marked on the gauge block, the size marked on the scale ruler, the angle marked on the angle gauge block, etc.
The smallest unit of measurement on a scale. If the difference between the values represented by two adjacent lines on the differential cylinder of an external micrometer is 0.01mm, the graduation value of the measuring instrument is 0.01mm. The division value is the minimum unit value that can be read directly by a measuring instrument. It reflects the reading accuracy and explains the measurement accuracy of the measuring instrument.
Within the allowable uncertainty, the range from the lower limit to the upper limit of the measured value that the measuring instrument can measure. For example, the measuring range of external micrometer is 0-25 mm, 25-50 mm, and the measuring range of mechanical comparator is 0-180 mm.
In the process of contact measurement, the contact pressure between the measuring head and the measured surface is measured. Too much measuring force will cause elastic deformation, and too small measuring force will affect contact stability.
The difference between the indication value of the measuring instrument and the true value to be measured. Indication error is the comprehensive reflection of various errors of measuring instrument itself. Therefore, the indication error is different at different working points within the indication range of the instrument. Generally, the indication error of measuring instruments can be verified by measuring blocks with appropriate accuracy or other measuring standards.
Selection of measuring tools
Before each measurement, it is necessary to select the measuring tools according to the special characteristics of the measured parts, such as caliper, height gauge, micrometer and depth gauge for length, width, height, depth, outer diameter and segment difference; micrometer and caliper can be used for shaft diameter; feeler gauge, block gauge and feeler gauge can be selected for hole and groove; right angle ruler is selected for measuring part’s right angle; R gauge is selected for measuring r value; measuring configuration is used When the tolerance is small, the accuracy is high or the form and position tolerance is required to be calculated, the cubic element and the quadratic element can be selected; the hardness tester is used to measure the steel hardness.
Application of caliper
The caliper can measure the inner diameter, outer diameter, length, width, thickness, segment difference, height and depth of objects; the caliper is the most commonly used and convenient measuring tool, and the most frequently used measuring tool in the processing field.
Digital calipers: Resolution 0.01mm, used for dimension measurement with small fit tolerance (high precision).
Watch card: The resolution is 0.02mm, which is used for conventional dimension measurement.
Vernier caliper: The resolution is 0.02mm, which is used for rough machining measurement.
Before using the caliper, clean white paper should be used to remove the dust and dirt (use the external measuring surface of the caliper to clamp the white paper, then pull it out naturally, and repeat for 2-3 times)
When measuring with a caliper, the measuring surface of the caliper should be parallel or vertical to the measuring surface of the object to be measured;
When using the depth measurement, if the measured object has R angle, it is necessary to avoid the R angle but close to the R angle, and the depth ruler should be perpendicular to the measured height as far as possible ；
When measuring cylinder with caliper, it is necessary to rotate and measure the maximum value in sections ；
Due to the high frequency of using the caliper, the maintenance work needs to be done the best. After using it every day, it is necessary to clean it and put it into the box. Before use, the accuracy of the caliper needs to be tested with a gauge block.
Application of micrometer
Before the micrometer is used, clean white paper should be used to remove dust and dirt (use micrometer to measure the contact surface and screw surface, jam the white paper, then pull out naturally, repeat for 2-3 times), and then turn the knob to measure the quick contact between the contact surface and the screw surface, use fine adjustment. When both sides are fully contacted, zero adjustment can be carried out.
When measuring hardware with micrometer, adjust the knob. When contacting the workpiece quickly, use the fine-tuning knob to turn in. When the sound of click, click and click is heard, stop and read the data from the display screen or scale.
When measuring plastic products, the measuring contact surface and the screw can touch the product gently.
When measuring shaft diameter with micrometer, at least two or more directions shall be measured and the maximum value shall be measured in sections. The two contact surfaces of micrometer in measurement shall be kept clean at any time to reduce measurement error.
Application of height gauge
The height gauge is mainly used to measure height, depth When measuring flatness, perpendicularity, concentricity, coaxiality, surface vibration, tooth vibration, depth and height ruler, it is necessary to check whether the probe and the connecting parts are loose.
Application of feeler gauge
The feeler gauge is suitable for measuring flatness, bending and straightness.
Place the parts on the platform, and measure the clearance between the parts and the platform with a feeler gauge (Note: keep the clearance between the feeler gauge and the platform during the measurement)
Place the part on the platform and rotate it for one circle, and measure the clearance between the part and the platform with a feeler gauge.
Place the parts on the platform, select the corresponding feeler gauge to measure the gap between the two sides or the middle of the part and the platform.
Place one side of the measured zero squareness on the platform, and let the square ruler close to it on the other side. Measure the maximum gap between the part and the square with a feeler gauge.
Application of plug gauge (rod and needle)
It is suitable for measuring the inner diameter, groove width and clearance of holes.
When the hole diameter of the parts is large and there is no suitable needle gauge, the two plug gauges can be overlapped, and the plug gauge can be fixed on the V-shaped block with magnetism according to the 360 degree direction measurement, which can prevent loosening and is easy to measure.
Bore measurement: When measuring the hole diameter, the penetration is qualified, as shown in the figure below.
Note: when measuring, the plug gauge should be inserted vertically instead of obliquely.
Precision measurement instrument
Quadratic element is a kind of non-contact measuring instrument with high performance and high precision. The sensing element of the measuring instrument does not directly contact with the surface of the measured part, so there is no mechanical measuring force; the image captured by the quadratic element is transmitted to the data acquisition card of the computer by means of projection, and then imaged on the computer display by software; various geometric elements (point, line, circle, arc, ellipse, rectangle) on the part can be carried out Distance, angle, intersection point, form and position tolerance (roundness, straightness, parallelism, perpendicularity, inclination, position, concentricity and symmetry) can be measured, and the outline can be described in 2D and output by CAD. Not only can the contour of the workpiece be observed, but also the surface shape of the opaque workpiece can be measured.
Conventional geometric element measurement: The inner circle in the following part is a sharp angle, which can only be measured by projection.
Observation of electrode machining surface: The lens of the second dimension has the function of amplification, and the roughness inspection after electrode processing (magnified image by 100 times).
Measurement of small size deep groove
Gate inspection: In mold processing, there are often some gates hidden in the slot, and all kinds of detection instruments are illegal for measurement. At this time, the rubber paste can be pasted on the rubber gate, and the shape of the rubber gate will be printed on the mortar. Then, the size of the gate can be obtained by measuring the size of the mastic seal with the quadratic element.
Note: since there is no mechanical force in the second-order measurement, the second-dimensional measurement should be used for thinner and softer products.
Precision measuring instruments: cubic dimension
Cubic element is characterized by high precision (up to μ m); versatility (can replace a variety of length measuring instruments); can be used to measure geometric elements (in addition to the elements that can be measured by the quadratic element, it can also measure cylinder and cone), and geometric tolerance (in addition to the geometric tolerance that can be measured by quadratic element, it also includes cylindricity, flatness, line profile, surface profile and coaxiality) As long as the three-dimensional probe can touch, its geometric size, mutual position and surface profile can be measured; and the data processing is completed with the help of computer; with its high precision, high flexibility and excellent digital ability, it has become an important means and effective tool for modern mold manufacturing and quality assurance.
In the modification of some molds, there is no 3D drawing file, which can measure the coordinate value of each element and the contour of irregular surface. Then, it can be exported by drawing software and made into 3D graphics according to the measured elements. It can be processed and modified quickly and correctly (after the coordinate is set, any point can be used to measure the bench mark value).
3D digital simulation import comparative measurement: for the finished parts, in order to confirm the consistency with the design or find the abnormal fit in the process of assembling the fit mold, when some surface profiles are neither arc nor parabola, but some irregular surfaces, and cannot be measured by geometric elements, 3D model can be imported for comparative measurement with parts, so as to understand the processing error; because the measured value is point-to-point It is easy to correct and improve quickly and effectively (the data shown in the figure below is the deviation between the measured value and the theoretical value).
Application of hardness tester
The commonly used hardness tester includes Rockwell hardness tester (desktop) and Leeb hardness tester (portable). The commonly used hardness units are Rockwell HRC, Brinell Hb and Vickers HV.
Rockwell hardness tester HR
The Rockwell hardness test method is to use a diamond cone with a top angle of 120 degrees or a steel ball with a diameter of 1.59/3.18mm, which is pressed into the surface of the tested material under a certain load, and the hardness of the material can be calculated from the indentation depth. According to the hardness of materials, it can be divided into three different scales to represent HRA, HRB and HRC.
HRA is the hardness obtained by using a 60kg load and a diamond cone indenter. It is used for materials with extremely high hardness. For example: cemented carbide.
HRB is the hardness obtained by using 100kg load and 1.58mm diameter hardened steel ball, which is used for materials with lower hardness. For example: annealed steel, cast iron, alloy copper, etc.
HRC is the hardness obtained by using a 150kg load and a diamond cone indenter, which is used for materials with high hardness. For example: quenched steel, tempered steel, Quenched and tempered steel and some stainless steel.
Vickers hardness HV (mainly for surface hardness measurement)
It is suitable for microscopic analysis. The diamond square cone indenter with a load less than 120kg and a top angle of 136 ° is pressed into the surface of the material. The length of the indentation diagonal is measured. It is suitable for the hardness measurement of larger workpieces and deeper surface layers.
Leeb hardness HL (Portable Hardness Tester)
Leeb hardness is a dynamic hardness test method. In the process of impact between the impact body of the hardness sensor and the workpiece to be measured, the ratio of rebound speed to impact speed of 1 mm from the workpiece surface multiplied by 1000 is defined as the Leeb hardness value.
Advantages: Leeb hardness tester made by Leeb hardness theory has changed the traditional hardness testing method. Since the hardness sensor is as small as a pen, it can directly test the hardness of the workpiece in various directions on the production site by holding the sensor in hand, so it is not suitable for other desktop hardness tester.
Source: China Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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