Metal materials belong to metallurgical products, and the production, ordering, transportation, use, storage and inspection of metal materials must be based on a unified technical standard - metallurgical product standards. Personnel engaged in metal materials must master the relevant content of the standard. The standards used for metallurgical products in China are national standards (codenamed national standard "GB"), ministerial standards (Ministry of Metallurgical Industry standard "YB", a machine standard "JB", etc.) enterprise standards.
1. Packaging inspection
It depends on the type, shape, size, accuracy, and anti-corrosion of metal materials.
1. Bulk: that is, no packaging, ingots, blocks (not afraid of corrosion, not valuable), large steel (large steel, thick steel plates, rails), pig iron, etc.
2. Bundles: small size and corrosion have little impact on use, such as small and medium-sized steel, pipe steel, wire rod, thin plate, etc.
3. Boxes (barrels): refers to anti-corrosion, small and thin products, such as tinplate, silicon steel sheets, magnesium ingots, etc.
4. Shafting: finger wire, wire rope, steel strand, etc.
For packing boxes and shaft packaging products, the packaging should be checked first to see if the packaging is complete.
Second, the mark inspection
The mark is a mark to distinguish the material and specification of the material, mainly stating the supplier's name, brand, inspection batch number, specification, size, grade, net weight, etc. The signs are;
1. Coloring: On the end face of metal materials, the end is coated with various colors of paint, mainly used for steel, pig iron, non-ferrous raw materials, etc.
2. Printing: the method of making steel stamps or spray paint on the specified parts (end faces, ends) of metal materials, explaining the grades, specifications, and standard numbers of materials. It is mainly used for medium and heavy plates, profiles, colored materials, etc.
3. Listing: Bundles, boxes, shafts and other metal materials are listed outside to explain their grades, sizes, weights, standard numbers, suppliers, etc.
The signs of metal materials should be carefully identified during inspection, and properly protected in the process of transportation and storage.
Third, the inspection of specifications and dimensions
Specification size refers to the nominal size of the main parts of the metal material (length, width, thickness, diameter, etc.).
1. Nominal size (nominal size): It is the ideal size that people want to get in production, but it has a certain gap with the actual size.
2. Dimensional deviation: The difference between the actual size and the nominal size is called the size deviation. Larger than the nominal size is called positive deviation, and less than the nominal size is called negative deviation. Within the range specified in the standard is called allowable deviation, exceeding the range is called size deviation, and deviation is a non-conforming product.
3. Accuracy grade: The allowable deviation of the size of the metal material is specified in several ranges, and is divided into several grades according to the size of the allowable deviation, which is called the accuracy grade, and the accuracy grade is divided into ordinary, higher, and advanced.
4. Delivery length (width): It is the main size of metal material delivery, which refers to the length (width) specification that metal materials should have when delivered.
5. Usual length (indefinite length): the length is not specified in a certain way, but it must be within a specified length range (according to different varieties, the length is different, according to the ministry and factory).
6. Short ruler (narrow ruler): the length is less than the lower limit of the specified normal length size, but not less than the specified minimum allowable length. For some metal materials, a part can be handed over according to the regulations"Short ruler" .
7. Fixed-length length: The length of the metal material must have the length specified by the buyer in the order contract (general positive deviation).
8. Length of the ruler: The length of the metal material must be an integer multiple of the length specified by the buyer in the order contract (plus sawing edge, positive deviation).
The inspection of specifications and dimensions should pay attention to the measurement of the material part and the selection of appropriate measuring tools.
Fourth, the quantity of inspection
The quantity of metal materials generally refers to the weight (except for individual cases of backing plates and fishtail plates in the number of pieces), and the quantity inspection methods are:
1. Measured by actual weight: All metal materials measured by actual weight should generally be weighed and inspected. For firm packaging (such as boxes, closures, barrels, etc.), the gross weight, net weight and tare weight are indicated on the packaging. If the number of thin steel plates, silicon steel sheets, and ferroalloys can be sampled at least 5% of a batch, if the sampling weight is very different from the marked weight, all must be unpacked and weighed.
2. Measurement according to theoretical conversion: the weight calculated by the nominal size (actual size) and specific gravity of the material can be converted according to the theory for those fixed-length plates, but it is necessary to pay attention to the conversion formula and the actual specific gravity of the material when converting.
5. Surface quality inspection
Surface quality inspection is mainly the inspection of materials, appearance, shape, and surface defects, mainly including:
1. Ellipsity: the phenomenon that the diameter of a metal material with a circular cross-section is unequal in all directions on the same cross-section. The ovality is expressed by the difference between the maximum and minimum diameters on the same cross-section, and the standards are different for different materials.
2. Bending and curvature: Bending is the rolling material. A general term for an uneven, curvilinear shape in length or width. If the degree of unevenness is expressed numerically, it is called curvature.
3. The twisted ** strip rolled material is twisted into a spiral along the longitudinal axis.
4. Sickle bend (side bend): refers to the bending of metal plates, strips and shapes close to rectangular sections along the length (narrow side of the side), one side is concave curve, and the other face is convex curve, which is called"Scythe bend" .Expressed in terms of recessed height.
5. Scoop curvature: refers to the undulating wave phenomenon that occurs in the length and width of the plate or belt at the same time, forming a scoop curvature, which is called scoop curvature. The numerical value that indicates the degree of curvature is called the curvature of the scoop.
6. Surface cracks: refers to cracks on the surface of metal objects.
7. Ears: Due to improper roll fitting and other reasons, the protrusions that extend along the rolling direction are called ears.
8. Bracketing: refers to the fact that the surface of the material is straight or arc-shaped, and the bottom of the groove can usually be seen.
9. Scarring: refers to tongue-like, nail-like or fish-scale flakes that are unevenly distributed on the surface of metal materials.
10. Bonding: the mutual adhesion between the layers and the points, lines and surfaces between the layers of metal plates, foils and strips during the annealing of stacking. After being lifted, there are traces of bonding left on the surface, which is called bonding.
11. Iron oxide scale: Iron oxide scale refers to the metal oxide generated on the surface of the material during the heating, rolling and cooling process.
12. Folding: It is a surface defect formed by the metal in the hot rolling process (or forging), and the surface is a bimetallic layer that folds with each other, which coincides in a straight line or curve.
13. Pockmarks: refers to the uneven rough surface of metal materials.
14. Subcutaneous bubbles: The surface of metal materials is irregularly distributed, with different sizes, different shapes, smooth small bumps around them, and cracked bubbles are chicken claw-shaped cracks or tongue-like scars, which are called bubbles.
The causes of surface defects are mainly due to improper production, transportation, loading and unloading, storage and other operations. Depending on the impact on use, there are defects that do not allow the limit to be exceeded at all. Some defects, although not present, are not allowed to be exceeded; Whether various surface defects are allowed to exist, or the extent to which they are allowed, are clearly stipulated in the relevant standards.
Sixth, the guarantee conditions of internal quality inspection
The inspection basis of the internal quality of metal materials is to adapt to different requirements according to the material, and the guarantee conditions are also different.
1. Basic guarantee conditions: the minimum requirements for material quality, whether proposed or not, must be guaranteed, such as chemical composition, basic mechanical properties, etc.
2. Additional guarantee conditions: refers to the items that are inspected according to the requirements indicated by the buyer in the order contract and ensure that the inspection results meet the requirements.
3. Agreement guarantee conditions: the project negotiated by the supply and demand parties and guaranteed in the order contract.
4. Conditions for participating in the reform: The two parties negotiate the inspection items, but only for reference conditions, not for assessment.
The internal quality inspection of metal materials mainly includes mechanical properties, physical properties, chemical properties, process properties, chemical composition and internal structure inspection. The first part of the mechanical properties and process properties has been introduced, and here only the principles and simple processes of the inspection methods for chemical composition and internal structure are summarized.
7. Chemical composition inspection
Chemical composition is the main factor that determines the performance and quality of metal materials. Therefore, the standard stipulates the chemical composition that must be guaranteed for most metal materials, and some even serve as the main quality and variety indicators. The chemical composition can be analyzed and identified by a variety of chemical and physical methods, and the most widely used method is chemical analysis and spectral analysis.
1. Chemical analysis method: determine the composition of metals according to chemical reactions, which is collectively referred to as chemical analysis method. There are two types of chemical analysis methods: qualitative analysis and quantitative analysis. Through qualitative analysis, it is possible to identify which elements the material contains, but not their content; Quantitative analysis is used to accurately determine the content of various elements. In actual production, quantitative analysis is mainly used. The quantitative analysis methods are gravimetric analysis and volume analysis.
Gravimetric analysis: The measured elements in the metal are separated from other components by appropriate separation methods, and then the element content is measured by gravimetric method.
Volumetric analysis: a standard solution (a solution of known concentration) is used to completely react with the measured element in the metal, and then the amount of the measured element is calculated based on the volume of the standard solution consumed.
2. Spectral analysis method: various elements can produce their own unique spectrum under high temperature and high energy excitation, and the method of determining the chemical composition and approximate content of the metal according to the characteristic spectrum generated by the element after being excited is called spectroscopic analysis method. Usually, the sample is excited by external energy sources such as arc, electric spark, laser, etc., so that the measured element emits a characteristic spectrum. After spectroscopy, it was compared with the spectral table of chemical elements for analysis.
3. Spark identification method: It is mainly used for steel, due to friction and high temperature under the grinding wheel grinding, the number, shape, bifurcation, color and other sparks generated when various elements and particles are oxidized, so as to identify the chemical composition (constituent elements) and approximate content of the material.
8. Common internal organizational defects in internal quality inspection are:
1. Looseness: In the solidification process of cast iron or castings, the melt in the area between the crystal branches finally solidifies and shrinks and releases gas, resulting in the production of many fine pores and gases and caused by non-compactness.
2. Slag inclusion: impurity phase or foreign body particles surrounded by a solid metal matrix.
3. Segregation: the uneven distribution of chemical composition in each area of the alloy metal.
4. Decarburization: the phenomenon that all or part of the carbon in the surface of the material or workpiece of steel and iron-based alloy is lost.
In addition, bubbles, cracks, delamination, white spots, etc. are also common internal structure defects, and the inspection methods for internal structure (grains, structure) and internal structure defects are commonly used
a.Macro Inspection:This is an inspection of the internal structure and defects of metal materials by using the naked eye or a low-magnification glass of less than 10 times. Commonly used methods include fracture inspection, low-magnification inspection, tower turning hairline inspection and sulfur mark test.
It mainly inspects bubbles, slag inclusions, delamination, crack grain coarseness, white spots, segregation, porosity, etc.
b. Microscopic examination:Microscopic inspection, also known as high-magnification inspection, is an inspection method that observes and determines the prepared sample under a phase microscope at a specified magnification to test the structure and defects of metal materials. General inspection of inclusions, grain size, decarburization layer depth, intergranular corrosion, etc.
c. Non-destructive testing:Non-destructive testing includes magnetic testing, fluorescence testing, and coloring testing. Magnetic testing is used to inspect the close surface cracks, inclusions, white spots, folds, shrinkage holes, scarring, etc. of ferromagnetic materials such as steel. Fluorescence and coloring are used to inspect fine cracks and loose holes on the surface of non-magnetic materials such as non-ferrous metals, stainless steel, and heat-resistant alloys.
d. Ultrasonic inspectionAlso known as ultrasonic flaw detection. Ultrasonic waves are used for linear propagation in the same homogeneous medium. However, at the interface between the two substances, there will be partial or total reflections. Therefore, when the ultrasonic wave detours to the material with pores, cracks, shrinkage porosity, and inclusions, the reflection occurs at the interface of the metal, and the larger the heterogeneous interface, the stronger the reflection ability, and vice versa. In this way, the location and size of the internal defect can be reflected by the waveform of the flaw detector screen. Commonly used ultrasonic flaw detection is X-ray and radiographic flaw detection.
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