Tempered glass

[gāng huà bō li]

A kind of prestressed glass

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Tempered glass/Reinforced glass surface has Compressive stress Glass. also called Reinforced glass 。 The reinforcement of glass by tempering method was started in France in 1874.^[1]

On March 15, 2024, March 15 Evening Party of China Central Radio and Television Station in 2024 Exposed the behavior of using ordinary toughened glass to mark fire resistance and impersonate fire resistance glass for sale.^[2]

Chinese name: Tempered glass
Foreign name: Tempered glass/Reinforced glass
Category: Safety glass
Role: Wind pressure resistance, cold and heat resistance, impact resistance, etc

Characteristic 1: High mechanical strength; Good elasticity; Self explosive
Characteristic 2: Good thermal stability; It is not easy to hurt people after being broken;
Application: Doors and windows; Automobile; Curtain wall; Window furniture, etc
Disadvantages: It cannot be cut, polished or extruded, and needs to be customized

catalog

Tempered glass/Reinforced glass belongs to safety glass. Tempered glass is actually a kind of prestressed glass strength , usually formed on the glass surface by chemical or physical methods Compressive stress When the glass bears external force, it first offsets the surface stress, thus improving the bearing capacity and enhancing the resistance to wind pressure, cold and heat, impact, etc. of the glass itself. Attention and FRP Distinguish.

characteristic

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Security

When the glass is subjected to External failure The fragments will form small obtuse angular particles similar to honeycomb, which is not easy to cause serious harm to human body.

high strength

The impact strength of tempered glass with the same thickness is 3-5 times that of ordinary glass, and the bending strength is 3-5 times that of ordinary glass.

thermal stability

Tempered glass has good thermal stability , the temperature difference that can withstand is ordinary Glass It can withstand 300 ℃ temperature difference change.

advantage

Tempered glass

The first is strength Compared with ordinary glass, it is several times more resistant to bending.

The second is Safe use The increase of its bearing capacity improves its fragility. Even if the tempered glass is damaged, it also presents small pieces with no acute angle, which greatly reduces the harm to the human body. Tempered glass has 3~5 times more resistance to rapid cooling and heat than ordinary glass. Generally, it can withstand temperature difference of more than 250 degrees, which has obvious effect on preventing thermal cracking. It is one of the safety glasses. To ensure the safety of qualified materials for high-rise buildings.

shortcoming

Disadvantages of tempered glass:

1. Tempered glass cannot be cut and processed again. It can only be processed to the required shape before tempering and then tempered.

2. Although the strength of tempered glass is stronger than that of ordinary glass, tempered glass has the possibility of self explosion (self rupture), while ordinary glass has no possibility of self explosion.

3. The surface of tempered glass will be uneven (wind spots), with slight thickness thinning. The reason for the thinning is that after the glass is melted and softened, it is cooled rapidly by strong wind, which makes the crystal gap inside the glass smaller and the pressure larger, so the glass is thinner after tempering than before. Generally, 4~6mm glass becomes 0.2~0.8mm thinner after tempering, and 8~20mm glass becomes 0.9~1.8mm thinner after tempering. The specific degree depends on the equipment, which is also the reason why tempered glass cannot be used as a mirror.

4. Building after passing through tempering furnace (physical tempering) plate glass Generally, there will be deformation, and the degree of deformation is determined by the equipment and technicians' process. To some extent, it affects the decorative effect (except for special needs).

preparation

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Tempered glass is made by ordinary annealing Glass before cutting To the required size, and then heated to approximately softening point It is obtained by fast and uniform cooling at 700 ℃ (usually 5-6MM glass is heated at 700 ℃ for about 240 seconds and cooled for about 150 seconds. 8-10MM glass is heated at 700 ℃ for about 500 seconds and cooled for about 300 seconds. In short, the heating and cooling time is different according to the thickness of glass). After tempering, uniform compressive stress is formed on the surface of the glass, while tensile stress is formed inside, which improves the bending and impact strength of the glass, which is about four times more than that of ordinary annealed glass. The tempered glass that has been tempered can not be cut, ground or damaged, otherwise it will be damaged due to the destruction of uniform compressive stress balance“ be smashed to pieces ”。

classification

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By Shape

1. Tempered glass can be divided into plane tempered glass and curved tempered glass according to shape.

Generally, the thickness of plane tempered glass is 11, 12, 15, 19 mm, etc; The thickness of curved tempered glass is 11 mm, 15 mm and 19 mm. The specific thickness after processing depends on the equipment and technology of each manufacturer. However, curved (i.e. bend toughened) tempered glass has a maximum radian limit for each thickness. That is to say, R R is the radius.

2. Tempered glass can be divided into flat tempered glass and curved tempered glass according to its appearance.

3. Tempered glass is divided into superior products and qualified products according to its flatness. Superior tempered glass is used for automobile windshield; Qualified products are used for architectural decoration.

By process

1. Physical tempered glass is also called quenching tempered glass. When ordinary flat glass is heated to a softening temperature (600 ℃) close to that of the glass in a heating furnace, the internal stress is eliminated through its own deformation, then the glass is moved out of the heating furnace, and then the high-pressure cold air is blown to both sides of the glass by a multi nozzle, so that it can be quickly and evenly cooled to room temperature to produce tempered glass. This kind of glass is in the stress state of internal tension and external pressure. Once local damage occurs, stress release will occur, and the glass will be broken into numerous small pieces. These small pieces have no sharp edges and corners and are not easy to hurt people.

2. Chemically toughened glass is to improve the strength of glass by changing the chemical composition of the glass surface, which is generally tempered by ion exchange method. The method is to convert Silicate glass Immerse into the molten lithium (Li+) salt to exchange Na+or K+ions on the glass surface with Li+ions, forming a Li+ion exchange layer on the surface. Since the expansion coefficient of Li+is less than Na+ K+ions, so that the outer layer shrinks less and the inner layer shrinks more during the cooling process. When the glass is cooled to normal temperature, it will also be in the tension state of the inner layer and the pressure state of the outer layer. The effect is similar to that of physically toughened glass.

According to the degree of steel

1. Tempered glass: Tempered degree=2~4N/cm, surface stress of tempered glass of glass curtain wall α ≥ 95Mpa;

2. Semi tempered glass: tempering degree=2N/cm, surface stress of glass curtain wall semi tempered glass 24Mpa ≤ α ≤ 69Mpa;

3. Super strong tempered glass: Tempered degree>4N/cm.

Product application

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Flat tempered and bent tempered glass belongs to Safety glass 。 Widely used in high-rise building doors and windows glass screen wall 、 Indoor partition Glass, daylighting ceiling, sightseeing elevator passage, furniture, glass guardrail Etc. Generally, tempered glass can be used in the following industries:

1. Building, building formwork, decoration industry (e.g. doors and windows curtain , interior decoration, etc.)

2. Furniture manufacturing industry (glass coffee table, furniture accessories, etc.)

3. Household appliance manufacturing industry (TV, oven, air conditioner, refrigerator and other products)

4. Electronics and instrument industry (mobile phones, MP3, MP4, clocks and watches and other digital products)

5. Automobile manufacturing industry (automobile window glass, etc.)

6. Daily products industry (glass chopping board, etc.)

7. Special industry (military glass)

After the tempered glass is broken, the fragments will break into uniform small particles and there is no common sharp corner like glass knife, so it is called safety glass and widely used in cars, interior decoration, and windows open to the outside of high-rise buildings.

Emergency methods

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quality

Tempered glass is obtained by cutting ordinary annealed glass into required size, heating it to near softening point, and then cooling it quickly and evenly. After tempering, uniform compressive stress is formed on the surface of the glass, while internal stress is formed Tensile stress The performance of the glass is greatly improved, the tensile strength is more than 3 times of the latter, and the impact resistance is more than 5 times of the latter.

It is also this feature that the stress feature has become an important symbol to identify the true and false tempered glass, that is, the tempered glass can see color stripes at the edge of the glass through the polarized light sheet, and black and white spots can be seen on the surface layer of the glass. The polarizing lens can be found in the camera lens or glasses. When observing, pay attention to the adjustment of the light source, so that it is easier to observe.

Self explosive defect

The automatic cracking of tempered glass without direct mechanical external force is called the self explosion of tempered glass. According to industry experience, the self explosion rate of ordinary tempered glass is about 1-3 ‰. Self explosion is one of the inherent characteristics of tempered glass.

There are many reasons for the expansion of self explosion, which can be simply summarized as follows:

① Glass Quality defects Impact of

A、 There are stones, impurities and bubbles in the glass: impurities in the glass are the weak points of tempered glass and stress concentration points. In particular, if the stone is located in the tensile stress zone of tempered glass, it is an important factor leading to cracking.

Stone exists in glass and has different expansion coefficient from that of vitreous body. FRP The stress concentration in the crack area around the stone increases exponentially after melting. When the expansion coefficient of stone is less than that of glass, the tangential stress around the stone is in tension. Crack propagation associated with stones is very easy to occur.

B、 The glass contains nickel sulfide crystals

Nickel sulfide inclusions generally exist as small crystalline spheres with a diameter of 0.1-2 mm. The appearance is metallic. These impurities are Ni3S2, Ni7S6 and Ni-XS, where X=0-0. 07。 Only Ni1-XS phase is the main reason for spontaneous explosion of tempered glass.

The known theoretical NIS is 379. There is a phase transition process at C, from α - NiS hexagonal crystal system at high temperature to β - NiS hexagonal crystal system at low temperature Trigonal system During the process, 2.38% volume expansion is accompanied. This structure is preserved at room temperature. If the glass is heated later, α - β state transition may occur rapidly. If these sundries are inside the tempered glass under tensile stress, the volume expansion will cause spontaneous cracking. If there is a-NIS at room temperature, it will also slowly change to beta state after several years and months. During this phase transition, the slow increase in volume may not cause internal fracture.

C、 The glass surface is scratched due to improper processing or operation Blast , deep bursting edge and other defects, which are easy to cause stress concentration or self explosion of tempered glass.

② Uneven and offset stress distribution in tempered glass

The temperature gradient produced along the glass thickness direction when the glass is heated or cooled is uneven and asymmetric. It makes the tempered products have a tendency of self explosion, and some produce "wind explosion" when chilling. If the tensile stress zone shifts to one side of the product or to the surface, the tempered glass will explode spontaneously.

③ The experiment shows that when the degree of tempering is increased to level 1/cm, the number of spontaneous explosion reaches 20%~25%. It can be seen that the greater the stress, the higher the degree of tempering, and the greater the spontaneous explosion amount.

Development history

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The development of tempered glass can be traced back to the middle of the 17th century. There was a prince of Rhine named Robert who once made an interesting experiment. He put a drop of molten glass into cold water and made an extremely hard glass. This high-strength granular glass is like a water drop, with a long and curved tail. It is called“ Prince Robert Xiaoli ”。 But when Xiaoli's tail was bent and broken, it was strange that the whole Xiaoli suddenly collapsed violently and even became a fine powder. The above method is very similar to the quenching of metal, which is the quenching of glass. such quench It does not change the composition of the glass, so it is also called Physical quenching (physical tempered), so tempered glass is called tempered glass.

The first patent for glass tempering was obtained by the French in 1874. The tempering method is to heat the glass to nearly Softening temperature After that, immediately put it into a relatively low temperature liquid tank to increase the surface stress. This method is the early liquid tempering method. German Frederick Siemens Obtained a patent in 1875, the United States Massachusetts Of Geovge E. Rogens In 1876, the tempering method was applied to glass wine glasses and lamp posts. In the same year, Hugh O'Heill of New Jersey obtained a patent.

In the 1930s, Saint Gobain of France, Triplex of the United States, and Pilkington of the United Kingdom began to produce large area flat tempered glass for automobile windshields. In the 1930s, Japan also carried out industrial production of tempered glass. Since then, the world has begun the era of large-scale production of tempered glass.

After 1970, the British Triplex The company successfully tempered glass with a thickness of 0.75~1.5mm with liquid medium, ending the history that thin glass cannot be tempered by physical tempering, which is a major breakthrough in tempered glass technology.

The history of tempered glass in China began in 1955. Shanghai Yaohua Glass Factory started trial production, and Qinhuangdao tempered glass factory succeeded in trial production in 1958. 1965 Qinhuangdao Yaohua Glass Factory It began to produce tempered glass for military use, and Luoyang Glass Factory was the first to introduce Belgian tempered equipment in the 1970s. At the same time, chemical tempered glass of Shenyang Glass Factory was put into production.

Since the 1970s, tempered glass technology has been comprehensively promoted and popularized worldwide. Tempered glass has been used in automobile, architecture, aviation, electronics and other fields, especially in architecture and automobile.

Self explosive solution

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Reduce stress value

The stress distribution in the tempered glass is that the two surfaces of the tempered glass are compressive stress, the core layer of the plate is in tensile stress, and the stress distribution in the thickness of the glass is similar to a parabola. The center of the glass thickness is the vertex of the parabola, that is, the place where the tensile stress is maximum; The compressive stress is near the two surfaces of the glass on both sides; The zero stress surface is located at about 1/3 of the thickness. By analyzing the physical process of tempered quenching, it can be seen that there is a rough proportional relationship between the surface tension of tempered glass and the maximum tensile stress inside, that is, the tensile stress is 1/2~1/3 of the compressive stress. Domestic manufacturers generally set the surface tension of tempered glass at about 100MPa, which may be higher in actual situation. The tensile stress of tempered glass itself is about 32MPa~46MPa, and the tensile strength of glass is 59MPa~62MPa. As long as the tension generated by nickel sulfide expansion is 30MPa, it is enough to cause self explosion. If the surface stress is reduced, the tensile stress of the tempered glass itself will be reduced accordingly, thus helping to reduce the occurrence of spontaneous explosion.

The surface stress range of tempered glass specified in American standard ASTMC1048 is greater than 69MPa; Semi tempered (heat strengthened) glass is 24MPa~52MPa. The curtain wall glass standard BG17841 stipulates that the semi tempered stress range is 24<; δ≤69MPa。 The new national standard GB15763 implemented in China. 2-2005 Safety Glass for Building Part 2: Tempered Glass requires that the surface stress shall not be less than 90MPa. This is 5MPa lower than the 95MPa specified in the old standard, which is conducive to reducing spontaneous explosion.

Uniform stress

The uneven stress of tempered glass will significantly increase the spontaneous explosion rate, which has reached a level that cannot be ignored. The self explosion caused by uneven stress is sometimes very concentrated, especially the self explosion rate of a specific batch of bent tempered glass will reach an alarming degree, and may occur continuously. The main reasons are the uneven local stress and the deviation of the tension layer in the thickness direction, and the quality of the original glass sheet itself has a certain impact. Uneven stress will significantly reduce the strength of the glass, which is equivalent to increasing the internal tensile stress to a certain extent, thus increasing the spontaneous explosion rate. If the stress of tempered glass can be evenly distributed, the spontaneous explosion rate can be effectively reduced.

Hot dip treatment

Hot dip treatment is also called homogenization treatment, commonly known as "detonation". Hot dip treatment is to heat the tempered glass to 290 ℃± 10 ℃ and keep it warm for a certain period of time, so as to promote nickel sulfide to rapidly complete the crystal phase transformation in the tempered glass, so that the tempered glass that could explode after use can be artificially broken in the factory's hot dip furnace in advance, thus reducing the self explosion of tempered glass in use after installation. This method generally uses hot air as the heating medium, which is called "Heat Soak Test" (HST) in foreign countries.

Hot dip difficulties. In principle, hot dip treatment is neither complicated nor difficult. In fact, it is not easy to reach this process index. The research shows that there are many specific chemical structure formulas of nickel sulfide in the glass, such as Ni7S6, NiS, NiS1.01, etc., not only the proportion of various components is different, but also other elements may be doped. The speed of its phase transition is highly dependent on the temperature. The research shows that the phase transformation rate at 280 ℃ is 100 times that at 250 ℃, so it is necessary to ensure that all glass in the furnace experience the same temperature regime. Otherwise, on the one hand, due to insufficient heat preservation time for glass with low temperature, nickel sulfide cannot completely transform, which weakens the effect of hot dip. On the other hand, when the glass temperature is too high, it will even cause the reverse phase transformation of nickel sulfide, causing greater hidden danger. Both of these situations will lead to ineffective or even counterproductive hot dip treatment. The uniformity of temperature during the operation of hot dip furnaces is so important, and the temperature difference in most domestic hot dip furnaces even reaches 60 ℃ during hot dip insulation. It is not uncommon for imported furnaces to have a temperature difference of about 30 ℃. Therefore, although some tempered glass has been heat soaked, the self explosion rate is still high.

In fact, the hot dip process and equipment have also been constantly improving. The insulation time specified in the German standard DIN18516 in the 1990 edition is 8 hours, while the prEN14179-1:2001 (E) standard reduces the insulation time to 2 hours. Under the new standard, the effect of hot dip process is very significant, and there are clear statistical technical indicators: after hot dip, it can be reduced to one case of spontaneous explosion per 400 tons of glass. On the other hand, the design and structure of the hot-dip furnace are constantly improved, and the heating uniformity has also been significantly improved, which can basically meet the requirements of the hot-dip process. For example, the self explosion rate of the hot dipped glass of CSG has reached the technical indicators of the new European standards, and has performed extremely satisfactorily in the 120000 square meter Guangzhou New Airport Mega project.

Although the hot dip treatment can not guarantee that there will be no spontaneous explosion, it does reduce the occurrence of spontaneous explosion and actually solves the problem of spontaneous explosion that puzzles all parties in the project. Therefore, hot dip is the most effective way to completely solve the problem of self explosion, which is unanimously recognized in the world.

Precautions Packaging

Product application Container Or packed in wooden cases. Each piece of glass shall be packed with plastic bags or paper, and the space between the glass and the packing box shall be filled with light and soft materials that are not easy to cause appearance defects such as glass scratches. The specific requirements shall comply with relevant national standards.

Packing mark

The packing mark shall comply with the provisions of relevant national standards, and each packing box shall be marked with words such as "upward, light handling and upright, careful breaking, glass thickness, grade, factory name or trademark".

transport

All types of transport vehicles and handling rules used for products shall comply with relevant national regulations.

During transportation, the wooden case shall not be placed horizontally or obliquely, and the length direction shall be the same as the moving direction of the transport vehicle. Rain proof measures shall be taken.

keep in storage

The product should be stored vertically in a dry room.