How did the increasingly popular hot bending glass come into being?

Hot bending glass is made by heating the flat glass to the softening temperature for the second time in a hot-bending furnace, deforming it under its own gravity or bending it with a mechanical structure, and molding it according to the shape of a pre-made abrasive tool. The formed bent glass is slowly cooled to reduce the existence of residual stress and avoid thermal cracking.

With the progress of industrial level and the improvement of people's living standards, hot-bent glass is used more and more in buildings and household occasions. Building hot bending glass is mainly used for interior and exterior decoration of buildings, lighting roofs, sightseeing elevators, arched corridors, etc., and is generally compounded into laminated glass. Household hot bending glass is mainly used as glass furniture, glass aquarium, glass absorption basin, glass counter, glass decoration and so on. Hot-bent glass also has a good application in the field of automobile glass. Hot-bent laminated glass is widely used as the front windshield of various vehicles, and a reasonable laminated glass structure can protect the driver to the greatest extent in car accidents.

1.Characteristics of hot bending glass
Hot bending glass is a curved glass made of flat glass which is heated and softened, molded in a mold and then annealed. Hot bending glass is generally processed in an electric furnace.
A continuous hot bending furnace generally has 5-6 chambers and 11-13 stations, and a finished product can be produced in about tens of minutes.
Generally, the intermittent hot bending furnace has only one chamber, and the heating, molding and annealing are all completed in one chamber, and the processing cycle takes several hours to one or twenty hours, which is suitable for making small quantities of extra-large hot bending glass.
Aesthetics: there is no connection port in the middle of the curved surface shape, and the lines are beautiful, achieving the overall harmonious artistic conception.
Specificity: various irregular curved surfaces can be made according to requirements.
Hot-bent glass is a curved glass made of high-quality glass by heating, bending, softening, molding in a mold and annealing in order to meet the high-quality requirements of modern architecture.
Beautiful style and smooth lines. It breaks through the singleness of flat glass and is more flexible and diverse in use.
Suitable for fish tanks, dining tables, balconies, mobile phone counters, cosmetics counters, hot-bending TV cabinets, doors, windows, ceilings, curtain walls and other special requirements of different shapes. Can produce hollow, sandwich and other composite hot bending glass products, can be customized according to customer requirements.
2.Technical requirement
Hot bending glass can be classified into three categories: single bending, bending and compound bending.
For a single curved building glass, glass hot bending is relatively easy. However, many manufacturers often fail to fit the mold well at the curved edge of the product, which is about 150mm away from the straight edge, and some of them exceed the standard requirements, which makes the installation difficult. To solve this problem, first of all, it is required that the electric heating arrangement of the hot bending furnace should be reasonable, local heating can be realized, and the placement direction of the products should be consistent with the direction of the electric heating wire.
Aquarium glass and counter glass are common in bending hot bending glass. The biggest technical difficulty in bending glass is that the straight edge is bent and the corner is prone to die marks. Therefore, bending glass is also very common, such as spherical glass, curved arched profile, glass hand basin, etc. This kind of glass requires a high technical level in hot bending operation, making accurate molds, and some need professional hot bending furnaces to complete it.

Characteristics: Hot bending glass is to heat the glass to near the softening point, and under the action of gravity or external force, the glass will become a specific non-planar shape in a specific mold to meet the requirements of curtain wall and interior decoration in non-planar parts of buildings.

3.The difference between bent steel glass and hot bent glass
Bending tempered glass is made by rapid air cooling with special equipment after bending forming; Hot bending glass does not belong to safety glass, but bent steel glass belongs to safety glass.
(1) Hot bending glass because it is a mold processing, in principle, as long as the mold is made, it can be hot bending glass.
(2)The minimum radius of bent steel is 500mm, the maximum arc length is 3000mm and the maximum height is 3000mm. But usually the minimum radius of the manufacturer is not less than 1500mm.
4.Hot bending process
Generally speaking, hot bending refers to the process of heating and pressurizing a 2D glass cover plate into a 3D curved glass cover plate by a hot bending machine. There are three kinds of molding methods. The first is self-weight molding, which has a slightly higher temperature and a slightly longer time, but the cost is low; The second way is mechanical pressurization, that is, the use of molds (usually graphite, heat-resistant steel with spray release agent, etc.); The third way is negative pressure molding, where a vacuum pump continuously sucks air under the sample to generate negative pressure. The whole hot bending process is to put the glass with finely carved shapes and holes into a graphite mold, then put the mold into a hot bending machine, and after preheating, pressing and cooling, the glass is formed into curved glass in the mold. The size of curved glass depends on the design of graphite mold. The appearance after molding depends on the molding process and graphite mold design.
The performance of the hot bending machine has a vital influence on the molding. The most important thing is that the temperature in the furnace body should be uniform during the molding process, and the glass can be heated evenly to avoid stress embrittlement. In order to make the glass heated as evenly as possible in the hot bending process, generally speaking, the station of the precision hot bending machine is more than 10, which mainly includes preheating, hot pressing and cooling. At present, many domestic equipment suppliers have achieved 30 stations, and the yield, efficiency and energy consumption have reached the advanced level in the industry.

5.Classification of glass hot bending furnaces
The glass hot bending furnace can be divided into four fuel types: coal-fired, oil-fired, gas-fired and electric heating. Coal-fired glass bending furnace is rare now because of its difficult temperature control, complex structure and easy pollution on the surface of glass products. Oil-fired and gas-fired glass bending furnaces, if assisted by electric heating, are lower in energy consumption index than electric heating furnaces, but they are rarely used because of their complicated structures. Electrothermal glass bending furnace is widely used because of its simple structure, convenient temperature control, easy operation and no pollution to glass products.
Glass hot bending furnace can be divided into multi-chamber circulating furnace, two-chamber reciprocating furnace and single-chamber furnace in structure. Single-chamber hot bending furnace is used for hot bending of large-size glass, which is mainly used in the manufacture of large building glass and front windshield of large passenger cars. The production efficiency is low, but it is used to produce hot bending glass with complicated specifications and complex shapes, and the effect is satisfactory. Compared with single-chamber hot bending furnace, two-chamber reciprocating hot bending furnace can give full play to the efficiency of heating furnace and has higher production efficiency. Multi-chamber circulating hot bending furnace is mostly used for mass production of automobile windshields with simple shape and small specifications.

1) Multi-chamber circulating glass hot bending furnace
The multi-chamber circulating glass hot bending furnace generally circulates up and down in structure. The upper part of the hot bending furnace is a preheating zone and a hot bending zone, and the lower part of the hot bending furnace is a cooling annealing zone. The hot bending chamber consists of a group of independent kiln cars, and each kiln car has a molding grinding tool. Glass is loaded from the product discharge area, rises to the upper layer of the hot bending furnace, and pushes in the kiln car. In the preheating area, the glass is preheated to 400 ~ 450℃ and enters the hot bending area. At about 600℃, the glass begins to be hot bent, and then enters the cooling annealing area. At about 400℃, the kiln car descends to the lower layer for annealing, and the glass is annealed at about 70℃. The forming abrasives in each kiln car are independent, so the error of the shape requirements of the abrasives in each room is very small when mass producing the same kind of hot bending glass. In a cycle, the grinding tools of each kiln car should be similar in shape, and the glass with too different shapes cannot be produced in the same cycle. The circulating hot bending furnace has the advantages of small floor space, low energy consumption and large output, and is suitable for mass production of products, such as automobile windshield. However, the one-time investment is large and requires large electric power. At present, the maximum size of bendable glass in domestic circulating glass hot bending furnace is 1.8x2.5m.
2)Reciprocating glass hot bending furnace
There are two kinds of reciprocating glass hot bending furnaces: 5 stations and 3 stations. The 5-station furnace has 2 loading and unloading areas, 2 preheating areas, 1 hot bending area and 2 kiln workers. The glass is preheated to about 400℃ in the preheating zone and enters the hot bending furnace. After hot bending, it returns to the preheating zone for cooling, and another car enters the hot bending zone again, and so on. The 3-station furnace has two preheating zones, which are also two kiln cars. In the hot bending zone, the glass is directly raised from room temperature to the hot bending temperature according to the temperature system, and then returned to the loading and unloading zone when it is cooled to 250 ~ 300℃ after hot bending. Reciprocating hot bending furnace can adapt to different glass products without continuous temperature control, but the sealing degree is not as good as that of single-chamber furnace, and the structure is more complicated than that of single-chamber furnace. At present, the largest reciprocating hot bending furnace in China is 3mx6m.
The advantage of the reciprocating glass hot bending furnace is that it can process various products with different specifications in two rooms, and it does not require a continuous process system. Each furnace formulates corresponding process parameters according to different products. Reciprocating glass hot bending furnace is simple to manufacture, and its production efficiency is satisfactory compared with single-chamber glass hot bending furnace.

3)Single-chamber glass hot bending furnace
There are two common types of single-chamber hot bending furnace: drawer type and lifting type. This kind of hot bending furnace is also the most widely used in China at present. Because of the small batch of building glass and various specifications, the single-chamber hot bending furnace is the most economical and convenient. The single-chamber hot bending furnace has only one station, and the glass is heated, hot bent and annealed at this station. The advantage of single-chamber hot bending furnace is that it is suitable for various products with different specifications, and it does not require a continuous process system. Each furnace formulates corresponding process parameters according to different products. The single-chamber glass hot bending furnace is simple to manufacture, easy to handle in structure, good in sealing and low in relative energy consumption. The disadvantages are low efficiency and long hot bending period. The structure of drawer-type single-chamber furnace is like a drawer, but at present, most kiln cars of single-chamber hot bending furnace have been interpreted as only the bottom and front face, with both sides and inner ends sealed by the kiln body and observation windows open on the kiln body. The kiln car is actually a flat car with only the front face, which provides great convenience for the loading and unloading of glass products. Therefore, the bendable glass specification of single-chamber hot bending furnace is also the largest among all hot bending furnaces. At present, the domestic largest drawer-type single-chamber furnace flexible glass specification is 12x3m. The periphery and upper part of the lifting single-chamber hot bending furnace body are completely sealed, and the bottom of the furnace has a certain space height, and glass enters from the bottom of the furnace. The bottom can be raised and lowered, and the hot bending grinding tool is sent to the hot bending platform by the outer connecting track and rises to the hot bending position. The biggest advantage of the hot bending furnace is that it uses space and saves land, and the biggest disadvantage is that it is difficult to assemble and disassemble glass and products, especially large plate glass. At present, the largest specification of this type of hot bending furnace in China is 4x3m.
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