What Is Plaster Veneer?

Gypsum is a monoclinic mineral and is a hydrate whose main chemical component is calcium sulfate (CaSO4). Gypsum is a widely used industrial and building material. Can be used for cement retarder, gypsum building products, model making, medical food additives, sulfuric acid production, paper filler, paint filler, etc.

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The microporous structure and heat dehydration of gypsum and its products make it excellent in sound insulation, heat insulation and fire resistance.

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Chinese name: plaster
Foreign name: Gypsum
nickname: Plaster
Category: Hydrated sulfate
Chemical formula: CaSO4 · 2H2O
Molecular weight: 172
colour: White, colorless, yellow-red with impurities
Guang Ze: Glass, silk or pearl
transparency: Transparent to translucent

Streak: White
Crystal system: Monoclinic
Cleavage: Extremely complete
Fracture: Scalloped, sometimes fibrous
Hardness: 2
Brittleness: Bendable
Crystal inertia: Plate, fibrous, lumpy or fine
Mineral density: 2.31 2.33
Application: Construction, medical, etc.
Distribution: widely distributed

Gypsum classification

Generally called gypsum can refer to two kinds of minerals, raw gypsum and anhydrite. The raw gypsum is calcium sulfate dihydrate (Ca [SO4] · 2H2O), also known as dihydrate gypsum, hydrogypsum or soft gypsum, theoretical composition CaO32.6%, SO346.5%, H2O + 20.9%, monoclinic system, crystal It is plate-like, usually dense or fibrous, white or gray, red, brown, glass or silk luster, Mohs hardness is 2, cleavage parallel {010} complete, density is 2.3g / cm3; anhydrite is Anhydrous calcium sulfate (Ca [SO4]), theoretical composition CaO41.2%, SO358.8%, orthorhombic system, crystals are plate-like, usually dense or granular, white, off-white, glass gloss, Mohs The hardness is 3 to 3.5, the cleavage parallel is {010} complete, and the density is 2.8 to 3.0 g / cm3. Two types of gypsum are often produced together and can be transformed into each other under certain geological effects.

Basic properties of gypsum

Natural dihydrate gypsum (CaSO4 · 2H2O) is also called raw gypsum. After calcining and grinding, -type hemihydrate gypsum (2CaSO4 · H2O) can be obtained. If the calcination temperature is 190 ° C, model gypsum can be obtained, and its fineness and whiteness are higher than that of building gypsum. If the raw gypsum is calcined at 400-500 ° C or higher than 800 ° C, the floor gypsum is obtained. Its setting and hardening are slower, but the strength, abrasion resistance and water resistance after hardening are better than ordinary building gypsum.

Usually white, colorless, colorless and transparent crystals are called trans-gypsum, sometimes gray, light yellow, light brown and other colors due to impurities. Streak white. Transparent. Glass luster, cleavage pearl luster, fibrous aggregate silk luster. The cleavage is extremely complete, and the cleavage pieces are split into rhombuses with angles of 66 and 114. Sexually brittle. The hardness is 1.5 ~ 2. Slight changes in different directions. The relative density is 2.3. Under the polarizer: colorless. Biaxial crystal (+). 2V = 58. Ng = 1.530, Nm = 1.523, Np = 1.521. 2V decreases with increasing temperature, and 2V is zero at about 90 ° C.
There are three stages of crystal water discharge during heating: 105 ~ 180 ° C, one water molecule is discharged first, and then half of the water molecules are discharged immediately, which is converted into calcined gypsum Ca [SO4] · 0.5H2O, also known as cooked gypsum or hemihydrate gypsum . 200 ~ 220 , the remaining half of the water molecules are discharged and transformed into type III anhydrite Ca [SO4] · H2O (0.06 < <0.11). At about 350 ° C, it turned into type II gypsum Ca [SO4]. At 1120 ° C it was further transformed into Type I anhydrite. The melting temperature is 1450 ° C.

Chemical composition of gypsum

^[1] Theoretical composition (wB%): CaO 32.5, SO3 46.6, H2O + 20.9. The composition does not change much. There are often mechanical mixtures such as clay and organic matter. Sometimes contains SiO2, Al2O3, Fe2O3, MgO, Na2O, CO2, Cl and other impurities.

Gypsum structure

Monoclinic system, a0 = 0.568nm, b0 = 1.518nm, c0 = 0.629nm, = 11823 '; Z = 4. The crystal structure consists of [SO4] 2-tetrahedron and Ca2 + connected to form a (010) double layer, and the double layers are connected by H2O molecules. Its complete cleavage occurs in this direction. The coordination number of Ca2 + is 8, which is linked to 6 O2- and 2 H2O molecules in the adjacent 4 [SO4] tetrahedra. H2O molecules are linked to O2- in [SO4] by hydrogen bonds, and water molecules are linked by molecular bonds.
Orthorhombic prisms, C2h-2 / m (L2PC). The crystal often develops into a plate shape, and it is also granular. Often simple shapes: parallel double-sided b, p, oblique square m, l, etc .; crystal plane and often with vertical stripes; sometimes lentils. Twin crystals are common, one is a Gary twin crystal with a double crystal plane (100) or a dovetail twin crystal, and the other is a Paris twin crystal with an (101) double crystal plane or an arrow twin crystal. The aggregates are mostly dense granular or fibrous. Fine-grained blocks are called alabaster; fibrous aggregates are called fibrous gypsum. Rare rose-like aggregates formed from lenticular crystals are rare. There are also soil-like, sheet-like aggregates.

Status of gypsum resources

Natural gypsum is the gypsum stone contained in nature, mainly dihydrate gypsum and anhydrite. China has rich reserves of gypsum mineral resources. The total proven reserves of various types of gypsum is about 57 billion tons, ranking first in the world. It is distributed in 23 provinces, municipalities and autonomous regions, of which 10 have reserves of more than 1 billion tons. : Shandong, Inner Mongolia, Qinghai, Hunan, Hubei, Ningxia, Tibet, Anhui, Jiangsu, and Sichuan. The poorer gypsum resources are in the Northeast and East China.
China's gypsum resources are mainly ordinary gypsum and anhydrite. Among them, anhydrite accounts for more than 60% of the total. As a premium and first-grade gypsum, it only accounts for 8% of the total, and fiber plaster only accounts for 1.8% of the total. . Therefore, while we are a country with large gypsum reserves, we are also poor countries with high-quality gypsum reserves. The high-quality gypsum resources are mainly distributed in Yingcheng and Jingmen, Hengshan, Hunan, Sanshui, Guangdong, Zaozhuang, Shandong, and Pinglu, Shanxi. Some of the mines have been over-exploited and nearly depleted, and some are caused by mixing with low-grade gypsum and difficult to separate, resulting in high-quality resources waste. Therefore, the proportion of high-quality gypsum resources that China can actually mine and effectively utilize is even smaller.
Although China's gypsum industry started late and has a poor foundation, it has developed rapidly. In 1995, the gypsum output soared to 26.59 million tons, surpassing the United States, and becoming the world's largest gypsum consumer. By 2004, the annual production of gypsum raw ore in the country was more than 30 million tons, and the total gypsum consumption was about 35 million tons. China currently has more than 500 gypsum mining mines, with about 50 large and medium-sized mines with an annual output of more than 100,000 tons. Its output accounts for 40% of the total output, and township small mines account for about 60% of the total output. According to production methods, open-pit mining accounts for about 30%, and underground mining accounts for about 70%. In underground gypsum mines, the average recovery rate is lower than 30% due to various reasons, and the high-quality resources that have been preferentially mined have not been reasonably developed and effectively used, and the waste of resources is serious and distressing!
The most widely used natural gypsum is dihydrate gypsum. Its active ingredient is calcium sulfate dihydrate. Generally, gypsum is classified according to the content of calcium sulfate dihydrate in the ore. Gypsum has a wide application field and many product types. Different applications have different requirements for the quality of gypsum raw materials. High-grade gypsum is mostly used as a raw material for the production of special gypsum products, such as food, medical, art, models, and chemicals. Fillers, etc .; gypsum ore with calcium sulfate dihydrate content of less than 60% is rarely used; gypsum ore higher than 60% is used in various fields such as building materials and construction according to its content.
The consumption structure of gypsum in different countries in the world is different. The consumption of gypsum deep-processed products in developed countries accounts for a large proportion. The gypsum consumption structure is: 45% of manufactured products, 45% of cement production, and 10% of other fields. Developing countries are more focused on the primary application of ore and rely on the cement industry. The proportion of gypsum products has gradually increased with economic development. China's consumption structure is roughly: 84% is used as a retarder for cement production, 6.5% is used for ceramic molds, 4.0% is used for gypsum products, wall materials, 5.5% is used for chemical and other industries; with China's cement output With the continuous increase in demand, the demand for gypsum will increase accordingly. At the same time, with the rapid growth of China's economy, there will be a great development space for the gypsum industry, especially gypsum products. The development of gypsum will inevitably increase. With the development of traditional ceramics and other special industries, high-quality gypsum resources continue to decrease, and the development and utilization of gypsum resources will be paid more and more attention. Therefore, in order to ensure the sustainable development of the overall gypsum industry, green, environmentally friendly and healthy gypsum building materials and products are more widely used in people's lives, and it is necessary to optimize the use of limited gypsum resources.

Main origin of gypsum

The world's largest producer of gypsum is the United States. In the United States, gypsum deposits are distributed in 22 states, with a total of 69 mines. The largest origin is in Fort Dodge, Iowa; followed by Canada; France leads in gypsum production in Europe; ^[2] again Germany, Britain, and Spain. China has rich gypsum resources. There are gypsum mines in 23 provinces (regions) of the country. There are 169 mining areas with proven reserves, with a total reserve of 57.6 billion tons of ore. In terms of regional distribution, Shandong has the most gypsum deposits, accounting for 65% of the country's reserves; Inner Mongolia, Qinghai, and Hunan are the second. The main gypsum mining areas are Dige Town, Zaozhuang, Shandong, Etuoke Banner, Inner Mongolia, Yingcheng, Hubei, Hunjiang, Jilin, Nanjing, Jiangsu, Dawenkou, Shandong, Qinzhou, Taiyuan, and Ningxia Zhongwei Gypsum.

Gypsum mineralization type

Gypsum deposits are mainly sedimentary deposits, with reserves accounting for more than 90% of the country's total. Metagenetic and hydrothermal metasomatic gypsum deposits are not very important. Gypsum deposits were produced in various geological times, with the Early Cretaceous and Tertiary sedimentary gypsum deposits being the most important.
It is mainly the product of chemical deposition. It often forms huge ore layers or lens bodies. It is found in limestone, red shale and sandstone, marl and clay rock series, and often coexists with anhydrite and stone salt. The anhydrite layer is converted to gypsum under the influence of surface water due to the reduction of external pressure at the near-surface area: CaSO4 + 2H2OCaSO4 · 2H2O; at the same time, the volume increases by about 30%, causing the gypsum layer to be destroyed.

Identifying characteristics of gypsum

Low hardness, a set of extremely complete cleavage, and various features can be identified. Dense lumpy gypsum can be distinguished from carbonates because of its low hardness and non-foaming when acidic.

One of the standard minerals in hardness classification.

Plaster medical application

Pharmacological action of plaster

1. ^[3] Antipyretic effect Gypsum has no cooling effect on normal body temperature, but has certain antipyretic effect on artificial fever animals, and has obvious antipyretic effect on rabbits with artificial fever, and its antipyretic effect may be related to its main component calcium. Nothing to do. Gypsum gypsum decoction 15g / kg has no antipyretic effect on rabbits with fever caused by injection of typhoid pentade vaccine; if rabbits are stomached with gypsum gypsum decoction 15g / kg, and then injected with typhoid five Significantly increased. Gypsum has a rapid but short-lasting antipyretic effect. The cooling effect of 5g / kg raw gypsum on fever-induced rabbits caused by typhoid vaccine is similar to that of 0.2g / kg antipyrine, with a significant drop in body temperature half an hour after taking the drug. The effect is strongest at 1 to 1.5 hours.

Both Baihu decoction and monogypsum gypsum decoction have certain antipyretic effect on experimental pyrogenic rabbits; gypsum-free licorice mixture and decalcified Baihu decoction have no obvious antipyretic effect, and gypsum can be considered as a white tiger The main antipyretic effect of decoction, gypsum effect can be enhanced by other drugs in the prescription, but it does not increase with the increase in the amount of gypsum. Measurements of blood calcium levels in experimental animals before and after administration showed that the elevated blood calcium levels were closely related to the antipyretic effect. It has been reported that the antipyretic effect of gypsum combined with Zhimu is stronger than that used alone. The antipyretic component of Zhimu is mangiferin, and pure calcium sulfate is not effective. Therefore, it is speculated that the antipyretic effect of gypsum is other than calcium sulfate. To. The experiment showed that the re-use of Ma Xing Shi Gan Decoction and Gypsum (re-use after decoction) was stronger than that of Ging Xing Shi Gan Decoction.

It has also been reported that the fever of rabbits caused by typhoid vaccine given by the supernatant of gypsum 1: 1 decoction and the supernatant plus gypsum powder did not show significant antipyretic effect. Experiments with useful experimental febrile rats abroad have shown that: no obvious antipyretic effect was found in gypsum gavage, subcutaneous injection or intravenous injection, but when drinking water is prohibited, fever caused by endotoxin, diuretics, feeding salt and When radiant heat and other methods cause animals to be "thirsty", gypsum can reduce the amount of water that rats drink, which can reduce their "thirsty" state.

2. ^[4] Effect on the cardiovascular system The gypsum infusion has no effect on the frog's in-situ heart. A small dose of gypsum infusion has an excitatory effect on isolated toad hearts and rabbit hearts, while a large dose has an inhibitory effect. The heart can return to normal. Intravenous injection of 0.1% / kg of 4% gypsum supernatant has no effect on the respiration, blood pressure, and blood flow of rabbits and cats. When injected above 1ml / kg, it exhibits respiratory depression, decreased blood pressure, decreased blood flow, and decreased heart rate. slow. Intravenous injection of gypsum solution 0.2ml / kg can reduce the blood flow of the femoral arteries of rabbits and cats temporarily, and then increase the blood flow of the coronary arteries.

3. Effect on smooth muscle A small dose of gypsum supernatant increases the amplitude of isolated small intestine and uterus in rabbits, while a large dose reduces tension and amplitude. Gypsum can also increase urinary excretion in mice, slow the small bowel advancing function, and increase bile excretion in rats and cats.

4. Other effects Gypsum is taken orally by gastric acid, part of which becomes soluble calcium salt, absorbed into the bloodstream of the intestine can increase the concentration of calcium in the serum, can inhibit the ability of nerve stress (including the temperature regulation function of the central nervous system), and reduce skeletal muscle. Excitability, relieve muscle spasms, and reduce vascular permeability.

In in vitro culture experiments, 1: 1 gypsum Hanks solution can significantly enhance the ability of rabbit alveolar macrophages to phagocytose Staphylococcus aureus and colloidal gold, and promote maturation of phagocytes. Ca ++ can increase the capture rate of alveolar macrophages, enhance their phagocytic activity and accelerate their clearance of dust particles, which is of great significance in maintaining the physiological functions of macrophages. Therefore, it can be considered that Ca ++ plays an important role in the above functions of gypsum.

Long-term feeding of gypsum can increase the calcium content of pituitary, adrenal, submandibular, pancreas and thymus in rats. In rats with thyroid and parathyroid glands removed, the thymus calcium content increased and the spleen content decreased.

In the presence of ATP in the body, gypsum, through the action of enzymes and APG, produces a sulfur isotope fractionation, which increases the plasma concentration of 34S and thus plays an antiviral role.

Gypsum is cool, with clearing heat and detoxifying

Contraindications to plaster

1. Deficiency of spleen and stomach, blood deficiency and yin deficiency fever should not be taken.
2. "Notes on Compendium of Materia Medica": "The chickens make it. Mangcao and Mamu poisoning."
3. "Medicine Theory": "Evil Croton, Iron Fear."
4. If the dosage is too large, fatigue, weakness, and poor appetite will appear after taking the medicine.
5. Gypsum is a product of great cold, which easily hurts yang.
6, plaster should not be used with the following Western medicine:
Tetracycline antibiotics, gypsum will reduce the solubility and absorption rate of antibiotics in this family.
Should not be taken with isoniazid, it will reduce its efficacy.
It should not be taken with prednisone to reduce its bioavailability.

Gypsum drug compatibility

1, with mulberry leaves, Qingxuan lung fever;
2, with Guizhi, double solution on the surface;
3, with Bai Zhi, clearing heat and purging fire, swelling and pain;
4, with Zhimu, clearing away heat and annoyance;
5, with pinellia, lung and stomach Shuangqing, Jiangni Huatan;
6, with licorice, Qingfei cough;
7, with bamboo leaves, remove heat and trouble.

Plaster traditional chinese medicine prescription

1. White Tiger Soup: Treatise on Febrile Diseases: Yangming Qifen's Heat;
2. Bamboo Leaf Gypsum Soup "On Typhoid Fever": After the typhoid has resolved, the residual heat is unclear;
3. "Ma Xing Shi Gan Decoction" on typhoid fever: exogenous wind evil, lung heat cough and asthma.
4. Shuang Yu San's "Su Wen Ji Bao Bao Ji Ji": phlegm is hot and wheezing, and sputum is like a spring.
5, Yu Lu San "pediatric medicine card straight tactics": Pediatric injury heat vomiting and diarrhea Huang Shou.
6. Gypsum powder "Pujifang": Those who are coughing hot.

7. Gypsum Antihypertensive Pillow According to Li Shizhen's "Compendium of Materia Medica", Volume 9 of the Ming Dynasty, "Gypsum is also known as fine stone, also known as" cold water stone ". It treats cold and heat in strokes, has sweating muscles, removes dry mouth and burns, and has headaches Pain and other functions are good medicines for dispel fever and relieve heat. According to the theory of traditional Chinese medicine and folk use, hypertension is a fever, gypsum-like cold, a gypsum antihypertensive pillow made of gypsum, and naturally regulates the brain and nerves with cold heat With the normal temperature of the human brain, the cerebral blood vessels can work normally, which can effectively control the increase in blood pressure. People in China have long used natural plaster to make pillows. Tang Feng Xue Fengyou's poem "Plaster Pillow" Colder than Chun Xuebai and Yu Yao. I was sent to the cold bed, I was afraid that the wind would be hot. "Gypsum pillow is a kind of specific health-care and medicinal effects such as antihypertensive spine protection, analgesia and analgesia, and so on. Pillows. ^[5]

Clinical application of gypsum

1, for fever, lung and stomach fever, high fever does not retreat, thirst, irritability, pulse flooding and other symptoms. Gypsum has a medicinal cold and is good at clearing qi and real heat, so it is suitable for the symptoms of real lung and stomach heat. It must be used with the mother-in-law to enhance the effect of clearing heat.
2. For fever and fever, and spot rash. Onset of mild disease, mostly caused by stomach fire and blood heat, this is a phenomenon of qi and blood. In clinical encountering this kind of symptoms, gypsum with strong heat-clearing and purging fire is commonly used, and medicines such as Xuanshen, Danpi, Chiba, Xianshengdi, Banlangen are used in conjunction with cooling blood and detoxification.
3. For headaches, toothaches, and swollen gums caused by hyperactivity of stomach fire. Gypsum can clear stomach fire, so the disease caused by hypergastric stomach fire can be used in conjunction with Zhimu, Achyranthes bidentata and raw land.
4, for lung heat cough, asthma. Fever heat hits the lungs, and the body has high fever, cough, shortness of breath, irritability, and thirst. You can use gypsum to relieve lung heat, and add ephedra and almonds to relieve lungs, relieve cough and asthma (ie Ma Xing Shi Gan Tang). ).
5, used for eczema water and fire burns, sores do not converge after ulceration and wounds do not close for a long time. Gypsum is used externally for the treatment of the above-mentioned surgical diseases, and has the effects of clearing heat, astringent, and muscle growth. Changhe Shengdan, Huangbai, Qingdai are equally used.

Common formulas for gypsum

1. For Sanyang combined disease, the belly is full and it is difficult to turn to the side. Insults, scum, slang, enuresis, sweating, slang, forehead, sweat, hands, feet, and cold. If you sweat from the sweat: Zhimu Liuliang. One pound (broken) licorice. (Sunburned) Two or two japonica rice. Simmer the four flavors with water-liter cooked rice noodle soup. One warm day and three warm days. ("Treatise on Febrile Diseases" Baihu Tang)
2. In the treatment of temperature disease, the pulse and floating body are strong and the body is hot, and when the cold is started, the person who is not cold and has a fever in his heart: raw gypsum two or two (rolled fine) raw japonica two or two halves. Fry three large bowls of water on the second flavor until the rice is cooked. You can get two large bowls of clear juice to drink as much as possible to make the whole body sweat. If Yangming is hot, it is not necessary to drink it slowly and warmly to dispel its heat. (Gypsum Japonica Soup of "Zhong Zhong Shen Xi Lu")
3, treatment of children's folder, cold headache, strong hot saliva, horror, crying, upset, and qi dysentery: gypsum, cold water stone each one or two brain musk. The upper part is adjusted for the last light heart soup. Size plus or minus. ("Puji Fang" Hongtao San)
4, cure typhoid fever saliva tide on the Jue Fu Liuyang headache dizziness can not bear: gypsum (calcined fine) per serving of light green tea withered for two dollars. Pediatric volume plus and minus it. ("Yin San Fang" Yu Yu San)
5. Treatment of fever, thirst, headache, yang, dysentery, headache, dizziness, yellow fever, hot sputum, and wheezing, etc .: gypsum sixty two (raw) powdery licorice one or two. The upper part is adjusted down for one or two or three dollars of freshly drawn water, or hot soup, or ginseng soup. It is also wonderful to add cinnabar to this money. ("Book of Jingyue" Yuquan San)
6. For treating Taiyin temperature disease, you should not sweat or sweat, but you will not get sweaty. If you sweat too much, you will be stunned. If you have slang, you will have gypsum: one or two mother-in-law, four money, licorice, three money, black ginseng, three money, rhino horn, two money, white rice. He. Eight cups of water, three cups of slag, three cups of slag, and one minute of night-serving. ("Distinguishing Warm Strips" Huaban Decoction)

Gypsum food industry applications

According to the hygienic standards for the use of food additives in China, gypsum is used as a coagulant in the production of canned and soy products, and the amount is added according to the needs of normal production. It is used to make tofu. Soymilk is added in an amount of 2 ~ 14g / L. An excessive amount will produce a bitter taste, that is, gypsum for summer is about 2.25% of raw materials, and winter is about 4.1% of raw materials. When used to make dry tofu, the amount of gypsum used in the summer is about 2% of the raw material, and in winter it is about 4.3% of the raw material. In the production of canned tomatoes and potatoes, calcium sulfate can be used as a tissue fortifier, which is added by 0.1% to 0.3% according to the production formula.

According to the provisions of FAO / WHO1984, canned tomatoes are used as coagulants in the amount of: 0.8g / kg for tablets, 0.45g / kg for whole packages (single or combined with other coagulants) ^[6] .

Gypsum industry applications

Gypsum is a monoclinic system with a high degree of cleavage and easily cracks into thin slices. Hemihydrate gypsum can be obtained by heating gypsum to 100-200 ° C and losing part of the crystal water. It is a kind of air-hardening gelling material. It has two forms of and , both of which are rhombic crystals, but have different physical properties. Alpha hemihydrate gypsum has good and solid crystals; beta hemihydrate gypsum is a flake-shaped and cracked crystal with very fine crystals and a specific surface area much larger than that of alpha hemihydrate gypsum.

When producing gypsum products, alpha-type hemihydrate gypsum requires less water than beta-type, and the product has a higher density and strength. Usually used in autoclave in saturated steam medium is -type hemihydrate gypsum, also known as high-strength gypsum; -type hemihydrate gypsum is calcined by wok or rotary kiln open device, that is, building plaster. Industrial gypsum chemical gypsum has the same properties as natural gypsum and does not require excessive processing. The slurry mixed with hemihydrate gypsum and water re-formed into dihydrate gypsum, which quickly coagulated and hardened during the drying process to obtain strength, but softened in contact with water.
Gypsum is the main raw material for the production of gypsum gelling materials and gypsum building products, and is also a retarder for portland cement. After calcining the gypsum at 600 800 ° C, adding a small amount of lime and other catalysts together to grind it can obtain an anhydrite cement (also known as King's cement); calcining and grinding at 900 1000 ° C can obtain high-temperature calcined gypsum . Products made from these two types of gypsum have higher strength than building gypsum products, and anhydrite cement has better heat insulation, and high-temperature calcined gypsum has better wear resistance and water resistance.

Drywall

The main building products produced using building gypsum are:
Paper plasterboard. After adding a small amount of adhesive, fiber, foaming agent, etc. to the building gypsum, it is continuously poured between two layers of facial paper after mixing with water, and then rolled, solidified, cut and dried. The thickness of the plate is 9 ~ 25mm, and the dry bulk density is 750 ~ 850kg / m3. The plate has good toughness, non-combustible, stable size, flat surface, and can be sawed for easy construction. It is mainly used for internal partition walls, interior wall veneers, ceilings, sound-absorbing panels, etc., but it has poor water resistance and should not be used in humid environments.
Fiber plaster board. The building gypsum slurry mixed with fibers and other admixtures is formed by winding, filtering or rolling, and then cut, solidified and dried. The thickness is generally 8-12 mm. Compared with paper-faced gypsum board, its bending strength is higher. It does not require cover paper and adhesive, but has a larger bulk density and has the same application as paper-faced gypsum board.
Decorative plasterboard. The prepared building gypsum slurry is poured into a mold frame with a pattern on the bottom mold, and is made by smoothing, solidifying, demolding, and drying, and the thickness of the plate is about 10 mm. In order to improve its sound absorption effect, it can also be made of perforated and blind hole boards, which are often used as ceilings and decorative walls.
Gypsum hollow slabs and blocks. The building gypsum slurry is poured into a mold, and is formed by demolding and drying after vibration molding and solidification. The thickness of the hollow slat is generally 60-100 mm, and the porosity is 30-40%. The size of the block is generally 600 × 600 mm, and the thickness is 60-100 mm. Blocks. Hollow slabs and blocks are built with special gypsum for easy construction and are often used as non-load-bearing internal partition walls.

Production of gypsum

Gypsum ore

Data from the USGS "Mineral Yearbook" states that natural gypsum mined and consumed worldwide in 2004 reached 106 million tons. The United States has the largest mining volume, reaching 18 million tons, accounting for 17% of the global mining volume; followed by Iran (10.8%), Canada (8.5%), Spain (7.1%), and China (6.5% or 6.9 million tons). (However, according to statistics from China's relevant departments, it is 29 million tons, which is mainly used for cement production.) Other top 10 countries are Thailand, Australia, France, and Germany. These 10 countries together account for 72% of the world's mining volume.

According to German OneStone consulting company, about 45% of the global natural gypsum mining volume is processed into mature gypsum. The annual world gypsum output is about 66.5 million tons, of which 60% or 40 million tons comes from natural gypsum, and 40% or 26.5 million tons comes from synthetic gypsum and recycled waste gypsum. It is estimated that the world's annual output of synthetic gypsum is about 160 million tons, of which about 35 million tons come from desulfurized gypsum produced by the desulfurization system of power stations, about 110 million tons are by-products of phosphate fertilizer production, and phosphogypsum is about 15 million tons Chemical plaster. 90% of the synthetic gypsum used in the gypsum industry comes from desulfurized gypsum.

For the gypsum industry, about 80% of plaster is used to produce building wallboards. About 20% is used to produce gypsum plaster or other gypsum products.

For gypsum board factories, shorter set times for gypsum are important. Co-production processes of flash, milling and calcination are commonly used. For the use of desulfurized gypsum, the calcining furnace and related supporting hammer mills are designed by each plant according to its own process. Milling and calcining systems and matching vertical roller mills account for approximately 40% of the market. The market leader is Claudius Peters Process, and in the past two years he has received orders for nine EM mill systems. Gebr.Pfeiffer AG's MPS gypsum mill can meet virtually any production requirement and allows up to 45% of desulfurized gypsum to be added during the calcination process.

The gypsum board factory is dried by a co-current dryer or a counter-current dryer. For fiber gypsum board drying, it is dried by a dry sieve. The gypsum board has a retention time of 32 to 40 minutes in a dryer that takes up as little space as possible. Each group is designed with 6 to 16 board surfaces and 3 drying areas. The accuracy of the co-current dryer feed unit is very important. First, the boards are cut and arranged on a series of boards, and then the stacking starts; the boards that follow must maintain the principle of "in and out" and maintain stable quality.

Gypsum board factory machine operation is becoming increasingly important. This involves the coordination of wet end equipment, dry feeding equipment and destacking equipment, as well as coordination of dry end equipment and stacking equipment. These devices must be able to operate flexibly to produce gypsum boards of different sizes, thicknesses and qualities. Manual production must meet safety requirements when producing different products. Although the transformation of mechanized production methods in modern factories can almost guarantee the preparation of raw materials and the manipulation of paper, the operation of the board is fully automated. However, the high-speed production rate also requires a complete palletizing system at the production end.