Ceramic Production Process

Time of issue: 2023-12-22 11:16:08

Table Of Content

1. Classification of ceramic raw materials

(1) Clay

Clay raw materials are one of the main raw materials for ceramics. Clay is the main raw material for ceramics because of its plasticity and sintering properties. The main clay minerals in the ceramic industry include kaolinite, montmorillonite and illite (hydrous mica), but the main clay raw material in our factory is kaolin, such as Gaotang kaolin, Yunnan kaolin, Fujian Longyan Kaolin, Qingyuan kaolin, Conghua kaolin, etc.

(2) Quartz

The main component of quartz is silicon dioxide (SiO2). In ceramic production, when it is added to the ceramic blank as a barren raw material, the plasticity of the blank can be adjusted before firing. The heating expansion of quartz during firing can partially offset the Shrinkage of the green body. When added to the glaze, it improves the mechanical strength, hardness, wear resistance, and chemical resistance of the glaze. The quartz raw materials of our factory mainly include: glazed quartz, Fogang quartz sand, etc.

(3) Feldspar

Feldspar is the most commonly used fluxing raw material among ceramic raw materials. It is used as basic components such as blanks and glaze fluxes in ceramic production. It melts at high temperature to form a viscous glass body, which is the main source of alkali metal oxides in the blank. It can reduce the melting temperature of the components of the ceramic body, which is beneficial to porcelain formation and lowering the firing temperature. Act as a flux in the glaze to form a glassy phase. The main feldspar raw materials of our factory include Nanjiang potassium feldspar, Fogang potassium feldspar, Yanfeng potassium feldspar, Conghua albite, Indian potassium feldspar, etc.

2. Preparation of blank and glaze

(1) Ingredients

Batching refers to weighing various raw materials according to the required weight according to the formula requirements, mixing them and loading them into the barrel of the ball mill. The ingredients of the blanks in our factory are mainly divided into three types: white crystal mud, high crystal mud and high aluminum mud, while the ingredients of the glaze can be divided into transparent glaze and colored glaze.

(2) Ball mill

Ball milling means adding water to the barrel of the ball mill where the raw materials are loaded for ball milling. The principle of ball milling is to rely on the impact and friction of the ball stones in the cylinder to grind the mud particles to the required fineness. Usually, medium-alumina ball stones are used for auxiliary ball-milling of the blank; high-alumina ball stones are used for auxiliary ball-milling of the glaze. In the ball milling process, some ingredients are generally put in for ball milling for a period of time, and then the remaining ingredients are added and milled together. The total ball milling time ranges from more than ten hours to more than thirty hours depending on the materials. For example: white crystal mud is generally ground for about 13 hours, high crystal mud is generally ground for 15-17 hours, high alumina mud is generally ground for about 14 hours, glaze is generally ground for 33-38 hours, but in order to make the slurry fine after ball milling To meet the requirements of the manufacturing process, the total ball milling time will fluctuate.

(3) Screening and iron removal

After the ball-milled slurry is tested to meet the fineness requirements, coarse particles and tailings are removed with a screen. Normally, the specifications of the screen cloth used in our factory are: the blank is generally between 160-180 mesh; the glaze is generally between 200 mesh -250 mesh. After sieving, a wet magnetic separator is used to remove iron impurities. This process is called iron removal. If iron is not removed, black spots will appear on the fired product, which are commonly referred to as spots or impurities. Screening and iron removal are usually done twice.

(5) Press filter

Pump the screened and iron-removed mud into a filter press through a plunger pump, and use the filter press to squeeze out excess water.

(6) Clay training (rough training)

The mud cake obtained after filtering has an uneven structure and contains a lot of air. If the mud cake with uneven structure is used directly for production, it will cause uneven shrinkage of the green body during subsequent drying and firing, resulting in deformation and cracks. After rough refining, the vacuum degree of the mud section is generally required to be between 0.095-0.1. Another benefit of the rough-cooked mud balls is that the mud cakes can be made into mud segments of a certain size for easy transportation and storage.

(7) Stale

The coarsely refined mud segments are placed in a certain temperature and humid environment for a period of time. This process is called aging. The main functions of aging are: making the moisture in the mud material more evenly distributed through capillary action; increasing the content of humic acid substances, improving the viscosity of the mud material, and improving the molding performance; some oxidation and reduction reactions occur to make the mud material loose and uniform. After aging, the strength of the green body can be improved and the chance of deformation during firing can be reduced. Usually the time required for aging is 5-7 days, and the fastest one is 3 days.

(8) Refined clay

Refining mainly involves vacuum treatment of the mud section again in a vacuum mud refiner. Through refining, the hardness and vacuum degree of the mud segment meet the requirements of the production process, thereby further improving the plasticity and density of the mud segment, making the composition more uniform, and increasing the dry strength of the molded body. At the same time, another purpose of this process is to provide various specifications of clay segments for molding in subsequent processes. The preparation process of grouting mud and glaze is basically similar to the preparation process of plastic mud. Generally, the ball-milled mud is dehydrated into mud cake through press filtration, and then the mud cake is broken into small pieces and electrolyte is added to the mixing tank. Stir into a slurry. In addition to using a filter press to dehydrate the glaze, there are also natural dehydrations.

3. Forming

(1) Production of mold

The production of molds is a prerequisite for the molding process. Usually the main material of molds in our factory is gypsum, because the cost of using gypsum is relatively low, easy to operate, and gypsum has good water absorption. However, the molds for relief products are made of silicone. When developing new products, the master first uses plaster to make a model that is the same as the original board, then uses plaster to pour a set of molds based on the model, and then processes the mold into a mold type. The production mold is copied based on the mold type. Usually embossed molds are made of silicone because silicone has better toughness.

Generally speaking, according to different molding methods, the molds in our factory can be divided into three types: rolling molds, extrusion molds and grouting molds. The rolling mold making process is relatively simple. You only need to mix a mixture of gypsum and water and then pour the mold. After ten minutes of solidification, pour it out. However, the dosage is very large and the consumption is relatively large. The extrusion mold needs to be drained and exhausted. The production process is complicated. Before pouring the gypsum, you need to install an exhaust pipe. Start exhausting at about 25 degrees Celsius and continue exhausting for 2 or 3 hours. This will help reduce pores and bubbles. The extrusion die requires fewer molds and is more durable. Grouting molds can be divided into hollow grouting molds and high-pressure grouting molds. The production process of hollow grouting molds is relatively simple, but the dosage is relatively large; the production of high-pressure grouting molds is relatively complex, and the mold itself requires a larger volume to match the high-pressure grouting machine.

(2) Forming

Molding is to use a prepared plaster mold to make the required blank using various molding methods. Currently, the three commonly used molding methods in our factory are roll molding, extrusion molding and grouting molding.

a.Roll forming

During roll forming, the model holding the mud and the rolling head rotate at a certain speed around their respective axes. The rolling head gradually approaches the model holding the mud and "rolls" and "presses" the mud. ” formed by the role of. Roll molding can be divided into male mold rolling and female mold rolling. Male mold rolling uses a roller head to form the outer surface of the blank. This method is often used for flat, wide-mouthed vessels and products with reliefs inside the vessels. Female mold rolling uses a rolling head to form the inner surface of the blank. This method is often used for small and deep vessels or products with relief on the outside of the vessel. Roll forming has fast production start-up and stable quality. Generally, this forming method will be given priority.

b.Extrusion molding

Extrusion molding is to place the refined mud material in an extrusion mold, and use the action of a hydraulic press to extrude green bodies of various shapes. Special-shaped parts are generally made by extrusion molding, such as triangular discs, elliptical discs, square discs, etc. Extrusion molding has a slow production start-up and relatively stable quality, but the mold manufacturing process is relatively complicated.

c. Grouting molding

Grouting molding can be divided into two types: hollow grouting and high-pressure grouting. The production of grouting molding is slow, and this method is often used in the production of some three-dimensional parts, such as hollow cans, pots and other products. Hollow grouting is to inject mud into the plaster mold, and water penetrates into the plaster model through the contact surface, thereby forming a hard layer on the surface. After the hard layer reaches a certain thickness, the excess mud is poured out. High-pressure grouting uses high pressure to inject mud into a pre-fixed gypsum mold. The water absorption of the gypsum mold is used to absorb the water in the mud. After the mud in the gypsum mold reaches a certain hardness, the high-pressure valve is closed and the injection mold is opened at the same time. Open the slurry valve to drain excess mud. Drying: After the product is formed, it should be sent to drying. If the product is a cup, it does not need to be sent to drying immediately. It should be air-dried first and sent to glue the cup ears. Before sticking the cup ears, the mouth of the cup should be smoothed first, and the cup should be smoothed with mud. After the ears are firmly glued, wash off the mud and dry them after completion. After drying, use a high-pressure air duct to check for air slurry and cracked ears. Trimming: Before trimming, use kerosene to check whether the product has a cracked bottom. If not, you can trim it. Use sandpaper on the roller to smooth the edges and sides of the upper and lower ends of the product.

4. Glazing

Glazing is to apply a layer of glaze on the surface of the body. Usually it can be divided into three types: dip glaze, wheel glaze, and pouring glaze.

(1) Dip glaze

Glaze dipping is to immerse the green body in the glaze slurry for a while and then take it out, using the water absorption of the green body to make the glaze slurry adhere to the green body. The thickness of the glaze layer is controlled by the water absorption of the blank, glaze slurry concentration, and dipping time.

(2) Wheel glaze

The wheel glaze is to place the green body on a rotatable turntable. When rotating, the employee uses a bowl or spoon to pour the prepared glaze slurry into the center of the green body. Due to the action of centrifugal force, the glaze slurry spreads evenly, making the product After applying a uniform thickness of glaze, the excess glaze slurry is thrown out. Wheel glaze is mostly suitable for flat objects such as dishes.

(3) Glaze

The glaze is applied semi-automatically by machine. The blank holder and the blank are placed on the conveyor belt of the machine, and the transmission wheel drives the conveyor belt. When the blank passes through a uniform glaze film, the front side (upward side) of the blank can be glazed. After one side is glazed, the employee turns the body over. At this time, the other side of the body passes through the glaze film and can be glazed. This glazing method is highly efficient and suitable for mass production. The bottom of the glazed body is generally subjected to bottoming treatment. The purpose of this is to remove the glaze at the bottom of the body to prevent the glaze at the bottom of the body from sticking to the boron plate during firing.

5. Burning

Firing is a very critical process in the porcelain making process. After shaping and glazing, the semi-finished product can only achieve a completely dense porcelain phenomenon when a series of physical and chemical reactions occur under the action of high temperature. Finally, the apparent porosity is close to zero. This process is called "firing".

(1) Tunnel kiln

Currently, tunnel kilns are usually used for firing factory utensils. The tunnel kiln is a long straight line (about 150 meters) with fixed walls and vaults on its sides and top, and kiln cars running on tracks laid at the bottom. The tunnel kiln is divided into three parts: preheating zone, firing zone and cooling zone. In addition to tunnel kilns, the factory also has roller kilns and shuttle kilns. The temperature of the comb kiln can be adjusted and the furnace can be turned off every day. The residual temperature in the kiln can be fully utilized in the product drying process, which is energy-saving and environmentally friendly, and consumes relatively little energy.

(2) Firing process

The firing of the green body is a process from quantitative change to qualitative change. Physical changes and chemical changes are intertwined, and the changes are complex. Generally, the firing process of ceramic tableware can be divided into four stages, namely: 1. Evaporation period; 2. Oxidative decomposition and crystal transformation period; 3. Vitrification into porcelain period; 4. Cooling period.

6. Sorting

Products that have been fired or roasted must be sorted in a sorting workshop to determine their grade. The sorting levels are divided into five levels: first level, third level and qualified products, fourth level and scrap products. First-class products and third-class products are exported at a certain ratio. Unqualified products must not be sold or circulated, but can only be sent to scrap warehouses for disposal.

7. Decoration and packaging

(1) Decoration

For the decoration of ceramics, our factory currently mainly uses color glaze, decals and relief. a. Color glaze refers to the process of applying glazes of various colors on the surface of the body. Color glaze is prepared by adding color materials to the glaze. b. Decal is a process in which colored materials are made into decorative paper, and then the decorative paper is affixed to the surface of the blank. For products that require decals, after they are fired and sorted, they can be sent to the decal workshop for decals. Decal paper is divided into three types: in-glaze, over-glaze and under-glaze. Over-glaze refers to decals on the fired product, which are then baked at a temperature of about 800 degrees Celsius. After baking, the pattern of the paper can be felt by hand; glaze Medium refers to decals on the fired product, and then bakes them at a temperature of about 1200 degrees Celsius. After baking, the decal pattern is deeply embedded in the porcelain; under-glaze is generally used for darker colors such as blue or black, such as the bottom of the product. To make a mark, the method is to apply a base mark or floral paper on it after washing it with white glaze, and then firing it into porcelain, or wash it and apply a base mark or floral paper, then apply a transparent glaze, and then fire it. Usually our factory uses two kinds of decorative paper, over-glaze and under-glaze. c. Relief refers to the process of pressing out concave and convex patterns on the surface of the body through a mold, such as Long series products.

(2) Packaging

At present, the packaging materials used in factory products are mainly partitions and cartons. Design appropriate carton sizes and corresponding partitions according to customer requirements so that products can be protected accordingly during transportation. The packaging department packages the products according to the design requirements and sends them to the export warehouse.