Jinan Xin Xiang Ceramic Mugs Industries Co.,Ltd

Jinan Xin Xiang Ceramic Mugs Industries Co.,Ltd

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Customized Ceramic Coffee Mugs - Grouting Process Explained

Date:2024-4-22 Xinxiang Ceramic From:Custom Ceramic Mugs Manufacturers China

Xinxiang Ceramic Mug Manufacturer,

1. Overview

Slurry molding is the use of gypsum mold water absorption, will have the fluidity of the mud into the gypsum mold, so that the mud dispersed adherence to the model, the formation and the model of the same shape of the billet layer of mud, and with the extension of time and the gradual thickening of the billet layer, when it reaches a certain thickness, after drying and contraction and the mold wall detachment, and then take out of the mold, the billet system is completed. Slurry molding is a large adaptability, high production efficiency molding method. Where large, complex shape, irregular or thin tire products, can be used to produce slurry molding method, so slurry molding in the daily ceramics, industrial ceramics, sanitary ware ceramics and modern ceramics and other fields are widely used.

2. Methods of slurry molding

1). the basic grouting method

(1). hollow grouting (single-side grouting) The method of plaster mold with no core. Operation, mud filled model after a certain period of time, the inner wall of the model adheres to a certain thickness of the blank. Then pour out the excess mud, the shape of the blank in the model is fixed, this method is suitable for casting small thin-walled products, such as ceramic crucibles, vases, fittings, ceramic mugs, pots and so on. Hollow grouting slurry density is small, generally in the 1.65 - 1.8g/cm3, otherwise after pouring the slurry surface of the billet there are strands of mud and not smooth phenomenon. Other parameters are as follows: fluidity is generally 10-15 seconds, the consistency should not be too large (1.1-1.4), the fineness is generally finer than the double-sided grouting.
(2). solid grouting (double-sided grouting) solid grouting is injected into the cavity between the two gypsum mold surfaces (model and mold core), the mud is absorbed by the model and the core of the working surface of the two sides, due to the continuous reduction of water in the mud, so grouting must be replenished one after another until the mud in the cavity is all turned into a billet until the time. Obviously, the thickness and shape of the blank are determined by the shape and size of the cavity between the model and the mold core, so there is no excess mud to pour out. The method can be manufactured on both sides of the pattern and the size of large and complex shape of the products: such as cups, fish plate, porcelain plate. Solid grouting commonly used thicker slurry, general density of 1.8g/cm 3 or more, in order to shorten the suction time. Thickness (1.5 -2.2), fineness can be coarser.

2). Enhanced grouting method

In order to shorten the grouting time and improve the quality of the injection, on the basis of the two basic grouting methods, some new grouting methods have been formed, which are collectively called reinforced grouting.
There are mainly the following kinds of reinforced grouting.
(1). Pressure grouting: the method of increasing the mud pressure is used to accelerate the diffusion of water, thus accelerating the rate of grout absorption. Pressure grouting is the simplest is to raise the position of the slurry bucket, the use of slurry itself from the bottom of the model gravity into the slurry, but also the use of compressed air will be injected into the model slurry. According to the mud pressure, pressure grouting can be divided into micro-pressure grouting, medium-pressure grouting and high-pressure grouting. Micro-pressure grouting grouting pressure is generally below 0.05MPa; medium-pressure grouting pressure in the 0.15-0.20MPa; greater than 0.20MPa can be called high-pressure grouting, at this time it is necessary to use high-strength resin mold.
(2). Vacuum grouting: using specialized equipment in the outside of the gypsum vacuum, or the reinforcement of the gypsum mold in a vacuum chamber under negative pressure, which can accelerate the formation of the billet, improve the density and strength of the billet.
(3). Centrifugal grouting: centrifugal grouting is to make the model in the rotating situation grouting, mud by the role of centrifugal force close to the model to form a dense billet, mud bubbles in the mud due to the lighter, in the model rotation, more concentrated in the middle, and finally rupture discharged, and therefore also improve the speed of grout suction and the quality of the product. However, the size of the solid particles in the mud used in this method can not be too large a difference, otherwise the coarse particles will be concentrated on the surface of the blank, fine particles are easy to concentrate on the inside of the model, resulting in uneven organization of the blank, drying and shrinkage of deformation.
(4). Hot slurry grouting: hot slurry grouting is to set electrodes at both ends of the model, and when the slurry is filled, connect the alternating current, use the conductivity of the electrolytes in the slurry to heat the slurry, warm up the slurry to about 50 ℃, which can reduce the viscosity of the slurry, and accelerate the speed of slurry absorption.

3. The core of the grout molding

The key to grout molding, to have a high-quality model and good performance of the grouting mud.

1).Requirements for plaster model

(1) The model is reasonably designed and easy to demold. The water absorption of each part is uniform, which can ensure the drying and shrinkage of each part of the body is consistent, that is, the density of the body is consistent.
(2) The model is not too porous, good water absorption, its porosity requirements in 30%-40%, the use of gypsum mold should not be too dry, its water content is generally controlled at 4%-6%. Model too dry will cause products of dry cracks, bubbles, pinholes and other defects, at the same time, shorten the service life of the mold. Model too wet will extend the blank time, or even difficult to mold.
(3) The working surface of the model should be smooth, no holes, no lubricant traces or soap film.

2).  the mud requirements

(1) good fluidity of the mud, that is, the viscosity of the mud is small, when used to ensure that the mud in the pipeline flow and can be fully flowed into all parts of the model. Good mud should be like cheese, outflow into a continuous thin line, otherwise pouring difficulties. If the model is complex, it will produce defects such as flow slurry is not in place and form missing corners.
(2) water content as low as possible, under the premise of ensuring mobility, reduce the water content of the slurry as much as possible, so as to reduce the grouting time, increase the strength of the billet, reduce the drying shrinkage, shorten the production cycle, and prolong the service life of the plaster mold. General slurry water content control in 30%-35%, density 1.65-l.9g/cm 3 .
(3) good stability, the mud will not precipitate any component (such as quartz, feldspar, etc.), mud parts can be maintained for a long time composition is consistent, so that the injection of uniform organization.
(4) filtration (permeability) to be good. That is, the water in the mud can pass through the mud layer attached to the model wall and be absorbed by the model. Filterability can be adjusted by adjusting the content of barren and plastic materials in the mud.
(5) Appropriate thixotropy. Mud after a certain period of time after storage viscosity change should not be too large, so that the mud is easy to transport and storage, and at the same time require demolded billet is not subjected to slight vibration and soft collapse, grouting with mud thixotropy is too large is easy to thickening, inconvenient to pour, and thixotropy is too small is the billet is easy to softly collapse, so there should be an appropriate thixotropy.
(6) the mud in the air content as little as possible, the slurry is usually mixed with a certain amount of air, so that there are a certain number of air holes in the injection, for the thicker slurry this phenomenon is more significant, in order to avoid bubbles and improve the mobility of the slurry, the production of vacuum defoaming treatment is often used.
(7) the formation of the billet should have sufficient strength.
(8) grout forming the body is easy to release the mold.

4. Slurry diluent

Types and selection of diluents in general, the lower the water content of the slurry mobility is worse, and the slurry injection process requires the slurry water content as low as possible and mobility to be good enough, that is, the need to prepare a thick slurry mobility is good enough, the production of such a water content is as low as possible, and the mobility of the thick slurry is good enough to take the measures is to join the diluent.

Ceramic industry production is often used in the diluent is divided into three categories.

1). Inorganic electrolytes

Such as water glass, sodium carbonate, sodium phosphate, sodium hexametaphosphate and so on. This is the most commonly used class of diluents. To get the desired viscosity of the mud, and the need to add the type and amount of electrolyte and the type of clay in the mud has a close relationship. Generally, the amount of electrolyte is 0.3%-0.5% of the mass of the dry blank. Water glass has the best effect on enhancing the suspension ability of kaolin clay slurry, which not only significantly reduces its viscosity, but also in a wide range of electrolyte concentration is very low viscosity, which is conducive to production operations. For the purple wood knotty clay slurry containing organic matter, sodium carbonate has a better dilution effect than water glass. Production is often used at the same time as water glass and soda ash as a diluent to adjust the speed of pulp and the degree of softness of the body. Because of the single water glass, the blank after demolding hardening faster, inside and outside the moisture difference is small, dense and hard, easy to crack. Single soda ash (Na2CO3), after demolding, the body of the slower hardening, inside and outside the moisture difference is large, the body of the softer, or outside the hard inside soft. When using electrolyte, pay attention to its quality. Soda ash will turn into sodium bicarbonate if it gets wet, and the latter will flocculate the mud. Water glass (Na2SiO3) is a soluble silicate composed of alkali metal oxides (usually Na2O) and silica in varying proportions. Its composition with SiO2/Na2O molar ratio (called water glass modulus) to express, when its modulus is greater than 4, long-term placement will precipitate colloidal SiO2. commonly used as a diluent of water glass modulus is generally about 3.

2). Organic acid salts

Such as sodium humate, sodium tannate, sodium citrate, rosin soap and so on. This kind of organic substances have several conditions as a diluent. Their dilution effect is relatively good. The amount of sodium humate is generally 0.25%. If exceeded, the viscosity of the mud increases again, which is similar to the dilution law of inorganic electrolytes. In addition, the dosage is too large, such as firing its organic matter is not burned clean, but also make the glaze dark. The amount of sodium tannate is generally about 0.3%-0.6%.

3). Polymerized electrolyte

Ceramic industry using this type of diluent history is much shorter than the above two types of diluent. Polymerization electrolyte is often used as a clay-free raw material slurry diluent. Commonly used gum arabic, peach gum, gelatin, carboxymethyl fiber sodium salt and other organic colloids, its dosage will make the slurry polymerization and sinking, the appropriate increase will dilute the slurry, the amount is generally in the 0.3% or so.

5. Operating process of grout molding

1). Slurry molding process Slurry molding process according to the product type, slurry nature of different roughly need to go through the following processes.
(1) Close the mold
Before closing the mold, the working surface of the model should be cleaned, no dry mud or dust. And check whether the working surface of the mold is clean, there are no holes and lubricant traces. If it is normal, you can close the mold, assembled model if there is a large gap, with soft mud to plug the gap at the joints, so as to avoid leakage of slurry. When using the model should not be too dry or too wet, the amount of water is generally controlled at 4% -6%.
(2) Grouting
For single-sided grouting, the slurry filled model can be, such as mud layer thickening to the required thickness, pour off the model of the excess slurry, in order to avoid pouring off a small amount of residual slurry in the billet in the body of the surface of the uneven distribution of the production of slurry also need to pour off the slurry after the billet with a blank model for the dumping of slurry to ensure that the residual distribution of mud to avoid the production of strands of mud. For double-sided grouting, must be supplemented with slurry until the model of the cavities within the slurry all into the blank. There is no need to pour and dump the slurry.
(3) Drying of green billets
Just formed due to the high water content of the injection, low strength and can not be immediately demolded, need to take the mold drying for a certain period of time, this drying is called green billet drying, in the green billet drying period, due to the evaporation of water and the mold continues to absorb water, the injection of water continues to decline, the billet contraction and detachment of the model, and at the same time gradually increase the strength, then can be demolded.
(4) demolding
After demolding, the blank should be held gently, put flat, put right, put stable, and prevent vibration.
(5) Bonding
Bonding is the manufacture of mugs, pots and some small vases, altars and other daily-use porcelain and art porcelain, porcelain, sanitary porcelain, etc. can not be molded in one body of the necessary processes, the bonding process refers to a certain consistency of the bonding slurry will be formed into their respective parts bonded together.
For the bonding process, attention should be paid to the following aspects.
(a). The degree of hardness and softness (water content) of each part. In bonding, the degree of hardness and softness of each part is not forced to be the same. Generally speaking, the part blanks should be slightly harder than the main blanks to prevent deformation, but not too big a difference, otherwise it will be due to different water content and contraction inconsistencies caused by cracked blank defects. Practice shows that the difference in moisture content between the two should not exceed 2% -3%.
(b). Bonding mud. Bonding slurry general and the composition of the blank, so that the two expansion coefficients will not be inconsistent resulting in cracks, at the same time, but also to control the viscosity and mobility of the slurry, the general mobility to be good, the relative density adjusted to 2.0 or more, so that the slurry bonding will not crack. In order to bond firmly, but also in the bonding mud to add a certain adhesive (dextrin, methyl cellulose, etc.), but also in the mud to add about 30% of the glaze or other fluxes, so that it is at high temperatures and the body of the blank firmly combined.
(c). Bonding contact surface. According to the bonding contact surface is different, the bonding can be divided into smooth surface bonding and hemp surface bonding. Sisal bonding refers to the two contact surfaces have a serrated knife scratched into a serrated shape, which can increase the contact area, so that the adhesive interface is more solid. Hemp surface bonding degree of hemp surface can also be based on the water content of the blank, such as low water content of the blank, the degree of hemp surface can be deeper; such as high water content, can be a little shallower. For large-scale sanitary ceramics have two different methods of operation; one is in the case of two bonding pieces of water content is appropriate, first of all, the two bonding paddle into the pavement; another case is the lower water content of the billet, so that the pavement can be used to brush the brush sticking to brush once again, directly with a thick slurry for bonding. These two operations can be mastered properly, you can get the same effect. After bonding, to scrape away the excess mud. At the same time, in order to prevent cracking and deformation, generally in the bonding place to stick a soft cloth or paper.
(6) Repairing the blank
For the bonded blank, because its surface is not very smooth, the edge of the mouth has a burr, and some still have mold seam trace, and some products need further processing, such as digging the bottom, punching holes, etc., so it needs to be further processed to fix the leveling, known as trimming blanks. Repair is a three-dimensional semi-finished product grinding process, so that it can adapt to the glaze operation and into the kiln firing of the fine billet. Repair is a necessary work in the injection molding and plastic molding industry. It has a great influence on the surface quality of the blank, and should be given enough attention. There are wet repair and dry repair. Wet repair is a lot of water in the body, still in the case of wet soft, suitable for more complex shape or need to be wet by the billet, this time the operation is easier and the knife is not easy to repair the billet is not easy to wear, the disadvantage is easy to move and operate in the process of the billet injury caused by deformation to improve the quality of the unfavorable. General custom ceramic coffee mugs, bowls, pots and other products that need to be processed, more wet repair, depending on the degree of moisture to be processed to determine. Need plastic processing (such as perforation, etc.) and bonding of the blank, the wet repair moisture can be slightly higher, 16% - 19%, such as porcelain and fine ceramic blanks are generally 16% - 18%, while the coarse ceramic blanks are generally 8% - 16%. Wet repair methods, available scraper, foam molding scraping and polishing. Dry repair is in the body of the moisture content down to 6% - 10% or even lower moisture after drying (2%). At this time the billet strength increase, can reduce the deformation caused by moving injuries, to improve the quality of favorable, the disadvantage is that the dust is larger, but also on the repair of blank knife resistance is larger, easy to jump knife, repair the blank knife wear and tear is also larger, the operation of the technology is more difficult to master. Dry repair due to the low water content of the billet, available foam, rags, brooms, etc. dipped in water to repair the billet, can also be used to knife, sieve, etc. directly dry repair. Repair of blanks using many types of scrapers, different products, the shape of its use is also different. For example, sanitary stoneware coffee mugs, according to its shape, can be divided into flat scraper, round scraper, crescent scraper three kinds. Flat scraper for the full semi-circular, generally adapted to repair the plane; round scraper is double arc, suitable for scraping the concave surface; crescent scraper for scraping the raised surface of the model counterpart seam traces, etc.. Scraper is generally double-sided blade, blade width in 5-10mm. scraping blanks according to the degree of convexity and concavity of the scraping blanks, change the scraper surface with the angle of the surface of the blank for the operation.
When repairing blanks, we should not only emphasize the appearance quality, but also pay attention to the prevention of other quality defects. Therefore, special care should be taken during the operation. For example, when dry repairing the body of the blank, the following points should be noted.
(a). the surface of the body of the plaster dirty, flannel dirty, sponge dirty and mud flake debris, be sure to remove clean, in order to prevent the appearance of the finished product has defects.
(b). to use mixed water to wipe the blank to paste the brown eyes on the surface of the blank, so as not to affect the quality of the finished product appearance.
(c). The blank itself has bubbles, usually about 5mm, you can use dry blanks crushed plug, and then rolled with a hard object. If the bubble is more than 5mm to see if it can be plugged, if not plugged, can be scraped with a scraper, so that there are no obvious traces, in order not to affect the appearance of good. If the bubble is large and has a certain depth, it is regarded as scrap.
(d).The surface of the blank must be scraped flat if there is obvious concavity or convexity on the surface of the blank.
(e). If there is a small crack with a length of 10mm and a depth of 2mm in a certain part of the body, you can use a scraper to scrape it until there is no crack, and then scrape the surrounding parts flat.
(f). The part of the body of the grouting eye with traces, must be scraped off with a scraper, in order to prevent the finished product from mud wisp defects. After dry repair of the blank body should also be polished, check. Check when a look at the body of the blank wash surface, hidden holes; two look at eye holes, etc.; three look at the mold seam; four look at the sticky mouth part; five look at the sanding of dry blanks when the defective parts of the technical processing effect; six look at the water. After the inspection, but also dry blanks to find cracks.

(7). Looking for cracks
The so-called dry billet to find cracks, that is, in the dry billet smeared with oil (kerosene, etc.) to look for cracks, it is the ceramic industry, a traditional experience, and its operational requirements are as follows: ① smeared with oil to find cracks in the dry billet, and its operational requirements are as follows.
(a). wipe oil to find cracks in the body must be after drying the whole dry billet, half-dry billet or billet with high water content is not good.
(b). anointing before the beginning of the sponge dipped in water will need to wipe the oil part of the wipe, and then use a flat pen dipped in oil to wipe the part, wipe the side of the light, and concentrate on observation, generally cracks, cracks will quickly absorb oil, the formation of a black trace. Once there is such a phenomenon, you need to use a scraper to scrape the billet layer by layer until the black trace disappears. Such cracks cannot be repaired if they are too deep. The key to finding cracks in the oiling experience is "three to", that is, pen to, lamp to, eyes to, to focus on finding cracks.
(c).looking for cracks is not the whole body of the blank are smeared with oil, generally sticky mouth parts, wet blanks have sticky cracks and doubtful places.
(d). from wiping water, wipe oil to observe, the shorter the better, drag the time is too long is not easy to find cracks. Repair and bonding in the formation of daily-use ceramics and sanitary ceramics in the process for a long time is operated manually, low efficiency, the need for a large number of artificial, how to achieve the mechanization of repair and bonding is the urgent need to solve the problem. At home and abroad, there are a number of mechanical trimming and bonding machine, but still can not keep up with the development of the molding process. In the future, with the development of automatic trimming machine and bonding machine, will make the whole forming process automation to a new level. At the same time, the use of new molding process, so as not to trim and bonding process. This will be the development trend of ceramic molding process.

2. Slurry molding operation notes
① new slurry should be made at least one day of storage (aging) before use, before use must continue to mix 5-10min.
② slurry temperature should not be less than 10-12 degrees Celsius; winter slurry is too cold, affecting the fluidity of the slurry; therefore, in the winter grouting workshop should be heated to maintain the indoor temperature at 20-25 degrees Celsius.
③ Gypsum mold should be used in sequence rotation, so that the model humidity to maintain consistent. For hollow grouting each time after the injection of blanks, mud in the mold residence time must be strictly controlled.
When injecting clay into the model, it should be injected along the funnel slowly and continuously at one time, so that the air in the mold can fully escape. Injection of billet is best mold placed on the turntable, one side of the injection, one side of the hand to make it turn, so that the role of centrifugal force, to promote the generation of mud layer and uniformity, reduce the billet air bubbles, reduce the deformation of the firing. In the solid grouting, mud injection should be slightly vibration of the model, so that the mud flow all over the place. At the same time, it is also conducive to the dissipation of air bubbles within the mud.
⑤ It is better to spray a layer of thin glaze slag and sprinkle a layer of talcum powder on the inner wall of plaster mold before grouting to prevent sticking to the mold.
(6) From the hollow grouting after pouring out of the residual slurry and trimming of the waste slurry, both some of the solvent, but also from the model mixed with some calcium sulfate. Recycling use, we should first add water to mix, wash away these soluble salts, and then sieve pressure, filter and then with the new slurry with.
(7) grouting billet after demolding should be held lightly, put flat, put right, put stable, and prevent vibration. High-footed or special type of billet, it is best to put on the pallet.

6. Grout molding common defects analysis

1). air holes and pinholes

The main reasons for the generation of air holes and pinholes:
(1) mud too little moisture, viscosity is too large, poor fluidity, so that the mud in the bubble is not easy to discharge.
(2) Mud storage time is too long, mud temperature is too high, resulting in mud fermentation; mud without aging.
(3) The type and dosage of electrolyte are improper.
(4) Stirring the mud is too violent, or the injection speed is too fast, so that the mud is entrapped with air bubbles.
(5) There are impurities mixed in the plaster mold, such as sand or calcium carbonate, etc.; the particles of plaster used for mold making are too coarse, resulting in uneven structure of the model; the surface of the model is stained with dust.
(6) The plaster mold is too dry, too wet, or the temperature is too high.

2) Cracking

The main reasons for cracking.
(1) Improper dosage of plastic raw materials in the mud, the particles are too coarse.
(2) The amount of electrolyte is not appropriate, or the mud is not aged, uneven mixing, poor fluidity.
(3) The model is not wet or dry, and the sex model is not cleared of surface oil impurities before use.
(4) grouting operation is not good, not completely pour net surplus slurry, resulting in uneven thickness of the injection, drying and shrinkage is not consistent.
(5) injection molding too early, too late, drying temperature is too high.

3). deformation

The main reasons for deformation.
(1) Mud mixed unevenly, resulting in inconsistent drying contraction.
(2) Too much water in the mud, resulting in large drying contraction.
(3) Pouring improper operation, uneven thickness of the body.
(4) The model is too wet or demolded too early, or improper operation out of the mold, the wet blank is not put flat, put right.

4). mud strand

The main reason for the mud strand.
The viscosity of the mud is large, poor fluidity; modeling work surface is stained with drops of paste; improper operation of the pouring residual pulp.

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