Causes and Quality Control of Dirty Spot Defects on the Glazed Surface of Sanitary Ceramics

Sanitary ceramics are deeply loved by users because of their novel shapes, various types, bright and delicate glazed surfaces, bright colors, excellent sewage discharge functions, and easy cleaning. Since their birth, they have always had strong vitality and are favored by users. In the past 20 years, my country's sanitary ceramics industry has developed rapidly, and production enterprises have sprung up like mushrooms. The output has increased year by year, the variety of products has continued to increase, and the export volume has also continued to increase. According to statistics, the current output has reached more than 80 million pieces, ranking first in the world, and the export volume is 40 million pieces. 50% of production. Although the product quality has also been greatly improved, but overall, there is still a big gap between product quality and market customer requirements. The market is still dominated by low-end products, and the products of most enterprises cannot be sold at a good price in the market. The main reason that restricts the price increase of these enterprises is the poor quality of the products, which is specifically manifested in the appearance of glazed surface defects. Dirty spots are common quality defects that affect the appearance of sanitary ceramic products.

Types, characteristics and causes of dirty spot defects

It is a general term for several kinds of raw material dirty point defects. It is specifically divided into iron points, copper points and mud dirty materials. The iron spots appear as small black and tan spots with a diameter of 0.3mm-1.5mm evenly dispersed on the glaze surface of the product after firing. Copper spots appear as individual green or light green spots on the glazed surface of the product after firing, with a diameter of 2mm-5mm, the central tone is darker, and gradually disappears as it extends to the surroundings. The reason for the above spot defects is that the raw materials used (especially raw materials for glaze) are of poor quality, and there are many impurities such as non-magnetic or weakly magnetic magnesite, limonite, pyrite, biotite, etc., and the selection is not good. Thoroughly; or because impurities such as iron and copper are brought in due to wear and tear of mechanical equipment; or because the iron removal and screening equipment or process is out of control, the iron removal is not strict, and the iron is not completely removed; or because the billet, glaze processing and storage sites or facilities are hygienic Poor due to impurities such as iron filings and copper filings. Dirty mud (dirty material block) is due to poor processing of mud, improper iron removal and sieving (overflow sieve or leaky sieve), and large coarse hard particles (such as ball stones, quartz, Datong sandstone, etc.) mixed into the mud During firing, due to the incompatibility with the carcass and expansion, the glazed surface of the finished product partially presents a circular convex porcelain block, and the glaze layer is lifted when it is serious.

Produced in the forming process, it is also called billet dirty. It is the general term for all formed dirty spot defects. In each link of grouting forming, due to improper operation, some impurities (such as gypsum slag, talc powder, sponge slag, fiber dirt, sand grains, etc.) are mixed into the mud, which exist on the surface of the green body, and the finished product after firing presents irregularly shaped melting holes. ; or the glazed surface of the finished product partially presents a circular convex porcelain block; or the glazed surface is lifted to reveal the smooth surface of the porcelain body. Sometimes it is easily confused with the block dirty defect of the raw material.

The root cause arises from the forming process. Because there are a lot of soil on the surface of the body when brushing the blank, and the slag has not been cleaned; after the water ring is pierced, the slag inside has not been cleaned, and the burrs at the mouth and eyes have not been removed (including the basin); If the soil is not cleaned thoroughly, the dirt will fall on the glazed surface of the product in a convex shape (the color of the unglazed body) due to vibration or kiln furniture shaking during firing. It is mainly concentrated in the parts that are easy to get dirty in the pots and pans of toilets, scrubbers, and basins.

Due to the lack of fineness in the forming operation or semi-inspection of the blank, foreign matter is not clean on the surface (or in the hole) of the blank during glaze spraying, or the glaze is subject to secondary pollution, or the glaze mechanical equipment is faulty, or the compressed air contains oil and water can cause this defect. Therefore, there are many forms of this defect. A small amount of gray or gray-black, black, or brown spots are scattered on the glaze surface with a diameter of 1-1.5mm; or the glaze is sticky on the slag and protrudes and the glaze surface is smooth, with a diameter of 1.5-2mm.

When the glaze is sprayed, the compressed air contains oil and water and is not clean. After the glaze is applied, the surface of the glaze blank is like a rain-beaten sandy beach. After firing, there are pits with a diameter of about 3 mm on the surface of the finished product, which makes the glaze surface uneven, or large yellowish-brown spots. .

The quality of the trademark itself is poor, coupled with the inspection and selection before use, and the work of trial firing is not careful; or the glue and brush used for labeling are not clean, and various colors are mixed; The broken label is not clear and dirty, and when it is severe, there will be trademark color spots with a diameter of 0.5-1mm.

If the kiln frame support is not clean, or the frame support shakes and is unstable, or the kiln installation operation is not fine and the green body is not blown clean, it may cause dirt on the glazed surface of the finished product. It is manifested by black iron spots, billet slag, kiln furniture slag, etc. in the pot and pan of the product; or dirty hands of kiln installers, mixed loading of various colors, irregular kiln installation, and improper operation can cause blue stains in the finished product.

Soil point is also called dust dirty or wind dust dirty (wind dirty). The environmental sanitation conditions of the white blanks after glazing are poor when they are stored for a long time. Dust will fall into them after long-term storage. In addition, if they are not blown clean before loading into the kiln, the surface of the finished product will locally appear dark red 0.3-0.5mm dense needle-shaped spots. It is mainly concentrated in the parts that are easy to get dirty in the pots and pans of toilets, scrubbers, and basins.

During the firing process of the product, due to the dirt falling from the top of the kiln, or the temperature of the kiln head preheating zone is too high, there are accumulated water droplets falling on the product, or the dirt is brought into the burner pipe during maintenance, or the SiC shed plate kiln furniture Poor quality slag explosion, so that the finished product presents individual black spots with a diameter of 1.5-2mm or a middle concave brown stain with a larger diameter (10-15mm).

Effective Measures to Control Dirty Spots and Improve Quality

From the above analysis of the causes of dirty spot defects, it can be seen that there are many types of dirty spot defects, which are produced in various processes in the production process of sanitary porcelain. Therefore, measures should be taken step by step from beginning to end. Strict quality control and quality management in the production process, and do a good job in basic work, in order to achieve results in visceral production.

1. Raw material process

Strengthen the management of raw material quality. Strictly follow the raw material procurement quality standards for raw materials, inspection, and use after passing the test. Raw materials that do not meet the standards must never enter the factory, and unqualified raw materials must not be put into use. Control the quality of raw materials from the source. Raw materials that meet the standards must also be strictly and carefully selected to pick out inferior materials that contain impurities such as iron, titanium, and mica. For some bulk mineral raw materials for glaze (such as quartz and feldspar), the quality should be controlled, and high-quality raw materials should be selected as much as possible, and they should be strictly selected and washed before use. Raw materials for glaze should be protected from wind and rain, and should be stored indoors or in silos. All kinds of raw materials should be stacked neatly, in squares and piles, and the stockpile should have strict boundaries; at the same time, the names of raw materials should be well marked to prevent mixing, and the raw material storage site should be kept clean.

Slime slurry should go through strict iron removal and sieving, increase the number of sieves as much as possible, the slurry should pass at least 80 mesh sieve, the glaze slurry should pass at least 160 mesh sieve, and check whether the sieve is damaged or not before each use Take timely measures.The new mud, return mud and return mud in the mill room and mud supply point, new glaze and return glaze must be removed by strong magnetic square magnets or iron removers, and the iron removers should be cleaned once every shift. The mud glaze processing and mud supply places should be hygienic and clean, and the ground should be washed every shift. Glaze buckets should be covered with thatch plastic cloth to prevent dust and dirt, and all kinds of glaze buckets should be marked with glaze type and status.

When the mud supply point is returned to the pool, a special person must be set up to check the quality. Strict selection should be carried out on the returned billet mud, and all sundries in the returned billet should be picked out. The back mud and back mud must be carefully screened for iron removal.

Before returning to the glaze and putting it into the mill or into the barrel, it should be carefully selected to pick out the sundries. Glaze back should be strictly iron-removed, sieved, and sample fired, and then put into use after passing the test. The equipment and utensils used for the sifting, storage and transportation of glaze slurry must be clearly marked, and the screen and iron remover must be rinsed after use and covered with a clean plastic sheet to achieve cleanliness, dust and Dirty, eliminate all factors that bring in sundries and pollute the glaze slurry.

2. Forming process

Before grouting and mold closing, the sundries in the model should be carefully cleaned. No mud flakes, plaster blocks, brush hairs and other sundries are allowed on the inner surface; gypsum powder and talcum powder are not allowed to be blocked on the inner surface of the model to prevent sticking to the billet during forming. Dirt is formed on the body. It is strictly forbidden to blow the model with compressed air to prevent dust from polluting the environment and damaging health.

40-mesh anti-rust filter must be used for sizing the high tank, and the filter should be cleaned once a day. The high tank should be covered or covered with a plastic sheet, and cleaned regularly to prevent the formation of dry mud flakes mixed into the mud and cause the billet to be dirty.

The billet return truck and the garbage truck should be well marked and placed separately so that the billet return can prevent the source of dirt. Before collecting the waste billets and back billet mud into the billet return car, carefully sort out gypsum blocks and other sundries. The back billet mud pieces that are too broken and dirty cannot be recycled and disposed of as garbage.

Before brushing blanks, poke holes and remove burrs. After grinding the body, break the soil, and before brushing the body, use a sponge to block the spray hole of the toilet to prevent soil powder, slag, and mixed water from entering, so as to prevent defects such as slag, dirty glaze, and rolling glaze in the finished product. Use light to carefully check whether there is dirt on the surface of the green body. When handing over the blanks, it is necessary to ensure that the surfaces of the blanks and the blanks are clean, free of soil powder and slag.

In the forming process (including the billet inspection process), it is strictly forbidden to use inferior towels, sponges, flannelettes and other materials for brushing and billet inspection.

3. Billet inspection process

Billet inspection personnel should strengthen their sense of responsibility and quality awareness, and strictly implement the semi-finished product quality standards and billet inspection procedures and methods. It is necessary to check the billet carefully, not to be mere formality, and not to be disturbed by various factors such as external production. Check and wipe the grooves of the product in place (including the hidden surface of the product), to ensure that there is no floating soil, no mixed water, no dirt, and no sundries on the surface of the fine body after inspection, and ensure that there is no slag in the fine body pot, etc. sundries.

Carefully check the ring holes with a mirror to prevent blockage. All holes should be smooth and free of burrs.

Slag blowers must strengthen their sense of responsibility, be serious and responsible, and prevent fraud. Blow the soil and dust in place one by one, and remove the scum. After the soil is blown, put a personal number on it, and make a mark that has been inspected and blown.

Keep the inspection work platform clean and tidy. To form the vehicle, it must be wiped one by one to ensure that the vehicle is clean and qualified.

4. Glazing process

Before spraying glaze, check whether the glaze pump, glaze tank and other equipment are operating normally. Check the fine body, mainly check the inside of the toilet bowl and various fine body grooves to ensure that the body is free of floating soil and sundries before glazing. Especially when the blank storage time is too long, pay special attention. Wipe clean water on the groove of the fine billet to prevent rolling glaze. Where conditions permit, all the blanks can be wiped with clean water before glaze spraying.

Each booth of the spray glaze should be equipped with an operating table for placing various tools and utensils. It is strictly forbidden to put tools, utensils, stamps, trademarks, etc. into the glaze spray cabinet or on the glaze bucket. It is strictly forbidden to blow dust, blow soil, repair the spray gun, polish the green body with emery cloth, pour the edge of the water tank, etc. in the spray cabinet. It is strictly forbidden to use gypsum brackets for spraying glaze, and wooden or plastic light-weight special brackets should be used.

Clean your hands and tools when applying the glaze to avoid touching the blue color. The brackets, tools and glaze pumps used are cleaned after work and placed in a fixed place.

Special tools should be used to recover the glaze, and ironware is strictly prohibited. Colored glazes of different colors are stored separately to prevent mixing. The storage place for recycled glaze should be clean and hygienic, and the type of glaze should be marked. Recycled glaze is used to cover dust and pollution. The structure of the glazing cabinet should be improved, and the outdated process of recycling dry glaze, centralized storage, and regular return to the glaze for grinding should be eliminated, and replaced by daily cleaning, daily production and Nissin, mixer stirring, iron removal and sieving, and trial firing of samples. Afterwards, the more advanced and reasonable process method used in proportion will be added on site, which will obviously overcome the stain and reduce the color difference defect, and at the same time reduce the waste of glaze.

Keep the glazing work area hygienic. Wash the working surface after finishing work every day. It is strictly forbidden to open the window, and the glaze bucket should be covered or sealed with a plastic sheet to prevent dirt from falling into the glaze slurry or on the white blank. For the white blank after glazing, thatch plastic sheeting should be added, or tarpaulins should be added to the roof to take dust-proof measures.

5. Labeling process

Each batch of trademarks must be strictly tested and fired, and can only be used after passing the test. Do a good job of qualified identification, store it in a fixed place, and manage it by a special person.

The trademarks put into use must be strictly selected by special personnel, and broken labels, dirty labels, double shadows, etc. are prohibited.

Before labeling, make sure that the surface of the blank is free of dust and clean.

Glue stays clean and prevents deposits. Use less glue and work more frequently, and utensils and brushes should be cleaned every shift to keep them clean.

The working platform for placing trademarks should be kept clean, and the trademarks can be used as soon as they are soaked, and the trademarks should be covered with plastic cloth to prevent sticking.

6. Firing process

All blank transport vehicles were changed to light-duty clean and dust-proof special vehicles. A special dust collection room is built, and all white billets are scraped and blown in the dust collection room before entering the kiln (including the overflow channels of products such as basins must be blown clean). It is strictly forbidden to scrape and blow dust beside the kiln, let alone blow dust white blanks on the kiln car.

The kiln loading surface should be clean, and each car should be cleaned. Kiln installers should strengthen their sense of responsibility and operate carefully. The back of the basin should be wiped clean, and the kiln frame support should be stable and anti-shaking to prevent it from getting dirty.

When loading the kiln and taking the billet, the hand should not touch the blue color. Pay attention to hand color when installing colored glaze products.

Vehicle inspectors should strengthen their sense of responsibility, check the lights, and vacuum each vehicle and piece by piece.

The filter screen of the fan should be replaced and cleaned regularly, and the kiln head should be cleaned regularly.

Do a good job in sanitation around the kiln and implement a closed working environment. The kiln furniture and supports are stacked neatly, and useless sundries are removed; the ground is piered after each shift to keep it clean and dust-free.