1.Spots
Copper spots: The spots are green, and the center of the green spot is darker in color. One or several exist independently, and the diameter is generally about Between 2-5㎜.
Iron spots: The spots are black or brown, unevenly distributed on the glaze surface, and the diameter is generally between 0.3-1.5mm.
*Cause:
(1) The blanks and materials contain or are mixed with copper, iron filings and other impurities.
(2) Copper or iron filings are mixed in due to mechanical wear during blank and glaze processing.
(3) The storage facilities for billet and glaze processing are not in good hygiene, and copper and iron filings are mixed in.
(4) When iron is removed from the blank and glaze slurry, the iron content appears to be completely removed because the screening equipment or process is out of control.
(5) When spraying glaze, the compressed air is not clean, bringing in impurities, and the smear blank is not clean.
(6) The surface of the semi-finished product is not blown clean before entering the kiln.
(7) The sulfur content of the fuel is too high.
*Solution
(1) Select and clean the raw materials, paying attention to removing the copper and iron impurity blocks.
(2) Improve the equipment and management of raw material stacking and processing sites, and strengthen the repair and maintenance of copper and iron equipment.
(3) Improve the iron removal and screening process of blanks and glaze slurries.
(4) Blow the surface of the semi-finished product before purification.
(5) Use fuel with low sulfur content or inject raw materials with high sulfur content for sulfur removal.
2. Brown eyes
Brown eyes refer to unglazed holes with a diameter of more than 1.5mm on the base body of the finished underglaze layer.
*Cause:
(1) The organic matter content in the raw materials is too high.
(2) Improper handling and storage of raw materials leads to a reduction in the density of the green body.
(3) Mud vacuum degassing is incomplete.
(4) If the moisture content of the mold is too large, the water absorption rate of the mud will decrease, which will reduce the density of the green body.
(5) The grouting speed is too fast during molding, and the surface of the green body is not wiped properly during rework.
(6) The dust on the bottom of the blank was not wiped clean when applying glaze.
*Solution:
(1) Selection of raw materials.
(2) Avoid overheating of the mud (generally below 25°C).
(3) Improve mud vacuum treatment facilities.
(4) Control the moisture content of the mold. If the mold is too wet, it should be stopped.
(5) Adjust the degree to control the grouting speed, and wipe the surface of the green body well during rework.
(6) The surface of the body should be wiped clean when applying glaze.
3. Dirty
Dirty glaze: foreign matter on the glaze surface with glaze.
Dirty blank: The foreign matter particles on the glaze surface are larger and have the same color as the blank.
Dirty dust: dust falls on the glaze, which turns dark red after firing, and feels rough and dense with small spots (0.3㎜)
*Cause:
(1) Impurities are mixed into the glaze slurry. The impurities fall on the glaze surface during glazing, and the surface of the body cannot be blown clean before glazing.
(2) Dirt and dust on the surface of semi-finished products were not blown away during loading.
(3) The kiln furniture is not cleaned cleanly or operated improperly during loading, causing particles or impurities from the kiln furniture to fall on the products.
(4) If the sagger or kiln furniture is damaged, debris may enter through the gaps during firing.
(5) During naked firing, dirt falls on the product from the kiln roof or air duct.
*Solution:
(1) Keep the glaze slurry storage area and facilities clean and the glaze application clean. The glaze slurry must be passed through a fine sieve before glazing to prevent overflowing.
(2) Blow out the products and kiln furniture when loading, and handle them with care.
(3) Replace damaged saggers and repair kiln doors promptly.
(4) Clean the kiln roof and air duct regularly.
(5) Improve workshop environmental sanitation. When marking, avoid color stains from contaminating the glaze.
4. Lack of glaze
The unglazed part that is larger than the brown eye and the body is not damaged.
* Cause:
(1) The glaze formula is improper and the base glaze is poorly bonded.
(2) The glaze particles are too fine and the glaze slurry is uneven.
(3) The high-temperature viscosity of the glaze is too high and the flowability is poor.
(4) Improper glaze additives.
(5) During the glaze slurry, the surface of the body is stained with oil, dust, etc.
(6) The body is overheated during glazing, and the glaze surface becomes damp after drying, resulting in the glaze layer being too thick.
(7) The glaze surface of the green body was knocked and dropped during transportation and loading.
*Solution:
(1) Adjust the glaze formula to make the base glaze bond well, or reduce the high wet viscosity of the glaze to increase fluidity.
(2) Adjust the type or dosage of additives.
(3) Adjust the degree to control the ball milling fineness of the glaze slurry and the thickness of the glaze layer.
(4) Before glazing, wipe the body clean with clean water and stick to a dry body for glazing.
(5) Appropriately lower the body temperature when applying glaze.
(6) Avoid collision with the product when transporting or loading the product.
5. Orange glaze
Orange glaze: The glaze lacks luster and looks like orange peel.
* Cause:
(1) The glaze formula is unreasonable and the firing range is narrow.
(2) The high-temperature viscosity of glaze is high, the surface tension is small, and the fluidity is poor.
(3) There are too many high-temperature volatiles in the billet, the high-temperature time is short, and the oxidation of organic matter is incomplete.
(4) The moisture content of the green body is high when entering the kiln, and the glaze layer is too thick.
(5) The density of the kiln is too high and the gas circulation is not smooth.
(6) The firing curve is unreasonable. When the glaze is melted, the temperature is opened too fast or the local temperature is too high, exceeding the maturity temperature of the glaze surface.
*Solution:
(1) Adjust the glaze formula and expand the firing range of the glaze.
(2) Adjust the slurry formula appropriately and appropriately reduce the amount of raw materials with high high-temperature volatile matter.
(3) Strictly control the moisture entering the kiln (generally below 1.5%)
(4) Appropriately reduce the density of kiln installation.
(5) Adjust and control the firing curve, reduce the temperature difference in the kiln, and properly moisturize the high-temperature stage.
6. Dirty color
Dirty glaze: The glaze surface shows dense or scattered brown spots of inconsistent sizes and the glaze melts into one and is smooth.
Mud traces: Locally striped or curved black or earthy brown traces appear on the surface. They mostly appear on the green body above the grouting mold or around the grouting port.
*Cause:
glaze dirty
(1) The raw material contains a lot of black organic matter, which is suspended in the slurry and attached to the surface of the body after grouting. It will show a different color after burning.
(2) Oil or other impurities are mixed into the glaze slurry.
(3) Improper labeling operation will cause the color of the trademark to contaminate other parts.
(4) Dirt from your hands sticks to the blank when loading.
(5) The fuel atomization is not good during burning, and oil drops fall on the green body.
Mud traces: The fluidity of mud is poor, the grouting speed is fast, and the mud leaves traces on the mold wall.
The finished product has ridges in some parts or the bonding technology is poor, and there are traces in the bonded parts.
The mold is not clean and the mold gap is too large.
* Solution:
(1) Select the raw materials, remove black organic matter, grind the mud through a fine screen, and adjust the fluidity of the mud.
(2) Improve the environment during glaze processing, storage and use. The mud glaze slurry pool should be covered and sealed tightly to keep the environment clean.
(3) Frequently clean the oil-water separator of the compressed air pipeline, and regularly clean the inner layer of the preheating zone vault; the flame baffle must be well sealed.
(4) Carefully clean the mold before grouting.
(5) Be careful when labeling and loading to avoid abnormal color contamination.
(6) Improve the nozzle or oil supply pressure of the kiln to ensure good fuel atomization.
7. Ripple
Ripple refers to the glaze cover of the product being corrugated or fish scale-like, with poor glaze gloss and yellowing of the porcelain.
*Cause:
(1) The glaze formula is improper, has high viscosity at high temperatures and poor fluidity.
(2) The additives of the glaze slurry are inappropriate or the viscosity of the glaze slurry is too high.
(3) Insufficient pressure when spraying glaze and poor glaze atomization, causing the glaze surface to appear dotted.
(4) The glaze spraying operation is poor and the thickness of the glaze layer is uneven.
(5) The firing temperature is low.
*Solution:
(1) Adjust the glaze formula to ensure good fluidity.
(2) Adjust the type or amount of glaze slurry additives to improve the viscosity of the glaze slurry.
(3) Adjust the degree to control the glaze spray pressure and improve the atomization power of the glaze spray.
(4) Adjust the degree to control the firing curve so that the surface is fully melted.
8. Blank foam
Foaming: There are tiny pits on the glaze surface of the product, with no unusual color at the bottom of the pits and bulges around the pits.
Bubble injection: The surface of the double-sided slurry suction part of the product presents several large convex bubbles of different sizes, and the inner surface of the bubbles is relatively smooth.
Firing bubbles: convex bubbles caused by excessive firing temperature. The inner surface of the bubbles is rough.
Repair adhesive bubbles: small bubbles that are raised only at the bonding part of the product.
*Cause:
(1) The initial melting temperature of the glaze is too low, so that the decomposition gas of the green body cannot be discharged.
(2) The billet contains too many raw materials that decompose at high temperature.
(3) Wipe the talc powder used for wiping the mold cleanly and adhere to the surface of the blank.
(4) The grouting speed is too fast during molding, which makes the air removal difficult and the grouting is not released in time, resulting in empty grout. Insufficient time for double-sided blowing or uneven thickness of the green body.
(5) The bonding mud is too thick, the air contained in it is not discharged or the bonding mud is mixed with impurities.
(6) The bonding mud overflows and cannot be scraped clean, forming floating slurry.
(7) The firing temperature is too high and the gasification is violent, causing convex bubbles of varying sizes to be formed on the surface of the green body.
*Solution:
(1) Adjust the glaze formula to increase the melting temperature of the glaze.
(2) Adjust the glaze formula to reduce the content of high-temperature decomposition raw materials in the blank.
(3) Clean the mold before grouting.
(4) Improve and control the grouting speed, ensure that the air holes in the mold are unobstructed, and replenish grout in time when empty grout occurs.
(5) Adjust the consistency of the bonding slurry (repeatedly adjust and discharge air) and avoid the mixing of impurities.
(6) After the green body is bonded, the remaining slurry must be scraped off and smoothed.
(7) When applying glaze, the dirt on the surface of the body should be removed.
(8) Adjust the degree to control the firing temperature to prevent local high temperatures.
9. Crack
Molding cracks: cracks in the bonding parts, small cracks in the base oil and holes, and cracks caused by blocked air holes. Cracks at the junction of single and double surfaces.
Dry cracking: The cross section of the crack has wrinkles.
Installation bumps and cracks: There are bruises on the glaze at the cracks or traces of shrinkage of the support pads.
The section is unglazed and the cracks are open.
The cracks at the kiln support pad installation parts are crescent-shaped or chicken-foot-shaped.
Fengjing crack: The cracks are extremely fine and penetrate the blank and glaze. The cross section is smooth and the edges are sharp.
Firing cracks: The cracks are larger and penetrate the blank and glaze. The cracked section is more detailed and wrinkle-free. Horizontal fractures and vertical cracks are common.
Impurity cracks: The cracks are dense and short and radial.
*Cause:
(1) The material contains plastic raw materials or excessive free quartz to cause stress.
(2) The slurry is improperly screened and overflow occurs, causing quartz, limestone and other particles to be mixed into the slurry.
(3) The mud storage time is insufficient.
(4) The mold wiping method is improper, the mold is too dry or too wet, and the moisture is uneven.
(5) Improper slurry placement before demoulding will result in too much slurry remaining at the interface within the green body, causing cracks at the inner interface during drying.
(6) Insufficient air pressure and time will cause the single-sided slurry to dry out and crack.
(7) Consolidate air pressure and air leakage to make the area around the stomata clean.
(8) Improper drilling tools or methods, and improper repairs.
(9) The position of the stomata is improperly arranged.
(10) There is no air pressure consolidation in the single-sided fasting position.
(11) The wet blank dries too quickly and shrinks unevenly in various parts.
(12) During bonding, the moisture in each part is inconsistent, the bonding slurry is not processed properly, and the bonding is not tight.
(13) Semi-finished products are shocked or bruised during transportation and loading.
(14) The semi-finished product has poor supporting pads, causing excessive firing shrinkage stress.
(15) The moisture entering the kiln is too high, and the kiln car collides during operation, causing the product to be vibrated and bruised.
(16) The firing system is unreasonable, the operation is improper, the temperature rises too fast or the temperature drops improperly.
*Solution:
(1) Adjust the billet formula and reduce the content of plastic raw materials and free quartz (plastic raw materials are generally less than 30%).
(2) Improve mud preparation and obsolete systems, improve facilities and management, and prevent the mixing of impurities.
(3) Ensure that mud performance meets technical requirements.
(4) Control the mold moisture well and make the mold moisture even when brushing the mold.
(5) Adjust the consolidation pressure and consolidation time.
(6) The air pressure consolidation port should be sealed with mud to prevent air leakage.
(7) Improve, adjust and consolidate the Qi position.
(8) Improve the mold so that the air pressure fills the emptying position of the single-sided pulp.
(9) Clear the remaining pulp before demoulding.
(10) When drilling holes, the knife or hole opener should be sharp, and smear water around the hole.
(11) Improve the bonding slurry and make the moisture content of each bonded part consistent.
(12) Adjust the degree to control the drying speed of the green body.
(13) Be careful when loading semi-finished products and handle them with care.
(14) Improve the contact between semi-finished products and kiln furniture (some quartz powder can be sprinkled between semi-finished products and kiln furniture to reduce stress during the firing process)
(15) Strictly control the moisture entering the kiln, and carefully control the center of gravity of the blank when loading the kiln.
(16) Adjust and control the firing curve, reduce the upper and lower temperature difference, and control cooling.
10. Deformation
Deformation: refers to the inconsistent shape of the product after firing, which can manifest in various forms.
*Cause:
(1) The formula is unreasonable, too much plastic is used in the blank, and the proportion of silicon, aluminum and flux is inappropriate.
(2) The particles of the mud are not fine, the 10,000-hole sieve is less than 1%, and the water content of the mud is too high.
(3) Poor mold wiping method, unreasonable demoulding time or the mold is too wet, causing the thickness of the green body to be screened or the supporting plate to be deformed.
(4) The air blowing is uneven during demoulding, and the demoulding is ineffective.
(5) The green body is too soft when drilling.
(6) The pallet or kiln furniture holding the blank is deformed, and the deformed glaze blank is mistakenly put into the kiln when loading.
(7) When loading the blank, the blank is placed at an inappropriate angle and the center of gravity is unstable.
(8) The sintering temperature is higher than the sintering temperature of the product, and the product with too much liquid phase cannot bear its own weight and deforms.
11. Smoke
When part or all of the product shows different colors such as blue-black, colorful yellow, muddy red, etc., it should be distinguished from mud stains.
If smoke appears at the bottom of the product, consider it related to the installation of kiln support pads.
*Cause:
(1) The density of billet loading is too high, resulting in poor ventilation in the kiln.
(2) The green body has a lot of moisture when entering the kiln, and the organic matter in the green body cannot be completely oxidized and eliminated, causing carbon mud to accumulate in the green body.
(3) The kiln furniture contains a large amount of moisture, and the temperature opening speed of the preheat zone is improperly controlled, which affects the oxidation of the green body.
(4) There is insufficient oxidation in the kiln. In the high-temperature reduction state, sulfides and carbides cannot be integrated with the glaze, making the glaze yellow.
12. Collision
*Cause:
(1) The semi-finished product is bruised during transportation, storage or filling.
After being fired in the kiln, it appears to be cracked or partially incomplete.
The remaining porcelain section is glaze-shaped and is bumpy to the blank.
(2) The product was knocked out of the kiln or during transportation.
The defective cross-section is fine and dull, with no glaze absorption phenomenon, and the edges of the glaze layer are sharp, indicating that it was bumped out of the kiln.
The semi-finished product was bumped when it was installed in the kiln, and there were scratches on the glaze surface of the bumped part, indicating that it was installed.
13. Color difference
1. Production reasons:
(1) The composition of raw materials fluctuates, and the water content of color-differentiated ions changes.
(2) Inaccurate weighing of ingredients and improper operation of the ingredient system.
(3) The control of mud specific gravity, moisture, viscosity and screen residue is unstable.
(4) Careless molding operation.
(5) The performance of the glaze slurry is unstable, the raw materials are not selected, and the glaze thickness is different.
(6) The maximum firing is improperly controlled.
Changes in the firing cycle and fluctuations in kiln furniture cause changes in the preheat zone, firing zone, and cooling zone, resulting in large kiln temperature differences.
14. Molten Cave
* Cause:
(1) The grouting molding operation was careless, and gypsum residues were attached to the blank and were not removed during repair.
After firing, the surface of the product was earthy brown, with melting spots and fusible holes.
(2) The grouting operation was careless, and sawdust, cloth, sponge slag, etc. were adhered to the blank, causing various fiber-like melting holes on the surface of the fired product without glaze coverage.
15. Failed flushing
*Cause:
(1) During molding, the angle at which the flushing holes are made does not comply with regulations.
(2) The location of the waterway bonding device is improper.
(3) The water channel is cracked and leaking.
(4) Insufficient water consumption or improper installation method.
