Xinxiang Ceramic Mug Manufacturer, pinhole is a ceramic glaze on the emergence of tiny holes (diameter usually 0.1-1mm), pinhole is the essence of the firing process gas can not be discharged from the glaze layer in a timely manner due to the specific causes can be traced back to the 5 major links.

1. What is a ceramic mug pinhole

Pinhole is a ceramic glaze on the emergence of tiny holes (diameter usually 0.1-1mm), shaped like a needle prick marks, when the seriousness of the dense honeycomb. According to the stage of occurrence can be divided into two categories: open air holes: through the glaze layer directly to the billet, the cross-section was funnel-shaped, easy to hide dirt; closed air holes: the glaze layer is not penetrated, the surface only left pits, affecting the appearance of gloss. Pinhole, as in the baking of cakes, the internal air bubbles are not discharged, the surface of the formation of collapsed pits.

2. pinhole is the essence of the firing process gas can not be discharged from the glaze layer in a timely manner due to the specific causes can be traced back to the 5 major links:

2.1. Raw material impurities generated by the gas
Pyrite (FeS₂) in the blank or humus in the clay, decompose at 300-800 ℃ to release SO₂, CO₂ gas. The use of cheap kaolin with sulfur content > 0.1%, the pinhole rate after firing surges to more than 20%.

2.2. Defects in glaze preparation
When the grinding fineness of the glaze is not enough, the glaze particles>30μm, the gas channel is formed in the gap between the particles, resulting in the glaze containing gas. Glaze paste contains air bubbles: excessive mixing introduces air, no defoamer (such as n-butanol) is added, and air holes are left after the glaze layer is dried. The glaze should be sieved through a 400 mesh sieve (pore size 38μm) during the screening stage to reduce pinholes by 60%. Glaze paste in the mixing process to add defoamer, not stirred too much, and storage should also refer to the previously described standards for storage.

2.3 Firing too quickly
Ceramic mug billet firing in the kiln, water evaporation period (room temperature ~ 300 ℃), if the rate of heating > 150 ℃ / h, then the ceramic mug billet inside the steam will break through the glaze layer to form pinholes. In the decomposition and oxidation period (300-900 ℃), the rate of heating > 200 ℃ / h, sulfur or carbide will decompose gas, the formation of pinholes.

2.4 Lack of heat preservation
If a 30-minute holding section is not set up for the raw ceramic mug during the firing heating phase, specifically before 900°C, gases will remain in the glaze and form pinholes.

2.5. Excessive air pressure in the kiln
Inside the kiln, when the exhaust fan power is insufficient, resulting in air pressure in the kiln > 10Pa, it will prevent the escape of gas, resulting in the ceramic mug gas can not be discharged normally, forming pinholes.

3. The formation of pinholes is mainly due to the above five reasons. So, how can ceramic mug factory improve in order to reduce the chances of pinholes in ceramic mugs?

3.1. raw material pretreatment
Since the sulfur in the clay raw materials can lead to the emergence of pinholes, then in the raw material preparation stage, we need to target the reduction of sulfur content in the clay, to control it within 0.1%. Specific methods include, washing and flotation of kaolin (removal of sulfides), or adding 1% barium carbonate (BaCO₃) high-temperature sulfur fixation; billet sealed aging for more than 15 days to promote the decomposition of organic matter, reducing the amount of fired gas production.

3.2. Glaze optimization
The grinding degree of the glaze is not enough particle gap is too large, it will be easy to make the air mixed into it, resulting in pinholes. Then, we have to glaze raw materials in the screening stage over 400 mesh sieve to reduce large particles. In the raw material grinding stage, the ball mill is used to grind to the 10,000-hole sieve residue <0.05%. In addition, add 0.5% magnesium oxide (MgO) to expand the melting range of the glaze and extend the gas discharge time. In the glaze slurry storage stage, 5% zirconium silicate (ZrSiO₄) can be added to improve the glaze high-temperature viscosity and close the external gas.

3.3. Firing temperature control
There are several temperature nodes mentioned above in the process of raising the raw billet from room temperature to 900°C. One is room temperature-300℃, to control the speed of heating, in the season that is not winter, to control the heating time should not be less than 2 hours. In 300-900 ℃, to control the time should not be less than 3 hours. In addition, every 100 ℃, to set aside 5 minutes of insulation period. Used to allow the ceramic mug billet in the body of the organic matter or sulfide, can be fully decomposed, and there is enough time for gas discharge. 900-1250 ℃, need 4 hours. Holding is also necessary during the vitrification stage of the glaze.

3.4. Control of kiln air pressure
The kiln needs to have an oxidizing flame and a reducing flame during firing. When ceramic mugs are fired, their content varies somewhat depending on the stage. The overall principle is to be a temperature section of a temperature section of the firing, in the firing of air pressure should be controlled at negative pressure -5 ~ 0Pa, the most appropriate. Can make the fired ceramic mug more stable, less pinhole defects.

In summary, the formation of pinholes in ceramic mugs, the root cause is that the gas is not discharged from the raw billet. The formation of pinholes is twofold, one is the raw materials, including clay and glaze raw materials, and the second is improper control of the firing process. Pinholes in ceramic mugs can not be avoided, Xinxiang Ceramic Mug Factory, through strict control of the quality of raw materials and improve the precision of firing control, to minimize the chances of pinholes, to provide customers with high quality and stability of ceramic mugs.