What is the plain firing process for raw ceramic mugs?

Xinxiang Ceramic Mug Manufacturer,  in the process of making ceramic mugs, raw materials made of clay after molding, drying, billeting and other processes, before the billet glaze. Some of the raw ceramic mugs need “plain firing” process, the rest is directly glazed. So, what is the plain firing in the end? What kind of situation needs to burn process? In fact, vegetarian firing is a kind of early firing, it has an important role in improving the quality of ceramic mugs, of course, this process will also increase the ceramic cup in the production of links in the cost and time.

1. What is vegetarian firing?

Vegetarian firing is a ceramic mug billet in the dry, repair billet, before the formal glaze firing, a low-temperature firing (usually 700-900 ℃), the mud “half-burned”. Burned blanks as crisp and hard as a cookie, but not yet turned into porcelain.

2. What needs to be fired?

2.1. 4 kinds of situations that need to be fired:

2.1.1. to do complex decoration: such as hand-painted patterns, underglaze color, underglaze appliqué (plain firing after the billet water absorption, underglaze color is easy to color without losing color).

2.1.2. the billet is too thin or complex shape: such as thin tire mug, shaped mugs (high strength after plain firing, not easy to break when handling and glazing).

2.1.3. with special glaze: such as matte glaze (matte glaze liquidity is poor, direct glaze on the blank is easy due to uneven absorption of water on the blank resulting in mottled glaze. Plain firing after billet water absorption stabilization, glaze distribution is more uniform.) The crystallized glaze (crystallized glaze firing temperature is high 1320 ℃, and need to keep warm for a long time. After firing, the body is strong enough to withstand the thermal stress of glaze firing, avoiding cracking.) .

2.1.4. Export or high-end products: Plain firing can expose the defects (such as dark cracks) of the blank body in advance and reduce the final firing scrap rate.

2.2. There are 3 kinds of cases that do not need to be burnt:

2.2.1. Ordinary mugs with large quantity and low price: direct raw glaze, saving time and money.

2.2.2. high strength clay: such as the addition of clinker (crushed porcelain powder) of coarse pottery mug, itself is not fragile. 3.

2.2.3. glaze is simple: such as monochrome glaze, direct spray glaze can also be attached.

3. The advantages and disadvantages of plain firing

3.1. The advantages of raw blanks after plain firing are:

3.1.1. the billet becomes hard, the handling is not fragile.

3.1.2. more uniform glaze, bright color.

c. early detection of cracking, deformation defects.

3.2. Disadvantages are:

3.2.1. firing more than once, time-consuming and gas-consuming.

3.2.2. vegetarian firing occupies kiln space, lower output.

3.2.3. Improper operation may overfire (glaze can't stick after porcelainizing the blank).

4. Vegetarian firing operation steps

4.1. Load the kiln

- How to set up: mugs face down, at least 2 finger width apart (to prevent sticking).

- Pad what: the bottom of the mug sprinkled with a layer of alumina powder or pad refractory sand (to prevent sticking to the kiln board).

4.2. Firing temperature

- Ordinary clay: Fired to 800-850 ℃ (the body becomes light red, knocking sound like tile).

- High-white porcelain clay: fired to 900-950 ℃ (the body of the white, knocking sound like tiles).

4.3. How long to burn?

- Warming up: from room temperature to the target temperature in about 5-6 hours (150℃ per hour).

- Holding time: 30 minutes after reaching the temperature (to let the heat penetrate into the center of the billet). Cooling: Turn off the kiln to cool down naturally.

- Cooling: Turn off the kiln and let it cool down naturally to below 100℃ before opening the door (rapid cooling will cause cracks!). Cooling: Turn off the kiln and let it cool down naturally to below 100℃ before opening the door (rapid cooling will crack!)

5. Precautions

5.1. Inaccurate temperature will turn over:

- Must use thermocouples to measure the temperature, can not rely on experience to see the color of the flame!

- Temperature is too low (<700 ℃): billet strength is not enough, a touch will be broken.

- Temperature is too high (> 950 ℃): body porcelain, glaze can not hang. 2.

5.2. Check after firing:

- Drip test: drop a drop of water at the bottom of the mug, within 5 seconds to seep in is considered qualified (water absorption rate of 12% -15%).

- Failed products: cracked sound muffled, no water seepage directly scrapped. 3.

5.3. Storage of plain billet:

- Put in a dry box (humidity <40%), otherwise the glaze will blister after absorbing moisture.

In summary, plain firing is a ceramic mug in the production process to improve the quality of the process. It can improve the quality of the raw ceramic mugs, in the later glazing, hand-painting, paste underglaze flower paper and other processes, is essential. Simply put, high-end ceramic mugs often need this plain firing process. The ceramic mugs made in this way are more environmentally friendly and exquisite. Of course, the vegetal firing process will increase the cost and time of production, which means that when customizing ceramic mugs, the price of such ceramic mugs is also higher. China ceramic mug factory thinks this kind of ceramic mugs after the plain firing process is more suitable for coffee shops, branded gifts and so on, which have higher requirements for quality.

Drying and trimming process of ceramic mug clay blanks

Xin xiang custom ceramic mug factory, the production of ceramic coffee mugs in the selection of good raw materials, raw materials will be mixed and processed, after dewatering and practicing clay. Then came to the introduction of the “billet molding” link. At this time, the prototype of the ceramic mug was formed, but not perfect, how to make the mud blank more exquisite? Then, drying and trimming the two links, is the next important step. Ceramic mugs of the role of the drying process is: to reduce the moisture in the mud, in order to prevent the firing process in the ceramic mugs cracked; repair is to make the ceramic mug size, weight and other parameters in line with customer demand, and will be ceramic mugs imperfect place for “beautification”. Therefore, these two links are very important, then how to operate, and what are the precautions? Please listen to my slow talk:

1. Drying operation guide

Purpose: to remove moisture from the body of the blank, to prevent the kiln firing burst.

1.1. Preparation before drying

- Placement of the blanks:

- Place the wet blanks of ceramic mugs (moisture content of 18%-22%) on a hollowed-out plastic tray, with the mouth of the mug facing downwards, to avoid water accumulation inside the mug.

- The blanks should be spaced ≥ 5cm apart to ensure even air circulation.

- Environmental control:

- Natural shade drying: choose a ventilated workshop without direct sunlight, humidity 60%-70% (can be monitored by hanging hygrometer).

- Drying room: preheat to 30℃, humidity set at 50% (assisted by industrial dehumidifier).

1.2 Practical operation of drying process

a. Initial drying (0-12 hours):

- Focus on removing surface moisture and observe every hour whether the billet is deformed.

- Natural drying: Close some of the vents at night to prevent a sudden drop in temperature.

- Drying room: Increase the temperature by 2℃ every hour to 40℃ and keep it stable.

b. Intermediate drying (12-24 hours):

- Turning the blanks: Place the mugs on their sides to avoid one-sided shrinkage too fast resulting in crooked mugs.

- Check the seam line: if the joint between the handle and the mug is white (difference in moisture content), gently rub the transition area with a damp sponge.

c. Final drying (24-48 hours):

- Moisture content test:

- Feeling method: touch the bottom of the cup without wet and cold feeling, fingertip flick cup wall issued a crisp “ding” sound.

- Instrumentation: infrared moisture meter detection (sampling the center of the bottom of the mug, reading ≤ 2%).

- Correction of deformation: If the mouth of the mug is slightly elliptical, it can be adjusted with the palm of the hand while the blank is slightly wet (moisture content of 5%).

1.3. Precautions

- Anti-cracking:

- Avoid direct fan blowing on the blank, give priority to natural convection.

- Thick parts of the mug (such as the root of the handle) can be wrapped with a wet cloth to slow down the drying process.

Anti-pollution: drying room filter is cleaned weekly to prevent dust from adhering to the blank.

2. Operation Guidelines for Trimming

Purpose: trimming the shape of the blank, remove burrs and seam lines.

2.1. Tool Preparation

- Wet trimming tools:

- Stainless steel scraper (blade width 10mm, thickness 0.5mm) - to cut off the parting line.

- Natural sponge (aperture 1-2mm) - to wet the joints to prevent chipping.

- Dry repair tools:

- Carbon steel trimming knife (curved tip) - trimming the curvature of the mug.

- Sandpaper (120 mesh coarse grinding, 400 mesh fine grinding) - handle polishing.

- Vacuum cleaner - real-time dust cleanup.

2.2 Wet dressing procedure (moisture content 8-12%)

a. Remove the mold line:

- Left hand fixed mug, right hand holding scraper and the wall of the cup at an angle of 30 °, along the mold line lightly scraping, strength to “see the mud flying out, not hurt the blank” prevail.

- Key point: the scraping direction is the same as the opening and closing direction of the mold (usually vertical direction).

b. Handle joints:

- Wet the joints with a sponge dipped in water, and cut the excess clay with a spatula at an angle of 45°, so as to form a smooth transition (the difference in thickness is ≤0.3mm). c. Flattening the mouth of the cup.

c. Flatten the mouth of the mug:

- Invert the mouth of the mug on the rotating disk, scraper horizontal fit the edge of the mug, rotate at a constant speed to remove burrs.

2.3 Dry repair operation steps (moisture content ≤ 2%)

a. Finishing the mouth of the mug:

- Use 400 mesh sandpaper wrapped in wood, along the inner wall of the mug clockwise sanding, to eliminate the “knife cutting edges.

- Detection standard: finger scratching the mouth of the mug without scratching, no reflective burrs under the light.

b. Foot trimming:

- Cut the bottom of the mug vertically with a carving knife to a depth of 2-3mm, forming a 45° chamfer (to prevent sticking to the kiln plate after firing).

- Sandpaper the edges of the foot until rounded (roughness Ra ≤ 6.3μm).

c. Handle polishing:

- Use toothbrush dipped in water to remove dust from the grooves of the handles, and sandpaper with 120 grit sandpaper along the grain until there is no graininess.

2.4 Quality control and problem handling

- Repair common defects:

- Fine cracks: Fill with brush dipped in mud, and partially sand after drying.

- Uneven seams: fill with mud (mud:water=3:1), re-scrape flat.

- Full inspection standard:

- Dimensional tolerance: tolerance of mug diameter ≤±0.8mm (10% sampling with vernier calipers).

- Weight deviation: weight difference of the same batch of mugs ≤ 3% (weighed by electronic scale).

3. Cleaning and quality inspection

Purpose: to ensure that the blanks are dust-free and free of defects, in preparation for glazing.

3.1. Dust removal:

- Use compressed air to blow the surface floating dust, or use a soft brush to sweep lightly.

3.2. Water immersion test:

- Immerse the blank in water for 2-3 seconds and observe whether there are bubbles (if there are, there are dark cracks).

3.3. Full inspection standard:

- Appearance: no cracks, bubbles, deformation;

- Dimension: error of mug diameter and height ≤±1.5%;

- Strength: no collapse of the mug wall when pressed by fingers.

3.4. Points of Attention:

- Non-conforming products need to be crushed and returned to the clay system (add proportion ≤ 5%);

- After the quality control of the blanks need to be glazed within 24 hours to avoid moisture absorption.

The drying process of ceramic mugs is a key link that affects the yield. Some ceramic mugs will blow up when pouring hot coffee, besides the raw material problem, the biggest problem is the drying process. The manual trimming link tests the technician's responsibility and proficiency. China Ceramic Mug Factory has introduced electronic equipment, including electronically controlled drying room and automatic trimming assembly line (for details, please check the video released by our factory). The drying process is strictly controlled by electronic equipment and the efficiency and consistency of the trimming process has been improved. If you need custom ceramic mugs, then please find a more professional, attentive and advanced ceramic factory.

Ceramic mug raw materials - clay preparation process

Xin xiang ceramic mug manufacturer, in the previous article, China Ceramic Mug Manufacturers introduced, the three basic raw materials for ceramic mugs. The three basic raw materials after processing, became the clay material for making ceramic mugs. Mud preparation is the basic link of ceramic production, directly affecting the stability of subsequent molding, drying and firing. For the compression molding of mugs, the clay's: plasticity, moisture content, particle uniformity and other indicators are particularly critical. This has gone through what process, different links in the quality control for the later ceramic mug quality has what impact? Well, I would like to know more about customized ceramic mug knowledge buyers, one by one to answer.

1, the composition and function of ceramic clay

a. Kaolin, bentonite, ball clay

Their main role is: to provide plasticity, so that the clay is easy to mold and maintain the shape.

b. Quartz sand, calcined kaolin

Their main functions are: to reduce drying shrinkage, enhance the strength of the blank and prevent deformation.

c.Feldspar, nepheline orthoclase

Their main role is: to reduce the firing temperature (1200-1300 ℃), promote the formation of glass phase, enhance the degree of porcelain.

d. CMC (carboxymethyl cellulose), sodium humate

Their main role is: to regulate the liquidity of the mud, enhance the strength of wet blanks, to prevent cracking.

2. Key indicators of clay performance

Plasticity: the ability of clay to deform and not crack under external force, determined by the proportion of plastic raw materials and particle fineness.

Water content: 18%-22% water content for billet molding (30%-35% for slurry molding).

Particle gradation: coarse and fine particles are reasonably matched to reduce porosity (ideal particle size: <0.1mm accounts for 60%-70%).

Drying shrinkage: generally controlled at 5% -8%, too high easily lead to cracking.

3. Formulation of clay

Kaolin (45%), ball clay (25%), quartz (15%), feldspar (12%), CMC (1.5%), water (adjusted to the total weight of 22%)

4.Process of making mud

Firstly, pre-treat the raw materials, then mix the ingredients, then sieve and remove the iron, and finally dewater the mud.

4.1 Pre-treatment of raw materials

a. Coarse crushing:

Large raw materials (such as quartzite, kaolin) with jaw crusher crushed to particle size ≤ 5mm.

b. Removal of impurities:

Magnetic separator to remove iron chips (to avoid black spots after firing);

Water washing to remove sediment and organic matter (soaked and precipitated to remove impurities).

c.Aging:

Mixed raw materials are stacked in a shady and humid environment, covered with wet cloth aging for 3-7 days to promote uniform penetration of moisture.

4.2. Ingredients and mixing

a. Weighing and proportioning: weigh each raw material accurately according to the formula (error ± 1%), for example: kaolin 45kg + ball clay 25kg + quartz 15kg + feldspar 12kg + CMC 1.5kg + water (adjusted to 22% of the total weight)

b. Dry mixing: put the raw materials into the wheel mill, low speed (20-30rpm) mixing 20-30 minutes until the color is uniform.

c.Wet mixing: add water and transfer to mixing tank, mix at high speed for 1-2 hours to form a fluid slurry without lumps.

4.3. Sieving and iron removal

a. Sieving: pour the slurry into 80-120 mesh vibrating screen to remove coarse particles that are not crushed (sieve residue ≤ 0.5%).

b. Iron removal: the slurry flows through the electromagnetic iron remover (magnetic field strength ≥ 1.2T), circulating 2-3 times to no iron residue.

4.4 Dewatering and mud training

a. Dewatering:

Mud is pumped into filter press, pressurized to 0.8-1MPa, and pressed into mud cake with 25%-30% water content.

Or use vacuum extruder to dewater directly to the target water content (18%-22%).

b. Clay practicing:

Put the mud into the vacuum mud trainer and repeatedly squeeze 3-4 times to expel air bubbles (vacuum degree ≥ -0.095MPa).

After practicing the mud cut into 10-15cm diameter cylindrical pieces of mud, sealed and kept in reserve.

In summary, this is the whole process of making clay for ceramic mugs. In this process, the quality of raw materials, the control of each link, directly constitute the quality of ceramic mug. For example: some ceramic mugs have black spots, this is the clay “in addition to iron” link, quality control is not enough reason. Also, ceramic mug cracks, many quality problems, from the source. China Ceramic Mug Manufacturer, has been strictly control the raw materials and production of each link, to provide high quality ceramic mug.