Ceramic mug crack causes and prevention methods
Xin xiang Ceramic Mug Manufacturer, we've had ceramic mug cracks appear in previous articles. Originally in “16 Flaws in the Making of Ceramic Mugs”, ceramic mug cracks are a type of defect in ceramic mugs. In “How to judge the quality of ceramic mugs”, the first criterion for judging the quality of ceramic mugs is cracks. Ceramic mugs produce cracks according to the overall division, can be divided into production link cracks and transportation damage. Transportation damage, is common, but also the easiest to understand. Because of the transportation process of bumping or violent transportation, resulting in ceramic coffee mugs produced broken or cracked. In the previous article we introduced how to avoid ceramic mugs transportation damage, if you are concerned about the transportation link, please refer to: “How to pack the ceramic mug so that it will not be damaged?”. So, what kinds of cracks are included in the production process? In fact, the appearance of cracks in the production of ceramic mugs throughout the production process. Including: raw material formulation, plastic molding, drying and trimming, glazing and firing. Next, Xinxiang ceramic factory for you to explain one by one.
2.1. Penetrating Cracks (Cracking)
Manifestation: Cracks penetrate through the wall of the mug, completely splitting from the inner wall to the outer wall. Usually a dull cracking sound rather than a crisp porcelain sound is produced when tapping with the hand (this is also the case with ceramic mugs that have cracked due to impacts during transportation).
Characteristics: This is the most serious, can not be repaired defects, ceramic mug directly scrapped, can not be used normally.
2.2. Hairline Cracks (Shock Cracks)
Performance: Cracks as fine as hairline, sometimes difficult to detect with the naked eye immediately after kilning, but will bleed when tested with ink or pigment.
Characteristics: This type of cracking usually becomes visible late in the firing cooling period or after kiln discharge, and is a typical manifestation of uneven internal stress release.
2.3. Cracking at the Mouth Rim (Mouth Blowout)
Presentation: Cracks occurring at the rim of the mouth of the mug, sometimes in a radial pattern.
Characteristics: the mouth of the mug is the most varied shape and the thinnest part of the mug, which is also the part where the stress is most easily concentrated.
2.4 Cracking of the foot (bottom cracking)
Performance: Cracks occurring at the combination of the bottom and the body of the mug, or at the edge of the foot rim.
Characteristics: the bottom of the mug is the thickest, drying and firing internal and external contraction inconsistency, resulting in pulling crack.
2.5. Glaze cracks (cracks)
Performance: only the surface of the glaze layer appeared network cracks, while the body itself did not crack. In the previous article “Reasons for custom ceramic mugs cracking”, we talked about the specific reasons and solutions for glaze cracking.
Characteristics: This is usually caused by the “coefficient of expansion of the glaze being greater than that of the blank”. When cooling, the glaze shrinks faster than the body and is pulled apart. Although sometimes used as an artistic effect (as in the case of kiln flakes), in the case of mugs, it is a defect that affects hygiene and longevity.
3.1. Raw material factors (clay “innate nature”)
Clay is the bone and blood of the ceramic mug, clay is the “foundation” of the ceramic mug, the quality of the clay is critical. If the foundation is not good, or the quality of the foundation is too poor, it is easy to cause the ceramic mug cracked in the later production. Clay in the previous article we have explained, clay is mainly composed of: kaolin, feldspar and quartz, plus a part of micro chat elements, such as: ball clay, CMC, etc., composition. These raw materials have to go through a number of processes, crushing, grinding, removing impurities, mixing, iron removal, dehydration before practicing mud. In the previous article “Ceramic mug raw materials - clay preparation process”, we have explained the specific clay preparation process. During the clay preparation process, if the recipe is not correct, the mug will crack. For example, too high a proportion of malleable raw materials such as kaolin or ball clay will cause the clay to be too “soft”, which in turn will result in a large shrinkage of the biscuit in the drying process, making it prone to deformation and cracking. If the proportion of quartz or clinker, which are barren raw materials, is too small, the clay will lack of support, and will also be easy to deform or crack in the drying process. If the mix of raw materials is not uniform, the contraction ratio of the clay is not consistent, and cracking will also occur during drying.
All of these are the clay in the production process is likely to lead to ceramic mug cracking reasons. In fact, after the completion of clay production, there is another link easy to lead to ceramic mug cracking, this link is often many ceramic mug production factory ignored. It is the clay aging, our industry commonly known as “boring material”. Clay aging, its main form of expression is to practice good clay, placed for a period of time. This link seems to be very simple and insignificant, but in fact it is very important. Lack of aging clay is like an army with insufficient training and poor internal communication, which will be easily dispersed once it goes into battle (into molding and firing). The purpose of aging is to create an elite force that will bring out the best in the clay. We will write an article about this later.
In the process of practicing clay, even if each link is accurate, precisely ignore the aging process of clay. Ceramic mugs made of such clay are also very prone to cracking during the drying and firing process.
Of course, there are other factors, such as air bubbles in the clay and uneven humidity, which can also cause the mugs to crack.
3.2. Molding and trimming factors (the production of the “acquired defects”)
Ceramic mug molding, we have talked about before, mainly is the pressure blank "Ceramic mug molding production process details" and grouting “Customized Ceramic Coffee Mugs - Grouting Process Explained”. Ceramic mugs come in a variety of shapes, depending on the shape of the mug required by the mug's purchaser. Ceramic mugs tend to be thinner at the mouth and thicker at the bottom. If not handled properly in the drying process, raw ceramic mugs are prone to cracking when dehydrated.
Accessories other than the body of the ceramic mug, such as the handle, are glued on. When bonding the handle, if the difference between the moisture content of the mug and the handle is too large, or the concentration of the joining mud is not suitable, or when bonding the handle is not standardized in terms of pressure and scraping operations, it will leave gaps, resulting in cracking later.
3.3. drying factors (moisture “gentle goodbye”)
artificial cause of ceramic mug cracking is relatively small, many cases of ceramic mug cracking is in the drying process. In the previous article “Drying and trimming process of ceramic mug clay blanks” we explained this in detail. Ceramic mug billet drying if the temperature is too high (for example, high temperature in summer), billet surface water will evaporate quickly and violently contracted, billet internal moisture has not come to release, will cause the hard shell of the ceramic mug billet by the internal burst, resulting in cracks. Even if the drying, billet did not crack, in the firing session, this did not complete a thorough drying of the billet in the firing, the internal physical water will also be rapidly vaporized, resulting in a strong steam pressure, directly from the inside of the mug to crack.
In fact, the wind will also cause ceramic mug cracking, if the billet for a long time by a fixed direction of the wind, then, the wind side of the fast drying, on the contrary, the leeward side of the slow drying, but also easy to cause uneven moisture content and lead to cracking. Similarly, when drying, if the mug is facing upwards, the mouth of the mug is thin and exposed to high winds, while the bottom of the mug is thick and exposed to low winds, which is also prone to uneven moisture content and lead to cracking.
3.4. Firing (the “ultimate test” of fire)
Firing is the most important process for ceramic mugs. In the previous article “In-depth analysis of the firing process of ceramic mugs”, firing is the test of the preliminary work of ceramic mugs, but also for the quality of ceramic mugs of good or bad determinants. If the preparatory work of the ceramic mug is not enough, then the firing of the ceramic mug must be unqualified; even if the preparatory work is well-prepared, the firing link for the various stages of control is not appropriate, but also can not generate a high-quality ceramic mug. Firing temperature, heat preservation and cooling, each link is not controlled properly may cause a large number of ceramic mug cracking. Heating up the early stage is to exclude the key period of residual physical water, if the temperature is too fast, the water is violently vaporized, it will cause shock or crack; insulation period if not enough time, the quartz occurs crystal transformation will not be uniform, resulting in shock crack. Cooling period is the main concern is the cooling amplitude, if the cooling amplitude is too large, the quartz in the cup in the reverse crystal transformation, the cup volume contraction, and the outer layer of the glaze has been fixed, can not be contracted, will produce cracks. Out of the kiln if the temperature is too high, cold air cooling rapidly, ceramic mugs are also prone to sharp contraction and shock crack.
1. Why does ceramic mug crack?
To understand ceramic mugs cracking, we must first understand the nature of ceramics. Ceramics are made of clay (raw materials) through molding, drying, and high temperature firing. This process is, in essence, a process in which the clay is stripped of physical and crystalline water, and the mineral structure undergoes a chemical reaction, eventually vitrifying and becoming hard. This process is full of “shrinkage” and “stress”. Cracking, is the tearing damage that occurs when the internal stress is greater than the structural strength of the material itself.2. Several major forms of mug cracking
Ceramic mugs do not crack in just one mold; different forms of cracking point to different etiologies.2.1. Penetrating Cracks (Cracking)
Manifestation: Cracks penetrate through the wall of the mug, completely splitting from the inner wall to the outer wall. Usually a dull cracking sound rather than a crisp porcelain sound is produced when tapping with the hand (this is also the case with ceramic mugs that have cracked due to impacts during transportation).
Characteristics: This is the most serious, can not be repaired defects, ceramic mug directly scrapped, can not be used normally.
2.2. Hairline Cracks (Shock Cracks)
Performance: Cracks as fine as hairline, sometimes difficult to detect with the naked eye immediately after kilning, but will bleed when tested with ink or pigment.
Characteristics: This type of cracking usually becomes visible late in the firing cooling period or after kiln discharge, and is a typical manifestation of uneven internal stress release.
2.3. Cracking at the Mouth Rim (Mouth Blowout)
Presentation: Cracks occurring at the rim of the mouth of the mug, sometimes in a radial pattern.
Characteristics: the mouth of the mug is the most varied shape and the thinnest part of the mug, which is also the part where the stress is most easily concentrated.
2.4 Cracking of the foot (bottom cracking)
Performance: Cracks occurring at the combination of the bottom and the body of the mug, or at the edge of the foot rim.
Characteristics: the bottom of the mug is the thickest, drying and firing internal and external contraction inconsistency, resulting in pulling crack.
2.5. Glaze cracks (cracks)
Performance: only the surface of the glaze layer appeared network cracks, while the body itself did not crack. In the previous article “Reasons for custom ceramic mugs cracking”, we talked about the specific reasons and solutions for glaze cracking.
Characteristics: This is usually caused by the “coefficient of expansion of the glaze being greater than that of the blank”. When cooling, the glaze shrinks faster than the body and is pulled apart. Although sometimes used as an artistic effect (as in the case of kiln flakes), in the case of mugs, it is a defect that affects hygiene and longevity.
3. The reasons for the cracking of the mug
ceramic coffee cup cracking, in addition to transportation damage, cracking caused in the production, we can categorize the reasons into four categories: raw materials, molding, drying and firing.3.1. Raw material factors (clay “innate nature”)
Clay is the bone and blood of the ceramic mug, clay is the “foundation” of the ceramic mug, the quality of the clay is critical. If the foundation is not good, or the quality of the foundation is too poor, it is easy to cause the ceramic mug cracked in the later production. Clay in the previous article we have explained, clay is mainly composed of: kaolin, feldspar and quartz, plus a part of micro chat elements, such as: ball clay, CMC, etc., composition. These raw materials have to go through a number of processes, crushing, grinding, removing impurities, mixing, iron removal, dehydration before practicing mud. In the previous article “Ceramic mug raw materials - clay preparation process”, we have explained the specific clay preparation process. During the clay preparation process, if the recipe is not correct, the mug will crack. For example, too high a proportion of malleable raw materials such as kaolin or ball clay will cause the clay to be too “soft”, which in turn will result in a large shrinkage of the biscuit in the drying process, making it prone to deformation and cracking. If the proportion of quartz or clinker, which are barren raw materials, is too small, the clay will lack of support, and will also be easy to deform or crack in the drying process. If the mix of raw materials is not uniform, the contraction ratio of the clay is not consistent, and cracking will also occur during drying.
All of these are the clay in the production process is likely to lead to ceramic mug cracking reasons. In fact, after the completion of clay production, there is another link easy to lead to ceramic mug cracking, this link is often many ceramic mug production factory ignored. It is the clay aging, our industry commonly known as “boring material”. Clay aging, its main form of expression is to practice good clay, placed for a period of time. This link seems to be very simple and insignificant, but in fact it is very important. Lack of aging clay is like an army with insufficient training and poor internal communication, which will be easily dispersed once it goes into battle (into molding and firing). The purpose of aging is to create an elite force that will bring out the best in the clay. We will write an article about this later.
In the process of practicing clay, even if each link is accurate, precisely ignore the aging process of clay. Ceramic mugs made of such clay are also very prone to cracking during the drying and firing process.
Of course, there are other factors, such as air bubbles in the clay and uneven humidity, which can also cause the mugs to crack.
3.2. Molding and trimming factors (the production of the “acquired defects”)
Ceramic mug molding, we have talked about before, mainly is the pressure blank "Ceramic mug molding production process details" and grouting “Customized Ceramic Coffee Mugs - Grouting Process Explained”. Ceramic mugs come in a variety of shapes, depending on the shape of the mug required by the mug's purchaser. Ceramic mugs tend to be thinner at the mouth and thicker at the bottom. If not handled properly in the drying process, raw ceramic mugs are prone to cracking when dehydrated.
Accessories other than the body of the ceramic mug, such as the handle, are glued on. When bonding the handle, if the difference between the moisture content of the mug and the handle is too large, or the concentration of the joining mud is not suitable, or when bonding the handle is not standardized in terms of pressure and scraping operations, it will leave gaps, resulting in cracking later.
3.3. drying factors (moisture “gentle goodbye”)
artificial cause of ceramic mug cracking is relatively small, many cases of ceramic mug cracking is in the drying process. In the previous article “Drying and trimming process of ceramic mug clay blanks” we explained this in detail. Ceramic mug billet drying if the temperature is too high (for example, high temperature in summer), billet surface water will evaporate quickly and violently contracted, billet internal moisture has not come to release, will cause the hard shell of the ceramic mug billet by the internal burst, resulting in cracks. Even if the drying, billet did not crack, in the firing session, this did not complete a thorough drying of the billet in the firing, the internal physical water will also be rapidly vaporized, resulting in a strong steam pressure, directly from the inside of the mug to crack.
In fact, the wind will also cause ceramic mug cracking, if the billet for a long time by a fixed direction of the wind, then, the wind side of the fast drying, on the contrary, the leeward side of the slow drying, but also easy to cause uneven moisture content and lead to cracking. Similarly, when drying, if the mug is facing upwards, the mouth of the mug is thin and exposed to high winds, while the bottom of the mug is thick and exposed to low winds, which is also prone to uneven moisture content and lead to cracking.
3.4. Firing (the “ultimate test” of fire)
Firing is the most important process for ceramic mugs. In the previous article “In-depth analysis of the firing process of ceramic mugs”, firing is the test of the preliminary work of ceramic mugs, but also for the quality of ceramic mugs of good or bad determinants. If the preparatory work of the ceramic mug is not enough, then the firing of the ceramic mug must be unqualified; even if the preparatory work is well-prepared, the firing link for the various stages of control is not appropriate, but also can not generate a high-quality ceramic mug. Firing temperature, heat preservation and cooling, each link is not controlled properly may cause a large number of ceramic mug cracking. Heating up the early stage is to exclude the key period of residual physical water, if the temperature is too fast, the water is violently vaporized, it will cause shock or crack; insulation period if not enough time, the quartz occurs crystal transformation will not be uniform, resulting in shock crack. Cooling period is the main concern is the cooling amplitude, if the cooling amplitude is too large, the quartz in the cup in the reverse crystal transformation, the cup volume contraction, and the outer layer of the glaze has been fixed, can not be contracted, will produce cracks. Out of the kiln if the temperature is too high, cold air cooling rapidly, ceramic mugs are also prone to sharp contraction and shock crack.
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