Glass cups are very popular among the public. Compared with other cups, glass cups do not contain organic chemicals and are beautiful and do not produce odor, making them the first choice for people to drink water safely. But many people have also had the experience that the high value glass cups filled with hot water, suddenly burst without warning, glass shards splashed onto the skin, causing injury to us, catching many people off guard.
Glasses pouring hot water why easy to burst?
Glass is a poor conductor of heat, not easy to conduct heat, so the windows inside the home using glass material, can play a thermal insulation effect, including the cotton clothes we wear in winter, are poor conductors of heat, so as to keep warm. And cooking with iron pots and pans and other metal products is a good conductor of heat, good thermal conductivity.
Glass can tolerate temperatures up to 800 degrees Celsius, boiling hot water less than 100 degrees Celsius, so the glass is not afraid of high temperature, even if used to hold hot water will not soften, and the real reason for the glass to break is uneven heating, simply put, "thermal expansion and contraction".
It is for this reason that the pressure on the outside glass becomes instantly greater, and so the glass shatters. That is, if there is a large temperature difference, the glass is easy to blow up, and the greater the temperature difference, the more easily the glass will be damaged. Similarly, just after the hot water glass do not quickly rinse with cold water, the same will cause the glass to break.
Now we can explain a lot of problems, looks very "strong" thick glass but because of the slow heat transfer, temperature difference, so it is easier to burst than the thin glass, of course, the bottom of the glass should be thin to not easy to break. In winter, the outside temperature is low, the glass poured into the hot water, the temperature difference between the inner and outer wall than in summer, so the winter glass appears more "brittle".
The improvement of the production process guarantees the quality of the glass
Previously, due to the limitations of the process, often using the pouring molding method, glass firing temperature is not high enough, if there are some solid impurities that can not be melted, condensation will allow the existence of a large internal glass stress, put into use after easy to crack, and today's high borosilicate glass is generally artificially blown.
An important step in the production of glass is annealing, because the glass production temperature is very high, it is necessary to continuously reduce the temperature to eliminate the internal stress of the cup, so that the cup will not be "fried" in the heat. In the past, the annealing method was intermittent, but now the continuous annealing method is used to ensure that the temperature drops at a uniform rate, which is a key step in determining the quality of the glass.
Why don't the glasses blow up nowadays?
Now the glass used in the production of materials and different from the past, the past commonly used is soda lime glass, the main components of silica, calcium oxide and sodium oxide, etc., this glass hardness, low price, but poor thermal stability, can only withstand the temperature difference of about 60 ℃, commonly used to make light bulbs, instruments, etc..
Now using the mainstream high-temperature glass is generally high borosilicate glass, due to the addition of boron, this glass coefficient of thermal expansion is small, about 1/3 of ordinary glass, the volume expansion after heating is very small, thermal expansion and contraction is not obvious, can withstand the instantaneous temperature difference of up to 150 ℃, even into the oven heating, and now the glass is also very thin, less prone to frying.
The safety of this high borosilicate glass is also higher, good stability, even if the temperature difference is too large and lead to shattering, due to its crack is larger, will not appear like ordinary glass broken a lot of small debris, causing less damage than ordinary glass.
Now the processing technology has improved, but in order to prevent the glass from bursting, we use the glass with hot water, it is best to pour a little hot water to preheat, and shake the cup, so that the overall temperature of the inner wall, and then we slowly pour more boiling water will not burst, do not let the cup hot and cold.
Glass is a cup made of glass. At present, high security, quality and good to belong to the high borosilicate glass, it is after more than 600 degrees of high temperature firing, so it has a very high heat resistance. However, in reality, when we buy glass cups, there is a risk of buying inferior products, and in the use of inferior products, due to improper use may explode.
Why the glass will explode? The reason is none other than because of the large temperature difference between the inside and outside of the glass. What does it mean? It means that the ordinary soda lime glass allows a sharp temperature difference of only 50 ℃. That is, if the room temperature of 25 ℃, in the ordinary glass filled with more than 75 ℃ water, the inner wall quickly heated extrusion of the outer wall, the glass has the possibility of rupture.
And the bottom of the glass cup is originally made of glass stretching is relatively large place, relatively fragile, so repeatedly several times into the hot water, the rupture is a probable event.
Explosions can occur not only glass. Like those tempered glass tableware will also occur in the case of an explosion. Because tempered glass is going to explode. This is because in the production of the cooling stage, the surface first hardened, shrinkage, tempered glass inside the presence of outward pressure, if the glass surface outward pressure is not equal, it will occur spontaneous explosion.
Therefore, the use of glass, it is best not to alternate between hot and cold water, for safety reasons, it is best to use cold water.