Tempered glass

Characteristics of the product

Tempered glass is ordinary glass that has been processed by heat-treating method. The transformation procedure of transforming glass into tempered glass must be the last stage of processing as tempered glass is the unified piece of glass. This means that tempered glass contains line of force around the glass except the areas near the edges where line of force cannot reach. There is also forces from the interior pushing line of force equally. This cause the glass to be highly durable towards all actions ranging from pressing, crashing, to even being exposed to changes in temperature. The glass will break if line of force was destroyed, and the internal force will cause the whole glass to break into small pieces. 

The process of producing tempered glass begins by bringing ordinary glass to undergo the process of heating until it reaches approximately 650 ºC, and the scorching glass will then be quenched by high-pressure air blast. The outer part of the glass will become stiff before the interior; consequently, molecules arrangement of the glass surface and the interior are different, creating tension in the glass. As a result of tension, two forms of forces are occurred: the first one is line of force surrounding the glass, and the other is interior force which will push out equally in all direction. This will generate the above-mentioned properties. 

Any types of flat glass, regardless of different production—plate process, sheet process, and float process, can all be transformed into tempered glass as long as that particular glass contains suitable materials, e.g., no excessive amount of silver. Glass products producing from those procedures include clear glass, super clear glass, tinted glass (grey tinted glass, dark grey tinted glass, bronze tinted glass, and blue tinted glass). Pattern glass can also be used as a raw material if there is one smooth side, otherwise it will harm ceramic roller inside the furnace. (This is because glass in general except pattern glass is produced by float process. Thus, ordinary glass typically refers to those made from float process in particular.)

It is important to note that tempered glass cannot be processed further. Glass products from aforementioned production can be transformed via various procedures to contain more special properties before going to the tempering process.

Manufactured glass that can be transformed into tempered glass are satin glass, sandblast glass, ceramic coated glass, and etc. For special glasses including reflective glass, Low-E glass, self-cleaning glass, hydrophobic glass, and anti-reflective glass, only some of them can be tempered glass raw materials. Thus, consultation with a producer is required. 

Mirror and color coated glass cannot be treated in tempering process, it is therefore necessary to proceed in tempered glass production before transforming into mirror or color coated glass. 


Advantage

  • 1. 4-5 times stronger than float glass, enabling it to be tolerant towards crash, press, and squeeze.

    2. High-temperature resistance up to 290 ºC with no risk of breaking.

    3. Tolerates acute temperature changes up to 150 ºC.

    4. In case of the glass breakage, it will break into small pieces unlike the shark-mouth breakage of ordinary glass which will be less harmful. 


Disadvantage

    • 1. Tempered glass cannot be cut, pierced, and chipped off.  

      2. As tempered glass has been exposed to high temperature during the production, the material becomes soft. Despite the fact that we exercise caution when moving glass inside the oven, there is still slightly wave and deflection. If required entirely smooth with no waves on glass such as the case of glass for photocopy machine, other types of glass are required.

      3. Tempered glass has a chance of spontaneous breaking phenomenon in case its components have been contaminated or exposed to nickel sulfide (NiS) in the process of producing float glass. An average of self-breakage is 8 from 1,000 sheets; however, if spontaneous glass breakage has been found, there will be more than 0.8% of glass breaking in that production lot. In contrast, in case of no self-breakage in that lot, there will be none of sheets broken. It is possible to detect whether the glass is spontaneous breaking or not by examine the center of breakage spot. If there are two big pieces attached with similar size at the center of breakage which look alike butterfly wings, the glass has broken spontaneously.


    Application

      • Due to the fact that tempered glass has a property resisting crash, press, and pressure and is less dangerous than other ordinary types of glass when broken, tempered glass is compulsory as a type of glass to use along with fitting equipment, e.g., frameless glass door set and shower door, rail preventing people from falling attached by fitting, and glass facade attached by fitting process.  
      • For areas that have to handle with high smash or exposure to heavy wind—squash room, the wall separating between audiences and sport fields (such as basketball field), ice hockey field, and ice skating areas, tempered glass is essential as well. There are high chances of bumping into glass in crowded areas, thereby, the law determines the use of tempered glass in various places including department stores, banks, and car showrooms. 
      • As tempered glass has unique properties in terms of resisting heat up to 290 ºC as well as tolerating to temperature changes up to 150 ºC, it can be used for spotlight lamp, fireguard for places near the fire, and the base for gas stove and hot pot support. 
      • It is noteworthy that tempered glass is not resistant to fire, thus it is unsuitable for being used as a fire resistance material and a peephole for oven that temperature can go beyond 290 ºC.

    Size and Thickness

      • Thickness of glass that can be produced: 4, 5, 6, 8, 10, 12, 15, 19 millimeters
        The smallest size that can be produced: 180 X 180 millimeters or with longer than 250 millimeter for diagonal  
        The largest size that can be produced: 2,800 X 6,000 millimeters
        Remark: The size of thin glass depends on raw materials; hence, please inquire about the size before ordering. 

    Caution in use

          • 1. Tempered glass cannot be cut, pierced, and chipped off after the production. Measuring areas carefully is therefore necessary, and we encourage to use the unit of 'millimeter' for an accuracy. Allowing it to be slightly loose will enable to install glass easier, yet it should not be too loose to slip out of glass moldings. 
          • 2. A single piece of tempered glass should not be used for making a roof or a wall of high-rise buildings as it is possible to fall over in case glass is broken. 
          • 3. A single piece of tempered glass should not be applied for floor making, pedestrian areas, or staircase as people can fall down immediately when the glass is broken, and it can harm people down there as well. 
          • 4. Tempered glass cannot be used as a substitution for fire-proof glass since tempered glass cannot resist fire and provide safety for residents according to the restriction of fire-proof. 


            The way to detect a tempered glass 
            In terms of visual property, it difficult to distinguish tempered glass from ordinary glass. Noticing waves can differentiate them in case raw materials are float glass. Unfortunately, this method is not effective in case of plate glass and sheet glass. This makes it complicated for customers to perceive whether the received glass is the tempered glass or not.
            For certain detection, smashing glass to examine whether the glass breaks into small pieces or not is required, nevertheless this will cause to the waste of that glass. If not smashing the glass, special instrument (Laser GASP) can be used for observing tension of the glass to see whether it is a tempered glass or not. In fact, this instrument is expensive, and accordingly is typically used by glass factories only.
            There is normal equipment, polaroid film, available at science equipment shops that can be used for detecting whether that particular glass was produced through heat treating process or not. The means to detect is to bring one sheet of polaroid film and place it at the back of a glass at the edge of the glass (there may be a part of the film outside the glass), following by placing another sheet of polaroid in front of the glass in order to look pass to the polaroid film at the back. In case rotating the polaroid film in front of the glass, it is possible to see the glass ranging from the least brightness up to nothing. This is because polaroid film at the back would cut light wave out in a single plane. The light that comes through would be cut out by frontal polaroid. If the plane of light that is cut out is perpendicular, there will be no light getting through. While rotating polaroid film, you could see black brownish line in parallel with the glass brim. Thin glass tends to have the parallel line nearer to the glass brim compared to thick glass. For glass with the same thickness, the glass that parallel line is closer to the glass brim has higher tension, yet this method cannot state whether the glass is a tempered one or heat-strengthened glass.

    Example of usage





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