Tempered glass products such as doors and windows,curtain walls,tables and chairs,electrical appliances,floors,etc.are becoming more and more common.Tempered glass is also known as"safety glass"because it does not form sharp edges like knives after being broken.However,recently there have been occasional reports online about tempered glass products such as glass countertops,shower rooms,mining lamp glass,oven door glass,and glass curtain walls self exploding.If the problem of self explosion is not solved,it will not only affect the promotion of tempered glass,but may even cause tempered glass products to lose public trust.

This article provides a detailed introduction to a tempered glass homogenizer,which can quickly self destruct glass with the potential for self explosion before use,thereby improving the safety of tempered glass.The self explosion of tempered glass is the main reason affecting its safety performance.Non vitreous substances(such as nickel sulfide)particles inside tempered glass can cause self explosion,which is brought into the glass by impurities in the raw materials used for glass production.Some nickel sulfide particles undergo a period of time,and their crystal structure changes fromαState transition toβDuring this transition,the volume of nickel sulfide particles undergoes significant expansion.This process of volume expansion creates strong internal stress on tempered glass,causing it to self explode.

Tempered glass,due to its superior performance,has been widely used in modern architecture,and its self destructiveness has always plagued the entire industry.At present,most enterprises control the self explosion rate of tempered glass within 1.5‰.After being treated by this homogenizing furnace equipment,the self explosion rate of tempered glass decreases to less than one in ten thousand.Therefore,this equipment can significantly improve the safety performance of tempered glass and has broad prospects for use.

Process principle

Tempered glass homogenization furnace is an indirect device for the safety of tempered glass.After the glass is tempered,it enters the homogenization furnace.Through the high-temperature heating principle of the homogenization furnace,detonation tests are carried out and residual nickel sulfide is eliminated.Tempered glass with the hidden danger of"self explosion",which is uneven stress inside the glass,is detonated in advance during the testing process,thus avoiding the occurrence of"self explosion"again after installation of tempered glass.The qualification rate of tempered glass after homogenization will be greatly improved,thereby improving the safety and reliability of tempered glass in buildings.

The nickel sulfide inside tempered glass,as a non vitreous material particle,has always been present in the glass and is the main factor causing self explosion of tempered glass.Nickel sulfide is brought into the glass by impurities in the raw materials used for glass production(quartz sand,silica powder,etc.).Some nickel sulfide particles undergo a period of time,and their crystal structure changes fromαState transition toβDuring this transition,the volume of nickel sulfide particles undergoes significant expansion.This process of volume expansion creates strong internal stress on tempered glass,causing it to self explode.Causing glass self explosion,nickel sulfide directly ranges from 0.04mm to 0.65mm,with an average particle size of 0.2mm.

Due to the crystal transformation of nickel sulfide,the volume increases,resulting in self explosion and the production of radioactive cracks locally.As shown in Figure 1,if the glass still remains in the frame after breaking,a"butterfly"shaped pattern feature can be easily found at the starting point of breaking.From the"butterfly spot"generated in the glass fragments after self explosion,at a 45 degree angle,it is easy to see a small black spot in the center of the glass plate.As for the"butterfly",it is located between the cracks,and the direction of the self exploded glass crack is scattered from the center to the surrounding area.

The homogenization treatment of tempered glass by secondary heating and annealing(also known as hot dip treatment)is recognized as an effective method to solve the problem of self explosion.Heat the tempered glass again to around 290-300 degrees Celsius and keep it warm for a certain period of time before slowly cooling down,so that the nickel sulfide particles in the tempered glass complete the crystal phase transformation in homogeneous treatment,allowing the glass that may self explode to break in advance in the factory.This method can effectively reduce the self explosion rate of tempered glass after leaving the factory,improve the yield,and reduce the impact on transportation,installation,and subsequent process rework caused by self explosion.At present,forced convection electric heating hot dip furnaces are mainly used in China to treat tempered glass.Most of the existing tempered glass homogenization furnaces have heating boxes located at the top or back of the furnace body.A fan is used to transport hot air through the air duct to the tempered glass that needs to be homogenized in the furnace,and the hot air is sucked back into the fan through the gap between the tempered glass.This is repeated continuously to heat the tempered glass to the rated temperature and maintain a constant temperature for a long time,achieving the goal of detonating the tempered glass with the risk of self explosion.But the shortcomings are poor temperature uniformity,high energy consumption,inconvenient maintenance and cleaning,which bring many inconveniences to production.

Structure of Tempered Glass Homogenizing Furnace

Firstly,when the temperature inside the furnace rises to 280 degrees Celsius,it is required to maintain insulation for more than two hours,which puts strict requirements on the insulation performance of the furnace body.If the insulation effect is not good,it will be difficult to control the temperature inside the furnace at a certain level,which will cause the temperature inside the furnace to fluctuate and seriously affect the quality of the glass.According to research,the phase change rate at 280°C is 100 times that at 250°C,so it is necessary to ensure that each piece of glass in the furnace undergoes the same temperature curve.Otherwise,on the one hand,some glass temperatures are too high,which can cause the reverse phase transformation of nickel sulfide;On the other hand,glass with low temperature may not undergo complete phase transformation of nickel sulfide due to insufficient insulation time.Both situations can lead to ineffective homogenization treatment.Therefore,in the insulation of the homogenization furnace itself,taking the processing space of 4400mm x 3700mm x 3300mm as an example,at least 200mm insulation layer should be used around the furnace body.However,since most homogenization furnaces use heating devices placed at the top of the furnace body,the insulation requirements at the top are more strict.This is because the upper part of the furnace body is mostly covered with cables,in order to have better insulation effect,at least 500mm insulation layer is required.This can not only improve the reliability of homogenization,but more importantly,save a lot of electricity and contribute to the construction of a resource-saving society.

Secondly,in order to ensure that the temperature inside the homogenization furnace can be at the same level,it is also required that there is unobstructed air flow inside the homogenization furnace to prevent blind spots in the airflow,which may cause local temperatures to be too high or too low and result in the failure of glass homogenization.The air flow inside the furnace is provided by a fan placed at the top of the furnace.Firstly,it is required that the fan is a high-temperature fan that can work in a high-temperature environment for a long time and withstand high temperatures of at least 400 degrees Celsius;Secondly,the air duct system is made of stainless steel material,which can improve its service life.The air is transmitted into the furnace through the air duct,and the circulation of the air in the furnace can be shown in Figure 2.The arrow direction in the figure indicates the direction of the air flow.The fan blows cold air into the heating area and forms hot air through heating to circulate in the furnace.Taking the size of the furnace,which is 4400mm x 3700mm x 3300mm,as an example,the internal air volume is required to reach 40000 m3/h or above,and the circulation speed is required to be around 1.5 m/s.In order to ensure uniform internal air circulation,it is recommended to use multiple fans and multiple air inlets to improve the uniformity of the air inside the furnace.It should be emphasized here that the insulation of air ducts and fans is also crucial.

The main skeleton of the furnace body should be made of high-quality steel as much as possible,because long-term heating and cooling have an extremely serious impact on the steel.Therefore,when selecting steel,it is important to pay more attention.Stainless steel materials should be selected for the inner wall of the furnace body.

Specific implementation methods

As shown in Figure 2,open the furnace door,place the A-shaped frame with existing glass into the chamber①of the homogenizing furnace,and close the self-locking device inside the furnace;Set the temperature and heat the modular heating element to form heater②;Start the fan③to send the airflow through the air inlet④into the heating chamber⑤,and the airflow flows along the heating chamber to send heat to the inlet duct⑥of the furnace body;The inlet duct of the furnace body is equipped with regular side holes⑦near the chamber surface,and the side holes are equipped with adjustable air flow control levers⑧.The airflow enters the chamber through these side holes,and the temperature is uniform;The airflow flows to the outlet duct⑨and then returns to the fan along the outlet duct to form a circulating constant temperature airflow.In order to more effectively ensure the uniformity of airflow temperature,in addition to adjusting the side wind plate,an internal air duct(10)is also added in the chamber,which effectively ensures the uniformity of temperature inside the chamber and achieves the homogenization treatment effect of glass.The insulation layer around the furnace body prevents heat exchange between the heating chamber and the outside world,greatly saving electricity.

The advantages of this homogenization furnace

Firstly,the homogenization furnace door utilizes a pneumatic linkage mechanism to flexibly open and close,facilitating the loading and unloading of glass and reducing labor intensity.It is worth noting that electric doors should be avoided as much as possible in the design of homogenization furnace doors,because during the glass heating process,the motor is prone to malfunctions when heated.Once the furnace door is not tightly closed,it will greatly reduce the homogenization effect.Secondly,an independent frame is welded in front of the top cabinet and inner cabinet inside the furnace to seal the furnace door,achieving a good sealing effect.Homogenization is achieved by heating the glass through thermal convection.If the sealing is not added,it will cause slow heating and reduce efficiency.Once again,this device intends to place the fan at a distance higher than the top of the furnace body to reduce the vibration generated by the fan during operation,and provide greater safety space for the connection between the furnace wire terminal and the power line.Finally,this device adopts modular heating to make each group of furnace wires into a compact rectangular shape,evenly distributed in the heating area,for easy maintenance and replacement of the heating element.Moreover,the air intake duct is equipped with an air volume adjustment device,which can make the upper,middle,and lower air speeds in the cavity uniform,helping to maintain a uniform temperature inside the cavity and maintain a constant temperature level.

According to experiments and statistics,after homogenization treatment with this equipment,the probability of tempered glass self explosion will be greatly reduced,and the probability of one self explosion per 10000 square meters of glass occurring within 2 years is less than one in ten thousand.At this point,tempered glass can be called true safety glass.After adopting homogenization treatment technology,the cost of tempered glass has increased to a certain extent,and the price of glass has also increased.However,from the perspective of social responsibility and public security,glass production enterprises should still recommend customers to purchase tempered glass that has undergone homogenization treatment.

(Source:Tianjin Nanbo Engineering Glass Co.,Ltd.)