Precautions for Glass Kiln Baking

It is very important to ensure a smooth transition from room temperature to working temperature after the completion of kiln masonry, and to ensure a smooth change in the volume of each part of the masonry. There have been many glass production lines both domestically and internationally that have had some parts rebuilt due to improper kiln operations, or have experienced glass quality problems shortly after production, seriously affecting the company's profitability and even endangering the lifespan of the kiln. The following are several issues that need to be noted during the baking process of glass kilns.

 

Preparation work before baking kiln

 

(1) Development of heating curve
 

Developing a reasonable heating curve and strictly controlling the heating rate are the foundation of kiln operation. The accuracy of temperature control in hot air baking kilns is relatively high, but with the improvement of gas stoves and operating levels, the heating rate of gas fired kilns can also meet the requirements of the heating curve. The heating rate is very slow between 120~350 ℃, which is a critical temperature range for the baking kiln. The quality of the baking process is directly related to the control and adjustment of this temperature range.

 

(2) Check if the reserved expansion joints during kiln masonry are suitable

 

Especially check the expansion joints of the large arch, the expansion joints between the partition wall of the heat storage chamber and the top of the arch, the expansion joints between the heat storage chamber wall and the top arch, the slope wall of the small furnace and the small furnace stack, the bottom plate and the breast wall support iron, and the expansion joints before and after the neck hanging wall.

 

(3) Check if there is any room for movement of the steel components hanging on the neck wall

 

Many glass companies have caused the expansion of suspended wall tiles due to insufficient space reserved for steel components, resulting in the steel components being unable to move and the tiles being cut off, which seriously causes the suspended wall to sink or even collapse. After the formal heating of the kiln, it is important to always pay attention not to top the hanging wall too tightly, otherwise it is easy to crush the hanging wall bricks.

 

(4) Maintain good insulation

 

Especially, it is necessary to do a good job of insulation for the neck hanging wall and the flat arch at the outlet of the cooling department.

 

2. Personnel allocation and measures

 

The adjustment process of tightening the top thread is a test of personnel's physical strength, especially when the temperature rises above 200 ℃. The number of personnel must be sufficient, labor protection equipment must be fully equipped, and tools must be easy to use.
 

Setting of 3 expansion rulers (Qiu Zhizi)

 

Reasonably set up a large expansion ruler. Three rows of expansion rulers are placed horizontally along the arch, with one row in the center of the arch top and one row on each side of the ribs. Each row has three pieces per section, one piece per arch head, and one piece in the middle. Other larger arches can be used as a reference.
 

4. Record and analyze

 

The temperature and expansion gauge records must be truthful. When the recording personnel discover any abnormalities, they should report them to the technical personnel in a timely manner. The kiln technical personnel should analyze the records and reports in a timely manner and take corresponding measures.
 

(1) Adjust the tension bars and top threads of the corundum brick arch as many times as possible and in small quantities.
 

The adjustment of the silicon brick arch tension strip should be repeated and sufficient between 200~350 ℃. Due to the high specific gravity of corundum and the high temperature of crystal transformation, the amount of loose top wire and pulling rod should not be too large, otherwise it cannot be saved if it is adjusted too much. Silicon bricks are in a dense crystal transformation temperature range between 200~350 ℃, with very concentrated volume expansion and large arch spans. Therefore, the number of adjustments should be as many as possible, and the amount of adjustment should be sufficient each time. Otherwise, it will cause the first adjustment part to need to be adjusted again before the adjustment is completed.

 

(2) The analysis of the expansion ruler record should be timely and careful.

 

Especially in the later stage of the baking kiln, when it is found that the center of a certain arch is rising while the two ribs are basically stationary or even falling, special attention should be paid and the cause should be actively investigated. Generally, it is caused by insufficient reserved expansion joints or inability to adjust the steel structure in a certain area. If the cause is unknown or the cause is identified but cannot be dealt with, the heating should be stopped immediately, temporary insulation should be carried out, and local pressure method should be adopted decisively to ensure the normal curvature of the arch and ensure its safety.

5. Pay attention to the bottom of the kiln and the top of the bottom pool wall

 

If it is a cold repair of the kiln, attention should also be paid to the bottom of the kiln and the top of the bottom layer of the tank wall. Due to incomplete treatment of residual glass in the gaps of the kiln bottom bricks or other reasons, the kiln bottom may not expand in the expected direction, which may result in limited expansion of the pool bottom bricks or the pool bottom driving the pool wall bricks on top to press against the top wire of the pool wall. If not discovered and treated in a timely manner, it is very likely that the pool wall will be tilted towards the inside of the kiln (especially for horizontal pool walls) or the pool bottom will be squeezed and bulging against each other. This requires that sufficient expansion joints be reserved during the kiln masonry process, covered with suitable corundum bricks, and the residual glass liquid in the brick joints cleaned up. Before baking the kiln, the top wire should be loosened in advance, and the front and rear pool walls of the cooling and melting parts should be checked at any time, especially.


6. Temperature control and adjustment after a large fire

 

6.1 During a major fire

 

Burning natural gas and heavy oil kilns over high fire is relatively much safer. When burning gas kilns, especially those using gas pipelines for baking, special attention should be paid to explosion prevention. In addition to sealing as mentioned earlier, the following points should also be achieved:

 

(1) Ensure that the temperature of the gas flue reaches 350-450 ℃. If it is too low, it is easy to explode, and if it is too high, it is easy to burn out the gate, exchanger bell cover, etc.

 

(2) The disc valve and the main gate of the kiln pipeline should be coordinated, and the gate of the kiln branch pipeline cannot be closed.

 

(3) The materials and personnel used to seal the kiln holes should be in place, with fast sealing speed and good sealing.

 

(4) Timely insert the five pre prepared blowing steam guns into the kiln pipeline (check the steam pressure in advance), and open the tail end release pipe at the same time. After the steam is released from the vent hole, the air gun in the main pipeline can be turned off. The remaining air guns were kept for 48 hours, but a glass factory experienced an explosion in the kiln pipeline due to pulling out the steam gun a few hours after the fire broke out. Fortunately, no casualties were caused.

 

6.2 After the Great Fire

 

After the fire, it is necessary to strictly follow the heating curve, followed by strict temperature control. Due to the large fire, the temperature is just around 900 ℃, which is far from the expansion point of around 1100 ℃ for zirconia alumina bricks. If the temperature is not well controlled, it is difficult to smoothly release the expansion of zirconia alumina masonry, such as the explosion and even displacement of pool walls and breast walls. A certain glass factory was repaired by draining water due to the inward tilting of the breast wall after baking the kiln.

 

The issues to pay attention to after a large fire are: the tongue arch of the small path, the top wire of the breast wall, the top wire of the longitudinal pool wall, and the heat storage chamber pull rod need to be closely monitored after a large fire. The adjustment of the top wire should be done multiple times and in small quantities, and if necessary, it can be personally checked by the kiln technician to avoid loosening too much and causing the flat arch to sink.

 

7 Common Problems

 

7.1 Pool wall brick explosion
 

The pool wall is one of the most important parts of a glass kiln, and its safety directly affects the safety of the kiln and the quality of the glass.

 

In the more than ten kiln operations, the most traditional method was initially adopted, which was to wait until the standard temperature rose above 500 ℃ before turning on the pool wall cooling fan. Later, it was gradually explored to gradually turn on and increase the fan opening from around 120 ℃, until the fan was fully open at 500 ℃. Make the pool wall form a relatively natural temperature gradient along the thickness direction as much as possible from the beginning, and specifically maintain the outer surface temperature of the pool wall between 100-200 ℃. After gradual improvement, the explosion of the pool wall bricks has been reduced by more than 90%, especially the turtle cracks that used to appear did not appear in the later baking kilns.

 

7.2 Internal inclination of chest wall

 

The inward inclination of the chest wall is generally caused by the deformation of the chest wall support iron, or the failure to loosen the top wire of the chest wall in a timely manner, or insufficient reserved expansion joints, which are pushed towards the inside of the kiln by the sloping wall of the small furnace. To avoid such incidents, it is necessary to ensure that the breast wall support plate is level and tightly integrated with the palm iron during masonry. During the baking process, always pay attention to checking whether the top thread of the chest wall and the slope wall are flexible.

 

8 Hot loading kiln and post adjustment

 

Before and one month after starting the hot loading process, it is necessary to adjust the tension bars and top threads of the kiln uniformly to ensure the structural integrity of the refractory material after high-temperature shrinkage.
 

9 Conclusion

 

The baking process is a complex technical task, and only by maintaining a clear mind, abundant energy, a high sense of responsibility, and checking and thinking more can we ensure the baking quality of the kiln, laying a solid foundation and guarantee for the normal production of the next step. The above are several issues that are easily overlooked in multiple kiln baking and theoretical analysis. Other normal operations are similar and will not be repeated here.