The melting rate refers to the ratio of daily output to the furnace‘s melting area. However, since the melting rate involves multiple factors, a more reasonable and comprehensive indicator is the periodic melting rate. When selecting the melting rate for furnace design, various aspects must be considered:
►The company’s technical level and management status (e.g., whether it is a new facility).
►Product type, specifications, forming method, quality positioning, and glass composition.
►Cullet ratio, raw material formulation, fuel type, furnace scale, and structural design.
A conservative approach is typically adopted in design, with the melting area increased by 4%–5% beyond the projected output. A slightly lower melting rate (by 4%–5%) allows for reduced furnace temperature, benefiting both furnace longevity and product quality while ensuring stable production. Thus, determining the melting rate requires a holistic evaluation of these factors.
1. Technical Level and Management Status of the Enterprise
2. Fusibility of the Glass Chemical Composition (Formula)
3. Particle Size and Gradation of Raw Materials
4. Uniformity of the Batch Materials
5. Moisture Content of the Batch Materials
8. Bubbling System of the Furnace
10. Types and Structures of Furnaces
11. Electric Boost Melting System
13. Types of Burners and the Use and Adjustment of Burners
1. Technical Level and Management Status of the Enterprise
The technical strength of an enterprise, whether the management is standardized, whether there is a management inheritance, and the technology are related to the entire enterprise team‘s understanding and implementation of the process system. Generally speaking, for a mature enterprise, "30% of it depends on technology and 70% on management".
However, for a new enterprise, if the process regulations are not strictly implemented, management problems will turn into technical problems, complicating the problem - solving process. For example, some enterprises do not strictly implement the process system. The mixing time of the batch materials is too short, and the uniformity of the batch materials cannot reach 90%, which seriously affects the melting rate and output, and also affects energy consumption. Only when the process system is strictly implemented and the batch material uniformity meets the standard can the output and energy consumption problems be solved.
A glass factory in Chengdu has a relatively standardized management and strong technical strength. More than 10 years ago, the furnace of this glass factory melted high - quality fine white materials with high requirements for glass quality. Its melting rate reached 2.3 - 2.4 t/(m²·d) in a short period (4 - 6 months) and remained at around 2.0 t/(m²·d) for a long time. With a low proportion of cullet, the high melting rate is directly related to the comprehensive technical management level.
The effect of glass production reflects the advantages and disadvantages of the continuous - production technical management system. Only when the management level is high, responsibilities are implemented in place, technical indicators are implemented, and the operating parameters of each link are stable can the production be stable, the product quality be stable, and the effective melting rate be improved.
2. Fusibility of the Glass Chemical Composition (Formula)
Generally speaking, the higher the silicon - aluminum content in the glass formula, the better the mechanical strength and chemical stability.
However, the higher the silicon - aluminum content, the more difficult it is to melt the glass, and the longer the clarification and homogenization time.The higher the content of fusible oxides such as R₂O, B₂O₃, and PbO in the glass composition, the easier it is to melt the glass, the higher the melting rate, and the lower the energy consumption.
In the design of modern glass formulas,
on the one hand, the use requirements of the products need to be considered, and on the other hand, the requirements of production volume and forming also need to be considered.
In high - speed glass formulas, a large amount of calcium oxide is introduced. When the silicon - aluminum content is the same, a difference of 0.5% in the content of sodium and potassium (generally, potassium oxide is not introduced in ordinary daily - use glass to reduce costs) in the glass formula can also lead to a large difference in the melting rate.
The fusibility of the glass chemical composition (formula) can be judged by the glass melting rate constant τ proposed by M. Wolf.
General industrial glass
Borosilicate glass
Lead glass
τ is the melting rate constant, a dimensionless value, which indicates the characteristic value of the glass being relatively refractory. Its corresponding melting temperature is shown in Table 1; SiO2, Al2O3, Na2O, K2O, B2O3, and PbO are the mass fractions of the corresponding oxides in the glass composition.
|
τ |
6.0 |
5.5 |
4.8 |
4.2 |
|
Melting temperature/℃ |
1450-1460 |
1420 |
1380-1400 |
1320-1340 |
τ is an empirical constant. Due to the wide range of glass compositions and the many and complex factors affecting glass melting, it is necessary to reasonably determine the melting temperature according to the actual situation and comprehensively consider various factors. When the silicon - aluminum content is the same, the proportion of alumina has a great influence on the melting speed and homogenization. Because the surface tension of the aluminum melt is greater than that of the silicon melt, and the influence of Al₂O₃ on the glass viscosity is much greater than that of SiO₂, different silicon - aluminum contents affect the melting rate. Even with the same Al₂O₃ content, there is a big difference between introducing it from mineral raw materials and chemical raw materials. Mineral raw materials introduce Al₂O₃ from feldspar, and some quartz sands already contain Al₂O₃, which is easier to melt and homogenize than chemical raw material Al₂O₃. There is also a large difference in the melting points of chemical raw material Al₂O₃ and Al(OH)₃. High - grade glassware often introduces Al(OH)₃ as a component for introducing Al₂O₃.
For enterprises that pursue a high melting rate, it is recommended to consider increasing the lithium oxide component in the glass formula under the premise of meeting the performance requirements to facilitate fluxing.
In addition, the type and dosage of the fining agent used in the glass formula will also affect the clarification and homogenization effect, thus affecting the melting temperature and energy consumption, and ultimately affecting the melting rate.
3. Particle Size and Gradation of Raw Materials
Quartz sand (SiO₂) is the most difficult to melt among the raw materials, with a melting point of 1,713°C.
The coarser the quartz sand particles, the smaller the surface area for receiving thermal radiation; the smaller the contact area between various raw materials, the slower the high - temperature reaction rate, and the longer the melting time. If the quartz sand is too fine, it will fly in the furnace, which is not conducive to the clarification of the glass and is likely to cause blockage of the checkerwork. Therefore, the particle diameter and particle - size composition of quartz sand are important quality indicators of quartz sand. Through production practice, it is considered that the most suitable particle size of quartz sand for melting in a tank furnace is generally 0.15 - 0.8 mm (100 - 24 mesh on a standard sieve). The particles of 0.25 - 0.5 mm (65 - 35 mesh) should not be less than 90%, and the particles below 0.1 mm (140 mesh) should not exceed 5%, which is the gradation requirement for raw materials (mainly referring to quartz sand).
In addition, the source, origin, and shape of quartz sand all have an impact on the melting speed. For example, quartz sand from Kunming is easier to melt than quartz sand crushed from quartzite. The angular shape of sand grains is better because the angular shape has a large surface area, more contact opportunities with fluxes, and is not easy to stratify during mixing and transportation.
4. Uniformity of the Batch Materials
Due to the high melting point of quartz sand (SiO₂), high requirements are placed on the flame temperature and refractory materials. In order to reduce the melting point of quartz sand (SiO₂), fluxes (mainly alkaline oxides) need to be added; in order to improve the properties of the glass, divalent and trivalent oxides such as alumina (Al₂O₃), calcium oxide (CaO), magnesium oxide (MgO), and boron oxide (B₂O₃) need to be added.
It is required that multiple raw materials are mixed and evenly distributed around the quartz sand. The better the uniformity of the batch materials, the faster the melting and the better the quality of the glass liquid.
The uniformity of the batch materials affects the melting rate and also indirectly affects energy consumption. A wine - bottle factory once had a large difference in the uniformity of the batch materials used in two furnaces (one with a uniformity of less than 90% and the other around 96%). The melting effects in the furnaces were quite different, and the melting rates also differed greatly, seriously affecting the output and product quality. The products produced with poor - uniformity batch materials have poor mechanical strength and are prone to breakage during the wine - filling process. Among all the raw materials, quartz sand (SiO₂) has the highest melting point, and the content of silicon dioxide (SiO₂) in wine bottles is also the highest, generally around 70%. Therefore, it is required that fluxes and modifying elements are wrapped around quartz sand (SiO₂). If these fluxes and modifying elements are too coarse, it is not easy to wrap around the quartz sand. Meeting the particle - size and gradation requirements of all raw materials and evenly distributing fusible and refractory raw materials can give full play to the role of flux components and improve the melting speed.
At present, the calcite (CaCO₃) used in some factories is relatively coarse, with a size of 2 - 3 mm, and even 4 - 5 mm. 
This will affect the uniformity of the batch materials. Special attention should be paid to preventing the stratification of the batch materials during long - distance transportation (belt conveying) with large vibrations. The calcite (CaCO₃) used in the past was about 60 - mesh. Due to its light weight, it was easy to fly during the feeding process and would crack and decompose at 700 - 800°C. Therefore, calcite (CaCO₃) is now required to be a little coarser, but it should not exceed 20 - mesh. If it exceeds 20 - mesh, it will affect the uniformity of the batch materials. A foreign factory had calcite (CaCO₃) that was too coarse. During the belt - conveying process, it stratified due to vibration. The coarse particles accumulated on the surface of the batch materials, affecting the uniformity and seriously affecting the melting rate of the glass. Poor uniformity of the glass batch materials leads to poor melting, clarification, and homogenization. Glass products will generate structural stress, and the mechanical strength of glass products is poor. Therefore, during the wine - filling process, wine bottles will burst automatically. So the uniformity of the batch materials not only affects the melting speed but also affects the product quality.
Therefore, the uniformity of the batch materials must be taken very seriously. Large - scale float glass furnaces have better control over batch materials. Chemical determination is carried out by the titration method, and only the Na₂CO₃ content is measured. The designed ±0.7% of Na₂CO₃ is the qualified target, and the qualification rate should reach 99%, with the unqualified rate less than or equal to 1%.
5. Moisture Content of the Batch Materials
If the batch materials are too dry, they are prone to stratify during transportation, and light - weight raw materials will fly. During the feeding process, dust will fly and deposit on the furnace cover, affecting the life of the furnace cover. It will also affect the health of employees, corrode equipment, cause corrosion and blockage of the checkerwork, affect the smooth passage of combustion - supporting air and waste gas, and reduce the heat - exchange effect.
If the batch materials are too wet, especially when the quartz sand is too wet, it will agglomerate, greatly affecting the uniformity of the batch materials. In severe cases, batch - material stones will be generated. In addition, a large amount of moisture entering the furnace will affect both energy consumption and the melting speed.
• An appropriate amount of moisture can improve the uniformity of the batch materials, making fluxes such as soda ash and glauber‘s salt adhere to the surface of quartz particles, thus contributing to the melting of quartz sand.
According to domestic and foreign experiments and experience summaries, the moisture content of batch materials is generally controlled between 3.5% - 4.5%. It can be seen that the moisture content of batch materials affects both energy consumption and the melting rate.
The proportion of cullet in the glass batch materials also has a huge impact on the melting rate. Generally, daily - use glass starts to soften at 600°C. The higher the temperature, the smaller the viscosity of the glass and the greater the fluidity. The glass liquid fills the pores in the batch materials, increasing the thermal conductivity of the batch materials and thus improving the melting rate of the glass.
Since there is no large amount of gas generated to take away heat during the melting process of cullet, the energy consumption is low. It is widely recognized in the glass industry that cullet is beneficial to melting and energy - saving. However, too much cullet will increase the viscosity of the glass liquid and make it difficult to clarify. Because when cullet is remelted, the alkaline oxides in it will volatilize again.
Therefore, according to the amount of cullet added, the amount of alkaline oxides, oxidants, and fining agents should be appropriately increased to supplement the broken bridge - oxygen bonds.
Different glass colors affect the transmission and absorption of light waves of different wavelengths. "Generally, colorless and transparent glass has almost no absorption in the visible light range (390 - 770 nm), and only a small part is lost due to scattering".
Therefore, the bottom temperature of a colorless and transparent glass pool is high, the temperature difference between the upper and lower parts of the glass liquid is small, and the melting rate of the furnace is high. Green (brown) beer - bottle glass will affect the quality and output of the glass if there is no bubbling.
Because green glass has poor heat conductivity and is easy to form a thick immobile layer and a slow - moving layer at the bottom of the pool. Once a large amount of immobile layers are formed at the bottom of the pool, the effective volume of the furnace will be reduced, and the convection in the depth direction will also slow down, affecting the melting rate and output.
When the output fluctuates, the furnace temperature rises, or other process states fluctuate, the relatively immobile layer and slow - moving layer at the bottom of the pool will enter the production flow.
When the amount of "dirty materials" at the bottom of the pool entering the glass production flow is relatively large, obvious streaks, stones, and other defects may occur, affecting the product quality and output (qualified rate and high - quality product rate).
Therefore, the output of colorless glass produced in the same furnace is 15% - 20% higher than that of colored glass (with the same composition and the same proportion of cullet).
8. Bubbling System of the Furnace
The function of the bubbling in a glass furnace is to stir the glass liquid at the bottom of the melting pool, allowing the glass liquid with a lower temperature at the bottom to rise to the surface with the bubbles.
As the bubbling forms a circulation flow, the glass liquid with a high surface temperature flows downward to fill the space below. Therefore, bubbling improves the temperature uniformity and composition uniformity of the glass liquid at that place. The rapidly rising bubbles and the shock waves generated by the bursting of the bubbles strengthen the convection of the glass liquid, which can effectively prevent the un - melted glass liquid from entering the clarification zone and the flow - through hole.
Therefore, the bubbling of a glass furnace has a significant effect on increasing the output, improving the quality, and enhancing the production stability, as well as improving the melting rate of dark - colored glass.
Charging machines replace manual feeding by delivering batch materials into the furnace.
Pusher-Type Charger: The pusher moves linearly back and forth. 
During retraction, batch material falls onto the molten glass surface in the charging pocket, and during advancement, the pusher scrapes the batch into the furnace. This design is simple and low-cost but does not improve batch thermal conductivity. When feeding large amounts, thick and narrow batch piles form, resulting in poor heat transfer and slower melting. This led to its gradual replacement by inclined blanket chargers.
Inclined Blanket Charger: The pusher moves along an inclined path with an L-shaped rake (50–100 mm wide). As the pusher retracts, batch material falls onto the glass surface. During forward motion, the L-shaped rake presses the batch downward, allowing some molten glass to penetrate, improving thermal conductivity. Additionally, the batch forms a "washboard" wave pattern (when using a wide, thin-layer feed), increasing heat absorption and accelerating melting.
Some factories misunderstand this mechanism and remove the L-shaped rake to cut costs, drastically reducing effectiveness. Without downward compression, it functions similarly to a pusher-type charger, merely pushing batch material in without enhancing thermal conductivity.
Swing-In (Horizontal Oscillation) Charger: The pusher follows a closed curved path with a 200–250 mm wide rake that fully presses the batch downward. This forces high-temperature glass into the batch, filling pores and improving thermal conductivity. As the rake rises, it also covers the batch with molten glass, further enhancing heat transfer. It can feed at left, center, and right angles, adjustable based on melting conditions. The batch is distributed in small piles across the rear melting zone (see Figure 1), maximizing melting area and heat absorption. This design saves about 5% energy.
Suspended Charger: Compact and well-sealed, it prevents flame and gas leakage. The pusher moves along an arc, feeding similarly to a pusher-type charger but without downward compression, so it does not improve thermal conductivity. An improved version allows multi-directional feeding. Its main drawbacks are unchanged batch thermal conductivity and higher heat loss due to cooling water. However, it offers better sealing and cleaner operation compared to swing-in chargers.
10. Types and Structures of Furnaces
Different types of melting furnaces such as
longitudinal - flame furnaces,
horseshoe - flame furnaces,
and unit furnaces have significant differences in indicators such as melting rate, maximum output, and energy consumption. Here, a comparison is made for the commonly used horseshoe - flame furnaces in the daily - use glass industry.
The structure of the furnace has a multi - faceted impact on the melting rate.
Generally, a multi - channel regenerator is more energy - saving and has a higher melting rate than a single - channel regenerator. Because the combustion - supporting air temperature is high, the flame temperature is high, and the batch materials melt quickly.
A furnace with a deep clarification tank structure has a higher melting rate than a furnace without a deep clarification tank structure. The furnace weir can not only strengthen the hot spot and change the direction of the liquid flow but also prevent the uneven substances in the bottom layer (slow - moving layer) from directly entering the flow - through hole when the output is large. The furnace weir also has a shallow - layer clarification function.
Combined with bubbling and a deep clarification tank, it can significantly accelerate the clarification and homogenization of the glass liquid and increase the output. The structures of the small furnace, the size of the flame space (the heat load of the flame space), and the structure of the feeding pool (pre - melting pool) all have a great impact on the melting rate of the furnace.
In addition, appropriately increasing the depth of the glass liquid is also beneficial to increasing the melting rate. Practice shows that for furnaces with a glass depth of 1.4 - 1.6 m in the melting area (varying depending on the type and color of the glass), the melting rate is 3% - 5% higher than that of furnaces with a glass - liquid depth of 1.2 - 1.3 m.
11. Electric Boost Melting System
Installing electrodes in a glass furnace can greatly increase the temperature of the glass liquid, thus accelerating the clarification and homogenization of the glass liquid and increasing the melting speed.
The bottom - inserted electrodes can also form a thermal dam near the hot spot of the furnace, strengthening the hot spot and enhancing the thermal convection. This can not only prevent the un - melted glass liquid from entering the working section but also return a large amount of high - temperature glass liquid to the feeding port, increasing the temperature of the batch materials and thus increasing the output of the glass furnace.
The bottom - inserted electrodes are also of great help in improving the quality of the glass liquid. They not only increase the temperature of the glass liquid but also improve the uniformity of the glass - liquid composition. Because the up - and - down convection of the glass liquid near the electrodes is strengthened after heating, which has a similar effect to bubbling. And the electrode layout is convenient, which is very effective for increasing the output of the furnace and reducing the overall unit consumption (ionic conduction, submerged heating).
Different types of fuels have different radiation coefficients of high - temperature flue gas after combustion.
The radiation capacity of solid fuels is greater than that of gaseous fuels. The blackness of the flame during heavy - oil combustion is higher than that during natural - gas combustion.
For gaseous fuels, the high - temperature radiation coefficients after combustion of mono - atomic fuels and poly - atomic fuels are also different. The high - temperature radiation coefficient after the combustion of producer gas is higher than that after the combustion of natural gas. It is not only the difference between mono - atomic and poly - atomic fuels, but also that producer gas contains a large number of tiny carbon particles.
The blackness of the flame during the combustion of bituminous coal with a high volatile content is 0.7, the blackness of the heavy - oil combustion flame is 0.85, while the blackness of natural gas is 0.2 during flameless combustion and can reach 0.6 during flamed combustion. Nowadays, many furnaces burning natural gas at home and abroad use the above - mentioned theory to increase the temperature of the glass liquid.
Therefore, the type of fuel and the combustion method also affect energy consumption and the melting rate.
13. Types of Burners and the Use and Adjustment of Burners
The types of burners (commonly known as spray guns) also affect the combustion effect. Taking natural gas as an example, there are diffusion - type burners, ejector - type burners, premix - type burners, TY sleeve - type burners, and low - nitrogen burners. Different combustion equipment is selected according to different needs. The flame of a diffusion - type burner burns slowly, the flame temperature is not high, and carbon particles are precipitated during the combustion process.
► The ejector - type burner does not require a blower to supply combustion - supporting air, is easy to use, and is used in places with low temperatures and low heating requirements.
► The premix - type burner uses a blower to introduce combustion - supporting air, and the two are premixed in a small space. Its flame is short and is used in annealing furnaces with a low local temperature.
Glass furnaces mainly use TY sleeve - type burners. It uses the different velocity differences between two gases to generate entrainment vortices, improving the premixing degree of gas and combustion - supporting air and controlling the length of the flame. The combustion mechanism of the low - nitrogen burner is similar to that of the diffusion - type burner. The flame burns slowly, the flame temperature is not high, which reduces the generation of nitrogen oxides.
However, a large number of carbon particles are precipitated, increasing the blackness of the flame and strengthening the radiative heat transfer.
For the same type of burner, during the use process, proper adjustment of the state such as the angle between the fuel and the combustion - supporting air also has a great impact on the melting effect. After the spray gun is adjusted, when the flame radiation temperature on the glass liquid surface is increased by 20 - 30°C and the temperature of the thermocouple on the furnace top remains unchanged, the flame temperature rises, and the melting speed is accelerated.
⇒ The former Chengdu Dongfang Glass Factory produced fine white materials with a high melting rate. In addition to a relatively high potassium - sodium content (14.8%) in the formula, the relatively fast flame velocity was also an important factor because it strengthened the convective heat transfer.
Selecting a spray gun of an appropriate size, the diameter of the fuel pipe in front of the spray gun, adjusting the internal "node position" of the spray gun itself properly, and having reasonable fuel supply pressure, atomizing gas pressure, and the flow and pressure parameters of the ejector gas or the inner and outer flame fuels can make the hot spot of the furnace combustion appropriate and stable, which is conducive to increasing the melting rate.
The larger the furnace, the smaller the ratio of its heat - dissipating surface area to its volume. Under the same heat - preservation conditions, the heat dissipation is smaller, and the energy consumption is lower. The larger the furnace, the higher the melting rate. Therefore, the melting rates are different for furnaces of different sizes.
The foundation for achieving optimal melting rates lies in equipping the furnace with premium-grade refractory materials that demonstrate exceptional thermal stability and corrosion resistance.
Henan SNR Refractory Co., Ltd. has been specializing in the production of fused cast AZS blocks for about 25 years. We use high-quality raw materials and advanced fusion technology to provide customers with high-quality products. From raw material procurement to finished product delivery, every step is strictly quality inspected to ensure that every indicator meets the standards, so you can use it with confidence.
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