Common Problems and Solutions of Glass Strengthening Furnaces
In the field of glass deep processing, the glass strengthening furnace is a core equipment for realizing strengthening treatments such as glass tempering and lamination. Its operating status directly determines the quality of finished glass products. However, in actual production processes, affected by various factors such as raw materials, operations, and equipment conditions, finished glass products often have various quality defects. Among them, the bubble phenomenon and poor adhesion are the two most common and seriously influential problems. This article will conduct a detailed analysis of the specific causes of these two major problems and provide scientific and implementable solutions to help enterprises improve the yield rate of glass strengthening processing.
I. Causes and Solutions for the Bubble Phenomenon in Finished Glass Products
Bubbles are a high-frequency quality problem in glass strengthening processing, especially in the lamination strengthening process of tempered glass. The existence of bubbles will seriously damage the aesthetics and structural stability of glass, and may even lead to the scrapping of entire batches of finished glass products. Through long-term industry practice summary, there are mainly six causes for the occurrence of bubbles in finished glass products, each with clear corresponding solutions.
1. Uneven Surface of Glass
In the lamination process of glass strengthening, the flatness of the glass surface is the basis for ensuring the close bonding between the laminated film and the glass. Especially for tempered glass, due to factors such as uneven cooling during its production process, slight surface unevenness or warpage may occur. When such uneven glass undergoes lamination strengthening, tiny gaps will form between the uneven parts and the film. The subsequent heating and pressing processes cannot completely expel these gaps, and finally, visible bubbles will form.
For this problem, the most direct and effective solution is to increase the thickness of the film. The thicker film has stronger ductility and filling properties, which can better adapt to the uneven areas on the glass surface and fill the tiny gaps between the glass and the film, thereby reducing the generation of bubbles from the source. It should be noted that the increase in film thickness should be controlled within a reasonable range, which needs to be determined based on the actual unevenness of the glass and the requirements of the strengthening process, to avoid other quality problems caused by excessively thick films.
2. Uneven Thickness of the Film
The film is the core bonding material for glass lamination strengthening, and the uniformity of its thickness directly affects the bonding effect between the glass and the film. In actual production, if the operators have misalignment, overlap, or splicing of the film when laying it, it will cause local excessive thickness of the film, while some areas may have insufficient thickness due to splicing gaps. After the film with uneven thickness is compounded with the glass, bubbles will form at the parts with sudden thickness changes due to inconsistent thermal shrinkage.
To solve this problem, the key lies in standardizing the film laying operation and avoiding misalignment, overlap, or splicing of the film. Production enterprises should formulate strict film laying operation standards, requiring operators to ensure that the film completely covers the glass surface during operation, and that the entire film is flat without overlap or splicing gaps. For large-sized glass that requires coverage with multiple pieces of film, special butt-joint tools should be used to ensure uniform thickness at the film butt-joints, thus eliminating the bubble problem caused by uneven film thickness from the operational perspective.
3. Moisture in Laminated Decorations
With the growing demand for decorative glass, many glass strengthening processes add various decorations (such as metal wires, colored paper sheets, dried flowers, etc.) into the lamination to improve the decorative value of the glass. However, if these laminated decorations are not fully dried before use, the residual moisture inside them will evaporate during the heating process of glass strengthening, forming water vapor. This water vapor is trapped between the glass and the film and cannot be discharged in time, eventually condensing into bubbles. At the same time, moisture may also affect the bonding performance of the film, causing multiple quality problems.
In response to this, the corresponding solution is to fully dry the decorations. Enterprises should establish a pretreatment process for laminated decorations. Before putting the decorations into production, they should be professionally dried using drying equipment. Reasonable drying temperature and time should be set according to the material and moisture content of the decorations to ensure that the moisture inside the decorations is completely evaporated. For some decorations with strong water absorption, a second moisture test can be conducted after drying. Only when the decorations meet the standards can they be used for glass lamination strengthening, eliminating the hidden danger of bubbles caused by moisture from the raw material end.
4. Premature Shutdown of the Vacuum Pump
The vacuum system of the glass strengthening furnace is crucial for ensuring no bubbles inside the laminated glass. Its function is to extract the air between the glass and the film to form a vacuum environment, so that the film can closely adhere to the glass during the subsequent heating and pressing processes. In the production process, if the operator is eager to complete the process and shuts down the vacuum pump before the temperature inside the furnace is completely reduced, the residual heat inside the furnace will cause the residual gas between the glass and the film to expand when heated. At the same time, after the vacuum environment is destroyed, external air may also infiltrate, and finally, bubbles will form in the finished glass products.
To solve the bubble problem caused by this operational error, the solution is to strictly follow the start-stop specifications of the vacuum system, and only stop the vacuum pumping when the temperature drops below 40 degrees Celsius. Enterprises should install temperature monitoring and linkage control devices on the operation panel of the glass strengthening furnace. When the temperature inside the furnace does not drop below 40°C, the vacuum pump cannot be manually stopped. At the same time, training for operators should be strengthened to make them fully aware of the hazards of prematurely shutting down the vacuum pump, ensuring that each process is strictly implemented in accordance with the process parameters.
5. Vacuum Bag Leakage or Vacuum Pump Failure
The vacuum bag is a core component of the glass strengthening furnace for realizing the vacuum environment, and the vacuum pump is the equipment that provides vacuum power. If either of them has a problem, it will lead to insufficient vacuum degree inside the furnace. When the vacuum bag has problems such as damage or poor sealing (resulting in air leakage), or the vacuum pump fails to reach the rated vacuum value due to parts aging or failure, the air between the glass and the film cannot be completely extracted. The residual air will expand when heated during the heating process, forming bubbles and seriously affecting the quality of the finished glass products.
To solve this problem, efforts should be made from two aspects: equipment maintenance and performance guarantee, namely replacing the silicone bag, ensuring the operation of the vacuum pump, and increasing the vacuum degree to ≥0.094Mpa. On one hand, enterprises should regularly inspect the vacuum bag. Once problems such as damage or seal failure are found, the vacuum bag should be promptly replaced with a new silicone vacuum bag. At the same time, daily maintenance of the vacuum bag should be done well to extend its service life. On the other hand, a regular maintenance system for the vacuum pump should be established. The filter screen of the vacuum pump should be regularly cleaned, the lubricating oil should be replaced, and faulty parts should be repaired or replaced in a timely manner to ensure the stable operation of the vacuum pump. This will keep the vacuum degree inside the furnace at a standard value of 0.094Mpa or above, providing a reliable vacuum environment for the bubble-free processing of glass.
6. Excessively Fast Temperature Rise
The heating rate of the glass strengthening furnace is a key process parameter affecting the fusion effect between the glass and the film. If the temperature rises too fast, it will cause uneven heating of the glass, the film, and the air inside the lamination. Especially for films of different materials, they require specific temperature ranges for softening and curing. An excessively fast temperature rise will cause the surface of the film to soften quickly, while the interior is not fully melted. At the same time, the air between the glass and the film cannot be discharged in time and is trapped inside, eventually forming bubbles.
To solve the bubble problem caused by excessively fast temperature rise, the core is to slow down the temperature rise rate and adopt stepwise temperature rise, and formulate differentiated temperature rise and heat preservation curves according to different film materials. Specifically, if EVA film is used, it is necessary to first raise the temperature to 70°C and keep it warm for 10 to 15 minutes, then raise the temperature to 120°C and keep it warm for 40 to 50 minutes; if PEV film is used, it is required to first raise the temperature to 75°C and keep it warm for 10 to 20 minutes, then raise the temperature to 130°C and keep it warm for 30 to 60 minutes. It should be particularly noted that the heat preservation time depends on the thickness of the glass; the thicker the glass, the longer the required heat preservation time. This ensures that the glass and the film can be fully fused, and the air inside the lamination has sufficient time to be discharged, completely avoiding the generation of bubbles.
II. Causes and Solutions for Poor Adhesion of Finished Glass Products
In addition to the bubble problem, the poor adhesion of finished glass products is also a common problem in the processing of glass strengthening furnaces. Poor adhesion will cause problems such as degumming and delamination in the glass lamination, greatly reducing the impact resistance and service life of the glass, and failing to meet the safety performance requirements for glass in fields such as construction and decoration. Through industry practice analysis, the poor adhesion of finished glass products mainly stems from three aspects: processing technology, raw material quality, and glass pretreatment. The corresponding solutions are as follows.
1. Insufficient Processing Temperature or Heat Preservation Time
In the lamination process of glass strengthening, temperature and heat preservation time are the core parameters determining whether the film can be fully cured and closely bonded to the glass. The adhesive performance of the film can only be fully activated within a specific temperature range and after sufficient heat preservation time. If the processing temperature of the glass strengthening furnace does not reach the standard value required by the process, or the heat preservation time is too short, the film cannot be fully melted and cured, and the intermolecular force between the film and the glass surface is insufficient. Eventually, this will lead to the poor adhesion of the finished glass products.
To solve the problem of improper control of process parameters, the solution is to ensure the heating temperature and heat preservation time in accordance with the process requirements. Enterprises need to formulate an accurate parameter table of temperature and heat preservation time based on the material of the film used, the thickness of the glass, and the model of the strengthening furnace, and input these parameters into the intelligent control system of the glass strengthening furnace to realize the automatic and accurate control of temperature and time. At the same time, during the production process, a dedicated person should be arranged to monitor the temperature inside the furnace in real time, and the temperature sensor should be calibrated regularly to avoid substandard process parameters caused by equipment temperature measurement errors, ensuring that each batch of glass completes the strengthening processing under the temperature and heat preservation time that meet the requirements.
2. Film Failure
As the core bonding material for glass lamination, the performance status of the film directly determines the bonding effect of the glass. If the film is stored in an improper environment (such as a long-term high-temperature, high-humidity environment or direct sunlight), it will cause premature aging and failure of the film; in addition, after the whole roll of film is opened, if it is not used up in time and not stored in a sealed manner, the film will absorb moisture and dust in the air. At the same time, the adhesive components inside the film will oxidize due to contact with air, resulting in a decrease in adhesive force. Using such failed films for glass strengthening processing will inevitably lead to the problem of poor adhesion.
To avoid the quality hidden dangers caused by film failure, two aspects of work should be done well: first, ensure the film storage environment. Enterprises should establish a dedicated film storage warehouse, control the warehouse temperature at 5-25°C and the relative humidity at 40%-60%. At the same time, the film should be kept away from corrosive substances and direct sunlight. Second, standardize the film use process. After the whole roll of film is opened, it should be used up as soon as possible or stored in a sealed manner. For films that have been stored for a relatively long time, it is recommended to first make small samples to verify whether the adhesive force of the film is normal. The bonding firmness between the film and the glass can be tested by means of edge grinding treatment on the samples. Only when the samples meet the standards can the film be put into mass production.
3. Unclean Glass Surface
The cleanliness of the glass surface is the prerequisite for ensuring good adhesion between the film and the glass. If there are impurities such as oil stains, dust, and fingerprints remaining on the glass surface, an isolation layer will be formed between the glass and the film, hindering the molecular bonding between the film and the glass surface, and further leading to the poor adhesion of the finished glass products. Especially in the pretreatment processes such as glass cutting and edge grinding, it is easy to leave processing debris and oil stains on the glass surface. If the glass enters the strengthening process without thorough cleaning, it will directly affect the final bonding effect.
The key to solving this problem is to do a good job in the pretreatment cleaning of the glass and clean the oil stains and dust on the glass. Enterprises should establish a complete glass cleaning process. Before the glass enters the glass strengthening furnace, the surface floating dust should first be removed by a high-pressure air knife, then the surface should be wiped with a special glass cleaning agent to remove oil stains and stubborn dirt, and finally rinsed with pure water and dried to ensure that no impurities remain on the glass surface. At the same time, the cleaned glass should be well protected against dust to avoid re-contamination with dust during transportation and waiting for processing, creating a clean surface condition for the good adhesion between the film and the glass.
