In the processing of glass products, local heating by hot air blowers is a key process used to achieve glass softening, bending, welding or repair. Because glass is sensitive to temperature and has poor thermal conductivity, it is necessary to precisely control the heating parameters to avoid cracking or deformation. The following is an explanation from aspects such as operating principles, equipment selection, heating techniques and precautions:
First, the principle of local heating of glass by a hot air blower
Heat conduction and softening
Glass begins to soften at 500℃ to 800℃ (depending on its composition). The hot air blower transfers heat to the surface of the glass through hot air, raising the local temperature to a malleable state.
The softening point of borosilicate glass is approximately 820℃, while that of ordinary soda-lime glass is about 700℃.
Wind speed and thermal uniformity
High-speed hot air can accelerate the temperature rise of the glass surface, but it is necessary to avoid direct impact of the airflow to prevent stress concentration. Low-speed hot air is suitable for heating fine areas.
Applicable scenarios
Glass tube bending, flat glass hot-melt forming, glass and metal sealing, glass crack repair, etc.
Second, equipment selection and parameter Settings
Key parameter Settings
Temperature: Adjust according to the type of glass
Soda-lime glass: 600℃ – 700℃
Borosilicate glass: 750℃ – 850℃
Wind speed: Medium to low gear (level 2 to 3), avoid air flow disturbance
Distance: The nozzle is 10 to 20cm away from the glass surface and moves evenly
Time: Heat for 5 to 15 seconds per square centimeter (adjust according to thickness)
Third, local heating techniques
Positioning of the heating area
Marking method: Use a high-temperature resistant marker pen to mark the heating area on the glass to avoid overheating the non-target area.
Shielding method: Cover non-heated areas with high-temperature resistant insulation materials (such as ceramic fiber cloth) to reduce the impact of heat radiation.
2. Heating method
Linear heating: It is used for bending glass tubes, uniformly heating along the axis that needs to be bent. After softening, it is immediately bent and fixed.
Point heating: It is used for crack repair. Point heating is applied at both ends and the middle of the crack to make the glass slightly melt and then naturally close.
Annular heating: It is used for sealing glass and metal. First, the edge of the glass is heated in a circular motion until it softens, and then it is pressed together with the metal part.
3. Dynamic monitoring
Color change: When the glass softens, its surface will change from transparent to slightly red (soda-lime glass) or light yellow (borosilicate glass).
Hand feel test: Gently touch the glass with a high-temperature resistant tool. If there is a slight indentation, it indicates that it has softened.
Fourth, safety and quality control
Safe operation
Wear heat-resistant gloves, goggles and protective clothing to avoid high-temperature burns or glass splashes.
The operation area should be kept away from flammable materials and fire extinguishers should be provided.
Quality control
Cooling method: After heating, the glass should be cooled slowly (such as by covering it with asbestos cloth) to avoid cracking caused by rapid cooling.
Dimensional accuracy: For curved glass, use molds or fixtures to fix the shape and maintain the designed dimensions after cooling.
Visual inspection: After repair, the glass surface should be free of bubbles, cracks or obvious deformations.
Fifth, case application
Case 1: Bending of Glass Tubes (Laboratory Equipment)
Step:
Mark the curved area (5cm in length) with a marker pen.
The temperature of the hot air blower is set at 650℃, with a wind speed of 2 gears, and it is 15cm away from the glass tube.
Slowly move the nozzle along the marked line and heat for 10 seconds until the glass turns slightly red.
Immediately bend the glass tube to 90° and fix it with a fixture for cooling.
Effect: Uniform bending radius, no cracks.
Case 2: Glass Crack Repair (Artwork)
Step:
Clean the surface of the crack and cover it with heat insulation cloth to expose only the crack area.
The temperature of the hot air gun is set at 700℃. It heats the two ends and the middle of the crack in a point-like manner, with each point heated for 8 seconds.
After the glass is slightly melted, gently press it with tweezers to close the crack and let it cool naturally.
Effect: The crack is invisible, and the repair strength reaches 80% of the original glass.
Sixth, Summary
The core of local heating of glass by a hot air blower lies in “precise temperature control, uniform heating, and dynamic monitoring”. By rationally selecting equipment, setting parameters and mastering operation skills, efficient softening and shaping of glass can be achieved. During operation, closely monitor the condition of the glass and adjust the parameters in a timely manner to avoid defects caused by overheating or uneven heating. For complex shapes or high-precision requirements, auxiliary technologies such as infrared heating and laser heating can be combined.
