Double-walled glass cups, with their advantages of heat insulation, scalding prevention, and crystal clarity, have become common utensils in daily drinking and office settings. Their seemingly simple double-walled structure actually conceals a sophisticated manufacturing process. From raw material selection to finished product delivery, they undergo rigorous control over multiple processes, each directly affecting the cup's quality and lifespan.
The core raw material for making double-walled glass cups is high borosilicate glass. This type of glass is heat-resistant, impact-resistant, odorless, and can withstand sudden temperature changes without breaking. The raw material is first crushed, cleaned, and impurities removed before being sent to a furnace to melt into a homogeneous glass liquid at a high temperature of approximately 1500℃. During the melting process, continuous stirring is required to ensure the glass liquid has a uniform texture and prevent the formation of air bubbles.
After the glass liquid cools to a suitable temperature, it enters the molding stage, the core step in creating the double-walled structure. Currently, the mainstream method uses a "two-stage molding process": First, the inner cup body is pressed out using a mold. After it cools and sets, the inner cup body is fixed in another mold. Then, molten glass is injected into the gap between the inner and outer layers, pressing out the outer cup body, ensuring a tight fit between the two layers and forming a sealed interlayer. The thickness of the interlayer needs to be precisely controlled between 0.3-0.5 mm. Too thin, and it will affect the heat insulation effect; too thick, and it will increase the weight of the cup and reduce its feel in hand.
After molding, the cup body needs to undergo annealing in an annealing furnace. This is a crucial step in improving the stability of the glass. The cup body is slowly cooled in the annealing furnace from 500℃ to room temperature, a process that lasts 4-6 hours. The purpose is to eliminate internal stress in the glass and prevent cracking due to temperature changes during subsequent use. After annealing, the cup body undergoes rough grinding, fine grinding, and polishing processes to remove burrs and imperfections from the rim and body, resulting in a smooth, rounded rim and a clear, glossy body.
After polishing, the cup body undergoes rigorous quality testing. Inspectors will use strong light to check for bubbles and cracks in the interlayer, measure dimensional accuracy with calipers, and check the seal through a water injection test-the interlayer of the double-walled glass cup must be kept in a vacuum state; if the seal is not tight, the heat insulation effect will decrease, and water vapor may enter and cause condensation. Qualified cups will also be decorated with printing, engraving, and other surface decorations as needed, and finally, after cleaning, disinfection, and packaging, they can be shipped to the market.