Understand the basic knowledge of glass materials

Glass is a colorless (white glass) transparent amorphous inorganic material made of quartz sand, limestone, feldspar, soda ash, clarifying agent, colorant/decolorizer, flux, broken glass, etc. The raw material is formed by melting, forming, annealing, cutting and other processes at high temperature from 1550 to 1600℃. Chemical composition of glass: the main component is SiO2, with a content of about 72%, Na2O content of about 15%, CaO content of about 9%, a small amount of AL2O3, MgO, etc. It has a series of very valuable properties: transparent, hard, good corrosion resistance, heat and electrical and optical properties; it can make products of various shapes and sizes with a variety of molding and processing methods; its properties can be changed by adjusting the chemical composition to meet different use requirements. In particular, the manufacturing raw materials are rich and the price is low.

Properties 

• 1. The density of glass is 2.45 ~ 2.55 g/cm ³, the compactness is 1, and the porosity is 0.
  
• 2. The optical properties are transmission, reflection and absorption
  
• 3. Thermal properties: The thermal conductivity of glass is poor. When the glass is partially heated, the heat cannot be transferred to the entire glass in time, and the heated part of the glass expands, causing internal stress in the glass and causing the glass to break.
  
• 4. Thermal stability of glass: the performance of glass to resist stable changes without damage.
  
• 5. Mechanical properties: The compressive strength of glass is high, generally 600 ~ 1200MPa, the tensile strength is very small, 40 ~ 80MPa, and the elastic modulus is 6 ~ 7.5 × 104MPa, which is 1/3 of steel and close to aluminum.
  

Production process

• 1. Process
  
• 1) Raw material preprocessing. Crush the massive raw materials (quartz sand, soda, limestone, feldspar, etc.) to dry the wet raw materials, and iron-containing raw materials are treated with iron to ensure glass quality.
  
• 2) Preparation of ingredients.
  
• 3) Melting. The glass complex is heated at a high temperature (1550~1600 degrees) in the pond kiln or crucible kiln to form a liquid glass that is uniform, bubble-free and meets the molding requirements.
  
• 4) Forming. Liquid glass is processed into the required shapes, such as plates, various utensils, etc.
  
• 5) Heat treatment. Through annealing, quenching and other processes, stress, phase separation or crystallization inside the glass are eliminated or generated, and the structural state of the glass is changed.
  
• 2. Forming method
  
• The melted glass liquid is converted into solid products with fixed shapes. Forming must be carried out within a certain temperature range. This is a cooling process. The glass first changes from viscous liquid to plastic, and then to brittle solid. Forming methods can be divided into two categories: artificial molding and mechanical molding.
  

Artificial molding

• 1) Blow, use a nickel-chromium alloy blow pipe, pick a ball of glass and blow it around the middle of the mold. It is mainly used to shape glass bubbles, bottles, balls (for scratching glasses), etc.
  
• 2) Pulling. After blowing into small bubbles, another worker sticks to the top plate, and the two are mainly used to make glass tubes or sticks while blowing.
  
• 3) Press, pick a ball of glass, cut it off with scissors to fall into the concave mold, and then press it with a convex mold. It is mainly used to form cups, plates, etc.
  
• 4) Free forming, after picking up materials, use pliers, scissors, tweezers and other tools to make handicrafts directly.
  

Mechanical forming

• Because of the high labor intensity, high temperature and poor conditions, except for free forming, most of them have been replaced by mechanical forming. Mechanical forming method:
  
• 1) For the rolling method
  
• It is used to produce thick flat glass, carved glass, wire glass, etc.
  
• 2) Casting method
  
• 3) Centrifugal forming
  
• The material is in the rotating mold. Due to the centrifugal force generated by the rotation, the glass unfolds and closes to the mold, and takes it out after coagulation. It is suitable for the molding of large glassware with uniform walls.
  
• 4) Sintering method
  
• It is used to produce foam glass. It adds foaming agent to the glass powder and heats it in a covered metal mold. The glass forms a lot of closed bubbles during the heating process, which is a good insulation and sound insulation material. In addition, the formation of flat glass has vertical introduction method, flat drawing method and float method. Floating method is a method of letting the glass liquid flow float on the surface of molten metal (tin) to form flat glass. Its main advantages are high glass quality (flat, smooth), fast pulling speed and large output.
  
• 5) Suppressing
  
• When manually molding, the material is manually cut into the iron mold, drive the punch, press it into an instrument shape, and remove the mold after the fixed type. Automated production of mechanical molding, large batches and high efficiency. The compression molding is suitable for small-shaped products that can exit the punch, such as cups, plates, ashtrays, etc.
  
• 4. Burn the edge
  
• The product has just been molded, and the general mouth is not smooth. Instead, it should be burned smoothly at high temperature and use more firepower.
  
• 5. annealing
  
• The glass has undergone intense temperature and shape changes during forming, which leaves thermal stress in the glass. This thermal stress will reduce the strength and thermal stability of glass products. If it is cooled directly, it is likely to rupture itself during the cooling process or later storage, transportation and use (commonly known as the cold explosion of glass). In order to eliminate the phenomenon of cold explosion, glass products must be annealed after forming. Annealing is to keep warm or slowly cool within a certain temperature range for a period of time to eliminate or reduce the thermal stress in the glass to the allowable value.
  

Prone to problems with glass products

• Explode
  
• Many bursting products do not burst after the fire is removed, but in the packaging box or due to collision or automatic explosion, mainly caused by insufficient annealing or poor packaging.
  
• Bubbles
  
• There are bubbles of different sizes on the product, mainly due to the purity of the material and the content of recycled material, as well as the temperature in the furnace. The more impurities the material contains or the higher the content of the added material, and the temperature in the furnace is not reached, bubbles may be produced.
  
• Water wave
  
• The surface is not smooth, with wrinkles or water ripples, mainly due to insufficient temperature or too low mold temperature.
  
• Impurities or spots
  
• It is due to the mixing of impurities or molten materials in the material, including material flowers, black spots, dark spots, etc.
  
• The side wall is too thin or too thick
  
• It is mainly caused by the more or less cutting of materials during manual operation.
  
• There are rust spots on the surface.
  
• Caused by the friction of the main mold or clamp.
  
• The molding line is too thick or too good.
  
• The match between the two molds is not good or the pressure is too high.
  
• The product is incomplete
  
• The font is not clear, caused by too little material or insufficient pressure, or too low temperature and poor exhaust.
  
• The surface of the product is dirty.
  
• Poor environment, insufficient cleaning or improper operation causes dirt to be adsorbed on the surface of the product.
  

Precautions for inspection of glass products

• 1. Glass products are damaged, bursting and notches. It must not be accepted by scrapers.
  
• 2. Glass products should not be deformed, and the mouth and bottom should not be uneven and skewed.
  
• 3. Bright material glass cannot be mixed with recycled materials. The heart of the product must be transparent and white, and there are no other miscellaneous colors. The tone of colored glass should be stable, pure, uniform and consistent.
  
• 4. Whether it is manually blown or machine-blown, the thickness of the glass should be average, not thin and thick on the other side.
  
• 5. Glass material should melt well and evenly, and avoid stones (unmelted slag) and stripes as much as possible. Defects such as bubbles.
  
• 6. THERE SHOULD BE NO BUBBLES ABOVE 1CM IN THE GLASSWARE PART (EXCEPT FOR BUBBLE EFFECT GLASS), AND THE NUMBER OF BUBBLES WITH A DIAMETER OF MORE THAN 2MM BELOW THE OR MORE THAN 1MM SHOULD NOT BE MORE THAN THREE PARTICLES IN DIAMETER. And the phenomenon of bubbles gathering together is also unacceptable.
  
• 7. After the finished glass is molded, the temperature should fade (fire) for about 8 hours, and at least 6 hours to ensure stable quality and prevent the product from bursting automatically over time. Glass bottles and tanks should have a certain thermal stability. When moving from hot water lees to cold water lees, the temperature difference below 39 degrees should be tested without damage.
  
• 8. There should be no too obvious water lines inside and outside the glass, and there should be no feel lines on the outer surface and inside, such as obvious wrinkles, scars, abrasions, shear marks and molding lines, etc. There should be no cracks and insufficiencies on the surface.
  
• 9. The mouth of glassware should be flat and smooth, without burrs and bumps, and lack of touch.
  
• 10. The inside and outside of the glass must be clean, and there must be no debris, dust, water stains, glass debris, etc. inside and outside the product. There should be no rust on glass products, and there should be no black spots, dust and other sundries in the glass. Note: The rust on glass products is usually caused by the rust of the clamps used to clip the glass when the fire is faded and the rust spots caused by the rust of the mold are stained on the glass, which cannot be removed later. Therefore. Whether the clamp and mold are rusty or not, it must be derusted before production to avoid this problem. It is also necessary to pay attention to avoid dust when dissolving materials. Impurities fall into the material, resulting in impurities in the product after molding.
  
• 11. Add acid glass. Be sure to avoid oil stains before adding acid, otherwise there will be uneven pickling during the acidification process, resulting in local shiny. After acidification, be sure to clean the white powder remaining inside and outside the glass.
  
• 12. Decal paper products. When decaling paper, it should be flat, not crooked, and there should be no bubbles. Generally, it should be naturally dried for 12 hours before baking. Because there will be small droplets of water left when the flower paper is soaked. When baking, small water droplets will appear on the top of flower paper, resulting in pinholes.
  
• 13. The product size should meet the requirements, and the error should not be too large. If you want to assemble a lid or other things, you should pay more attention to whether the inner caliber of the product meets the assembly requirements.
  
• 14. The appearance of the product is very important, but no matter what the product is, the most important thing is to check whether the functionality of the product is intact.
  
• 15. Glass is fragile. The product must be placed upright in the process of transportation, loading and unloading. Each product should be wrapped in paper, and the product should be separated with egg grids to avoid collision and damage to each other. The specific packaging method depends on the product and order requirements, but one point is that the packaging of the product must pay attention to safety to ensure that the export will not be broken and arrive at the destination safely.
  
• 16. During the inspection process, it is necessary to carefully check whether the packaging method of the product, the labels and contents used, the contents of the attached instructions, and the label information of the inner and outer boxes are correct.