Glass has a long history in human development. For us, glass is one of the most incredible and useful materials, and it has been used in every field of human beings. At the same time, we also know that glass is a man-made material.
1. Preparation of batch materials
The batching room is where the raw glass materials are placed in different silos according to requirements before the mixed materials enter the kiln. The process steps are shown in the figure:
Step 1: Raw materials are transported to the glass batching room by train or truck, and visual inspection and sample inspection are performed to ensure the size and composition are correct.
Step 2: Raw materials are placed at their respective unloading points, then transported to the batching room by elevator and finally delivered to their respective silos.
Step 3: Before entering the kiln, raw materials are batched by electronic scales under their respective silos according to batches and proportions.
Step 4: Usually, one raw material is weighed at a time, and the batch must be accurate.
Step 5: The sensitivity of the scale is monitored daily and calibrated every week to ensure accuracy.
Step 6: Once weighed, the raw materials are conveyed to the mixer.
Step 7: In some factories, cullet is added after mixing to minimize the wear and tear of cullet on the mixer.
Step 8: After mixing, the mixture is transported to the kiln by horizontal belts or monorails.
Step 9: To reduce dust, stratification and flying materials during transportation, appropriate moisture is often added before mixing
Step 10: Wet materials enhance batch control in the kiln, which is very beneficial for efficient melting.
2. Melting process
The mixture is continuously fed into the kiln by means of a feeder.
-~100°C: drying of the mixture (~humidity around 4%)
-~700°C: solid phase reaction between carbonates
From 800°C: elimination of carbonates and reaction with silica (approximately 16% by weight)
From 850°C: reduction of sulfates and iron oxides by carbon
From 1200°C, clarification with dissolution of silica
In the soda-lime-silica glass container industry, there are two main types of kilns, horseshoe flame kilns and transverse flame kilns. The following figure shows the structure of a horseshoe flame regenerative chamber kiln.
This kiln has two small furnaces, side by side on the back wall of the kiln, and the regenerator is located behind the kiln. Each small furnace is equipped with 2-4 heating guns, which can use different fuels, such as heavy oil and natural gas, depending on the size of the kiln. The flame comes out of the small furnace on one side, then turns 180° and exits from the other small furnace. The route taken by the flame and the exhaust gas is like a horizontal "U". This design allows the combustion gases to have a relatively long residence time in the kiln, thus saving energy.
This kiln is also equipped with a combustion air preheating system, which is what we often call a regenerator. The regenerator allows us to reuse the heat energy of the combustion exhaust gas. One of the two regenerators absorbs the heat from the combustion exhaust gas (about 1300℃) to heat the grid refractory in the regenerator. The combustion air enters the kiln through the other regenerator. After a certain period of time, the flow of combustion air and combustion exhaust gas will reverse. The combustion air flows through the regenerator that has just been heated by the exhaust gas and enters the kiln. The heat stored in the lattice is transferred to the combustion air, heating the air. Through this heat exchange with refractory materials, energy can be saved and reused.
3. Forehearth used to transport molten glass to the molding machine
Normally, the temperature of the glass coming out of the kiln is too high for container glass forming. Therefore, the molten glass first flows into a refractory flow channel, which is what we call a forehearth (see the figure below). The function of the forehearth is to cool the glass to the working temperature and make the temperature of the cooled glass uniform.
In the forehearth, the glass with good thermal uniformity will be sheared into droplets by the scissor system, and then enter the forming machine to be finally formed into bottle-shaped glass.
4. Molding process
The forming process of glass bottles and jars refers to a series of actions (including mechanical, electronic, etc.) that are repeated in a given programming sequence, with the goal of making a bottle with a desired specific shape.
There are currently two main processes for the production of glass bottles and jars: the blow-blow method for narrow bottle mouths and the press-blow method for larger diameter bottles and jars.
1.The dripping material enters the primary mold
2.Neck shaping
3.Downward Blow
4.Forced bottle
5.Transfer into bottle mold
6.Blowing to finished product
7.Finished bottle
1.The dripping material enters the primary mold
2.Core pressing
3.Initial mold pressing
4.Forced preform
5.Transfer to bottle mold
6.Blowing to finished product
7.Finished cans
In both processes, molten glass, at its material temperature (1,050-1,200°C), is cut by shear blades to form cylindrical glass drops, called "drops". The weight of the drop is enough to produce a bottle. Both processes start with shearing the glass, and the drop falls under the action of gravity, through the trough and turning chute, into the blank mold, and then the blank mold is closed and sealed by the "buckle" on the top.
During the blowing process, the glass is first pushed down by the compressed air passing through the blind head, so that the glass at the mouth mold is formed; then the core moves down slightly, and the compressed air passing through the gap at the core position expands and squeezes the glass from bottom to top to fill the initial mold. Through such glass blowing, the glass will form a hollow prefabricated shape, and in the subsequent process, it will be blown again by compressed air in the second stage to obtain the final shape.
The production of glass bottles and jars takes place in two main stages: in the first stage, the mouth mold is formed with all the details, including the inner opening, but the main shape of the glass product will be much smaller than its final size. This semi-formed glass product is called a parison, and in the next moment, it will be blown into the final shape of the bottle.
From the perspective of mechanical action, the mouth mold and the core form a closed space below. After the mouth mold is filled with glass (after the puffing is completed), the core retracts slightly, causing the glass in contact with the core to soften slightly. Then the compressed air (backward blowing) from bottom to top passes through the gap under the core to form the parison. Then the blind head rises, the primary mold opens, and the flip arm flips to the mold side together with the mouth mold and the parison.
When the flip arm reaches the top of the mold, the molds on both sides will close and clamp to wrap the parison. The mouth mold will open slightly to release the parison; then the flip arm will return to the primary mold side and wait for the next round of action. The blowing head descends to the top of the mold, and compressed air is poured into the parison from the middle, squeezing the glass to expand into the forming mold to form the final bottle shape.
In the pressure-blowing process, the parison is no longer formed by compressed air, but by squeezing the glass in the closed space of the primary mold cavity through a longer core. The subsequent flipping and final molding are consistent with the blowing method.
The bottles are then clamped out of the forming mold by the bottle clamps and placed on a bottle stop plate with cooling air from bottom to top, waiting to be transferred to the annealing process.
