Понятие и классификация стеклянных бутылок и банок в китайской отрасли стеклянной упаковки

The Concept and Classification of Glass Bottles and Jars in China's Glass Packaging Industry

A hollow glass product that can be sealed with a cap or a stopper and can hold various materials in measured quantities. It is widely used as a packaging container for beverages, alcoholic drinks, chemicals, medicines, stationery and cosmetics. Glass bottles and jars are transparent, easy to clean, chemically stable, do not contaminate the contents, highly airtight, excellent in storage performance, rich and varied in shape and decoration, can be recovered and reused many times, and come from abundant raw materials. But glass bottles and jars break easily and have a high weight-to-capacity ratio. These shortcomings are gradually being improved as process technology advances.

In the production of glass products, the output of glass bottles and jars is the highest. In 1980 world output of glass products was 68 Mt, of which glass bottles and jars accounted for 40.8 Mt.

From 2000 to 500 BC humans could already make hollow glass vessels. After the blowpipe came into use in 200 BC, the oil and winemaking industries began to use hollow glass as containers. During the Roman Empire demand for glass containers increased, and the great majority of products had round bottoms that had to be supported by iron or wooden stands. Only later, with the development of molds for blown glass, were stand-free flat-bottomed bottles produced. From the 5th to the 15th century, pressing, drawing and blowing techniques developed greatly, laying the foundation for the mechanization of glassmaking. In 1867 the Siemens brothers of Germany applied the regenerative continuous melting tank furnace to the glass industry, making large-scale production of glass bottles and jars possible.

From 1880 to 1890 the press-and-blow process for making wide-mouth bottles and the blow-and-blow process for making narrow-mouth bottles were invented (see glass manufacturing). In 1900 the first bottle-making machine driven by an electric motor appeared. In 1904-1905 M.J. Owens of the United States created the fully automatic vacuum suction-fed bottle-making machine. From 1910 onward gob feeders began to develop. In 1914 the semi-automatic blow-and-blow process matured. In 1925 the Hartford-Empire Company of the United States successfully developed the individual section bottle-forming machine, which used the blow-and-blow method and was later developed so that the press-and-blow method could also be used.

This individual section machine is still the main type in use today and has gradually developed toward multiple sections and multiple gobs.

In China, blowpipes were already used to blow hollow glass containers during the Tang and Song dynasties. The modern glass industry took shape in 1904-1908. The Shanghai Jinghua Glass Factory, established in 1931, was China's first plant to manufacture glass bottles and jars continuously using cross-fired and horseshoe-flame regenerative tank furnaces and automatic bottle-making machines. After the 1950s a number of fairly large modern bottle-making plants were built. In the 1980s the greatest improvement in the production of glass bottles and jars was the lightweighting of glass bottles, which saves raw materials and fuel, raises production speed and lowers transport costs.

Classification Glass bottles and jars come in a great many varieties and can be classified in many ways. (1) By shape, there are general bottles and jars, handled bottles and jars, and tubular bottles and jars, with capacities from 1 ml to 25 l. (2) By bottom shape, there are round, oval, square, rectangular and flat bottles and jars, with round ones predominating. (3) By mouth size, there are wide-mouth, narrow-mouth and sprinkler-mouth bottles and jars. Those with an inner mouth diameter greater than 30 mm and no shoulder or only a slight shoulder are called wide-mouth bottles and are often used for semi-fluid, powdery or lumpy solid items; those with an inner diameter less than 30 mm are called narrow-mouth bottles and are often used for various fluid items.

(4) By the form of fit between mouth and closure, there are continuous-thread mouths, cork-stopper mouths, pouring mouths, crown-cap mouths, roll-on cap mouths, plastic closure mouths, sprinkler mouths, press-on/twist-off mouths, side-seal/pry-off mouths, ground glass-stopper mouths, handled mouths and tubular mouths. Mouth dimensions and tolerances are all standardized. (5) By usage requirements, there are single-use bottles and jars and returnable bottles and jars. Single-use ones are discarded after one use; returnable ones can be recovered and rotated for use many times. (6) By forming method, there are molded bottles and tubing bottles. Molded bottles are formed directly from molten glass in a mold; tubing bottles are made by first drawing the molten glass into a glass tube and then forming it.

(7) By color, there are colorless, colored and opal bottles and jars. Most glass bottles and jars are clear and colorless, which keeps the contents looking normal. Next come green and brown. Green ones usually hold beverages; brown ones are used for medicines or beer. They can absorb ultraviolet light, which helps protect the contents. The United States stipulates that the average wall thickness of such colored glass bottles and jars should give a transmittance of less than 10% for light with a wavelength of 290-450 nm. A small number of items such as cosmetics, cold creams and ointments are packed in opal glass bottles and jars.

Raw materials and chemical composition The batch for container glass generally consists of 7-12 raw materials. The main ones are quartz sand, soda ash, limestone, dolomite, feldspar, borax, and compounds of lead and barium. In addition there are auxiliary materials such as refining agents, colorants, decolorizers and opacifiers (see glass manufacturing). Coarse quartz particles are difficult to melt completely; particles that are too fine tend to generate scum and dust during melting, which affects melting and easily clogs the regenerator of the melting furnace. The suitable particle size is 0.25-0.5 mm. To make use of waste glass, cullet is generally added as well, usually at 20-60% and up to 90%.

The chemical composition of container glass varies with its usage requirements, forming method, forming speed, process characteristics and raw material types. The vast majority of bottles and jars use soda-lime-silicate glass. The main components of soda-lime-silicate glass are SiO2, Na2O and CaO. Introducing appropriate amounts of Al2O3 and MgO can lower the devitrification tendency of the glass, enhance its chemical stability and mechanical strength, and improve its forming performance. The chemical composition of soda-lime container glass in most countries of the world is: SiO2 70-74%, CaO and MgO 10-14%, Na2O and K2O 13-16%, Al2O3 1.5-2.5%.

When colorless glass bottles and jars are made, the Fe2O3 content in the quartz sand is very low (generally around 0.03%). In ordinary soda-lime glass, adding Cr2O3 and Fe2O3 turns the glass emerald green, while adding sulfur-carbon or MnO2 and Fe2O3 turns it brown. Bottles and jars for medicines require higher chemical stability and are made of borosilicate glass. High-grade cosmetic bottles are often made of crystal glass containing lead, barium or zinc; some are opal glass, generally using fluoride as the opacifier.

Quality requirements Glass bottles and jars should have certain properties and meet certain quality standards.

(1) Glass quality: pure and uniform, free of defects such as sand, striae and bubbles. Colorless glass has high transparency; colored glass has uniform and stable color and can absorb light energy of certain wavelengths.

(2) Physicochemical properties: it has a certain chemical stability and does not react with the contents. It has a certain thermal shock resistance and mechanical strength, can withstand washing, sterilization and other heating and cooling processes as well as filling, storage and transport, and remains undamaged under ordinary internal and external stress, vibration and impact.

(3) Forming quality: it maintains a certain capacity, weight and shape, with uniform wall thickness and a smooth, flat mouth to ensure convenient filling and good sealing. There are no defects such as distortion, rough or uneven surfaces, or cracks.

Manufacturing process The manufacture of glass bottles and jars mainly covers batch preparation, melting, forming, annealing, surface treatment and finishing, inspection and packing.

(1) Batch preparation: includes storage, weighing and mixing of raw materials and conveying of the batch. The batch is required to be uniformly mixed and chemically stable.

(2) Melting: container glass is mostly melted in continuously operating flame tank furnaces (see glass melting furnace). The daily output of cross-fired tank furnaces generally exceeds 200 t, with large ones reaching 400-500 t. The daily output of horseshoe-flame tank furnaces is mostly below 200 t. The maximum glass melting temperature reaches 1580-1600°C. Melting energy consumption accounts for about 70% of total energy consumption in production. Energy can be saved effectively through measures such as fully insulating the tank furnace, increasing the capacity of the regenerator checker bricks, improving the distribution of the batch pile, raising combustion efficiency and controlling convection of the molten glass. Bubbling in the melting tank improves convection of the molten glass, strengthens the refining and homogenizing process and increases the draw-off. Electric boosting in a flame furnace can raise output and improve quality without enlarging the furnace.

(3) Forming: molding is mainly used, with the blow-and-blow process forming narrow-mouth bottles and the press-and-blow process forming wide-mouth bottles (see glass manufacturing). The tubing process is used less often. Modern production of glass bottles and jars widely adopts high-speed forming on automatic bottle-making machines. Such machines set certain requirements for the weight, shape and uniformity of the gob, so the temperature in the feeding channel must be strictly controlled. There are many types of automatic bottle-making machines, among which the individual section machine is the most commonly used. With this machine the gob follows the machine rather than the machine following the gob, so there is no rotating part, operation is safe, and any individual section can be stopped separately for maintenance without affecting the operation of the other sections (Figure 1). The individual section machine has a wide production range and great flexibility and has developed to 12-section, double-gob or triple-gob forming with microcomputer control.

(4) Annealing: annealing of glass bottles and jars serves to reduce the residual permanent stress in the glass to an allowable value. Annealing is usually carried out in a continuous mesh-belt annealing lehr, with a maximum annealing temperature of about 550-600°C. The mesh-belt annealing lehr (Figure 2) uses forced air circulation heating to make the temperature distribution uniform across the furnace cross-section and to form an air curtain that restricts longitudinal airflow, ensuring uniform and stable temperatures in all zones of the lehr.

(5) Surface treatment and finishing: the surface of glass bottles and jars is generally treated by hot-end and cold-end coating in the annealing lehr. Hot-end coating places the newly formed bottles and jars, still at incandescent temperature (500-600°C), in an environment of vaporized tin tetrachloride, titanium tetrachloride or butyltin trichloride, so that these metal compounds decompose and oxidize on the hot bottle surface into an oxide film that fills the microcracks in the glass surface, prevents the formation of surface microcracks and raises the mechanical strength of the glass bottles and jars.

Cold-end coating uses monostearate, oleic acid, polyethylene emulsion, silicone or silane, sprayed at the outlet of the annealing lehr onto the surface of bottles and jars at about 100-150°C to form a lubricating film that improves the wear resistance, lubricity and impact strength of the bottle surface. In production, cold-end coating and hot-end coating are often used in combination. For large-capacity bottles and jars of 1 l and above, some are given a foam polystyrene or polyethylene film sleeve on the surface. The sleeve is heat-shrinkable; once fitted and heated it tightly hugs the bottle body, is tough and elastic, absorbs shock and resists friction, and when the bottle breaks no fragments fly out, so personal injury can be avoided.

Reagent bottles, sample bottles and perfume bottles fitted with glass stoppers are ground at the mouth and the stopper using mortar or emery plus water as the abrasive. High-grade cosmetic and perfume bottles are often ground and polished to remove mold marks and add gloss. High-end liquor bottles or artistically decorated bottles and jars are etched with hydrofluoric acid to produce diffuse surface light and a fine feel. To print trademarks and decorations on the glass surface, spray coloring, screen printing or decal processes can be used, applying glass enamel to the surface of the bottles and jars and baking at 600°C so that the enamel fuses with the glass to form a permanent pattern. If organic pigments are used for decoration, baking at only 200-300°C is needed.

(6) Inspection: to detect defective products and ensure product quality. Defects in glass bottles and jars fall into two main categories: defects of the glass itself and forming defects of the bottle. The former include bubbles, stones, striae and off-color; the latter include cracks, uneven thickness, deformation, cold marks and wrinkles. In addition, the weight, capacity, dimensional tolerances of the mouth and body, internal stress resistance, thermal shock resistance and degree of stress relief of the bottles and jars must be checked. Because beer bottles and beverage and food bottles are produced at high speed and in large batches, visual inspection is no longer adequate, and automatic inspection equipment is now available, such as pre-selectors (checking the exterior shape and dimensional tolerances of bottles and jars), mouth inspectors, crack detectors, wall thickness measuring devices, squeeze testers and pressure testers.

(7) Packing: there are corrugated fiberboard box packing, plastic crate packing and pallet bulk packing. All have been automated. In corrugated box packing, the same carton is used from the packing of empty bottles through filling and sale. The plastic crates used in plastic crate packing can be recovered and reused. Pallet bulk packing arranges inspected and qualified bottles into a rectangular array, moves them onto a pallet and stacks them layer by layer, strapping them once the specified number of layers is reached. Generally a plastic film sleeve is also placed over them and heated so that it shrinks and tightly wraps them into a solid whole before strapping; this is also called shrink-wrap packing.

——This article is reprinted from China Packaging Network (pack.cn), original link: http://news.pack.cn/show-369991.html