An important role in some products production and, firstly liquids production is played by closing means. These special units are responsible for packed products safety.
Corking means classification occurs by various criteria, conditionally it can be presented as follows:
- purpose and frequency use rates: usual (repeated use) and branded;
- material: metal (tin, aluminum, crown corks), polymeric, wooden, traditional cork, combined, etc.;
- way of opening: pressing and turn; compression and turn; pressing and rise; turn; pressing (for a latch);
- method of fixing on a neck: corks, covers, combined. Covers close a filling opening on external perimeter; corks are pressed or screwed on a container neck. Kinds of covers are the bushona screwed on tubas, and capsules applied to closing flasks and bottles.
- structural elements: fixing on a neck, consolidations, openings of packing, functional purpose protecting from accidental opening.
Usual closing means can be reused, without any irreversible changes in packing. Opening of branded packing leads to irreversible change (destruction) of packing. Branded, original closing means are intended for single use.
A closing mean can be fixed with the help of single pass and the multiple carvings; elastic elements; bayonet connections; welding or pasting; coupling rings, carbine, wedge and lever locks. Listed methods are often combined.
Production of closing means also develops due to development of engineering, technologies and new materials emergence. Closing means for beer can be a great example. The first beer corks appeared in 17-18 centuries when humanity mastered production of a glass container. Beer demanded special conditions of transportation as the drink continued fermentation, emitted carbon dioxide and sought to push out the cork holding it. Rubber and ceramic corks popular in those days did not fit. The first spoiled taste, the second did not keep in a bottleneck. Therefore, the beer cork which was manually cut out from Spanish or Algerian oak bark was invented. Interacting with liquid, the cork inflated and densely blocked a neck, creating almost tight packing. It became possible to store and transport beer within several days. For reliability a cork and a bottleneck were additionally covered with a sealing wax or wax layer. The grades of beer which needed bigger endurance were closed by the cork strengthened by means of a special wire frame (similarly with wine-making technologies).
Such cork was replaced by a Crown Cork invented by American William Peynter. The new cover was disposable, cheap and easy in use. It was made from varnished from two sides steel. The corrugated flange edge reminded a crown and tightly adjacent to an outer surface of a neck, providing sealed bottle closing. The internal surface of a crown-cover was covered by the thin cork or paper layer protecting a metal bottom from contact with liquid. Crown corks were a successful invention and gradually started to be used not only for beer but also for closing of carbonated drinks, gaining popularity that time, and the principle of tightness assurance used by William Peynter did not undergo changes up to our time.
Requirements to bottle caps increase nowadays. Their purpose is not only to provide sealed closing, but also to be hypoallergenic and non-toxic. It is also important for caps to be easily opened, cheap, convenient in transportation and have an esthetic appearance.
Several subspecies of caps appeared during evolution. One of the most known is twist-off screwed on a bottleneck. Cloves were replaced with the guide rail pressed obliquely into a cap side in this version, that allows to open a bottle without using the opener and repeatedly close it.
Crown-covers made of aluminum are also demanded. This soft material is crumpled without any effort therefore the opener is also not required. The next invention is ring-pull cork, which differs from predecessors by an existence of a convenient ring for opening.
Caps for PET appeared after the appearance of plastic container. They are hats screwing on a neck of PET-bottles which can be used for a long time. Plastic caps were made from uniform plastic originally. Two-component caps appeared later (with additional internal laying from the polylineer). It allowed better hold carbon dioxide in a bottle, and protect a neck from deformation during transportation. Plastic caps became more reliable after the advent of a plastic ring which is put on a neck of a bottle and pointwise solder to a cover.
All listed advantages of plastic caps directly depend on quality of plastic they are made from. Good food plastic is inert, easily resists to environment changes, resistant to deformation. It is not oxidized and does not change taste.
Development concerned not only beer closing caps. Therefore the introduction of the covers for conservation designed for jars with a screw throat is begun. For GKR container (glass canning rounding, I type) are made covers with a rubber ring. In the process of rolling up the roller of the closing machine bends edges of a cover, the rubber ring is condensed and provides sealing of a jar. The GKR container is tightly closed, however it is difficult to open such jars. The glass container of the II type (blooming) is closed by tin covers by pressing a cover and a vacuum which is created in the sterilized jars after cooling. Sealing is provided due to putting condensing paste on a cover. This way is widely applied abroad, naming "Evrokan", and it characterized by easy opening and good sealing.
The German system of closing "PANNO" is a new invention. The cover is made from aluminum, and consolidation is made from polyvinylchloride. The neck of jars is issued by double-thread cutting. Aluminum covers do not have carving and perfectly adapt to roughness of a neck. The screw thread of glass during closing is pressed into vertical position of a cover. The main lack of this way is the high cost of aluminum covers (more expensive than tinned tin covers).