Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 125

When they leave the annealing lehr, containers have a temperature between 80 and 120°C. They are coated a second time in a spray process. The main purpose of this cold‐end coating is to protect the container against scratches upon further handling and later at the filling line. Usually a polyethylene wax is used to decrease surface friction, hence making the containers less susceptible to scratches when being handled or touching one another. The cold‐end coating also serves to provide a surface suitable for good adhesion of the label, which is usually fixed at the filler.

After application of the cold‐end coating, another inspection takes place in a highly automated way such that additional inspection by human eye is applied only in rare cases. Most inspection systems are based on various sophisticated optical systems, each checking for a certain type or group of potential defects that include flaws, scratches, cracks, blisters, seeds, loose or stuck glass particles, or dimensional errors of the container. Because special attention is paid to the finish of the container, mechanical inspection systems are, for instance, applied for testing that it is free of obstacles. Finally, random checks are made offline, e.g. to check that the strength exceeds definite values that depend on the kind of container. For impact strength, usually a minimum lot‐size of 30 containers is tested on a shift, daily or some other regular basis, depending on the container made and plant procedures. The container is hit by a pendulum of a certain weight – depending on the chosen specification and domain of the container – in a well‐defined matter until it breaks. As for the burst pressure strength, which is especially relevant for carbonated liquids such as sparkling wine, water, and champagne, the container is filled with water and its pressure is increased until breakage. Also here, due to the Weibull‐characteristics of brittle materials, a minimum of at least 30 containers should be tested. After inspection, the containers are pelletized, wrapped, and prepared for shipment.