Everyone actively involved with the manufacture of glass containers knows that, in almost every instance, glass containers are coated with two substances: one coating occurs at the hot-end of the lehr immediately after forming (the hot-end coating) and the other occurs as the bottles exit the annealing lehr (the cold-end coating). Since there is such an intimate relationship between the hot and cold-end coatings, it is probably not possible to discuss one without the other. In the past, when glass containers were heavy and line speeds slow, there was little necessity for surface treatment. For instance, a glass plant in Southeast Asia was visited recently and it was observed that the plant used neither hot-nor cold-end systems. The ware was incredibly heavy, the speed exceedingly slow, and the lehr was covered with broken glass. This was, apparently, a normal everyday occurrence in the plant. However, in most modern manufacturing plants, bottles have become increasingly lighter in weight ad speeds have accelerated enormously, both in the glass plant and on the filling line. Because of these changes, the need for surface treatment is vital. This article describes in detail how cold end coatings are applied, why they are applied, and how they work.
