Читать книгу Encyclopedia of Glass Science, Technology, History, and Culture - Группа авторов - Страница 119

The IS‐machines can be separated into three groups:

1 Pneumatic‐controlled IS‐machines with angular mold‐opening.

2 Pneumatic‐controlled IS‐machines with parallel mold‐opening.

3 Servo‐electric‐controlled IS‐machines with parallel mold‐opening.

In the earliest types of IS‐machines, all movements are controlled by pneumatic valves. The mold opening and closing is in an angular motion, which means that in a multi‐gob setup at the blank‐mold‐side, the inner blanks are more widely opened than the outer blanks, causing difference in radiation between the glass and the open blanks. At the blow‐side, the inner molds are not opened as wide as the outer molds, which may lead to difficulties in machine accuracy and forming.

A significant step forward, therefore, was the introduction of pneumatic‐controlled IS‐machines with parallel mold‐opening and closing. Here the mold‐halves from the inner, middle, and outer cavity open in a parallel motion to each other. This leads to more comparable conditions between the molds of a given section. Furthermore, the parallel closing and opening is more precise, leading to a more reliable forming. In the color section of this Encyclopedia, a picture of a modern pneumatic‐controlled IS‐machine is shown.

The next logical improvement was to exchange the pneumatic‐controlled movement for a servo‐electric‐controlled motion to take advantage of the enhanced stability, reliability, and precision of servo‐electric drives. In this way, motions are much more easily cushioned and are gentler for the hinges, molds, and also for the glass itself. In the latest generation of IS‐machines, mold opening and closing, plunger motion, invert, blow‐head, take‐out, pusher, and other parts are thus servo controlled.

The machine speed is a general parameter to describe the production performance for a given container. It is expressed as the cavity rate (C), namely the number of containers produced per minute (cpm) for each cavity considering the total numbers of cavities (N_S) of the IS‐machine:

(5)

For a 12‐section machine with a triple‐gob setup and container output of 324 containers per minute, the cavity rate C is, for instance, 324/12 × 3= 9. Hence, a 12‐section IS‐machine with a triple‐gob setup producing 240 containers per minute is running a lower cavity rate than a 10‐section IS‐machine with the same triple‐gob setup producing the same number of containers per minute. Highly efficient IS‐machines can go up to cavity rates of 25 for small container sizes. This rate translates to production speeds of more than 700 containers per minute. In general, one can state that the higher the gob weight and the larger the container size, the lower is the corresponding cavity rate.

As illustrated in Figure 8 for 0.3‐l beverage bottles, the performance of IS forming machines has steadily improved since their inception in the 1920s. In 90 years, one forming line has been producing 26 times more containers per minute. And in the same period the weight of such containers could be decreased from more than 300 to less than 170 g. These figures show vividly the very strong potential that this forming process had when it was invented.

Figure 8 Performance increase of IS forming machines over the years in containers per minute.