still was a strenuous business, involving much manual labor and sweat. In 1903, Michael J. Owens developed in Ohio the world's first fully automatic glass‐forming machine (Chapter 10.9). The concept consisted of a rotating machine that sucked glass from a pool of melt into forming molds. A preform of the final container (the so‐called “parison”) was first produced, and then transferred into a second mold where the parison was blown to its final shape to form the container itself. This truly revolutionary concept gave major advantages over semiautomatic methods since it cut labor costs by 80% and also led to the end of child labor in glass‐manufacturing companies. But this concept still had its drawbacks because the machine itself was expensive and cumbersome and a true monster of tons of rotated, lowered, and lifted metal.
In 1915, Karl E. Peiler and F. Goodwin Smith established a fully automatic press‐and‐blow rotary machine, which was fed with glass from above by an automatic paddle‐needle gob‐feeder (Chapter 10.9). Although this design resulted in a much less complex forming cycle, the machine was still a rotating system that involved again much mechanics and moving metal. And, most importantly, as soon as one section of a rotating machine experienced any problem, the machine as a whole had to be stopped. Hence, yield was significantly decreased when the complete machine had to be paused because only one section was experiencing problems.
With gob‐feeding getting more and more sophisticated, a search began for a more efficient forming process. In 1924, F. Goodwin Smith and Henry W. Ingle developed a totally new concept for automated glass‐container forming: the IS‐machine, where “IS” stands for Individual Section. The machine sections were no longer arranged in a circle but in a row. This meant that each section of the forming machine operated independently from the others. Hence, if failure occurred in one section, just this section and not the complete machine had to be stopped and fixed. This made production much more efficient and flexible. Production speed and container quality also were greatly increased.
With 4 individual sections in the first IS‐machine, the concept was soon improved and enhanced from initially 4 single gob sections (in total, therefore, 4 containers in one complete machine cycle) to nowadays 12 section‐systems with multi‐gob delivery to each section. In the most recent form, IS‐machines can consist of 12 sections, with 4 forming molds per section (quad‐gob system), summing up to 48 containers produced in one machine cycle.
Looking at a modern IS‐machine, however, one should nonetheless recognize the basic features that were designed when the concept was first developed. As shown in Figure 1, one section is made of the following zones, which will be explained more in detail later in this chapter:
1 Delivery equipment, consisting of scoop, trough, and deflector.
2 Blank‐side with plunger, neck‐ring, guide‐ring, mold‐halves. and baffle.
3 Invert with invert‐arm holding neck‐ring and guide‐ring.
4 Blow‐side with bottom‐plate, blow‐head, and mold‐halves.
5 Take‐out with tongs, dead‐plate, and pusher to conveyor belt.
Figure 1 Schematic overview of one section of an Individual‐section machine (here Narrow‐Neck Press & Blow process, double‐gob set‐up).
Several major improvements have been implemented in the forming process since its beginnings. We will, for instance, describe how, following the Press & blow (PB) and Blow & blow (BB) processes, the Narrow‐neck press & blow (NNPB) process has recently met with much success because of its more efficient forming. And it should also be stressed that the original pneumatic control of IS‐machines has given way to servo‐electric devices with which higher precision and reliability has been achieved.
2 Principles of Glass‐Container Forming
Before a glass can be formed, it usually has to be melted out of the respective raw materials. The melting of container glass bears some peculiarities such as a high usage of foreign (external) recycled cullet or auxiliary devices such as batch and cullet preheaters. Because these features and the basics of the melting of container glass are described elsewhere in Chapter 1.3, we will focus solely on forming.
Glass containers for mass‐market are formed with the aid of molds in which the molten glass is blown or pressed. The forming process consists of two steps. First a “parison” is made in cast‐iron “blank‐molds.” Then, in the second step, this parison is formed into the final container in “blow‐molds” that are made of either cast iron or aluminum bronze.
2.1 Heat Management in Glass‐Container Forming
A basic feature of the forming process is that it is highly non‐isothermal. On the one hand, temperature differences over the dimensions of the glass component are present and on the other, the glass experiences a great change in temperature and thus in glass properties. As a result, the forming process has of course to be designed to cope with these changes, which are the largest for viscosity.
When the gob enters the mold in the first forming step, it has a bulk temperature of about 1050°C. The mold itself has a temperature of 450–520°C at the end of the parison forming cycle, depending on forming conditions and container type. The glass–metal interface temperature TC, which is a very important parameter for the forming, is almost constant (Figure 2) because of the short contact time t of only a few seconds between the gob and mold material. It depends on the temperature of the glass T1, on that of the contact material (mold) T2, and on the thermal conductivity λ, heat capacity Cp, and density ρ of both the glass and the mold material [1–3].
For soda‐lime‐silica glass, at the relevant temperatures these values can be taken as λ ≈ 10 W/m⋅K, Cp ≈ 870 J/kg⋅K, and ρ ≈ 2500 kg/m3. For laminar cast iron, appropriate parameters are λ ≈ 55 W/m⋅K, Cp ≈ 500 J/kg⋅K, and ρ ≈ 7300 kg/m3. From these values, one can estimate TC with:
Figure 2 Temperature gradients and interface temperature between contact‐material and glass over time.
(1)
One finds in this way that temperatures of 1050°C for the gob and 470°C for the blank mold yield an interface temperature of ca. 614°C if no oxide layer resulting from corrosion of the mold is present and if the heat balance of the blank mold is correctly managed.
A certain cooling of the glass during the forming process is mandatory to achieve a stable enough product that does
