the current IS‐machines, the loading speed of the gob is often so high that the finish is already formed at the gob‐loading step, which would make the settle‐blow unnecessary for the finish forming. This step is nonetheless maintained in the process to guarantee a constant heat transfer between the glass and the blank, from cycle to cycle, before counter‐blow. During settle‐blow, a vacuum can be applied through cavities in the molds to support the parison and finish forming. Some modern BB IS‐machines work without a funnel. They control the switch between settle‐blow and counter‐blow by a valve in the baffle to exhaust the compressed air that is used for settle‐blow.
After settle‐blow, the baffle is quickly lifted, the funnel is removed, and the baffle settles again and closes the blank‐mold completely. A counter‐blow is applied from the down side through the formed finish, blowing the glass fully into the mold shape and forming the parison (Figure 3c).
This two‐step blowing process with settle‐blow and counter‐blow on the blank‐side causes an inhomogeneity in the container because of different contact times between the glass and the mold above and below the loading line. Such an inhomogeneity can be seen as a horizontal, optical streak in the body of the containers. It is called settle‐ or feeder‐wave and can be reduced in several ways, but not fully avoided. When looking at a final container, the existence or nonexistence of a settle‐wave thus indicates whether or not the container has been produced with the BB process.
Figure 3 (a–d) Blow & blow process, blank‐side.
After the parison has been formed, the baffle is removed (Figure 3d), the mold opens, and the parison is transferred via the invert mechanism to the blow‐side.
The final forming of the container is in principle the same for all three forming processes. The following description will thus apply to all of them. When transfer to the blow‐side is over, the parison lengthens into the blow‐mold as determined by its viscosity and the machine parameters. This causes the outside of the parison to be reheated by the heat stored in the hot inside and temperature to homogenize within the parison (Figure 4a). This reheat is essential to ensure that the container is to be precisely formed to its intended shape. The blow‐mold is then closed, leaving the finish outside. The invert‐tongs open and the container is released from the invert. Directly after releasing, the blow‐head with a blowing‐tube is placed on top of the finish (Figure 4b). Through this blow‐head, the final‐blow is applied, giving the parison the final shape of the container (Figure 4c). Strictly speaking, the reheat ends when the final‐blow is triggered.
After the container has been released by the blow‐mold, a take‐out grips it by its finish (Figure 4d) and places it over a dead‐plate through which air is blown from below to cool it further. Finally the container is transferred via a pusher onto a conveyor belt.
3.3 Press & Blow Process
The PB process is used for wide‐mouth containers of all weights, such as jars and baby‐food containers. It differs significantly from the BB process at the blank‐side. After loading the gob (Figure 5), the blank‐mold is closed fully by the baffle and a plunger presses in an upward movement the glass from below into the mold (Figure 5b). The plungers usually are made out of tungsten carbide (WC) or another hard metal to ensure a long lifetime. In contrast to BB‐forming, the process causes the finish to be formed at the end of the blank‐mold process (Figure 5c) and no disturbance such as settle‐wave is introduced into the parison because it is formed by a single (smooth) motion at the blank‐side. As in BB, the baffle is removed after the parison has been formed, the mold opens (Figure 5d), and the parison is transferred to the blow‐side to get its final shape as described above.
Figure 4 (a–d) Forming of the final container at the blow‐side (same for all processes).
3.4 Narrow‐Neck & Blow Process
The NNPB process is mainly used for lighter containers such as beer bottles, small water and juice containers, and other lightweight containers. It is the most advanced forming process because it yields not only the highest machine speeds but also a homogeneous glass distribution in the final container. It is similar to the PB process in that the gob is not blown into the parison but pressed via a plunger. After loading the gob (Figure 6), the mold is closed fully by the baffle and a plunger smaller in diameter than in PB presses in an upward movement the glass into the mold (Figure 6b). The plungers are also made out of tungsten‐carbide. As with PB, the finish is formed at the end of the blank‐mold process (Figure 6c). Again, the baffle is removed after the parison has been formed, the mold opens (Figure 6d), and the parison is transferred to the blow‐side.
Figure 5 (a–d) Press & blow process, blank‐side.
Restrictions in usage of the NNPB process are due to the plunger dimensions and finish openings and the corresponding cavities pressed into the parison. The parisons are usually shorter for NNPB than for BB if the same final container shape is to be produced (e.g. a 0.33 l beverage bottle). Another significant difference between NNPB and BB is that the required gob temperature is from around 20 to 50°C higher in NNPB because of difficult pressing conditions. This difference in consequence leads to different thermal requirements during the process in terms of mold‐cooling and reheat‐timing.
4 Making of the Gob: Forehearth, Feeder, and Shears
Most forming processes take place at a viscosity of 102–104 Pa⋅s. Hence, for soda‐lime‐silica containers, the glass needs to be cooled from melting and fining at ca. 1500°C and a viscosity of 10 Pa⋅s down to ca. 1050°C and a viscosity of 103 Pa⋅s. This quite demanding task is accomplished in the forehearth. The forehearth is directly connected to the working‐end and ensures the required homogeneity of the glass while bringing it to the desired temperature and viscosity.
After the forehearth, a feeder enables glass‐portioning and gob pre‐shaping (Figure 7). It consists
