The production of container glass often requires many cost-intensive trials on the production line until the container has the requested quality. By simulation of the container forming process you can compare different variants of your container and you receive a solid basis for every optimization, which leads to cost reductions and time savings. Our CFD simulation software NOGRID pointsBlow was developed especially for the glass container industry. With this software the container forming process can be computed in full 3D in a practicable time.
Figure 1: Result view of some selected time steps
The following kinds of container glass forming processes can be simulated:
- BB (Blow and Blow)
- PB (Press and Blow or Wide Mouth PB)
- NNPB (Narrow Neck Press and Blow)
- PB (Press and Blow for the tableware industry)
As in reality, the simulation starts with gob loading and ends at take out. All process steps are integrated in one simulation model and all walls are activated and deactivated at the corresponding time step given by the IS machine time data. As shown in figure 2 the shape of the bottle can be each possible 3D shape. Also bottles with a handle or perfume bottles can be computed. Thus, there are no limits regarding bottle design and the user can test and evaluate a container design without restrictions.
Figure 2: Steps during BB process and different bottle designs
In the past many many container designs were computed and compared to real bottles with perfect results. The weights of bottles to be computed can be between 20 g (for example small perfume bottles) and 2000 g. The computation time depends on gob weight and is in the range of minutes for 2D computations and in the range of hours for 3D computations.
NOGRID pointsBlow needs input data before starting the simulation: Geometry, material data and process data.
GEOMETRY
The first question for the user starting to work with NOGRID pointsBlow is how to generate the geometry (figure 3), the shape of the blank mold, the shape of the final mold, the plug or plunger shape and of course, the geometry of the initial glass gob immediately before loading. The gob geometry is freely selectable. The temperature of the gob is assumed to be homogeneous, but can also be considered as inhomogeneous (see references: Moeller, A., Effects of asymmetric gob temperature on container glass forming, Proceedings 13th International Congress on Glass, ICG, Prague, 2013).
Figure 3: Geometry view
Because all companies use their own CAD system to model molds and other parts the software can import all shapes required using the well known STEP interface. This means the user can simply extract the shapes required into one CAD file and export this file to the STEP format; most CAD packages support exporting to the STEP format. If all material properties and process properties are given, the user can start the computation immediately. No meshing is required and the points within the initial gob are filled automatically.
MATERIAL PROPERTIES AND PROCESS DATA
In the glass container production process, glass composition and therefore glass properties can vary, although usually a soda lime composition is used. The composition for soda lime glass containers is not always the same (it can vary from company to company and from one plant to the next), so the user can apply individual glass data or use fix (default) data.
Figure 4: Material properties and process data
The most important and most sensible material property for the forming process is the viscosity of the glass, which depends on temperature. For this reason, it is essential to set the temperature for the initial gob precisely. Unfortunately, the temperature of the initial gob is usually completely unknown and can be measured only with considerable effort. NOGRID pointsBlow software can determine the initial homogeneous gob temperature automatically by the given gob weight using an empirical law.
Figure 5: Results view (temperature [°C] is selected)
RESULTS
In figure 5, the temperature at the last time step is selected. In order to analyse the results, the software computes the thickness of the walls at each time step by solving an additional differential equation. The user can select the thickness distribution like a usual variable such as, for example, the temperature (see figure 6). The XY-plot displayed in figure 6 shows the thickness distribution over the height of the bottle. In addition, the user can select certain single points within the glass volume and the software probes and displays all variables at that position.
Figure 6: Thickness [mm]: 3D view, xy-plot and point probing
NOGRID pointsBlow computes the forming process using all IS machine time data including pressure data, plunger movement and heat transfer data. The plunger movement can be driven by force or can be given by time position curve. It is clear that IS time machine settings can improve or worsen the quality of thickness distribution, so NOGRID software helps with the following:
- Finding the optimal blank mold shape
- Reducing the number of mold design tests
- Finding the best IS time machine data
- Reducing the number of trials in production
- Finding the lowest possible container weight
Last but not least NOGRID pointsBlow helps to understand the origins of glass defects in the container. Therefore, simulation helps to understand how the forming process is working in detail, which is the basis for all improvements.
SUMMARY
NOGRID pointsBlow software allows all main glass container forming processes being simulated in full 3D and in a practicable time. The graphical user interface is designed especially for the glass container industry and all modeling and simulation steps are easy to understand and perform.
By using the software, the number of mold and production design trials can be reduced significantly and the license investment costs can be amortized after the first new bottle design.
NOGRID pointsBlow is unique on the market: Any software but NOGRID pointsBlow can simulate the glass forming process of container glass for the forming processes Blow Blow (BB), Press and Blow (PB), Narrow Neck Press and Blow (NNPB) and PB for tableware in full 3-D and in feasible computation time.
