Simulation, especially fluid flow simulation or CFD (Computational Fluid Dynamics) is not usually easy to operate and companies commonly need CFD experts to compute such tasks. To overcome this sticky situation, in the last two years Nogrid has developed a forming simulation software especially for the glass container industry. The name of the software is NOGRID pointsBlow and the software computes the glass container forming process in full 3D. Figure 1 shows the process steps that occur during the BB process schematically.
Figure 1: Result view of some selected time steps
NOGRID pointsBlow software is able to simulate the following kinds of container glass forming processes:
- 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 switched on and off 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 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 choice of experimental verified bottles
All bottles shown in figure 2 and more were computed with NOGRID pointsBlow software and the results were compared with bottles produced by an actual production line. The focus of attention during this investigation lay on the wall thickness distribution of the final bottle (see also figure 7) and the agreement between simulation results and actual bottle measurement results were perfect. The weights of the bottles evaluated were in the range between 200g and 1500g. The computation time depends on gob weight and can increase from one hour up to eight hours using a conventional high end PC (eg Intel i7 990x). For 3D simulations, there are noticeably small values and the user can run several jobs each day.
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.
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. Although 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), the software currently applies fix 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 gob temperature automatically by the given gob weight using an empirical law which was found during a project where more than 30 bottles were investigated. As shown in figure 5, if the expert options are activated, the user can specify the heat transfer parameters for the solids that come into physical contact with the glass. If the expert options are disabled, the user simply selects the corresponding material (eg cast iron, steel or Minox). Selecting the process tabulator, the user can specify the process type (BB, PB, NNPB), as well as all IS machine data.
Figure 5: Results view (temperature [°C] is selected)
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 7 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
As mentioned above, the results of the simulation were compared with a large experimental data pool. Figure 7 shows three bottle cross-section examples, including the cross-section obtained by simulation at the corresponding right side.
Figure 7: How the results were evaluated
These comparisons were made for all bottles available and the main results are:
- The limiting heat flux from glass to the mold is the glass heat conductivity, not the conductivity of the molds.
- In a correct mold design, it is important to cool down the molds with air and to prescribe the contact temperature between mold and glass. However, for a high quality forming process, the glass needs the same thermal conditions, independent from the shape of the container.
- The initial gob temperature decreases with the gob weight.
Independent from bottle shape, the gob needs the same thermal conditions. Thus, mold designers have to create molds in such a way that within the given time and considering the given glass energy loss, the glass contact sides of the molds consistently have the same temperature immediately before glass contact. This means mold designers do not usually need to compute the exact fluid flow of the forming process.
Provided that mold conditions are ideal, the NOGRID pointsBlow computes the forming process using all IS machine time data including pressure data, plunger movement and heat transfer data. 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, the NOGRID pointsBlow helps to understand the origins of glass defects in the container. Therefore, the simulation helps to understand how the forming process is working in detail, which is the basis for all improvements.
NOGRID pointsBlow software allows all main glass container forming processes to be simulated in full 3D and in a practicable time. The graphical user interface is designed especially for the glass container industry and all modelling 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 ROI can be achieved after the first new bottle design.
With our new software NOGRID pointsBlow we have put a product in the market, that is unique: Any software but NOGRID pointsBlow can simulate the glass forming process of container glass based on the Blow Blow (BB), Press Blow (PB) and Narrow Neck Press Blow (NNPB) Process in full 3-D and in feasible computation time.
If you are a manufacturer of container glass you should not miss testing our software. You won't find any other software worldwide for the belongings of simulation of the container glass forming process that is able to generate solid solutions in a very short time. Even complicated forms of glass containers, such as bottles with handles, can be simulated with NOGRID pointsBlow.
Don't miss your chance to simulate the glass forming process absolutely professional. You'll be more effective, you'll save time and resources with NOGRID pointsBlow software. You will be convinced and inspired if you decide to test our software. Please contact us for a trial version.