By removing material that is not required from the component core and the internal after-pressure that operates nearly without pressure loss through the fluid, new designs and an otherwise unachievable component quality are possible. Competitiveness also improves drastically thanks to huge cost reductions (saving of material and cycle time).
Here, a key question is: gas versus water
Both processes have their specific area of application, although this is defined mainly by the component requirement.
Gas tends always to be preferred when shrinkage is to be compensated for, mass accumulations are not avoidable, channel cross-sections are very small, the water cannot be removed from the component or the structural size of the injector is key.
Water is used when the cross-sections and the channel length as a function of the material become too big for the gas injection technology. However, in addition to distortion, the residual wall thickness generally plays a central role.
From a business perspective, the significantly shorter cycle times and the non-incurred fluid costs are key factors leading to the selection of water. In the case of large unit numbers, this can lead to a reduction in investment costs of up to 50 %.
Part filling process
The mould is filled only partially with melt (generally 50–60 %), as the complete component filling takes place by means of the formation of the fluid bubble. Here, the fluid bubble drives the plastic melt away, so that, in the case of correct component design and pre-filling, the component is completely filled at the end.
Either water or gas is used as fluid.
Where it is sensible, this process is the most economically efficient, as material use and closing force requirements of the injection moulding machine are optimally reduced.
Suitability: Rod-shaped components, such as handles, etc.
Mass back pressure process
First, the cavity is filled completely with melt and then the overflow drain is opened before introducing the fluid. The fluid pushes the liquid melt right back into the space in front of the screw of the injection moulding machine. The pressed-back material lies at the front in the space in front of the screw and immediately forms the outer skin of the following component in the next cycle.
A semi-stable mixture of repeatedly reused material, as when recycling residual materials from the overflow process, is thus prevented.
Thanks to the hot runner systems that we developed, thermal and mechanical material decomposition is prevented. This process offers high reproducibility, maximum process capability, lower material use, and a reduction in the energy costs.
Suitability: Typical application examples include roof racks and pipes but also more complex components such as the plastic frame of the Karro wheelbarrow.
Projectile injection process
Once the cavity filling phase is completed, the fluid drives the projectile through the component. The special injectors that take on the projectile must be re-equipped for each cycle.
A thinner wall thickness – even in the case of larger cross-sections – can be achieved using this technology, in contrast to pure fluid technology.
In principle, this works with water and gas. Our pressure-dependent volume flow control, in particular, offers major advantages here, as it directly regulates the forward travel speed of the projectile. Thus, the projectile is prevented from “trundling” and a consistently smooth surface is produced.
Suitability: The geometry of the component should be designed as constant over the entire length, without contractions and flat areas. Hence, typical areas of use are cooling water pipes or charging air pipes with a larger diameter.
Aerosol is a relatively newly developed process variant of fluid injection.
The aim is to combine the advantages of the WIT and GIT technology without having to accept the respective disadvantages.
The aerosol process combines the advantages of WIT and GIT described above.
Aerosol on the GIT; however, here, finely dispersed water is fed to the N² during the injection.
By means of the water proportion, it can be set whether the inner cooling effect is to predominate or the option of pressure transfer to compensate for shrinkage.
Thanks to the supporting, solidified internal edge layer, the maximum cross-section of GIT components can be enlarged.
Typical components can come from the WIT area if the use of water is not suitable due to the geometry or the material, or if the shrinkage of mass accumulations must be compensated for.
Components whose cycle time is to be reduced or where the cross-sections are too big for pure gas application come from the GIT area.