Lighter Through Foaming
Foaming of thermoplastic polymers is used to achieve weight reduction and simultaneously keep the special mechanical properties of the polymers.
A lot of thermoplastic polymers can be used to foam. The specialists of AKRO-PLASTIC recommend our carbon-fibre reinforced compounds - ICF compounds.
During the development of technical compounds for lightweight construction, the focus was not placed on obtaining absolute weight reduction, but rather on finding a combination of maximum weight saving with the best-possible preservation of mechanical properties exhibited by technical plastics, such as
• maintaining rigidity
• good strength
• good surface
• microcellular foam structure
The lightest polymers of AKRO-PLASTIC
Carbon-fibre-reinforced compounds drastically reduce the weight of high-strength components.
AKRO-PLASTIC has developed new ways to incorporate dry, conditioned carbon-fibre fabrics into a polymer melt in a manner which enhances the added value.
This involves shredding the fabrics in a multiple-step process so that they can be gravimetrically dosed on an extruder, like conventional cut-carbon fibres.
Tensile testing shows that even at higher temperatures, approximately the same strengths can be achieved with lighter ICF compounds from AKRO-PLASTIC than with significantly higher glass-fibre reinforcement.
Using ICF polymers will be the perfect choice to achive the best results when foaming thermoplastic polymers.
Foaming of Thermoplastic Polymers
In its search for weight-saving potentials, the plastics industry is continuously finding new solutions. By adding a chemically coupled polypropylene, and after moisture absorption, a newly developed polyamide blend (PA+PP) from AKRO-PLASTIC GmbH in Niederzissen, Germany, exhibits the same strength as a standard polyamide. Depending on application and the degree of reinforcement, the blends already save 7-10 % of density compared with standard polyamides, and have a better flowability. In order to reduce component weight even more, one approach is to charge the melt with a chemical or physical foaming agent.
Advantages of foaming thermoplastic polymers:
• weight reduction / material saving
• reduction of sink marks
• reduction of shrinkage and warpage / deformation
• realisation of parts with bigger walls
• strength-to-weight ratio is equal or higher
Lighter Through Foaming
Chemical Foaming Process
In the process of Chemical Foaming the foaming agent is mixed with the granulate in the form of a masterbatch or powder.
Chemical Foaming = Injection Moulding with Blowing Agent.
With chemical foaming, a chemical foaming agent is added to the plastic by means of a masterbatch. During processing, and under the melting conditions, the propellant is formed in the plasticising unit. Here, it dissolves in the melt and foams the plastic during processing after pressure relieve. Apart from flexibility, the advantage of this masterbatch solution lies in the option of including other components in the masterbatch formulation. This has further positive effects on foam formation, and depending on the polymer used, the processing method can be optimised even further.
Physical Foaming Process
In the process of Physical Foaming a gas (N2 or CO2) is injected directly in the polymer melt. Additional equipment is needed to inject the gas with high pressure into the melt.
Foam injection moulding is one possibility for further weight reduction. For that, a propellant is injected into the melt under pressure, which foams the plastic after or during mould filling. With these so-called physical foams, the gas is injected directly into the melt under high pressure in a sophisticated process. The resolution of patent issues has helped to increase popularity of this process. Typically weight reductions of 6-7 % can be achieved.
The mould is filled completely, compacted, and the shut-off nozzle is closed without a hold pressure phase (energy saving), so that the machine can already start the next metering stroke. This method achieves a weight reduction of 4% compared with the standard process without foaming agent.
The mechanical values remain practically identical. The advantage of this method is that the components can be produced practically warpage-free, because the hold pressure is maintained by the compound itself, and is therefore equally effective everywhere.
The mould is filled almost completely, but without compacting the melt. Also this method does not use hold pressure, and achieves a weight reduction of 13% compared with the zero value. The modulus of elasticity is reduced by 15%, i. e. roughly the same amount as the weight reduction. However, the flexural modulus remains above the zero value. The reason for this is explained by the second moment of area: The external surface area is included in rigidity with x³. This has an effect on the lower shrinkage of the system charged with foaming agent. On the other hand, there is 13% less of matrix material, which results in a corresponding reduction of rigidity.