Sub Zero Polypropylene Grade Selection for Packaging Molders
Heterophasic polypropylene copolymers with controlled rubber dispersion prevent brittle container shattering during sub-zero cold chain transport and drop impact.
Structural Rigidity
Meaning
Resistance of a complete part to deformation under an applied load reflects both the material properties and the physical geometry of the design. Maintaining structural rigidity ensures that a moulded component can perform its intended function without bending or failing during use. This characteristic is a product of the flexural modulus of the resin and the moment of inertia provided by the part shape.
The term stops applying once the load exceeds the elastic limit and permanent deformation or fracture occurs.
Geometry Influence
Placement of ribs and gussets in a design increases the stiffness of a plastic part without adding excessive weight. Because structural rigidity is highly dependent on the thickness of the material, doubling the wall thickness can increase the stiffness by a factor of eight. Engineers use complex shapes to maximize the efficiency of the polymer.
These features also help manage the flow of the melt during the injection process.
Load Response
Analysis of how a part reacts to stress helps determine if it will meet its service requirements. A part with high structural rigidity will show very little deflection when a weight is placed on it. If the rigidity is too low, the part may interfere with other components or fail to seal properly.
Stress concentrations must be avoided to prevent premature failure.
Material Efficiency
Optimization of a part design allows for the use of less material while maintaining the necessary stiffness. Since resin costs are a major part of the production budget, achieving high structural rigidity with a thin wall is a primary goal. Using reinforced plastics can further enhance this property.
The final design must balance the ease of moulding with the mechanical needs of the application. Control of the cooling process ensures that the internal stresses do not reduce the stiffness of the finished component.