Meaning
Non-dimensional ratios compare the elasticity of a fluid to its rate of viscous deformation during a flow sequence. In polymer processing, the weissenberg number quantifies how much the long molecules are stretched out by the machine’s speed versus how quickly they can curl back to their resting shape. High values indicate that the fluid has a strong memory and will likely swell or warp at the die exit.
Processing Limits
Engineers use this metric to decide if a machine run will maintain its dimensional stability. At a low weissenberg number, the fluid behaves much like simple water or oil with few elastic surprises. When the value rises, the complex internal stresses lead to effects like die swell or uneven corner filling.
Stability Boundary
Predicting the onset of turbulence and instability requires this number to be calculated for each specific dye geometry. While the shear rate measures the intensity of the push, the weissenberg number shows how the polymer structure fights back against it. This distinction identifies if a resin is capable of being processed at high output speeds without snapping or breaking in the die.
Material Comparison
Different batches of plastic with the same nominal viscosity might show vastly different levels of elasticity under pressure. This figure provides the technical audit needed to switch suppliers without risking a line failure. It defines the point where production yield begins to drop due to purely structural behaviors of the melt.