Mechanical Ink Set off Dynamics in Printed Web Rolls
Optimize roll winding tension and UV cure density to eliminate mechanical ink set-off and hold specific photoinitiator migration below legal regulatory limits.
Radial Pressure Profile
Meaning
Flow simulation results for extrusion dies typically feature a detailed map of the force distribution across the melt stream. Radial pressure profile arises due to the shear-thinning nature of polymers and the cooling effect of the channel walls. This variation influences the velocity of the melt and the orientation of the polymer chains across the thickness of the part.
It is a critical factor in determining the uniformity of the melt as it exits a die or fills a cavity.
Shear Gradient
Highest shear rates occur at the wall where the pressure gradient and friction are most intense. This leads to a thin layer of highly oriented material, often called the skin layer, while the core remains less oriented. If the radial pressure drop is too steep, it can cause melt fracture or surface defects like sharkskin.
Die Design
Balancing the pressure across the entire opening is necessary to prevent the profile from surging or thinning. In pipe or tube extrusion, an uneven radial profile leads to wall thickness variations around the circumference. Engineers use flow simulation software to optimize the geometry of the mandrel and die land to achieve a uniform exit pressure.
Melt Temperature
Thermal gradients across the flow contribute to the pressure variation by altering the local viscosity.