melt fracture

melt fracture

[′melt ‚frak·chər]
(mechanics)
Melt flow instability through a die during plastics molding, leading to helicular, rippled surface irregularities on the finished product.
References in periodicals archive ?
In the 1960s, the accidental discovery that fluoropolymer polymer processing aids (PPAs) cannot only decrease the main polymer melt viscosity, but also retard the occurrence of sharkskin melt fracture on extrudates, allowed processors to increase the throughput, reduce energy consumption, and enhance processing quality.
Melt fracture, or sharkskin, can be a problem at high die shear rates.
Introducing Viton FreeFlow Z-100 and Z-200 fluoroelastomer process aids that eliminate melt fracture and reduce die build-up in polyolefin films, pipe, and wire/cable.
Melt fracture can manifest itself in the form of either small-amplitude periodic distortions appearing on the surface of extrudates (surface melt fracture (SMF) or shark-skin) or severe irregular distortions at higher throughput rates (gross melt fracture (GMF)).
Types of rheameters * Data analysis procedures * Constitutive equations * Rabinowitsch and Bagley factors * Melt elasticity and melt fracture * Die swell effects
In a conventional way, the stability of the melt can be characterized by a number of terms such as extrudate swell, sharkskin and melt fracture (3).
Melt Fracture, Sharkskin and Interfacial Instability
It is said to eliminate melt fracture, die build-up, and gel formation while also reducing energy use and boosting output.
Flow instabilities such as surface, stick-slip, and gross melt fracture also occur depending on the molecular characteristics of the polymer and flow conditions (1-4).
1% to 1% siloxane, the new additive offers reduced melt fracture, better mold filling, less extruder torque, internal lubrication, mold release, and less warpage of the molded part.
Examples are Tyrin CPE for use in weatherable PVC; Engage polyolefin elastomers, which can be used in PP and functionally grafted for use in engineering resins; Nordel IP EPDM, which functions as an impact modifier and low-profile additive in thermoset polyester SMC and BMC; and Viton freeflow fluoroelastomer, which increases throughput in polyolefin manufacturing and reduces melt fracture.
The processing rate in most of these techniques is limited by the appearance of flow instabilities collectively known as melt fracture phenomena (1-3).