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 ?
To estimate an impact of the die material on the efficiency of PPA and the conditioning time "to clear sharkskin melt fracture," we made extrusion trials of LLDPE with PEG 10,000 in concentration of 0.
Two new fluoroelastomer processing aids for polyolefins are said to eliminate melt fracture, reduce extrusion pressure, amperage, torque, and die build-up.
For film converters, the additive eliminates melt fracture quickly, facilitating the production of smooth, clear films with a high-gloss finish.
The stick-slip instability has been the subject of experimental studies since the late 1950s and has been given many different names such as stick-slip, cyclic, bamboo, cork flow, and oscillating melt fracture by researchers studying polymer extrusion instabilities [7, 8].
Bound Brook, New Jersey, was the first to describe the importance of the combination of land shear stress and exit extensional flow as the cause of sharkskin melt fracture.
Surprisingly, it is reported here that oscillating melt fracture flow details are extremely sensitive to such subtle changes in the structure of polymers.
The POP masterbatch is also said to reduce or eliminate melt fracture or excessive parison hang time and to aid column crush strength.
Melt fracture, or sharkskin, can be a problem at high die shear rates.
Specifically, wall slip, surface melt fracture, stick-slip (pressure oscillations), and gross fracture may be obtained like other instabilities.
Types of rheameters * Data analysis procedures * Constitutive equations * Rabinowitsch and Bagley factors * Melt elasticity and melt fracture * Die swell effects
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.
If the extrusion rate increases further, more severe roughening appears (small amplitude periodic distortions) described as "surface melt fracture," "land fracture," or "sharkskin" [5-9].