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Ultra-high molecular weight polyethylene molding process
by：CSSSLD
2021-02-03
Melt fracture appear when the shear rate is called the critical shear rate, its relationship with polyethylene is inversely proportional to the relative molecular mass of the.
High relative molecular mass of UHMWPE may be produced when the shear rate is very low melt fracture phenomenon, so the extrusion process often encounter will be caused by the melt fracture and crack phenomenon, therefore in the injection molding processing speed cannot too fast.
In injection molding, caused by a jet flow state porosity and delaminating phenomenon, this is another big problem in the processing of UHMWPE.
people usually think of the melt was broken when shear rate is called the critical shear rate. Practice has proved it and decreases as the molecular weight of polyethylene. So for high molecular weight of UHMWPE in low shear rate, melt fracture may be produced. Under the strong and rate lower, will produce the phenomena of flow or jets. So in ultra-high molecular weight polyethylene extrusion processing when cracks due to easy to burst phenomenon, in there was a jet in the ultra-high molecular weight polyethylene plastic injection products appear porous or delaminating phenomenon. This is a processing problem of ultra-high molecular weight polyethylene thermoplastic method.
it is sticky while ordinary polyethylene melt flow pattern, from the mouth out immediately after prolapse, and fused UHMWPE, mouth when die extrusion with high temperature of melting stiffness, not immediately prolapse, translucent solid level to the lower direction to move forward, characterized by high viscoelastic state. Thus, UHMWPE melt viscosity is extremely high, the special melt flow is poor. UHMWPE friction factor is extremely low, even in the molten state, so in the process of feeding easy slippage in charging period, unable to move forward, this is also the problem encountered in the process of screw extrusion processing.
as thermoplastic engineering plastics UHMWPE in solid state has excellent comprehensive performance, but the melt characteristics and ordinary polyethylene thermoplastic and distinct, bring difficulties to processing. Ultra-high molecular weight polyethylene melt flow rate even in 10 times more cases is almost zero, so it can be seen that the liquidity is poor. Ordinary polyethylene processed in the extruder, the hopper to join solid granule or powder material in the barrel and screw under the action of shear, gradually transformed into a viscous fluid, even if the screw design and temperature condition is not very ideal, also won't produce the material blockage in the barrel fixed or fully crowded not to come out.
state of laminar flow, material flow within the low speed first, can appear in the nose of the export from inflation, melt fracture flow dynamics, extrudate are sharkskin melt is rough. Slip flow status, the melt is not affected by shearing action, melt no relative displacement between the layers, but it's different from laminar state, he does not produce from inflation. Flow state, the melt under high speed shearing melt was cut into powder, this state of affairs in common injection molding processing of polyethylene is invisible. This is due to the general polyethylene is only produced under high shear rate flow phenomenon, but in common injection molding machine is cannot produce such a high shear rate.
UHMWPE material on the screw motion approximation for solid conveying, moving process, namely the powder - Semi solid - The changing process of high viscoelastic body, is a typical flow conveying mechanism. Without the free flow of viscous flow, the material easy to plug in compression coated screw rotation to squeeze together, this phenomenon also is material, that is common to use, without transforming single screw extrusion machining encountered the biggest problem of UHMWPE.
more excellent articles: relative molecular quality test, click directly.
http://www。 csssld。 cn//html/2016/Info_1209/427。 HTML
nantong on suye's official website: http://www. csssld。 cn//
people usually think of the melt was broken when shear rate is called the critical shear rate. Practice has proved it and decreases as the molecular weight of polyethylene. So for high molecular weight of UHMWPE in low shear rate, melt fracture may be produced. Under the strong and rate lower, will produce the phenomena of flow or jets. So in ultra-high molecular weight polyethylene extrusion processing when cracks due to easy to burst phenomenon, in there was a jet in the ultra-high molecular weight polyethylene plastic injection products appear porous or delaminating phenomenon. This is a processing problem of ultra-high molecular weight polyethylene thermoplastic method.
it is sticky while ordinary polyethylene melt flow pattern, from the mouth out immediately after prolapse, and fused UHMWPE, mouth when die extrusion with high temperature of melting stiffness, not immediately prolapse, translucent solid level to the lower direction to move forward, characterized by high viscoelastic state. Thus, UHMWPE melt viscosity is extremely high, the special melt flow is poor. UHMWPE friction factor is extremely low, even in the molten state, so in the process of feeding easy slippage in charging period, unable to move forward, this is also the problem encountered in the process of screw extrusion processing.
as thermoplastic engineering plastics UHMWPE in solid state has excellent comprehensive performance, but the melt characteristics and ordinary polyethylene thermoplastic and distinct, bring difficulties to processing. Ultra-high molecular weight polyethylene melt flow rate even in 10 times more cases is almost zero, so it can be seen that the liquidity is poor. Ordinary polyethylene processed in the extruder, the hopper to join solid granule or powder material in the barrel and screw under the action of shear, gradually transformed into a viscous fluid, even if the screw design and temperature condition is not very ideal, also won't produce the material blockage in the barrel fixed or fully crowded not to come out.
state of laminar flow, material flow within the low speed first, can appear in the nose of the export from inflation, melt fracture flow dynamics, extrudate are sharkskin melt is rough. Slip flow status, the melt is not affected by shearing action, melt no relative displacement between the layers, but it's different from laminar state, he does not produce from inflation. Flow state, the melt under high speed shearing melt was cut into powder, this state of affairs in common injection molding processing of polyethylene is invisible. This is due to the general polyethylene is only produced under high shear rate flow phenomenon, but in common injection molding machine is cannot produce such a high shear rate.
UHMWPE material on the screw motion approximation for solid conveying, moving process, namely the powder - Semi solid - The changing process of high viscoelastic body, is a typical flow conveying mechanism. Without the free flow of viscous flow, the material easy to plug in compression coated screw rotation to squeeze together, this phenomenon also is material, that is common to use, without transforming single screw extrusion machining encountered the biggest problem of UHMWPE.
more excellent articles: relative molecular quality test, click directly.
http://www。 csssld。 cn//html/2016/Info_1209/427。 HTML
nantong on suye's official website: http://www. csssld。 cn//
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