Extrusion flow

SOLID PHASE OR EXTRUSION FLOW DISCONTINUOUS DENSE PHASE... 

Fridman ML, Isayev AI, Smyslova ES (1973) Study of extrusion flow under conditions of molding tool vibration. Proceedings of 18th All-Union Conf. on HMC, Kazan, p. 226... 

Figure 3.2. AFM image of a (a) a PE and (b) PE with 10 wt% MWCNT. The samples were taken parallel to the extrusion flow direction, with permission from Elsevier (16).

An examination is made of past and future trends in extrusion tooling. Trends in high speed extrusion, inexpensive tooling, flexible tooling, dual extrusion, flow simulation, bypass rheometry, melt homogenisation, process documentation and customer education. 

K.P. Chen and D.D. Joseph, Elastic short wave instability in extrusion flows of viscoelastic liquids, J. Non-Newtonian Fluid Mech., 42 (1992) 189-211. 

Figures 322(a) and (b) show again the conditions in a pelleting machine with concave die. Figure 322(a) depicts the mechanisms of compression and extrusion in the work area , the material volume wedged in between the press roller and die. Figure 322 explains the phenomena. Feed deposited in a layer on the die is pulled into the space between the roller and die and compressed. Neither the roll force nor the force from the die resisting extrusion (flow) are constant. The roll force increases with progressing densification while the flow-resisting force remains constant until a threshold pressure, defined by the static friction in the die holes, is surpassed. After extrusion (movement in the die holes) has started, both the resisting and the roll forces decrease.

The classical measurement unit of the linear density of a fibre is the denier , i.e. the mass in grams of 9000 m of fibre. The denier of the extrusion product depends essentially on the nature of the polymer compound and of the extrusion flow. For nylon, the linear density varies from 30 to 300 denier. The ultimate stress is of the order of 500 newton/cm2 (like common steel). 

Simple Dripping, Electrostatic Extrusion, Flow Focusing, and Coaxial Flow..193... 

Mechanical or flow-induced degradation of polymers may occur under extreme shear or extrusion flow conditions giving rise to unfolding of macromolecules in extensional flow with subsequent chain scission. 

The extrusion process tends to align the particles in the extrusion flow direction and extruded graphite has a pronounced anisotropy, particularly in the strength and electrical properties. The isostatic-pressing process, on the other hand, results in a material that is much more uniform and is generally considerably stronger. 

Karagiannis, A., A. N. Hrymark, and J. Vlachopoulos, Three-dimensional non-isothermal extrusion flows, Rheol. Acta 25 121-133. 

Marcus and Vogel (1979) and coworkers have studied dense-phase transfer of solids achieving loading rates up to 500. By use of a conical throttle valve they were able to maintain a homogeneous flow having neither plugs nor dunes. They term this extremely dense flow extrusion flow. 

The orifice angle of the cone can signiflcantly influence the flow anomalies that are frequently found with high molecular polyethylene (PE). In such cases, changing the melt temperature has little effect. Computer programs are available to calculate the distribution of shear rate in the extrusion flow channel. It is important to ensure that the critical shear rate occurs near the die exit resp. is confined to as narrow a region as possible. With the accumulator head, the effects of flow anomahes can be influenced by the extrusion velocity. To achieve the shortest cycle times with continuous extrusion, the plastic usually exits from the orifice at close to critical shear rate. 

In the extrusion flow porometry, a wetting liquid, such as galwick, is used to fill the hydrophilic and the hydrophobic pores of the sample. The inert gas is used to remove the liquid from pores and permit gas flow. The airflow rate and differential air pressures are measured using dry and wet samples. The differential pressure is related to pore diameter as... 

H.J. Song, J.L. White, K. Min, N. Nakajima, F.C. Weissert. Rheological properties, extrudate swell, and die extrusion flow marker experiments for rubber carbon black compounds. Adv. Polym. Technol, 8,421-449,1988. 

Camphell, G. A., P. A. Sweeney, and J. N. Felton, Experimental Investigation of the Drag Flow Assumption in Extruder Analysis, Po/yw. Eng. Set, 32, 1765-1770,1992. Fenner, R. T., Extrusion (Flow in Screw Extruders and Dies), in Computational Analysis of Polymer Processing, J. R. A. Pearson and S. M. Richardson (eds.), Applied Science, London, 1983. 

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