Melt spiral flow

MSF melt spiral flow (test) NAAEE North America Association for Envi-... 

However this solution is not always convenient and may prevent high productivity and/or the production of intricate forms which require high temperature processing. Fortunately, some fire retardants dramatically increase the flowability of fire retardant plastics melts. For example ABS, flame retarded with F-2016 or F-2016M (brominated epoxy) has much higher flowability, melt flow index (MFI), and spiral flow index, than virgin ABS (Fig. 1). 

A widely used test for mouldability evaluation is the spiral flow test (Fig. 24.4). In this test the mould has the form of a spiral the polymer melt flows into this mould under pressure and freezes in the spiral, the length of the polymer spiral being the test result. Mould geometry, temperature and pressure are standardised. 

The mouldability index is the length of the elongated flow path that is filled before solidification of the injected molten polymer composition at specified moulding conditions, i.e., volumetric injection rate, mould temperature, polymer melt temperature. The mouldability index of the moulding compositions of this invention is characterised by spiral flow. 

Rheology is a complex subject, and in the formulated colorant industry two simplified approaches have served well in the majority of cases. These are the single-point method, melt flow, and the molding simulation test, spiral flow. 

Fig. 3 Schematic of spiral mandrel blown film die operation (1) ring-shaped melt distribution (2) die body (3) spiral flow mandrel (4) sizing ring (5) spreader (6) film bubble (7) frost line (8) solidified film (9) bubble collapsing rollers (10) nip rollers (11) external bubble cooling air (12) internal bubble cooling air inlet (13) internal bubble cooling pipe and (14) heated internal bubble air return.

The blends were prepared in a twin-screw extruder. The spiral flow was determined at a melt temperature of 288°C (550°F) for the PC and 266°C (510°F) for the transparent DB. The mold release energy was determined by measuring the force required to eject a disc measuring 76 mm in diameter and 3.2 mm thick with 6.4 mm high ribs. The chemical resistance was determined by measuring the maximum allowable outer fiber strain on 2.0 mm tensile bars, which did not reduce tensile elongation. 

Spiral-flow test n. A method of evaluating the molding flow of a resin to injection or transfer molding in which the melt is injected into a spiral runner of constant trapezoidal cross-section with numbered and subdivided centimeter (or inches) marked along the runner. The mold is filled from a sprue at the center of the spiral and pressure is maintained until flow stops, the number just aft of the molded-spiral tip giving the flow distance. The spiral-flow test has been widely used since it was introduced in the early 1950s but has been standardized in USA only for thermosetting resins, in ASTM D 3123. 

Blown film lines use three major die designs side fed, spider arm, and spiral flow. In side-fed dies (Fig. 5.39a ), the melt is fed into one side of the die body while air is introduced into the bottom of the mandrel. Since this produces a relatively low pressure drop, such dies are good for high-viscosity materials. However, the melt encircles the mandrel and joins in a single, relatively weak weld line. The pressure drop around mandrel deflects the mandrel to produce nonuniform flow. 

With a spiral-flow die (Fig. 5.39c ), melt is fed into the bottom of the die flows along the spiral channels of the die and also jumps from channel to channel. Air is introduced into the bottom of the die. This creates uniform flow and minimizes gauge bands (thick and thin areas in the film). However, high pressure drops [—35 MPa (5000 Ib/in )] make the die unsuitable for high-viscosity materials. High levels of... 

Udipi [2] has discovered that polymer blends comprising a PC, amorphous polyester such as PETG, poly(ethylene terepthalate), and a nitrile rubber can form an alloy with superior balance of properties. Improved melt flow and spiral flow was demonstrated in injection molding applications. Udipi prepared a polymer alloy with 30% aromatic polycarbonate, 30% of PETG made of a condensation copolymer of terepthalic acid and a mixture of ethylene glycol and 1,4-cyclohexanedimethanol, and 3% nitrile rubber. This blend has a spiral flow of 27 cm, heat distortion temperature of 75°C, and Izod impact resistance of 130 J/m. 

Testing of lubricants is based on the determination of the flow behavior of plastic melts (capillary viscosi-metry, spiral flow test, demolding force, by plasto-graph, extrusiometer, melt strength, roll-mill tests, etc.) or by finished part testing (gloss and smoothness, slip measurements, determination of static friction, etc.). 

The flow properties of a material can also be investigated using a spiral flow test. The melt is injected into a spiral mould cavity. The melt will freeze at a certain distance along the spiral charmel (spiral flow length) depending on the flow properties and cross-sectional thickness of the spiral. The raw material manufacturer usually gives these values as material specifications. 

Receiving Inspection. Many types of tests have been devised for testing raw materials. Depending upon the severity of the need for inspection, the types of tests selected may vary from being basic and simple to sophisticated and complex. Some of the most common basic tests are the melt index test, specific gravity, bulk density, spiral flow test, and viscosity tests. Gel permeation chromatography, infrared analysis, thermal analysis, and rheometry are some of the more elaborate raw material quality control tests. These tests are discussed in detail in Chapter 7. Some processors also choose to mold test bars from a small sample of raw material and conduct physical tests such as tensile, impact, and flexural tests and then evaluate the results to see if they meet the preestablished specifications. 

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