Spiral mold flow

Viscosity is affected by the discussed additives in different ways. Figure 10.36 shows a marginal decrease in viscosity with concentration. Addition of ultrahigh molecular weight silicone additive, which is used as a mold release, decreases viscosity of polyethylene melt and thus lowers energy input in extrusion (Figure 10.37). Addition of 0.2 wt% of silicone additive reduced Brabender torque by 40%, elongational viscosity by a factor of four, and increased spiral mold flow by 30%. ... 

SF Spiral Flow index, the length of specimen molded into spiral mold Injection molding machine. Allrounder 221-75-350 Arburg... 

Since the materials have a very soft plasticity rating, or inches of flow on spiral mold, the materials are all molded in special transfer molding presses and specially designed transfer molds. Because an acid catalyst and glass or mineral fillers are used to make the compound, these materials may have an adverse effect on the hardened steel mold with the result that there may be excessive runner and gate wear. 

Figure 9. Spiral mold test. Melt flows of the injection molded spirals at 230°C.

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. 

Spiral mold cooling n. A method of cooling injection molds (or heating transfer molds) wherein the heat-transfer medium flows through a spiral passage in the body of the mold. In injection molds, the cooling medium is introduced at the center of the spiral, near the sprue section, because more heat is concentrated in this area. 

Figure 4. Spiral flow of high impact alloys. Injection machine Toshiba IS-90B mold 10 mm x 3 mm (spiral) molding conditions injection pressure 78 MPa injection speed 20 mm/s mold temperature D°C.

The tangential flow of a power-law fluid through an annulus under only an imposed pressure gradient with both cylinders stationary is useful in the analysis of spiral molds [14]. In this case, F = 0 so, Eq. (20) with A-+ x yields... 

Flow tests are run in an actual injection molding machine. Results are usually direct, tangible, and easy to interpret. Typically the flow length mold forms a part in the form of a graduated spirals. The flow length is measured and can be related to flow conditions in an actual production mold. Spiral Flow Length (SFL) data is used especially for comparing various resins for ease of fill [13]. 

ASTM D3123 Spiral Flow - This test measures how a filled molding compound will behave when injection or transfer molded. It enables the molder to set the optimum mold temperature. The compound is forced into a heated spiral mold under controlled conditions. Once cure is complete the part is removed and the flow length is measured directly from the specimen. 

Spiral flow was measured in an injection molding machine with a spiral mold. The flow length (in cm) in the mold was measured under the given test conditions. Melt temperatures, mold temperature, gauges of spiral flow, and boost pressure were 250 °C, 270 °C, 80 °C, 0.75 mm. 

The brominated phosphate is an efficient flame retardant for polycarbonate resin. UL-94 ratings of V-0 with oxygen index values of greater than 40 are obtained. Polycarbonate resin containing brominated phosphate processes with greater ease than resin containing brominated polycarbonate as measured by injection molding spiral flow measurements. The heat distortion temperature is reduced... 

The three flame retardants are compared in Table VI. Brominated phosphate disperses readily in the resin presumably due to its high solubility in aromatics. Resin containing brominated polycarbonate is relatively difficult to process as measured by injection molding spiral flow measurements. 

ASTMD3123, Thermosetting Molding Compounds, Spiral Flow, Low Pressure, Vol. 8.02, ASTM, Philadelphia, Pa., 1994. 

Some of the test methods being used to measure the processing stability of polypropylene include melt flow drift measurements at elevated temperatures using an extrusion plastometer (melt indexer), melt viscosity retention measurements using a torque rheometer, retention of melt flow after repeated extrusions, and injection molded spiral test measured by the flow in inches at various temperatures and the retention of melt flow of the injected spirals. The nine commercial resins were evaluated by these methods. 

The location of the nozzle should also be carefully planed because the different flow velocity in various areas within the cavity can appear as flow lines. The extrusion blow molding process with the accumulator unit can also be the reason for flow lines. Usually the incoming melt is separated by the ram, which causes a flow line in the back. This can sometimes be moved to the parting line of the tool, where it becomes almost invisible. In cases where this is not feasible, it may be possible to create a spiral action (turbulence) when filling the accumulator system. The resulting flow patterns are then mixed as they exit, creating the parison. 

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. 

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