Diameter draw ratio

It should be noted that sometimes the area draw ratio is represented by the letters DDR as an acronym for drawdown ratio. Obviously, this can cause confusion with the diameter draw ratio. Often the area draw ratio is called simply the draw ratio. It is important therefore to check what exactly is meant when the term draw ratio is used. The ADR can be calculated from the WDR and the DDR as follows ... 

Thus, the wall and diameter draw ratios determine the area draw ratio in the extrusion process. A high ADR increases orientation and the chance of pinholes and breakaways. A low ADR reduces orientation and increases the chance of melt fracture. 

The draw ratio balance should be equal to or larger than one DRB 1. Yet another parameter that is used is the sizing ratio or SR. This is the wall draw ratio divided by the diameter draw ratio. 

F. Forming with billow plug is often used to produce thin-wall items with depth-to-diameter-draw ratios up to 1.5 1. 

Already solution processable conducting polymers have been used to develop fiber producfs fhaf may be used in the applications described above. In one commercial operation (Santa Fe Science and Technology, Inc.) continuous lengths of polyaniline fibers are made by a wet spinning operation. The continuous nature of fhe operations enables control of fiber diameter, draw ratio and properties and the company offers fibers of various denier. Conductivities of up fo 1000 S cm" have been reported and the mechanical properties are described as being similar to Nylon-6. Figure 7.5 shows the SFST fiber-spinning operation. 

Example 4.8 A small flower pot as shown in Fig. 4.56 is to be thermoformed using negative forming from a flat plastic sheet 2.5 mm thick. If the diameter of the top of the pot is 70 mm, the diameter of the base is 45 mm and the depth is 67 mm estimate the wall thickness of the pot at a point 40 mm from the top. Calculate also the draw ratio for this moulding. 

Filaments about 0.12 mm in diameter were obtained from unfractionated high-density polyethylene (Mi] = 8.0 x 104) by a melt-spinning at 220 ° C with a draft ratio of about 17. They were next stretched at 100 °C in polyethylene glycol with a molecular weight of 380—400 to different draw ratios, which are defined as the ratios of the drawn length to the original. NMR spectroscopy was carried out for the drawn filaments randomly packed into a glass tube 18 mm diameter. The three-component analysis of the spectrum at different temperatures was performed the results are discussed in relation to the phase structure of samples. 

Film blowing. A tubular 50 pm thick low density polyethylene film is blown with a draw ratio of 5 at a flow rate of 50 g/s. The annular die has a diameter of 15 mm and a die gap of 1 mm. Calculate the required pressure inside the bubble and draw force to pull the bubble. Assume a Newtonian viscosity of 800 Pa-s, a density of 920 kg/m3 and a freeze line at 300 mm. 

The polystyrene simulation followed the experiments of Bell and Edie (12) with good agreement. Figure 14.8 shows the simulation results for fiber spinning nylon-6.6 with a draw ratio of 40. The figure demonstrates the wealth of information provided by the model. It shows the velocity, temperature, axial normal stress, and crystallinity fields along the threadline. We see the characteristic exponential-like drop in diameter with locally (radially) constant but accelerating velocity. However, results map out the temperature, stress, and crystallinity fields, which show marked variation radially and axially. 

Isothermal draw resonance is found to be independent of the flow rate. It occurs at a critical value of draw ratio (i.e., the ratio of the strand speed at the take-up rolls to that at the spinneret exit). For fluids that are almost Newtonian, such as polyethylene terephthalate (PET) and polysiloxane, the critical draw ratio is about 20. For polymer melts such as HDPE, polyethylene low density (LDPE), polystyrene (PS), and PP, which are all both shear thinning and viscoelastic, the critical draw ratio value can be as low as 3 (27). The maximum-to-minimum diameter ratio decreases with decreasing draw ratio and decreasing draw-down length. 

Fig. 3. Variation of extrusion pressure with extrudate velocity. Extrusion temperature M °C, nominal draw ratio IS, die diameter 15.5 mm, sample R (for sample description see Table 2). R mes at lower and higher velocities are isothermal and adiabatic, respectively ...

Figure 4 demonstrates the influenco of the product diameter on the product properties. For a given nominal draw ratio of 10 the axial tensile modulus, as determined from a three-point bending test, decreased with increasing product diameter. The authors attrib-... 

The degree of diametrical die swell depended strongly on the draw ratio and on the product diameter, as shown in Fig. 5. Ihe influence of the extrusion velodty on the die swell was raffia small. For extrusions at draw ratios larger than 10 and for extrudates with diametors smaller than 8 mm the authors did not observe any die swell. 

Thus, it seems to be of interest to examine the influence of stress-induced polymorphic changes on the microhardness. While in the case of f-PP two samples comprising the a or phase were characterized, here we wish to follow the microhardness behaviour during the a-j6 polymorphic transition caused by a mechanical field. For this purpose PBT has been selected as a suitable material because of its ability to undergo stress-induced polymorphic transition from the a (relaxed) to the P (strained) form. Bristles of commercial PBT with a diameter of about 1 mm were drawn at room temperature via neck formation (final diameter about 0.5 mm and draw ratio of 3.4) and thereafter annealed in vacuum at 200°C for 6 h with fixed ends (Fakirov etal., 1998). 

Fig. 32. (a) Two-dimensional small-angle X-ray scattering pattern of an SBS block copolymer with 33% aliphatic oil content and stretched to a draw ratio X = 4. (b) Long period L in SBS Meek copolymers as a function of the draw ratio X (pure SBS and SBS with different oil contents), (c) height of the polystyrene cylinders h in SBS block copolymers as a function of the draw ratio X (pure SBS and SBS with different oil contents), (d) diameter of the polystyrene cylinders 2r in SBS block copolymers as a function of the draw ratio X (pure SBS and SBS with different oil contents)... 

Fig. 4. Variation of the axial tensile modulus with product diameter. Extrusion temperature 100 °C, nominal draw ratio 10, sample R 40 (for sample description see Table 2)Z7>...

An important consideration in designing dies and tips for wire coating is draw-ratio balance (DRB) defined by Eq. (6.4). The ideal value of DRB is 1, which means that the interior and exterior surfaces of the tube are drawn to the same extent. For FEP and PFA, the DRB range is 0.9-1.15. Concentricity suffers at DRB <0.9 while a DRB >1.1 can result in tears. ETFE has a more narrow range, 1.04-1.07. Drawdown ratios for large diameter cables may range from 2 1 to 3 1. 

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