Die land length

You are to extrude a polystyrene tube at an average speed of 0.1 m/s. The relaxation time, A, of the polystyrene, at the processing temperature, is 1 second. The die land length is 0.02m. Will elasticity play a significant role in your process. 

Figure 6.14 Schematic diagram of die with two different die land lengths and thicknesses.

Die design with two die land thicknesses. Determine the die land length ratios, L2/L1 for a die land thickness ratio, /i2/ i of 3, for various power-law indeces. Using eqn. (6.54), we can easily solve for the land length ratios for several power-law... 

Using the geometry and notation given in Fig. 6.14, relate the die land length ratio, L1/L2 for a die land thickness h //i2 = 2 to the power law index of a shear thinning polymer. 

Use modular design with stacked plates for manufacturability, convenient assembly, and disassembly, as well as convenient modifications and cleaning. Die land length should be at least 10 times the product thickness (or gap) to facilitate the polymer melt stress relaxation within the die. 

The melt parison is extruded from an annular die. The wall thickness of the parison depends both on the annular gap setting and on the shear rate of the melt in the die. The melt will swell after the parison exits from the die and the die swell Increases with increasing shear rate. The die swell is also a function of the temperature, the type of polymer, and its elastic melt properties. Usually the shear rate in the die varies from 10 to as high as 700 s . As a rule of thumb one uses a die land length 8 times the annular gap. The parison should normally not be blown up beyond 3 1 (i.e., bottle parison diameter). 

Resin Type Reduction Ratio Lubricant Content Lubricant Type Die Cone Angle Die Land Length Extrusion Speed Temperature... 

Profiles comprise cross sections that are not a circle, annulus, or wide sheet. Like pipe and tubing lines, profile extrusion lines consist of an extruder, profile die, calibration device, cooling system, puller, and a cut-off saw and stacker or wind-up unit. The main differences are the dies and calibration units. Due to lack of symmetry, obtaining a correct cross section in a profile die is difficult. Differential flow resistance in different parts of the cross section alters the flow rate for these parts of the die. In addition, die swell may vary due to the differences in flow. Consequently, the extrudate may bend as it exits the die. To equalize flow, the die land length is varied or restricting plates are used in channels where the flow is too rapid. Many profile dies are split into sections, with the die sliced perpendicular to the major axis. Thus, sections can be altered in the process of die development. Flow simulation software is particularly useful in profile die design. 

Fig. 3-23 Diagram of an end-fed manifold sheeting die. Land length of lips L is measured in direction of small arrows emerging from lips [3].

L = Die land length, mm P = Pressure drop across the die, MPa q = Volumetric flow rate, mmVsec Q = Extrusion rate, kg/hour g = Estimated shear rate at wall, sec ... 

Example No. Resin Melt Flow Rate (g/lOmin) Spinning Temp., Die Diameter, mm Die Land Length, mm Shear Rate, sec Wind-up (Draw) Speed, m/min Spin Stretch Factor... 

FIGURE 1.14 Effect of the annular die land length on the flhn tear strength of polybutylene extruded at the rate of 10 m/min for two different flhn thicknesses. 

Die swell is present in this problem, and the radius and thickness at the maximum die swell level will be noted as Rp and Hp, respectively (see Fig. 3.1). Note that the dimensions at this die swell level will be considered as the initial dimensions for the film blowing process. From Table 1.1 we get that Hp = 0.018 in. = 0.0457 cm for a die land length of 3.81 cm. Thus, the reduction in film thickness becomes... 

EFFECT OF DIE LAND LENGTH ON DIE PRESSURE DURING FOAM EXTRUSION... 

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