*3.2.4 Pressure distribution*

The graph with the pressure distribution was obtained, since at the entrance of the flow of the molten material to the head the pressure is maximum and is the one generated in the extruder at the exit of the dosing zone, with values that depend on flow rate and material temperature, as well as screw and die design (back pressure).

The pressure decreases as the flow advances inside the head, as can be seen in **Figure 18**, so that at the exit of the matrix (blue area), it is zero, as it should be since the flow of the material cast is stress free.

It is observed that the pressure value obtained from the simulation in the area where the pressure sensor is located in the head (light blue color) has values between 142 and 68 bar (in **Figure 19** the pressures are expressed in Pascal (Pa) and

**Figure 18.** *Pressure distribution inside and outside the head.*

**Figure 19.** *Cooling and vacuum calibration pan.*

the The value measured with said pressure sensor is 51 bar for a flow rate of 8.5 kg/h and a temperature measured with another sensor in the head of 200°C.

This difference between the simulated and real pressures of the process may be due to the high shear deformations that occur inside the head and that when using the Power Law or Ostwald model, the same is for deformations, much lower and on the order of 50–100 1/s.

The large difference between the shear deformations obtained as a result of the simulation (between 5.2107 and 5.6107 1/s in the highest values of red color) and that used by the Power Law affects the results of the pressure distribution that delivers the software.

#### **3.3 Tests with the extruder equipment**

An optimization of the process and the design of the calibrator is carried out through three tests carried out with the extruder, its auxiliary equipment, and the experimental calibrator installed. The conclusion of these machine tests showed that small modifications should be made in the caliper design, such as grooves to improve the application of the vacuum, and also the machine parameters were adjusted, in particular the screw revolutions and the drag speed. The said tests are carried out at a temperature of the molten material in the head of 200°C, obtained by means of a sensor located therein (**Figure 12**) and modifying the flow rate by varying the revolutions of the extruder screw. The pressure values in the head are recorded by means of another sensor (**Figure 13**) that the equipment has and which is also located in the head, observing its value on the extruder control panel. Each of these tests is detailed below: 3.3.1. First test: The screw speed is adjusted for a mass flow rate of 5 kg/h, measuring with the sensor a pressure = 55 bar, being the dimensions of the extruded profile at the exit of the gauge of width = 26 mm and thicknesses: 2.6 mm on one side and 2.9 mm on the other side of the width. It is determined that the cause of not reaching the required dimensions (width = 30 mm and thickness = 3 mm) is a vacuum deficit in the calibration pan by vacuum and cooling (**Figure 14**). The vacuum is generated by a pump located in the water tank that is located at the bottom of the vacuum and cooling calibration pan and this vacuum is measured with a pressure measuring instrument or manometer (**Figure 19**).

*Design, Simulation, and Analysis of the Extrusion Process of a PVC Thermoplastic Profile… DOI: http://dx.doi.org/10.5772/intechopen.100909*

#### *3.3.1 Second test*

The screw revolutions were adjusted to 48 rpm so as to obtain a mass flow rate of 5.7 kg/h and a pressure of 47 bar was measured.

To increase the vacuum, a calibrator will be made with internal grooves that communicate the place (hole) where the final geometry of the profile is defined, with the room where the mentioned vacuum is applied.

The dimensions of the profile were measured at the exit of the caliper and the following values were obtained: width = 29.6 mm and thicknesses in the central area of the profile = 3 mm and at each end of the width = 2.7 mm.

Therefore, although the dimensional value of the width is improved, the geometry is still not copied well on the sides and also the geometry is not rectangular, since the thickness in the central part is 3 mm and decreases toward the edges reaching a value at both ends of 2.7 mm; therefore, the process is not yet suitable to correct this defect.

#### *3.3.2 Third test*

The screw revolutions are again modified to 65 rpm, obtaining a mass flow = 8.5 kg/h, and it is noteworthy that this flow value is the same that is used as one of the input variables in the simulation software.

The measured pressure was 51 bar (in this case, there is a difference with the values obtained in the simulation, since for the area where the pressure sensor is located, the results were between 142 and 68 bar.

The increase in the mass flow, accompanied by an increase in the drag speed and using the calibrator with the grooves to improve the application of vacuum on the flow of molten material that comes from the head and that is calibrating and cooling, achieves the desired geometry of the outlines, which is the output of the caliper.

On the other hand, the required dimensions are achieved with an error of less than 5% at the ends of the width, since it was measured with a coliza foot that the width = 30 mm and at the ends = 2.9 mm, that is, the error was 3.3%.

The flow measurement was performed by taking the amount of material that was extruded per unit of time and it coincides with the flow rate that was used as an input variable in the simulation software, that is, 8.5 kg/h, working with the screw at 65 rpm.

The sensed pressure was 51 bar and that obtained from the simulation software ranged between 142 and 68 bar, and the explanation of these differences is due to the fact that the Power Law model used is for low deformation speeds and in the simulation, said deformation shear was very high, especially in the area where the geometry of the channel was modified from conical to rectangular (transition zone).
