Automatic control system design and calcuation program writing of capillary rheometers

Rheology is necessary to know the behavior of materials to comprehend the flow and deformation properties of plastics during industrial manufacturing processes.Two types of rheometers, which are rotational and capillary, are used in flow behavior determination of materials. Rotational rheometers are generally used to determine the flow and elastic properties of plastics in low shear rates. Other than that, capillary rheometers are preferred to determine the flow properties at higher shear rates than rotational ones.In this study automatic control system of a shear rate controlled capillary rheometer, which is designed to determine the flow properties of materials with the cooperation of Dizayn Group, is designed and to see the apparent shear rate, yield stress, average shear stress, apparent shear viscosity, corrected shear rate, corrected shear viscosity and power law index directly a calculation program is written via simulink. Then because of the incapability of this program in automatic data acquisition an another program is written via matlab codes. This second program consists of two parts which are a preliminary data acquisition program in simulink codes and a data processing calculation program in matlab codes to calculate the mentioned results.System simply consist of a barrel, piston, heating and temperature control devices, pressure sensor, speed sensor and die. Required constant piston speed in this rheometer is generated by a tensile-testing machine. Since the testing machine is used also in other tests, it wouldn?t be possible to make revisions on the device. Because of this, the pressure inside the barrel and the piston speed values are acquired automatically by the program via sensors which are placed to the barrel. Afterwards data acquisition procedure is repeated with different die lengths. Finally with the collected data, the necessary calculations are made and the results and the graphs are displayed on the screen via another program.Consequently, the results were compared with other rheometers which are produced by the manufacturers Malvern and Dynisco Instruments in Sabancı and Middle East Technical University and it is seen that there is maximum %1 difference between the results. As a result of this comparison it shows that it is succeeded to make the production of rheometers possible in our country with one fifteenth of the imported products which are very expensive.Keywords: Capillary Rheometer, Data Acquisition, MATLAB, Programming, LabView