Kompozit malzeme kürleme süreci için mini otoklav sistemi

Composite materials which are formed of at least two constituents are highly dependable to manufacturing quality. Since the composites are two-phased, custom methods are preferred to fabricate them even in coupon test specimen level. One very widely used method is the autoclave curing of them under high temperature and pressure which helps to achieve minimum voids and very good quality. Today, autoclave systems are frequently used in systems requiring the application of temperature, pressure and vacuum processes together. Autoclaves are produced in desired sizes according to the physical dimensions of the processes and they are generally used in sterilization, vulcanization and curing based production. The application areas are wide ranging from tool sterilization in the medical sector to production of much larger structures in the aerospace sector. As a system for different purpose uses, sterilization autoclaves considers the temperature control as a priority however for advanced composite manufacturing autoclaves, temperature, pressure and vacuum control are the major controlling mechanisms, respectively. The design and fabrication parameters of autoclaves depends on the field of use for the instrument but generally, temperature, pressure and the amount of vacuum are the most important aspects. Automatic control devices provide a complex control of the system for the requirements of user/process by adjusting important parameters within time. Proportional, integral and derivative (PID) control algorithm is generally used in autoclave systems where the temperature, pressure and vacuum must be changed stepwise depending on the time. In order to use this algorithm, the mathematical model of the system needs to be extracted first. After the mathematical model of each part of the system is derived as differential equations, it is converted to Laplace domain and the transfer function of the system is obtained, respectively. This transfer function is used to design the PI controller of the autoclave system mathematically and/or in a simulation environment. The PI control algorithm, designed for the autoclave system, controls the system by implementing an electronic controller. The controllers for the required algorithm might be programmable logic controllers (PLC), microprocessors and micro-controllers, as well. The temperature required by autoclaves is provided by electricity and/or flammable gases. The heater source is selected according to the size of the autoclave and the maximum temperature it must reach. While sterilization autoclaves are generally heated by electricity, the autoclaves which are vulcanizing and producing composite are heated by electricity and/or flammable gases. The purpose of the autoclave systems in aerospace industry is to meet the requirement of very high quality production of large-sized composite parts. These parts are produced by curing the composite fabrics prepared as layers, under temperature, pressure and vacuum, to give strength. In order to increase the mechanical performances of thermoset-based composite materials, it is necessary to increase the fiber/resin ratio or completely eliminate the air gaps formed in the material during production. The remaining voids during production reduce the strength of the part. In standard composite manufacturing methods, the part is produced under 1 atm of air pressure. During composite production by vacuum bagging, the air gaps in the material can be reduced to minimum if the part is under a high air pressure which is regular, controllable and more than 1 atm. Autoclave systems are devices with temperature and vacuum control that can be applied to the external pressures needed to increase the physical properties of the composite material produced. The amount of external pressure varies according to the type of composite to be produced and is designed and manufactured according to this requirement in the autoclave system. Since the parts that need to be produced in the aviation sector are large in size, autoclave systems can be also designed and manufactured within these requirements. The purpose of the autoclave systems used in the aerospace industry is the requirement of very high quality production of large-sized parts, especially those used in the construction of air vehicles. These parts are produced by curing the composite fabrics prepared as layers, under temperature, pressure and vacuum, to give strength. In order to increase the mechanical performances of thermoset-based composite materials, it is necessary to increase the fiber/resin ratio or completely eliminate the air gaps formed in the material during production. The remaining voids during production reduce the strength of the part. In standard composite manufacturing methods, the part is produced under 1 atm of air pressure. At the moment of composite production by vacuum bagging, the air gaps in the material can be reduced to minimum if the part is under a high air pressure which is regular, controllable and more than 1 atm. Autoclave systems are devices with temperature and vacuum control that can be applied to the external pressures needed to increase the physical properties of the composite material produced. The amount of external pressure varies according to the type of composite to be produced and is designed and manufactured according to this requirement in the autoclave system. Since the parts that need to be produced in the aviation sector are large in size, autoclave systems can be also designed and manufactured within these requirements. In this thesis, the designed and produced autoclave system aims to cure composite materials in the temperature, pressure and vacuum environment. The autoclave produced is much smaller (30x30x5 cm) than the size of the autoclaves used in the industry. The main reason for this small work area is the ability to produce composite materials that have been researched and developed for use in the aerospace industry in coupon specimen dimensions for the mechanical testing defined through American Society of Testing Materials (ASTM) standards. The ability to produce composite materials with different structural components in the research and development phase is of great importance for the mechanical characterization of prototype materials. The purpose of producing composites is to have more flexible, lighter, higher strength, and more flexible materials than the previous material type for aerospace applications. The autoclave to be designed and implemented in this thesis will serve to achieve high quality composite specimens for mechanical testing indicated within the standards mentioned. The autoclave designed and produced in this thesis has a working temperature of maximum 250oC, 7 bar pressure and -1 bar vacuum environments and the system should not undergo plastic deformation at the relevant temperature and pressure. The autoclave has to withstand the forces generated at the inner surface of the chamber at a high temperature and pressure. During these forces applied to the inner surface, the autoclave system must deformed in elastic region. When the forces in the inner surface are removed, the material can be fully restored to its original shape. The wall thickness analysis of autoclaves was made on the basis of this criterion. While the system is operating at maximum operating conditions, the amount of flexure of the material from which the autoclave produced must remain in the elastic deformation zone. For this reason, stainless steel metal is preferred for the autoclave produced in this thesis. The wall thickness of the autoclave is optimized by Von Misses analysis and the diameter of the bolts, which connecting the housing that cover the device to the main body, are again calculated by Von Misses analysis. The amount of heat required for the device to perform the relevant production processes is calculated and the plate heater is preferred to provide this heat. After the autoclave design and production were completed, composite material production tests were carried out and the instrument was calibrated. This special autoclave is used at Istanbul Technical University, Aerospace Research Center (ITUARC), under the development of several research and development project that focuses on the mechanical property investigation of nano-engineered and polymer nanocomposites.