4.Place a strip of the cork-rubber material(9)along each edge of the panel,making sure that no gaps exist and a complete dam is formed around the laminate.The dam around the lay-up prevents lateral motion of the panel,and minimizes resin flow parallel to the alu- minum plate and through the edges of the laminate (9). 5.Completely encircle the prepreg stack and dam with bagging adhesive making sure that the adhesive material is adjacent to the dam.The purpose of the adhesive material is to form a vacuum seal. 6.Place a peel-ply(4)and a ply of Teflon-coated glass fabric(5)(with the same dimensions as the panel)on top of the prepreg stack.The purpose of the Teflon-coated glass fabric is to prevent the bleeder sheets(6)from sticking to the laminate. 7.Place the proper number of glass bleeder sheets(6)(e.g.,style 181 glass cloth with the same dimensions as the prepreg stack)over the Teflon-coated fabric(5).The bleeder sheets absorb the excess resin from the laminate. 8.Place a sheet of perforated Teflon film (7)(0.025 mm)over the bleeder material.The Teflon film,perforated on 50 mm centers, prevents excess resin from saturating the vent cloth(8). 9.Place a porous continuous-vent cloth(8)(e.g,style 181 glass cloth)on top of the lay-up.Extend the cloth over the vacuum line attachment. Make sure that the vacuum line is completely covered by the vent cloth.The vent cloth provides a path for volatiles to escape when the vacuum is applied and achieves a uniform distribution of vacuum. 10.Place nylon bagging film over the entire plate,and seal it against the bagging adhesive.Allow enough material so that the film conforms to all contours without being punctured. 11.Place the plate in the autoclave and attach the vacuum line(Figure 3.7). An autoclave is generally a large pressure vessel equipped with a temperature-and pressure-control system.The elevated pressures and temperatures,required for processing of the laminate,are com- monly achieved by electrically heating a pressurized inert gas (nitrogen).The use of an inert gas will reduce oxidizing reactions that otherwise may occur in the resin at elevated temperatures,and will prevent explosion of evolving volatiles. 12.Turn on the vacuum pump and check for leaks.Maintain a vacuum of 650 to 750 mm of mercury for 20 min and check again for leaks. 13.After closing the autoclave door,apply the pressure and initiate the appropriate cure cycle(see example shown in Figure 3.8).As the temperature is increased,the resin viscosity decreases rapidly and the chemical reaction of the resin begins.At the end of the temperature hold,at 127C in Figure 3.8,the resin viscosity is at a minimum and pressure is applied to squeeze out excess resin.The ©2003 by CRC Press LLC
4. Place a strip of the cork–rubber material (9) along each edge of the panel, making sure that no gaps exist and a complete dam is formed around the laminate. The dam around the lay-up prevents lateral motion of the panel, and minimizes resin flow parallel to the aluminum plate and through the edges of the laminate (9). 5. Completely encircle the prepreg stack and dam with bagging adhesive making sure that the adhesive material is adjacent to the dam. The purpose of the adhesive material is to form a vacuum seal. 6. Place a peel-ply (4) and a ply of Teflon-coated glass fabric (5) (with the same dimensions as the panel) on top of the prepreg stack. The purpose of the Teflon-coated glass fabric is to prevent the bleeder sheets (6) from sticking to the laminate. 7. Place the proper number of glass bleeder sheets (6) (e.g., style 181 glass cloth with the same dimensions as the prepreg stack) over the Teflon-coated fabric (5). The bleeder sheets absorb the excess resin from the laminate. 8. Place a sheet of perforated Teflon film (7) (0.025 mm) over the bleeder material. The Teflon film, perforated on 50 mm centers, prevents excess resin from saturating the vent cloth (8). 9. Place a porous continuous-vent cloth (8) (e.g., style 181 glass cloth) on top of the lay-up. Extend the cloth over the vacuum line attachment. Make sure that the vacuum line is completely covered by the vent cloth. The vent cloth provides a path for volatiles to escape when the vacuum is applied and achieves a uniform distribution of vacuum. 10. Place nylon bagging film over the entire plate, and seal it against the bagging adhesive. Allow enough material so that the film conforms to all contours without being punctured. 11. Place the plate in the autoclave and attach the vacuum line (Figure 3.7). An autoclave is generally a large pressure vessel equipped with a temperature- and pressure-control system. The elevated pressures and temperatures, required for processing of the laminate, are commonly achieved by electrically heating a pressurized inert gas (nitrogen). The use of an inert gas will reduce oxidizing reactions that otherwise may occur in the resin at elevated temperatures, and will prevent explosion of evolving volatiles. 12. Turn on the vacuum pump and check for leaks. Maintain a vacuum of 650 to 750 mm of mercury for 20 min and check again for leaks. 13. After closing the autoclave door, apply the pressure and initiate the appropriate cure cycle (see example shown in Figure 3.8). As the temperature is increased, the resin viscosity decreases rapidly and the chemical reaction of the resin begins. At the end of the temperature hold, at 127°C in Figure 3.8, the resin viscosity is at a minimum and pressure is applied to squeeze out excess resin. The TX001_ch03_Frame Page 42 Saturday, September 21, 2002 4:51 AM © 2003 by CRC Press LLC
FIGURE 3.7 Vacuum bag sequence and tool plate placed in an autoclave. 200 160 Temperature 9 80 2C/min Pressure 88星 0.6 40 0.4 Maintain Vacuum Inside Bag 0.2 0 0 0 100 200 300 Time,min FIGURE 3.8 Typical cure cycle for a carbon/epoxy prepreg. temperature hold controls the rate of the chemical reaction and prevents degradation of the material by the exotherm.The pressure is held constant throughout the cure cycle to consolidate the plies until the resin in the laminate is in its glassy state at the end of the cooling phase.The vacuum should be checked throughout the cure cycle.The vacuum is applied to achieve a uniform pressure on the laminate and draw out volatiles created during the cure.Loss of vacuum will result in a poorly consolidated laminate. 14.After the power is turned off to the autoclave,maintain pressure until the inside temperature has dropped to about 100C. 15.Carefully remove the laminate from the aluminum plate.Gently lift it in a direction parallel to the main principal direction of the laminate. 16.Clean the aluminum plate,and store it for future use. ©2003 by CRC Press LLC
temperature hold controls the rate of the chemical reaction and prevents degradation of the material by the exotherm. The pressure is held constant throughout the cure cycle to consolidate the plies until the resin in the laminate is in its glassy state at the end of the cooling phase. The vacuum should be checked throughout the cure cycle. The vacuum is applied to achieve a uniform pressure on the laminate and draw out volatiles created during the cure. Loss of vacuum will result in a poorly consolidated laminate. 14. After the power is turned off to the autoclave, maintain pressure until the inside temperature has dropped to about 100°C. 15. Carefully remove the laminate from the aluminum plate. Gently lift it in a direction parallel to the main principal direction of the laminate. 16. Clean the aluminum plate, and store it for future use. FIGURE 3.7 Vacuum bag sequence and tool plate placed in an autoclave. FIGURE 3.8 Typical cure cycle for a carbon/epoxy prepreg. TX001_ch03_Frame Page 43 Saturday, September 21, 2002 4:51 AM © 2003 by CRC Press LLC