![]() Demolding large structured areas on a thin residual layer may therefore result in problems due to the ejector pins arranged at the circumference. If the ejector pins are arranged around a mold insert only, bending during demolding cannot be avoided and will result in forces on the microstructures that are perpendicular to the demolding direction. If the molding area increases, the situation will change unfavorably. Nevertheless, the thickness of the residual layer has to be large enough to transmit the forces otherwise, the residual layer will break if higher forces at the ejector pins are needed for demolding. For mold inserts with a small microstructured area, the ejector pins transmit the demolding forces nearly in a vertical direction, such that microstructures can be demolded vertically. The ejector pins act at the circumference of the residual layer. Therefore, only an arrangement around mold inserts is recommended. From the sizes of mold inserts and their fabrication processes, it is obvious that ejector pins cannot be positioned easily into the mold insert. This concept may be transferred to micro replication processes. The purpose of the ejector is to increase the suction flow pressure from P 2 to P 1.Įjector pins are state of the art in the demolding of macroscopic molded parts, especially in the injection molding process. The flow finally diffuses in a diffuser and its pressure reaches P 1 at the exit ejector. The motive and suction flows mix with each other at a constant pressure of M, then the mixture passes through a throat and its pressure increases to P 5. As the picture shows, a motive high-pressure flow is expanded in a nozzle and its pressure drops to draw in the suction flow. In Figures 2.44 and 2.45, the geometry of a CPJE and its enthalpy-entropy diagram are illustrated. Besides having no moving parts, ECC benefits from lower maintenance expenses and lower capital costs than the compressor. The CPJE provides better performance than the CAJE due to better turbulent mixing. The CPJE is more suitable for a wide condensing pressure range while the CAJE is better for drawing more mass flow rate. The first one is the constant pressure jet ejector (CPJE) and the other one is the constant area jet ejector (CAJE). The ejector is the heart of an ECC and is classified into two types based on the mixing method in the primary nozzle exit. They are usually installed in conjunction with power cycles and organic Rankine cycles. They use a high-pressure motive flow of steam to circulate the ECC working fluid. ![]() ![]() The aesthetics and functionality of the finished component should also be considered when selecting an ejector pin location.Įjectors use neither heat nor electricity directly as the running input energy of ejector cooling cycles (ECC). Ejector pins are located where the greatest ejection force is required, for example near bosses, cored holes, and ribs. #EJECTOR PIN MARKS CRACK#Rectangular ejector bars are sometime used in special cases however, the radius associated with the corner of the bar causes issues with fit-up and long-term integrity of the steel in thin sections, since these corners can act as stress concentrators for crack initiation in the tool. Ejector pins are typically round, since round ejector pins are available in many standard sizes and the ejector pin housing in the cavity block is most easy to EDM. The size of the pin should be selected to allow the cavity where the pin fits to be opened to accommodate larger ejector pins as the tool ages. These witness marks become more evident as the tool ages owing to the wear between the pin and the cavity where the pin resides. Figure 2.2 shows a typical ejector pin blemish. As a natural consequence, witness marks where these ejector pins were located are evident. A sufficient quantity of these pins is required to ensure that the green component can be removed without distortion or cracking. Ejector pins are required to remove the green component from the tool. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |