Transfer moldings or also Resin transfer Moulding (RTM) is a procedure for the production of shaped parts from thermosetting polymers and elastomers. In the comparison to pressing here the molding material is injected by means of pistons by a usually heated pre-chamber over distributor channels into the forming nest, where it hardens under warmth and pressure.
As molding material formaldehyde resins (PF, MF etc.) and reaction resins (UP, EP) with small filler particles can be used and elastomers.
Depending upon arrangement of the Spritzkolben, in three basic procedures one divides. The Unterkolbenverfahren (two-piston procedure) with that the Spritzzylinder underneath the tool sits, which upper piston procedure (a piston procedure) with that the Spritzzylinder sits above the tool and possesses horizontal arranged spraying automat those usually a snail before plasticizing.
The differential Pressure Resin transfer Moulding (DP-RTM) is far procedure developed by the German center for air and space travel (DLR).
At the beginning of a Zykluses a vorplastifizierte and proportioned molding material usually already is in the pre-chamber. First the tool is closed. Afterwards the molding material is injected and released from form after a retention time for the reaction or vulcanization of the molding material, the remainder cake stayed in the pre-chamber and filled again proportioned molding material. Now if the shaped part has the desired degree of reaction, it is released from form, the tool is cleaned and a new cycle can begin.
In order to process also long fibers or fiber semi-finished material (Prewovens), the this into the tool are put before and with the Formmassse umspritzt. In order to avoid cavities, additionally the cavity (form cavity) is usually evacuated.
The "Prewovens procedures" can be divided according to number and organization of the resin dead heads. In the following the entry of the resin is designated into the fiber semi-finished material as injection, produced independently of it in which way the pressure gradient.
As injection resins resins are used, which possess a low viscosity. Thus flow resistance remains small when flowing through the form and it is necessary smaller differences of pressure for filling. Reaction resins for RTM procedures are offered as special injection resins, which consist of a resin and a hardener component. Lowreactive resin systems can be already mixed before the infusion. If one would like to use highly reactive resin systems, then resin and hardeners can be mixed only directly in the infusion line and/or the form. In this way smaller Takzeiten is possible. Procedures, with which the injection resin components are mixed only directly before the injection, are well-known as RIM procedure (Reaction Injection Moulding).
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