Transfer molding

Resin transfer or resin transfer MouldingBE MoldingAE (RTM) is a process for the production of moldings from thermosetting plastics and elastomers. In comparison with the case presses the molding material is injected by means of a piston usually heated antechamber through distribution channels in the mold cavity in which it is cured under heat and pressure.

As a form of mass can formaldehyde resins ( PF, MF, etc.) and reactive resins (UP, EP ) can be used with small filler particles and elastomers.

Classification

Depending on the arrangement of the injection plunger is divided into three basic procedures. The lower piston method ( dual-piston method ) in which the injection cylinder sits below the tool, the upper piston method ( Einkolbenverfahren ) in which the injection cylinder sits above the tool and horizontally arranged spray machines which usually have a Schneckenvorplastifizierung.

The Differential Pressure Resin Transfer Moulding ( RTM DP ) is one of the German Aerospace Center (DLR ) more advanced procedure.

Standard Procedure

At the beginning of a cycle is a preplasticated and dose form composition in the pre-chamber. First, the mold is closed. Thereafter the molding material is injected into the mold and left in place for a certain time in the mold. In this so-called dwell time, it comes to reacting or curing of the molding material. It is dependent on various factors ( type of resin, filler, processing pressure and temperature). The dwell ended, the tool can be opened. The previously charged molding mass is now fixed ( hardened) and is now referred to as a molded part. This can now be removed from the mold from the mold. Thereafter, the cleaning of the tool, and a new cycle is to begin. The amount of need when pressing and re-pressing molding compound should it always be greater than the volume of the final molded part, so that the tool is completely filled. Thus, it is guaranteed that the mold part is formed completely and no air is injected. The excess in the antechamber there, retarded molding compound, also referred to as residual cake must be removed before the start of the new cycle and are replaced by new molding compound.

Processing of Prewovens

In order to process even long fibers or fiber semi-finished products ( Prewovens / preform ), these previously inserted into the tool and molded with the molding composition. To avoid air bubbles, the cavity ( cavity ) is usually also evacuated.

Angus species for Prewovens processing

The " Prewovens method" can be classified according to the number and design of Harzangüsse. Following the entry of the resin into the fiber semi -finished product is referred to as an injection, is produced in which way the pressure gradient regardless.

  • Point injection: The resin is injected only in one place in the semis. When pin gate the flow front can trap air, resulting in defects.
  • Multi-point injection: Multiple injection sites, the mold can be filled faster with resin. Air entrapment can be prevented through skilful positioning.
  • Line injection: In line injection is not injected at one point but punktfömigen linear manner on the edge of the mold. This may be the case of components with a large aspect ratio is advantageous since only the shorter edge length to be passed through.
  • Flow channel injection: The resin is injected through a wide channel which is above or below the fiber semi-finished product.
  • Cascade injection: In order to keep low the pressure gradient, a plurality of injection points arranged in the direction of the flow front. However, it is this necessary following to open the injection lines of the flow front and close.

Shape Styles

  • Solid forms
  • Soft shapes
  • Mixed forms ( for example, tube-blowing RTM)

Reaction resins for Prewovensverarbeitung

As injection resins are used resins having a low viscosity. Characterized the flow resistance when flowing through the shape is low, and there are small pressure differences necessary for filling. Reactive resins for RTM process are offered as a special injection resins, which consist of a resin and hardener components. Low reactive resin systems can be mixed prior to the infusion. If you want to use highly reactive resin systems, as resin and hardener can only be mixed directly into the infusion line or shape. In this way, lower cycle times are possible. Methods in which the injection of resin components are mixed immediately before the injection, are as RIM ( reaction injection molding ) are known.

  • Plastics Processing
  • Faserverbundtechnik
  • Urformen
Polyester
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