What is the function of a laboratory hydraulic press in C/C-SiC preparation? Achieve Precision CFRP Green Body Densification

A laboratory hydraulic press functions as the critical stabilization tool in the preparation of Carbon/Carbon-Silicon Carbide (C/C-SiC) green bodies. Specifically within the Liquid Silicon Infiltration (LSI) process, it applies controlled heat and pressure to densify and cure resin-impregnated carbon fiber fabric laminates.

This process transforms loose fabric layers into a solid, structurally compact Carbon Fiber Reinforced Polymer (CFRP) preform, which serves as the "green body" for the subsequent manufacturing stages.

Core Takeaway The hydraulic press is not merely a shaping tool in this context; it is a reactor for consolidation. By simultaneously applying thermal energy (e.g., 240 °C) and mechanical force, it cures the polymer matrix to lock carbon fibers in place, establishing the necessary structural density required to survive high-temperature pyrolysis.

The Role of the Press in the LSI Process

In the creation of C/C-SiC composites, the "green body" is typically a laminated composite rather than a pressed powder block. The hydraulic press serves two simultaneous functions: mechanical compaction and thermal curing.

Precision Densification

The primary function of the press is to eliminate voids between the layers of carbon fiber fabric.

By applying specific pressure (for example, 5.8 kPa), the press squeezes out trapped air and excess resin.

This ensures that the fiber volume fraction is maximized, creating a dense, uniform structure that is free of large gaps or air pockets.

Thermal Curing of the Matrix

Unlike simple cold-pressing used in powder metallurgy, the preparation of C/C-SiC green bodies requires heat.

The press operates at elevated temperatures (such as 240 °C) to initiate and complete the chemical cross-linking of the resin (polymer) matrix.

This turns the liquid or soft resin into a rigid solid, effectively gluing the carbon fiber layers together into a cohesive unit.

Establishing Structural Integrity

The output of this stage is a CFRP preform. This preform must be robust enough to be handled, machined, and subjected to extreme heat in the next steps.

The hydraulic press ensures the material has the structural compactness necessary to maintain its shape during pyrolysis, where the resin is converted into porous carbon.

Understanding the Trade-offs

While the hydraulic press provides essential consolidation, improper parameter control can lead to defects in the green body that are impossible to fix later.

Pressure Calibration

If pressure is too low: The laminate will contain voids and air pockets. These voids result in weak spots and uneven silicon infiltration later in the process.

If pressure is too high: You risk crushing the carbon fibers or squeezing out too much resin, leading to a "dry" preform that lacks structural cohesion.

Temperature and Curing

Thermal Uniformity: The press must deliver heat evenly across the plates. Uneven heating leads to warping or internal stresses within the green body.

Curing Time: The material must be held under pressure until the resin is fully cured. Premature release can cause the green body to spring back or delaminate.

Making the Right Choice for Your Goal

The specific settings of your hydraulic press will dictate the quality of your final C/C-SiC composite.

• If your primary focus is Structural Homogeneity: Ensure your press can maintain a uniform pressure distribution across the entire surface area of the laminate to prevent density gradients.
• If your primary focus is Process Efficiency: Utilize a press with programmable thermal cycles to automate the ramp-up, hold (curing), and cooling phases, ensuring repeatability without constant manual monitoring.

Ultimately, the hydraulic press transforms a stack of loose fabric into a unified engineering material, setting the baseline quality for the entire composite.

Summary Table:

Feature	Function in C/C-SiC Preparation	Impact on Green Body
Mechanical Pressure	Compresses carbon fiber laminates (e.g., 5.8 kPa)	Eliminates voids and maximizes fiber volume fraction.
Thermal Curing	Provides elevated temperatures (e.g., 240 °C)	Triggers resin cross-linking to solidify the polymer matrix.
Structural Consolidation	Simultaneous heat and force application	Transforms loose fabric into a rigid, compact CFRP preform.
Process Control	Precise ramp-up and holding cycles	Prevents warping, internal stresses, and material delamination.

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References

1. Wenjin Ding, Thomas Bauer. Characterization of corrosion resistance of C/C–SiC composite in molten chloride mixture MgCl2/NaCl/KCl at 700 °C. DOI: 10.1038/s41529-019-0104-3

This article is also based on technical information from Kintek Solution Knowledge Base .