Long-Fiber Hard Felt vs. Short-Fiber Hard Felt: Core Differences and Application Scenario Matching Guide
In the field of high-end thermal insulation materials, long-fiber hard felt and short-fiber hard felt are critical consumables in industries such as semiconductors, photovoltaics, and aerospace, thanks to their excellent high-temperature resistance and low thermal conductivity. While both belong to the carbon fiber hard felt category, they differ significantly in raw materials, production processes, performance focus, and application scenarios. Understanding these differences is key to material selection. This article breaks down their distinctions across multiple dimensions to serve as a reference for industrial applications.
1. Core Differences: Raw Materials and Production Processes
1.1 Raw Material Basis
- Long-Fiber Hard Felt: Uses continuous long carbon fibers as the core raw material, with fiber lengths typically exceeding 50 mm, some even retaining their original continuous state. High-purity virgin carbon fibers are required, resulting in relatively higher costs.
- Short-Fiber Hard Felt: Uses chopped carbon fibers (including recycled scraps) as raw material, with fiber lengths generally ranging from 1 to 50 mm. This allows efficient utilization of carbon fiber production scraps, offering broader material sources and cost control advantages, aligning with resource recycling trends.
1.2 Production Processes
- Long-Fiber Hard Felt: The core process involves "weaving - needling - composite molding." Continuous long carbon fibers are first woven into a base material, then needled to enhance fiber interweaving density, and finally combined with high-temperature-resistant binders for curing. The process emphasizes preserving fiber continuity, requiring precise weaving and needling control.
- Short-Fiber Hard Felt: The mainstream process is "wet molding" (e.g., technologies used by Hunan Shuanghuan and Guanhe New Materials), sometimes upgraded with "supercritical fluid-assisted molding." Short fibers are dispersed in an aqueous solution, followed by vacuum filtration, press molding, and high-temperature curing. The process focuses on uniform fiber dispersion and binder system stability, enabling flexible shape customization.
2. Performance Comparison: Distinct Core Advantages
| Performance Indicator | Long-Fiber Hard Felt | Short-Fiber Hard Felt |
|---|---|---|
| Temperature Resistance | 2500–2800°C, strong structural stability at high temperatures | Above 3000°C (some domestic products reach 3200°C), superior extreme thermal field resistance |
| Thermal Conductivity | Low (0.04–0.06 W/(m·K)), uniform heat conduction | Ultra-low (0.03–0.038 W/(m·K)), outstanding thermal insulation |
| Mechanical Strength | High (tensile strength ≥3 MPa), excellent tear and impact resistance | Moderate (tensile strength ≥1.5 MPa), meets basic strength requirements for insulation scenarios |
| Thermal Field Stability | Good, continuous fiber structure reduces thermal field drift | Excellent (with uniform dispersion), thermal field error controllable within 3% |
| Forming Flexibility | Poor, difficult to adapt to complex irregular shapes | Excellent, customizable for irregular shapes, thin plates, etc. |
| Cost Level | High (due to raw material and process costs), 1.5–2 times the price of short-fiber felt | Low (scrap utilization + optimized wet process), significant cost advantages after domestic production |
| Environmental Impact | High virgin fiber consumption, relatively higher carbon emissions | Over 90% scrap utilization, some processes achieve zero wastewater discharge |
Key Performance Insights
- Long-Fiber Hard Felt: Core advantages lie in mechanical strength and structural integrity. The continuous fiber network resists damage under high temperatures, making it suitable for scenarios requiring both insulation and structural support.
- Short-Fiber Hard Felt: Core competitiveness includes extreme temperature resistance, low thermal conductivity, and cost advantages. Uniform fiber dispersion and specialized binder technology address traditional short-fiber thermal instability issues, making it the "cost-effective choice" for high-temperature insulation.
3. Application Scenarios: Precise Matching to Industrial Needs
3.1 Long-Fiber Hard Felt: Focus on "High Strength + Structural Support" Scenarios
- Aerospace: Thermal protection systems for spacecraft, engine flame insulation shields requiring both insulation and impact/airflow resistance.
- Large Industrial Furnaces: Load-bearing insulation layers and furnace door seals, enduring mechanical wear from furnace weight and frequent operations.
- High-End Machinery Manufacturing: Core insulation components for precision heat treatment equipment, requiring shape stability at high temperatures to avoid deformation affecting process accuracy.
3.2 Short-Fiber Hard Felt: Dominates "Extreme Temperature + Low-Cost" Scenarios
- Semiconductor Industry: Thermal field systems for monocrystalline silicon growth furnaces and SiC substrate PVT furnaces (insulation cylinders, flow guides, furnace bottom insulation), requiring above 3000°C resistance and ultra-low heat loss. Domestic products like Guanhe New Materials have achieved mass import substitution.
- Photovoltaics: Comprehensive insulation for polysilicon ingot furnaces and monocrystalline silicon pulling furnaces, where low cost and high stability reduce production costs.
- Special Metallurgy/Powder Metallurgy: Insulation linings for vacuum sintering furnaces and hot isostatic pressing furnaces, emphasizing ultimate insulation and cost control over high strength.
- Nuclear Industry: Radiation insulation components for high-temperature experimental devices, suited for harsh environments due to low thermal conductivity and radiation resistance.
4. Domestic Manufacturing Progress: Short-Fiber Hard Felt Leads, Long-Fiber Accelerates
- Short-Fiber Hard Felt: Domestic production has reached over 80%. Companies like Guanhe New Materials and Hunan Shuanghuan master core technologies, with product performance rivaling international top-tier levels and costs 15–20% lower than imports, achieving large-scale substitution in semiconductors and photovoltaics.
- Long-Fiber Hard Felt: Domestic production is still catching up. Core raw materials (high-end continuous long carbon fibers) and weaving processes partially rely on imports. Currently used mainly in mid-to-low-end industrial scenarios, while high-end aerospace applications still depend on imported products. Breakthroughs focus on raw material independence and process precision.
5. Selection Recommendations: Match Needs to Core Principles
- Choose long-fiber hard felt for scenarios requiring both high-temperature insulation and structural support/impact resistance (e.g., aerospace, load-bearing parts of large furnaces).
- Choose short-fiber hard felt for extreme temperature (3000°C+), low thermal conductivity, and cost control scenarios (e.g., semiconductor and photovoltaic thermal fields), where domestic products offer mature solutions.
- Short-fiber hard felt excels in custom irregular shapes and small-batch production due to its forming flexibility.
- For high-end equipment with ample budgets and stringent mechanical strength requirements, consider imported long-fiber hard felt or high-end domestic long-fiber products.
Conclusion
Long-fiber and short-fiber hard felts are not "substitutes" but "complements" based on performance strengths. Long-fiber hard felt dominates high-end structural insulation with its strength advantages, while short-fiber hard felt leads in mainstream high-temperature insulation scenarios due to its temperature resistance, cost-effectiveness, and flexibility. With breakthroughs in domestic technology, short-fiber hard felt has transitioned "from substitution to leadership," while long-fiber hard felt is advancing in domestic production. Together, they drive China's high-end thermal insulation materials industry from "import dependency" toward "self-reliance."