Low Ash Rayon Graphite Felt | High-Temp Insulation for Semiconductor Furnaces| Flexible Thermal Insulation for Sintering Furnaces

▍Product Overview: What is viscose-based graphite felt?

Viscose-based graphite felt, also known as rayon-based graphite felt, is a flexible, porous, high-performance material manufactured from high-quality viscose staple fiber needle-punched felt that has undergone pre-oxidation, low-temperature carbonization, high-temperature carbonization, and graphitization at temperatures exceeding 2000°C.

This unique fiber structure makes it an exceptionally effective high-temperature thermal insulation material, capable of more effectively blocking heat transfer and helping your equipment achieve significant energy savings. At the same time, it retains the characteristics of carbon fiber materials, including light weight, flexibility, corrosion resistance, and high chemical stability.

Flexible Rayon-Based Graphite Felt

Standard Roll Rayon Graphite Felt

Large Industrial Packaged Graphite Felt

▍Key Advantages: Why Choose Viscose-Based Over PAN-Based?

Viscose-based graphite felt offers excellent resistance to high temperatures and ablation, and can withstand continuous high temperatures without significant damage. Compared to PAN-based graphite felt, viscose-based graphite felt has a lower thermal conductivity, resulting in superior thermal insulation properties.

                                                   (in an oxygen-free environment or under an inert gas atmosphere)

▍Technical Principles

The process from viscose staple fibers to high-performance graphite felt requires passing through four “flame thresholds”:

1. Pre-oxidation (200–300°C): The fiber molecular chains cross-link and solidify, preventing subsequent high-temperature melting.

2.  Low-temperature carbonization (800–1000°C): Non-carbon elements (H, O, N) volatilize, forming a carbon skeleton.

3. High-temperature carbonization (1500°C): The carbon network expands, establishing preliminary conductive and thermally conductive pathways

4. Graphitization (≥2200°C): Carbon atoms rearrange into ordered graphite crystals, yielding high thermal conductivity, high temperature resistance, and low electrical resistance

Ningheda employs continuous graphitization furnaces with a temperature uniformity of ±15°C, ensuring consistent graphitization throughout each meter of the felt roll. The finished product has a carbon content of ≥99% and ash content controlled below 500 ppm, meeting the semiconductor industry’s stringent requirements for ultra-pure thermal environments.

Rayon Graphite Felt Rolls & Sheets

Bulk Rayon-Based Graphite Felt Roll

Customizable Graphite Felt Sheet

▍Product Advantages (6 Key Selling Points)

▍In-Depth Analysis of Performance

Why does lower density actually result in better thermal insulation?

This may seem counterintuitive, but the thermal insulation mechanism of viscose-based graphite felt is entirely different from that of traditional dense materials:

• Thermal conductivity in solids: There are very few contact points between the fibers, and graphite crystals conduct heat along the fiber axis while providing thermal insulation radially, creating a natural thermal barrier.

• Gas-mediated heat transfer: The thermal conductivity of inert gases trapped within pores is much lower than that of solids, and gas convection is suppressed when pore sizes are <<1 mm.

• Radiative heat transfer: At high temperatures, thermal radiation dominates, and the high emissivity of the graphite fiber surface forms an “infrared shield.”

Consequently, the thermal insulation performance of the lightweight felt (0.15 g/cm³) at 1000°C is actually superior to that of the dense felt (0.25 g/cm³)—though, of course, excessively low density can reduce mechanical strength. Ningheda offers a full range of densities from 0.15 to 0.28 g/cm³, allowing you to select the option that best suits your needs.

▍Typical Applications and Benefits

Our viscose-based graphite felt is an ideal choice for high-temperature equipment and processes in the following fields:

• High-Temperature Vacuum/Atmospheric Furnaces: Widely used as thermal insulation linings in the hot zones of sintering furnaces, quenching furnaces, annealing furnaces, brazing furnaces, carburizing furnaces, and similar equipment.

  Advantages: Significantly reduces energy consumption, improves temperature uniformity, and shortens heating and cooling cycles.

• Semiconductors and Photovoltaics: High-temperature insulation layers for monocrystalline silicon furnaces (Czochralski method), polycrystalline silicon ingot furnaces, and gallium arsenide crystal growth furnaces.

  Advantages: A high-purity environment ensures contamination-free crystal growth, improving the yield of semiconductors and photovoltaic cells.

• Specialty Glass and Metallurgy: Used for thermal insulation in specialty glass melting furnaces and metal powder injection molding (MIM) debinding and sintering furnaces.

  Advantages:High-temperature resistance and thermal shock resistance, ensuring process stability.

Vacuum Heat Treatment Furnace

Semiconductor Crystal Growth Furnace

Glass & Metallurgy Production Lines

▍FAQ

• Q1: When using graphite felt for thermal insulation, how should I choose between viscose-based and PAN-based graphite felt?

  A: If your primary goal is thermal insulation, viscose-based graphite felt is the better choice. It has a lower thermal conductivity, provides better insulation, and is softer in texture, making it easier to wrap around complex shapes. PAN-based felt has higher mechanical strength and is suitable for applications requiring greater structural support.

• Q2: Can the thickness of graphite felt be customized? What is the thinnest thickness available?

  A: Yes. The standard thickness range is 3–15 mm, which can be achieved by adjusting the needling density and the number of layers. Thinner graphite paper/foil (1–2 mm) is also available, but that is a different type of dense product. For soft felt, thicknesses below 3 mm result in reduced fiber cohesion and increased susceptibility to tearing, so it is not recommended.

• Q3: What is the service life of graphite felt?

  A: The service life depends on the operating temperature, frequency of use, and the cleanliness of the furnace. Under normal maintenance and operating conditions, it typically lasts between 6 months and 2 years. If the felt becomes hard, sheds significant amounts of powder, or shows a noticeable decline in thermal insulation performance, replacement is recommended.

• Q4: Can you customize the dimensions to fit my oven cavity?

  A: Yes. We can customize the width and thickness of our products to meet your needs, and we also offer a cutting service for finished products. This eliminates the need for additional processing on your end, allowing for a direct fit into your oven cavity.

• Q5: Can this soft felt be used for extended periods in the open air?

  A: We do not recommend prolonged use in an oxygen-rich environment, as graphite felt is prone to oxidation and degradation at high temperatures in such conditions. We recommend using it in an oxygen-free or inert gas (nitrogen, argon) atmosphere to fully utilize its temperature resistance up to 2800°C.