Process key points and product characteristics of carbon fiber graphite soft felt

Carbon fiber graphite soft felt is generally made of viscose fiber, PAN fiber and other raw fibers through nonwoven process to make felt, and then through impregnation (mainly the viscose base needs to be impregnated), pre-oxidation, carbonization, graphitization, cutting, and finally get the finished product.

The forming of graphite soft felt is mainly in the front nonwoven process, nonwoven is a series of complex processes, there are many factors that will affect the quality of the finished product, such as: when the fiber is carded into a net, PAN fiber or viscotic fiber is fine, light, dry, easy to generate static electricity under the mechanical action of the equipment, affecting the normal operation of the equipment, so it is necessary to reduce static electricity by adding antistatic agents; When laying nets, there are many types of laying nets, such as parallel type, cross type, combined type, vertical type, etc. The number of laying nets can reach dozens of layers; Acupuncture reinforcement, can choose different types of acupuncture needles, different acupuncture arrangements, different times of acupuncture.

These are just a small part of the dry netting and needling reinforcement used in the nonweaving process, and there are many different technical routes for nonweaving.

Compared with the felt before pre-oxidation, the length, width and thickness of the graphite soft felt will shrink due to the gradual reduction of non-carbon elements in the felt from pre-oxidation. However, the uncut graphite felt is still a huge area of material, up to 40m in length and 1.6m in width.

According to the application requirements, the uneven parts of both ends and sides of the graphite felt can be cut, and can continue to cut into rectangular felt, circular felt, and various shapes for the production of hard felt.

From the main performance indicators, the density of graphite felt is only about 0.10g/cm³, which is about one-tenth of the density of water. The graphitized fibers themselves are light and thin, and the small space formed between a large number of fibers makes the density of the felt so low.

The thermal conductivity of high purity/high efficiency viscotic cornerstone ink felt is about 0.10-0.15W/m·k at 1150℃, and the lower the thermal conductivity, the better the thermal insulation performance.

Process key points and product characteristics of carbon fiber graphite hard felt

There are two main ways of forming hard felt: laminated curing of soft felt and wet forming. The common lamination method for making carbon fiber graphite hard felt takes soft felt as raw material, and the production process begins with cutting: cutting several blanks from the soft felt that are slightly larger than the size of the final product hard felt. After cutting, impregnate the adhesive material such as resin, and lay the impregnated blank multiple layers according to the required hard felt thickness.

The impregnation in the production of soft felt is mainly impregnated catalyst, so that the viscose fiber is more stable in the subsequent heat treatment; The impregnation of hard felt is mainly impregnated with thermosetting resin. In the subsequent heating and curing process, the liquid resin solidifies, and the multi-layer soft felt is closely combined with the resin.

Resin + carbon fiber graphite soft felt, so that the material can achieve the effect of "1+1 > 2" in some properties. The multi-layer laminated felt impregnated with resin can not be rolled up like felt after temperature curing, and the density and compressive strength of the material are also increased.

Carbon fiber graphite hard felt is formed by multi-layer soft felt and resin curing

But this is not carbon fiber graphite felt. Because the resin contains a lot of other elements other than carbon, it needs to be removed by carbonization, graphitization and other processes.

The carbon in the resin acts as the matrix, and the carbon fiber graphite soft felt acts as the reinforcement, and they are combined together to eventually become the composite material of hard felt. So carbon fiber graphite hard felt is also known as graphite hard composite felt.

After the small space between the fibers of the felt is filled with resin and cured, the density of the semi-finished product is inevitably higher than that of the raw felt. After carbonization and graphitization, the resin loses hydrogen, oxygen atoms, etc., and the density is reduced, but the carbon left in the resin makes the graphite hard felt density still higher than the density of the raw material soft felt. The density of hard felt is about 0.13-0.25g/cm³.

The area of the hard felt after graphitization is almost the same as that of the semi-finished product after curing, which is generally smaller than the raw felt before cutting.

According to the shape and apparent requirements, the hard felt also needs to be machined, coated or pasted carbon cloth, graphite paper and other processing.

Compared with carbon fiber graphite felt, hard felt has a slightly higher thermal conductivity and less thermal insulation than soft felt, but its service life is longer, for example, the service life of soft felt in a single crystal furnace is about 6 months, and hard felt is replaced once every 12 months.