Carbon fiber tube is a common type of carbon fiber product, which is made by compounding carbon fiber and resin through molding, hot pressing, winding and other processes. This article will provide a simple process analysis for one of the techniques.
1. Manufacturing of inner core molds
The inner core mold should be made according to the customer's requirements for pipe specifications, as the fiber winding is subjected to compression force, requiring its assembly shape to remain basically unchanged. Therefore, in the selection of core mold raw materials, metal materials with good rigidity, such as steel and hard aluminum, should be chosen. Steel has a higher density and hardness than hard aluminum, but its thermal expansion coefficient is lower than that of hard aluminum. High performance carbon nanotube products are cured at high temperatures. If a hard aluminum core mold is used, the density and mechanical properties of carbon nanotubes can be improved by the curing internal pressure generated by the thermal expansion of hard aluminum. Therefore, in the winding process of high-performance carbon nanotubes, the core mold should be made of metal material, and hard aluminum is the material.
The design of the head of the core mold should preferably use a flattened ellipsoid shape, which can maintain uniform winding of the cylinder body without accumulation and prevent "slip" and "overhead" phenomena. The cylinder body of the core mold can be made of equal diameter, but if the product length is long, considering the processing accuracy of the machine tool and the limitations of demolding conditions, it may be difficult to apply the equal diameter cylinder body. However, if a tapered core mold is adopted, this problem can be solved. Experimental results have shown that a taper of 1:1500-3500 is more suitable for processing the cylinder body of the core mold. For longer products, segmented docking of the core mold can be considered when making the core mold to ensure product size stability.
Usually, a release agent is applied to the surface of the core film before winding to facilitate subsequent demolding. However, for high-performance carbon nanotubes, organic release agents are prone to penetrate into the resin during the curing process, causing product defects and affecting product performance. If a layer of fluorine-containing release agent is coated on the surface of the core mold, this defect can be eliminated.
2. According to the specifications, design the fiber stacking method
Firstly, determine the thickness of the board to be made, calculate the required number of layers according to the thickness, then stack them in the order of 0 °, 45 °, 90 °, and -45 °, and then mold them.
3. Roll the fiber layer onto the inner core mold and wrap it.
The processing and forming methods of carbon fiber tubes mainly involve the following three methods: winding forming method, which wraps carbon fiber monofilaments around carbon fiber shafts, especially suitable for making cylindrical and hollow vessels; The extrusion molding method involves completely immersing carbon fibers, removing resin and air through extrusion, and then curing and molding them in a furnace. This method is simple and suitable for preparing rod-shaped, tubular parts, etc; The vacuum bag hot pressing method involves stacking layers on a mold and covering them with a heat-resistant film, applying pressure to the layers using soft pockets, and curing them in a hot pressing tank.
4. Bake and harden, remove OPP, and remove the core
Take out the finalized coil material from the winding machine and solidify it in the curing furnace. After the pipe is cured, the core model is removed to obtain the composite material wrapped pipe, which is also called curing demolding. During the demolding process, the lathe or fitter removes the head and then removes the product, which may damage the surface of the core mold and affect its repeated use. High temperature resistant adhesive can be used to level or welded and ground in place.
5. Cut off the uneven and flat parts at both ends, and polish and polish them through multiple processes
The preliminarily completed carbon fiber tube still needs further processing. Firstly, according to the specifications of the finished product, the excess parts at both ends of the semi-finished product are removed to form a uniform and neat cut surface. Then, it is polished and polished by professional polishing machines and manual labor to form a smooth and glossy surface.