In order to improve the heat-resistant temperature structure of the hollow carbon fiber rim, there are several methods:
(1) Improve the drop of glass transition temperature of carbon fiber by epoxy resin system, thereby improving its heat resistance. You can choose epoxy resins, curing agents and accelerators with good heat resistance. Epoxy resins, such as cycloaliphatic epoxy resins, bisphenol S epoxy resins, novolac epoxy resins, epoxy resins, and silicone epoxy resins. High temperature curing agent, such as aromatic curing agent. At the same time, the curing ratio should be reasonable, and the curing temperature should be gradually increased. After curing, the temperature is high and the time is long, and the heat resistance will be improved.
(2) In order to improve the high-temperature performance of the braking zone, the common market is that the outer surface of the rim braking zone has a layer of wear-resistant, low thermal conductivity and heat-sensitive aluminum metal rim or protective film, so that the brakes The sheet is in direct contact with the protective plate, they will not be in direct contact, and the heat generated by friction cannot be directly transferred to the rim. But for gamers, the brake pads must be replaced frequently, which is not the best way to use them. Except for the braking area, it is coated with high temperature ceramics.
Another way to increase the rigidity of the hollow structure carbon fiber rim structure and improve the structural stability is to fill the middle with a low-density lightweight foam core material.
PMI foam sandwich structure for carbon fiber rims
The foam sandwich structure is a structural material composed of high-strength and low-density lightweight skin core materials. The core purpose of the connection is to maintain the distance between the two plates, which can increase the section moment of inertia and bending rigidity of the sandwich plate under the premise of increasing the weight, and greatly improve the rigidity of the structure.
Referred to as the semi-hollow sandwich structure of carbon fiber and the sandwich foam sandwich structure of carbon fiber rim. The carbon fiber semi-hollow sandwich structure in the braking area is filled with foam reinforcement and processed by combining the airbag method and the molding process. By molding the carbon fiber of the sandwich structure, the rigid structure is the best.
The foam sandwich bicycle rim is the core material of rigid foam and polyurethane foam, with a density in the range of 29-52kg/m3. Polyurethane foam is made by in-mold foaming process, with a density of about 30kg/m3, which is cheap, but it is difficult to have uniform foam density, low center density, high skin density, large internal defects, poor mechanical properties, and long-term internal cracks. The bubbles burst, and squeaks can be heard when the grinding wheel rotates.
PMI foam core material is a 100% closed-cell rigid foam with the highest specific strength and stiffness, and a high heat distortion temperature of 180-240°C.
In the rim design stage, PMI foam is a structural core material, which can be used as a stress unit in the sandwich structure to improve the stability of structure and function. The carbon fiber skin of the rim reduces the prepreg layer. 1- 2. Carbon fiber rim, Reduce weight and increase product added value.
In the paving process, the foam core machine or thermoforming plays a core role, so that the carbon fiber prepreg is smoothly laid and the mechanical properties of the carbon fiber skin are improved.
During the curing stage, the PMI foam core can withstand high temperatures. The PMI foam core has a certain degree of interference, that is, the core size is slightly larger than the cavity size, and the curing time is long. The foam core can provide enough back pressure to make the carbon fiber composite skin more dense.
The PMI foam core has good fatigue resistance. During use, it can be firmly combined with the CFRP panel for a long time. It is an ideal structural core material for manufacturing bicycle rims.