Carbon/carbon composites is reinforced by carbon fiber and matrix carbon in two parts, according to the carbon fiber in the matrix form of carbon can be divided into the following three types:
The first: carbon fiber in the form of short fiber bundle randomly distributed in the matrix carbon.
The second: carbon fiber with continuous filament woven cloth, then composite laminated plates of forms exist in the matrix carbon.
The third: carbon fiber to between carbon cloth laminated plates and the transition between the two kinds of structure of 3 d braid structure, namely the form of a needled felt exist in the matrix carbon.
Carbon matrix according to its source and form can be divided into liquid phase method and gas phase method of two categories:
Such as liquid liquid phase method refers to use resin or asphalt. Carbon impregnated carbon fiber and solidification and carbonization, and organic matter removal of volatile organic matter composition, leaving the carbon composition, forming the matrix carbon composite material.
Gas phase method refers to the low molecular organic hydrocarbon through bake in a preheated in gas phase of carbon fiber reinforced body, and under the high temperature cracking and polymerization, forming the matrix carbon.
The distribution shape of carbon fiber reinforced, and the formation of the matrix carbon together, formed a variety of carbon/carbon composite material preparation pads, the actual use of the technology points of three categories:
The first category: short fibre moulded dipping carbonization process.
The process is first and foremost with resin impregnated carbon fiber filament formation of presoak belt, then cut short into a certain length of short fiber bundle, hot-pressing forming in the mold, after solidifying, carbonization treatment, reoccupy resin or pitch impregnation carbonization, and cycle times, until meet the requirements of material density. Finally after a certain processing to form carbon/carbon composites brake pads.
The process according to the coking pressure and other parameters can be divided into such as normal pressure, medium pressure and high pressure. The United States Honeywell and ABSC company mainly carbon brake was produced by the technology, its products are mainly applied in B767, MD11 aircraft, etc.
This process has the advantage of carbon fiber utilization ratio is high, the craft is simple, low production cost. The production of carbon/carbon composite material is isotropic state. Defect is low mechanical properties (see table 1), process in brake pad friction surface fracture phenomenon. The reason is for chopped carbon fiber reinforced body did not form a complete structure of the bundle. Another disadvantage is the wear rate is large, this is because the matrix carbon is ball, easy to form the abrasive abrasive wear.
The second category: carbon cloth laminated or needled felt precast body with chemical vapor deposition (CVD) process.
The process carbon fiber woven cloth first, then cut composite into prefabricated body or carbon fiber woven needle into needled felt kind of precast body, in the chemical vapor deposition in furnace using low molecular hydrocarbon deposits, until you reach the required density, finally after a certain processing to form carbon/carbon composites brake pads.
The process in the manner of precast body heat and air flow direction can be divided into isothermal constant pressure, differential pressure method, the temperature difference method, etc. Chinese bjgreatwall company can production
This process has the advantage of matrix carbon gradually grow along the carbon fiber surface and form, so closely matrix between carbon and carbon fiber structure. So the process of material mechanical properties of high (see chart 1). In addition, CVD carbon for the class of graphite layer structure, friction in the process of friction surface is easy to form a layer of graphite crystallite film, reduce material wear rate (see chart 1). The disadvantage is that the technology deposition efficiency is low, deposition time is long.
Third class: composite technology.
So-called composite process is the above two kinds of combination of preparation of carbon/carbon composites brake pads, such as the CVD process is the matrix of carbon fiber surface formed gradually grow. Suitable for smaller gap between the carbon fiber. Because big gap around small pore filling and block sedimentary gas source, formation of materials in the big hole, and dipping carbonization process, as a result of the impregnated resin or pitch carbonization is internal contraction form spherical matrix carbon, often out of contact with the surrounding carbon fibre, forming uniform small gaps. Big hole left by the CVD technology so easily be impregnated carbonized matrix carbon in small gaps formed between the fiber is suitable for CVD carbon offset. Can reduce the increase of the combination process time, improve production efficiency. The drawback is that process equipment complex, large investment. Adopting the technology producing carbon brake disc manufacturers have bjgreatwall company
