CFC Heat-Treating Racks for Ultrahigh Temperatures
The components in the hybrid grid combine to allow for high stability, long service and easy application with working temperatures of more than 2000˚F (1093˚C). These conditions are commonly seen in processing high-speed steel and aerospace applications. This provides numerous applications in high-temperature treatment where cast-steel racks were the only alternative for many years.
TTU, a subsidiary of Japan’s Toyo Tanso Company Ltd., has historically produced different isostatic-molded carbon and graphite products, but the development of carbon racks and C/C grids for the entire heat-treatment spectrum increases their involvement in the market. These principles can be applied in a myriad of heat-treating applications in various markets, including the automobile industry with their large component runs, tool manufacturers, aviation and medical parts.
Doug Garda, TTU’s sales manager, said, “We are proud and excited to explore new ground and expand our successful company history.”
Physical Superiority of CFC
Carbon-fiber-reinforced carbon (CFC) is a high-performance fiber-composite material. It consists of a matrix of carbon or graphite. Its high stability and extreme distortion resistance are decisive advantages that come into play in automated processes where warpage is a deal breaker for indexing. Instead of the classical steel and cast-iron trays used in the past, charging racks made of CFC are the first choice in many cases.
The thermal treatment of steel in continuous and multi-purpose chamber furnaces places exceptionally high demands on all components due to the extreme temperature differences. This applies to both the furnace itself and, more importantly, the charging elements that are exposed to the highest loads. The low density and weight of CFC trays not only facilitate handling but also ensure an exceptional energy balance as compared to trays made of steel or cast iron. Summarized, the advantages of CFC in heat treatment are: high distortion resistance, low density, excellent energy balance, high thermal stability, high thermal-shock resistance and long service life.
CFC in Vacuum Furnaces
First, is vacuum-furnace construction, where many graphite components such as heaters, insulation, etc. are used. CFCalso provides a number of clear advantages over conventional materials for vacuum furnaces. Another critical component presently employed is CFCused for charging racks in a similar way as in continuous facilities. It is also suitable for the construction of furnaces themselves because of its excellent material properties. CFCcharging racks are optimally suitable for use in most vacuum furnaces. At customary temperatures in vacuum furnaces, CFCdoes not react with process gases such as nitrogen and argon. Their high thermal-shock resistance ensures a long service life and, thus, predictable processes and cycles. Low weight and easy handling are additional reasons for using CFC.
At first glance, there is no economic advantage in using CFC instead of steel racks. The price of CFC is normally three to five times higher than for comparable steel grids. However, the higher costs are quickly recovered by longer life and higher loading. CFC charging racks provide obvious and calculable advantages even at a higher initial price. They enable shorter cycle times with significantly longer service life, are up to 10 times lighter than steel racks and do not distort at all. This makes handling easier and reduces the amount of work involved because it eliminates the straightening work on distorted racks and ensures continuous production. These advantages play a key role, especially when using automatic charging and removal systems since they enable expansion of production with unchanged facility size. There is another factor that is becoming more and more important: With the ever-increasing costs of energy, the excellent energy balance is a very good reason for using CFC racks, which have a lower overall heat-absorbing capacity.
No Longer Difficult: Temperatures of More Than 2000˚F
Specific requirements in heat treatment, such as temperatures of more than 2000˚F (1093˚C), determine CFCreactions like oxidation, methanization or the developing of carbonization. The fusion of the parts to the carbon can occur because of direct contact, and the enrichment of carbon can cause a lower fusing temperature. The hybrid rack avoids these contact reactions and makes CFCracks usable for temperatures of more than 2000˚F, which is necessary for aerospace materials or high-speed steel.
This innovation already made a successful integration into the European automotive and aerospace industries. The German sister company of TTU, GTD Graphit Technologie, developed the hybrid grid in 2009 and successfully boosted their sales distribution of these items over the last few years.
The CFC-hybrid system was developed to combine the special characteristics of CFC and ceramics in thermal treatment. The specific performance of the materials has to be consistent within the system. Particularly, the different thermal-expansion coefficients of the materials being combined had to be considered. The ceramic parts of the hybrid grid are bound in a dovetail. This enables the system to be installed on walls without losing the ceramic elements when they are transported or flipped. This also means that a hybrid grid can be used to load working parts with different contact points due to their shape (e.g., turbine blades).
Other advantages of the hybrid grids are no contact reactions or distortion, light weight, excellent energy balance for low costs and long service life. IH