{"id":9166,"date":"2020-03-11T13:34:24","date_gmt":"2020-03-11T13:34:24","guid":{"rendered":"https:\/\/phiheating.com\/knowledge-center\/c-c-composites-for-brazing\/"},"modified":"2022-01-07T10:12:08","modified_gmt":"2022-01-07T03:12:08","slug":"c-c-composites-for-brazing","status":"publish","type":"knowledge-center","link":"https:\/\/phiheating.com\/ja\/knowledge-center\/c-c-composites-for-brazing\/","title":{"rendered":"C\/C Composites for brazing"},"content":{"rendered":"\n

C\/C Composites \u201cNeftec\u201d<\/a><\/strong><\/h2>\n\n\n\n
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The use of carbon-fiber-reinforced carbon (C\/C) composites<\/a><\/strong> in the brazing world is gaining a lot of momentum these days and for good reason. Brazing furnaces today often contain a lot of very heavy fixturing materials in their brazing chambers. This \u201cfixture\u201d includes all the heavy-metal structures in the furnace hot zone (e.g., grates, trays, racks, baskets, etc.).<\/p>\n\n\n\n

C\/C composite<\/a><\/strong> is a carbon-carbon composite material reinforced by high strength carbon fiber for improving mechanical strength and thermal shock resistance. C\/C is a high strength lightweight material suitable for fixtures. C\/C\u2019s density is only 1\/5 of steel, so C\/C fixtures are much easier to handle. Also, it is about 10 times stronger than steel at 1000\u00b0C and there is no thermal deformation. Because of these excellent features, C\/C fixtures realize process capacity increase and running cost reduction.<\/p>\n\n\n\n

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Major Advantages
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Less Gross Weight Means Added Productivity<\/strong><\/h4>\n\n\n\n

In heat-treating, including brazing, the furnace heating capacity and maximum load weight are two important factors that determine the amount of total load capacity processed in a heat-treat cycle. Using C\/C fixtures, a significant increase is achieved in the quantity of parts that could be processed per cycle.<\/p>\n\n\n\n

Decrease in Defect Rate<\/strong><\/h4>\n\n\n\n

With metal-jig brazing, when the parts are aligned too closely, the shadow of the supplementary weights have a tendency to block radiant heat waves. This, in addition to the heat capacity of the dead weights, compromises the heating uniformity and leads to defective brazed parts. With a C\/C fixtures setup, the C\/C itself is very compact and does not encounter these problems. Hence, a decrease in the defect rate and an increase in process quantity is achieved.<\/p>\n\n\n\n

Longer Service Life<\/strong><\/h4>\n\n\n\n

After long-term service, the metal fixtures tend to deform due to high-temperature deformation, which also has a negative effect on the distortion of the parts. On the other hand, C\/C fixtures maintain high strength from room temperature up to 2000\u00b0C (3500\u02daF), thereby assuring a positive effect on part distortion. Also, C\/C has a very high deformation resistance, which leads to longer service life.<\/p>\n\n\n\n

Production savings<\/strong><\/h4>\n\n\n\n

The production savings is significant, and these saving can offset the cost differential between C\/C fixtures and alloy fixtures. The resultant overall cycle time savings (door to door) was 45 minutes, which overall cost saving in production hours when using C\/C fixturing is 15%.<\/p>\n\n\n\n

What happens if C\/C fixtures contact the metal during brazing?<\/strong><\/h4>\n\n\n\n

For some metals, direct contact between the C\/C fixture and the metal being brazed is not acceptable. This is especially the case with stainless steels, in which contact with the C\/C fixture could result in large carbon diffuse to the stainless, which can cause two problems:<\/p>\n\n\n\n

1) Loss of corrosion resistance if the carbon from the fixture reacts with the chromium in the stainless to form chromium-carbides, which then migrate to the grain boundaries and this, in turn, robs the surface of needed chromium-oxide protection.<\/p>\n\n\n\n

2) It may be possible for those metals to then pick up carbon from the fixturing. This could cause carburization of those base metals and possibly result in the formation of low-melting iron-carbon eutectics in any ferrous materials sitting on those C\/C fixtures. Eutectic melting can occur with C\/C materials at temperatures exceeding 1050\u00b0C (1922\u00b0F), but it is highly dependent on the alloy(s) being run, thus literally causing some portions of the base-metal assembly to sag or melt during brazing.<\/p>\n\n\n\n

Therefore, to prevent both of these problems from occurring; coat the surface of the C\/C fixtures with a brazing stop-off or keep the fixtures covered, either with a ceramic cloth or thin sheets of solid ceramic.<\/p>\n\n\n\n

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Fig. 4<\/strong> \u2013 Ceramic pieces placed on top surface of furnace grid. (courtesy of Schunk Graphite\u2019s CarboGard channels)<\/figcaption><\/figure><\/div>\n\n\n\n

You need to know this and take precautions to ensure that metal does not come into direct contact with the C\/C fixtures during heating in the furnace. A couple of other metals that can react strongly with carbon are titanium and chromium.<\/p>\n\n\n\n

Conclusion<\/strong><\/h2>\n\n\n\n

The uses for C\/C composites<\/strong><\/a> as fixtures are almost limitless. It is a great product, just making its way into brazing production, and has a great future. Consider its benefits of strength, durability, light weight, and lack of distortion when you are designing fixtures for your brazing needs. As C\/C technology continues to develop, the costs of C\/C fixturing are steadily coming down as more and more shops buy them and use them and find out the many advantages of switching to this \u201cnew\u201d technology.<\/p>\n\n\n\n

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Reference:<\/strong><\/p>\n\n\n\n

Dan Kay, Specialized C\/C Fixtures for Today\u2019s Brazing Needs, Industrial Heating, August, 2018.<\/p>\n\n\n\n

Dan Kay, Carbon-fiber reinforced carbon (C\/C) fixturing for brazing?, Kay & Associates brazing consultants, August, 2018.<\/p>\n\n\n\n

Bill Warwick, Robert Hill Jr., and Daniel H. Herring, Technical Considerations for the Use of Carbon\/Carbon Composite Materials For Fixtures and Grids, Industrial Heating, December, 2013.<\/p>\n","protected":false},"excerpt":{"rendered":"

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