Semco has made its name in graphite manufacturing, an industry that requires great investment in tools, technology, and training. Our machining capabilities and ability to customize graphite elements for clients’ manufacturing systems make us a go-to for companies that require industrial components made of carbon. This series of blogs will focus on a more behind-the-scenes, but no less important, aspect of our business: the selection and utilization of high-quality graphite material. At Semco, we take choosing the right graphite grade for each project very seriously because we know that the finished component, no matter how skillfully tooled, will only be as effective and durable as the material with which it is made. Occasionally, a client will request that we use their graphite material. To these requests, we generally respond that we prefer to provide the graphite (although we do take jobs where the client insists we use their graphite). This series of blogs will explore what can go wrong with graphite material and why it is crucial to any project that raw material be examined and chosen by experts in the field of graphite manufacturing.
hen discussing porosity, we must differentiate porosity from excessive porosity. All graphite is porous, so it is important to understand when porosity becomes a trait of graphite that necessitates quarantine of the material. In fact, porosity is a material characteristic that is in fact specified and engineered in the production of every graphite grade. Material spec sheets clearly define porosity as a percentage of the total volume. Some materials require very low porosity, which facilitates machinability and a finer level of detail. Other materials are engineered with larger porosity, allowing the materials to be impregnated with other elements or materials to give the finished product greater density or other specific qualities. Sometimes, greater airflow is the desired outcome of manufacturing more porous graphite. These are just a couple examples of how the porousness of graphite is a controlled and desired quality of the material. There are a multitude of graphite grades, with various porosity levels, that accommodate the varied needs of our clients.
Porosity only becomes an issue when we observe deviations from the material specs. These deviations could be general, where an entire block has been manufactured outside the spec., or localized within the larger mass of the material. Semco’s engineers are skilled in observing either case, and, as mentioned, Semco does quarantine and returns to the manufacturer material with porousness that does not match its specs.
So what causes excessive porosity? Most often the causes are similar to the blend contamination causes discussed in the previous blog of this series. Although there are not two different graphite grades present in the same block, the same mixing issues that cause contamination can also allow oxygen to concentrate in certain spots in the graphite block. Although oxygen will off-gas in the heat treat phase of manufacturing, larger than normal voids remain; hence, excessive porosity.
Various problems can arise when excessively porous material is used in the manufacture of graphite components. For example, parts being heat treated can end up taking the shape of the carrier, including the voids on the surface. In addition, phenolic treated materials, which are designed to be impervious, may lack that quality due to the impossibility of sealing the larger porosity areas of the raw material. In short, Semco wants to stress that, while we can, and will, work with customers’ materials, it’s always best to use graphite materials produced and inspected under our strict supervision. Both you and Semco want the highest quality graphite elements rolling out of our manufacturing center and to your business.