Graphite
Select graphite by named grade, forming route, porosity, impregnation and test basis; distinguish thermal, electrical and finished-part requirements.
Tags: materials, graphite, carbon, machining, electrical
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SGL’s isostatically pressed SIGRAFINE R4550 has a mean thermal expansion coefficient of 4.2 × 10⁻⁶ K⁻¹ from 20 to 200°C under DIN 51909, averaged across block sizes. A free 100 mm length heated uniformly over that interval expands by 0.0756 mm (100 × 4.2 × 10⁻⁶ × 180). Check the grade, orientation and restraint for a mounted part. SGL R4550 datasheet
Identify the grade and supplied form
Graphite is a material-family description, not a finished-component specification. SGL Carbon distinguishes isostatically pressed artificial graphite from extruded and vibration-molded products. It describes isostatic processing as producing the most isotropic form among those routes and offers multiple grades with different properties. Preserve the named grade and manufacturing route rather than assigning one generic graphite strength or conductivity. SGL isostatic graphite overview
An order should identify manufacturer/grade, product form and orientation, density/porosity requirements, purification or impregnation, dimensions, surface finish and required inspection. A solid machined billet, flexible graphite sealing foil, copper-infiltrated EDM electrode and carbon-fiber-reinforced carbon are distinct products. A coating or impregnation is an additional material/process feature that must remain visible in the record.
A named isostatic-grade reference
SGL's SIGRAFINE R4550 sheet is marked TDS R4550.00 / 04 2019/0 E. It identifies an isostatically pressed graphite for continuous casting and explicitly labels the following values typical:
| Property | R4550 reference value | Source test basis |
|---|---|---|
| Bulk density | 1.83 g/cm³ | DIN IEC 60413/204 |
| Open porosity | 10 vol.% | DIN 66133 |
| Flexural strength | 60 MPa | DIN IEC 60413/501 |
| Resistivity | 13 µΩ·m | DIN IEC 60413/402 |
| Thermal conductivity at 20°C | 105 W/(m·K) | DIN 51908 |
| Mean thermal expansion, 20–200°C | 4.2 × 10⁻⁶ K⁻¹ | DIN 51909 |
The footnote describes averages across different rectangular and round block sizes, with individual values varying by dimensions and format. These are not universal graphite properties or guaranteed design minima. SGL R4550 datasheet
Evaluate contact stress and thermal shock separately for the mounted geometry.
EDM grades and impregnation are separate choices
Entegris' Typical Properties of EDM Graphite Grades, ©2020, code 0000-10716ENT-0220, lists:
| Named grade | Typical flexural strength | Typical electrical resistivity |
|---|---|---|
| EDM-3 | 13,300 psi | 615 µΩ·in |
| EDM-C3 | 20,300 psi | 127 µΩ·in |
These are manufacturer reference entries, not a universal relationship between strength and resistivity. The product page specifically identifies EDM-C3 as copper-infiltrated graphite. Its behavior should not be assigned to unimpregnated stock. Entegris EDM grade chart, EDM-C3 product description
Keep units explicit: 615 µΩ·in × 0.0254 m/in = 15.621 µΩ·m. That conversion does not make the value interchangeable with the R4550 entry, whose grade and test basis differ. For an electrode, qualify wear, removal rate, detail retention and surface outcome under the actual machine, workpiece, flushing and operating conditions; one material number cannot select the entire EDM process.
Porosity, fluids and cleanliness
Entegris' industrial-graphite post-processing sheet distinguishes resin impregnation, which blocks the pore structure for fluid-exposure applications, from oxidation-inhibiting treatment. Those are specific treatment routes, not properties implied by the graphite name. Confirm the exact supplied treatment and its limitations. Entegris industrial graphite and post processes
Bulk density, open porosity and permeability are different acceptance quantities. A dense-looking surface or a nominal purity value does not establish leak tightness. Specify relevant fluid, pressure, temperature, leakage limit, cleaning and contamination requirements for the finished part. Include seals and joints in that assessment rather than qualifying only the raw block.
Where high purity matters, retain the grade's impurity/ash definition, treatment and analytical evidence. An application listing for semiconductor or vacuum equipment is not a cleanliness certificate for every machined component. Agree the final cleaning, handling and packaging state with the supplier.
Thermal environment and restrained assemblies
The Entegris post-processing sheet discusses graphite oxidation typically above 450°C and separate treatment-dependent improvements. This is supplier guidance, not one universal safe temperature: atmosphere, exposure duration, geometry and treatment belong with the actual service assessment. Do not use a very high inert-atmosphere capability to rate a component operating in air. Entegris oxidation-inhibition discussion
SGL's SIGRAFLEX thermal-stability note concerns flexible graphite foil and seals. It explains that oxidation comparisons require matching measurement conditions; its foil examples are not a service-life model for a dense R4550 block. Keep that product and test scope intact. SGL flexible-graphite oxidation guidance
For a graphite/metal assembly, evaluate differential expansion, support, restraint and gradients as well as peak temperature. Define how the part is located and loaded. A material's favorable thermal behavior cannot establish a safe clamp load, a thermal-cycle life or an allowable stress for an arbitrary geometry.
Machining and release
Entegris' Graphite Precision Fixtures sheet, ©2012 / 6205-7182ENT-0512, describes isotropic grades, machining capabilities and final ultrasonic cleaning with deionized water to remove machining dust. These are named supplier capabilities, not a universal machining or cleaning recipe for all graphite and impregnation combinations. Entegris precision-fixture guidance
Define datum surfaces, thin features, edge condition, thread details and finish before machining. Inspect the released part, including damage at handled edges and functional surfaces. Use representative trials for fragile geometry or a new grade/process, and obtain the applicable product handling information for the actual supplied material.
Release against the ordered grade, dimensions, surface/cleanliness requirements and functional tests. Retain lot identity, treatments, machining/cleaning history and inspection results. Distinguish supplier typical data, contracted limits, batch results and demonstrated assembly performance. Sources were reviewed November 1, 2026; printed document dates/codes are preserved without treating crawl dates as revisions.