Estimate torque, check thread geometry and prepare an RFQ for carbon-carbon hot-zone bolts.
Published and reviewed · By SiC Graphite. Grade and joint qualification required.
Request a drawing reviewEnter target preload and assembly K. Defaults are examples, not safe-load recommendations.
Set diameter, target preload and assembly K, then calculate. Geometry and temperature assumptions can be expanded on the form. Missing tested load data? Request a drawing and load review.
Architecture, density and fiber direction vary. A public comparison sheet cannot certify the proposed bolt.
[1][2][6]Nominal tensile area is only a geometric reference. Head bearing, thread stripping and the mating part may govern.
[4][7]A target load and K give an estimate. Friction variation and the thermal cycle require separate evidence.
[3]Agree analytical methods and elemental limits. An ash number alone cannot establish semiconductor process suitability.
[8]C/C describes a material family rather than one isotropic grade. Reinforcement and processing must be specified alongside the finished drawing. The classification reference records architecture and properties; it does not prescribe one weave for every fastener. [1][6]
| Feature | Decision it affects | Evidence to request |
|---|---|---|
| Planar / laminated reinforcement | Machining can interrupt load-carrying layers | Orientation drawing; head-transition and thread tests |
| Needled / multidirectional reinforcement | Through-thickness behavior depends on the preform | Fiber content, density distribution and shear test direction |
| 3D reinforcement | Additional fiber directions do not establish a finished-thread allowable | Representative machined-bolt tests and failure location |
| Coated threads | Deposition changes fit and local contact | Final coated dimensions, mating gauges and assembly trials |
| Output | Method and units | What remains unknown |
|---|---|---|
| Illustrative torque | T = K × F × d; F in kN, d in mm gives N·m | K calibration, allowable preload and wrench/process variation |
| Nominal tensile area | Aₜ = π/4 × (d − 0.9382p)², in mm² | Machined composite failure strength and damage |
| Nominal axial stress | σ = 1000 × F / Aₜ, in MPa | Stress concentration and multiaxial stresses |
| Engagement ratio | Actual engagement / nominal diameter | Female-thread strength and local load distribution |
| Free thermal mismatch | ΔL = Lgrip × (T − 20) × (αstack − αbolt); inputs use ×10⁻⁶/K | Stack stiffness, thermal gradients and retained clamp load |
Torque follows the generic relation discussed in NASA-STD-5020B; it supplies no C/C-specific safe preload percentage. Nominal area follows the cited geometric reference. Thermal mismatch uses a linear free-expansion model with user-entered average axial CTE over the temperature range. The tool assumes a uniform temperature, a single equivalent stack and room-temperature assembly at 20°C. [3][4][9]
Default F = 1 kN, K = 0.20 and CTE values are illustrative inputs, not material recommendations. No strength increase with temperature, fixed stripping penalty for fine pitch, universal washer prescription or safe torque band is inferred. The synchronous calculation runs locally; no server request is needed.
| Size | Coarse pitch (mm) | Coarse Aₜ (mm²) | Selected fine pitch (mm) | Fine Aₜ (mm²) |
|---|---|---|---|---|
| M6 | 1.00 | 20.1 | 0.75 | 22.0 |
| M8 | 1.25 | 36.6 | 1.00 | 39.2 |
| M10 | 1.50 | 58.0 | 1.25 | 61.2 |
| M12 | 1.75 | 84.3 | 1.25 | 92.1 |
| M16 | 2.00 | 156.7 | 1.50 | 167.2 |
| M20 | 2.50 | 244.8 | 1.50 | 271.5 |
| M24 | 3.00 | 352.5 | 2.00 | 384.4 |
These are selected nominal pitches, not every possible fine-pitch series or a stock-availability promise. Both the table and estimator use the same pitch-specific formula. Specify the mating tolerance, root geometry, coating allowance and under-head transition on the drawing. Steel proof loads in reference tables do not transfer to C/C. [5][4]
The SIGRABOND Mechanical sheet provides one identifiable comparison, not a certificate for SiC Graphite parts. Its printed revision is 2018/1.0; the listed values are typical averages. [2]
| Property | SIGRABOND Mechanical sheet | SiC Graphite bolt status on this page |
|---|---|---|
| Density | 1.5 g/cm³ typical | Not established; request the proposed grade and batch report |
| Tensile strength | 65 MPa typical | Not established; direction and hot test conditions required |
| Interlaminar shear strength | 11 MPa typical | Not a machined-thread stripping allowable |
| Purified-grade ash | <10 ppm typical | Not established; agree method and elemental limits |
| Maximum application temperature | 2000°C in vacuum or inert gas | Not a transferable service rating |
| Bolt torque / cycle life | Not specified in this sheet | Matched-joint qualification required |
Do not combine the highest strength, lowest ash and highest temperature from different grades into an invented product specification. No batch certificate, retained-preload curve or service-life dataset is published here. Request those records for the offered part.
| Environment | Unresolved risk | Minimum next step |
|---|---|---|
| Vacuum / inert | Residual oxygen, moisture, process vapors and mass loss | Specify pressure, gas purity, peak temperature, dwell and leak history |
| Reactive / reducing gas | Chemistry may attack the substrate, coating or adjacent parts | Review actual gas composition and exposure with the grade supplier |
| Air / oxidizing | Carbon oxidation; coating flaws or wear can expose carbon | Hold for process-specific oxidation and thermal-cycle tests |
| SiC coated | Final thread fit and coating integrity after assembly | Check a matched coated bolt/nut pair through the intended cycle |
| PyC treated | Pore sealing alone does not establish oxidation protection | Agree treatment purpose and test it under the actual atmosphere |
The public comparison-grade temperature statement applies to vacuum or inert gas. It does not establish operation in air or reactive gas. Our air-service hold at ≥400°C is a conservative review trigger, not an oxidation-rate model or a safe limit below that temperature. No universal 1600°C coating guarantee is made. [2][7]
| Candidate | Reason to evaluate | Qualification / cost question |
|---|---|---|
| C/C composite | Low-mass furnace hardware with directional reinforcement | Will machining, densification, purification and testing justify the installed cost? |
| Isostatic graphite | Machined carbon hardware for a compatible load path | Do brittle features, handling and threads survive the required load and cycle? |
| Molybdenum / TZM | Refractory metal hardware where process chemistry permits | Compare grade-specific hot strength, creep, contamination and post-cycle handling |
| Tungsten | Candidate for selected refractory applications | Check mass, machining cost, joining geometry and the actual atmosphere |
| Ceramic fasteners | Candidate where electrical insulation or chemistry matters | Check grade-specific thermal shock, mating expansion and contact stresses |
This table is a purchasing framework, not a quantitative performance ranking. C/C is one candidate, supported by documented furnace uses; a final substitution requires a common test cycle and acceptance criteria. Compare total cost per qualified campaign: purchased parts, inspection, replacement labor, downtime and rejected process output. Prices and replacement intervals require a current quotation. [1][7]
| Symptom or risk | Investigate | Action before reuse |
|---|---|---|
| Stripped or chipped threads | Actual pitch/fit, cut fibers, engagement and assembly history | Quarantine damaged parts; test a matched joint before changing preload |
| Head or bearing-face damage | Transition radius, seating geometry, eccentric load and contact pressure | Review the drawing and bearing washer; qualify the modified load path |
| Loss of clamp load after cycling | Stack stiffness, temperature gradients and washer consolidation | Measure retained load; agree a cold inspection and retorque procedure |
| Erosion or coating loss | Atmosphere, leaks, moisture, deposition and assembly abrasion | Stop reuse pending dimensional and process-compatibility review |
| Contamination concerns | Sampling, cleaning, packaging and exposed coating/substrate | Obtain element-level results with detection limits and lot traceability |
| Unexpected campaign cost | Replacement labor, scrap and inspection requirements | Compare alternatives with the same campaign and acceptance criteria |
These are investigation prompts, not diagnoses. Establish inspection and retirement rules in the released procedure. No fixed retorque schedule, 100% failure-prevention claim or guaranteed retained-preload percentage is supported by the evidence here. [3][7]
Illustrative calculations and hold decisions, not customer installations or service-life results. Load capacity remains unverified in every example.
Assume M10 × 1.5, F = 1 kN and K = 0.20. T = 2.00 N·m and nominal stress ≈17.2 MPa. For a 30 mm grip, 1400°C and assumed average CTEs 1/4.5, free mismatch is 144.9 µm.
Next: verify actual CTE, head bearing, matched-thread strength and torque–tension scatter. This is not an installation setting.
Assume M12 × 1.25, F = 1.5 kN, K = 0.15 and 24 mm engagement. Nominal area ≈92.1 mm²; T = 2.70 N·m; engagement ratio = 2.00d.
Next: confirm the mating pitch and test the finished threads. Larger nominal area does not prove a larger safe load.
Assume the default geometry but change atmosphere to air and temperature to 700°C. The estimator withholds torque and flags atmosphere review, including when SiC coating is selected.
Next: review a compatible material or qualify the complete coating/assembly under the actual exposure.
Run captured on 1 November 2026: M10 × 1.5, preload 1 kN, K 0.20, 30 mm grip, 18 mm engagement and 1400°C vacuum, using the displayed example CTEs. Select Reset all inputs, then Calculate estimate to reproduce 2.00 N·m, 17.2 MPa nominal stress and 144.9 µm free mismatch.
Links and public scopes reviewed on 1 November 2026. Standards are cited for their stated purpose, not as product certification. Confirm the contractually required edition before procurement; public summaries do not replace the full method. SiC Graphite owns this guide; see our company information and quality review scope. Review sources and assumptions again by May 2027, or sooner if specifications change. Suggested acceptance actions elsewhere on this page are engineering review recommendations.
Material families and Mechanical grade for fasteners; general context, not SiC Graphite product certification.
Source 12018/1.0 printed revision. Typical comparison-grade values only; not a current batch report or a bolt allowable.
Source 22021 edition, §4.3 and Appendix A: torque/preload relation, variation and thermal effects. Not a C/C furnace-bolt torque specification.
Source 3Nominal metric geometry formula only. It does not establish composite strength.
Source 4Nominal thread reference. Steel strength classes and proof loads in this document do not apply to C/C.
Source 5Public scope: classification by architecture and properties. Classification is not an assembly release or a universal minimum strength.
Source 6Public scope: originally nuclear applications, with applicability to other structural uses. Not cited as a source of a fixed preload percentage or engagement ratio.
Source 7Public scope: residue estimation with stated limitations for purified graphite; not an element-by-element semiconductor acceptance limit.
Source 8Linear free-expansion model. Temperature-dependent, directional CTE must be supplied for the actual stack.
Source 9Carbon fibers reinforce a carbon matrix. C/C threaded parts are candidates for furnace insulation and hot-zone connections where low mass and thermal expansion matter. The selected grade and joint still need qualification for the atmosphere, loads and cycle.
No universal architecture rule is established here. Fiber direction and through-thickness reinforcement affect machined threads and head transitions. Ask for tests on the proposed architecture and actual geometry instead of accepting a weave label as proof of strength.
It is grade- and process-specific. The cited SIGRABOND Mechanical comparison sheet lists 2000°C in vacuum or inert gas. That value is neither a SiC Graphite batch rating nor approval for 2200–2400°C service. Obtain hot mechanical and mass-loss data for your process.
No universal threshold is established by the sources here. Agree element-specific limits, detection limits, sampling and cleaning with the process owner. Total ash is not interchangeable with GDMS or ICP-MS elemental results.
No. It shows T = K × F × d for your entered target preload and assembly nut factor. It does not verify that the bolt, nut, head or substrate can carry that load. A representative torque–tension test and joint release are needed.
K summarizes friction and geometry in a particular assembly. It is not the friction coefficient itself. Surface finish, lubricant, coating, bearing face and reuse can change it; no generic dry-carbon or paste value is certified here.
The nominal tensile area increases for the listed fine pitch at the same diameter. Composite thread stripping depends on the cut fibers, mating thread and engagement; the tool does not turn that area increase into an allowable-load increase.
No. The default 18 mm for an M10 bolt is an illustrative input. Female-thread material, head geometry, process damage and load distribution determine the required engagement. Verify it with matched-joint tests.
A coating selection is not a service qualification. Thread fit, coating defects, cycling, gas composition and dwell time need review. This estimator withholds torque for air service at or above a conservative 400°C screening point; that is not an oxidation-onset or safe-below limit.
Not necessarily. A washer may distribute contact load or introduce compliance, but compression, relaxation, contamination and stack stiffness need checking. Free expansion mismatch alone cannot specify washer thickness or retained preload.
Use the released furnace maintenance procedure. Inspect cold after the agreed commissioning cycle, record thread and coating damage, and qualify any retorque procedure. No universal cycle count or retained-preload percentage is supported here.
Send the part and mating-thread drawings, usable length and grip, head and washer details, grade/fiber direction, operating temperature and atmosphere, load history, elemental purity requirements, inspection plan, quantity and delivery needs. Paste the tool brief as preliminary context.
Evidence for the material, assembly and purity answers: [1][2][3][4][6][7][8]
Images illustrate possible part forms. They do not establish grade, purity, dimensions, current stock or process suitability.
Use the estimator’s selectable brief or Email this brief to carry your current inputs into the inquiry. Without validated preload data, send the drawing and service conditions first.
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