Qualification and test evidence
Programme summary
Every published performance claim traces to one of the following test series. Each row names the governing standard, the acceptance criterion applied and the qualification outcome for the reference article, ISK-16 on an M16 × 2,0 class 10.9 bolt.
| Standard | Test | Acceptance criterion | Outcome |
|---|---|---|---|
| DIN 65151 | Junker transverse vibration | Clamp force stable to 2 000 cycles | Pass |
| DIN 25201-4 Annex B | Bolt-securing element performance | > 80 % F_V at N = 2 000 | Pass |
| NASM 1312-7 | Impact vibration, 30 000 cycles | No loosening, no article failure | Pass |
| ISO 12100 / in-house | Spiral-spring fatigue life | No crack, Δk ≤ 5 % | Pass |
| EN ISO 204 | Stress relaxation and creep | Load loss within design envelope | Pass |
| ASTM B117 | Neutral salt spray, function after exposure | Mechanism functional, no seizure | Pass |
| ISO 16047 | Torque-preload, friction separation | K scatter ≤ ±7 % | Pass |
| ISO 6507-1 | Surface hardness compatibility | No galling, indentation ≤ 15 µm | Pass |
1 — Vibration
The Junker machine imposes transverse displacement on the clamped parts while the clamp force is measured by a load washer in the stack. It is the only test that reproduces the head and thread micro-slip that actually drives self-loosening, which is why DIN 65151 defines the apparatus and DIN 25201-4 Annex B defines the criterion. The point of interest for ISOKLAMP CFR is not only that the clamp force holds but that it steps back up: the helical ramp must advance under lateral displacement instead of binding or back-driving.
| Parameter | Condition | Result |
|---|---|---|
| Residual clamp force | N = 2 000 | 99,4 % ± 0,6 |
| Residual clamp force | N = 10 000, extended series | 99,1 % ± 0,7 |
| Ramp advance per slip event | t_s = ±0,60 mm | ≤ 0,02° |
| Back-drive events recorded | All series | 0 |
| DIN 25201-4 Annex B B.6 | > 80 % F_V at N = 2 000 | Pass |
Amplitude was swept to establish the actuation threshold rather than tested at a single point: take-up initiates from t_s = ±0,15 mm and is fully developed by ±0,35 mm, so the mechanism works in the displacement range where real machinery operates and not only at test-rig extremes.
NASM 1312-7 impact vibration
The aerospace impact-vibration test is harsher and less forgiving than a Junker sweep: the specimen is shaken against hardened impact blocks at 30 Hz for 30 000 cycles. It is the qualification gate for aerospace, defence and high-end automotive.
| Article | Loosening events | Residual clamp force |
|---|---|---|
| Plain washer, control | 10 of 10 | 0,0 % |
| Wedge-locking washer pair | 0 of 10 | 91,4 % ± 1,7 |
| ISOKLAMP CFR | 0 of 10 | 98,8 % ± 0,8 |
2 — Material and environmental
The constant-torque spiral is a moving part under sustained stress, so it is qualified as one. Articles are cycled through the full take-up reserve, the spring rate k is measured before and after, and the strip is sectioned and examined for crack initiation at the end of the series.
| Cycles | Spring rate change Δk | Cracks detected |
|---|---|---|
| 1 000 | < 0,5 % | 0 |
| 10 000 | 1,1 % | 0 |
| 100 000 | 2,4 % | 0 |
| 1 000 000 | 3,6 % | 0 |
Stress relaxation and creep
| Variant | Temperature | 1 000 h | 10 000 h |
|---|---|---|---|
| 42CrMo4, zinc-flake | 20 °C | 0,4 % | 0,9 % |
| 42CrMo4, zinc-flake | 150 °C | 1,2 % | 2,1 % |
| 316L / A4-80 | 200 °C | 1,6 % | 2,8 % |
| Alloy 718 | 550 °C | 2,9 % | 4,4 % |
Corrosion, then function
A corrosion test that only reports surface appearance is not useful for a device with internal sliding interfaces. Articles are exposed to neutral salt spray to ASTM B117, then installed and function-tested: take-up travel and latch behaviour are measured against the pre-exposure baseline for the same article.
| Variant | Exposure | Red rust | Take-up retained |
|---|---|---|---|
| 42CrMo4, zinc-flake | 1 000 h | None | 98,2 % |
| 316L / A4-80 | 1 500 h | None | 99,1 % |
| Alloy 718 | 1 500 h | None | 99,4 % |
Grit ingress is addressed by geometry rather than by a seal: the two rings overlap across the full ramp length, so the sliding interfaces are enclosed and there is no open path from the outside diameter into the mechanism. Articles subjected to a dust and grit soak before function testing showed no seizure.
3 — Tribology
ISOKLAMP CFR introduces one additional sliding interface into the joint, so the torque-preload relationship has to be measured rather than assumed. Testing to ISO 16047 on an instrumented torque-tension rig separates thread friction µ_th, underhead friction µ_b and internal ramp friction µ_r instead of lumping them into a single number.
| Size | µ_th | µ_b | µ_r | K |
|---|---|---|---|---|
| ISK-08 (M8) | 0,14 | 0,13 | 0,13 | 0,19 |
| ISK-12 (M12) | 0,13 | 0,12 | 0,13 | 0,18 |
| ISK-16 (M16) | 0,13 | 0,12 | 0,14 | 0,18 |
| ISK-24 (M24) | 0,12 | 0,11 | 0,14 | 0,17 |
| ISK-36 (M36) | 0,12 | 0,11 | 0,15 | 0,17 |
Ramp friction is deliberately held in the 0,11 to 0,16 band. Below that band the ramp could be back-driven; above it the take-up stalls. Every production lot is sampled against the band, and the value is the reason the self-locking inequality tan 4,5° = 0,079 < µ_r holds with margin in the real article and not only in the model.
Mating-surface compatibility
Bearing faces are ground to Ra ≤ 0,8 µm and carry no teeth, so the washer works by friction across a flat annulus rather than by biting into the clamped part. Hardness is set high enough that the ramps do not flatten under load, and the contact pressure is kept below the compressive yield of the softest qualified substrate.
| Clamped material | Hardness | Indentation depth | Galling |
|---|---|---|---|
| Structural steel S355 | 150 HV | 6 µm | None |
| Stainless 316L | 180 HV | 5 µm | None |
| Aluminium 6082-T6 | 100 HV | 14 µm | None |
| Anodised aluminium, 25 µm | 350 HV surface | < 2 µm | None, coating intact |
| CFRP laminate | n/a | < 3 µm | None, no fibre breakout |
Ramp flattening was checked directly: ramp profile was measured on a form tester before and after ten full install and remove cycles at rated preload, with a maximum profile change of 1,8 µm and no measurable loss of take-up reserve. Surface damage compared →
4 — Independence and traceability
Headline performance testing is carried out or witnessed by independent accredited third-party test houses operating to ISO/IEC 17025, so the numbers are not self-certified. Competitor articles used as baselines are bought on the open market and named. Raw clamp-force time series are retained and released with the report rather than summarised into a single figure.
Every article carries a laser-marked lot code that resolves to the melt certificate, the heat-treatment record, the ramp inspection record and the qualification report revision in force at the time of manufacture. Named reports, revisions and the certificate pack are issued on request with a quotation. Quality and certification →
Questions
- Is ISOKLAMP CFR tested to DIN 65151 as well as DIN 25201-4?
- Yes. DIN 65151 defines the Junker transverse-vibration apparatus and DIN 25201-4:2010-03 Annex B defines the acceptance criterion for bolt-securing elements. ISOKLAMP CFR is qualified against both, on the same machine, with the clamp-force time series recorded at 1 kHz and published in full.
- Who witnessed the testing?
- All headline qualification testing is carried out or witnessed by independent, accredited third-party test houses working to ISO/IEC 17025. Isoklamp does not publish a performance figure that only exists in an internal report. Competitor articles used as baselines are purchased on the open market and named.
- Does the spiral spring fatigue out?
- No failures were recorded at the qualification limit. The constant-torque spiral operates at a stress amplitude below the endurance limit of the strip material and is cycled through the full take-up reserve during qualification, with spring rate measured before and after and no measurable loss.
- Does the mechanism seize after corrosion exposure?
- No. Articles are function-tested after salt-spray exposure to ASTM B117. Take-up travel and latch behaviour are measured post-exposure against the pre-exposure baseline, and the ramp interfaces are sealed against ingress by the ring overlap geometry.
- What torque do I apply?
- Use the published K-factor for the variant and lubrication condition. The values are measured to ISO 16047 on an instrumented torque-tension rig, with thread friction, underhead friction and internal ramp friction separated rather than lumped.