The coupling head body is the structural heart of a light-trailer overrun brake: it carries the drawbar loads, houses the overrun damper and linkage, and transfers braking force into the rod system that actuates the wheel brakes. Ningbo Ruican investment casts and CNC machines this body to your print, holding bore concentricity and damper-seat geometry so the coupler engages cleanly, damps shudder and passes type-approval pull tests without rework.
Specifications
| Item | Specification |
|---|---|
| Casting process | Silica sol lost-wax investment casting (water glass option for cost-down volumes) |
| Material options | Carbon steel 45 / S355, low-alloy steel 42CrMo, ductile iron 500-7, stainless 304 |
| Dimensional tolerance (ISO 8062-3 CT grade) | CT5-CT6 as-cast, CT4 on machined datums and bores |
| Machining | 4-axis VMC, 3+2 turning-milling; damper bore, pivot bores, ball-seat and mounting faces finish machined |
| Surface finish (Ra) | Ra 3.2 um as-cast, Ra 1.6 um on machined faces, Ra 0.8 um on damper bore |
| Weight range | 1.2 kg – 6.5 kg per body |
| Typical lead time | Tooling 25-35 days, samples 15 days after tooling, production 30-40 days |
Scope and options
Key features
- Moreover, One-piece lost-wax body replaces welded fabrications, removing heat-affected zones at the drawbar throat.
- Generally, Damper bore and pivot bores machined in a single setup to hold concentricity within 0.05 mm TIR.
- Ball-seat profile cast near net shape and finish reamed, giving consistent 50 mm ball retention.
- Integrated boss pads for the breakaway cable bracket and handbrake lever stop cast in, not added later.
- Additionally, Non-destructive tested: 100% magnetic particle inspection on load-path walls, plus sample dye penetrant on critical sections.
- Shot-blasted and zinc-flake or hot-dip galvanised to survive road-salt and launch-ramp immersion.
Applications
- Light braked trailers from 750 kg to 3,500 kg gross trailer weight
- Caravan and leisure chassis with AL-KO or Knott type overrun devices
- Boat, jet-ski and personal watercraft launching trailers with repeated saltwater immersion
- In general, Horse boxes, livestock and box-van trailers on European and UK chassis
- Small plant and mini-excavator site trailers
- Municipal refuse and grounds-care trailers behind light commercial vehicles
Quality & compliance
Every coupling head body programme is run under Ningbo Ruican’s IATF 16949 quality system, from feasibility study and DFMEA through APQP gate review to PPAP submission at level 3 or 4 as your supplier manual requires. We supply EN 10204 3.1 material certification with heat-lot traceability, full first-article dimensional reports against ballooned drawings, capability studies on the damper bore and ball seat, and magnetic particle inspection records. Salt-spray validation to ISO 9227 and cyclic corrosion testing, plus fatigue and static pull-to-failure testing on the overrun linkage, are carried out on request with calibrated third-party or in-house equipment before production release.
FAQ
What information do you need to quote a coupling head body?
Send the 3D model or 2D drawing with GD&T, the material and heat-treatment specification, annual volume, surface coating requirement and any type-approval standard the assembly must meet. With that we return a feasibility study, tooling proposal and budgetary piece price within five working days, including a draft control plan for review.
Can you machine the damper bore and ball seat in one setup?
Yes. We fixture the as-cast body on machined datums and complete the damper bore, pivot bores, ball seat ream and mounting faces in a single 4-axis setup. This keeps concentricity within 0.05 mm TIR and removes the stack-up error that appears when the body is moved between machines for secondary operations.
Do you supply castings without machining?
We do. Many trailer assemblers prefer to receive the coupling head body as a shot-blasted raw casting with machining allowance on the damper bore and faces, then finish it on their own line. We can also deliver a semi-machined variant with datums established and only the final bore left for your assembly plant.
What corrosion protection do you recommend for boat trailers?
For saltwater launching we recommend zinc-flake basecoat plus a topcoat, or hot-dip galvanising after machining, with all threaded holes masked or re-tapped. We validate to ISO 9227 neutral salt spray, typically targeting 480 hours to red rust, and can extend to 1,000 hours with a duplex coating system on higher-specification programmes.
How is the breakaway cable bracket attached?
We cast a dedicated boss pad and stop face directly into the body, then drill and tap it during machining. This removes a welded bracket that would otherwise create a heat-affected zone on a safety-critical load path and gives a repeatable pull-off point that satisfies type-approval inspectors across markets.
CTA
Send your coupling head drawing or sample part to Ningbo Ruican for a build-to-print quotation, feasibility review and tooling proposal. Contact Wendy She — sales@cnsandcasting.com — WhatsApp +86-13777124360 for RFQ support, sample status or APQP documentation.
