Technical article · 4 min read
Rubber-to-metal bonding: why the insert surface decides the bond
An NVH bush is only as good as the bond between rubber and steel. That bond starts with the inner metal — its shape, its steel and its surface.
Suspension and engine-mount bushes isolate noise, vibration and harshness (NVH). Inside each one is a metal insert — an inner metal or inner sleeve — that is bonded to rubber during moulding. If the bond fails, the bush fails, however good the rubber is.
How the bond is made
- Surface preparation — the insert is cleaned and given a surface the adhesive can hold on to: steel-grit blasting for a mechanical key, or a zinc-calcium phosphate conversion coating.
- Primer and adhesive — a bonding system is applied to the prepared surface.
- Moulding — rubber is moulded around the insert and vulcanised; the adhesive cures and bonds at the same time.
What the insert maker controls
- Geometry — flanges, slots and bulged profiles give the rubber something to grip and set the bush stiffness.
- Steel and strength — boron steel such as 10B21, hardened to the drawing, keeps the insert stiff under load.
- Surface — even blasting or an even phosphate layer, free of oil, so the bond is the same all round.
- Cleanliness and packing — bonding-ready parts must reach the moulder without rust or oil.
Standards and values are summarised for general guidance — always work to your drawing and the current edition of the standard. Related REL page.
