A silent block (anti-vibration mount) is a rubber-to-metal component that connects two parts of a structure while damping vibration, shock and noise. It's used anywhere metal must not rest directly on metal — from railway bogies, engines and compressors to construction machinery and industrial equipment.
A poorly chosen silent block doesn't fail immediately. It fails after a few months: cracked rubber, a loosened joint, vibration transmitted into the rest of the structure. That's why selection is worth doing systematically. Here's what to look at.
1. Load — Static and Dynamic
The first question is always: how much force does the mount carry, and in which direction?
- Static load is the weight the mount carries at rest (e.g. the mass of an engine divided by the number of mounts).
- Dynamic load covers the forces generated in operation — vibration, shocks, acceleration, braking.
A practical rule: size the silent block so that the static load uses only part of its rated capacity, leaving reserve for dynamic forces. If you work with our engineers, it's enough to send us the assembly mass, the number of mounting points and a description of service conditions — we handle the calculation.
Load direction matters too: rubber behaves differently in compression, shear and tension. It carries the most in compression and the least in tension. Good installation design avoids loading a silent block in pure tension.
2. Rubber Hardness (Shore A)
The hardness of the rubber compound, expressed in Shore A degrees, directly determines the stiffness of the mount:
- Softer rubber (40–50 ShA) — better vibration isolation, more travel, lower load capacity. For sensitive equipment and lower frequencies.
- Medium hardness (55–65 ShA) — the most common choice for industrial applications; a balance of capacity and damping.
- Harder rubber (70–80 ShA) — higher capacity and stability, weaker isolation. For heavy loads and applications where position matters more than comfort.
If you're replacing an existing silent block, we can measure the hardness of the original on a sample and reproduce the compound.
3. Type and Geometry
The basic types you'll encounter in practice:
- Cylindrical mounts (types A, B, C) — with threaded studs or nuts on one or both sides; the universal choice for engines, pumps and fans.
- Bushings — rubber vulcanized between an inner and outer metal sleeve; typical for suspension arms, linkages and chassis mounting.
- Conical and profiled mounts — for combined loads in multiple directions, common in rail vehicles.
- Buffers (bump stops) — work in compression and impact, limiting travel.
Geometry is chosen based on available space, mounting method and force direction. If a standard geometry doesn't fit, a silent block can be manufactured to drawing or sample — in our case, with tooling designed for the specific part.
4. Temperature and Operating Environment
Standard compounds based on natural rubber (NR) and SBR damp vibration excellently, but have limits:
- NR/SBR: roughly −40 °C to +80 °C; the best mechanical properties and dynamic fatigue life.
- EPDM: up to +150 °C, excellent resistance to ozone, UV and weathering — for outdoor installation.
- NBR: where oil or fuel is present (engine compartments, hydraulics).
Also check exposure: oil, ozone, direct sunlight, salt, steam, chemicals. The wrong compound in the wrong environment ages many times faster. More on choosing between the two most common compounds: EPDM vs NBR — how to choose.
5. The Rubber-to-Metal Bond
In a quality silent block, the rubber is not glued to the metal — it is vulcanized directly onto a prepared metal surface during molding. A properly executed bond is stronger than the rubber itself: under destructive testing, the rubber tears before the bond fails.
What to look for in a supplier: metal preparation (blasting, bonding agent application), controlled vulcanization and bond testing on samples. That's the difference between a mount that lasts for years and one that delaminates after its first winter.
6. Replacing an Existing Part or Custom Manufacturing?
If you're replacing a worn silent block, the fastest route is to send us a sample or a dimensioned drawing — diameter, height, thread, hole pattern. With a library of over 2,500 tools, we often already have suitable tooling, which means no tooling cost and a shorter lead time.
If you're designing a new assembly, involve the manufacturer early: small geometry changes at the design stage (radii, rubber thickness, mounting arrangement) can significantly extend part life without affecting price.
Pre-Order Checklist
To receive an accurate quote, prepare:
- Mass/load per mount and force direction
- Dimensions or a drawing (or a physical sample)
- Operating temperature and environment (oil, outdoor, steam…)
- Quantity and ordering schedule
- Special requirements (hardness, certificates, metal material)