What Are Rubber Bushes?
If you take apart the suspension of a car or look at the connecting parts of a factory machine, you will find some black or brown rubber rings – these are rubber bushes. This is the rubber bushing. It has three core tasks: to dampen vibration and noise, to isolate shocks and to compensate for displacement.
Rubber bushes are usually made of synthetic rubber (e.g., nitrile rubber) and are typically between 10 and 50 mm thick. Its modulus of elasticity (a measure of the softness or hardness of a material) is about 1/1000th of that of metal, which means that rubber deforms 1,000 times as much as metal when the same force is applied. This characteristic makes it a key player in mechanical systems that are ” overcome hardness with softness “.
You can think of it like a shoe insole: when your foot hits the ground, the insole absorbs the impact by deforming slightly, preventing your knee from taking the full brunt of the pressure. A rubber bushing serves a similar purpose in machinery, except that it is confronted with an impact force measured in tons.
Core Function of Rubber Bushes
Vibration Damping and Noise Reduction
When a car is driven on a rough road surface, the wheels generate hundreds of high-frequency vibrations per second. If metal parts are directly connected to the car body, these vibrations are transmitted to the interior of the car without attenuation, which can cause the steering wheel and seats to shake, and can also lead to metal fatigue and fracture. Rubber bushes absorb 60-80% of high-frequency vibration energy through their own elastic deformation.
Comparative experiments have shown that industrial pumps with rubber bushes can reduce noise from 85 dB to 72 dB – the equivalent of going from the noise level of a vacuum cleaner to the sound of normal conversation.
Isolating impacts
In 2018, a car brand found in tests that chassis components without rubber bushes were subjected to instantaneous impacts of up to 1,200 kilograms when passing through speed bumps, while this value dropped to less than 400 kilograms for the version fitted with rubber bushes. This protective effect is directly related to the service life of key vehicle components.
Compensation for displacement
If rigid connection is used, repeated thermal expansion and contraction will lead to bolt breakage. The rubber bushing allows an elastic displacement of 0.3-1.2 mm, which ensures a solid structure and avoids stress concentration.
Field of Application
Railway Vibration Damping
The bogie of China’s high-speed rail CR400AF train adopts multi-layer rubber bushes, which can effectively absorb the vibration caused by track unevenness. The measured data show that the vertical vibration acceleration in the carriages is reduced from 0.25g to 0.08g (68% reduction), and the rate of passenger motion sickness is reduced by 42%.
Industrial Robot Joints
The rubber bushes in the rotary joints of ABB robotic arms need to meet the fatigue life requirements of 30 cycles per minute and 10 years of continuous operation. The damping coefficient (energy absorption capacity) needs to accurately match the inertial impact of the motor when starting and stopping.
Medical equipment protection
The Siemens 3T Magnetic Resonance Imager (MRI) mount uses a Viton bushing that insulates it from external ground vibrations (accuracy required: amplitude < 1 micron) and prevents metal parts from interfering with the magnetic field. The design reduces image artifacts by 37%.
Aerospace
The titanium hydraulic line fittings of the Boeing 787 landing gear are embedded with low-temperature resistant silicone bushes. They remain flexible at -55°C (ambient temperature at cruising altitude), preventing the metal from expanding and contracting and leading to hydraulic fluid leakage, and reducing the failure rate from 1.2 to 0.3 failures per 1,000 sorties.
Rubber Bushing VS Other Materials
We compare the key metrics of four common material bushes:
| Norm | Rubber Bushe | Metal bushes | Plastic Bushes | Polyurethane |
| Modulus of Elasticity (MPa) | 5-20 | 200,000 | 2000-3000 | 30-100 |
| Damping Factor (tanδ) | 0.15-0.30 | 0.001-0.005 | 0.02-0.08 | 0.10-0.25 |
| Temperature Resistance Range (℃) | -50~120 | -200~1000 | -20~80 | -40~90 |
| Fatigue resistance (number of cycles) | 1×10⁶~5×10⁶ | 1×10⁴~10×10⁶ | 5×10⁴~2×10⁵ | 2×10⁵~1×10⁶ |
| Installation Difficulty | Low (elastic deformation adaptation) | High (requires precision machining) | Medium (brittle) | Medium (harder) |
| Environmental | Recyclable but complex process | Fully recyclable | Difficult degrade | Partially hydrolytically degradable |
Metal is durable but transmits road bumps directly to the body; plastic is low cost but tends to soften and deform at high temperatures. Rubber bushes arguably find the optimal balance.
Rubber Bushing Cost
A logistics company has carried out statistics on forklift maintenance costs: without the use of rubber bushes, the annual cost of bearing replacement due to vibration is 3,200 yuan/unit; after the installation of rubber bushes, this expenditure is reduced to 900 yuan/unit. Calculated on the basis of 100 forklifts, the annual maintenance cost savings of 230,000 yuan, far more than the purchase cost of bushes (about 80,000 yuan).
However, rubber bushes are not a perfect solution. If they are exposed to long-term oil contamination (e.g. in construction machinery), the rubber will melt and deteriorate, requiring replacement every 2-3 years. In this case, it is necessary to evaluate the cost of replacement in terms of labor and risk of failure.
Disadvantages of rubber bushes
Of course, rubber bushes are not perfect, and they have some tricky problems waiting to be overcome.
Aging Cracking
Rubber gradually develops cracks on its surface when exposed to UV light. The solution is to add carbon black to the material (to make the bushing black), which absorbs more than 90% of UV rays. The outdoor service life of modern rubber bushes has been increased from 3 to 8 years.
Extreme Temperature
Ordinary rubber becomes brittle at -30℃ and starts to soften at 120℃. Silicone rubber modified by adding silicone oil can extend the temperature resistance range to -60℃~250℃, and this material has been applied to high-speed rail bogie bushes.
Compatibility With Lubricating Media
Long-term exposure of rubber bushes in construction machinery to hydraulic oil or gear oil may result in swelling or hardening. Hydrogenated Nitrile Butadiene Rubber (HNBR) is selected, which has a volume expansion rate of <5% (12% for ordinary NBR) after being immersed in engine oil at 120°C for 1000 hours, or the surface of the bushing can be fluorine-coated to increase the oil resistance by 3 times.
Future Trends in Rubber Bushes
The German company BASF is testing a “self-healing rubber”: when a tiny crack occurs in the bushing, the liquid rubber wrapped inside will automatically ooze out to fill the gap. This technology could extend the life of the bushing by up to 40%.
In the wind power sector, a 3D-printed gradient rubber bushing has entered the trial stage. Its internal density gradually changes from the center to the edge, which can withstand the huge torque of the blade and also filter vibration waves of different frequencies.
Summarize
The essence of choosing rubber bushes is to resolve rigid conflicts with elasticity:
- For engineers: focus on the Shore hardness of the rubber (bushes labeled 60HA-80HA are suitable for most scenarios)
- To owners: when you hear a chassis rattle, prioritize checking the suspension bushes (replacement costs 70% less than repairing a broken swingarm)
- For buyers: ASTM D2000 standard is the central basis for judging rubber quality
Next time you get into your car, keep an eye out: that rubber ring hidden in the shadow of the chassis is making sure your ride is smooth and quiet with tiny deformations hundreds of times per second.
About Vista Motion
Give us your rubber vibration damping project and you will surely get a satisfactory answer. We will complete the requirement analysis in 72 hours, material selection → mold development → prototype trial production will not exceed 30 days. We have a team of experienced engineers and have successfully passed many certifications such as IAFT16949, ISO3834, ISO14001, ISO9001 and ISO45001.
We can also provide you with free vibration spectrum diagnostics → structural optimization recommendations → whole life costing three levels of value-added services for your project to save more costs.
