It‍‌‍‍‌ may happen that you want to make sure that some parts of the system have the correct behavior in terms of absorbing energy and that these parts also are designed with mounting details that result in a good rubber buffer.

In general a rubber buffer is at a machine where it is needed for cushioning after it reaches full travel, in these cases a small rubber buffer is used because it is working under a limited space and time condition. Besides, it needs to decelerate the moving mass, limit the maximum force applied and still be able to withstand for the repetitive usage. Hence, the static load capacity itself is not the right job descriptor for such a rubber.

Molded rubber buffers provide protection for machine stops, material-handling equipment, doors, carts, moving assemblies, etc. The behavior of rubber buffers depends on the energy of the impact, velocity, temperature, the shape and the way parts are assembled. An item selected merely by outside diameter can be either too hard or can get easily ‍‌‍‍‌crushed.

Begin‍‌‍‍‌ With Energy Rather Than Weight

When dealing with forces at the point of collision, a mass of the carriage not only represents the main source of impact but also carries energy which can be only partly absorbed by a limited distance, and which the stop will then have to cope with, as it was the case in this example.

An industrial shock absorber must allow for the maximum compression stroke to be precisely defined. In case the absorber is pushed until solid compression, this may result in force spike, and thus impact being transmitted to the frame or the fastener. On the other hand, when the shock absorber is too soft, the moving part may continue beyond the safe limits.

Event frequency is another very important factor. Monthly emergency situations allow plenty of time for equipment to cool down and for the parts to be recovered. However, the repeated impacts that occur every few seconds can lead to a close spaced heating of the rubber and a change in its stiffness, which will affect the subsequent contact.

Shape Determines the Force Curve

Depending on the way the shock absorber is shaped, it will show different deformation curves. One shape of the contact area might cause a gradual increase of the force. A void or a tapered wall, for instance, could extend the travel of the shock absorber but at the same time strain might be focused on the corners or thin parts of the shock absorber.

Rubber buffer design should take into consideration lateral movement and misalignment.

Offcenter collision can bend the mounting stud or shear the rubber without compressing it. A broad contact face and a moving guided member will help maintain the load path.

The production of custom rubber bump stops may involve adding a bonded metal strip, inserting metal elements or drilling through the block. While these techniques ease the installation of the bump stop, they may lead to the development of bond-line, corrosion, stress-concentration areas.

Consideration of the maximum deflection should be given to the geometry of the metal during the design.

Dynamic Stiffness Does Not Equal Static Stiffness

The response of rubber is generally more rigid or rigid during rapid deformation than its deformation under slow compression. Hysteresis, which is the energy loss, is partly transformed into heat. In fact, the same mechanism which is useful to diminish rebound also raises internal temperatures during repetitive impact situations.

Trelleborg calls the ANB buffer it produces a bonded, cylindrical, nitrile rubber body which it says high-hysteresis compound helps to limit equipment movement. The published range specifies various maximum loads based on size and also highlights cranes, forestry vehicles and material-handling equipment as typical applications.

In that example of the catalog, we see that a buffer's rating is only given after considering its structural construction. It is not able to support a different compound or geometry under the same load.

You should perform tests on rubber impact buffers using conditions that are consistent with the speed, energy and mounting of the application intended for the buffer (the final use).

Selecting the Material is about Having Enough Energy and Recovery

Some of the mechanical applications can be made more durable and resistant against wear with the right kind of rubber, i.e., natural rubber.

You can choose nitrile butadiene rubber NBR when mineral oil is involved because it is less affected by it whereas weather and sun exposure will not affect ethylene-propylene rubber EPDM much. Abrasive materials will wear down polyurethane quickly but if the loading needs are met then it can last longer.

All those options have a range of temperatures and chemicals where they can be applied. You need to find that out for each one.

Hardness is only one property of the material you use.

Other factors like hysteresis, modulus, compression set, resistance against tears, and resistance against aging due to the effect of heat will determine the shape, or the curve, that force follows and how much that force is going to recover back.

Two products of rubber with an identical shore A rating may show different behavior under impact.

Designing a rubber buffer needs knowing the service temperature that will be the lowest. A compound that gets hard when it is very cold may transmit higher peak force.

On the contrary, low tensile strength together with cumulative heat generation caused by low shear resistance at high temperature, could be responsible of deformation that goes beyond ‍‌‍‍‌limits.

Common Tests Answer Limited Questions

ASTM D575 measures compressive behavior under specified test conditions. It can compare compounds or provide a controlled load-deflection reference. A standard specimen does not reproduce the buffer's changing contact area, insert or impact rate.

ASTM D395 evaluates compression set after a defined compression and recovery period. It helps compare recovery tendency, but it does not predict the complete return of a shaped buffer after thousands of high-speed impacts.

ASTM D624 measures tear strength under a defined specimen geometry. It can support compound screening where cracks are a risk. The standard itself cautions that the result may not relate directly to service performance.

A Finished Buffer Validation Sequence

Inspect dimensions, molded surface and insert location. Measure the initial force-deflection curve slowly to establish the part condition. Check that the buffer has clearance to deform without contacting sharp edges or trapping material against the frame.

Run impact tests with the representative moving mass, velocity and alignment. Measure deflection, rebound and peak force where the equipment risk requires it. Start below the maximum event and increase through a controlled test plan with suitable guarding.

For industrial shock absorption, cycle the part at the expected event frequency and temperature. Monitor surface temperature and permanent height change. Repeat the impact measurement after conditioning so drift in the force curve is visible.

Inspect the rubber-to-metal bond, fold or bulge zones, contact face and fastener after cycling. Cracks, loosened inserts or permanent lean can indicate an off-axis load. Acceptance criteria should include both equipment clearance and buffer condition.

Information Needed for Development

Provide moving mass, impact speed, drop height where applicable, maximum available deflection and event frequency. Add temperature, oils, weather, allowable peak force, mounting space and the consequence of a failed stop.

For custom rubber bump stops, include the contact angle, fastener details and any lateral movement. Photographs or a section of the assembly can reveal interference and load-path issues that a buffer drawing alone does not show.

Working With Yida

Dalian Yida Precision Rubber Products Co., Ltd. develops custom molded elastomer parts and rubber-to-metal components. For rubber impact buffers, Yida can review manufacturability, compound options, insert geometry and critical dimensions against the customer's load case.

Molded rubber buffers should be approved by testing the finished part in representative hardware. When the energy, stroke and event frequency are defined, the sample plan can measure what the equipment actually needs rather than relying on a generic hardness value.