A moving carriage slams into its end stop, shaking the frame and loosening bolts. The hard stop was supposed to catch it, but the impact energy was never calculated. Hard stops wear and fatigue. Shock absorbers convert kinetic energy into heat and bring a load to a controlled stop. They are sized by energy, not by stroke.
What a shock absorber does
A hydraulic shock absorber, or industrial damper, decelerates a moving mass by forcing oil through an orifice as the piston enters. It turns impact energy into heat and dissipates it. Unlike a rubber bumper, which stores energy and rebounds, a shock absorber absorbs it. This gives smooth, repeatable stops and protects the machine and product.
Size by energy per cycle
The rating of a shock absorber is in joules per cycle and joules per hour, not stroke. Calculate the kinetic energy of the moving mass at impact speed, plus any driving force or gravity assist. Choose a damper rated above that energy per cycle, and also above the total energy absorbed per hour for continuous cycles. Undersize it and it bottoms out or overheats; oversize it and it is stiff and expensive.
Mass, speed, and driving force
Energy depends on mass and the square of velocity. A small load at high speed can carry more energy than a heavy load slowly. If the cylinder or motor keeps pushing during deceleration, that driving force adds energy over the stroke. Include both. A load driven by air or hydraulics into the stop needs the driving force times the stroke added to the kinetic energy.
Stroke and deceleration force
The deceleration force is the energy divided by the stroke. A shorter stroke means higher peak force on the machine. Choose a stroke long enough to keep the deceleration within the machine’s structural limits. A damper that stops a fast load in 10 mm puts huge force on the frame; a longer stroke spreads it. The available mounting distance often sets the stroke.
Adjustable vs non-adjustable
Adjustable shock absorbers have a setting screw to match the load. Set them so the stop is smooth but not too soft: the load reaches the end of stroke gently, without rebound or bottoming. Non-adjustable, or self-compensating, dampers are tuned for a range of loads and are used where the cycle is consistent. Start adjustment nearly open and tighten until the stop feels right.
Multiple stops and mounting
Mount the shock absorber squarely to the impact surface. Side load or misalignment damages the seal and rod. Use a plunger button or a mounting bracket that takes the impact axially. Don’t let the carriage hit the side of the rod. For high-energy applications, one or more dampers share the load; size them for the total energy they share.
Heat and cycling rate
Continuous high-cycle damping heats the oil. The per-hour energy rating matters for indexing machines that stop many times a minute. A damper rated for the per-cycle energy but not the hourly energy overheats and fails. For high-frequency work, choose a model with a higher thermal rating or add cooling.
When a damper still bottom out
If the shock absorber bottoms out with a bang, it is undersized, the setting is too soft, or the impact speed is higher than calculated. Recheck the actual speed and driving force. A damper that was fine when the line was light may bottom out after a heavier product was introduced. Recalculate, don’t just tighten the screw.
A worked energy calculation
Take a 100 kg carriage moving at 1.5 m/s. Its kinetic energy is half mass times velocity squared, about 112 J. A cylinder pushing during the stop adds its force times the damper stroke. If the cylinder pushes 500 N over a 50 mm stroke, that adds 25 J. Total energy per stop is roughly 137 J. A damper rated for 200 J per cycle and a suitable hourly rating handles it. Choosing a small bumper rated for 20 J would bottom out every cycle. The calculation tells you which size to buy.
Vertical loads and gravity
A load descending vertically gains energy from gravity along the stop distance. Add the weight times the vertical stopping distance to the energy. A lifting platform or a descend-to-stop application is heavier than it looks at first. Don’t size horizontal energy only; include gravity assist.
Rotating masses and moment of inertia
A rotating arm or drum stopping at a crank creates energy from rotational inertia. Convert the rotational energy using the equivalent mass at the contact point, or use the damper manufacturer’s moment-of-inertia method. A fast-rotating arm can carry surprising energy. Don’t treat it as a light contact.
Rubber bumpers as backup
A hard stop or rubber bumper often remains as backup behind the shock absorber, in case the damper fails or is misadjusted. The rubber takes over in an emergency, but the damper handles normal stopping. Don’t size the damper to share energy permanently with the rubber; the rubber will degrade.
Adjustment procedure
Start with the adjustment screw fully open. Cycle the machine and tighten in small increments until the stop is smooth and the load reaches the end without rebound or a hard bottom. Test at the actual product weight and speed. A damper set for an empty line may be too stiff when loaded. Record the screw position. After setting, check the damper temperature after an hour; if it is too hot to touch, the cycling energy is too high.
Maintenance and wear
Shock absorbers are sealed and generally maintenance-free, but they wear. A damper that leaks oil, bottoms out, or rebounds needs replacement. Inspect the rod for scoring and the mounting for looseness. Keep the rod clean; debris damages the seal. A failed damper means the next impact goes to the frame, so replace it when symptoms appear rather than waiting for a crash.
Common mistakes
Sizing by stroke instead of energy, ignoring driving force and gravity, undersizing for hourly cycling, side-loading the rod, and running on a misadjusted screw are the recurring errors. A shock absorber is an energy-dissipating device. Calculate the energy, choose the rating, and adjust for the real load. The machine will stop quietly and last longer.
Choosing between one large and multiple small dampers
A wide carriage may need two or four dampers across its width rather than one large central unit. Multiple smaller dampers distribute the stopping force and prevent twisting. If they share the load, size each for its share of the total energy, and make sure they engage at the same time. A single damper on a long carriage can twist the frame. For long, light loads, use two matched units.
Environmental and mounting notes
Shock absorbers work over a temperature range; extreme heat or cold changes the oil viscosity and damping. Washdown or dirty areas need sealed or corrosion-resistant models. Keep the rod protected from weld spatter and impact. Mount them so the moving part contacts the center of the plunger, not the edge. A side-loaded rod leaks within months even if the energy rating is correct.
Verifying the stop on the machine
After installation, run the machine at production speed and feel the stop. It should be smooth, without a sudden catch or a rebound. Listen for a hard bottom. Measure the damper body temperature after an hour of cycling; if it is hot, the hourly energy is too high. Adjust the screw in small steps and retest. If the carriage still shakes, recheck the actual speed and mass, because the calculated energy was probably underestimated. Record the setting and the stop feel in the commissioning report, so maintenance can restore it after a damper change.
A well-set shock absorber is almost silent: the carriage just comes to rest. If the stop is loud or rattling, the damper is not doing its job. Check the actual cycle speed again, because lines often run faster than the design assumed. Up-sizing once is cheaper than replacing a cracked frame.
A well-set shock absorber is almost silent: the carriage just comes to rest. If the stop is loud or rattling, the damper is not doing its job. Check the actual cycle speed again, because lines often run faster than design assumed. Up-sizing once is cheaper than replacing a cracked frame later.
A well-set shock absorber is almost silent. If the stop rattles, the damper is undersized. Check actual cycle speed. Up-sizing once is cheaper than replacing a cracked frame later.
A well-set shock absorber is almost silent. If the stop rattles, the damper is undersized. Check actual cycle speed. Up-sizing is cheaper than a cracked frame.
Bottom line
Size hydraulic shock absorbers by energy per cycle and per hour, including mass, impact speed, and driving force. Choose a stroke that keeps deceleration within the frame, mount them squarely, and adjust for a smooth stop. Hard stops and rubber bumpers are for light loads; real stopping needs a properly sized damper. If the machine shakes on every stop, calculate the energy before replacing the stop again.
