Air cylinders are pneumatic actuators that use compressed air to create a force in a linear direction. They come in a variety of styles, sizes, and configurations to suit a wide range of industrial automation applications. While air cylinders may seem simple on the surface, there are some nuances to their design and operation that are easy to overlook if you’re not familiar with them. In this article, we’ll highlight 8 key aspects of air cylinder functionality that people often don’t fully consider. Being aware of these details will help ensure you select, install and maintain air cylinders properly for optimal performance.
Air Cylinder Mounting Orientation Matters
One of the first decisions to make when implementing air cylinders is how to orient them. Air cylinders can be mounted in vertical, horizontal or angled orientations. The orientation impacts how forces are transmitted through the cylinder and its mountings. It also affects how the piston seals wear over time.
Generally, vertical mounting is optimal to take advantage of gravity’s assistance with piston return on single-acting cylinders. Horizontal mounting often works too but side loads on the piston rod will accelerate seal wear. Angled mounting between 15-45 degrees from horizontal or vertical is usually acceptable. However, the cylinder may need reinforced mounting to handle increased torque from side loads.
Considering the orientation early in the design process enables optimizing the cylinder mounting and support to minimize stress while maximizing seal life. This prevents premature failures or replacement costs down the road.
Strokes Lengths Should Align with Requirements
Air cylinders are available with stroke lengths ranging from less than an inch up to several feet. The stroke controls the linear travel distance of the rod and piston during extension. Matching the stroke length to the application requirements helps optimize performance.
For example, having an oversized stroke length adds unnecessary weight on the rod that can reduce acceleration under load. It also allows the piston to impact the cylinder ends, causing wear or damage over time. Conversely, an undersized stroke may not provide the full travel distance needed, limiting functionality.
Take time upfront to analyze the stroke length needed for the longest required movement, with a little extra clearance. This ensures smooth movement through the full range without bottoming out at the cylinder ends. Buying the right stroke length avoids wasted capacity or functionality issues.
Bore Diameters Affect Output Force
The bore represents the interior diameter of the cylinder tube. Along with pressure, it determines the potential output force from the cylinder. Larger bore sizes have greater output force capabilities. However, they also require more input air volume to drive the piston.
Make sure to match the bore diameter to the force requirements of the application. Oversizing adds unnecessary weight and air consumption. Undersizing results in inadequate force capacity.
Analyze the maximum load requirements and use that to determine the target bore size range. Also factor in the air supply capacity when choosing bore diameter, as larger bores need more airflow. Getting the bore size right optimizes the force output for the application without overdoing it.
Rod Diameters Should Align with Load Capacity
In addition to bore size, the piston rod diameter also affects a cylinder’s load capacity. Rods come in different diameters to suit various load requirements. Smaller diameters around 0.5″ can handle several hundred pounds of force. Large diameters around 2″ or more can handle tens of thousands of pounds.
Make sure to match the rod diameter to the expected side load requirements. Too small of a rod risks bending, buckling or breakage under peak loads. Too large wastes money and adds unnecessary weight. Get the rod spec’d correctly by analyzing maximum side load needs including a safety factor. This balances strength with weight and cost.
Cushioning Controls Shock at Stroke Ends
Rapid deceleration of a air cylinder piston at the end of a stroke can cause damaging shock loads on the cylinder and mounting equipment. Cushioning is used to gradually slow down the piston as it approaches the end of its travel.
There are several types of cushioning available:\n\n- Air cushions use compressed air resistance to slow the piston.
- Mechanical cushions use spring or elastomeric bumpers.
- Adjustable air cushions allow tuning the deceleration rate.
Consider adding cushioning on both the extend and retract strokes if the application involves rapid cycling or moving large inertia loads. Properly tuned cushioning protects equipment while reducing noise and vibration. Make sure cushions are sized appropriately for the payload weight and speeds involved.
Speed Control Options for Precise Movement
The piston velocity in an air cylinder depends on the operating pressure and supply flow rate. Certain applications require slowing down the cylinder’s motion for improved control, precision or safety. Adding speed control enables tuning the velocity.
Options for controlling cylinder speed include:
- Flow control valves restrict air supply flow to reduce speed.
- Needle valves fine tune the air exhaust flow to provide resistance.
- Dashpots use hydraulic fluid resistance to slow cylinders.
- Servo valves enable precise speed regulation with electronics.
Consider required move profiles and cycle times when deciding if speed control is beneficial. The right method can enable better process control and repeatability.\n\n## Mounting Hardware Matters
The air cylinder mounting attachments transmit side loads into the machine structure. Proper mounting is critical to avoid stress concentration issues over time.
Follow best practices on orientation and hardware selection:
- Use recommended bolt sizes and tightening torques.
- Allow room for rotation on single-mount clevises.
- Align trunnions properly with bearing mounts.
- Use sleeve bushings to handle eccentric loads.
Taking time to optimize mounting linkage protects the cylinder while transferring forces efficiently into the base structure. It also reduces vibration and wear for more consistent performance.
Maintenance Is Key for Long Seal Life
Air cylinder seals wear over time with use due to friction and exposure to particulates. Good maintenance practices extend seal life for reduced operating costs. Follow guidelines such as:
- Use clean, dry air supplies to avoid contamination.
- Implement inlet air filtering to trap particulates.
- Follow proper lubrication procedures to condition seals.
- Clean surfaces and seals during rebuild or replacement.
With routine inspection and maintenance, air cylinder seals can often last for millions of duty cycles. Taking care of cylinders prevents premature leaks or failures.
Conclusion
To summarize, optimizing air cylinder performance requires paying attention to details like orientation, stroke length, bore size, cushioning, and hardware selection. Following best practices for sizing, installation and maintenance enables getting the most value and productivity out of air cylinders. Keeping these easily overlooked design factors in mind allows air cylinders to operate reliably at their full capabilities for years to come. Let us know if you have any other insights into critical considerations for air cylinders.