By Kyle Lewis
Hydraulic cylinders are commonly utilized to withstand high loads in demanding operations systems and are often relied upon for a few years at a time. That being said, when improperly implemented and utilized, these cylinders can deteriorate quickly, leading to mechanical issues, such as side loading and rod bending as a result.
Cylinders, in their basic form, are designed to move a load with linear force and motion. When operating at its optimal performance, the compression and tension forces perfectly align in the rod’s direction. With this in mind, side loading will occur as a result of a mass pushing the rod to the side, or up and down.
This bending occurs due to a reduced capacity for the piston. When functioning properly, a retracting cylinder has high resistance to aside load due to low bending forces and a rod supported by bushing in the head and piston. However, as this cylinder extends, the piston will move closer to the head, causing the capacity of the piston to act as a bearing, leading to bending. So, as a rule of thumb, the longer the cylinder stroke and the further the rod must go, the higher the chance of side loading and column bending.
With all this in mind, when a rod is out of alignment, fixed cylinder mountings will no longer function as they should, and side load is likely the culprit for this failure. For this reason, avoiding a hydraulic cylinder side load is essential not only to a well-running machine but to avoiding fluid leaks and seal failure, too.
But how can we avoid this misalignment and repair of Hydraulic cylinders requirement? We are breaking down 4 steps to assist and avoid this unnecessary system damage.
Hydraulic cylinder mountings are essential to holding your cylinder in position and preventing shock. As a result, choosing the right mount out of all the hydraulic cylinder mounting options is essential to your performance and reducing the chance of misalignment.
The types of cylinder mountings vary based on needs and strength requirements, with different strokes and designs to suit different use cases. For instance, heavy-duty applications with long strokes require higher mount strengths, while clevis brackets require more space to operate.
To help you choose the best mounting to keep your system aligned, here are a few of the most popular cylinder mounting types.
There are a few options of flange mounts available, including both rod-end rectangular flanges and cap-end mountings. These mounts have a circular, rectangular, or square design with a flat finish that won’t require joints or bearings to mount. With this design, flange mounts are built to be incredibly strong and rigid, and are best used for stationary hydraulic cylinders. In addition, flange mounts are ideal when the mount face is attached to a machine support member, and can handle full-rated pressure.
Keep in mind that while flange mounts are strong, they do not do well with misalignment, and can quickly break down as a result.
Another hydraulic cylinder mounting type is the clevis mount. These mounts are pivot mounts and are designed to allow the cylinder too, as the name suggests, “pivot” in a single range of motion.
This style of mount is ideal for numerous applications, specifically when the cylinder is required to pivot during extension and retraction. Ideal for mobile equipment, this is a common mounting type that is fixed to the end of the cylinder rod, and inserted into the clevis to be held in place.
Typically, a clevis mount is best used for short-stroke and small to medium-bore cylinders. While they do pivot, they only allow for one range of motion and are susceptible to side loading.
Trunnion mounts are another form of pivot mount, often positioned at the head, cap, or intermediate position of the hydraulic cylinder. With a trunnion mount, you can get more strength and stability than the clevis mount counterpart and can be attached with bearings as opposed to pins.
Typically, trunnion pins are designed for shear loads only, and should not be put under bending stress. To avoid this, pillow blocks can help to avoid damage.
The intermediate fixed-trunnion mount is typically considered the best of this type and is used to balance the weight of the cylinder or between the head and cap.
A fixed-style mounting, lug mounts are characterized by rectangular tabs designed from, or welded to, the head and cap of the cylinder. This type of mount is best touted for its rigidity and strength but does have an intolerance to misalignment like other fixed mount styles.
Specifically, side lug mounts will encounter the most issues with misalignment. These mounts are implemented on one side of the machine and will require reinforcements to protect from beginning with heavy loads or high-shock situations.
Pivot mounts, which include clevis and trunnion mounts, are ideal for use when loads travel on an arc, and allow for movement while absorbing the force for a well-running system.
A pivot mount is great for absorbing force in their centerlines and thus is used in some dynamic machines with curved paths. Both the clevis and trunnion designs can be used on tension or thrust applications when a full-rated pressure is used, but are not suited for long-stroke applications.
In the case of longer-stroke thrust applications, an oversized piston rod must be used to prevent buckling using a hydraulic cylinder stop tube.
A side-mount hydraulic cylinder is designed to absorb force away from the cylinder. This type of mount is available in some staples, including side lug, end lug, and side tapped options. With this design, cylinders are mounted on one side of the head and cap and do not go through the cylinder centerline.
As a result of this application, side mounts create a turning moment when the cylinder applies force. However, if it is not well-secured, the turning motion will side-load the gland and piston. To avoid this, it’s essential that a stroke length equal to at least 1.5 times the bore diameter is chosen.
Typically, the best way to support a cylinder is along the centerline with centerline mounts. This fixed mount style helps absorb force along the centerline. This type of mount includes extended rod ties, centerline lug, and flange mounts.
Extended tie-rod mounts are symmetrical, so thrust and tension forces on the piston rod are uniformly distributed. With this in mind, the mounting style can handle full-rated pressure, making it one of the most ideal mounting options.
Centerline lug mounts, on the other hand, are another type of fixed mount with lugs holding the cylinder in place. Friction between the lug underside and surface prevents the cylinder from moving laterally.
After implementing the correct cylinder mount for your needs, you should calculate the load capacity. Keep in mind that load affects every component of your hydraulic cylinder, and your bearings, couplings, and all other components must have the right load capacity to maintain proper alignment. Components made with high-strength materials will have better durability, and so will better quality ones. Be sure to use components that are held to the same standards as the cylinder itself for proper load capacity.
Next on the checklist is the rod size. By choosing the right rod size for your system, you can enhance your system's resistance to bending, sagging, and buckling, as well as reduce the chance of side loading.
The final factor to prevent side loading is to utilize a hydraulic cylinder stop tube to provide additional support for extended piston rods, while simultaneously increasing the bearing separation between the rod bearing and piston. With this, you can reduce the bearing stress and chance of side loading.
From a hydraulic cylinder spacer to hydraulic cylinder column load, there’s a lot to know to maintain your hydraulic cylinders and avoid side loading and other misalignment complications. However, by starting with the toper hydraulic cylinder mountings and ensuring ample load capacity, rod size, and stop tubes are in place, you can avoid complications for a well-running system.
Whether you need assistance with a misalignment or are looking for a hydraulic cylinder repair company to step in and repair your cylinder, Cylinders, Inc. has the expertise to help. For more information, contact us today.
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