Cylinders allow hydraulic systems to apply linear motion and drive without mechanical gears or levers by transferring the pressure from fluid through a piston to the point of operation.
Hydraulic cylinders are at work in both industrial applications (hydraulic presses, cranes, forges, packing machines), and cellular applications (agricultural machines, construction equipment, marine equipment). And, when compared with pneumatic, mechanical or electric systems, hydraulics can be simpler, more durable, and provide greater power. For instance, a hydraulic pump provides about ten times the power density of a power motor of comparable size. Hydraulic cylinders are also obtainable in an impressive array of scales to meet a wide selection of application needs.
Selecting the right cylinder meant for an application is crucial to attaining maximum overall performance and reliability. Which means considering several parameters. Fortunately, an assortment of cylinder types, installation techniques and “guidelines” are available to help.
The three most common cylinder configurations are tie-rod, hydraulic cylinder welded and ram styles. Tie-rod cylinders make use of high-strength threaded steel tie-rods, typically externally of the cylinder casing, to provide additional stability. Welded cylinders feature a heavy-duty welded cylinder casing with a barrel welded directly to the end caps, and require no tie rods. Ram cylinders are simply what they audio like-the cylinder pushes straight ahead using high pressure. Ram cylinders are used in heavy-duty applications and more often than not push loads rather than pull.
For all sorts of cylinders, the crucial measurements include stroke, bore diameter and rod diameter. Stroke lengths vary from less than an inch to several feet or more. Bore diameters can range from an in . up to a lot more than 24 in., and piston rod diameters range from 0.5 in. to more than 20 in. In practice, however, the decision of stroke, bore and rod dimensions may be tied to environmental or design conditions. For example, space could be too limited for the ideal stroke size. For tie-rod cylinders, raising how big is the bore also means increasing the number of tie rods needed to retain stability. Increasing the diameter of the bore or piston rod is certainly an ideal way to compensate for higher loads, but space considerations may not allow this, in which particular case multiple cylinders could be required.
Cylinder mounting methods
Mounting methods also play an important role in cylinder performance. Generally, set mounts on the centerline of the cylinder are best for straight line force transfer and avoiding put on. Common types of installation include:
Flange mounts-Very strong and rigid, but have little tolerance for misalignment. Experts recommend cap end mounts for thrust loads and rod end mounts where major loading puts the piston rod in pressure.
Side-mounted cylinders-Easy to install and service, but the mounts create a turning moment as the cylinder applies force to lots, increasing wear and tear. In order to avoid this, specify a stroke at least provided that the bore size for part mount cylinders (large loading tends to make short stroke, huge bore cylinders unstable). Side mounts need to be well aligned and the load supported and guided.
Centerline lug mounts -Absorb forces on the centerline, but require dowel pins to secure the lugs to prevent movement at higher pressures or under shock conditions.
Pivot mounts -Absorb force on the cylinder centerline and let the cylinder alter alignment in one plane. Common types consist of clevises, trunnion mounts and spherical bearings. Because these mounts enable a cylinder to pivot, they must be used in combination with rod-end attachments that also pivot. Clevis mounts can be used in any orientation and are generally recommended for brief strokes and little- to medium-bore cylinders.
Operating conditions-Cylinders must match a particular application in terms of the quantity of pressure (psi), push exerted, space requirements imposed by machine design, etc. But knowing the operating requirements is half the task. Cylinders must also withstand high temperature ranges, humidity and actually salt water for marine hydraulic systems. Wherever temps typically rise to more than 300° F, standard Buna-N nitrile rubber seals may fail-choose cylinders with Viton synthetic rubber seals instead. When in doubt, assume operating conditions could be more rugged than they appear at first glance.
Fluid type-Most hydraulics use a type of mineral oil, but applications involving synthetic fluids, such as phosphate esters, require Viton seals. Once more, Buna-N seals may not be adequate to take care of synthetic liquid hydraulics. Polyurethane can be incompatible with high water-based fluids such as for example water glycol.
Seals -This is just about the most vulnerable aspect of a hydraulic program. Proper seals can decrease friction and put on, lengthening service life, while the wrong type of seal can result in downtime and maintenance headaches.
Cylinder materials -The kind of metal used for cylinder head, base and bearing can make a significant difference. Most cylinders use SAE 660 bronze for rod bearings and medium-grade carbon steel for heads and bases, which is sufficient for some applications. But stronger materials, such as 65-45-12 ductile iron for rod bearings, can offer a big performance advantage for tough industrial tasks. The type of piston rod materials can be important in wet or high-humidity environments (electronic.g., marine hydraulics) where17-4PH stainless steel may be more durable than the regular case-hardened carbon metal with chrome plating used for most piston rods.