Duties of Hydraulic Cylinders

Duties of Hydraulic Cylinders

Duties of Hydraulic Cylinders

These are circuit elements used to obtain linear motion in hydraulic systems. They are elements that convert hydraulic energy linearly into mechanical energy. They work by moving back and forth regularly. They transform the conventional mechanical linear movements with spline gears, connecting rods and levers into alternative linear movements with the power of pressurized fluid in hydraulic systems.

Elements of Hydraulic Cylinder

The elements of a hydraulic cylinder are:
Ø Cylinder liner
Ø Piston
Ø Piston rod
Ø Sealing elements
Ø Covers
Ø Cylinder liner:

Structure:
They are manufactured from cast steel, cast iron and alloy steel pipes, depending on the characteristics of the place where they are used. If the inner surfaces of cold-drawn pipes are ground and honed, it is possible to use them as cylinder liner. No matter what material the cylinder liners are made of, their inner surface must be well machined and honed. In order to achieve efficiency, the friction between the cylinder liner and the piston must be minimized. Otherwise, efficiency will decrease due to leaks and leaks.

Calculation of liner wall thickness in hydraulic cylinders is made according to the highest working pressure that can occur in the cylinder.
Wall thickness calculation of pipes
According to cross section
It is calculated in two ways: according to the longitudinal section.

The wall thickness calculated based on the longitudinal section is more durable than the wall thickness calculated based on the cross section. For this reason, cylinder liners made according to the wall thickness calculated according to the longitudinal section are more durable and guaranteed. When calculating the cylinder liner wall thickness, a constant number such as (C) is added to the result as the corrosion allowance for corrosion resistance.

Piston
It is a circular section element mounted on the piston rod inside the cylinder. They are generally made of aluminum alloy and brass bronze. There are also ones made of cast iron or steel. Sealing elements of various profiles and types placed around the piston enable the piston to move more easily within the cylinder.

Pistons must be resistant to the pressure that may occur within the cylinder. Thanks to the thrust force on the pistons, the piston rod moves and linear movement is achieved. The piston rod may be on one or both sides of the piston. In this case, the thrust forces change. If the piston rod is one-sided, there will be a volume difference between one side of the piston and the other in the cylinder. This affects the pressure of the compressed oil, and therefore the thrust force produced by the piston during its movement in both directions will be different.
Piston Rod
The piston rod is the cylindrical rod made of steel that is produced by the piston and transmits linear motion. The piston rod is made of alloy steel resistant to torsional forces. The outer surface of the piston rod must be machined to be ground. During the movement of the piston rod, a friction force occurs between the bearing caps and the piston rod. This reduces the efficiency of the hydraulic cylinder. The diameter and length of the piston arms are determined according to the length and diameter calculations of the machine elements that are forced to buckle. L=Piston length (cm) F=Force forcing the piston to twist (kg) EMF=Safety coefficient D=Piston rod diameter (cm) Fk=Critical force forcing the piston rod to twist (kg)

Types of Hydraulic Cylinder

single acting cylinder

double acting cylinder

special cylinder

Double arm cylinder

telescopic cylinder

tandem roller

Rotary cylinder (angular engine)

single acting cylinder

It is a type of cylinder in which the fluid affects the piston from one side. While the piston is moved in one direction by the fluid, the return occurs with the help of a spring or weight. Single acting cylinders are similar to double acting cylinders and are not used as much.

There is 1 inlet hole for fluid entry into the cylinder. A small diameter hole is used on the other side to evacuate the leaking fluid and allow air to enter and exit the cylinder.

double acting cylinder

It is a type of cylinder in which the fluid acts on the piston from both directions. The movement of the cylinder in two directions is provided by the fluid. Such cylinders can perform work both forward and reverse. Double acting cylinders are used in almost all cylinder applications. Its courses can be increased up to 5000 mm in length.

Two conditions are required for a cylinder to work. First condition; It is a force (caused by the effect of the load or fluid pressure) that pushes the piston forward or backward. The second condition is; fluid discharge. If one of these two conditions is not met, the cylinder will not move. If there is a restriction in the line entering the cylinder or leaving the cylinder and going to the tank, that is, if the fluid flow rate is low (for example, due to crushing, clogging in the pipes, etc.), the cylinder speed is observed to decrease.

Unless the piston rod is fixed somewhere, the moving parts in the cylinder are the piston and piston rod. In the following topics, it should be understood from the expressions such as the cylinder moved forward or backward that the piston and piston rod moved.

special rollers

Double-arm cylinder: Due to the piston rod, the areas and volumes in both parts of the piston are different. This situation not only affects the thrust forces of the cylinder, but also causes the forward and reverse speeds of the cylinder to be different. In some applications, it is desired that the thrust forces and cylinder speeds be the same in both directions. In such cases, cylinders with piston rods on both sides are used.

Telescopic cylinder: It is used to obtain high courses. It consists of many interlocking cylinders of different diameters. As the cylinders come out, the pistons open in turn. When closing, the rollers engage each other. Thus, it is possible to obtain a lot of courses while taking up very little space. It is used more frequently in work machines than in industrial systems.

When calculating the thrust force of these cylinders, the smallest diameter cylinder diameter is taken into account. Although they are generally made single-acting, they are also used as double-acting. Lifting the bodies of cargo trucks, etc. It is used in places.

Rotary cylinder: Rotary table, robot etc. It is used to obtain the required angular movements in places. In industrial applications, angular movements of 900 and its multiples are required. The most commonly used angular movement is 1800. Angular motor or oscillating motor for rotating cylinders

Also called engine. It is made of toothed or winged type.

Tandem cylinder: In order to significantly increase the thrust force of a cylinder in an existing hydraulic circuit, there is no other option than increasing the cylinder diameter or pressure. Increasing the pressure requires replacing the pump. Increasing the cylinder diameter creates space problems as it increases its dimensions.

A special type of roller called tandem roller is used to increase the thrust forces of the rollers. These cylinders are formed by adding more than one cylinder with equal courses end to end. Depending on the number of cylinders, the number of inputs and outputs and thrust force increases.

Fı= I. Thrust force of the cylinder (Newton) A1= Cylinder diameter (mm) P= Pressure (Bar) r 1= I. Efficiency of the cylinder F2= II. thrust force of the cylinder (Newton) A2= II. area of the cylinder (mm) P= Pressure (Bar) r|2= II. efficiency of the cylinder Depending on the thrust force of the cylinder F1, II. If we call the thrust force of the cylinder F2; The thrust force of the tandem cylinder is F total =Fi+F2. This shows that the thrust force of the cylinder has been increased significantly without changing the cylinder diameter and pressure.

Piston Push Force in Cylinders

In hydraulic cylinders, the pressurized fluid entering the piston applies force to the piston surface. This force varies depending on the size of the piston surface. As the piston cross-sectional area decreases, the resulting force decreases. Since there may be a loss of efficiency during the operation of the piston, calculations must be made accordingly. In single-arm cylinders, the cross-sectional areas of the two sides are different. The thrust force (F1) on the inlet side will be large.