SELECTION AND WORKING PRINCIPLES OF HYDRAULIC EQUIPMENT USED IN MINING MACHINES
SELECTION AND WORKING PRINCIPLES OF HYDRAULIC EQUIPMENT USED IN MINING MACHINES
SELECTION AND WORKING PRINCIPLES OF HYDRAULIC EQUIPMENT USED IN MINING MACHINES
SUMMARY
In this study, what are the hydraulic equipments that enable mining machines to do heavy work easily with great power, how these equipments are selected to direct the hydraulic fluid correctly, and safe working methods in the hydraulic system are presented.
LOGIN
Hydraulic systems are used primarily in mining machines, agricultural machinery, road cleaning vehicles, cranes, work machines, scissor lifts, presses, ships and yachts, iron and steel factories, aircraft, military vehicles and even recreational vehicles in amusement parks. For this reason, the place and importance of hydraulics in the industry is great. Hydraulic systems are known and applied in many countries of the world. Since this sector is newly developing in our country, it is important that we have information on these issues.
As with all mining machines, if there is a heavy work to be done or an application that requires great power, it is quite easy to do these operations with hydraulic systems. If the hydraulic system equipment is not selected correctly, it is inevitable that there will be problems or disruptions in the operation of the mining machine. In addition, it is inevitable that major work accidents will occur as a result of the wrong hydraulic equipment selection. Consideration should be given to product selection and cost analysis by making necessary calculations for equipment such as pumps, valves, filters, cylinders, and hydromotors used for hydraulic systems in mining machines.
2. DESCRIPTION OF HYDRAULIC
The word hydraulic is derived from the Latin word hydor, meaning water. As a hydraulic subject, it studies the behavior (applied mechanics) of fluids. Due to the fact that hydraulic systems transmit forces and movements more easily and more efficiently than friction systems, hydraulics began to be widely used in machinery manufacturing and industrial applications in the second half of the 20th century. The structure formed by the elements that operate a mechanism with the transmission of pressurized fluid power is called the hydraulic system.
The hydraulic pump in the hydraulic system absorbs the oil from the tank and directs it to the system with effective pressure. If the System Pressure is higher than the designed value, the system is secured by returning the Pressure Adjustment valve to the tank. The oil sent to the Direction control valve by the hydraulic pump is directed to the user elements (Hydraulic cylinder, Hydraulic Motor, etc.) and the user element, which moves with the hydraulic oil flow rate and pressure, operates the machine it is connected to. The speed of the machine (mechanism) can be changed by the flow adjustment of the oil passing through the flow control valve.
In order to ensure the back and forth movement of the user element, the flow and return paths of the oil are alternately changed by the directional control valve.
The main parts of the hydraulic circuit are:
1- Hydraulic Tank (Hydraulic Tank)
2- Hydraulic Pump
3- User Elements (Hydraulic Cylinder – Hydraulic Motor etc.)
4- Hydraulic Valves
5- Hydraulic Accumulators
6- Hydraulic Installation Pipe – Hydraulic Hose – Hydraulic Fittings
7- Hydraulic Sealing Elements
8- Hydraulic Filters
9- Hydraulic System Cooler
10- Accessories, Indicators
3. HYDRAULIC TANK
The task of the hydraulic oil tank provides cooling of the fluid circulating in the system. It separates the air, water and foreign materials in the hydraulic oil.
The tank is the element that houses and rests the hydraulic fluid. An irregular flow occurs as the oil drains into the tank. Intermediate curtain It eliminates the flow irregularity in the hydraulic oil. Hydraulic Oil is sucked again by the pump.
Equipment Used in Hydraulic Oil Tank
a) Steel sheet, Aluminum or plastic based Tank
b) Oil filler cap (Ventilated)
c) Oil fill Filter
d) Oil level indicators
e) Thermometer
f) Return Filter
g) Suction filter
h) Suction pipe
i) Return pipe
i) Oil drain plug
j) Intermediate curtain
k) Cleaning cover
l) Fasteners
Features of oil tank:
1. The intermediate curtain acts as a breakwater for the oil returning to the tank.
2. The slope of the base facilitates the accumulation of foreign materials. It is important for cleaning.
3. It is recommended that the ends of the pipes be 2 times their diameter above the base.
4. The inclination of the pipe ends provides ease of suction and rotation.
5.Minimum oil level should be 10 cm above the pipe end.
Oil is filled into the tank through the strainer of the filler cap. The air filter provides clean air to the tank. Level indicators show the required amount of oil. The thermometer checks the oil temperature. The plug provides convenience in oil draining. The amount of oil to be filled into the tank should be sufficient to feed the circuit. While the surface area of the tank is being designed, it should be preferred that it is in dimensions that can transfer the heat of the oil to the outside in the operating system. The transfer of excess heat from the oil in the system to the outside of the tank reduces power loss.
4. HYDRAULIC PUMP
Description and symbol of hydraulic pump:
The element that absorbs the fluid from the tank with the mechanical energy it receives from the engine and transfers it under pressure at a certain flow amount is called a hydraulic pump.
Hydraulic pumps convert the Mechanical Energy they receive into Hydraulic Energy with the pressure and flow formation of the hydraulic fluid. The pressure and flow rate of the fluid supplied by the hydraulic pump to the hydraulic circuit fed by the hydraulic pump must be of sufficient value for the needs of the user components (also considering the combined works).
Hydraulic Pump Types
Gear Pumps
Vane Pumps
Piston Pumps
Gear pumps:
Gear pumps are fixed displacement pumps and are produced in 2 different models as spur gear and helical gear.
1. Oil fills the suction cavity formed at the inlet
2. Oil is taken from the tooth cavities to the environment
3. Forced flow and pressure are created in the volumes between the pump body and the gears.
Vane Pumps:
These pumps have floating pallets around the rotor (eccentric rotating element). According to the rotation direction of the rotor, the pallets absorb the oil from the tank and transfer it to the pump outlet with flow and pressure formation.
Piston Pumps:
Pistons located around the rotating shaft in a circular way transfer a certain volume of oil to the pump outlet by suctioning from the Tank, creating flow and pressure.
Piston elements, which rotate together with the rotation of the shaft, operate in conjunction with the position of the inclined plate (Camshaft in Radial Piston pumps).
When the pistons come across the inlet channel on the distribution plate, there is a compression process when they come across the suction and the outlet channel.
Inclined Axis Piston Pumps
Inclined Disc Piston Pumps
Working principle of pumps:
Hydraulic Fluid, which is sucked by vacuum effect at the suction mouth, works with the principle of transferring the fluid with positive transmission by creating compression at the discharge port. Thus, if there is a resistance in front of the fluid transferred by the pump, pressure is created. The hydraulic pump is the power transmission source in the circuit.
The power transmitted by the pump depends on the Hydraulic Fluid Pressure and the Fluid Flow. If the cross-sectional area A, flow rate v, through which the fluid passes, is the flow rate (the amount of fluid flowing per unit time),
Q = A . It is calculated with the formula v .
In order for the pump to create pressure in the fluid transfer, the flow cross section
F = p. A force must be applied.
If the fluid reaches the velocity v with the force applied by the pump effect, the generated transmission power is
It will be P = F.v = p.A.v.
Q = A . v. 3 / 50
The transmission power of the pump is calculated from the formula.
Working conditions and pump:
Pump selections should be made in accordance with the work that will be needed in the hydraulic circuits and the power transmission needs. In case of using more than 1 pump in a hydraulic system, the pumps are designed to work in a certain order. Fluid flow rate for speed requirement and pressure values for force requirement should be calculated.
Features to consider when choosing a Hydraulic Pump:
1. Fluid properties
2. Working pressure range
3. Flow requirement
4. Number of revolutions
5. Operating temperature range
6. How to drive the pump
6. Ease of maintenance
7. Service life
8. Dimensions and assembly
9. Cost elements
10. Advantages and disadvantages
11. Number of flow directions
5. HYDRAULIC CYLINDERS
Hydraulic energy is converted into linear motion (mechanical energy) with the help of a cylinder.
SINGLE-ACTING CYLINDERS
It is the type of cylinder in which the hydraulic fluid is acted on the piston from one direction. The return of the piston to its back position is provided by external forces (spring, weight, etc.).
DOUBLE-ACTING CYLINDERS
It is a type of cylinder in which the hydraulic fluid is acted on the piston from both directions. The forward and backward movement of the piston is provided by the pressure fluid effect. It is the most commonly used cylinder type, as work is generally required in both directions in applications.
TELESCOPIC CYLINDERS
It is used where high stroke is required. The most important reason for preference is that they do not take up much space. It consists of intertwined pistons of different diameters. It is usually done in a single action. It is frequently used in construction machines and tipper vehicles.
CUSHIONED CYLINDERS
Especially in cases where the piston speed exceeds 6m/min and when moving heavy objects, a blow occurs at the end of the piston stroke. These pulses reduce the operating life of the circuit elements. It can also cause the work done to be unorganized. Therefore, impact is an absolutely undesirable feature in hydraulic systems. In such cases, cylinders are used to prevent strokes by slowing down the piston speed at the end of the stroke. These types of cylinders are called padded cylinders. Cushioning process; It is provided with a cushioning bush and a cushioning journal with a tapered end. At the end of the course, the section through which the fluid passes is narrowed and the velocity is reduced. Padded rollers can be single-sided or double-sided padded.
Hydraulic Cylinder Assembly
Hydraulic Cylinder Force Calculation
6. HYDRAULIC ENGINES
The hydraulic motor is a circuit element that produces circular motion with hydraulic energy. They are the hydraulic elements that take the hydraulic energy transferred by the hydraulic pump and transform it into work.
1) Gear Motors
2) Piston Engines
Advantages of Hydraulic Motors
Speed can be adjusted without stopping the engine.
The speed setting range is unlimited between certain values.
Great forces are transmitted.
Since hydraulic fluids cannot be compressed, uniform velocities can be achieved.
The direction of rotation can be changed while the movement is in progress.
Can be stopped at overloads using the safety valve
DISADVANTAGES OF HYDRAULIC ENGINES
Since hydraulic fluids have high frictional resistance, their rotational speed is low. Their prices can be expensive. They can be large in size. It is not recommended for use at high temperatures.
It is very sensitive to pollution.
7. HYDRAULIC VALVES
Valve:
It is the circuit element that determines the direction of the hydraulic fluid, changes its direction when desired, and controls the pressure and flow of the fluid.
Duties of Hydraulic Valves
It opens and closes the path of the fluid.
It changes the direction the fluid will go.
It sends the fluid to the tank.
It adjusts the operating speed of the receivers by controlling the flow rate of the fluid.
It protects circuit elements against high pressures. It sends the fluid whose pressure rises to the tank.
By controlling the pressure of the fluid, it ensures that the circuit elements operate at certain pressures.
It controls the pressure, flow and direction of the fluid at certain time intervals.
Some valves can perform one or more of the tasks listed above.
PRESSURE CONTROL VALVES
These are the valves used in the pressure lines of hydraulic systems, ensuring that the pressure of the fluid is at the desired value.
Types According to the Places Used;
Pressure Relief valves
It allows the formation of enough pressure to overcome the resistance that occurs for the work to happen, In the resistance that may occur above it ( = end of stroke),
imposes a limit on pressure.
pressure reducing valves
It may be necessary to use more than one user element (cylinder, hydromotor) in hydraulic circuits, which are required to be operated at different pressures, and the user elements may need to work at different pressures. In such cases, pressure reducing valves are used. It is normally open. When the pressure rises, it switches to closed position. There are different types, including two-way and three-way.
pressure sequence valves
Pressure sequence valves are used to operate multiple user elements such as cylinders and motors at different times and pressures in a hydraulic circuit. Its working principle is similar to Pressure safety valves. It is normally closed. It opens at the desired pressure and activates other user elements.
unloading valves
It is used to send the hydraulic fluid to the Hydraulic Tank. The normally closed valve opens when the warning comes and sends the fluid to the tank.
DIRECTIONAL CONTROL VALVES
It is the valves that determine when and which path the fluid should follow in hydraulic circuits. They change the flow path at will; They open and close the flow path when desired.
SCHEMATIC DESCRIPTION OF DIRECTIONAL CONTROL VALVES
Each position of the valve should be indicated by a square.
The flow directions of the fluid are indicated by arrows.
Closed roads are marked with a horizontal line.
Valve connections are indicated by dashes.
Marking of valve positions; valve positions are marked with letters from left to right. For three-position valves, the center position is indicated by 0.
Lettering of valve connections;
P=Pressure line A,B,C....=Work line or work line
R,S,T=Warehouse(return) line
X,Y,Z=Pilot(warning) line
L=Leakage line
Identification of directional control valves;
2 / 2 = Number of paths/ Number of locations
When 3 /2 valve is defined, it is understood that the valve is 3-way, 2-position.
Normal positions of the valves;
In hydraulic circuit drawings, valves are drawn and lettered in their normal position.
FLOW CONTROL VALVES
These are the valves used to adjust the fluid flow rate in hydraulic systems. By changing the amount of flow, we can adjust the speed of the cylinders, the number of revolutions of the motors. Flow control valves Cause significant pressure drop; therefore, large amounts of heat are also released. The flow rate is adjusted by changing the flow section with the help of the adjustment screw.
HYDRAULIC ACCUMULATORS
It is the circuit element that stores the pressurized hydraulic fluid to give it to the system when necessary. When there is a pressure drop in the hydraulic system or there is a need for flow, the pressurized oil in the accumulator is higher than the operating pressure for a short time
becomes high. In this case, the nitrogen gas compressed by the hydraulic fluid expands. The accumulator sends the required amount of fluid to the system and ensures that the oil is lost in the system. If there is a shock pulse in the system during operation,
Some of the fluid, whose pressure has increased, enters the accumulator and acts as damping, preventing the system from being damaged by compressing the nitrogen gas. Accumulators are made of high pressure resistant steel tubes.
Hydraulic accumulators prevent impacts and shocks in hydraulic systems and compensate for leaks in the system. It provides backup power to stop the system at the desired location in case of pump failure or power cut.
9. FITTINGS USED IN HYDRAULIC SYSTEMS
It is used in the transfer of fluid in hydraulic systems, in the process of sending the fluid from the tank to the user elements and in the process of sending the finished fluid to the reservoir in the user elements. The circuit elements that connect the elements used in the Pump, Valve, Engine, Hydraulic Cylinder and Hydraulic system are called connectors.
Fasteners are the name given to elements such as pipes, hoses, unions, clamps.
The selection of fittings should be determined to provide the required pressure, flow and flow rate, and should be in a structure to withstand the working pressure.
Hydraulic Pipes
It is the circuit element that carries the fluid between certain points in the system and guides the fluid. Pipes are made of stainless steel and light metals, either by cold drawing or welded. Welded pipes are not resistant to high pressures. One of the two important factors in pipe selection in hydraulic circuits is the desired inner diameter, and the other is the wall thickness that can meet the working pressure. In order to provide the desired pressure and flow rates in hydraulic systems, the pipe diameters must be calculated and determined with the right methods.
FLOW RATES THAT MUST BE USED:
PRESSURE LINE:
4m/s up to 50 bar
5m/s up to 100 bar
up to 150 bar 5m/s
up to 200 bar 5m/s
6-7m/s after 200 bar
SUCTION LINE:
5 to 1.5m/s
RETURN LINE:
2 to 3 m/s
CALCULATION OF PIPE DIAMETER:
Q=Flow rate.........It/min
V= Average speed........m/s
D= Pipe inner diameter..........mm
Hydraulic Hoses
It is used especially in hydraulic systems to connect moving circuit elements to each other. Since the hoses have high flexibility, it is suitable to be used in situations where the system pressure changes frequently, vibrates, and the temperature difference is high. Hoses are made of synthetic rubber. In order to increase their compressive strength, there is one or more steel wire braid-wrapping between the rubber layers.
Hydraulic Unions
It is a circuit element used to connect fittings such as pipes and hoses to each other and to other elements (pump, valve, valve block, cylinder, hydromotor, etc.). The unions are usually screw-connected. Plug-in system unions are also used.
MATTERS TO BE CONSIDERED IN PIPE AND HOSE CONNECTION:
Different pipe diameters should not be used in hydraulic systems, sudden cross-section narrowing or cross-section increase should be avoided.
Sharp corners should be avoided in turns in lines used in hydraulic systems.
Excessively long and unnecessary pipe and hose lines should be avoided.
In order to prevent vibration and cavitation in the system, pipes should be fixed at regular intervals with the help of clamps.
The suction pipe should be short.
The return pipe must be short.
Hoses should be used in moving and vibrating places.
Thermal expansions must be taken into account in pipe connections.
Pipe diameters should be sufficient to provide the desired flow and pressure.
Pipe wall thickness and hose type should be selected to meet the working pressure and temperature values.
Pipe and hose connections must be leak-proof.
Pipe inner surfaces must be smooth.
The innermost layer of the hose must be resistant to the fluid used in the system.
-
HYDRAULIC SEALING ELEMENTS
SEALING ELEMENTS ACCORDING TO THE MATERIALS OF THEIR MADE:1 ) SEALING ELEMENTS MADE OF FABRIC MATERIALS:
Cloth NBR: It is prepared by impregnating cotton cloth with NBR (nitrile). Operating temperatures are between -30 and +105 C. It can withstand pressures of 400 bar.
Cloth FKM: It is prepared by impregnating cotton cloth with FKM (viton). It is used in special conditions (high temperature, special fluid, various chemicals, etc.). Operating temperatures are between -30 and +225 C. It can withstand pressures of 400 bar.
2 ) SEALING ELEMENTS MADE OF FLEXIBLE MATERIALS:
Silicone (MVQ): Operates at temperatures between -60 and +200 C. It is used in static applications.
Nitrile (NBR): It is the most used material in hydraulic and pneumatic systems. It operates at temperatures between –30 and +105 C. They are highly resistant to oil and grease.
Viton (FKM): Operates at temperatures between -30 and +225 C. It is used in sealing elements that need to work under special conditions. Prices are very expensive.
Neoprene (CR): Operates at temperatures between -45 and +100 C. It is not used very often in hydraulic and pneumatic systems. They have high resistance to grease.
Polyurethane (PU): It works at temperatures between -40 and +80 C. It is frequently used in hydraulic and pneumatic systems. Because of their high resistance to friction,
is long lasting.
Ethylene propylene rubber (EPDM): It works at temperatures between -40 and +145 C. It has high resistance to automobile brake oils. It is recommended to be used in systems operating with water and water vapor.
Styrene butadiene rubber (SBR): Operates at temperatures between -50 and +100 C. It has a very high resistance against glycol based brake oils, inorganic acids and bases.
Natural rubber (NR): Operates at temperatures between -60 and +100 C. It is used where high flexibility is required. It is recommended to be used in vibrating places.
11. HYDRAULIC SYSTEM ACCOUNTS
Hydraulic pump and Hydraulic Cylinder Selection
While designing a hydraulic system, firstly the dimensions of the moving elements (cylinder or hydraulic motor) are determined, and then the size of the power unit (pump, motor, valve, hydraulic tank, etc.)
SAFE WORKING TECHNIQUES IN HYDRAULIC SYSTEM
Injuries caused by injecting hydraulic oil into the body Dangerous toxic effect of hydraulic oil. This substance, which is injected into the body, quickly passes through the skin tissue and goes deep into the nerve cells and hand/body cavities. A pinhole-shaped leak in the hydraulic hose causes the toxic oil to eject at a speed of 180m/s under high pressure. This is almost close to the speed of the bullet that comes out of the gun. For this reason, only experienced people who have been trained in this field should intervene in the hydraulic system before intervening. The person who will respond to a hydraulic system failure should wear all protective clothing. The valves in the hydraulic system should be taken to the neutral position. It is checked whether the hydraulic cylinders are under load and the cylinders under load are taken to neutral position. The hydraulic system is stopped and all switches are checked. Manometers in the hydraulic system are checked to ensure that the pressure values are "0". Since hydraulic cylinders are moving parts, necessary precautions must be taken to prevent the equipment connected to the cylinder from moving before removing the hoses connected to this line.
12. RESULTS
Hydraulic system equipment is used at high working pressures. Small mistakes that can be made in the selection, application or assembly of hydraulic components are of great importance in addition to paying high costs, as well as the damage they can cause to human health. It should not be forgotten that fatal accidents occur as a result of wrong practices. It is important that hydraulic equipment is selected and installed by personnel who have been trained in this regard, and that commissioning and applications are always made by checking.