MT 212A: Machine Tools Operation Week 7 PDF

MT 212A: Machine Tools Operation Week 7 – Hydraulic System/Drive Ceajay O. Flores – Instructor I Manufacturing Engineering Technology Objectives: Identify the principles of hydraulic systems; and Determine the parts and functions involved in the hydraulic system. Introduction...

MT 212A: Machine Tools Operation Week 7 – Hydraulic System/Drive Ceajay O. Flores – Instructor I Manufacturing Engineering Technology Objectives: Identify the principles of hydraulic systems; and Determine the parts and functions involved in the hydraulic system. Introduction In modern metalworking plants, hydraulic pressure is widely used to operate various machine tools due to its simplicity and flexible control. Hydraulics, though not a new science, is commonly seen in daily applications such as hydraulic jacks, lifts, chairs, presses, and elevators. Recently, hydraulic systems have been integrated into production tools like broaching, grinding, and milling machines, and are now standard in general machine shops and toolmaking departments. Hydraulic Principles Hydraulics is the study of liquids in motion, and its widespread use in force multiplication and control mechanisms is attributed to the unique physical properties of liquids that enable efficient power transmission. Hydraulic Principles Liquids are largely incompressible, making them effective shock absorbers that cushion impacts during starts and stops. Even under high pressure, liquids experience minimal volume changes. Pressure applied to one surface of a confined liquid is transmitted uniformly to other surfaces. Hydraulic Principles Unlike mechanical systems, liquid pressure can be easily redirected through pipes, eliminating the need for additional components. This makes hydraulic systems a more efficient method for transmitting power. Hydraulic Principles The second property that makes confined liquids ideal for the transmission of power is their ability to multiply force.This property was discovered on the seventeenth century by a French scientist named Pascal and is known as Pascal’s Law. According to it, “ A pressure exerted on a confined liquid is exerted undiminished throughout all portions of the liquid.” Conditions 1. The force given by fluid is given by the multiplication of pressure and area of cross section. 2. As the pressure is same in all direction, the smaller piston feels a smaller force and a large piston feels large force. 3. Therefore, a large force can be generated with a smaller force input by using hydraulic systems. Principle of Hydraulic System Principle of Hydraulic System Essential Parts of a Hydraulic System Basic Hydraulic System Two Basic Methods of Controlling the flow of oil in Hydraulic systems 1. Constant-Volume System – characterized by a fixed volume where pressure and temperature can change, but the total volume remains constant throughout the process. 2. Variable-Volume System - allows for dynamic changes in volume, which facilitates work production and energy transfer in various applications. Elements of Hydraulic Systems Pumps – the pump, which runs at constant speed, usually by an electric motor, takes the oil from the supply reservoir and delivers it at sufficient and pressure to do the work required. Gear Pumps The simplest commercial medium-pressure constant-delivery pump has been widely used for raising and circulating liquids. Its popularity in hydraulic power transmission stems from its ability to handle large volumes at medium pressure, quiet operation at high speeds (ball bearings and helical gears), simplicity, low cost, and compact size. Vane Pumps This system is called "hydraulically balanced" because it features two opposing pumping chambers that cancel out thrust forces, preventing heavy bearing loads during high operating pressures. This design offers advantages in size, weight, quiet operation, long life, and high efficiency. Plunger Pump The piston or plunger draws in oil as it moves outward and expels it when pushed back. Pumps typically have five or more radial cylinders, each with its own plunger. Well-suited for variable delivery, high pressure, and smooth flow, making them crucial in various hydraulic applications, either alone or in combination with constant-delivery units. Elements of Hydraulic Systems Valves - the purpose of the valves is to control the flow of oil. The flow is through passages called ports; in through the suction (intake or inlet) port; out through the pressure (outlet) port. Valves may be operated mechanically, electrically, or hydraulically, and for most actions may be automatic. Piston–type Valves Most valves in hydraulically operated machines are of the plunger or piston type. These valves close ports using the "land" of the plunger to shut off oil flow, while "spools" between the lands create connections between adjacent ports. Ports are formed as annular grooves or radial holes in the valve chamber. For smooth operation, it is essential that the oil pressure is balanced, which is characteristic of plunger-type valves. Control Valves Is a power-operated valve used to regulate or manipulate the flow of fluids, such as gas, oil, water, and steam. The pump generates pressure in the oil to provide power to the machine, while the valves control the oil flow, directing power to where it is needed. Modern Control Valves A modern plunger-type control valve features drilled flanges for easy integration into hydraulic systems, typically alongside the pump. Installation involves connecting the pipeline to one or more cylinders and linking the valve stem to the control mechanism, which can be operated mechanically (via cam action or ram arm), electrically (using a solenoid), or hydraulically (through a pilot valve). Resistance (foot) Valves The device is mounted vertically, with a steel ball that seals the check valve by gravity. Oil entering from the side can exit through the top connection by raising the ball. However, oil flowing in from the top is restricted by spring pressure, requiring the entire plunger to move against the spring to allow flow. The spring pressure can be adjusted using a screw. Directional Control Valves (DCV) Used to stop, start, route, and revert fluids without affecting the pressure level or the flow rate of the system. Identified by the number of ways that fluid can flow and the number of positions the valve can produce. Ways = number of ports Position = number of discrete operating positions of the internal valve element. Hydraulic Oil Requirements A properly selected hydraulic oil must have : a) Exceptional chemical stability – to resist oxidation and thus the formation of sludge or grummy deposits b) Maximum demulsibility – to separate readily from water, and thus to minimize the formation of emulsions c) Adequate film strength – to minimize the wear of pumps, valves, cylinders, pistons, etc., and in some machines, to prevent chatter of tables and sticking of slides d) Proper viscosity and minimum change of viscosity – to minimize leakage, and at the same time assure ready flow and prompt response to all controls, and to assure uniformly high production during the warming – up periods.