Chapter 1.docx

CHAPTER 1 INTRODUCTION

A quick return mechanism is a mechanism that converts rotary motion into reciprocating motion at different rate for its two strokes. When the time required for the working stroke is greater than that of the return stroke, it is a quick return mechanism. It yields a significant improvement in machining productivity. Currently, it is widely used in machine tools, for instance, shaping machines, power-driven saws, and other applications requiring a working stroke with intensive loading, and a return stroke with non-intensive loading. . By using quick return mechanism in air compressor unit the time of return stroke will be reduced, therefore the overall efficiency of air compressor will be increased.

Several quick return mechanisms can be found in the literatures including the offset crank-slider mechanism, the crank-shaper mechanisms, the double crank mechanisms, and the Whitworth mechanism. All of them are linkages. A linkage has its strengths and weaknesses. It is inexpensive to make and easy to lubricate; however, it is bulky and difficult to balance. In situations, if compact space is essential to the design, then a linkage may not be a good choice.

CHAPTER 2 QUICK RETURN MECHANISM

2.1 USAGE OF QUICK RETURN MECHANISM IN AIR COMPRESSOR Quick return mechanism is used in shaping and slotting machines to cut metals.

Here we

used this mechanism in air compressor to reducing the return stroke of the piston. The return stroke is sucked the air from atmosphere and forward stroke compressed it. However the power required on return stroke is lesser then, power required to move the piston in forward. So by reduce time taken of return stroke is increase the efficiency of air compressor.

2.2 MECHANISM:

Fig 2.1 Quick return mechanism

Fig 2.2 Slider positions

2.2.1 FORWARD STROKE: Initially, the slider at point C1, then the point M will be on position of connecting rod is extremely in left position then the crank rotate at counter clockwise from C1 to C2 by covering of an angle K. By the results the pistons connecting rod will move M to N in normal speed. The distance between M and N is called stroke length. And the angle (K) between C1 and C2 called as forward stroke angle.

2.2.2 RETURN STROKE: When the crank further rotates counter clockwise from C2 to C1 the slider will be move N to M now the pistons connecting rod move backward. The angle between C2 to C1 is known as the return stroke angle. Is denoted at L . The angle L is lesser then the angle k. Due to this reduction of angle gives the quick return motion comparing to forward motion.

When the driving crank rotates at uniform angular speed (N), we can write, Time for forward stroke= Time for return stroke=

𝑲 𝟐𝝅𝑵 𝑳

𝟐𝝅𝑵

Now the ratio of cutting stroke to return stroke time is given by,

𝑻𝒊𝒎𝒆 𝒐𝒇 𝒇𝒐𝒓𝒘𝒂𝒓𝒅 𝒔𝒕𝒓𝒐𝒌𝒆 𝑻𝒊𝒎𝒆 𝒐𝒇 𝒓𝒆𝒕𝒖𝒓𝒏 𝒔𝒕𝒓𝒐𝒌𝒆

Where,

K - Angle of forward stroke L-Angle of return stroke

=

𝑲 𝟐𝝅𝑵 𝑳 𝟐𝝅𝑵

=

𝒂𝒏𝒈𝒍𝒆 𝑲

=

𝑲

=

𝒂𝒏𝒈𝒍𝒆 𝑳 𝟑𝟔𝟎−𝑲

𝟑𝟔𝟎−𝑳 𝑳

CHAPTER 3 GEARS

3.1 GEARS: A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed parts to transmit part to transmit torque. Geared devices can change the speed, torque, and direction of a power source. Two meshing gears transmitting rotational motion. Note that the smaller gear is rotating faster. Since the larger gear is rotating less quickly, its torque is proportionally greater. One subtlety of this particular arrangement is that the linear speed at the pitch diameter is the same on the both gears.

3.2 TYPES OF GEAR:

There are four principal types of gear,

 SPUR GEARS: The simplest type of gears. The teeth are parallel to the axis of rotation, as seen in the figure. It transmits rotation between two straight shafts.

 Helical gears: The teeth are inclined with respect to the axis of rotation, as seen in the figure. Same as spur gears, it transmits rotation between parallel shafts, but it is less noisy than spur gears because of the more gradual engagement of the teeth during meshing and thus it is more suitable for transmitting motion at higher speed

 Bevel gears: The teeth are some how similar to those of a spur gear but they are formed on conical surfaces instead of cylinders. Bevel gears transmit rotation between intersecting shafts. The gear shown in the figure has straight teeth where this is the simplest type. However, there are other types were the teeth form

circular arcs and it is called spiral bevel gears, as shown in the figure. With spiral bevel gears, the teeth engagement will be more gradual and thus it is less noisy and it is suitable for speeds.

 Worms

and

worm

gears:

Transmit

rotation

between

perpendicular shafts (not intersecting, there is an offset between them). The worm resembles a screw which can be right handed or left handed. Worm gear sets are usually used when high reduction in speed is desired (speed ratios of 3 or higher). It transmits rotation from the worm to the worm gear, but not the opposite. Fig3.1

Nomenclature Since spur gears are the simplest type, it will be used for illustration and to define the primary parameters of gears and their

relations.

The

figure

illustrates the terminology of spur gears.

 Pitch circle: A circle upon which all gear calculations are based and its diameter is called the “pitch diameter”.

Fig3.2

.

 Addendum and Dedendum circles: The circles defining the top and bottom faces of the teeth.

 Addendum : The radial distance from the pitch circle to the top surface of the teeth.

 Dedendum: The radial distance from the pitch circle to the bottom surface of the teeth.

CHAPTER 4 PNEUMATIC CYLINDER

4.1 PNEUMATIC CYLINDERS:

Many industrial applications require linear motion during their operating sequence. One of the simplest and most cost effective ways to accomplish this is with a pneumatic actuator, often referred to as an air cylinder. An actuator is a device that translates a source of static power into useful output motion.

It can also be used to apply a force. Actuators are typically mechanical devices that take energy and convert it into some kind of motion. That motion can be in any form, such as blocking, clamping, or ejecting.

Pneumatic actuators are mechanical devices that use compressed air acting on a piston inside a cylinder to move a load along a linear path. Unlike their hydraulic alternatives, the operating fluid in a pneumatic actuator is simply air, so leakage doesn’t drip and contaminate surrounding areas.

Fig4.1

4.2 SINGLE ACTING CYLINDER:

A single-acting cylinder in a reciprocating engine is a cylinder in which the working fluid acts on one side of the piston only. A single-acting cylinder relies on the load, springs, other cylinders, or the momentum of a flywheel, to push the piston back in the other direction. Single-acting cylinders are found in most kinds of reciprocating engine. They are almost universal in internal combustion engines (e.g. petrol and diesel engines) and are also used in many external combustion engines such as Stirling engines and some steam engines. They are also found in pumps and hydraulic rams.

Fig4.2

CHAPTER 5

ELECTRIC MOTOR

5.1 MOTOR:

An AC motor is an electric motor driven by an alternating current (AC). The AC motor commonly consists of two basic parts, an outside stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft producing a second rotating magnetic field. The rotor magnetic field may be produced by permanent magnets, reluctance saliency, or DC or AC electrical windings. Less common, AC linear motors operate on similar principles as rotating motors but have their stationary and moving parts arranged in a straight line configuration, producing linear motion instead of rotation.

5.1.1 WORKING PRINCIPLE OF MOTOR:

The two main types of AC motors are induction motors and synchronous motors. The induction motor (or asynchronous motor) always relies on a small difference in speed between the stator rotating magnetic field and the rotor shaft speed called slip to induce rotor current in the rotor AC winding. As a result, the induction motor cannot produce torque near synchronous speed where induction (or slip) is irrelevant or ceases to exist. In contrast, the synchronous motor does not rely on slip-induction for operation and uses either permanent magnets, salient poles (having projecting magnetic poles), or an independently excited rotor winding. The synchronous motor produces its rated torque at exactly synchronous speed. The brushless wound-rotor doubly fed synchronous motor system has an independently excited rotor winding that does not rely on the principles of slipinduction of current. The brushless wound-rotor doubly fed motor is a synchronous

motor that can function exactly at the supply frequency or sub to super multiple of the supply frequency. Other types of motors include eddy current motors, and AC and DC mechanically commutated machines in which speed is dependent on voltage and winding connection.

5.1.2 MOTOR DETAILS:

2.4.5 ‘C’ CHANNEL:

Fig 2.9 ‘c’ channel