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Monday, 14 January 2019

PUMP POWER CALCULATION

SUMMARY
          In order to move and increase the pressure of a fluid, power is consumed by a pump, fan or compressor. The power requirement of pump depends upon many factors, including pump and motor efficiency, differencial pressure, density of fluid, viscosity and fluid flow rate. In this article we are going to discuss the relationships to determine the pump power requirement.

DEFINITIONS
Ph​​
:
Hydraulic power of the pump (kW).
Ps​​
:
Shaft power of the pump (kW).
Pm
:
Required power to the Motor (kW).
Q
:
Volumetric flow of fluid through the pump (m3/h).
ρ
:
Density of the fluid being pumped (kg/m3).
g
:
Gravity (9.81 m/s2).
h
:
Head produced by the pump (m).
dP
:
Differential pressure across the pump (kPa)
ηp​​
:
Pump efficiency (%).
ηm​​
:
Motor efficiency (%).

HYDRAULIC POWER
          Hydraulic power, also known as absorbent power, indicates the power imparted on the fluid which is to be pumped to increase the fluid's pressure and velocity. Hydraulic power can be calcuated using one of the formulae below:

Units
Formula
P - kW
Q - m3/h
ρ - kg/m3
g - m/s2
h - m
Ph = Qρgh/3.6 x 10^6
P - kW
Q - m3/hr
dP - kPa
Ph = QdP/3,600​​
P - kW
Q - L/min
dP - kPa
Ph= QdP/60,000​​
P - kW
Q - L/s
dP - kPa
Ph = QdP/1,000​​

SHAFT POWER
          The power supplied by the motor to the pump shaft is called "Shaft power". It is defined as the sum of the hydraulic power and power loss due to inefficiencies in the transmission of power from the shaft to the fluid. The shaft power of pump is generally calculated as the ratio of hydraulic power of the pump to the pump efficiency. 

                        Ps = Ph/ηp
P= Shaft power
Ph = Hydraulic power of pump (dicussed above)
η= Pump efficiency

MOTOR POWER
          The power consumed by the pump motor inorder to turn the pump shaft is called as "motor power". The motor power is the sum of shaft power and power losses while converting electrical energy into kinetic energy. Mthematically motor power is calculated as "shaft power devided by motor efficiency".

Pm = Ps/ηm
P= Motor power
Ps  = Shaft power
η= Motor efficiency

Some OTHER FACTORS WHICH INCREASE REQUIRED POWER
          In addition to the motor we can use some other drive features which will increase the power requirement of pump to transfer a perticular fluid. 
These are :
1) Belt drives 
2) Gear drives
3) VSD's (Variable speed drives)

Tuesday, 1 January 2019

Suction couch roll

Couch roll (also known ascooch) is used in paper machine to remove water by application of vacuum. It acts as the last wrap where the wet web leaves the forming wire (wire part) and enter into the wet-press section (press part). On the surface of the couch roll we found rows of small holes to suck the water. Inside the roll baffles (long and end strips) are present. These baffles direct the vacuum towards the portion of the roll where the wet web of paper is on the fabric. Below of the long baffle strips air tubes are present for strip movement. Below the end baffle strips springs are present to seal the roll for vacuum suction creation. In the vacuum box one shower will present, it cools the rubber material on the roll. In vacuum boxes if we increase the vacuum we need more power to drive the forming fabric. But in couch roll if we applied too high vacuum it produces visible suction-hole “shadows” due to the movement of fines within the sheet.




Tuesday, 20 November 2018

G AND M-CODES FOR CNC MACHINES

CNC G codes
G00 - Rapid traverse; Mill and Lathe
G01 - Linear interpolation (machining a straight line); Mill and Lathe
G02 - Circular interpolation clockwise (machining arcs); Mill and Lathe
G03 - Circular interpolation, CCW Polar co-ordinates; Mill and Lathe
G04 - Dwell time; Mill and Lathe
G09 - Mill and Lathe, Exact stop
G10 - Polar co-ordinates linear interpolation; Mill and Lathe
G12 - Circular pocket milling, clockwise; Mill
G13 - Circular pocket milling, counterclockwise; Mill
G14 - Exact spindle stop
G17 - X-Y plane for arc machining; Mill and Lathe with live tooling
G18 - Z-X plane for arc machining; Mill and Lathe with live tooling
G19 - Z-Y plane for arc machining; Mill and Lathe with live tooling
G20 - Inch units; Mill and Lathe
G21 - Metric units; Mill and Lathe
G27 - Reference return check; Mill and Lathe
G28 - Automatic return through reference point; Mill and Lathe
G29 - Move to location through reference point; Mill and Lathe (slightly different for each machine)
G31 - Skip function; Mill and Lathe
G32 - Thread cutting; Lathe
G33 - Thread cutting lead constant; Mill
G34 - Thread cutting lead increasing; Mill
G35 - Thread cutting lead decreasing; Mill
G40 - Cancel diameter offset; Mill. Cancel tool nose offset; Lathe
G41 - Cutter compensation left; Mill. Tool nose radius compensation left; Lathe
G42 - Cutter compensation right; Mill. Tool nose radius compensation right; Lathe
G43 - Tool length compensation; Mill
G44 - Tool length compensation cancel; Mill (sometimes G49)
G50 - Set coordinate system and maximum RPM; Lathe
G52 - Local coordinate system setting; Mill and Lathe
G53 - Machine coordinate system setting; Mill and Lathe
G54~G59 - Workpiece coordinate system settings #1 t0 #6; Mill and Lathe
G61 - Exact stop check; Mill and Lathe
G65 - Custom macro call; Mill and Lathe
G70 - Finish cycle; Lathe
G71 - Rough turning cycle; Lathe
G72 - Rough facing cycle; Lathe
G73 - Irregular rough turning cycle; Lathe
G73 - Chip break drilling cycle; Mill
G74 - Left hand tapping; Mill
G74 - Face grooving or chip break drilling; Lathe
G75 - OD groove pecking; Lathe
G76 - Fine boring cycle; Mill
G76 - Threading cycle; Lathe
G80 - Cancel cycles; Mill and Lathe
G81 - Drill cycle; Mill and Lathe
G82 - Drill cycle with dwell; Mill
G83 - Peck drilling cycle; Mill
G84 - Tapping cycle; Mill and Lathe
G85 - Bore in, bore out; Mill and Lathe
G86 - Bore in, rapid out; Mill and Lathe
G87 - Back boring cycle; Mill
G90 - Absolute programming
G91 - Incremental programming
G92 - Reposition origin point; Mill
G92 - spindle speed limit, Thread cutting cycle; Lathe
G94 - Feed rate, Per minute feed; Mill
G95 - Feed rate, Per revolution feed; Mill
G96 - Constant surface speed control; Lathe
G97 - Constant surface speed cancel
G98 - Per minute feed; Lathe
G99 - Per revolution feed; Lathe

CNC M Codes
M00 - Program stop; Mill and Lathe
M01 - Optional program stop; Lathe and Mill
M02 - Program end; Lathe and Mill
M03 - Spindle on clockwise; Lathe and Mill
M04 - Spindle on counterclockwise; Lathe and Mill
M05 - Spindle stop; Lathe and Mill
M06 - Tool change; Mill
M07 - Flood Coolant on; Lathe and Mill
M08 - Coolant on; Lathe and Mill
M09 - Coolant off; Lathe and Mill
M10 - Chuck or rotary table clamp; Lathe and Mill
M11 - Chuck or rotary table clamp off; Lathe and Mill
M19 - Orient spindle; Lathe and Mill
M30 - Program end, return to start; Lathe and Mill
M97 - Local sub-routine call; Lathe and Mill
M98 - Sub-program call; Lathe and Mill
M99 - End of sub program; Lathe and Mill

What are Numerical Control Machine? What are NC Machines?

          Numerical control, popularly known as the NC’. Numerical control is defined as the form of programmable automation, in which the actions are controlled by the direct insertion of numerical data such as numbers, letters, and symbols. In case of the machine tools, these programmable automation machines are used for the operation.
          In other words, the numerical control machine is defined as a mechanical machine that is controlled by the set of instructions (input information) called as a program via punched paper tapes or magnetic tapes. The name Numerical control is given to this type of programming, since numbers form the basic program instructions. When the type of job changes, the program instructions of the job also change. Writing new instructions for each job is easy, hence NC offers a lots of flexibility in its use and also more economical for producing a single or a large number of parts.
          The NC machines are used in variety of applications like inspection, assembly, sheet metal work etc., but it is mainly used for machining operations like drilling, milling, turning etc.,

The main elements of a NC machine tool are,
1. The control unit, also known as console or director - it sends the command signals to the drive units.
2. The drive units.
3. The position feed back package.
4. Magnetic box - It acts like electrical control cabonet
5. Manual control - To perform functions manually. 

Classification of NC Machine Tools:

          According to various features, NC machine tools are classified as the following
1. According to the type of power to the drives
1. Electrical
2. Hydraulic
3. Pneumatic
2. According to motion control system of slides
1. Point- to – point system -- Used for drilling machines
2. Straight line system -- Used for turning machines
3. Contour (or) continuous path system -- Used for milling machines
3. According to the feedback system
1. Open loop system -- In this system, there is no ‘feed back’ and no return signal to indicate whether the tool has reached the correct position at the end of the operation or not.
2. Closed loop system -- A feed back is built into system, which automatically monitors the position of tool.
4. According to axis identification
1. 2- axis
2. 3- axis
3. 4- axis
4. 5- axis

Method of Listing Coordinates of Points in NC/ CNC System

Coordinates of Points
          Two types of co-ordinate systems are used to define and control the location of the tool in relation to the work piece. Each system has its own applications and the two co-ordinate systems can be used independently or may be mixed within a NC part program based on the machining requirements of the work piece. The co-ordinate systems used are
1. Absolute co-ordinate system and
2. Incremental co-ordinate system.

(a) Absolute Co-ordinate System: In this system the co-ordinates of a point are always referred with respect to one reference point that is, datum. The datum positions in the X-axis, Y-axis and Z-axis are defined by the user / programmer before starting the operation on the machine. A main advantage of using absolute system is that it is very easy to check and fix a program written using this method. If a mistake is made in the value of any dimension in a particular block, it will affect that dimension only and once the error is corrected there will be no further problems.

(b) Incremental Co-ordinate System: In the incremental system the co-ordinates of any point are calculated with reference to the previous point i.e. the point at which the cutting tool is positioned is taken as datum point for calculating the coordinates of the next point to which movement is to be made. It is difficult to check a part program written in incremental dimension mode.

Absolute and Incremental Programming

Point
Absolute system  
Incremental System 
P1
1,3
1,3
P2
3,2
2,-1
P3
4,2
1,0
P4
4,3
0,1

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