## Posted tagged ‘function’

### Design of Screw Conveyor

September 8, 2011

The size of screw conveyor depends on two factors

1. The capacity of the conveyor

2. The lump size of the material to be conveyed (Maximum dimensions of the particle)

Usually there are three ranges of lump sizes which are considered for selection of screw size. These are:

· A mixture of lumps and fines in which not more than 10% are lumps ranging from maximum size to one half of the maximum, and 90% are lumps smaller than one half of the maximum size.

· A mixture of lump and fines in which not more than 25% are lumps ranging from the maximum size to one half of the maximum, and 75% are lumps smaller than one half of the maximum size.

· A mixture of lump only in which 95% or more are lumps ranging from maximum size to one half of the maximum size and 5% or less are lumps less than one tenth of the maximum size.

The allowable size of a lump in a screw conveyor is a function of the radial clearance between the outside diameter of the central pipe and the radius of the inside of the screw trough, as well as the proportion of the lumps in the mixture.

The lump size of the material affects the selection of screw diameter which should be at least 12 times larger than the lump size of a sized material and four times larger than the largest lumps of an un-sized material.

Example, if screw diameter is 250mm means radial clearance is 105mm, & Maximum lump size is 60mm of 10% lumps.

Capacity of Screw Conveyor:

The capacity of a screw conveyor depends on the screw diameter, screw pitch, speed of the screw and the loading efficiency of the cross sectional area of the screw. The capacity of a screw conveyor with a continuous screw:

Q = V. ρ

Q = 60. (π/4).D2.S.n.ψ.ρ.C

Where,

Q = capacity of a screw conveyor

V = Volumetric capacity in m3/Hr

ρ = Bulk density of the material, kg/m3

D = Nominal diameter of Screw in m

S = Screw pitch in m

N = RPM of screw

Ψ = Loading efficiency of the screw

C = Factor to take into account the inclination of the conveyor

Screw Pitch:

Commonly the screw pitch is taken equal to the diameter of the screw D. However it may range 0.75 – 1.0 times the diameter of the screw.

Screw Diameter:

 Nominal Size D Trough height from center of screw shaft to upper edge of the trough Trough width C Thickness of Tough Tubular shaft (d1 * Thickness) Outside diameter of solid shaft Coupling diameter of shaft Heavy Duty Medium Duty Light Duty 100 63 120 – 2 1.6 33.7*2.5 30 25 125 75 145 – 2 1.6 33.7*2.5 30 25 160 90 180 5 3.15 1.6 42.4*2.5 35 40 200 112 220 5 3.15 2 48.3*3.5 40 40 250 140 270 5 3.15 2 60.3*4 50 50 315 180 335 5 3.15 – 76.1*5 60 50 400 224 420 5 3.15 – 76.1*5 60 75 500 280 530 5 3.15 – 88.9*5 70 75

RPM of Screw:

The usual range of RPM of screw is 10 to 165. It depends on the diameter of screw and the type of material (Max RPM of screw conveyor is 165)

The value of loading efficiency should be taken large for materials which are free flowing and non abrasive, while for materials which are not free flowing and or abrasive in nature, the value should be taken low:

Ψ = 0.12 to 0.15 for abrasive material

= 0.25 to 0.3 for mildly abrasive material

= 0.4 to 0.45 for non abrasive free flowing materials

Inclination Factor:

The inclination factor C is determined by the angle of screw conveyor with the horizontal.

 Angle of screw with the horizontal 0° 5° 10° 15° 20° Value of factor C 1 0.9 0.8 0.7 0.65

Types of screw flight:

The screw of the conveyor may be right hand or left hand, the right hand type being the usual design. The threads of the screw may be single, double or triple.

The flight of the screws may be made in either of the two ways:

1. As Helicoids

2. As Sectional flight

Helicoids Flight:

They are formed from a flat bar or strip into a continues helix. The threads are thinner at the outer edge and thicker at the inner edge.

Sectional flights:

Sectional flights are formed from a flat disc and the thickness of the thread is uniform throughout. A continuous helix is made by joining a number of sectional flights together on a piece of pipe and butt welded them. Various styles of screw flights are in use, depending on the service required.

Some of the typical configurations are:

1. Short pitch or continuous flight:

If the conveyor is required to handle dry granular or powdered materials that do not pack, this style of flight may be selected. It is of regular construction and recommended for inclined conveyors having a slope of 20 or more, including vertical conveyors. This style is extensively used as feeder screw.

2. Ribbon flight:

If the conveyor is to handle lumpy, clinging, sticky, gummy or viscous substances, this type flight may be selected. It consists of continuous helical flight formed from steel bar and secured to the pipe by supporting lugs.

3. Cut flight:

In this type of flight screws have notches cut in the periphery of the flight. These notches supplement the conveying with moderate mixing action. They are recommended for conveyors required to handle light, fine, granular or flaky materials.

4. Cut and folded flights:

This type of flight is characterized by notches as in cut flight, together with folded segments. This type of flight creates agitation and aeration resulting in better mixing. This type of flight is used to handle light or medium weight materials having fine, granular or flaky materials.

5. Some screw conveyors have cut flight with paddles mounted at regular intervals. The paddles counteract the flow of material past the flight resulting in greater agitation and mixing.

6. Sometimes screws are made of stainless steel to suit special requirements, like the sanitation requirements for handling food, drugs and other hygienic materials.

### Sum it Up

August 24, 2011

Problem: you are given a sequence of numbers from 1 to n-1 with one of the numbers repeating only once. (example: 1 2 3 3 4 5). how can you find the repeating number? what if i give you the constraint that you can’t use a dynamic amount of memory (i.e. the amount of memory you use can’t be related to n)?
what if there are two repeating numbers (and the same memory constraint?)

### Solution

as a programmer, my first answer to this problem would be make a bit vector of size n, and every time you see the number, set its correspond index bit to 1. if the bit is already set, then that’s the repeater. since there were no constraints in the question, this is an ok answer. its good because it makes sense if you draw it for someone, whether they are a programmer, mathemetician, or just your grandpa. its not the most efficient answer though.

now, if i add the constraint that you can only use a fixed amount of memory (i.e. not determined by n) and it must run in O(n) time… how do we solve it. adding all the numbers up from 1 to n-1 would give us a distinct sum. subtracting the total sum of all the numbers from the sum of n to n-1 ( which is (n)(n-1)/2 ) would give us the secret extra number.

what if you can only use a fixed amount of memory, and TWO of the numbers are repeated? we know that the numbers have a distinct sum, and the difference would be equal to the sum of our unknowns
`c = a + b`
where c is the sum and a and b are the unknowns – c is a constant
if we had another similar formula we could solve the two unknown equations. my first thought was that the numbers would have a distinct product – (n-1)!
if we divide the total product by the (n-1)! product, we would get another equation
`c2 = ab`
we could then solve the two equations to get them into quadratic formula notation
`0 = ax^2 + bx + c`
and solve for the two values of x. this answer is correct but factorial grows really fast.

some sort of sum would be better. the sum of the squares from n-1 to 1 would work. that would yield a function of the form
`c2 = a^2 + b^2`
which could also be solved by using the quadratic equation.

i think its fine to remind someone of the quadratic equation… (maybe only because i myself had to look it up to solve the problem) i mean really though, the last time i used it was probably in 10th grade. as long as they get the idea that given two unknowns and two equations you can solve for the unknowns – thats the point.

### And The Phrase” The Sun Is On…!” Hurts..!

August 23, 2011
It is the day that i have awaited more than My 20th B’day. Ofcourse i dint worked that hard to deserve anything!
TORQUE_ A Technical Orchid……..Quest for Excellence is the event that i have wauted for.!The last event in the year 2011 in UCE…!
Initial hiccups couldn’t deter the determined organizers from conducting the event.!With a modest support from the department and a meagre amount of Rs.20,000/- funds!
I still wonder how these guys had managed such an event to fare far better than other events in University!
The very first day saw many fresh faces in department…
Enormous inflow of new waters flooded into old still waters.
With a big question mak on my face i continued to wonder ” Will it be a success..?”
There isn’t even a single instant from which i could learn nothing right from the startig of inagural function to the last word of Thanks gving speech of Valedictory!
Its alwaz irritating to sit in an audi hearing to some blah blah…of eminent speakers with all doors either closed or guarded by some self proclaimed coordinators.!
Somehow they got crowd for that Inagural!
I have managed to escape to stalls.!
I was participating in every torque…
This is my 3rd Torque and 3rd time i have been in stall!
When i was in 1st yr we dint celebrated even though we got some profits….!!
But as the time gre my mind started transforming and i found that celebration of every possible ocassion will be the essence of Engineering life.!
3 different teams in 3 Torques!
Ofcourse i(We) have started celebrating in 2nd yr!
The cricket fever which was feared of was perfectly battled!
Achievable target and dogged performance from Men In Blue and of course some luck of Mr.Cool MSD could have costed us dearly.!
But thanks to performers who kept the audience to glue to their chairs.!
U happened to be computer operator for that day’s culturals ” ROCK ON”
Very close to stage!
I Torque-10 It was ” MY Love Is Gone”
And In Torque-11 It was MJ’s ” DANGEROUS”
Everyone is going crazy of MJ these days….
I feel that MJ fever is still on even though MJ Departed.!
And the thing i came to know
and which has adrenalized my thoughts of organising a whole college event is That JNTU is under transformation!
I’m in the university since 3 yrs…
But i haven’t spotted A Jr Anchoring an Event…
Thanks to all enthusiastic jrs….
I expect their cooperation for whole college Techno-Cultural Fest!
And the other thing is A Boy and Girl from same class dancing together on same stage…!!
A welcomed sign for a world class university!
And the good news came by air in the midst of celebration that Men In Blue had edged Kangaroo’s out of CWC-11
Thunderous applause to MIB rocked the Whole university campus…!
Finally the show halted at 1:00 am
for the next few hours i have slept and when i woke up i found the Sun is Just on….
Another day of surprises is waiting!

### FMEA

August 23, 2011

Failure Mode – A particular way in which an item fails, independent of the reason for failure.

Failure Mode and Effects Analysis (FMEA) – A procedure by which each credible failure mode of each item from a low indenture level to the highest is analyzed to determine the effects on the system and to classify each potential failure mode in accordance with the severity of its effect.

Indenture Levels – The hierarchy of hardware levels from the part to the component to the subsystem to the system, etc.

Redundancy – More than one independent means of performing a function.  There are different kinds of redundancy, including:
(1) Operational – Redundant items, all of which are energized during the operating cycle; includes load-sharing, wherein redundant items are connected in a manner such that upon failure of one item, the other will continue to perform the function.  It is not necessary to switch out the failed item or switch in the redundant one.

(2) Standby – Items that are inoperative (have no power applied) until they are switched in upon failure of the primary item.

(3) Like Redundancy – Identical items performing the same function.

(4) Unlike Redundancy – Non identical items performing the same function

THE FMEA PROCESS

• Define the system to be analyzed.  A complete system definition includes identification of internal and interface functions, expected performance at all indenture levels, system restraints, and failure definitions.  Also state systems and mission phases not analyzed giving rationale for the omissions.

• Indicate the depth of the analysis by identifying the indenture level at which the analysis is begun.

• Identify specific design requirements that are to be verified by the FMEA.

• Define ground rules and assumptions on which the analysis is based.  Identify mission phases to be analyzed and the status of equipment during each mission phase.

• Obtain or construct functional and reliability block diagrams indicating interrelationships of functional groups, system operation, independent data channels, and backup or workaround features of the system.

• Identify failure modes, effects, failure detection and workaround features and other pertinent information on the worksheet.

• Evaluate the severity of each failure effect in accordance with the prescribed severity categories.

FMEA Flow Diagram:

History:

The FMECA was originally developed by the National Aeronautics and Space Administration (NASA) to improve and verify the reliability of space program hardware.

FMECA Flow Diagram: ( Failure Mode, Effects and Criticality Analysis )

Criticality Analysis Flow:

##### Who is the Team ?

Areas to be represented are:

• Quality
• Logistics
• Engineering