Posted tagged ‘resistance’

Introduction | Fluid Mechanics | Fluid properties

September 16, 2011

Fluid Mechanics – Introduction

01-Fluid Mechanics example - Static and Turbulent Flow - Analysis -Dynamic  analysis - CFD

Fluid Mechanics is that section of applied mechanics, concerned with the statics and dynamics of liquids and gases.

A knowledge of fluid mechanics is essential for the Mechanical engineer, because the majority of Mechanical processing operations are conducted either partially or totally in the fluid phase.

The handling of liquids is much simpler, much cheaper, and much less troublesome than handling solids.

Even in many operations a solid is handled in a finely divided state so that it stays in suspension in a fluid.

Fluid Statics: Which treats fluids in the equilibrium state of no shear stress

 02-Fluid Mechanics example - Static and Turbulent Flow - Analysis -Dynamic  analysis - CFD

Fluid Mechanics: Which treats when portions of fluid are in motion relative to other parts.

03-Fluid Mechanics example - Static and Turbulent Flow - Analysis -Dynamic  analysis - CFD

Fluids and their Properties

Fluids

In everyday life, we recognize three states of matter:

  • solid,
  • liquid and
  • gas.

Although different in many respects, liquids and gases have a common characteristic in which they differ from solids: they are fluids, lacking the ability of solids to offer a permanent resistance to a deforming force.

fluid is a substance which deforms continuously under the action of shearing forces, however small they may be.Conversely, it follows that:
If a fluid is at rest, there can be no shearing forces acting and, therefore, all forces in the fluid must be perpendicular to the planes upon which they act.

Shear stress in a moving fluid

Although there can be no shear stress in a fluid at rest, shear stresses are developed when the fluid is in motion, if the particles of the fluid move relative to each other so that they have different velocities, causing the original shape of the fluid to become distorted. If, on the other hand, the velocity of the fluid is same at every point, no shear stresses will be produced, since the fluid particles are at rest relative to each other.

Vertical screw conveyors

September 8, 2011


01-Vertical screw conveyors- Vertical screw pump- Vertical screw conveyor design- Vertical screw conveyor calculations

A vertical screw conveyor conveys material upward in a vertical path. It requires less space than some other types of elevating conveyors. Vertical screw conveyor can handle most of the bulk materials provided there is no large lump. The maximum height is usually limited to 30m.

A vertical screw conveyor consists of a screw rotating in a vertical casing. The top bearing for the screw shaft must be designed to stand against radial and thrust loads. A suitable inlet port at the lower end and a discharge port at the upper end of the casing are provided. Feeding a vertical screw conveyor deserves careful consideration. Most materials are fed to the vertical conveyor by a straight or offset horizontal feeder conveyor. The ideal operation of a vertical screw conveyor is to have a controlled and uniform volume of material feeding.

Uneven feeding and start stop operation may adversely affect the performance of the vertical screw conveyor in terms of speed, capacity and horse power.

Average capacities and speeds of vertical conveyor

Nominal diameter of screw in mm Capacities in m3/hr Speed of screw
150 10 Up to 400 RPM
250 35 300 RPM
300 75 250 RPM
400 170 200 RPM

Vertical screw conveyors or some special design of vertical screw conveyor finds wide application in ship unloading.

01-Vertical screw lift- Vertical screw elevator- Vertical screw feeder- vertical screw conveyor-vertical screw pump

Practical experience with these conveyors has shown that the resistance factor for vertical conveyors is higher than those of the horizontal conveyors. Resistance factor λ may be taken as 5.5 to 7.5 for grains. 6.5 to 8.3 for salt.

01-screw conveyor design calculation- screw conveyor power calculation- screw conveyor efficiency- screw conveyor theory- screw conveyor formulae- screw conveyor flow rates

The driving power of the loaded screw conveyor is given by:

P = PH + PN + Pst

Where,

PH = Power necessary for the progress of the material

PN = Driving power of the screw conveyor at no load

Pst = Power requirement for the inclination of the conveyor

Power necessary for the progress of the material PH:

For a length L of the screw conveyor (feeder), the power PH in kilo watts is the product of the mass flow rate of the material by the length L and an artificial friction coefficient λ, also called the progress resistance coefficient.

PH = Im.L. λ.g / 3600 (kilowatt)

= Im.L. λ / 367 (kilowatt)

Where,

Im = Mass flow rate in t/hr

λ = Progress resistance coefficient

Each material has its own coefficient λ. It is generally of the order of 2 to 4. For materials like rock salt etc, the mean value of λ is 2.5. For gypsum, lumpy or dry fine clay, foundry sand, cement, ash, lime, large grain ordinary sand, the mean value of λ is 4.0.

In this connection it should be noted that the sliding of the material particles against each other gives rise to internal friction. Other resistance due to grading or shape of the output discharge pattern contributes to the resistance factor. That is why the parameter λ is always higher than that due to pure friction.

Drive power of the screw conveyor at no load, PN:

This power requirement is very low and is proportional to the nominal diameter and length of the screw.

PN = D.L / 20 (Kilowatt)

Where,

D = Nominal diameter of screw in meter

L = Length of screw conveyor in meter

Power due to inclination: Pst

This power requirement will be the product of the mass flow rate by the height H and the acceleration due to gravity g.

Pst = Im.H.g / 3600

= Im.H / 367

H should be taken positive for ascending screws and will be negative for descending screws.

Total power requirement:

The total power requirement is the sum total of the above items

P = (Im (λ.L + H) / 367) + (D.L /20) (Kilowatt)

FINISHING OPERATIONS

August 23, 2011

Sizing:

Repressing the sintered component in a die to meet required tolerances.

06-measurement-sizing-tolerance-measurement

02-Sizing-Sintering-Height gauge

Coining:

Repressing the sintered component in a die to increase the density and to give additional strength.

03-coldforge-coining

Infiltration:

Filling the pores of sintered product with molten metal to improve the physical properties.

Impregnation:

Filling of Oil, Grease or other Lubricants in a Sintered components such as Porous Heating

Machining:


Removing excess material by using cutting tool to imparts specific features such as Threads, Grooves, Undercuts etc, which are not practicable in powder metallurgy process.

04-thread cutting-powder metallurgy

Heat Treatment:

Process of Heating & Cooling at a desired rate to improve Grain Structure, Strength & Hardness.

05-heattreatment-metals-hardening

Plating:

Used for obtaining Resistance to Corrosion or better appearance.

05-electro plating-methods-examples

05-electro plating-application-examples

Powder metallurgy is used in the following industries:

  • Automotive (Brake pads, Gear parts, Connecting rods, Planetary carriers, Sintered Engine Bearings);

07-composite gears-automobile-parts

  • Aerospace (Light weight Aluminum base structural materials, High temperature Composite materials);

07-Aeroplane-boeing-powder-metallurgy-applications

07-composite-parts-Aerospace

  • Cutting tools (Hard metals, Diamond containing materials);

07-milling-cutters-tooling

  • Medicine (Dental implants, Surgical instruments);

07-medical-applications-powder metallurgy

  • Abrasives (Grinding and Polishing wheels and Discs);
  • Electrical, Electronic and Computer parts (Permanent magnets, Electrical contacts).

 

07-electronics-computer parts

FINISHING OPERATIONS

August 23, 2011

Sizing:

Repressing the sintered component in a die to meet required tolerances.

06-measurement-sizing-tolerance-measurement

02-Sizing-Sintering-Height gauge

Coining:

Repressing the sintered component in a die to increase the density and to give additional strength.

03-coldforge-coining

Infiltration:

Filling the pores of sintered product with molten metal to improve the physical properties.

Impregnation:

Filling of Oil, Grease or other Lubricants in a Sintered components such as Porous Heating

Machining:


Removing excess material by using cutting tool to imparts specific features such as Threads, Grooves, Undercuts etc, which are not practicable in powder metallurgy process.

04-thread cutting-powder metallurgy

Heat Treatment:

Process of Heating & Cooling at a desired rate to improve Grain Structure, Strength & Hardness.

05-heattreatment-metals-hardening

Plating:

Used for obtaining Resistance to Corrosion or better appearance.

05-electro plating-methods-examples

05-electro plating-application-examples

Powder metallurgy is used in the following industries:

  • Automotive (Brake pads, Gear parts, Connecting rods, Planetary carriers, Sintered Engine Bearings);

07-composite gears-automobile-parts

  • Aerospace (Light weight Aluminum base structural materials, High temperature Composite materials);

07-Aeroplane-boeing-powder-metallurgy-applications

07-composite-parts-Aerospace

  • Cutting tools (Hard metals, Diamond containing materials);

07-milling-cutters-tooling

  • Medicine (Dental implants, Surgical instruments);

07-medical-applications-powder metallurgy

  • Abrasives (Grinding and Polishing wheels and Discs);
  • Electrical, Electronic and Computer parts (Permanent magnets, Electrical contacts).

 

07-electronics-computer parts

PRESSURE FORMING

August 22, 2011

01-pressure forming-products-intricate contours-tight radii-


Material & Description

ABS

Good general purpose material, very tough yet very hard and rigid, good impact and electrical. Available in gauges from .040 to .475 with several extruded textures. Comes opaque and can be matched in custom colors.

ABS/PC

A blend or alloy of ABS and polycarbonate that thermoforms well, weathers well, good color retention, very hard, excellent impact.

ABS/PVC

Flame retardant, tough.

Acrylic

Outstanding weather resistance, excellent optics and electrical properties, poor impact, high gloss and deep luster. Available in standard gauges from .080 to over 1″. Available in clear, transparent and opaque colors.

Acrylic, cell cast

Excellent optics and hot strength, more expensive. Acrylic, continuous and extrusion cast.
Large volume use and best price, good optics.

Acrylic film

3 or 6 mil film for laminating, decorating, and weathering of extruded ABS.

DR Acrylic

Modified acrylic with higher impact properties.

Acrylic/PVC

A blend of acrylic and PVC that is a tough, chemical-resistant material that weathers well and is flame resistant. Available in custom colors.

HDPE (high-density polyethylene)

Crystalline, very tough materials, good weather resistance with UV inhibitors, resistant to many chemicals. Available in standard gauges from .040 to .500. Available in opaque custom colors. Tough and stiff. Good low temperature. Economical.

HMWPE (high molecular weight)

Excellent environmental stress crack properties, thermoforms well, good low temperature.

HIPS (high impact polystyrene)

Good general-purpose material, rigid. Available in clear but usually opaque custom colors from .030 to .350, low cost.

PVC (vinyl)

Good general-purpose material, good abrasion and chemical resistance. Available in clear but usually opaque custom colors from .030 to .125.

Expanded PVC

Stiff, light, flat, thermoformable. Available in stock colors and gauges, generally 3 and 6 mm but others also available.

PETG

Clear, higher impact than acrylic, easy to form. Available in gauges from .030 to .500.

01-pressure forming-blow forming-Thermoform-Console-automobile parts

Pressure Forming:

Pressure Forming is the method used to produce injection mold quality, high definition plastic component parts, housings and containers without the huge expense of tooling. It involves positive pressure to force the heated plastic into the mold cavity. This is called pressure thermoforming or blow forming

Pressure Forming Working Operation:

01-pressure forming-20-150 psi pressure-temperature controlled mold cavity

The highly versatile pressure forming process utilizes air pressure, from 20 to 150 psi, to force the heated sheet into a temperature controlled mold cavity. Vent holes are provided in the mold to exhaust the trapped air. The final part features sharp definition of intricate contours and tight radii. Textures and accurate details are built right into the tooling. Low-cost, highly aesthetic plastic parts of varying sizes are possible due to the application of air pressure, as well as more sophisticated process controls that better monitor tool and sheet temperatures while controlling material shrinkage during forming.

01-pressure forming-products-intricate contours-tight radii-

Types Of Molding operation:

  • Positive Mold
  • Negative Mold

01-pressure forming process-positive molds-cost advantages-pressure forming over thermo forming

Negative molds  have concave cavities. A positive mold has a convex shape.

Pressure Forming over Thermo Forming:

The basic advantage of Pressure Forming over Thermo forming is the cost advantage for small production items. The mould cost for thermo forming is considerably higher in comparison to pressure forming thus for a lower quantity precision job the best suitable method used is pressure forming.

Application:

Pressure forming is used to create in a wide array of plastic products used for packaging of food trays, blisters, covers, internal parts, housings equipment, bezels, bases, and spare parts for use in business machines, electronics, computers and peripherals, bio-medical applications, and instruments.

Features:

Pressure forming achieves features beyond the capabilities of vacuum forming including louvers, ribs, recessed areas, crisp details and logos.

Pressure forming is ideal for small to medium sized production runs that do not justify the high cost of injection molding dies. Additionally, because the aluminum tooling used in pressure forming has an unlimited lifecycle, due to the non-abrasive process versus injection, it saves a great deal of money over many years of continued use. Pressure form tooling usually costs less than 10% the cost of an injection tool. There is also a significant time savings (sometimes 25%) in tooling lead time. Sheet gauges .020″ – .500″ are capable of being pressure formed.

METALLURGY INTERVIEW

August 22, 2011

01-interview-interview questions-placement paper-interview questions and answers-interview tips-company or firm - interview skills-interview preparation

  • What is the composition of Grey cast iron Grade 20?

Carbon      : 3.10 – 3.25%         Silicon : 1.75-1.95%    Manganese : 0.50 – 0.7%Sulphur : 0.05 – 0.07%       Phosporous : 0.04 – 0.07%

  • What is the composition of Cast iron Grade 35?

Carbon=2.90-3.10%Manganese=0.60-1.00%Silicon=1.50-1.90%Sulphur=0.10%

Phosphorus=0.15%  Chromium=0.30%        Molybdenum=0.30%   Cupper=0.25%

  • What are the super alloys?

Super alloys is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, having good surface finish.

  • Why the Super alloys used for land-based turbines?

Super alloys are the top most alloys used for their excellent strength and corrosion resistance as well as oxidation resistance. No other alloys can compete with these grade.

  • What kinds of NDT methods are available?

1.Visual Inspection

2.Microscopy inspection

3.Radiography Test

4.Dye Penetrate technique

5.Ultrasonic testing

6.Magnetic Particle inspection

7.Eddy Current technology

8.Acoustic Emission

9. Thermograph

10.Replica Metallographic

  • What is Stress Corrosion cracking?

Stress corrosion cracking (SCC) is a process involving the initiation of cracks and their propagation, possibly up to complete failure of a component, due to the combined action of tensile mechanical loading and a corrosive medium.

  • What is meant by D2 Material used for Die tooling?

 

D2 – High Carbon Cold Work Tool Steel

D2 is a high Carbon, high Chromium, Molybdenum, Vanadium, Air hardening alloy tool steel which offers good wear resistance, high surface hardness, through hardening properties, dimensional stability and high resistance to tempering effect. D2 tool steel is also suitable for vacuum hardening.

Typical Composition

C.-1.50%

Si.-0.30%

Cr. -12.00%

Mo. -0.80%

V. -0.90%

  • What is Vacuum Induction Melting?

As the name suggests, the process involves melting of a metal under vacuum conditions. Electromagnetic induction is used as the energy source for melting the metal.

Induction melting works by inducing electrical eddy currents in the metal. The source is the induction coil which carries an alternating current. The eddy currents heat and eventually melt the charge