METALLURGY

Definition:

The Process of producing components from metallic powder parts made by powder metallurgy may contain non-metallic constituents to improve the bonding qualities and properties.

Number and variety of products made by powder metallurgy are continuously increasing:

1. Tungsten Filaments for Lamps
2. Contact Point relays
3. Self lubricating bearings
4. Cemented carbides for cutting tools etc.

 

Characters of Metal Powders:

• Shape:

It is influenced by the way it’s made. The shape may be spherical (atomization) (Electrolysis) flat or angular (Mechanical crushing). The particle shape influences the flow characteristics of powders.

• Particle Size (Fineness) and size distribution:

Particle Size and Distribution are important factors which controls the porosity, Compressibility and amount of shrinkage. Proper particle size and size distribution are determined by passing the powder through a standard sieves ranging from 45 to 150 micrometer mesh.

• Flowability:

The ability of the powders to flow readily and conform to the mould cavity. The flow rate helps to determine to possible production rate.

• Compressibility:

It’s defines as the volume of initial powder (Powder loosely filled in cavity) to the volume of compact part. Depends on particle shape & size distribution.

• Apparent Density:

The Apparent density depends on particle size is defined as the ratio of volume to weight of loosely filled mixture.

• Green strength:

It refer to strength of a compact part prior to sintering. It depends on compressibility and helps to handle the parts during the mass production.

• Purity:

Impurities affects sintering & Compacting Oxides & Gaseous impurities can be removed from the part during sintering by the use of a reducing atmosphere.

• Sintering ability:

It is the ability which promotes bonding of particles by the application of heat.

 

Powder Metallurgy Process steps:

 

 

 

 

Manufacture of Metal Powders:

Methods:

• Mechanical pulverization:

Machining, Drilling or Grinding of metals is used to convert them to powders.

• Machining:

It Produces coarse particles (Flack form) especially Magnesium powders.

• Milling or Grinding:

It suitable for brittle materials.

• Shorting:

The process of dropping molten metal through a Sieve or small orifice in to water. This produces Spherical particles or larger size. Commonly used for metals of low melting point.

 

• Atomizing:

In this molten metal is forced through a nozzle, and a stream of compressed air, stream or Inert gas is directed on it break up into five particles. Powders obtained in irregular in shapes. Atomization commonly used for aluminium, Zinc, Tin, Cadmium and other metals of low melting point.

 

• Electrolytic deposition:

It’s used mainly for producing iron and copper powders. These are dense structure with low apparent density. It consists of depositing metal on cathode plate by conventional electrolysis processes. The Cathode paltes are removed and the deposited powder is scraped off. The powder is wasted, dried, screened & oversized particles are milled or ground for fineness. The powder is further subjected to heat treatment to remove the work hardening effect.

• Chemical reduction:

It’s used for producing iron, Copper, Tungsten, Molybdenum, Nickel & Cobalt powder process consists of reducing the metal oxides by means of carbon monoxide or Hydrogen. After reduction, the powder is usually ground & Sized.

 

Forming to shape:

1. The process of mixing the powders is called Blending.
2. The Loose powders are formed in to shape by compacting.

METALLURGY

Definition:

The Process of producing components from metallic powder parts made by powder metallurgy may contain non-metallic constituents to improve the bonding qualities and properties.

Number and variety of products made by powder metallurgy are continuously increasing:

1. Tungsten Filaments for Lamps
2. Contact Point relays
3. Self lubricating bearings
4. Cemented carbides for cutting tools etc.

 

Characters of Metal Powders:

• Shape:

It is influenced by the way it’s made. The shape may be spherical (atomization) (Electrolysis) flat or angular (Mechanical crushing). The particle shape influences the flow characteristics of powders.

• Particle Size (Fineness) and size distribution:

Particle Size and Distribution are important factors which controls the porosity, Compressibility and amount of shrinkage. Proper particle size and size distribution are determined by passing the powder through a standard sieves ranging from 45 to 150 micrometer mesh.

• Flowability:

The ability of the powders to flow readily and conform to the mould cavity. The flow rate helps to determine to possible production rate.

• Compressibility:

It’s defines as the volume of initial powder (Powder loosely filled in cavity) to the volume of compact part. Depends on particle shape & size distribution.

• Apparent Density:

The Apparent density depends on particle size is defined as the ratio of volume to weight of loosely filled mixture.

• Green strength:

It refer to strength of a compact part prior to sintering. It depends on compressibility and helps to handle the parts during the mass production.

• Purity:

Impurities affects sintering & Compacting Oxides & Gaseous impurities can be removed from the part during sintering by the use of a reducing atmosphere.

• Sintering ability:

It is the ability which promotes bonding of particles by the application of heat.

 

Powder Metallurgy Process steps:

 

 

 

 

Manufacture of Metal Powders:

Methods:

• Mechanical pulverization:

Machining, Drilling or Grinding of metals is used to convert them to powders.

• Machining:

It Produces coarse particles (Flack form) especially Magnesium powders.

• Milling or Grinding:

It suitable for brittle materials.

• Shorting:

The process of dropping molten metal through a Sieve or small orifice in to water. This produces Spherical particles or larger size. Commonly used for metals of low melting point.

 

• Atomizing:

In this molten metal is forced through a nozzle, and a stream of compressed air, stream or Inert gas is directed on it break up into five particles. Powders obtained in irregular in shapes. Atomization commonly used for aluminium, Zinc, Tin, Cadmium and other metals of low melting point.

 

• Electrolytic deposition:

It’s used mainly for producing iron and copper powders. These are dense structure with low apparent density. It consists of depositing metal on cathode plate by conventional electrolysis processes. The Cathode paltes are removed and the deposited powder is scraped off. The powder is wasted, dried, screened & oversized particles are milled or ground for fineness. The powder is further subjected to heat treatment to remove the work hardening effect.

• Chemical reduction:

It’s used for producing iron, Copper, Tungsten, Molybdenum, Nickel & Cobalt powder process consists of reducing the metal oxides by means of carbon monoxide or Hydrogen. After reduction, the powder is usually ground & Sized.

 

Forming to shape:

1. The process of mixing the powders is called Blending.
2. The Loose powders are formed in to shape by compacting.

MEASUREMENT

Calibration:

If a known input is given to the measurement system the output deviates from the given input, the corrections are made in the instrument and then the output is measured. This process is called “Calibration”.

Sensitivity:

Sensitivity is the ratio of change in the output signal to the change in the input signal.

Readability:

Refers to the ease with which the readings of a measuring instrument can be read.

True size:

Theoretical size of a dimension which is free from errors.

Actual size:

Size obtained through measurement with permissible error.

Hysteresis:

All the energy put into the stressed component when loaded is not recovered upon unloading. so the output of measurement partially depends on input called Hysteresis.

Range:

The physical variables that are measured between two values. One is the higher calibration value Hc and the other is Lower value Lc.

Span:

The algebraic difference between higher calibration values to lower calibration values.

Resolution:

The minimum value of the input signal is required to cause an appreciable change in the output known as resolution.

Dead Zone:

It is the largest change in the physical variable to which the measuring instrument does not respond.

Threshold:

The minimum value of input signal that is required to make a change or start from zero.

Backlash:

The maximum distance through which one part of the instrument is moved without disturbing the other part.

Response Time:

The time at which the instrument begins its response for a change in the measured quantity.

Repeatability:

The ability of the measuring instrument to repeat the same results during the act measurements for the same quantity is known as repeatability.

Bias:

It is a characteristic of a measure or measuring instruments to give indications of the value of a measured quantity for which the average value differs from true value.

Magnification:

It means the magnitude of output signal of measuring instrument many times increases to make it more readable.

Drift:

If an instrument does not reproduce the same reading at different times of measurement for the same input signal, it is said to be measurement drift.

Reproducibility:

It is the consistency of pattern of variation in measurement. When individual measurements are carried out the closeness of the agreement between the results of measurements of the same quantity.

Uncertainty:

The range about the measured value within the true value of the measured quantity is likely to lie at the stated level of confidence.

Traceability:

It is nothing establishing a calibration by step by step comparison with better standards.

Parallax:

An apparent change in the position of the index relative is to the scale marks.

 

 

MEASUREMENT

Calibration:

If a known input is given to the measurement system the output deviates from the given input, the corrections are made in the instrument and then the output is measured. This process is called “Calibration”.

Sensitivity:

Sensitivity is the ratio of change in the output signal to the change in the input signal.

Readability:

Refers to the ease with which the readings of a measuring instrument can be read.

True size:

Theoretical size of a dimension which is free from errors.

Actual size:

Size obtained through measurement with permissible error.

Hysteresis:

All the energy put into the stressed component when loaded is not recovered upon unloading. so the output of measurement partially depends on input called Hysteresis.

Range:

The physical variables that are measured between two values. One is the higher calibration value Hc and the other is Lower value Lc.

Span:

The algebraic difference between higher calibration values to lower calibration values.

Resolution:

The minimum value of the input signal is required to cause an appreciable change in the output known as resolution.

Dead Zone:

It is the largest change in the physical variable to which the measuring instrument does not respond.

Threshold:

The minimum value of input signal that is required to make a change or start from zero.

Backlash:

The maximum distance through which one part of the instrument is moved without disturbing the other part.

Response Time:

The time at which the instrument begins its response for a change in the measured quantity.

Repeatability:

The ability of the measuring instrument to repeat the same results during the act measurements for the same quantity is known as repeatability.

Bias:

It is a characteristic of a measure or measuring instruments to give indications of the value of a measured quantity for which the average value differs from true value.

Magnification:

It means the magnitude of output signal of measuring instrument many times increases to make it more readable.

Drift:

If an instrument does not reproduce the same reading at different times of measurement for the same input signal, it is said to be measurement drift.

Reproducibility:

It is the consistency of pattern of variation in measurement. When individual measurements are carried out the closeness of the agreement between the results of measurements of the same quantity.

Uncertainty:

The range about the measured value within the true value of the measured quantity is likely to lie at the stated level of confidence.

Traceability:

It is nothing establishing a calibration by step by step comparison with better standards.

Parallax:

An apparent change in the position of the index relative is to the scale marks.