POWDER SAMPLING

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POWDER SAMPLING

• By
• Satyan Choudhary CH05B038
• Ramcharan CH05B042
• Samvith CH05B058
• Arun Kumar CH05B021

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Sampling

• Sampling is the process of securing a
  representative portion of materials for the
  purpose of gaining information regarding the
  type, quality, or composition, and therefore the
  acceptability and unit value of the total lot
  inspected by investigation of the part.

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Fundamentals of Sampling

• Sample for measurement should be representative
  of the bulk in particle size and relative
  fraction of their various constituents .
• Total sampling error errors due to the primary
  sampling subsequent sample dividing errors in
  the analysis itself
• Accurate sampling depends on its extent of being
  biased , that is error of sampling is random
  variable about the true mean .
• Differences between a sample and bulk may be
  attributed to the expected difference on the
  statistical basis

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Major sampling errors

• Errors due to segregation of the bulk , this
  depends on the history of the powder and can be
  minimized by suitable mixing and building up the
  sample from large number of increments
• Statistical errors that cannot be prevented. Even
  for an ideal random mixture the quantitative
  distribution in samples of a given magnitude is
  not constant but is subject to random
  fluctuations. It can be pre-estimated and reduced
  by increasing the sample size

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Sample selection

• Samples are withdrawn from a population to
  estimate certain characteristics of that
  population and to establish confidence limits for
  that characteristics
• If several samples are taken their
  characteristics will vary and if these samples
  are representative, the expected variation can be
  estimated from statistical analysis but equipment
  efficiency will also introduce some errors

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• Different stages of sample reduction (depending
  on their weight)

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Segregation

• Free flowing powders tend to segregate during
  handling and storage, hence spot samples are
  rarely representative .
• Cohesive powders tend to retain their
  characteristics during handling but if they are
  segregated during manufacture or packaging they
  will tend to remain segregated
• If material is fed into containers and conveyor
  belts it might lead to vertical and horizontal
  segregation

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Segregation in free flowing powders
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Golden Rules of Sampling

• Powder should always be sampled when in motion.
• The whole of stream of powder should be taken for
  many short increments of time in preference to
  part of the stream being taken for the whole of
  time.
• e.g. for a stream
  flowing through a pipe , the entire cross
  sectional area should be taken for sampling at
  repeated intervals rather than a part of cross
  sectional area at all times

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Sampling stored materials

• Sampling stored non flowing materials
• Non flowing materials consist of cohesive
  powders, sticky materials , moist materials or
  fibrous solids.
• A pre-supposition is that the powder was mixed
  before storage
• Sampling accuracy improves if several samples
  are taken
• Equipment used Sampling Spear (Thief), Self
  burrowing probes

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Sampling stored materials

• Sampling from heaps
• Method used Coning and Quartering process

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Sampling stored materials

• Sampling stored bulk free-flowing powders
• best if avoided !!! (because of the severe
  segregation )
• Sampling from bags and drums
• Sampling from trucks and railcars

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Sampling flowing streams

• Sampling from a conveyor belt
• The best position for collecting the sample is
  where the materials falls in stream from the end
  of the belts.
• Sampling may be continuous or intermittent

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Sampling flowing streams

• Point Samplers
• Sampling from falling streams

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Sampling flowing streams

• Traversing Cutters
• In-line Sampling

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Sample Reduction

• (gross sample ? laboratory sample)
• The gross sample is frequently too large to be
  handled easily and has to be reduced to a more
  convenient weight
• Methods employed should conform with the golden
  rules of sampling
• Some methods for Sample Reduction
• Scoop sampling

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Sample Reduction

• Cone and Quartering
• Table Sampling
• Chute Splitting

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Sample Reduction

• Spinning rifflers

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Sampling technique reliability

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Sampling technique comparison
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Weight of sample required

• The minimum weight of the gross sample may be
  calculated using the following formula (error
  obtained is within pre-designated limits) -
• Ms ½ (?/si2) (1/wt 2) dt3 x 103
• Ms limiting weight in gm
• ? powder density (g/cm3 )
• si2 variance of the tolerated
  sampling error
• wt fractional mass of the coarsest
  size class being sampled
• dt3 arithmetic mean of the cubes of
  the extreme diameter (cm3 )

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Weight of sample required

• For sampling a moving stream of powder, the gross
  sample is made up of increments. The minimum
  incremental weight
• Ms µowo/?o
• where,
• Ms average mass of the
  increment
• µo average rate of flow
• wo cutter width for a
  traversing cutter
• ?o the cutter velocity

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Sample containers (used for storing samples)

• A large range of sample containers, made from a
  variety of materials are available for a wide
  range of applications.
• Size from 5ml upwards
• Transparent containers available
• Screw caps or simple push on lids

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Examples of some sampling equipment used in
industry

• UP Free Glide In-line Powder Sampler for
  installation in a down pipe
• ? Guaranteed not to get stuck during
  operation
• ? Suitable for in-line sampling of both free
  flowing and cohesive powders
• ? Automatic and manual versions available

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Bibliography

• Powder sampling and particle size determination
  by T. ALLEN
• http//www.sampling.co.uk/guide
• http//www.pharmtech.com/pharmtech/data
• www.dnsc.dla.mil/iamthekey
• http//www.particlescic.com
• Video and images from Google search

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Thank You