Thursday, November 15, 2018
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DIRT, SLAG and OTHER INCLUSIONS in CASTINGS AND FORGING

DESCRIPTION

 

Inclusions are surface or subsurface particles of sand, slag, dross, oxides or other materials imbedded in the metal.  They may originate from the molds, cores, metal, ladles or careless practices.

 

CAUSES

 

  1. CASTING AND PATTERN DESIGN
  2. Those design factors which contribute to scabs, cuts, washes and erosion will

intensify the tendency toward inclusions in a casting or forging billets

 

 

  1. PATTERN EQUIPMENT
  2. Improper coating for materials involved. Some pattern coatings produce a tendency towards sticking of the sand
  3. Insufficient clearance for setting cores and closing
  4. Lack of fillets
  5. Insufficient draft
  6. Loosely mounted pattern or gating system
  7. Worn flask landing areas can create a crush or disrupt sand grains
  8. Inaccurate partings

 

III. FLASK EQUIPMENT AND RIGGING

  1. Any factor in the rigging which creates a rubbing or gouging effect during the closing of the mold, or setting of cores
  2. Warped or dirty flasks
  3. Worn or crooked pins or bushings
  4. Inaccurate core setting assembly or inspection jigs
  5. Dirty pins and bushings
  6. Inadequate locators

 

  1. GATING AND RISERING
  2. Factors causing scabs, cuts and washes
  3. Gating systems that create slow pouring can cause scabs particularly on cope

surfaces

  1. Gating systems which create a non-filled runner should be avoided since the

cope of such runners will eventually scab and drop sand into the gating system

  1. Gating which promotes high velocity metal flow
  2. The choke or the area of the choke core in the gating system may be inadequate to stop the flow of slag or dross
  3. Exothermic materials if used in such a way as to permit the by-product of the reaction to enter the mold or casting

 

  1. MOLDING SAND
  2. Sands with low physical properties, such as low green, dry and hot

compressive strength

  1. Mold gas – metal reaction
  2. Low fusion point materials
  3. Coatings too heavy, not dried, or wrong for the purpose

 

  1. CORE PRACTICE
  2. Improperly bonded or cured cores
  3. Excessive core gas – metal reaction
  4. Improperly cleaned cores
  5. Premature collapse of cores in molds and gating system
  6. Core wash too heavy, not dried, or wrong for the purpose
  7. Broken cores

 

VII. MOLDING PRACTICE

  1. Any molding factor which contributes to displaced or loose sand in the mold cavity
  2. Sloppy or careless molding
  3. Excessive use of liquid parting
  4. Loose sands from cores or molds
  5. Loose sand from molds left open too long

 

VIII. METAL COMPOSITION

  1. In many metals, it is possible for off-analysis to create a separation of slag or slaglike materials
  2. In cast steels, a high sulfur may lead to sulfide slag, which could separate during cooling
  3. Oxides and intermetallic compounds in steel (carbon and alloy steel)

 

  1. MELTING PRACTICE
  2. Undissolved alloy addition, inoculant, or de-oxidizer
  3. Dross resulting from alloy addition or inadequate fluxing
  4. Too low a melting temperature may result in ability of the slag or dross to separate
  5. Insufficient slag cover during melting to maintain metal cleanliness
  6. Thin watery slag
  7. Refractory – metal reaction can easily release impurities into the metal
  8. Excessive fluxes or deoxidizers

 

  1. POURING PRACTICE
  2. A wet or boiling lip on a ladle can promote, or interfere with proper separation

of slag

  1. Careless skimming of the ladle can result in excessive slag being carried into the metal
  2. Low pouring temperature
  3. Intermittent or slow pouring
  4. Dirty ladles
  5. Ladle linings must be adequate, to avoid mechanical or chemical loss

 

  1. MISCELLANEOUS
  2. Careless maintenance, handling, and general housekeeping
  3. Metallic oxides from ladle entering the mold to cause inclusions (can be corrected by proper gating)
  4. Poorly designed pouring basin may prevent proper choke permitting slag to enter mold
  5. Slag inclusions originating from refractory lining material
  6. Intermittent pouring traps slag in the metal stream and permits it to enter the mold
  7. Core wires in casting cavities
  8. Poorly skimmed ladle may permit slag to enter the mold cavity

 

admin
Hi, I m Abhijeet Patil, an aspiring blogger with an obsession of all things mech. This blog is dedicated to helping people learn about Mech-Foundry technology.
http://mechfoundry.com

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