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Historic Preservation - Technical Procedures

Spectitle:

Duplicating Cast Iron Ornament

Procedure code:

0501014R

Source:

Developed For Hspg (Nps - Sero)

Division:

Metals

Section:

Metal Materials

Last Modified:

02/24/2012

Details:

Duplicating Cast Iron Ornament



DUPLICATING CAST IRON ORNAMENT


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on duplicating cast iron
         ornament in "green sand" molds.  Green sand means the
         sand is wet, cohesive and will hold an impression.

    B.   Recreating damaged or missing pieces is required when
         deterioration is so great that patching with metal filler
         or sheet metal is not sufficient.

    C.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precautions

         3.   Submittals

         4.   Quality Assurance

         5.   Delivery, Storage and Handling

         6.   Project/Site Conditions

         7.   Sequencing and Scheduling

         8.   General Protection (Surface and Surrounding)

         These guidelines should be reviewed prior to performing
         this procedure and should be followed, when applicable,
         along with recommendations from the Regional Historic
         Preservation Officer (RHPO).

    D.   For general information on the characteristics, uses and
         problems associated with cast iron, see 05010-04-S.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Casting Companies:

         1.   Gorsuch Foundry
              120 E. Market St.
              Jeffersonville, IN  47130
              812/283-3585

         2.   Robinson Iron Corporation
              Robinson Road
              Alexander City, AL  35010
              205/329-8484

         3.   The Johnson Atelier
              Technical Institute of Sculpture
              743 Alexander Road
              Princeton, NJ  08540
              609/452-2661

2.02 MATERIALS

    A.   New castings as required (see manufacturers above)

    B.   Casting flasks or boxes:

         1.   Use a 2-part mold for a solid casting with relief
              on both sides.  

         2.   Use an open top mold for castings to have one side
              with relief and the other side flat.  

         3.   Use a 2 or more part mold for hollow castings.
              Note:  In this type of casting, the parts are
              bolted, brazed or welded together.

    C.   "Green Sand" for making the molds:

         1.   "Green" refers to its wet consistency.  It is
              actually black in color.

         2.   It is very fine, similar to beach sand, and it is
              mixed every day in 900-pound batches with baronite
              (flour with clay as a bonding agent) and about 3
              gallons of water.  When the sand is the right
              consistency, it holds together like a snowball.

    D.   Parting sand

    E.   Sprues:  Used to form channels for pouring molten iron
         through.

    F.   Screws and bolts

    G.   Ni rods (Nickel Alloy welding rods)

2.03 EQUIPMENT

    A.   Wiping cloths

    B.   Eye and skin protection

    C.   Hammer

    D.   Screwdriver

    E.   Wrench

    F.   Welding equipment

    G.   Electric drill


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Before proceeding with steps to repair cast-iron
         features, it is important to first determine the cause
         and extent of the problem.  Determine the age of the
         features and examine the condition of the entire surface.
         Inspect for:

         1.   Wear - especially moving parts such as hardware.

         2.   Parts - which have failed or which are unsecured,
              broken, cracked, missing, distorted, or loose
              (check screws and bolts).

         3.   Paint - coating failures such as chips, losses,
              peeling, checks, bubbling, and wear.

         4.   Rust corrosion - caused by moisture, sea water and
              sea air, deicing salts, acids, soils, gypsum
              plasters, magnesium oxychloride cements, ashes,
              clinkers, and sulfur compounds.

         5.   Galvanic action - corrosion caused when iron is
              exposed to cupro-nickels, aluminum bronzes, gun
              metals, copper, brasses, lead, soft solders, and
              some stainless steels and chromium.

         6.   Determine the source of the moisture which causes
              the deterioration.

         7.   Determine if the feature can be salvaged.

         8.   Measure the dimensions of the various metal parts
              needing replacement.

3.02 ERECTION/INSTALLATION/APPLICATION

    NOTE:  USUALLY EVERY DIFFERENT ELEMENT TO BE RE-CASTED
    REQUIRES EITHER ONE PATTERN OR ONE PROTOTYPE FROM WHICH SAND
    MOLDS CAN BE TAKEN.

    A.   To replace a pre-existing piece, order cast iron pieces
         from a foundry.  The foundry needs an accurate pattern,
         a model from which it can take a mold.  

         1.   Obtain an exact duplicate of the piece needed to be
              duplicated, or provide the foundry with one of the
              following:

              a.   A piece closely resembling the piece to be
                   duplicated along with the exact dimensions of
                   the part to be duplicated, if the exact piece
                   is not available.

              b.   A scaled photograph or good detail drawing of
                   the item.

              c.   Original specifications or construction
                   drawings describing the piece.

              d.   Contact the company which made the product.
                   They may still have a copy of the wooden
                   pattern and would be willing to lend it to the
                   foundry.

         2.   The foundry pattern-maker should look at the entire
              piece (i.e. a railing/balustrade) before attempting
              to recast any missing portion.  If only a small
              piece from a large part is missing, the pattern-
             maker may be able to fill in the missing piece with
              Pattern-Build (a material rather like plastic wood)
              or auto-body filler.  Then it can be used as a
              whole pattern.  

    C.   Pattern making:  Making an original from which one or
         more castings can be made.

         1.   Patterns are typically made from timber, glass
              reinforced plastic, wax, plaster or another metal.

         2.   Patterns are typically produced by a specialist.

         3.   Patterns should be made slightly over-sized to
              allow for contraction.

    D.   Molding (for a casting with relief on both sides):  

         1.   Assemble mold board and risers.

         2.   Dust 1/2 of pattern with parting sand and place in
              bottom half of mold or "Cope".

         3.   Fill cope with sand and ram until thoroughly
              packed.

         4.   Place mold board on top of the cope and turn over.

         5.   Remove mold board from bottom of cope (now
              inverted) and place other 1/2 of pattern.

         6.   Dust face of "green sand" and pattern with parting
              sand.

         7.   Set top of mold or "Drag" in place on top of cope.
              Place sprues vertically on either end of pattern.  

         8.   Fill drag with sand and ram until thoroughly
              packed.

         9.   Remove sprues and place mold board on top of drag.

         10.  Separate cope and drag and invert drag.

         11.  Remove 1/2 pattern from cope and cut flow gates at
              ends of pattern impression to connect with
              channels.

         12.  Remove 1/2 pattern from drag.

         13.  Reassemble cope and drag by setting drag on top of
              cope and bolt together.

    E.   Casting:

         1.   Pour molten iron into the channels to make the
              cast.  Cool to room temperature.

         2.   Remove frame and cut off sprues and risers.

    F.   Fettling:  

         1.   Remove the casting's pouring gates and risers.

         2.   Dress off the mold line or 'flash' and brush the
              raw casting clean.

    G.   Attach the replacement castings.  One of two methods may
         be used:

         1.   The casting may be friction fit with screwed
              connections such as 'tap bolts' (this is the
              traditional method).

              -OR-

         2.   The casting may be attached by welding (see 05010-13-R for guidance).

                         END OF SECTION