Duplicating Cast Iron Ornament
- Procedure code:
- Developed For Hspg (Nps - Sero)
- Metal Materials
- Last Modified:
Margot Gayle, David Look, John Waite. Metals in America's Historic Buildings. Washington,DC: National Park Service, 1995.
L. William Zahner. Architectural Metals. New York: John Wiley & Sons, 1995.
- 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.
- Recreating damaged or missing pieces is required when deterioration is so great that patching with metal filler or sheet metal is not sufficient.
- See 01100-07-S for general project guidelines to be reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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).
- For general information on the characteristics, uses and problems associated with cast iron, see 05010-04-S.
Also do a web search, review periodicals oriented to the building trades including among others: Traditional Building, Period Home; check local industrial directories; contact local preservation architects, general contractors, and metal subcontactors.
- Casting Companies:
- Robinson Iron Corporation www.robinsoniron.com
- New castings as required (see manufacturers above)
- Casting flasks or boxes:
- Use a 2-part mold for a solid casting with relief on both sides.
- Use an open top mold for castings to have one side with relief and the other side flat.
- Use a 2 or more part mold for hollow castings.Note: In this type of casting, the parts are bolted, brazed or welded together.
- "Green Sand" for making the molds:
- "Green" refers to its wet consistency. It is actually black in color.
- 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.
- Parting sand
- Sprues: Used to form channels for pouring molten iron through.
- Screws and bolts
- Ni rods (Nickel Alloy welding rods)
- Wiping cloths
- Eye and skin protection
- Welding equipment
- Electric drill
- 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:
- Wear - especially moving parts such as hardware.
- Parts - which have failed or which are unsecured, broken, cracked, missing, distorted, or loose (check screws and bolts).
- Paint - coating failures such as chips, losses, peeling, checks, bubbling, and wear.
- Rust corrosion - caused by moisture, sea water and sea air, deicing salts, acids, soils, gypsum plasters, magnesium oxychloride cements, ashes, clinkers, and sulfur compounds.
- 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.
- Determine the source of the moisture which causes the deterioration.
- Determine if the feature can be salvaged.
- Measure the dimensions of the various metal parts needing replacement.
NOTE: USUALLY EVERY DIFFERENT ELEMENT TO BE RE-CASTED REQUIRES EITHER ONE PATTERN OR ONE PROTOTYPE FROM WHICH SAND MOLDS CAN BE TAKEN.
- 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.
- Obtain an exact duplicate of the piece needed to be duplicated, or provide the foundry with one of the following:
- 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.
- A scaled photograph or good detail drawing of the item.
- Original specifications or constructiondrawings describing the piece.
- 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.
- 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.
- Pattern making: Making an original from which one or more castings can be made.
- Patterns are typically made from timber, glass reinforced plastic, wax, plaster or another metal.
- Patterns are typically produced by a specialist.
- Patterns should be made slightly over-sized to allow for contraction.
- Molding (for a casting with relief on both sides):
- Assemble mold board and risers.
- Dust 1/2 of pattern with parting sand and place in bottom half of mold or "Cope".
- Fill cope with sand and ram until thoroughly packed.
- Place mold board on top of the cope and turn over.
- Remove mold board from bottom of cope (now inverted) and place other 1/2 of pattern.
- Dust face of "green sand" and pattern with parting sand.
- Set top of mold or "Drag" in place on top of cope. Place sprues vertically on either end of pattern.
- Fill drag with sand and ram until thoroughly packed.
- Remove sprues and place mold board on top of drag.
- Separate cope and drag and invert drag.
- Remove 1/2 pattern from cope and cut flow gates at ends of pattern impression to connect with channels.
- Remove 1/2 pattern from drag.
- Reassemble cope and drag by setting drag on top of cope and bolt together.
- Pour molten iron into the channels to make the cast. Cool to room temperature.
- Remove frame and cut off sprues and risers.
- Remove the casting's pouring gates and risers.
- Dress off the mold line or 'flash' and brush the raw casting clean.
- Attach the replacement castings. One of two methods may be used:
- The casting may be friction fit with screwed connections such as 'tap bolts' (this is the traditional method).
- The casting may be attached by welding (see 05010-13-R for guidance).