casting faults (1)

FINS & FLASHING

Fins (also called FLASHING) occur when cast metal penetrates the fine cracks that can develop in a fired refractory mould. Metal penetration causes a fin like edge to be raised on the cast’s surface – though in extreme cases, molten metal can push right through the refractory wall and rupture the mould. Flashing can also flow into any cracks in the internal CORE MASS, leading to difficulties in extracting core refractory from the cast’s cavity. Most fins and flashes though are minor and easily removed by a cold chisel, coarse file or even a coarse grit abrasive cloth. This type of fault is most commonly seen in plaster and grog investments because refractory material is especially prone to cracking in the kiln. Flashing may also occur in sand casts – in this case the fin is usually raised by metal running into any hairline gaps between individual sand pieces, or across the PARTING LINE between poorly secured flask parts.

METAL PENETRATION OR ‘SPUDS’

SPUDS are globules of cast metal which have broken through the investment during casting. Small spuds are very similar in character to WELD SPATTER and are typically found in the grooves and depressions of textured surface detail. These small globules are easily removed with a cold chisel. Larger faults of this type are often seen in those parts of a cast that join in a sharp apex or junction (for example the armpit and groin areas of a figurative work). Large spuds can become firmly lodged within these tight angles and may require some force to remove. One effective method of removal is to locally heat the spud with a welding torch (taking care to heat the surrounding cast as little as possible). Once at red heat, the offending item can more easily be broken-up with a cold chisel.

MISALIGNED JOINTS

Misaligned joints are oten associated with sand piece moulds, particularly where piece parts have been poorly registered during the flask’s final assembly. Also known as LOBBED JOINTS, these misalignments are clearly visible as being offset and mismatched with the rest of the cast (rather like a protruding or recessed brick along a wall course). These faults are often treated as if they were a ‘patch’ repair. Rectification usually requires the affected section to be cut out of the cast, then reset to merge smoothly with the rest of the design. As lobbed joints usually also affect the wall thickness of the cast, this type of fault may sometimes be accompanied by other faults such as MIS-RUNS (on thin areas of the cast) or POROSITY (on thick areas), the problem being variable according to the direction of misalignment.

Misalignments can also occur in lost wax casts, either through incorrect registration of the reproduction mould (which should be rectified up during waxworking), or more usually, by the displacement of a section of the refractory mould during mould construction, firing or casting. Deliberate use of seams and misalignments to a creative end can be seen in the plaster and bronze studies by Auguste Rodin (1840-1917), many of which clearly show the position of seam lines and offset plaster waste moulded pieces. Similarly, the assemblage bronzes of Eduardo Paolozzi (1924-2005), often make use of misalignment, primarily through pattern cutting and manipulation, to achieve a strong constructed collage effect.

CASTING FAULTS 2 >

Section of flashing on a cast. The flash has been severe enough to move the cast surface either side of the fault resulting in a misalignment or 'lob' .

WARNING: Wear safety glasses/visor and protective clothing when using welding equipment, chisels and power tools. Be extra careful when working hot materials.

HOME | SEARCH | CONTRIBUTE


< FINE FINISHING FINS & FLASHING Fins (also called FLASHING) occur when cast metal penetrates the fine cracks that can develop in a fired refractory mould. Metal penetration causes a fin like edge to be raised on the cast’s surface – though in extreme cases, molten metal can push right through the refractory wall and rupture the mould. Flashing can also flow into any cracks in the internal CORE MASS, leading to difficulties in extracting core refractory from the cast’s cavity. Most fins and flashes though are minor and easily removed by a cold chisel, coarse file or even a coarse grit abrasive cloth. This type of fault is most commonly seen in plaster and grog investments because refractory material is especially prone to cracking in the kiln. Flashing may also occur in sand casts – in this case the fin is usually raised by metal running into any hairline gaps between individual sand pieces, or across the PARTING LINE between poorly secured flask parts. METAL PENETRATION OR ‘SPUDS’ SPUDS are globules of cast metal which have broken through the investment during casting. Small spuds are very similar in character to WELD SPATTER and are typically found in the grooves and depressions of textured surface detail. These small globules are easily removed with a cold chisel. Larger faults of this type are often seen in those parts of a cast that join in a sharp apex or junction (for example the armpit and groin areas of a figurative work). Large spuds can become firmly lodged within these tight angles and may require some force to remove. One effective method of removal is to locally heat the spud with a welding torch (taking care to heat the surrounding cast as little as possible). Once at red heat, the offending item can more easily be broken-up with a cold chisel. MISALIGNED JOINTS Misaligned joints are oten associated with sand piece moulds, particularly where piece parts have been poorly registered during the flask’s final assembly. Also known as LOBBED JOINTS, these misalignments are clearly visible as being offset and mismatched with the rest of the cast (rather like a protruding or recessed brick along a wall course). These faults are often treated as if they were a ‘patch’ repair. Rectification usually requires the affected section to be cut out of the cast, then reset to merge smoothly with the rest of the design. As lobbed joints usually also affect the wall thickness of the cast, this type of fault may sometimes be accompanied by other faults such as MIS-RUNS (on thin areas of the cast) or POROSITY (on thick areas), the problem being variable according to the direction of misalignment. Misalignments can also occur in lost wax casts, either through incorrect registration of the reproduction mould (which should be rectified up during waxworking), or more usually, by the displacement of a section of the refractory mould during mould construction, firing or casting. Deliberate use of seams and misalignments to a creative end can be seen in the plaster and bronze studies by Auguste Rodin (1840-1917), many of which clearly show the position of seam lines and offset plaster waste moulded pieces. Similarly, the assemblage bronzes of Eduardo Paolozzi (1924-2005), often make use of misalignment, primarily through pattern cutting and manipulation, to achieve a strong constructed collage effect. CASTING FAULTS 2 >


		Section of flashing on a cast. The flash has been severe enough to move the cast surface either side of the fault resulting in a misalignment or 'lob' . © ARTENERO PUBLISHING

		WARNING: Wear safety glasses/visor and protective clothing when using welding equipment, chisels and power tools. Be extra careful when working hot materials.

HOME \| SEARCH \| CONTRIBUTE