investment casting ledger end scaffolding accessories for scaffolding.
 
Specifications:
 

 

 
 
 
 
 
 
Description:
Investment casting is an industrial process based on and also called lost-wax casting, one of the oldest
 
known metal-forming techniques.From 5,000 years ago, when beeswax formed the pattern, to today’s high-
 
technology waxes, refractory materials and specialist alloys, the castings allow the production of
 
components with accuracy, repeatability, versatility and integrity in a variety of metals and high-
 
performance alloys. Lost-foam casting is a modern form of investment casting that eliminates certain steps in the process.
 
There are a variety of materials that can be used for the investment casting process, including stainless
 
steel alloys, brass, aluminum, and carbon steel. The material is poured into a ceramic cavity designed to
 
create an exact duplicate of the desired part. Investment casting can reduce the need for secondary
 
machining by providing castings to shape.
 
Casts can be made of the wax model itself, the direct method; or of a wax copy of a model that need not be
 
of wax, the indirect method. The following steps are for the indirect process which can take two days to one
 
week to complete.
 
Produce a master pattern: An artist or mould-maker creates an original pattern from wax, clay, wood,
 
plastic, steel, or another material.
Mouldmaking: A mould, known as the master die, is made of the master pattern. The master pattern may
 
be made from a low-melting-point metal, steel, or wood. If a steel pattern was created then a low-melting-
 
point metal may be cast directly from the master pattern. Rubber moulds can also be cast directly from the
 
master pattern. The first step may also be skipped if the master die is machined directly into steel.
Produce the wax patterns: Although called a wax pattern, pattern materials also include plastic and frozen
 
mercury. Wax patterns may be produced in one of two ways. In one process the wax is poured into the
 
mold and swished around until an even coating, usually about 3 mm (0.12 in) thick, covers the inner surface
 
of the mould. This is repeated until the desired thickness is reached. Another method is filling the entire
 
mould with molten wax, and let it cool, until a desired thickness has set on the surface of the mould. After
 
this the rest of the wax is poured out again, the mould is turned upside down and the wax layer is left to
 
cool and harden. With this method it is more difficult to control the overall thickness of the wax layer.
 
If a core is required, there are two options: soluble wax or ceramic. Soluble wax cores are designed to melt
 
out of the investment coating with the rest of the wax pattern, whereas ceramic cores remain part of the
 
wax pattern and are removed after the workpiece is cast.
 
Assemble the wax patterns: The wax pattern is then removed from the mould. Depending on the
 
application multiple wax patterns may be created so that they can all be cast at once. In other applications,
 
multiple different wax patterns may be created and then assembled into one complex pattern. In the first
 
case the multiple patterns are attached to a wax sprue, with the result known as a pattern cluster, or tree;
 
as many as several hundred patterns may be assembled into a tree. Foundries often use registration marks
 
to indicate exactly where they go.The wax patterns are attached to the sprue or each other by means of a
 
heated metal tool.The wax pattern may also be chased, which means the parting line or flashing are rubbed
 
out using the heated metal tool. Finally it is dressed, which means any other imperfections are addressed
 
so that the wax now looks like the finished piece.
 
Investment: The ceramic mould, known as the investment, is produced by three repeating steps: coating,
 
stuccoing, and hardening. The first step involves dipping the cluster into a slurry of fine refractory material
 
and then letting any excess drain off, so a uniform surface is produced. This fine material is used first to
 
give a smooth surface finish and reproduce fine details. In the second step, the cluster is stuccoed with a
 
coarse ceramic particle, by dipping it into a fluidised bed, placing it in a rainfall-sander, or by applying by
 
hand. Finally, the coating is allowed to harden. These steps are repeated until the investment is the
 
required thickness, which is usually 5 to 15 mm (0.2 to 0.6 in). Note that the first coatings are known as
 
prime coats. An alternative to multiple dips is to place the cluster upside-down in a flask and then liquid
 
investment material is poured into the flask. The flask is then vibrated to allow entrapped air to escape and
 
help the investment material fill in all of the details.Common refractory materials used to create the
 
investments are: silica, zircon, various aluminium silicates, and alumina. Silica is usually used in the fused
 
silica form, but sometimes quartz is used because it is less expensive. Aluminium silicates are a mixture of
 
alumina and silica, where commonly used mixtures have an alumina content from 42 to 72%; at 72%
 
alumina the compound is known as mullite. During the primary coat, zircon-based refractories are
 
commonly used, because zirconium is less likely to react with the molten metal.Chamotte is another
 
refractory material that has been used. Prior to silica, a mixture of plaster and ground up old molds was
 
used.The binders used to hold the refractory material in place include: ethyl silicate (alcohol-based and
 
chemically set), colloidal silica (water-based, also known as silica sol, set by drying), sodium silicate, and a
 
hybrid of these controlled for pH and viscosity.
Dewax: The investment is then allowed to completely dry, which can take 16 to 48 hours. Drying can be
 
enhanced by applying a vacuum or minimizing the environmental humidity. It is then turned upside-down
 
and placed in a furnace or autoclave to melt out and/or vaporize the wax. Most shell failures occur at this
 
point because the waxes used have a thermal expansion coefficient that is much greater than the
 
investment material surrounding it, so as the wax is heated it expands and induces great stresses. In order
 
to minimize these stresses the wax is heated as rapidly as possible so that the surface of the wax can melt
 
into the surface of the investment or run out of the mold, which makes room for the rest of the wax to
 
expand. In certain situations holes may be drilled into the mold beforehand to help reduce these stresses.
 
Any wax that runs out of the mold is usually recovered and reused.
 
Burnout & preheating: The mold is then subjected to a burnout, which heats the mold between 870 °C
 
and 1095 °C to remove any moisture and residual wax, and to sinter the mold. Sometimes this heating is
 
also used as the preheat, but other times the mold is allowed to cool so that it can be tested. If any cracks
 
are found they can be repaired with ceramic slurry or special cements. The mold is preheated to allow the
 
metal to stay liquid longer to fill any details and to increase dimensional accuracy, because the mold and
 
casting cool together.
 
Pouring: The investment mold is then placed cup-upwards into a tub filled with sand. The metal may be
 
gravity poured, but if