In a
foundryA foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...
, a
ladle is a vessel used to transport and pour out molten metals. Ladles range in size from small hand carried vessels that resemble a kitchen
ladleA ladle is a type of spoon used to scoop up and serve soup, stew, or other foods. Although designs vary, a typical ladle has a long handle terminating in a deep bowl, frequently with the bowl oriented at an angle to the handle to facilitate lifting liquid out of a pot or other vessel and conveying...
and hold 20 kilograms (44.1 lb) or to large steelmill ladles that hold up to 300 tonne. Many non-ferrous foundries also use ceramic crucibles for transporting and pouring molten metal and will also refer to these as ladles.
Types
The basic term is often pre-fixed to define the actual purpose of the ladle. The basic ladle design can therefore include many variations that improve the usage of the ladle for specific tasks. For example:
- Casting ladle: a ladle used to pour molten metal into moulds to produce the casting.
- Transfer ladle: a ladle used to transfer a large amount of molten metal from one process to another. Typically a transfer ladle will be used to transfer molten metal from a primary melting furnace to either an holding furnace or an auto-pour unit.
- Treatment ladle: a ladle used for a process to take place within the ladle to change some aspect of the molten metal. A typical example being to convert cast iron to ductile iron by the addition of various elements into the ladle.
Unless the ladle is to be used with alloys that have very low temperature melting point, the ladle is also fitted with a refractory lining. It is the refractory lining that stops the steel vessel from suffering damage when the ladle is used to transport metals with high melting temperatures that, if the molten metal came in direct contact with the ladle shell, would rapidly melt through the shell. Refractory lining materials come in many forms and the right choice very much depends on each foundry's working practices. Traditionally ladles used to be lined using pre-cast firebricks however refractory concretes have tended to supersede these in many countries.
Foundry ladles are normally rated by their working capacity rather than by their physical size. Hand-held ladles are typically known as
handshank ladles and are fitted with a long handle to keep the heat of the metal away from the person holding it. Their capacity is limited to what a man can safely handle. Larger ladles are usually referred to as geared crane ladles. Their capacity is usually determined by the ladle function. Small hand-held ladles might also be crucibles that are fitted with carrying devices. However, in most foundries, the foundry ladle refers to a steel vessel that has a lifting bail fitted so that the vessel can be carried by an overhead crane or monorail system and is also fitted with a mechanical means for rotating the vessel, usually in the form of a gearbox. The gearbox can either be manually operated or powered operation. (See the paragraph below for further details).
For the transportation of very large volumes of molten metal, such as in
steel millA steel mill or steelworks is an industrial plant for the manufacture of steel.Steel is an alloy of iron and carbon. It is produced in a two-stage process. First, iron ore is reduced or smelted with coke and limestone in a blast furnace, producing molten iron which is either cast into pig iron or...
s, the ladle can run on wheels, a purpose-built
ladle transfer carA ladle transfer car is a material handling tool which is used in foundries. It carries a metal ladle from one location to another for processing molten liquid metal.. It can also be called a molten steel transporter or a Tundish transfer car....
or be slung from an overhead crane and will be tilted using a second overhead lifting device.
The most common shape for a ladle is a vertical cone, but other shapes are possible. Having a tapered cone as the shell adds strength and rigidity to the shell. Having the taper also helps when it comes time to remove the refractory lining. However straight sided shells are also fabricated as are other shapes.
The most common of these other shapes is known as a drum ladle and is shaped as a horizontal cylinder suspended between two
bogieA bogie is a wheeled wagon or trolley. In mechanics terms, a bogie is a chassis or framework carrying wheels, attached to a vehicle. It can be fixed in place, as on a cargo truck, mounted on a swivel, as on a railway carriage/car or locomotive, or sprung as in the suspension of a caterpillar...
s. Large versions, often having capacities in excess of 100 tonnes are used in steel mills are often referred to as torpedo ladles. Torpedo ladles are commonly used to transport liquid
ironIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
from a
blast furnaceA blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally iron.In a blast furnace, fuel and ore and flux are continuously supplied through the top of the furnace, while air is blown into the bottom of the chamber, so that the chemical reactions...
to another part of the steel mill. Some versions are even adapted so that they can be carried on special bogies that can be transported by either road or rail.
Pour designs
Ladles can be "lip pour" design, "teapot spout" design, lip-axis design" or "bottom pour" design:
- For lip pour design the ladle is tilted and the molten metal pours out of the ladle like water from a pitcher
A pitcher is a container with a spout used for storing and pouring contents which are liquid in form. Generally a pitcher also has a handle, which makes pouring easier.A ewer is a vase-shaped pitcher, often decorated, with a base and a flaring spout...
.
- The teapot spout design, like a teapot, takes liquid from the base of the ladle and pours it out via a lip-pour spout. Any impurities in the molten metal will form on the top of the metal so by taking the metal from the base of the ladle, the impurities are not poured into the mould. The same idea is behind the bottom pour process.
- Lip-axis ladles have the pivot point of the vessel as close to the tip of the pouring spout as can be practicable. Therefore as the ladle is rotated the actual pouring point has very little movement. Lip-axis pouring is often used on molten metal pouring systems where there is a need to automate the process as much as possible and the operator controls the pouring operation at a remote distance.
- For bottom pour ladles, a stopper rod is inserted into a tapping hole in the bottom of the ladle. To pour metal the stopper is raised vertically to allow the metal to flow out the bottom of the ladle. To stop pouring the stopper rod is inserted back into the drain hole. Large ladles in the steelmaking industry may use slide gates below the taphole.
Ladles can be either open-topped or covered. Covered ladles have a (sometimes removable) dome-shaped lid to contain
radiant heatThermal radiation is electromagnetic radiation generated by the thermal motion of charged particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation....
; they lose heat slower than open-topped ladles. Small ladles do not commonly have covers, although a ceramic blanket may be used instead (where available).
Medium and large ladles which are suspended from a crane have a bail which holds the ladle on shafts, called
trunnionA trunnion is a cylindrical protrusion used as a mounting and/or pivoting point. In a cannon, the trunnions are two projections cast just forward of the centre of mass of the cannon and fixed to a two-wheeled movable gun carriage...
s. To tilt the ladle a gearbox is used and this is typically a
worm gearA worm drive is a gear arrangement in which a worm meshes with a worm gear...
. The gear mechanism may be hand operated with a large wheel or may be operated by an electric motor or pneumatic motor. Powered rotation allows the ladle operator to be moved to a safe distance and control the rotation of the ladle via a pendant or radio remote control. Powered rotation also allows the ladle to have a number of rotation speeds which may be beneficial to the overall casting process. Powered rotation obviously also reduces the effort required by the ladle operator and allows high volumes of molten metal to be transferred and poured for long periods without operator fatigue. Where the ladle is fitted with a manually operated gearbox, the type of gearbox most commonly used is the worm and wheel design because in most practical circumstances, and when correctly maintained it can be considered as "self-locking" and doesn't need an internal friction
brakeA brake is a mechanical device which inhibits motion. Its opposite component is a clutch. The rest of this article is dedicated to various types of vehicular brakes....
to regulate the tilting speed of the ladle. Other types of gear system can be also be used but they have to be fitted with an additional braking system that can hold the ladle if the operator takes his hand off the hand-wheel.
Lip-axis ladles may also use hydraulic rams to tilt the ladle. The largest ladles are un-geared and are typically poured using a special, two-winch crane, where the main winch carries the ladle while the second winch engages a lug at the bottom of the ladle. Raising the second winch then rotates the ladle on its trunnions.
Ladles are often designed for special purposes such as adding
alloyAn alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...
s to the molten metal. Ladles may also have porous plugs inserted into the base, so inert gases can be bubbled through the ladle to enhance alloying or metallic treatment practices.
External links
- About ladles and perlite
Perlite is an amorphous volcanic glass that has a relatively high water content, typically formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently...
used in a foundryA foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal in a mold, and removing the mold material or casting after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron...