Used Melting Furnaces for Sale — 44

Melting of metals, glass, and other materials has been a vital manufacturing process for several thousand years, producing molten liquids that can be poured and solidified into useful shapes. Since the dawn of the industrial age, the tremendous progress in the melting process equipment (melting furnaces), the range of molten materials, control on thermal behavior and the complexity of the finished products has enabled cast components to be an integral part of various products such as automobiles, power generators, oil pipelines, medical instruments, etc. The process of melting is accomplished for years with the help of a furnace. A furnace is an equipment to melt ferrous or non-ferrous metals for casting or simply heat materials for changing their shape or for altering their mechanical and metallurgical properties (heat treatment). An ideal furnace should melt as much of material as possible to a uniform temperature with the least possible fuel and labor.

Furnace and its Parts

A typical furnace is constructed with the help of the following principal components:

• Steel Shell – For supporting and casing
• Refractory chamber – Made of insulating materials to retain heat at higher operating temperatures
• Hearth - To support or carry the steel. It consists of refractory materials or an arrangement of metallic supports which may be water cooled.
• Burners – To raise and maintain the required temperature in the chamber by using liquid or gaseous fuels.
• Chimney – For removing combustion exhaust gases from the heating chamber
• Charging and discharging doors – Openings through which the metal is introduced into the chamber and also for removing the molten metal.
• Loading and unloading devices – Roller tables, conveyors, charging machines and furnace pushers are the commonly used equipments for loading and unloading charges of the furnace.

Efficiency of a Furnace

Thermal efficiency of any heating equipment is defined as the ratio of heat delivered to a material and heat supplied to the heating equipment. For most of the heating equipments, a large amount of the heat supplied is wasted in the form of exhaust gases. Furnaces operate with relatively low efficiencies at around 7% when compared to other combustion equipments such as boilers which are very efficient at an efficiency rate of 90%. The low efficiency of melting furnaces can be attributed to the high operating temperatures in the furnace and significant heat losses. The major factor which affects the energy efficiency of a furnace is the heat losses due to the following reasons:

• Heat storage in the furnace structure

• Losses from the furnace outside walls or structure

• Heat transported out of the furnace by the load conveyors, fixtures, trays, etc.

• Radiation losses from openings, hot exposed parts, etc.

• Heat carried by the cold air infiltration into the furnace

• Heat carried by the excess air used in the burners.

A furnace is carefully selected by giving due consideration to the following factors: type and composition of the metal to be melted, maximum temperature required (melting point of the metal), delivery rate of the molten metal (pouring rate), mode of discharging the molten metal, initial set-up and operational cost.

Types of Furnaces

Furnaces can be classified based upon several aspects into various types. Furnaces are broadly classified into two types based on the heat generation method as combustion melting furnaces which use fuels to melt and electric melting furnaces in which electricity is utilized to melt the metal. Combustion melting furnaces can be further sub-divided into three types based on the kind of fuel used: oil fired, gas fired and coal fired. Furnaces in general are also classified based on the mode of charging as Intermittent or Batch, Periodical (Forging, Pot melting furnaces) and Continuous (Pusher, Walking beam, Walking hearth and rotary hearth melting furnaces). One more way of categorizing the melting furnaces is based on the mode of waste heat recovery (Recuperative and Regenerative). Based on the mode of heat transfer to the stock, the melting furnaces are classified into two types as Radiation (from the flame, hot combustion products, furnace walls and roof) and Convection (movement of hot gases over the surface of the metal).

Some of the commonly used melting furnaces are discussed below:

• Crucible Furnaces – This is the least expensive melting method preferred for melting small volumes of non-ferrous metals such as bronze, brass, alloys of zinc and aluminium. Metal is melted without direct impingement of the burning fuel mixture with this small melting furnace.
• Cupola Furnaces – They are vertical cylindrical furnace equipped with a tapping spout near base and are used primarily for the melting of cast iron in the large tonnage foundries. The energy efficiency of cupola melting ranges from 40 to over 70%.
• Induction Melting Furnace – Heating in an induction furnace is based on the basic principle of electromagnetic induction and joule’s heating effect. It employs an electric coil which produces a charge.
• Electric Melting Furnace (Arc) – They use electrodes that are lowered to strike an arc on the cold scrap and the arc provides heat by radiation and current resistance through the metal to melt the scrap. An inherent advantage of melting by electrical arc is the lower metal loss.
• Immersion Heaters – They are typically used for low temperature melting of zinc alloys. The heat is generated by combustion or electrical resistance inside a tube submerged in molten material.
• Oxy Fuel Furnace – It uses a fuel gas such as propane, natural gas or acetylene combined with oxygen and heat from combustion melts the charge.

Melt Furnace Manufacturers

SECO/WARWICK, GADDA, Can-Eng Furnaces International Limited, Fives Stein, UTTIS, Inductotherm, CARBOLITE, Ambrell, Topcast and Nabertherm are some of the companies worldwide involved in the production of various kinds of melting furnaces.