What Is a Crucible Furnace?

Crucible furnace is one of the simplest melting equipment. It is mainly used for melting non-ferrous metals with low melting point, such as copper, aluminum and its alloys. In this furnace, the alloy is melted in the crucible, and the heat is transferred to the charge through the crucible. The combustion products of the charge are not directly contacted. Therefore, the chemical composition of the alloy is hardly affected by the furnace gas, and the temperature of the alloy liquid is relatively uniform. advantage. Its disadvantages are low thermal efficiency, large fuel consumption, small crucible capacity, and poor working conditions. ^[1]

Crucible furnace is one of the simplest melting equipment. It is mainly used for melting non-ferrous metals with low melting point, such as copper, aluminum and its alloys. In this furnace, the alloy is melted in the crucible, and the heat is transferred to the charge through the crucible. The combustion products of the charge are not directly contacted. Therefore, the chemical composition of the alloy is hardly affected by the furnace gas, and the temperature of the alloy liquid is relatively uniform. advantage. Its disadvantages are low thermal efficiency, large fuel consumption, small crucible capacity, and poor working conditions.

During smelting, the metal is placed in a container called a crucible. The crucible is placed in a furnace and heated with diesel, heavy oil, gas or coke as fuel. According to different requirements, crucibles can be made of different materials such as graphite, refractory clay, cast iron. There are several types of furnace body: pit type, fixed type and rotary type. There is also a resistance crucible furnace, which generally has a small capacity and is mostly used in laboratories.

The crucible furnace has a simple structure, small investment, and fast production. It is widely used in the casting workshops of small and medium-sized non-ferrous alloy processing plants and machine manufacturing plants. However, the crucible furnace has low heat utilization rate, small output, and poor labor conditions, and large-scale production is no longer applicable. ^[1]

(1) Types of type crucible furnaces are categorized as follows by operation method.

Fixed crucible furnace The structure of the fixed crucible furnace for burning heavy oil includes the primary air and secondary air, and the secondary air enters the burner brick through the air conditioner.

Tilt-type crucible furnace Tilt-type crucible furnace is roughly divided into center tilt and forward tilt according to the position of tilt support.

Except manpower for center tilting fulcrum, electric motor, hydraulic pressure and hydraulic pressure are used. For example, it is called the front fulcrum hydraulic tilting type, and the center fulcrum electric tilting type.

The tilting state of the front fulcrum hydraulic tilting crucible furnace shows that the crucible furnace is best equipped with a front fulcrum, because it can ensure that the ratio of copper liquid to the furnace is always the same. The central fulcrum-type tapping position changes too much, and the operating conditions deteriorate significantly.

Fixed holding furnace for smelting light alloys The furnaces in and above, the upper part of the furnace cover is open, and the material is preheated by the flame. However, the special insulation furnace does not need to do this, but instead tries to reduce the smoke exhaust from the upper part by improving the operating conditions, and adopts the chimney exhaust method.

(2) Combustion device

There is one turbo blower and one turbo fan for the copper alloy crucible furnace widely used at present. The former is used to provide primary air and the latter is used to provide secondary air. The outstanding feature of this device is to play a role either to increase the melting speed or to control the melting atmosphere. The same method is used when burning heavy oil and gas. In addition, a rotating cup nozzle made of a nozzle and a blower is used. Although it is difficult to control the atmosphere in the furnace, it has the advantages of light weight, easy movement, and low price except for nozzles with special specifications.

(3) Controlled atmosphere in the furnace during melting

When melting a copper alloy, the atmosphere in the furnace has a great influence on the molten metal, especially the hydrogen gas is easily absorbed and the quality of the molten liquid is reduced.

The atmosphere in the furnace includes a reducing atmosphere and an oxidizing atmosphere. The former refers to carbon monoxide (

) And hydrogen (

), Which means oxygen (

) Has a high concentration, so that the melt is oxidized significantly. In order for the controlled atmosphere in the furnace to be somewhere in between,

with

. At present, the c characteristic value is generally used as an approximate measurement benchmark.

The definition of the characteristic value is:

Characteristic value =

.

In other words, the excess air coefficient of the heavy oil furnace is slightly larger than that of the gas furnace, otherwise it will not be completely burned. This section omits the discussion of the actual operation of the furnace, but it is important to understand the characteristics of various furnaces, especially to fully grasp the characteristics of the atmosphere in the furnace, which is extremely important for the production of good quality products. ^[2]

Coke crucible furnace

Coke crucible furnaces are divided into natural ventilation crucible furnaces and artificial ventilation crucible furnaces. As shown on the right

Working temperature: 1100

Maximum temperature: 1200 ° C

Temperature control method: intelligent programmable control

The fastest heating rate: 20 / min

Constant temperature accuracy: ± 1

Furnace door structure: top open

Working power: AC220V

Rated power: 3KW