How to Choose fuming furnace?

As early as 29,000 years before Christ, people relied on specially designed fireplaces, which they used for the production of bricks and ceramics. At the beginning of the 17th century, the first cast-iron stoves appeared, which were used mainly in industry. The first gas stove became popular in the 18th century, and about 100 years later Thomas Ahearn developed the "archetype" of the electric stove.

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Muffle furnaces, which are still relevant today in science and research, first appeared on the market in the mid-19th century. Initially, they were used exclusively for the extraction of zinc in corresponding industrial plants. Today, they have continued to develop and are indispensable in laboratories for testing, burning, melting, drying, ashing, sintering and vulcanizing.

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Whether for hardening, annealing, forging, preheating, or debinding - laboratory furnaces are perfect for a wide variety of heat treatment applications and shine with maximum functionality and an outstanding performance portfolio. Thus, there are different types of laboratory furnaces for every need.

These generally differ in terms of their structural characteristics, their heating elements, for example, with regard to technologies. Other criteria include the furnace volume and the temperature that can be achieved. Whether elevator furnaces, chamber and muffle furnaces, tube furnaces, high-temperature chamber furnaces, or annealing and curing furnaces: whatever your choice, you will find it here. In addition, our online assortment holds an extensive selection of furnaces for the discerning customer. Compared to devices for industry, laboratory furnaces are significantly smaller and more compact. But what should you look for when choosing a suitable furnace? We have summarized our 5 most important tips for you:

The 5 best tips for choosing the right laboratory furnace

1. be aware of your own requirements

Always be aware of your own requirements before choosing the furnace, and then weigh the advantages of each. For example, the elevator furnace is a further development of the muffle or chamber furnace and is characterized by its compact furnace chamber and movable furnace floor. The advantages of this furnace variant are high user comfort, low wear and tear, and the fact that models in this product category are particularly low-maintenance.

Moreover, the heat elements, designed in a U-shape, can be removed from the bottom. This not only reduces the opening size, but also makes it easier to detect and eliminate potential weak points. If you don't want to give up a high performance portfolio and easy handling, the elevator furnace is just what you need.

2. precision is everything

If you place the highest value on precision and good usability in everyday laboratory work, high-temperature chamber ovens are ideal. Drying ovens are also recommended in this regard. These usually have a maximum working temperature of up to 300 °C. You can use them for numerous tasks, such as hot storage, sterilization or drying.

There are high-temperature chamber ovens and drying ovens in classic design, as a tabletop unit as well as in the mobile version. With metallic ovens, you benefit from excellent temperature uniformity inside the oven chamber, ideal atmospheric unity, and a final vacuum that meets your needs. Modern high-temperature chamber furnaces with metallic insulation are predestined for metallization, metal injection molding and experiments requiring a carbon-free atmosphere.

Fuming Furnace Structure

The four walls of the fuming furnace are all composed of water jackets. The lowermost water jacket on the side is provided with a tuyere. The inner wall of the water jacket is welded with Φ16mm and 50mm long pins, and the distance between the nails is 50mm, so that the condensed slag adheres to it and forms slag layer protects the water jacket and reduces heat loss.

There is a slag outlet on the water jacket at the front end of the furnace.

The lower layer of the water jacket and the inclined flue are water-cooled and circulated, and the upper layer of the water jacket is cooled by vaporization.

The tuyere structure adopts a tuyere with a ball valve, and there are two branch pipes. The one near the water jacket is called the primary air coal pipe, and the one outside is the secondary air pipe.

In order to prevent pulverized coal from escaping out of the furnace, the secondary air pressure is slightly higher than the primary air pressure (about 100mmHg).

There are three air outlets on the upper part of the furnace, which is convenient for operation and observation, and can inhale air oxidized metal vapor.

Fuming Furnace Operational

In order to achieve good results in the fuming process, the following conditions must be well controlled:temperature, fuel and air supply volume, slag composition, molten pool depth.

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1. Temperature

If the temperature is too high (such as exceeding °C), iron deposits or Zn-Fe, Sn-Fe alloys may be formed, which is harmful to the fuming operation. If the temperature is too low, the reduction rate of metal oxides will slow down, the volatilization rate will decrease, the fluidity of the slag will deteriorate, and there may even be a danger of furnace formation, so the temperature in the fuming practice is kept in the range of - °C.

2. Fuel and air supply volume

The most active factor affecting the volatilization rate in the fuming process is the air supply volume. Because the temperature in the furnace, the ratio of CO/CO2, the amount of gas, and the vapor pressure of the metal are all related to the air supply volume. The volume of the air supply depends on the pulverized coal consumption and the air utilization coefficient (α). The larger the air utilization coefficient, the higher the thermal effect of the fuel, the greater the partial pressure of CO2, and the higher the temperature in the furnace; the smaller the air utilization coefficient , the thermal effect is reduced, the partial pressure of CO becomes larger, and the reducing ability is enhanced.

Pulverized coal is both a reducing agent and an exothermic agent in the fuming process, so the CO/CO2 should have an appropriate ratio during combustion. The air utilization factor actually adopted by the factory is variable. Usually, at the beginning of fuming, an air utilization factor close to 1.0 causes almost all carbon to be burned into CO2 to increase the temperature of the slag. In the reduction stage, adjust the air utilization factor to make carbon into CO as much as possible to improve the reduction ability.

3. Slag composition

In practical the actual zinc content of the slag feed into the fuming furnace should be >6%. Below 4%, fuming treatment is uneconomical.

Regarding the effect of slag composition on the volatilization rate of zinc, it can be summarized as follows:

The increase of CaO content can increase the volatilization rate of zinc;

The increase of FeO content in slag has little effect on ZnO activity;

The content of SiO2 increases, and the volatilization rate of zinc decreases. Therefore, the silicic acidity of the slag is preferably in the range of 1.1 to 1.2.

4. Molten pool depth

The thickness of the slag layer in production is generally in the range of 700-mm above the tuyere area.