Continuous furnaces

HEAT TREATING FURNACES

Heat treating furnaces may be classified into two general categories, batch and continuous, and there are many different types in each group. The simplest furnaces are the direct-fired batch type, with manual controls. Installations for large production lines are more elaborate and are usually continuous furnaces, with automatic programming controls. In some cases controls are included in the furnace for controlling the atmosphere in the working chamber in order to obtain the desired surface condition. In general, the most common heat treatments performed in furnaces are annealing, normalizing, hardening, spheroidizing, tempering, carburizing, and stress relieving. As a rule heat treating furnaces are not designed for temperatures higher than 2000˚F and, in general they operate at from 800˚F to 1600˚F. Insulation is important in maintaining uniform temperatures and the furnaces are built tight to prevent infiltration of air or loss of special atmospheres. For handling batch loads of material to be heat treated, quenched and tempered quench tanks and cranes should be located so that there is a minimum of time expended in transporting material from the furnace to the quenching medium. Furnaces should also be so arranged as to have a second furnace available for taking material after quenching for such additional treatment as may be required. As a rule, three furnaces are used in operations of this type two for heating and one for tempering the work.

CONTINUOUS FURNACES

Continuous furnaces are designed with or without auxiliary equipment for atmosphere, control heat being applied either by direct or indirect firing, or electrically. They are especially adapted to zone heating and cooling. A furnace of this type is usually a rotary-hearth furnace used for heating pieces that are to be handled individually, such as gears, shells, cylinders, billets, etc. where they are to be fixture-quenched or handled individually for scale-free hardening without decarburization, for normalizing or drawing. This type of furnace is also used for heating smaller parts loaded in lightweight trays and for pack-carburizing. In this furnace charging and discharging are both accomplished at the same work station. Rotary-hearth furnaces are designed in a wide variety of sizes, to heat from just a few pounds up to 60 tons per hour.

Another type of continuous heat treating furnace is the roller-hearth type used for high production. This is particularly suited for uniform treatment of large quantities of the same material as in the bright annealing of tubes, stampings, drawn parts, etc., and for normalizing, annealing, hardening and tempering steel bars. It is also used extensively for annealing malleable irons, small steel and iron castings and forgings. It is also useful in normalizing flat-rolled products. The roller-hearth furnace is constructed ofasimple furnace or a line of furnaces for zone heating and cooling and, at times, such furnaces have an intermediate section with a tank for quenching.

Conveyor-type furnaces are similar to roller-hearth furnaces, except that in this case belt conveyors are used to carry materials through the furnace. They are particularly adopted for accurately heat treating small pieces which would not ride properly on the roller-hearth. The production rate, or heating cycle, of the continuous conveyor-type furnace iscontrolled by both temperature setting desired and the speed of the conveyor. The belt conveyors are made of an alloy material sufficiently at high temperature to carry the load and are resistant to heat, corrosion, oxidation and abrasion.

Task 1. Find in the text English equivalents to the following words:

піч періодичної дії, піч неперервної дії, полум’яна піч прямої дії, робоча камера, відпал, цементація, зняття напруження, ванна для закалювання, середовище закалювання, зонний нагрів, зонне охолодження, карусельна піч (з подом, що обертається), світле закалювання, піч з роликовим подом, світлий відпал, тверда цементація (навуглецювання), стальний брус, плоско-прокатаний.

Task 2. Match the words in column A with their meanings from column B:

A	B
1. annealing	a) охолодження, закалювання
2. normalizing	b) відпуск, пом’якшення
3. hardening	c) навуглецювання
4. tempering	d) відпал
5. carburizing	e) зняття напруження
6. stress relieving	f) зміцнення, закалювання
7. quenching	g) нормалізація
8. decarburizing	h) зневуглецювання

Task 3. Make up sentences using the information from the text:

Continuous furnaces A rotary-hearth furnace A roller-hearth furnace Conveyor-type furnace Heat treating furnaces

is used are used are not designed are adapted is suited

- bright annealing of tubes, stampings. - for heat treating small pieces which would not ride on the roller-hearth. - for temperatures higher than 2000˚F. - for heating pieces that are to be handled individually. - for pack-carburizing. - to zone heating and cooling. - for annealing malleable irons, small steel and iron castings. - for annealing and tempering steel bars.

Task 4. Give Ukrainian equivalents to the following words:

heat treating furnaces, manual control, automatic control, insulation, cranes, tempering the work, auxiliary equipment, heating and cooling, gears, billets, drawing, wide variety of sizes, stamping, malleable iron, heating cycle, conveyor.

Task 5. Answer the following questions:

1. What are the two main types of heat treating furnaces?

2. What are the simplest furnaces?

3. What kinds of heat treatments can be performed in furnaces?

4. What temperatures are usually used in heat treating furnaces?

5. Why is insulation important in furnaces for heat treatment?

6. Where should the quenched and tempered tanks be located?

7. What types of continuous furnaces do you know?

8. When is a rotary-hearth furnace used?

9. What are the sizes and capacity of rotary-hearth furnaces?

10. For what is a roller-hearth furnace especially suited?

11. What is the construction of a roller-hearth furnace?

12. What is the main difference between roller-hearth and conveyor-type furnaces?

13. By what is the production rate of conveyor-type furnaces controlled?

14. What material is used for making conveyors of conveyor-type furnaces?

Дата добавления: 2015-10-31