Arrangement and a Method For Heating Metal Objects
The invention relates to a an arrangement and a method for heating metal objects such as metal bars by convection. The metal objects are passed on a conveyor through a series of chambers where hot air is blown through the conveyor. The temperature is controlled by a sensor connected to a control devise such as a thyristor.
The present invention generally relates to the field of heating metal objects, in particular such objects as elongate metal bars.
BACKGROUND OF THE INVENTIONIt is a known practice to heat a metal object before performing a working operation on the object. In for example U.S. Pat. No. 4,343,209, a method is disclosed in which bars are heated by a heating coil at localized zones along the length of the bars. The bars are incrementally advanced one piece length at specified intervals through the heating coil to a shear. After each incremental advance of a bar, a piece is sheared from the end of the bar at the then presented heated zone. It is stated that the disclosed method makes it possible to shear without substantial cracking or shattering.
It is an objective of the present invention to provide an improved arrangement and an improved method for heating metal objects in order to facilitate cutting of the metal objects. Such an improved arrangement and improved method may advantageously be used for the purpose of heating metal objects that will subsequently be cut into smaller pieces.
DISCLOSURE OF THE INVENTIONThe invention relates to an arrangement for heating metal objects. The inventive arrangement comprises a shell that envelops an inner space. The shell has an entry opening and an exit opening. Inside the shell inner walls divide the inner space into a rear chamber, at least one intermediate chamber and a forward chamber. A permeable conveyor extends from the entry opening of the shell to the exit opening of the shell through the rear, intermediate and forward chamber. In this way, objects loaded on the conveyor can be transported through the chambers. In the at least one intermediate chamber, a fan is arranged to direct a flow of gas towards the conveyor and objects placed on the conveyor. A heating element is also arranged in the intermediate chamber. The heating element may heat a gas flowing from the fan before the gas reaches the conveyor. The chambers are connected to each other in such a way that at least one outlet of the at least one intermediate chamber communicates with the rear chamber, at least one outlet of the intermediate chamber communicates with the forward chamber and at least one inlet of the intermediate chamber communicates with outlets of the rear and forward chambers. In this way, operation of the fan will generate a rear circulation of gas passing twice through the conveyor and a forward circulation of gas also passing twice through the conveyor.
In one embodiment, a temperature sensor is located inside the shell and connected to a control device that controls the temperature of the heating element as a function of a nominal value and a valued indicated by the temperature sensor. The temperature sensor may be placed in the forward chamber between the conveyor and outlet of the forward chamber.
In some embodiments, the arrangement comprises a plurality of fans and a plurality of heating elements arranged in rows extending perpendicularly to the direction of movement of the conveyor. The heating arrangement may be followed by a cutting device that cuts metal objects that have been heated by the heating arrangement.
The invention also relates to a method for heating metal objects. The method comprises passing the metal objects on a permeable conveyor through an inner space enclosed by a shell and divided by inner walls into a rear chamber, at least one intermediate chamber and a forward chamber. As the conveyor passes through the at least one intermediate chamber, air is heated and the heated air is blown through the conveyor. A first part of the heated air that has passed through the conveyor in the at least one intermediate chamber is diverted into a rear circulation of air. The rear circulation of air is passed through the conveyor in the rear chamber and back to the at least one intermediate chamber. A second part of the heated air that has passed through the at least one intermediate chamber is diverted into a forward circulation of air. The forward circulation of air passes through the conveyor in the forward chamber and back to the at least one intermediate chamber.
In an embodiment of the invention, the temperature of the air is measured inside the shell and the heating of air is controlled as a function of a nominal value and the measured value. A suitable nominal value for the temperature may be 70° C. If the temperature is measured, this may be done in the forward chamber at such a location that the temperature of the air is measured after it has passed through the conveyor in the forward chamber.
In an advantageous embodiment, the air is heated by a heater located inside the at least one intermediate chamber and the temperature of the heater is kept in the range of 200° C.-300° C.
The metal objects are elongate metal bars. The heating operation may advantageously be followed by a subsequent operation such as cutting of metal bars. The heating operation itself can then be regarded as a part of a method for heating and cutting metal bars.
With reference to
The heating arrangement 1 comprises a shell 2 that envelops an inner space 3. The shell 2 has an entry opening 4 and an exit opening 5. Inside the shell 2, inner walls 6, 7 divide the inner space 3 into a rear chamber 8, at least one intermediate chamber 9 and a forward chamber 10. The conveyor 17 is permeable to air and extends from the entry opening 4 of the shell 2 to the exit opening 5 of the shell 2 through the rear 8 intermediate 9 and forward chamber 10. In this way, objects 19 loaded on the conveyor 17 can be transported through the chambers 8, 9, 10 from the entry opening 4 to the exit opening 5. In the embodiment of
In the at least one intermediate chamber 9, a fan 21 is arranged to direct a flow of air (or possibly another gas) towards the conveyor 17 and objects 19 placed on the conveyor 17. A heating element 22 in the intermediate chamber 9 is arranged to heat air flowing from the fan 21 before the air reaches the conveyor 17. In the embodiment illustrated in
The chambers 8, 9, 10 are connected to each other in such a way that at least one outlet 14 of the at least one intermediate chamber 9 communicates with the rear chamber 8, 10. At least one outlet 14 of the intermediate chamber 9 communicates with the forward chamber 10 and at least one inlet 13 of the intermediate chamber 9 communicates with outlets 12, 16 of the rear and forward chambers 8, 10. In this way, operation of the fan 21 will generate a rear circulation of air passing twice through the conveyor 17 and a forward circulation of air also passing twice through the conveyor 17. As indicated in
In one embodiment, a temperature sensor 25 is located inside the shell 2 and connected to a control device 26 that controls the temperature of the heating element 22 as a function of a nominal value and a valued indicated by the temperature sensor 25. The temperature sensor 25 is preferably placed in the forward chamber 10 between the conveyor 17 and outlet 16 of the forward chamber 10 but it could also be located on other places, for example in the intermediate chamber. The heating element 22 may be, for example, an electric coil.
As indicated in
The operation of the inventive arrangement is as follows. Metal objects 19 are passed on the permeable conveyor 17 through the inner space 3 enclosed by the shell 2 and through the chambers 8, 9, 10 of the inner space. In
When the hot air has passed the conveyor 17 and transferred a part of its heat energy to the metal objects 19, a first part of the heated air is diverted into a rear circulation of air RA that is passed to the rear chamber 8, through the conveyor 17 in the rear chamber 8 and back to the at least one intermediate chamber 9. A second part of the heated air that has passed through the conveyor 17 in the intermediate chamber 9 is diverted into a forward circulation of air FA that is passed to the forward chamber 10 and through the conveyor 17 as the conveyor 17 passes through the forward chamber 10. The air in the forward circulation of air FA is then sent back to the intermediate chamber 9.
It is preferable that the motor M of the fan 21 be located inside the shell 2 of the arrangement. Locating the motor M outside the shell 2 would result in a more complicated design. If the motor M is an electric motor, is must realistically be expected that the motor will fail or collapse if the ambient temperature becomes to high. For currently available electric motors that the inventors are aware of, ambient temperature should preferably not exceed 70° C. In a preferred embodiment of the invention, the temperature of the air is measured inside the shell 2 and the heating of air is controlled as a function of a nominal value and the measured value. In the embodiment illustrated in
If electric coils are used as heating elements, the temperature of the coil or coils 22 could be kept in the range of 22 is kept in the range of 200° C.-300° C. such that the air that reaches the conveyor in the intermediate chamber 9 has a temperature which is also in the range of 200° C.-300° C. The life expectancy of electric coils is highly dependent on the temperature to which the coils are heated. For such coils that are currently commercially available, the life expectancy of the coils is almost unlimited if the temperature does not exceed 300° C. Of course, the temperature of the air will be much lower after the air has passed twice through the conveyor 17 and a part of the heat in the air has been transferred to the metal objects 19. The metal objects to be heated could normally be heated to temperatures well over 300° C. without harmful effects to the metal objects themselves. The temperatures employed are instead limited by the motor M or the desired life expectancy of the coils 22.
As previously mentioned, the heating arrangement 1 may be followed by a cutting device 31. With reference to
In one realistic embodiment, the heating arrangement and method could be used to heat stainless steel bars having a length of about 5.5 m and a diameter of 16-25 mm. With currently available cutting devices, such bars can subsequently be cut into 180 pieces in a period of about 50 seconds. This means that new bars must be continuously and rapidly supplied.
The inventors have found that the use of heated air entails an advantage compared to the use of heating by induction. When objects such as elongate metal bars 19 are heated, it may be difficult to achieve an even heating of the bars when inductive heating is used. For example, when elongate bars of stainless nickel steel are heated by induction, the surface of the bars may become heated to a temperature that is harmful while inner parts of the bar are still to cold to allow the bar to be cut as easily as one would desire. Moreover, the inventors have found that objects with a bright surface are more difficult to heat by induction. Objects with a bright surface could include objects of stainless steel. Stainless steel bars have a poor thermal conductivity which makes it more difficult to heat such objects. The inventors have found that heating metal objects such as stainless steel bars by convection is more efficient than heating the metal objects by induction. A practical way of heating by convection is to pass the bars through a flow of heated air. As previously indicated, one realistic embodiment of the invention may comprise 12 fans and 12 heating coils where each heating coil has a capacity of 3.5 kW such that the entire heating arrangement is capable of 42 kW. To achieve a comparable heating effect on stainless steel bars by induction, the required effect would be about 100 kW. Moreover, the induction heating could cause harm to the surface of the stainless steel bars.
One practical problem associated with the heating process is that the metal objects heated by the hot air may have very different starting temperatures. Bars to be cut may often be stored outdoors and may be taken from an outdoor storage directly to cutting. Depending on the season and the climate, the temperature of the bars may well vary from less than −30° C. to above +30° C. This means that the requirements on the heating operation can vary a lot. Moreover, the size of the objects, for example the diameter of stainless steel bars, also influence the amount of heating that is needed. In order to control the temperature of the bars to be cut, it is desirable that the amount of heating can be controlled. The use of the temperature sensor and control equipment such as the thyristor makes it possible to control the temperature to which the bars are heated. This ensures that, when the bars reach the cutting device, the bars will always have the same temperature. In addition, the motor M of the fan can be protected from heat and it is easier to ensure a high life expectancy for the coils 22.
The division of the heating device into three separate chambers 8, 9, 10 is a very advantageous design for the following reason. Immediately downstream of the fan 21, there will be an overpressure during operation of the fan. However, the throttle formed by the conveyor 17 in combination with the suction effect that the fan 21 generates in the rear chamber 8 and the forward chamber 10 will have the effect that there will be an underpressure in the rear and forward chambers. This counteracts leakage of heated of heated air to the environment. Consequently, this has the advantage that less energy will be required for operation of the process.
For heating stainless steel bars having a diameter of 16-25 mm, it may be suitable to keep the bars spaced from each other on the conveyor by about 50 mm. The spacing is determined by the distance between the teeth 18 of the conveyor 17. In realistic embodiments of the invention, the distance from the entry opening 4 to the exit opening 5 may be about 700-1000 mm which allows about 14-20 bars to be inside the heating arrangement 1 at the same time.
It should be understood that the temperature control system described above could be used also for a heating arrangement which is not divided into three separate chambers. It should also be understood that the idea of using three separate chambers can be used independently of whether temperature is measured and controlled or not. However, the temperature control is preferably combined with the principle of using three separate chambers.
Possibly, there could be two or more intermediate chambers, each having its own set of fans 21 and heating elements 22.
An alternative embodiment will now be explained with reference to
An alternative way of describing this embodiment would be to say that there is only a first chamber 9 and a second chamber 10, the fan(s) 21 and heating element(s) 22 being located in the first chamber 9.
Except for the elimination of the rear chamber 8, the embodiment of
Hence, the invention can be described in a more general way as relating to an arrangement and a method where air is heated in one chamber 9 and blown by a fan or fans 21 through a permeable conveyor 17 and at least a part of the air flow is diverted to at least one additional chamber 8, 10 and passed back in a loop to the chamber 9 in which the air has first been heated. In principle, this could even include embodiments with two chambers where heating takes place in the second chamber 10, even if such an embodiment is believed by the inventors to being less advantageous compared to the embodiments of
While the invention has been described above in terms of an arrangement and a method, it should be understood that these categories reflect different aspects of the invention. Consequently, the inventive method may include any method step that would be the natural consequence of operating the inventive arrangement, regardless of whether such steps have been explicitly mentioned or not.
Claims
1) An arrangement for heating metal objects, the arrangement comprising:
- a) a shell that envelops an inner space, the shell having an entry opening and an exit opening;
- b) inside the shell, inner walls dividing the inner space into a rear chamber, at least one intermediate chamber and a forward chamber;
- c) a permeable conveyor extending from the entry opening of the shell to the exit opening of the shell through the rear, intermediate and forward chamber such that objects loaded on the conveyor can be transported through the chambers;
- d) in the at least one intermediate chamber, a fan arranged to direct a gas flow towards the conveyor and objects placed on the conveyor;
- e) in the at least one intermediate chamber, a heating element arranged to heat a gas flowing from the fan before the gas reaches the conveyor;
- f) and wherein the chambers are connected to each other in such a way that at least one outlet of the at least one intermediate chamber communicates with the rear chamber, at least one outlet of the intermediate chamber communicates with the forward chamber and at least one inlet of the intermediate chamber communicates with outlets of the rear and forward chambers such that operation of the fan will generate a rear circulation of gas passing twice through the conveyor and a forward circulation of gas also passing twice through the conveyor.
2) An arrangement according to claim 1, wherein a temperature sensor is located inside the shell and connected to a control device that controls the temperature of the heating element as a function of a nominal value and a valued indicated by the temperature sensor.
3) An arrangement according to claim 2, wherein the temperature sensor is placed in the forward chamber between the conveyor and outlet of the forward chamber.
4) An arrangement according to claim 1, wherein the arrangement comprises a plurality of fans and a plurality of heating elements arranged in rows extending perpendicularly to the direction of movement of the conveyor.
5) A method for heating metal objects comprising the steps of:
- a) passing the metal objects on a permeable conveyor through an inner space enclosed by a shell and divided by inner walls into a rear chamber, at least one intermediate chamber and a forward chamber;
- b) heating air and blowing the heated air through the conveyor as the conveyor passes through the at least one intermediate chamber;
- c) diverting a first part of the heated air that has passed through the conveyor in the at least one intermediate chamber into a rear circulation of air that is passed through the conveyor in the rear chamber and back to the at least one intermediate chamber; and
- d) diverting a second part of the heated air that has passed through the at least one intermediate chamber into a forward circulation of air that is passed through the conveyor in the forward chamber and back to the at least one intermediate chamber.
6) A method according to claim 5, wherein the temperature of the air is measured inside the shell and the heating of air is controlled as a function of a nominal value and the measured value.
7) A method according to claim 6, wherein the temperature is measured in the forward chamber at such a location that the temperature of the air is measured after it has passed through the conveyor in the forward chamber.
8) A method according to claim 5 wherein the air is heated by a heater located inside the at least one intermediate chamber and the temperature of the heater is kept in the range of 200° C.-300° C.
9) A method according to claim 6, wherein the nominal value is 70° C.
10) A method according to claim 5, wherein the metal objects are elongate metal bars.
11) An arrangement for heating metal objects, the arrangement comprising:
- a) a shell that envelops an inner space, the shell having an entry opening and an exit opening;
- b) inside the she, at least one inner wall dividing the inner space into separate chambers;
- c) a permeable conveyor extending from the entry opening of the shell to the exit opening of the shell through separate chambers such that objects loaded on the conveyor can be transported through the chambers;
- d) in at least one of the chambers, at least one fan arranged to direct a gas flow towards the conveyor and objects placed on the conveyor;
- e) at least one heating element arranged to heat a gas flowing from the at least one fan before the gas reaches the conveyor;
- f) and wherein the chambers are connected to each other in such a way air which has been heated in one chamber and blown by the at least one fan through the conveyor is diverted to at least one additional chamber and passed back in a loop to the chamber in which the air has first been heated, the additional chamber being a chamber with an entry opening or an exit opening for the conveyor.
Type: Application
Filed: Nov 6, 2006
Publication Date: Oct 2, 2008
Applicant: HYNELL PATENTTJANST AB (Hagsfors/Uddeholm)
Inventors: Kurt Dahlberg (Karlskoga), Dan Borgstrom (Karlskoga)
Application Number: 12/092,759
International Classification: C21D 11/00 (20060101); C21D 9/54 (20060101);