BRPI0618637A2 - arrangement and method for heating metal objects - Google Patents

Abstract

ARRANGEMENT AND METHOD FOR HEATING METAL OBJECTS. The invention relates to an arrangement and method for heating metallic objects, such as metal bars by convection. The metallic objects are passed on a conveyor through a series of chambers where heated air is blown through the conveyor. The temperature is controlled by a sensor connected to a control device, such as a thyristor.

Description

"ARRANGEMENT AND METHOD FOR HEATING METAL OBJECTS"

FIELD OF INVENTION

The present invention generally relates to the heating field of metal objects, in particular objects such as elongate metal bars.

BACKGROUND OF THE INVENTION

It is a known practice to heat a metal object before performing an operation on the object. In, for example, United States Patent 4,343,209, a method is disclosed in which the bars are heated by a heating coil in zones located along the length of the bars. The bars are incrementally advanced one piece length at specific intervals through the heating coil to a shear. After each incremental advance of a bar, a part is sheared from the end of the bar then into the heated zone shown. It is quoted that the disclosed method makes it possible to shear without fracture or cracking.

It is an object of the present invention to provide an improved arrangement and an improved method for heating metal objects to facilitate cutting of metal objects. Such improved arrangement and improved method can be advantageously used for the purpose of heating metal objects which will subsequently be cut into smaller pieces. DISCLOSURE OF INVENTION

The invention relates to an arrangement for heating metal objects. The arrangement of the invention comprises a housing that encloses an internal space. The housing has an inlet opening and an outlet opening. Inside the enclosure, inner walls divide the inner space into a rear chamber, at least one intermediate chamber and a front chamber. A permeable conveyor extends from the inlet to the outlet outlet of the enclosure through the rear, intermediate and front chamber. In this way, objects loaded on the conveyor can be transported through the chambers. In at least one intermediate chamber, a fan is arranged to direct a flow of gas toward 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 such that at least one discharge of the at least one intermediate chamber communicates with the rear chamber, at least one intermediate chamber discharge communicates with the front chamber and at least one intermediate chamber inlet. communicates with discharges from the rear and front chambers. In this way, operation of the fan will generate a rear gas circulation that passes twice through the conveyor, and a forward gas circulation also passing twice through the conveyor. In one embodiment, a temperature sensor is located within the housing and is connected to a control device that controls the temperature of the heating element as a function of a setpoint and a value indicated by the temperature sensor. The temperature sensor may be placed in the front chamber between the conveyor and the front chamber discharge.

In some embodiments, the arrangement comprises a plurality of fans and a plurality of heating elements arranged in series extending perpendicular to the conveyor direction of movement. The heating arrangement may be followed by a cutting device that cuts 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 housing and divided by inner walls in a rear chamber, at least one intermediate chamber and a front chamber. As the conveyor passes through the at least one intermediate chamber, air is heated and heated air is blown through the conveyor. A first portion of the heated air that has passed through the conveyor in at least one intermediate chamber is deflected in a rear air circulation. Rear air circulation is passed through the conveyor in the rear chamber and back to at least one intermediate chamber. A second portion of the heated air that has passed through at least one intermediate chamber is deflected in a front air circulation. Front air circulation passes through the conveyor in the front chamber and back to at least one intermediate chamber.

In one embodiment of the invention, air temperature is measured inside the enclosure, and air heating is controlled as a function of a setpoint and the measured value. A suitable temperature setpoint may be 70 ° C. If the temperature is measured, this can be done in the front chamber at such a location that the air temperature is measured after it has passed through the conveyor in the front chamber.

In an advantageous embodiment, air is heated by a heater located within at least one intermediate chamber, and the temperature of the heater is maintained in the range of 200 ° C-300 ° C.

Metallic objects are elongated metal bars. The heating operation may advantageously be followed by a subsequent operation such as cutting metal bars. The heating operation itself may then be related as part of a method for heating and cutting the metal bars.

DESCRIPTION OF DRAWINGS

Figure 1 is a schematic cross-sectional view of a heating arrangement according to the present invention.

Figure 2 is a cross-sectional view taken along line II-II in Figure 1. Figure 3 is a schematic representation of a cutting device.

Figure 4 illustrates the operation of the cutting device shown in Figure 3.

Figure 5 is a schematic cross-sectional view of a heating arrangement according to an alternative embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Figure 1, the invention relates to an arrangement 1 for heating metal objects 19, in particular as a preliminary operation preceding a subsequent cutting operation. In the embodiment illustrated in Figure 1, metal objects, such as elongate bars 19, are placed in a storage 20. Metal objects 19 may be located on a conveyor 17, and transported through heating arrangement 1. In order to disperse objects, such as elongate bars 19, from storage 20, storage 20 may be provided with one or more flexible elements 37 in which the metal objects rest in storage 20. If the flexible element 37 is shortened, the bars 19 are raised, and gravity will cause the bars 19 to fall on the conveyor 17. The flexible element 37 may be, for example, one or more belts 37 which may be produced shorter by winding one end of the belt 37 onto a carriage (not shown). In the embodiment illustrated in Figure 1, the conveyor 17 is provided with teeth 18 which produce safer transfer to the conveyor, and also keep the bars 9 spaced apart on the conveyor 17.

The heating arrangement 1 comprises a housing 2 surrounding an inner space 3. The housing 2 has an inlet opening 4 and an outlet opening 5. Inside the housing 2, inner walls 6,7 divide the internal space 3 into one. rear chamber 8, at least one intermediate chamber 9 and a front chamber 10. The conveyor 17 is air permeable, and extends from the inlet opening 4 of housing 2 to the outlet opening 5 of housing 2 through the rear chamber 8, intermediate 9 and forward 10. Thus, objects 19 loaded on conveyor 17 may be conveyed through chambers 8, 9, 10 from inlet opening 4 to outlet opening 5. In the embodiment of Figure 1, the The carrier extends beyond the housing 2 on both sides of the housing. The conveyor 17 may be followed by a cutting device 31 which is symbolically indicated in Figure 1. After a metal object such as an elongate bar 19 has been heated in the heating arrangement 1, it is somewhat softer, and may easily be cut into smaller pieces by the cutting device 31.

In the at least one intermediate chamber 9, a fan 21 is arranged to direct an air flow (or possibly other gas) towards the conveyor 17, and the 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 2 before air reaches the conveyor 17. In the embodiment illustrated in Figure 1, the fan 21 is driven by a motor M which may be an electric motor Μ. The electric motor M is preferably located within the intermediate chamber 9, together with the fan 21.

The chambers 8, 9, 10 are connected to each other such that at least one discharge 14 of the at least one intermediate chamber 9 communicates with the rear chamber 8, 10. At least one discharge 14 of intermediate chamber 9 communicates with the front chamber 10, and at least one inlet 13 of the intermediate chamber 9 communicates with the discharges 12, 16 of the rear and front chambers 8, 10. Thus, operation of the fan 21 will generate a double passing rear air circulation through the conveyor 17, and a forward air circulation also passes twice through the conveyor 17. As indicated in Figure 1, a separation wall 23 may be located in the outlet 14 of the intermediate chamber 9. The separation wall 23 serves to separate the air flow from the intermediate chamber 9 into a front air circulation and a rear air circulation.

In one embodiment, a temperature sensor 25 is located within the housing 2, and is connected to a control device 26 that controls the temperature of the heating element 22 as a function of a setpoint and a value indicated by the temperature sensor 25 The temperature sensor 25 is preferably placed in the front chamber 10 between the conveyor 17 and discharge 16 of the anterior chamber 10, but it may also be located elsewhere, for example, in the intermediate chamber. The heating element 22 may be, for example, an electric coil.

As indicated in Figure 2, embodiments of the inventive arrangement may comprise a plurality of fans 21 and a plurality of heating elements 22 arranged in series extending perpendicular to the direction of movement of the conveyor 17. In a realistic embodiment of the invention, the arrangement it may comprise 12 fans 21 and 12 heating elements 22. Each heating element 22 may be sized to about 3500 W in a realistic embodiment. With 12 heating elements, the total heating arrangement would then be capable of 42 kW.

The operation of the arrangement of the invention is as follows. The metal objects 19 are passed on the permeable conveyor 17 through the inner space 3 enclosed by the housing 2, and through the chambers 8, 9, 10 of the inner space. In Figure 1, the metal objects 19 move through the inner space 3 from left to right in the direction of arrow A. Air is blown by the fan 2 toward the permeable conveyor 17, and through the conveyor 17 as the conveyor 17 passes through the intermediate chamber 10. Before air reaches conveyor 17, air is heated by a heating element 22 which may be an electric heating element 22. When heated air passes through conveyor 17, metal objects 19 are heated by the air. Permeable conveyor 17 and objects loaded on the conveyor act as a regulator that forces air to increase its velocity as it passes through conveyor 17. Increased air velocity enhances heat transfer to metallic objects 19. In In a realistic embodiment, the air velocity may be about 8-10 m / sec when hot air passes through the carrier 17. Preferably, there is no other regulator than the regulator represented by the carrier 17. In other parts of the system, the Airflow can be relatively slow, reducing losses due to friction. Immediately downstream of the fan 21, air velocity may be about 4 m / sec in a realistic embodiment of the invention.

When hot air has passed into the conveyor 17 and a portion of this heat energy is transferred to the metallic objects 19, a first portion of the heated air is diverted into a rear air circulation RA which is passed to the rear chamber 8 via the conveyor 17. in the rear chamber 8, and back to at least one intermediate chamber 9. A second portion of the heated air which has passed through the conveyor 17 in the intermediate chamber 9 is diverted in a forward air circulation FA which is passed to the front chamber 10. , and through the conveyor 17 as the conveyor 17 passes through the front chamber 10. Air in the front air circulation FA is then sent back to the intermediate chamber 9.

It is preferable that the fan motor M 21 is located within the housing 2 of the arrangement. Locating motor M outside housing 2 would result in a more complicated design. If motor M is an electric motor, it must realistically be expected that the motor will fail or be damaged if the ambient temperature becomes high. For currently available electric motors that the inventors are aware of, the ambient temperature should preferably not exceed 70 ° C. In a preferred embodiment of the invention, the air temperature is measured within the housing 2, and the air heating is controlled as a function of a set value and the set value. In the embodiment illustrated in Figure 1, a temperature sensor 25 is located in the front chamber 10 adjacent the conveyor 17 such that the air temperature is measured after it has passed through the conveyor 17 and lastly before reaching the fan 21 once more. While temperature sensor 25 may be located anywhere, this particular location is considered adequate because the air temperature will not change much from this point until it reaches fan 21 again. Other suitable locations for sensor 25 may additionally be downstream in the forward circulation FA, i.e., closer to the fan 21. The position of the sensor 25 may thus be anywhere in the front chamber 10 between the conveyor 17 and the discharge 16 from the front chamber. The sensor 25 may also be located in the intermediate chamber downstream of the fan 21 and its motor M. As indicated in Figure 1, the temperature sensor 25 may be connected by a cable 28 to a control device 26 such as, for example. a thyristor. In the embodiment shown in Figure 1, the thyristor 26 may be connected by a cable 30 to an additional control device 27, for example a computer 27. The thyristor 26 may also be connected by a cable 29 to the heating element 22 Computer 27 gives a temperature setpoint to thyristor 27, while the current temperature setpoint is given by sensor 25 via cable 28. The thyristor can then control the discharge of the element (s). 22 to increase or decrease the discharge. In order to protect motor M from fan 21, the temperature measured by temperature sensor 25 should preferably not be allowed to exceed 70 ° C. This means that the nominal value given by computer 27 is 70 ° C. Of course, to the extent that motor M is capable of operating safely above 70 ° C, the temperature measured by temperature sensor 25 may be allowed to be correspondingly higher. In the embodiment shown in Figure 1, cables or wires 28, 29, 30 connect the thyristor 26, the heating element, the temperature sensor 25 and the computer 27. However, the thyristor 26 may also have wireless communication with these elements. .

If electric coils are used as heating elements, the temperature of the coil or coils 22 may be maintained in the range of 200 ° C-300C such that the air reaching the conveyor in the intermediate chamber 9 has a temperature which is also in the range. 200 ° C - 300 ° C. The life expectancy of electric coils is highly dependent on the temperature at which the coils are heated. For such coils that are currently commercially available, coil life expectancy is almost unlimited if the temperature does not exceed 300 ° C. Of course, the air temperature will be much lower after the air has passed twice through the conveyor 17, and some of the heat in the air has been transferred to the metal objects 19. The metal objects to be heated can usually be heated to temperatures. well above 3000C without damaging the metal objects themselves. The temperatures employed are instead limited by 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. Referring to Figure 3, a possible drawing of a cutting device will now be explained. The cutting device may comprise a fixed tool 32 and a movable tool 33. A channel 34 extends through the fixed tool 32 and the movable tool 33. A punch 35 is arranged to contact the movable tool 33. A damping element 36 can be included to receive impact from a cutting stroke and return the moving tool 33 to its original position. To cut a metal bar, the bar is inserted into the channel 34 such that it extends through the fixed tool 32 and the movable tool 33. The punch 35 contacts the movable tool 33 as indicated in Figure 4, and the bar 19 is cut . Of course, a suitable cutting device 31 may take any other forms. If the bars have been heated before the cutting operation, cutting will be easier, and the surface in the current cut may be smoother and flatter.

In a realistic embodiment, the heating arrangement and method may be used to heat stainless steel bars having a length of about 5.5 m and a diameter of 16-25 mm. With the currently available cutting devices, such bars can subsequently be cut into 180 pieces within 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 has an advantage compared to the use of induction heating. When objects such as elongate metal bars 19 are heated, it may be difficult to achieve constant bar heating when inductive heating is used. For example, when elongated stainless steel nickel bars are heated by induction, the surface of the bars may become heated to a detrimental temperature, while internal parts of the bar are yet to heat to allow the bar to be cut. In addition, the inventors have found that objects with a shiny surface are more difficult to heat by induction. Objects with a shiny surface may include stainless steel objects. Stainless steel bars have poor thermal conductivity which makes them more difficult to heat such objects. The inventors have found that heating metallic objects, such as stainless steel convection bars, is more efficient than induction heating metallic objects. A practical way of convection heating is to pass the bars through a heated air flow. As indicated above, a 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 total heating arrangement is capable of 42 kW. To achieve a comparable heating effect on induction stainless steel bars, the required effect would be about 100 kW. In addition, induction heating causes damage to the surface of stainless steel bars.

A practical problem associated with the heating process is that metal objects heated by hot air may have different starting temperatures. Bars to be cut can often be stored outdoors, and can be taken from external storage directly for cutting. Depending on the season and climate, bar temperatures may range from below -30 ° C to above + 30 ° C. This means that the requirements for heating operation can vary greatly. In addition, the size of objects, for example the diameter of stainless steel bars, also influences the amount of heating that is required. In order to control the temperature of the bars to be cut, it is desirable that the amount of heating can be controlled. Use of the temperature sensor and control equipment, such as the thyristor, makes it possible to control the temperature at 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 fan motor M can be protected from heat and is easier to ensure 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 fan 21, there will be overpressure during fan operation. However, the regulator formed by the conveyor 17 in combination with the suction effect of what the fan 21 generates in the rear chamber 8 and the front chamber 10 will have the effect that there will be less pressure on the rear and front chambers. This prevents leakage of heated air into the environment. Consequently, this has the advantage that less energy will be required for process operation.

For heating stainless steel bars having a diameter of 16-12 mm, it may be suitable to keep the bars spaced from each other on the conveyor for about 50 mm. The spacing is determined by the distance between the teeth 18 of the conveyor 17. In the realistic embodiments of the invention, the distance from inlet opening 4 to outlet opening 5 may be about 700-1000 mm, which allows about 14 -20 bars are inside heating arrangement 1 at the same time.

It should be understood that the temperature control system described above may be used for a heating arrangement that is not divided into three separate chambers. It should also be understood that the idea of using three separate chambers can be used regardless of whether the temperature is measured and controlled or not. However, temperature control is preferably combined with the principle of using three separate chambers.

Possibly there may be one 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 Figure 5. In Figure 5, the rear chamber 8 according to embodiment 1 has been completely eliminated, and the inlet port 4 leads directly into chamber 8 where the fan (s) ( 21 and heating element (s) 22 are / are located. In this embodiment, there is no intermediate chamber, but only an inlet chamber 9 and an outlet chamber 10.

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) and heating element (s) 22 being located in the first chamber 9.

Except for the elimination of the rear chamber 8, the embodiment of Figure 5 operates in substantially the same manner as the embodiment of Figure 1. Since heater (s) 22 and fan (s) are / are located (s) in the first chamber 9 bordering the exterior of the housing 2, it can be expected that heat losses through the inlet opening 4 will be greater than in the embodiment according to Figure 1. Accordingly, the embodiment of Figure 5 is believed by the inventors to be less advantageous than the embodiment of Figure 1. However, leakage of hot air into the ambient atmosphere will still be reduced to some extent as there will be overpressure in the second chamber 10 which prevents hot air from leaking through the outlet port. 5

Accordingly, the invention may be described more generally with respect to an arrangement and method wherein air is heated in a chamber 9 and blown by a fan or fans 21 through a permeable conveyor 17, and at least a portion thereof. The air flow is diverted to at least one additional chamber 8, 10, and passed back in a closed circuit to the chamber 9 in which the air was first heated. In principle, this may further include two-chamber embodiments where heating occurs in the second chamber 10, even if such an embodiment is believed by the inventors to be less advantageous compared to the embodiments of Figure 1 and Figure 5.

While the invention has been described above in terms of an arrangement and method, it should be understood that these categories reflect different aspects of the invention. Accordingly, the method of the invention may include any method step that would be the natural consequence of operating the arrangement of the invention, or whether such steps were explicitly mentioned or not.

Claims (11)

1. Arrangement (1) for heating metal objects (19), the arrangement comprising: a) a housing (2) surrounding an internal space (3), the housing (2) having an inlet opening (4) and an outlet opening (5); b) within the housing (2), inner walls (6,7) dividing the inner space (3) into a rear chamber (8), at least one intermediate chamber (9) and a front chamber (10); c) a permeable conveyor (17) extending from the inlet opening (4) of the housing (2) to the outlet opening (5) of the housing (2) through the intermediate rear chamber (8) (9) and front (10), such that objects (19) loaded on the conveyor (17) may be transported through the chambers (8, 9, 10); d) in at least one intermediate chamber (9), a fan (21) arranged to direct a gas flow towards the conveyor (17) and objects (19) placed on the conveyor (17); e) in at least one intermediate chamber (9), a heating element (22) arranged to heat a gas flowing from the fan (21) before the gas reaches the conveyor (17); f) and in which the chambers (8, 9, 10) are connected to each other such that at least one discharge (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 front chamber (10) and at least one inlet (13) of the intermediate chamber (9) communicates with discharges (12, 16) of the front rear chambers. (8, 10) such that operation of the fan (21) will generate a rear circulation of gas passing twice through the conveyor (17), and a forward circulation of gas also passing twice through the conveyor (17). Arrangement according to Claim 1, characterized in that a temperature sensor (25) is located within the housing (2) and is connected to a control device (26) which controls the temperature of the heating element. (22) as a function of a setpoint and a value indicated by the temperature sensor. Arrangement according to claim 2, characterized in that the temperature sensor (25) is placed in the front chamber (10) between the conveyor (17) and the discharge (16) of the front chamber (10). Arrangement according to claim 1, characterized in that the arrangement comprises a plurality of fans (21) and a plurality of heating elements (22) arranged in series extending perpendicular to the direction of movement of the conveyor ( 17). 5. Method for heating metal objects (19), characterized in that it comprises the steps of: a) passing the metal objects (19) in a permeable conveyor (17) through an internal space (3) enclosed by a casing ( 2) and divided by inner walls (6, 7) into a rear chamber (8), at least one intermediate chamber (9) and a front chamber (10); b) heating the air and blowing the heated air through the conveyor (17) as the conveyor (17) passes through at least one intermediate chamber (10); c) diverting a first portion of the heated air which has passed through the conveyor (17) in at least one intermediate chamber (10) into a rear circulation of air which is passed through the conveyor (17) in the rear chamber (8) and returns to at least one intermediate chamber (9); and d) diverting a second portion of the heated air which has passed through at least one intermediate chamber (9) into a front air circulation that is passed through the conveyor (17) in the front chamber (10) and back to at least one. an intermediate chamber (9). Method according to claim 5, characterized in that the air temperature is measured inside the enclosure (2) and the air heating is controlled as a function of a nominal value and the measured value. Method according to claim 6, characterized in that the temperature is measured in the front chamber (10) at such a location that the air temperature is measured after it has passed through the conveyor (17) in the front chamber (10). 10). Method according to claim 5, characterized in that the air is heated by a heater (22) located within the at least one intermediate chamber, and the temperature of the heater (22) is maintained in the range of 200 ° C. ° C - 300 ° C. Method according to claim 6, characterized in that the nominal value is 70 ° C. Method according to claim 5, characterized in that the metal objects (19) are elongated metal bars. 11. Arrangement (1) for heating metal objects (19), the arrangement being characterized by: a) a housing (2) surrounding an internal space (3), the housing (2) having an inlet opening (4) and an outlet opening (5); b) within the housing (2), at least one inner wall (6, 7) dividing the inner space (3) into separate chambers (8, 9, 10); c) a permeable conveyor (17) extending from the inlet opening (4) of the housing (2) to the outlet opening (5) of the housing (2) through the separate chambers (8, 9, 10); such that objects (19) loaded on conveyor (17) may be transported through chambers (8, 9, 10); d) in at least one of the chambers (9), at least one fan (21) arranged to direct a gas flow towards the conveyor (17) and the objects (19) placed on the conveyor (17); e) at least one heating element (22) arranged to heat a gas flowing from at least one fan (21) before the gas reaches the conveyor (17); f) and in which the chambers (8, 9, 10) are connected to each other such that air that has been heated in a chamber (9) and blown by at least one fan (21) through the conveyor (17) is diverted to at least one additional chamber (8, 10) and passed back in a closed circuit to the chamber (9) in which the air was first heated, the additional chamber (8, 10) being a chamber (8, 10 ) with an inlet opening (4) or an outlet opening (5) for the conveyor (17).