Arrangement and a Method For Heating Metal Objects

Abstract

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.

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.