Patent Application
20180116013
This invention, relating to the metallurgical industry, particularly to the field of auto parts, is about an automatic electric heating device for the production of high strength stamped parts by tool hardening from hot stamping of the material with specific raw material, granting greater hardness and mechanical resistance to the part, which allows the creation of lighter finished products which support greater loads and impacts.
The production of stamped parts of high hardness from the high temperature forming process consists of heating a metal sheet (specific material) and hardening of this material, by transforming the microstructure of the metallic material to conditions of higher hardness through quick cooling of the sheet already formed into its final shape inside the tool. This requires heating the plate from room temperature to the temperature called austenitizing temperature of the material, when its microstructure will have been transformed into austenite.
In the current state of the art, the heating of this plate consists of using specific equipment for this purpose, and can be carried out in the following ways: by heating, through radiation; by burning fuel (commonly natural or LPG); by electric heating (resistors); or by heating through electric induction.
In equipment that use fuel heating, electric heating or mixed (electric+fuel) heating options of continuous furnaces, in which the part goes through a long path inside the furnace (over 10 meters in length), the part receives throughout the course the heat generated by fuel burning or by heating of electrical resistances, to progressively raise its temperature until it reaches the desired temperature at the furnace outlet. Usually these furnaces have zones with different and increasing temperatures, where the plate is exposed along the path equaling its temperature with the temperature of each zone. Stationary furnaces can also be used. In these cases the material is deposited in a high temperature chamber and the piece remains in its interior for a certain time until reaching the desired temperature when the piece is removed.
In induction heating, the heat in the part is generated through an electric current induced by a coil, in which circulates a determined electric current, placed around the part to generate an electric current in its inside consequently its heating due to this internal current. These furnaces may also be continuous or stationary, where in the continuous furnace the piece is led by a conveyor belt close to the heating coil, entering from one side at ambient temperature and leaving the other end at the desired temperature; in the stationary furnace the part is deposited in a chamber where the coils are located, and upon reaching the required temperature the piece is withdrawn from the interior.
In analyzing the existing equipment, it has been observed that in the case of continuous fuel and electric furnaces, as well as in continuous induction furnaces, there is a large consumption of space due to the length of the course required to be traveled in order to raise the temperature of the product. Space-efficient utilization inside a shed is of great value for the companies, since other productive processes can be accommodated, as well as storage, logistical improvements, etc.
Another point observed in such equipment is the heating rate, which affects the time required for heating and has a great impact on the productivity of a process. In the case of radiation heating, heating rates of approximately 6.5° C./sec can be achieved and in cases of induction heating, heating rates of 200° C./sec can be achieved.
As well as the previously mentioned shortcomings, energy consumption from inefficiencies in the heating process may generate a high cost of production for the company, and a more efficient process is always necessary so that costs can be reduced. In the case of radiation heating, the efficiency of a continuous furnace is approximately 26% and for induction heating this value lies between 40 and 60%.
To this extent, the present invention provides a heating device in which the heating takes place by conduction (heating by Joule effect), which does not occupy an area much larger than the part to be heated, obtaining a better utilization of the area used by the production line. With this type of heating, heating rates up to 400° C./sec may be reached, with a speed higher than twice as fast as induction heating and 61 times faster than radiation heating. Thus, with regard to the efficiency of the process, i.e. the efficiency of energy utilization to carry out the heating of the plate, heating by conduction can reach 87%, promoting a major economy in costs of transforming metal sheets.
Conduction heating, on which the equipment is based, eliminates some problems encountered in the known processes as used for this purpose in the present state of the art, promoting a better space utilization in its installation, in view of the equipment dimensions required in view of the dimensions of the metal sheet to be heated. It also provides the possibility of a faster heating in view of the rate of heating to be obtained with the application of this technology. Another point that promotes great gain in the use of this technique is its energy efficiency, since the greater percentage of the energy spent during heating is turned into real gain of temperature of the product, thus improving productive costs and reducing energy waste.
The automatic controlled electric heating equipment for the production of high-strength parts, object of this invention, may be better understood by reporting to the enclosed figures, which are part of this descriptive report and contain numerical references together with the description of their technical particularities. These figures do not restrict their configuration as to their dimensions, proportions and possible types of finishing inserted nor the scope of their practical application.
According to these figures and their numerical references, the subject of this invention relates to (1) an automatic controlled electric heating device for the production of high-strength parts consisting basically of the following parts: heating controller system (2), power controller system (3), power transformer (4), data acquisition system (5), mechanical fastening device (6) of the plate and implementation of electric contact and expansion compensation system (7).
In this equipment (1) the heating controller system (2) performs closed-loop heating control of the part, receiving signals from the temperature sensor (St) (thermocouple, thermal camera, etc.) acting on the power controller (3) in order to provide the electrical power (voltage and current) required to achieve a homogeneous heating according to the specified parameters.
The power controller system (3), fed by the electrical network (R) of the installation site and upon command from of the heating controller system (2), supplies the power transformer (4) with the required power during heating, and is responsible for supplying all energy demand for heating.
The power transformer (4) converts the voltage and current values supplied by the power controller system (3) to the levels applied directly to the plate from an established transformation ratio.
The data acquisition system (5) closes the control loop by performing temperature measurements of the part, feeding said information to the heating controller system (2), so that control can be made. This heating control system (2) promotes precise and efficient temperature control and monitoring.
The mechanical device (6) for securing the plate (P) and implementation of electrical contact mechanically fixes the plate to be heated promoting the electrical contact of the electrodes with the plate (P). This device (6) contains the following movable parts for fixing the plate: support structure (6.1), thermal expansion compensator set (6.2), fixing cylinders (6.3), copper electrodes (6.4) with cooling channels (6.4.1), a mechanical device (7) for securing and closing the electrodes (6.5), which are connected to the electric power assembly formed by the power controller system (3) and the power transformer (4). All power equipment (3 and 4), including the electrodes (6.4), are cooled to avoid any heat build-up that may lead to undesired efficiency loss in the equipment.
The electrodes (6.4) used in the automatic heating equipment (1) are made of material (copper) of high electrical conductivity and good mechanical resistance in order to conduct the electrical current used in the heating in an efficient way to reduce the losses of the system, having internal cooling channels (6.4.1) for low temperature maintenance to increase energy transfer efficiency.
In practice, when a plate or part (P) is deposited in the device (1), it is in contact with the electrodes (6.4) and the fixing cylinders (6.3) are closed to promote the best contact of the electrodes (6.4) with the plate (P). With the plate (P) in position, the heating control system (2) starts the operation, sending to the power controller system (3) a reference for releasing electrical energy to the power transformer (4).
The power controller system (3) when receiving the power to be used in its power supply (grid of the installation) performs its treatment through rectification/modulation and releases the heating controller system (2) to start the heating by applying a voltage to the power transformer (4) specific for that moment of heating. The power transformer (4) performs the transformation of this received voltage and applies the transformed value on the electrodes (6.4), on which the plate (P) is positioned. The application of this voltage to the plate (P) promotes the appearance of a high electric current on its inside, generating the heating.
Upon initiation of heating, the data acquisition system (5) performs temperature measurements and sends them to the heating controller system (2), which in turn processes the information and sends commands so that the power controller system (3) can adjust the voltage/current values applied to the transformer and consequently to the plate (P) being heated.
During heating the plate undergoes thermal expansion due to the promoted heating, when the expansion compensation system (7) moves the electrodes (6.4) to avoid warping of the plate (P) during the process, ensuring that it is always flat.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102016024974-0 | Oct 2016 | BR | national |
