DE1045572B - Method and device for heating billet or rod-shaped semifinished products using electrical resistance heating - Google Patents

Description

To bring workpieces that are to be hot-formed to the required temperature, stand the most varied of heating options are available, including the use of electric Electricity for this purpose. For example, it is also known to make billets out of steel for the following Hot deformation in the immediate passage of current, d. H. that is, by electrical resistance heating to bring to the desired thermoforming temperature. This is always to be done economical when the electrical resistance of the item to be heated compared to the resistance the necessary electrical supply lines plus the resistance at the contact points proportionally is high. The resistance is, apart from the influence of the material properties, dependent on the geometric design of the piece to be heated and the respective. Temperature. A simple one Consideration shows that a billet has a relatively large longitudinal extension with good efficiency and without any major difficulties at the contact points can be heated in the immediate passage of current, because due to the large longitudinal extension the voltage required for the heating current is relatively high if the current is not too high.

For heating billets for subsequent hot forming, for example in wire or Belt lines, heating in the direct passage of electricity is therefore often used.

However, it is often the task to bring blocks or slugs to hot-forming temperature bring, and this is the case, for example, in connection with plammers, presses or forging machines. These block-shaped pre-pieces required here are cut to length from billets or rods, and for deformation reasons, they have a proportionate to their cross-section low longitudinal extension. In general, the length exceeds five to ten times this value the edge length or the diameter. The one required for a specific heating output As a result, the voltage of the electric current is very small at relatively high currents. This leads to disproportionately high electrical losses in the supply lines and at the contact points. In addition, current displacement occurs in the area of the contacts. It has therefore proven to be practically impracticable proved to be such block molds, which are required as pre-pieces for subsequent hot forming can be brought to the required temperature by electrical resistance heating.

The invention is intended to make it possible to produce such blocks or slugs that are made from billets, rods or the like. Elongated semi-finished product are to be cut to length, method and device

for heating billets

or rod-shaped semi-finished products

using the electrical

Resistance heating

Applicant:
German stainless steel works

Aktiengesellschaft,
Krefeld, Oberschlesienstr. 16

Dr.-Ing. Gerhard Seulen, Remscheid,
has been named as the inventor

in the immediate passage of current through electrical resistance to hot forming temperature in order to be able to use the method, which is elegant in itself, for this purpose. There one Forging machine, press or the like but can only process one piece at a time, it is not possible to solve the task in such a way that the entire billet or the entire rod is in each case at the forming temperature is brought in order to then cut off the individual blocks from the semi-finished product thus heated and then process them. During the Processing the first pieces would have already cooled down the remaining pieces to a temperature that would require hot forming would no longer allow. As stated at the beginning, however, it is an economic warming only possible if the entire billet or rod is of considerable length and not the individual ones Blocks are heated in the electrical resistance process.

To solve the problem posed, a method known per se is assumed that is contained therein consists, billet-shaped or bar-shaped semi-finished product using electrical resistance heating and to heat the passage of current non-uniformly in the axial direction, in each case only the one to be separated End section is brought to hot forming temperature. According to the invention, this is done in the way that two workpieces by means of two solid

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and two movable contacts in series with a sequence that changes with increasing temperature Power source can be connected and that a work-resistance ratio. But it comes for the piece in each case for the other as variable ancestor does not depend on the individual temperature resistance serves. First of all, the moving areas are sharply separated from one another at the points Contact of a workpiece are gradually so far that the individual blocks are pushed off afterwards, until a certain, the fixed tone become. Rather, it just depends on cycle opposite workpiece section that the respective piece to be cut to length the hot deformed Temperature has reached, whereupon an expansion temperature as evenly as possible over the length of this section and an advancement of the length, it does not hurt if Workpiece takes place up to the fixed contact. io this temperature also part of the subsequent The contact on the other workpiece is also recorded in the corresponding section.

in accordance with the cut off on the first workpiece In Figs. 1 to 3, a power source is

Pieces set back in sections, whereupon the foreground indicates. Two workpieces 1 are connected to this power source

gear accordingly in reverse order and 2 with their front ends on fixed contacts 3

runs. To continuous heating several 15 and 4 connected to this power source. aside from that

To ensure workpieces, two movable contacts and 6 can be provided,

the workpiece needed to be replaced by a new one. wherein the contact 5 on the workpiece 1 and the

In this way it is ensured that the heating contact 6 can slide on the workpiece 2. the

current a relatively large distance in the two contacts 5 and 6 are through a flexible

must cover heating material and consequently 20 conductors 7 connected to one another.

which finds the necessary resistance, so that at the beginning of the process, the workpiece 1 is a the electrical losses in the supply lines and on the auxiliary workpiece that can be discarded later, The contact transition points are comparatively small or it can be a special piece that holds water will. As a result, contact cooling is also possible, or even a particular resistance body difficulty avoided. 25 per, for example a copper sleeve that is used by cooling water

The moving contacts are flowed through on the worker. For the description of the

piece. that is processed, step by step, it is assumed, however, that the workpiece 1

moved that initially a section that corresponds to the structure and shape of the workpiece 2.

Block format corresponds to a comparatively low The contact 6 on workpiece 2 is set so that

rige temperature is heated. In the next step 30 that the distance from the fixed electrode of the

the moving contact is set back so far that corresponds to the length of the block. Contact 5 on the

that two sections, which are twice the dimension of workpiece 1, are set at a point that

of the block format are energized. indicates that the resistance value of the

In doing so, the front piece achieves during this piece the section through which the flow has passed plus the counter-

step a correspondingly higher temperature value of the section on workpiece 2 in comparison

than the back section. By gradually aligning with that of the leads and contacts as a whole

reset is finally achieved that the front is sufficiently large.

Piece has reached the hot forming temperature The flowing current heats the set output

and can be cut off, whereupon the new cut on workpiece 2 to about 250 ° C. At the same time

The front end is moved into the fixed contact 4 °, the larger section between

will. At the same time as this step-by-step review of Kontakt and Kontakt3, also to 250 ° C

If one contact is made, the other is also heated. When this temperature is reached, it becomes how

clock shifted on the other workpiece, and can be seen from Fig. 2, the contacts shifted so

in such a way that the current path in this workpiece is that the path through which current flows in workpiece 2

is shortened accordingly. 45 becomes twice as large.

The workpiece serving as a series resistor can be connected to workpiece 1 accordingly.

initially and until the first processing of the reset. The first section on workpiece 2 is

whose workpiece must be water-cooled. But it is due to the flowing current on 500 and in the second

it is also possible to bring the section to 250 ° C. in the initial stage of the process. Gradually becomes like that

second workpiece through a water resistance or 5 °, until finally the shown in Fig. 3

to replace. In this way the initially set state is reached. It can now with

unnecessary generation of heat from the outset with the help of suitable cutting devices, such as scissors

prevented. When sawing out at regular intervals, continuously or at 1250 ° C, that is the desired one

The methods practiced, however, will be applied according to the hot-forming temperature, brought to the end Workpiece can be separated by processing a new 55. The workpiece 2 is

Workpiece inserted, and the two workpieces see the front end, which has a temperature of 1000 ° C

alternately as series resistors for each other. has, retracted into contact 4, and the ar-

The procedure is of particular interest for the sample game to go on. The workpiece 1 has

Heating of workpieces made of steel, but can meanwhile any medium-high temperature It goes without saying that it is used for all metallic works and is discarded. Instead, a

Pieces are used, regardless of whether it is a cold workpiece used. Until the

are pure metals or alloys. Workpiece 2, contact 5 remains on contact 3.

In the drawing there are three different phases. On the workpiece 2, the contact 6 also remains in the same state Process shown, in connection with rather spatial location, while this step with itself a schematically indicated device, which is advanced 65 and heated the individual according to the invention for practicing the method block sections are separated. Is a rest of service can. length reaches five times the length of the block

In the following description of the process, the contact 6 gradually moves into

it has to be taken into account that this is indicated as the present direction on contact 4 with. In the same stride length ncmmene temperature image can shift in 7 °, contact 5 on workpiece 1 moves in the opposite direction.

When contact 6 has reached contact 4, contact 5 is the same distance from contact 3 as Fig. 3 for contacts 4/6. Workpiece 1 is now processed with contact 5 at a standstill. Instead of de? Used workpiece 2, a cold workpiece is inserted. The insertion of the new stick must be done whenever the other stick has a length that is four times the length Corresponds to the length of the block.

In the example chosen, four temperature steps are provided, up to and including the final step the thermoforming temperature is made. But it is also possible with other temperature intervals and thus to work more or less temperature steps, practically for example in one Step sequence from 150 to 350, to 600, to 1000 ° C. At other hot-forming temperatures, also change the temperature intervals and their number.

For the heating a current of normal mains frequency is expediently used, which over a transformer is fed to the workpieces at a suitable voltage. In a manner known per se can by taps or switching options on the primary and secondary winding of the transformer the power supply can be regulated. Instead of a current with a normal mains frequency, Currents with lower or higher frequency can be used, for example in the range from 500 to 10000 Hz. It is also possible to heat with direct current, either through generators or contact rectifiers or rectifier vessels is generated.

With regard to the structure of the device, modifications are possible; for example, the contact and 4 also attack the side of the stick or rod end.

The contacts 3, 4, 5 and 6 can also be designed as contact pairs that come from two sides attack the workpieces. Internal or external water cooling can be provided.

The step-by-step feed movement of the workpieces is expediently controlled by time relays. For the Infeed itself, rollers, walking beam conveyors, block pushers or similar means of transport are provided. The clockwise relocation of the contacts as well as the automatic opening and closing are dependent from the cyclical feed movement of the workpieces via cams, control disks, drivers, eccentric disks or the like. Controlled. The opening and closing is expediently performed pneumatically or hydraulically operated drives. The mutual assignment of the individual movements can be implemented with known means of kinematics.

Claims (5)

Patent claims: 1. Process for heating billet-shaped or bar-shaped semi-finished products using the electrical resistance heating and current passage in the axial direction under non-uniform Heating in such a way that only the end section to be separated is at hot-forming temperature is brought, characterized in that two workpieces by means of two fixed and two movable contacts in series can be connected to a power source and one workpiece is more variable for the other The series resistor is used, with the moving contact of a workpiece initially being made step-by-step is shifted until a certain contact is opposite to the fixed contact Workpiece section has reached the desired temperature, whereupon this section is cut to length and the workpiece is advanced to the fixed contact while the contact is made on the other workpiece in sections corresponding to the pieces cut off on the first workpiece is reset, whereupon the process continues in reverse order and possibly with continuous Heating the used workpiece is replaced by a new one. 2. The method according to claim 1, characterized in that serving as a series resistor Workpiece initially water-cooled until the other workpiece is processed for the first time or is replaced by a fluid resistance. 3. Apparatus for performing the method according to claim 1 and 2, characterized by a power source with two fixed, for connection to the workpiece ends, preferably Frontal, suitable contacts and two movable ones together with a flexible conductor connected contacts that at selectable points along the length of the workpieces this concern. 4. Apparatus according to claim 3, characterized by separating devices such as scissors or Sawing in the vicinity of the two fixed contacts. Considered publications:
U.S. Patent Nos. 2,518,905, 1,900,843;
German patent application E 4126 VI / 18 c (published June 11, 1952); "Werkstatt u. Betrieb" magazine, 1952, H. 5, p. 188. 1 sheet of drawings © «09 · 697/469 11.5S