DE1020132B - Low frequency induction furnace - Google Patents

Description

GERMAN

Induction furnaces with solenoid coils are often used for partial heating of rod ends or for heating used from cut pieces or clubs over their entire length. The axial length is always used here made the furnace coil slightly longer than the length of the workpiece to be heated to full temperature. Through this in high-frequency furnaces with a constant winding density, one achieves that the workpiece is practically uniform over the entire length (when billet heating) or over the prescribed partial length (when bar heating) is heated.

As now, in recent years, the low frequency furnace for 50 or 60 Hz for heating large pieces Has found widespread use, especially for the heating of large magnetic billets up to the Curie point, one has the same design of the furnace coil with protruding ends and the same current in taken over all turns of the coil, but it was found in low frequency furnaces of this type that the free ends of the workpiece always remained colder than the middle part. It is the purpose of the invention to remedy this grievance.

The invention will be described with reference to the drawing in which

1 shows a spool with a main section and two protruding sections and
Figures 2a and 2b show circuit diagrams.
To understand the invention, it must first be explained why the low-frequency and high-frequency furnaces behave differently in the above-mentioned relationship, for example when billets are heated. If one looks at Fig. 1, where the main section of the coil is marked with a and the two protruding sections with δ and V, the laminated core with c and the billet with d , the following explanation is obtained:

If the ends of the stick are to be as warm as the middle part of the block, the flux Φ of the coil must be the same at the end of the stick (Φ _δ ) as in the middle of the block {0 _m ). However, this presupposes that a flux Φ ₆ = Φ _η already enters axially at the end faces of the stick, and it is precisely the protruding winding sections outside the stick length that must generate this flux. Now the flux 0 _{m of} the coil consists of two components, namely the surface flux 0 _my within the penetration depth and the leakage flux <P _ma outside the same between the stick and the coil. Φ _ηα is always in phase with the current I _{m of} the coil. 0 _my, on the other hand, lags below the Curie point with a phase shift of about 54 ° Φ _7ηα and I _m . The phase position of the resulting flux Φ = 0 _my + 0 _ma depends on whether the flux Φ _ην in the stick or the leakage flux predominates 0 _ma.

In this respect, however, the high-frequency and low-frequency ovens behave differently. at Low frequency induction furnace

Applicant:

Allmänna SvenskaElektriska Aktiebolaget, Västeräs (Sweden)

Representative: Dipl.-Ing. H. Missling, patent attorney,
Giessen, Bismarckstrasse. 43

Claimed priority:
Sweden, 22 November 1955

Dr. Ludwig Dreyfus, Västeräs (Sweden),
has been named as the inventor

the high-frequency furnace with its small penetration depth, 0 _{my is} much smaller than 0ma, and therefore on the whole 0 _{ma determines} the phase position of the resulting flux 0 _m . This is thus approximately in phase with the current I _{7n of} the coil, and of course the flux Φ _{6 of} the protruding sections is in phase with the current I _{6 of} these sections, which until now has always been identical to I _m . In the high-frequency _furnace, Φ ΏΙ and Φ _{δ have} approximately the same phase position, and if the number of turns N _{t of the protruding winding sections} is made sufficiently large, Φ _{6 can} also reach the same size as Φ ΎΙί, which means that the stick over the entire length is heated evenly.

The low-frequency furnace behaves completely differently. Due to the often greater penetration depth of the field, the flux 0 _mv through the stick is much greater than the leakage flux Φ _Μσ . In this case it is the flow Φ _Μυ that by and large determines the phase position of the resulting flow. This lags behind I _m by about 45 °, while the flux Φ _{6 of} the protruding winding sections is still in phase with I ₆ . _{If, as before, I 5} = I _{m is} made by connecting all winding sections in series , Φ _{Μ lags behind Φ 6} by approximately 45 °, and the condition for uniform heating, i.e. Φ _υ equal and in phase with Φ _Μ, cannot even come close will.

The invention overcomes this problem in a simple manner. Using special taps, the coil is divided into different winding sections, namely the main section with N _a row

709 807/228

switched turns, which covers the length of the billet, or, generally speaking, the length of the workpiece to be heated, and in one or two protruding sections at the end of the coil outside the length of the workpiece to be heated with a number of turns N _b or (and) IV ₆ '. Phase equality between the associated fluxes <P _m and Φ _υ or 0 _b is then achieved quite simply by applying in-phase voltages E _a> E _b or E _b 'to these winding sections. Furthermore, the winding factors f of the sections are defined by

E _a = ω N _a f _a Φ _α IQ- ⁸ ,

Ii ₆ = CiJiY ₆ It b lv ~ ^a ,

so the condition Φ _κ = Φ _υ = Φ _δ 'for uniform heating is fulfilled by the design specification:

in ■ £ & -ti-i,

_ ₁

N _b f

_b f _b

N _h

For practical cases it is sufficient if one estimates

f "~ l, A = / Y ^ 0.86
power.

When the billet is heated, N _b = N _b 'is also made, in which case both sections are expediently connected in series and with a voltage E _b + E _b according to the equation

E _a E _b + E _b '

will. £ _ο and E _b - \ - E _b can thus be obtained from a transformer with a transformation ratio EJE _b + E _b . These voltages are fed in parallel to the winding sections. Such a transformer, a so-called voltage divider, is shown in Fig. 2a. A three-winding transformer with two secondary windings can also be used, from which the winding sections N _a and N ₁ + AY of the coil are fed (see FIG. 2).

Claims (2)

PaTENTA NSPR υ C H E: 1. Low-frequency induction furnace with a solenoid which is longer at one or both ends than the workpiece to be heated (for example rod or billet), characterized in that the furnace coil is divided into a main section by special taps, the N ₁₁ turns includes over the length of the workpiece to be heated, as well as in bar heating in one or in billet heating in two protruding sections at the end of the coil, the Λ ^τ _δ or AY windings comprise outside the heated length of the workpiece, and that the main section and the other sections are fed separately with in-phase voltages E _a and E _b or E ₁ , 'of such magnitude that F F F-, ' ¹ ^ b * -Ό, ^ 6 be fed. The voltages required to practice the invention can be obtained in a number of ways Na f « ΛΥ / V ' where f are the winding factors of the winding sections. 2. Low-frequency induction furnace according to Claim 1 with two projecting winding sections N _b and AY, characterized in that these sections are connected in series for feeding with a single voltage (see Figs. 2a and 2b). 1 sheet of drawings © 709 807/228 11:57