DD156719A1 - METHOD FOR REGULATING A ZONENSCHMELZANLAGE - Google Patents

Abstract

The invention relates to the field of production of pure substances. Their goal is to record error-free measured values with reduced effort and to control the zone melting plant independently of the substance to be melted, as well as the homogeneity and the constancy of the diameter of the starting rod, and to determine the phase boundary angles in a numerically stable manner. The invention has for its object to provide a method in which the detection of the horizontal and vertical distribution of Strahlungsintensitaet is not separated and the influence of vaporized lenses on the measured value of the intensity is turned off. According to the invention, the object is achieved by a method in which an image of the surroundings of the melting zone is scanned with an electron beam by means of a photoelectric receiver and the intensity signals obtained as a controlled variable via an intermediate control loop with process computer for influencing the advances of the melting and solidification rod and / or the melting power can be used. Field of application of the invention is the crucible zone melting.

Description

tease SSr = O

Method for hoisting a zone melting plant Field of application of the invention

The invention "relates to the field of production of pure substances and is suitably applicable to crucible zone melting" _e

Characteristic of the known technical solutions

There are a number of devices and methods for crucible zone melting known _y all aiming to measure the geometric sizes of the rod-shaped materials to be melted and / or the Schmelzzpne and zu.r control of the stationary or the unsteady drawing process to use » Thus, it is known from DE-AS 1231671, the diameter of the solidification front of the melting zone by means of a photoelectric! To control the receiver by the image of the environment of the Erstarriingsfront is scanned line by line with an electron beam "The diameter control is done with a loop j between the, the photoelectric receiver and the feed of the rod ends regulating device is connected, the fact is that erroneous Measurements can not be ruled out »By steaming the lenses, the absorption conditions and thus the absolute value of the measurable intensity change. In addition, this method is not applicable to the majority of substances because. the emissivity does not change significantly at the melting point. Another shortcoming is that only-homogeneous output rods of constant diameter can be used, because only then

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the sole Bestiirmiung the diameter of the melting zone provides sufficient information to control the process «In addition, a relatively large effort erforderliehj da there is the determination of the horizontal and vertical intensity distribution with separate recording and measuring j occurs individually and must be evaluated. According to DE-OS 2247 651 a method for crucible zone melting is known; in which the melting zone is monitored with a television camera under constant recording conditions and from the pulses supplied by the television camera information about the volume of the melting zone, excellent angles on the melting and solidification front and the diameter of the rod on the solidification front are obtained. "This information used to change the distance of the melting zone bounding bar ends and to change the supplied energy. As a deficiency occurs also the erroneous data acquisition due to the steaming of the lenses and also the phase limit angle determined numerically unstable due to the determination of the difference quotient from the diameter differences of the melt zone at the phase boundary.

Object of the invention

The aim of the invention is to detect error-free measured values with reduced effort and to control the zone melting plant independently of the substance to be melted and the homogeneity and the constancy of the diameter of the output bar and to determine the phase boundary angle numerically stable.

Explanation of the essence of the invention

The invention is based on the object. Indicate a method in which the detection of the horizontal and vertical distribution of the radiation intensity is not carried out separately, the influence of vaporised lenses on the measuring

value of intensity is turned off, no significant erratic change in emissivity at the melting point is required, not; works only with the determination of diameters of the molten zone and does not use the Diff'erenzquotienten diameter differences of the molten zone at the phase boundary. "According to the invention the object is achieved by a method in which scanned by means of a photoelectric receiver, an image of the environment of the melting zone with an electron beam and the intensity signals thereby obtained are used as a controlled variable via an intermediate control loop with a process computer for influencing the feed rates of the melting and solidification bar and / or the melting power. The measurement of the intensity of the intrinsic radiation of the zone and bar surface along the surroundings of the melting zone becomes , by opto-electric scanning of the image at intervals transversely and longitudinally to the rod axis. "From this, the gradient of the intensity distribution and its derivative, and from the position of the discontinuities of the gradient to the distribution along to the rod axis the position of the phase boundaries solid-liquid and thus the length of the melting zone determined from the position of discontinuities of the gradient .zur distribution transverse to the rod axis, the diameter of the melting rod and the solidifying rod and the melting zone at least three selected places determined » The process computer, the received measured values are passed and entered the target variables and coefficients and from this to control functions

= ^P s

V ^(IV)

'R ₂ = R ₂ (Eg, V ₂ )' (V)

which are formed by linear combinations and products of power and exponential functions from measured values, target variables and coefficients, the manipulated variables melting power,

mm. mm

Feed rate Melting rod and feed Rate of solidification bar calculated and transmitted to the respective actuators. The measured values according to Table 3, for example, by means of regression for a zone function, the z. B _{e may be} a polynomial of degree 3, or determined by spline-smoothing the phase angle γ> -α . The coefficients represent parameters to be adjusted, process-specific and material-related, which are expediently determined experimentally, or are obtained by simulation on a mathematical model the control functions are formed by linear, quadratic or exponential functions or »their sums and products from measured data, setpoints and coefficients« ·

Embodiment.

In a zone melting plant, a monocrystalline rod of 4 mm diameter is to be produced from a molybdenum rod of 6 mm diameter. For this purpose, first the target values and input values are defined according to Tables 1 and 2 and entered into the process computer. The zone melting plant thereby positions itself on the starting position Z or the initial diameter of the melting zone D by moving the melting rod past a television receiving device until Z or D is measured with the television recording device. Now, after the puncture (I), the process computer becomes Melting power P determined as a manipulated variable and the Schnielzleistungserzeuger a corresponding

Control signal issued "If the thermal expansion is reached, a modified melting rate P is set after puncture (II). The television recording device now begins with the evaluation of the measured data. If two phase boundaries are measurable, the contact angle at the solidification front S ^ Tj is determined and when the preset value οί * is reached, the process computer calculates all measured values according to the table from a curve fitting Nach According to the punctuations (III), (IV) and (V ) then determine the manipulated variables in accordance with Table 4 'and use the actuators for the rod

Feeds and transmitted to the vehicle power generator «In function (IV), the WinkeIC / Vo ^J is controlled by a control radio

/ SX

tion determines the given thickness growth of the

stalls D ₀ contains «1st target diameter D _x - reached,

(o) according to function (IY) the angle C / χΛ ^{J is used} to keep the diameter constant. "The process computer checks that j is maintained with the value 9p & i- ^e condition D ^ ₁ = const * and determines if necessary for. · CP π a new value «If the length of the solidified rod S reaches the specified target size _} the melting starts * For this purpose, in function (IV) the angle ^ ₁ . ^{J used} for the final phase

D-rp diameter of the solidification rod

S Length of the solidified rod Table 2 ~ Input values

Λ ¹ ' contact angle for growth i = 1 in initial phase

i = O with constant diameter

i = 2 in final phase

C / -DA limit values of the contact angle with static Aufschmelzvor- ^/ gear

R growth rate D. Minimum diameter limits Z Initial position Melting front D Initial diameter j

V initial volume y of the molten zone H initial length

^ ' ³ Ro ^ · ^η ^ ^αη ε sv / inkel

L initial length of the bar

PL reflow height ) relative to the far H.2 solidification fron height J visual recording device

Dp diameter of the solidifying rod

ψ, -η contact angle at the solidification front

V "volume of the melting zone

P Schiiielzleistung

v ^ velocity of the melting front

Vp velocity of the solidification front

Z position of the solidification front with respect to H

Tabe ll 4 - - Stellgrößen

P cutting rate R / j feed rate j on melting bar

R ₉ feed, solidification rod

Claims (3)

invention claim β method for controlling a zone melting plant in which by means of a photoelectric receiver, an image of the environment of the melting zone is scanned with an electron beam and the intensity signals obtained as a controlled variable via an intermediate control loop with process computer for influencing the feeds of the melting and solidification rod and / or the melting performance characterized in that the intensity of the intrinsic radiation of the zone and rod surface along the vicinity of the melting zone is measured by opto-electric scanning of the image at intervals transverse to and along the rod axis, hence the gradient of the intensity distribution and its derivative From the position of the discontinuities of the gradient to the distribution along the rod axis, the position of the phase boundaries solid-liquid and thus the length of the melting zone and zur'Verteilung transverse to the rod axis, the diameter of the melting rod u nd the solidifying rod and the melting zone are determined at least three selected locations, the measured values obtained as well as the target variables and coefficients of the process computer over or entered, of this according to control functions P ₃ = P ₈ (V ₁₅ D ₁ , R _s5 D _min ) (III) R ₁ ^ R ₁ (R _s , ^, ^ (i) i V ₁ , D ₁ ) (IV)., R ₂ = R ₂ (Rg / V ₂ ) ·, (V) which are calculated by linear combinations and "products of exponential and exponential functions from measured values, target values and coefficients, the manipulated variables melting rate, feed rate of melting and feed solidification bar are calculated and transmitted to the respective actuators" -. 8th - 2 «method according to item 1, characterized in that the coefficients as parameters to be matched, process-specific and material value-related parameters are obtained experimentally or by simulation on a mathematical model * 3 * A method according to _item% gekennseichnet characterized in that the control functions from measured values, target values and coefficients or preferably by linear or exponential functions _f * square whose sums and products are made "