GB2108878A

GB2108878A - Vibration of a continuous casting machine mould

Info

Publication number: GB2108878A
Application number: GB08133468A
Authority: GB
Inventors: Ian Stewart
Original assignee: British Steel Corp
Current assignee: British Steel Corp
Priority date: 1981-11-06
Filing date: 1981-11-06
Publication date: 1983-05-25

Abstract

The mould (1) is mounted in a spring suspension system (4) for movement in the vertical sense only, and a vibrator (6) vibrates the mould vertically at the natural resonant frequency of the mould/suspension system. The frequency of vibration may be of the order of 20Hz to 15 KHz and the amplitude may be of the order of 1 mm. <IMAGE>

Description

SPECIFICATION Continuous casting machine moulds This invention relates to continuous casting machine moulds, i.e. open-ended water-cooled moulds into one end of which molten metal is charged and from the other end of which a metal strand is withdrawn having a solidified skin.

During this process the mould reciprocates vertically whilst the cast strand, e.g. steel, is being withdrawn, the resulting reiative movement between the mould and this product restricting the friction between their surfaces and assisting in mould lubrication by forcing the oil or molten flux on the surface of the molten steel behind the freezing meniscus.

A particular surface defect, known as mould reciprocation marks, is known to be associated with mould reciprocation - which-, incidentally, is now commonly of the order of 3 Hz - combined with the strand withdrawal speed, and it is costly and time-consuming to remove these marks, e.g.

by grinding, before rolling.

It is an object of this invention to reduce or eliminate the incidence of these surface marks.

From one aspect, the present invention provides a continuous casting machine mould mounted in a resilient suspension system for movement in a vertical sense only, and a vibrator for vibrating the mould vertically at the natural resonant frequency of the mould/suspension system.

The suspension system may comprise springs and the frequency of the vibration may be designed to be in the range 20 Hz to 1 5 KHz.

The amplitude of vibration may conveniently be of the order of 1 mm, and since the frequency chosen is at resonance this vibration is achieved with minimum power input.

In accordance with this invention therefore, the significant gross movement of the mould as occurs with conventional reciprocation is avoided, the movement imposed being of very small amplitude but high in frequency, leading to the manifestation of a 'rippled' surface the depths of this surface imperfection being much less than hitherto and thus much easier to remove by machining.

In order that the invention may be fully understood, one embodiment thereof will now be described with reference to the accompanying drawing which schematically shows a mould and suspension/oscillatory system.

Referring now to the drawing a rectangularsection copper mould 1 for billet casting contains water-coolant channels 2 and outstanding flanges 3 on each side which serve as lower supports for mounting springs 4, these springs being secured to a fixed platform 5 at their upper ends. Mounted beneath each flange 3 and physically attached to it is a vibrator 6, which in turn is secured to a fixed platform 7; these vibrators, e.g. electromagnetic or servo-hydraulic devices, are of course synchronised with one another, e.g. by conventional electronic control means (not shown).

The mould is restrained to move only in the vertical direction and this may conveniently be by way of guides remote from the immediate vicinity of the mould.

With this design the mould acts as a weight on a spring and has a natural period of oscillation dependent on the sprung mass (the mould together with the associated water cooling etc.) and the stiffness factor of the resilient mounting system.

In operation the mould 1 'bounces' on the springs 4; the natural resonant frequency of the system may be in the lower sonic regime, e.g.

20 Hz to 100 Hz and the amplitude of vibration may be of the order of 1 mm - this will be affected by the vibrator power and the damping in the system from the mountings and the guide as well as the resistance of the cast product (8) in the mould.

As described, the emerging product has a shallow 'rippled' surface resulting from this vibratory movement as distinct from the deeper more pronounced mould reciprocation marks hitherto.

Although the invention has been described and illustrated with reference to the particular embodiment illustrated it is to be understood that various modifications may readily be made without departing from the scope of this invention.

For example, piezo-electric devices could be employed as the vibrator or alternatively eccentric bob weight systems may be utilised; the manner in which the vibrators are mounted may readily be different from that shown consistent with operating in the vertical mode only, indeed with eccentric bob weights the mould must be freely suspended, and the mould suspension may not necessarily comprise mechanical springs.

CLAiMS

1. A continuous casting machine mounted in a resilient suspension system for movement in a vertical sense only, and a vibrator for vibrating the mould vertically at the natural resonant frequency of the mould/suspension system.

2. A mould as claimed in Claim 1 wherein the suspension system comprises springs and the frequency of the vibration is in the range 20 Hz to 15KHz.

3. A mould as claimed in Claim 1 or Claim 2 wherein amplitude of vibration is of the order of 1 mm.

4. A mould as claimed in any one of the preceding claims wherein the vibrator comprises piezo-electric devices.

5. A continuous casting machine including a mould mounted in a resilient suspension system for movement in a vertical sense only, and a

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Continuous casting machine moulds This invention relates to continuous casting machine moulds, i.e. open-ended water-cooled moulds into one end of which molten metal is charged and from the other end of which a metal strand is withdrawn having a solidified skin. During this process the mould reciprocates vertically whilst the cast strand, e.g. steel, is being withdrawn, the resulting reiative movement between the mould and this product restricting the friction between their surfaces and assisting in mould lubrication by forcing the oil or molten flux on the surface of the molten steel behind the freezing meniscus. A particular surface defect, known as mould reciprocation marks, is known to be associated with mould reciprocation - which-, incidentally, is now commonly of the order of 3 Hz - combined with the strand withdrawal speed, and it is costly and time-consuming to remove these marks, e.g. by grinding, before rolling. It is an object of this invention to reduce or eliminate the incidence of these surface marks. From one aspect, the present invention provides a continuous casting machine mould mounted in a resilient suspension system for movement in a vertical sense only, and a vibrator for vibrating the mould vertically at the natural resonant frequency of the mould/suspension system. The suspension system may comprise springs and the frequency of the vibration may be designed to be in the range 20 Hz to 1 5 KHz. The amplitude of vibration may conveniently be of the order of 1 mm, and since the frequency chosen is at resonance this vibration is achieved with minimum power input. In accordance with this invention therefore, the significant gross movement of the mould as occurs with conventional reciprocation is avoided, the movement imposed being of very small amplitude but high in frequency, leading to the manifestation of a 'rippled' surface the depths of this surface imperfection being much less than hitherto and thus much easier to remove by machining. In order that the invention may be fully understood, one embodiment thereof will now be described with reference to the accompanying drawing which schematically shows a mould and suspension/oscillatory system. Referring now to the drawing a rectangularsection copper mould 1 for billet casting contains water-coolant channels 2 and outstanding flanges 3 on each side which serve as lower supports for mounting springs 4, these springs being secured to a fixed platform 5 at their upper ends. Mounted beneath each flange 3 and physically attached to it is a vibrator 6, which in turn is secured to a fixed platform 7; these vibrators, e.g. electromagnetic or servo-hydraulic devices, are of course synchronised with one another, e.g. by conventional electronic control means (not shown). The mould is restrained to move only in the vertical direction and this may conveniently be by way of guides remote from the immediate vicinity of the mould. With this design the mould acts as a weight on a spring and has a natural period of oscillation dependent on the sprung mass (the mould together with the associated water cooling etc.) and the stiffness factor of the resilient mounting system. In operation the mould 1 'bounces' on the springs 4; the natural resonant frequency of the system may be in the lower sonic regime, e.g. 20 Hz to 100 Hz and the amplitude of vibration may be of the order of 1 mm - this will be affected by the vibrator power and the damping in the system from the mountings and the guide as well as the resistance of the cast product (8) in the mould. As described, the emerging product has a shallow 'rippled' surface resulting from this vibratory movement as distinct from the deeper more pronounced mould reciprocation marks hitherto. Although the invention has been described and illustrated with reference to the particular embodiment illustrated it is to be understood that various modifications may readily be made without departing from the scope of this invention. For example, piezo-electric devices could be employed as the vibrator or alternatively eccentric bob weight systems may be utilised; the manner in which the vibrators are mounted may readily be different from that shown consistent with operating in the vertical mode only, indeed with eccentric bob weights the mould must be freely suspended, and the mould suspension may not necessarily comprise mechanical springs. CLAiMS

5. A continuous casting machine including a mould mounted in a resilient suspension system for movement in a vertical sense only, and a vibrator for vibrating the mould vertically at the natural resonant frequency of the mould/suspension system.

6. A mould for use in a continuous casting machine substantially as herein described with reference to the accompanying drawing.