Strand guiding means to be used in a continuous casting plant

A strand guiding means has at least two framing parts arranged in pairs and opposite each other, which are connected by drawing anchors. Upon each of the drawing anchors an outer and an inner bushing, having corresponding helical sliding faces and an angle of inclination that is smaller than the pertaining angle of friction, are arranged. Each one of the inner bushings is rotated relative to the outer bushing by a pressure medium cylinder, whereby one of the two framing parts is movable and the strand guiding rollers accommodated by the framing parts are brought into and out of an engagement position.

BACKGROUND OF THE INVENTION 
The invention relates to a strand guide in a continuous casting plant 
having frame or stand parts, lying opposite each other in pairs and being 
connected by drawing anchors for accommodating the strand guide rollers, 
and a relief means having a pressure medium cylinder. 
When operational disturbances cause a stand-still of the continuous casting 
plant during casting, the already greatly cooled strand may get stuck when 
conveyed, whereby strand guide parts may be damaged or a rupture of the 
strand may be caused. 
A known strand guide (German Offenlegungsschrift No. 2,062,792) has a 
relief means for detaching the strand guide rollers from the strand, 
consisting of two wedges arranged with their inclined faces toward each 
other. One of the wedges is displaceable along a slide path relative to 
the other one in the horizontal direction. The wedge angles are bigger 
than the angles of friction so that the two wedges slide upon each other 
when the displacement path is not limited. As a result the strand guiding 
rollers arranged on both sides of the strand and facing each other can be 
moved apart. The displacement path of the two wedges is limited in this 
construction by a further wedge that is adjustable by means of a pressure 
medium cylinder which is withdrawn in case of a disturbance, thus freeing 
the displacement path. During casting the pressure medium cylinder must 
always be actuated, otherwise the ferrostatic pressure of the strand would 
press the three wedges apart. An undesired loss of pressure thus also 
causes a yielding of the strand guide parts and consequently the strand 
may bulge. A further disadvantage of the known relief means is that the 
wedges, after an actuation of the relief means for freeing the strand, 
must be made to slide upon one another and on the partly open slide paths 
by a force to be created by the strand, and this is complicated by 
pollution or grit along the slide path and the influence of temperature on 
the shape of the path during the rough casting operation. 
Summary of the Invention 
The invention aims at preventing the above mentioned disadvantages and 
difficulties and has as its object to create a strand guide of the above 
described kind whose relief means is self-locking, i.e. the strand parts 
do not move during unintended losses of pressure, and whose relief means, 
when it has been actuated, allows the frame or stand parts to freely move 
apart without a restricting wedge or the like having to be moved along on 
a dirty slide path by the strand. 
According to the invention this object is achieved in that the drawing 
anchors on one side of the frame or stand part are provided with two 
bushings that have corresponding helical slide faces having an angle of 
inclination that is smaller than the pertaining angle of friction. The 
outer bushing is always fixedly connected to the drawing anchor and the 
inner bushing, which is supported on the frame part, is rotatable relative 
to the outer bushing by means of a pressure medium cylinder, whereby one 
frame or stand part is movable and thus the rollers can be brought into 
and out of the engagement position. 
It is suitable that the movable frame or stand part can be supported on 
annular consoles connected to the drawing anchor. Advantageously, 
exchangeable spacers are insertable between the consoles and the movable 
frame or stand part, and between the movable frame or stand part, and the 
inner bushings for adjusting a pre-determined distance between the 
rollers. 
According to a preferred embodiment, the movable framing or stand part is 
connected with a fixed point on the opposite framing or stand part or on 
the drawing anchor by a pressure medium cylinder. Between the movable 
framing or stand part and the inner bushings exchangeable spacers are 
insertable for adjusting a given roller distance. This embodiment may also 
be used for an infinitely variable adjustment of the distance between the 
strand guide rollers. First, the general adjustment to the given strand 
thickness is effected by means of the spacers, while for a precise 
adjustment the rotatable bushings are rotated until the rollers of the 
framing or stand part that is movable by the pressure medium cylinder, are 
precisely at the distance of the thickness of the strand above the rollers 
of the fixed stand part. A further rotation of bushing causes a relief or 
space between the rollers and the strand. It is especially advantageous to 
surround the bushings by a protective sleeve. Thus the helical slide faces 
of the bushings are reliably protected from dirt.

DESCRIPTION OF EXEMPLARY EMBODIMENTS 
With reference number 1 a cast strand is denoted, which is extracted from a 
mould (not shown) and guided between supporting rollers 2 and 3 lying 
opposite each other. The rollers 2 supporting the strand at its outer or 
lower side are -- via longitudinal carriers 4 -- mounted on a 
base-supported framing or stand part 5 at whose ends one drawing anchor 6 
each is rigidly secured. The strand guiding rollers 3 arranged at the 
inner or upper side of the strand are mounted -- via longitudinal carriers 
7 -- on a framing or stand part 8 that is displaceable along the drawing 
anchors 6 by means of pressure cylinders 18 connected between framing 
parts 5 and 8. Both of the drawing anchors have annular consoles 9 
restricting the movement of the framing part 8 in the direction of the 
framing part 5. The movement of the framing part 8 in the opposite 
direction is restricted by two bushings 10 and 11, placed upon each one of 
the drawing anchors 6. These bushings form a thread with their helical 
slide faces corresponding to each other. Each of the outer bushings 10 is 
fixedly connected to a drawing anchor, whereas the inner bushings 11 are 
mounted to be rotatable around the drawing anchors. For actuating the 
rotatable bushings 11, one pressure medium cylinder 13 each is provided, 
whose piston rod is articulately connected to lever-like projections 12 of 
the bushings 11. The pressure medium cylinder 13 is hinged to a pin 14, 
which is secured to the movable frame part 8 by two brackets 15 so as to 
be displaceable in the same direction as frame part 8. For setting the 
rollers at a pre-determined distance, horseshoe-shaped spacers 16 
surrounding the drawing anchor are inserted between the consoles 9 and the 
movable framing part as well as between the framing part 8 and the 
rotatable bushings 11. By using spacers of different thicknesses, the 
distance between the strand guiding rollers 2 and 3 can be altered; 
however, the total thickness of all the spacers inserted on the two sides 
of the framing part 8 has to remain constant. The motion of framing part 8 
during the placement of the spacers is by means of pressure cylinders 18. 
Before the continuous casting is started and after the strand guide has 
been adjusted to the desired strand thickness, the rotatable bushings 11 
are moved into a clamped position by the pressure medium cylinders 13. 
This position is reached when the framing part 8 rests on the consoles 9 
and the rotatable bushings 11 are braced relative to the frame 8 and 
relative to the bushings 10 rigidly connected to the drawing anchors. The 
frame part 8 thus is fixed between the annular consoles 9 and the bushings 
11. The frame part 8 remains in this fixed position, even when the 
pressure medium cylinders 13 are no longer actuated, since the helical 
slide faces of the bushings 10 and 11 have an angle of inclination that is 
smaller than the pertaining angle of friction. An unintended loss of 
pressure thus does not cause a yielding of the strand guiding members. 
If, in the course of casting, the strand gets stuck, the rotatable bushings 
11 are rotated by an opposite actuation of the pressure medium cylinders 
13 into a relief position, in which the framing part 8 is movable from the 
strand surface by an amount corresponding to the angle of rotation and the 
thread ascent. The bushings 10 and 11 are enveloped by a protective sleeve 
17 reliably protecting the parts sliding upon each other against dirt, so 
that the friction conditions always remain constant. 
In FIG. 4 a preferred embodiment of the strand guide according to the 
invention is shown. The movable framing part 8 is connected with the 
drawing anchors by the two pressure medium cylinders 18 and is movable 
along the drawing anchors. If these pressure medium cylinders are actuated 
in the direction of the ferrostatic pressure, a distance between the 
strand guiding rollers results that is dependent on the rotation position 
of the bushings 11, the cylinders 18 and on the thickness of the spacers 
16; thus the distance between the strand guiding rollers is infinitely 
variable by various positions of the bushing 11. 
It is especially advantageous to provide the strand guide of the invention 
with a built-in overload indicator that automatically actuates the relief 
means when a pre-selected pressure upon the strand guiding rollers is 
exceeded. Such an overload indicator may consist, e.g., of a 
spring-mounted roller pressed to the strand, which roller swings out when 
a pre-selected pressure is exceeded and by this movement transmits an 
impulse to a relay. This relay then activates the pressure medium 
cylinders 13 so that they rotate the bushing 11 into the relief position.