Slide-gate pouring appliances of the known type have a pair of holed plates made of refractory material, of which one fixed and one mobile, so that the relative movement of said plates allows the pouring appliance to be brought from a closed to an open position and vice versa.
In general the fixed holed plate is secured to the bottom of the ladle by means of a fixed metal frame.
In turn, the mobile holed plate is inserted in a metal frame which slides on a second metal frame, removable and tilting, which, in its working position, is pushed against the bottom of the ladle to as to keep the two opposite surfaces of the two fixed and mobile refractory plates in contact.
There are suitable sliding guides between the sliding frame, also known as the third frame, and the removable frame.
In order to enable the removable frame, also called the second frame, to push the sliding refractory plate in a controlled manner against the fixed refractory plate, it must be secured against the bottom of the ladle by some adjustable tightening means capable of accomplishing the following contrasting needs:
ensuring sealing of the two refractory surfaces in contact with one another; PA1 allowing relative sliding during the slide-gate opening and closing movements.
In the oldest slide-gate pouring appliances the removable frame was secured by means of slots and bolts which were tightened one after another in several stages, until a sufficiently constant pressure on the boundaries of the removable frame was achieved.
This system called for relatively long adjustment tines, since the tightening torque of the whole series of fixing bolts had to be checked two or three times, using special torque wrenches.
More recently, the use of tightening means which are quicker to adjust has been introduced.
According to previous patents owned by the applicant, the removable frame was secured to the fixed frame with a clearance and subsequently the correct compression between the mobile plate and the fixed plate was achieved by suitable wedge-shaped means sliding longitudinally or along arcs of a circle.
According to another invention by the applicant, after having secured the removable frame against the fixed frame with a clearance, the required compression between the mobile and the fixed plates was achieved by means of torsion bars of a suitable length to allow recovery of the clearances and elastic application of a constant load all round the boundary of the removable frame by means of suitable squares protruding radially from these torsion bars.
These systems gave, and still give good results for medium-sized slide-gate pouring appliances.
Indeed the force or moment applied to said tightening means increases progressively and continuously and reaches its maximum value in the final stages of tightening.
Since the tightening operation, albeit with suitable means for amplifying the effort, must be made by hand, the operator must apply a gradually increasing load leading up to the maximum value required over a relatively long time (several seconds); this calls for a strong physical effort for large slide-gate pouring appliances.
The known state of the art envisages, furthermore, in addition to said torsion bars invented by the applicant, the use of spring-operated means to be dynamic compressed during the phase of tightening the fixed and mobile refractory plates between said upper fixed and lower removable frames.
The use of spring-operated means, however, does entail some difficulties due to the fact that the pressure must be evenly applied to the whole surface of contact between the fixed and mobile refractory plates, in any relative position.
A uniformly distributed pressure, moreover, requires a uniform state of compression of these spring-operated means and this is not easy to achieve due to the large number of springs involved.
An equal state of compression of the various springs calls for an equal distance between the shouldering surface of the springs themselves, which entails considerable difficulties considering that one of the linear dimensions on which said distance depends is the thickness of the refractory plates.
The problem is further complicated by the fact that the characteristics of the springs in question change considerably with temperature and therefore in order to achieve an evenly distributed pressure over the surfaces of contact of the refractory plates, the springs involved must be maintained at the same temperature or at very similar temperatures to one another.
In order to overcome this drawback, the known state of the art envisages, for example, the use of a ring of springs around the hole in the sliding refractory plate, so as to bring the springs near to the annular area of the plate in which sealing must absolutely be accomplished: on the other hand, the closeness of the springs allows if not a uniform temperature, at least a reciprocal cooperation of the various springs, since the areas of influence of these springs overlap one another. The disadvantage of this system is that the springs are applied basically against the back of the sliding refractory plate with high local specific pressures; this may lead to premature breaking of the sliding plate; in addition, these springs are located in the vicinity of the pouring hole, which entails high temperatures.