1. A centrifugal caster comprising: a motor driven centrifuge arm; a weight arm connected to said centrifuge arm, both said arms being rotatable about a vertical axis; a counterweight mounted to said weight arm for horizontal movement relative to said weight arm; a casting muffle; a casting chamber connected to said centrifuge arm, said casting chamber being provided with a region for mounting said casting muffle; a melting crucible disposed in said casting chamber; a guide carriage accomodating said casting muffle for horizontal movement relative to said centrifuge arm; first and second spindles having different, oppositely oriented threads; and a hand wheel coupled with said carriage and said counterweight via a respective one of said first and second spindles for horizontally displacing said casting muffle and said counterweight with respect to said centrifuge arm and said weight arm, respectively.Patent Information Search Body
The invention relates to a centrifugal caster, particularly for dental purposes, comprising a motor driven centrifuge arm which is rotatable about a vertical axis and includes a casting chamber which, if required, may be evacuatable and in which there is disposed a melting crucible and a casting muffle mounted in a muffle cage, the caster further comprising a balance arm likewise rotatable about the same vertical axis and provided with a counterweight. Centrifugal casters of the above-mentioned type operate at rotary frequencies from 350 to 500 rpm. Therefore, after clamping in the muffle, any imbalances existing must be eliminated before the machine is put into operation. The elimination of the imbalance, on the one hand, is in the interest of the smoothest possible operation without vibratory movements which may damage the machine; on the other hand, this avoids any adverse influence on the quality of the centrifugal casting to be produced. According to the prior art, differences in weight are eliminated in that the counterweight is moved manually until a possibly existing imbalance has been compensated.
The quality of the centrifugal casting additionally depends on the temperature constancy and possibly on the quality of the vacuum in the vacuum casting chamber which must be insulated and sealed in a suitable manner.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a centrifugal caster with which the above-mentioned prerequisites for producing high quality cast alloys can be met. It is an additional object of the invention to permit easy and fast operation of the centrifugal caster even if different size casting muffles are used.
This is accomplished by a centrifugal caster wherein the counterweight is firmly attached and wherein each muffle is held in an exchangeable muffle cage that is associated with the muffle according to its size and weight. The advantage of this centrifugal caster is that the previously required tedious and time consuming setting and adjusting work at the counterweight is no longer necessary and instead the balancing can be effected more accurately. The total weight of the muffle cage with the muffle inserted is such that upon rotation of the centrifuge arm, the latter is in equilibrium with the counterweight arm. The work required before the centrifugal caster is put into operation is limited advantageously to insertion of a casting muffle into the muffle cage which is then placed into the casting chamber. Each type of casting muffle has its associated specific type of muffle cage of a certain size.
In a modification of the invention, the casting chamber is provided with cavities which are adapted to accommodate the muffle cages. For centering the muffle in the muffle cage and to further facilitate operation, supports are provided in the muffle cage. The association of the casting muffle with a particular type of muffle cage then becomes unequivocal.
The required temperature constancy is assured by double-walled muffle cages and/or muffle cages provided with a heat insulating coating or material.
To facilitate removal of the hot muffle cages from the centrifugal caster, projections are provided at the outside of the muffle cage at which a suitable tool can engage to easily lift the muffle cage together with the casting muffle. In the simplest case, such tools could be holding levers with insulated handles and a tongue which can be pushed into the projection.
According to a further feature of the invention, operation is additionally facilitated if the casting chamber--particularly if it is a vacuum chamber--is provided with a cover which can be arrested by means of a lever lock. Advantageously the cover is provided with seals at its contact faces and is provided with a viewing pane.
However, the problem on which the invention is based is solved equally as well by a centrifugal caster in which the counterweight and the inserted casting muffle are each disposed in a guide carriage which can be moved horizontally over the axis of the centrifuge arm or the axis of the weight arm, respectively, both carriages being movable by a single setting device. This centrifugal caster also has the advantage that it can be operated without lengthy adjustment of the counterweight. Operating errors are avoided in a simple manner.
According to a further feature of the invention, the centrifugal caster is provided with a hand wheel as the setting device with which the guide carriages can be displaced via two spindles having different, oppositely oriented threads. After insertion, the muffle is clamped in by rotating the hand wheel which simultaneously aligns the counterweight by means of the second spindle. If different size muffles, which thus also have different weights, also differ in length, i.e., the heavier muffles are also correspondingly longer, the centrifugal caster according to the invention permits the use of any desired muffle size, a decision having to be made as to a certain shape of the muffle. Opening or closing, respectively, of the muffle mount on the guide carriage automatically aligns the counterweight.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1a is a cross-sectional view of the centrifuge arm of a centrifugal caster in accordance with the invention;
FIG. 1b is a top view of the centrifuge arm of FIG. 1a;
FIGS. 2a and 2b show a muffle cage in cross section and longitudinal section, respectively;
FIG. 2c is a holding lever for holding the muffle cage according to FIGS. 2a and 2b;
FIG. 3a is a cross-sectional view of a different embodiment of a centrifuge arm of a centrifugal caster in accordance with the invention; and
FIG. 3b is a top view of the centrifuge arm of FIG. 3a.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The centrifugal caster shown in FIGS. 1a and 1b essentially includes a centrifuge arm 2 mounted on a motor-driven shaft 1 and a weight arm 3 with counterweights 4 and 4'. A casting chamber 5, which includes a melting crucible 6 and a chamber 7 for accommodating a muffle cage 8 (see FIGS. 2a and 2b), is disposed on centrifuge arm 2. An upper side 9 of casting chamber 5 is further provided with an opening which can be closed by means of a cover 10. In order to open and close casting chamber 5, cover 10 is actuated via a lever 11 and can be arrested by means of slots 12 in cover 10 and pins 13 at casting chamber 5. If casting chamber 5 is designed as a vacuum casting chamber, seals 14 are additionally provided at casting chamber 5. Advisably, cover 10 is provided with a viewing pane 15 which may be tinted if required.
A muffle set comprising an exchangeable muffle cage 8 and a casting muffle 32 are shown in FIGS. 2a and 2b. Muffle cage 8 has a cube shape and is equipped with supports 16 for the casting muffles 32 so as to center the casting muffles 32 while they are being inserted, and with a projection 17. An arrangement for a casting cavity 33 within a casting muffle 32 is also shown in FIGS. 2a and 2b. A tongue 19 of holding lever 18 shown in FIG. 2c can be pushed into projection 17 so as to facilitate transport of muffle cage 8. Holding lever 18 is provided with a handle 20 made of wood or that is otherwise heat-insulated.
The apparatus sketched in FIGS. 1 and 2 is easy to operate. Depending on the muffle employed, the associated, matching muffle cage 8 is located which is then placed into chamber 7. Thereafter, the casting chamber 5 is closed by means of cover 10 and by actuation of lever 11. The production of a centrifugal casting known in the art can thus begin.
As an alternative to the centrifugal caster illustrated in FIGS. 1a and 1b, the centrifugal caster shown in FIGS. 3a and 3b can also be used. This caster essentially also comprises a centrifuge arm 21 fastened on a shaft 22, a weight arm 31 with counterweight 23 as well as a melting crucible 24. The casting chamber is not shown, but is designed to correspond to FIG. 1. However, the centrifugal caster differs in the device for setting the rotational equilibrium. This is accomplished by a hand wheel 25, the rotation of which on two differently threaded spindles 26 and 27 causes the simultaneous displacement of a counterweight 23 and of holding wall 28 of guide carriage 29, respectively, into which a casting muffle can be inserted.
The centrifugal caster according to FIGS. 3a and 3b is likewise easy to operate. The casting muffle is inserted into guide carriage 29, whereupon hand wheel 28 is actuated until the muffle has been firmly clamped between the wall 30 of guide carriage 29 and holding wall 28. At the same time, counterweight 23 is moved via spindle 26 into the position corresponding to a weight equalization. The centrifugal casting then can be produced.