DE2120592B2 - ELECTRICALLY HEATABLE FURNACE FOR CERAMIC GOODS - Google Patents

Description

25th

The invention relates to an electrically heatable furnace for ceramic goods, in particular for Manufacture of artificial teeth in which the furnace consists of a vertical combustion chamber closed at the top and one pneumatically movable from bottom to top with a lift rod into the combustion chamber Firing tray with a vacuum-tight closing plate that closes the firing chamber.

Electrically heated furnace for ceramic work with a vertical furnace, vertical Management of the items to be fired and the vertically displaceable base of the items to be fired are already known, with the The furnace is open at the bottom so that the items to be fired can be introduced from below through a base that is fully can be loaded when extended. However, this known oven is not intended for purposes and suitable, which, as in the above-mentioned dental ceramic work, are sensitive Fired goods are and where the fired object, z. B. dental crowns, the combustion chamber temperature can be exposed and which is a vacuum fire, which is a very specific one Assumes the condition of the items to be fired at the beginning of the vacuum firing period, if a faultless one Result is to be achieved.

A kiln has therefore already been proposed (German Auslegeschrift 1081 816) in which a vertical combustion chamber, firmly closed at the top, vertically from bottom to top through an in this direction movable fuel base is charged, which in turn from a combustion chamber downwardly limiting locking stone and from a closing the kiln from the outside End plate is formed and wherein support columns between the breech block and the end plate leave a cavity free. The cavity between the breech block and the end plate is included dimensioned and designed in such a way that the material to be treated is accommodated therein for preheating, if necessary can be. By means of an end plate below the base of the fuel and a seal even the preheating space and the combustion chamber can be sealed in a vacuum-tight manner.

When carrying out a sequence of several firing processes, it has proven to be disadvantageous that before reloading the combustion chamber and carrying out the burner, if necessary, under Each time a lowering of the combustion chamber temperature is necessary, because for the vacuum Evacuation of the furnace housing has to be waited for a certain period of time during which the material to be fired must not be exposed to the temperature in question for burning.

If that were the case, premature solidification of the molten surface coating, e.g. B. Silicate sintering can occur in artificial teeth or at least skin formation occurs, which would no longer make it possible to remove air inclusions from the melt, which is aimed at by vacuum firing. However, these necessary in each case reducing the firing temperature means that the heating coil each time is not insignificant temperature fluctuations exposed and the load is greater, than is usually the peak temperature strives to reach again possible λ fast for burning. The associated stress on the furnace and above all on the muffle heating means a limitation of the service life, in particular more frequent renewal of the heating muffle or spiral.

All known ovens of the type mentioned have the disadvantage that on the one hand a lowering of the Combustion chamber temperature is necessary before loading and that, on the other hand, the running-in process not exactly on the respective requirements and regardless of any incorrect manipulation of the Operator can be done.

A kiln based on the German interpretation document brings a significant improvement in this regard 1 926 874, which is designed so that the end plate and the carrier arranged above it for the Brenngutsockel are each provided with a piston, the piston of the carrier in the as a pot piston trained and engaging in the compressed air cylinder with its closed end piston sits, which piston is provided with a fine bore for the controllable application of the carrier | piston.

With this known proposed solution, a lowering of the combustion chamber temperature is not necessary, because the object is not brought directly into the hot zone, but controlled according to a specific one Dwell time in the evacuation zone reaches the actual combustion zone. This solution takes into account also the usability of the furnace for firing processes that do not take place under vacuum, d. H. whereby the carrier of the base of the fuel cannot be lifted by the resulting vacuum.

This known proposed solution now has certain disadvantages insofar as it is with a pneumatic Lift is not readily possible, the firing chamber end plate and thus the material to be fired to go up slowly (in about 6 minutes) over a relatively short distance and then after the If the fire occurred, it should be quickly lowered back into the cool-down position. To remedy this difficulty, offers the use of a hydraulic system or an additional hydraulic system, but apart from that, that in consideration of the instruments and any leaks in the furnace part of hydraulics, the use of which is undesirable

is worth using a hydraulic system with a relatively large additional and structural associated with demanding effort.

The invention is accordingly based on the object, a kiln, based on those of the type mentioned to create a fully automatic slow and even start-up and enables the firing tray to be lowered and lowered quickly after the firing, so that even inexperienced operators can handle the furnace due to its fully automatic system can, whose essential task is then only

■ consists of placing the objects to be fired on the base of the base and after it has cooled down to take out again.

This task is possible with a kiln of the

'called type solved, according to the invention thereby is marked. that in addition to the pneumatically operated lift rod, an additional, mechanically driven one Lifting finger is arranged, which is programmatically controlled from below, loosely against the end plate is designed to be mobile and lowerable again.

In this training, the mechanically driven lifting finger initially takes over the slow one Raise (about 12 mm in about 6 minutes) through the preheating area, being in the end position then the firing object is in the actual firing chamber. After the fire is over while which the lifting finger goes back to the cooling position is a quick move out to a to avoid unwanted afterburning, it is necessary to move from the combustion chamber to the cooling position, which is done by means of the pneumatics, with the end plate waiting for the in the cooling position Lifting finger touches down in a damped manner.

After the cooling period, which in the present case lasts about 12 minutes and during which a temperature drop takes place of about 300 °, then the lifting lever with the end plate or the firing tray is lowered to the end position, what with the pneumatics alone would not be possible to time-regulate.

A simple crank drive is advantageously used for the mechanical drive of the lifting finger, in its circulation path corresponding program or limit switches for the program start, the cooling position and the end of the program are arranged.

For the breaks in which it is important to close the combustion chamber again quickly because of the heat losses to close and open, only the pneumatics are used.

On the basis of the graphic representation of an exemplary embodiment, the kiln is described below explained in more detail according to the invention.

The embodiment shown is a furnace operated with protective gas, however the special lifting device can also be used on furnaces operated in other ways.

In the kiln shown schematically, 1 is the vacuum pump, and 2 is a pneumatic one Lifting cylinder, with 3 a timer and with 4 the lift rod for the firing tray 5 denotes. 7 is a further timer. The protective gas is taken from a protective gas pressure bottle 11 with a pressure regulator 10. 14 and 18 are throttle valves between which a check valve 15 is connected. From the timer 3 a solenoid valve 19 for the vacuum and the timer 7 are solenoid valves 16,17 for the Shielding gas actuated.

The lifting finger 6 is operated mechanically by the crank mechanism 12, whose actual drive (servomotor) is not shown. The lifting finger 6 lies loosely with its upper end 6 'in the position shown against the underside of the combustion chamber end plate 20. In the circulation path of the crank mechanism 12 are the Limit switches 8 (program start), 9 (cooling position) and 13 (program end) are arranged, which when the corresponding Position of the connecting rod 21 can be operated. The travel from limit switch 13 to Limit switch 8 corresponds, viewed in clockwise direction, to the preheating period and the position of the limit switch 8 up to the limit switch 9 of the lowering period up to the cooling end position. From 9 to 13 descends the lifting finger 6 down to its lowest position.

1 sheet of drawings

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Claims (2)

Patent claims: 1. Electrically heatable vacuum furnace for ceramic goods, especially for production artificial teeth, consisting of a vertical combustion chamber closed at the top and a The firing tray can be pneumatically moved from bottom to top with a lift rod in the firing chamber with vacuum-tight closing plate closing the combustion chamber, characterized in that that in addition to the lift rod (4) an additional, mechanically driven lifting finger (6) is arranged, the program-controlled from below, loosely against the end plate (20) is designed to be mobile and lowerable again. 2. Kiln according to claim 1, characterized in that the lifting finger (6) with a Crank drive (12) is in an articulated connection, in the circulation path of which limit switches (8, 9, 13) are arranged are.