DE19606493C1 - Method of firing dental-ceramic material - Google Patents

Abstract

The material is placed on an adjustable firing material (16) carrier (15) built into a heat-insulated combustion chamber. The material is fired in a combustion unit comprising a heat-resistant housing, inside which is the combustion chamber, heated by thermo-sensor controlled heating elements (5). The chamber creates a temperature gradient via the heating elements which are irregularly arranged and differently heated. The carrier has a thermo-sensor (17) and can be moved along the temperature gradient by a mechanical device (18). A temperature regulating unit (19), coupled to the thermo-sensor and a temperature regulator (7), compares the actual and intended temperature values and passes on the impulse to the mechanical adjustment device.

Description

The invention relates to a method for burning dental ceramic material in a combustion chamber by one or more, controlled by thermal sensors Heating elements is heated, and in which an adjustable Firing tray is installed on which the metallic Carrier located. It also affects a kiln Performing this procedure.

Today, metallic dentures are mostly made with dental ceramics blinded. For this purpose dental ceramic masses on the metal parts in a furnace at higher Branded temperatures. The temperature of the firing material will by controlling the temperature of the heating elements of the Kiln set. One strives to be one temperature distribution in the To reach the combustion chamber of the kiln.

The quality of the veneered dentures depends crucial from the temperature control in the combustion chamber from. When controlling the temperature in the combustion chamber is about controlling the temperature of the heating elements not to be ruled out that when necessary Temperature changes on the firing object an overshoot of the Actual temperature against the setpoints. The Evaluation results on many ovens showed one here average deviation of ± 20 ° C compared to the target Temperature. Some ovens have been put into practical use also significantly higher deviations of up to more than 60 ° C registered. The temperature measurements were made in each case carried out directly on the object. The more the actual Temperature approximates the solidus temperature of the alloy,  the greater the risk of warping the scaffolding in the Oven placed work. With the increasing lately low melting metal ceramic systems and also with conventional gold-platinum alloys, which as so-called palladium and copper free alloys traded can be a clear sensitivity to Deviations of the firing temperature from the target values to register. As a result, there is an increased Distortion tendency due to the excessive temperature observe.

From DE 91 13 284 U1 it is known that Improve temperature control on the firing object by the temperature inside the combustion chamber as close as possible to Firing object measures. For this purpose, a thermal sensor in the Central axis of the combustion chamber above the firing tray built-in. A firing tray is also used is adjustable relative to the furnace housing. This arrangement however, does not eliminate the drawbacks of overshoot the temperature when temperature changes are required.

It was therefore an object of the present invention Process for firing dental ceramic material in to find a combustion chamber made up of one or more is heated by heating elements controlled by thermal sensors, and in which an adjustable firing tray is built, on which the dental ceramic work is located, whereby the temperature at the firing object is always as close as possible to the desired target temperature should be kept. A corresponding kiln should also be developed will.

This object is achieved in that in the combustion chamber generates a temperature gradient and over a built-in thermal sensor in the firing tray Comparison of the actual temperature with the target temperature of the  adjustable firing tray along the temperature gradient is driven into the desired temperature zone.

The formation of the temperature gradient can by Arrangement of the heating elements and / or the type of heating can be achieved. The orientation of the temperature gradient is arbitrary, but should be as simple as possible mechanical movement of the firing tray be turned off.

Used to carry out the method according to the invention one advantageously a kiln consisting of a heat-resistant housing in which there is a heat-insulated Combustion chamber located by one or more of Thermal sensors controlled heating elements is heated, and in which an adjustable firing tray is installed to which the dental part is attached. This kiln is characterized in that the heating elements for training of a temperature gradient in the combustion chamber is irregular arranged or unevenly heated, the firing tray provided with a thermal sensor and along the Temperature gradients using a mechanical device can be moved.

The displacement of the firing tray can be electromotive, done pneumatically or hydraulically. Best proven has the electromotive shift.

The shift along the temperature gradient is from made a control technology that the on Firing tray measured actual temperature values with the Comparing target temperature values and the mechanical Adjustment device delivers the appropriate impulses.

Surprisingly, it has been shown that the control of the Temperature of the firing material by moving the firing material along the temperature gradient it becomes much more accurate Firing results is coming. For example for the hydrothermal dental-ceramic materials necessary exact  Compliance with the target firing temperature can be achieved with this Procedure also with arbitrarily arranged burning objects reach under all circumstances. This doesn't just apply to a defined controlled heating process, but also for the also very important, defined controlled Hold and cool down phase.

The new combustion process enables, for example, through rapid changes in distance between the heating element and Burning object any rapid change of the Object temperature, which essentially only depends on the Heat capacity and surface quality of the Burning object itself is affected. For use modern ceramic materials, especially hydrothermal dental ceramic masses, as well as with newer ones distortion sensitive precious metal alloys showed that this procedure is essential to the Is successful.

There is a sealable one for loading the combustion chamber Opening in the combustion chamber required. This one is expediently below the firing tray this, at least in part, advantageously heat insulating and / or reflective material executed. Can be used to achieve good vacuum properties the firing tray is made of gas-tight material, or partially gas-tight with suitable material to be encased. Through one or more holes in the Firing trays are one or more supplied from outside Thermocouples attached, which near the Firing objects measure the temperature.

An example is shown schematically using the figure Embodiment of the kiln according to the invention shown.

The furnace consists of a quartz tube ( 1 ), the lower part ( 11 ) of which is gas-tightly connected to a metal flange ( 2 ). The wall of the metal flange ( 2 ) is provided with a gas inlet connector ( 3 ), the upper, rounded part of the quartz tube ( 1 ) with a vacuum connection ( 4 ). On the upper part of the quartz tube ( 1 ) there is a heater ( 5 ) which is controlled via one or more thermocouples ( 6 ) and one or more temperature controllers ( 7 ).

The metal flange ( 2 ) is closed in a vacuum-tight manner by means of sealing rings ( 8 ), which is provided with a vacuum-tight passage ( 9 ) for the guide tube ( 10 ). The guide tube ( 10 ) is covered at the upper end by the firing base plate ( 12 ) with a hole on which the firing base ( 13 ) is placed. The firing base ( 13 ) consists of gas-tight ceramic, preferably of ceramic fiber insulating material, which is melted on all sides in quartz glass. A metal mirror ( 14 ) can also be melted in the upper part of the firing base ( 13 ) for better heat reflection. The firing tray ( 15 ) with the firing stock ( 16 ) is placed on the firing base ( 13 ). The firing tray ( 15 ) and the firing base ( 13 ) have a feedthrough for one or more thermocouples ( 17 ) which are arranged in the immediate vicinity of the firing stock ( 16 ).

The thermocouple (s) ( 17 ) are guided through the firing base ( 13 ) and the guide tube ( 10 ) and sealed in a vacuum-tight manner. The thermocouple ends are connected to a temperature controller unit ( 19 ), the pulses of which are passed on to the guide tube ( 10 ) via a lifting / lowering device ( 18 ).

To load the kiln with the kiln ( 16 ), the closing plate ( 8 ) is lowered by means of an electrical mechanism or the quartz tube ( 1 ) is raised.

The entire kiln is heat-resistant Cased case, being in the vertical area of the  Quartz tube an observation section for the operator is spared. In addition, the Observation section with a heat and light-absorbing glass pane closed if necessary will.

At the beginning of the firing process, the firing base ( 13 ) is lowered to the closure plate ( 8 ) so that the firing material ( 16 ) with the firing material carrier ( 15 ) can be placed on the firing base ( 13 ). The thermal sensor ( 17 ) is arranged approximately at the level of the material to be burned. The quartz tube ( 1 ) is now lowered onto the closure plate ( 8 ) so that the furnace is closed. The temperature controller unit ( 19 ) is coupled to the temperature controller ( 7 ), a differential temperature between the thermocouple ( 17 ) on the material to be fired ( 16 ) and the temperature controller ( 6 ) of the heater ( 5 ) being freely selectable. A base temperature of 800 ° C is specified, for example, and the temperature control unit ( 19 ) is entered.

The firing program starts after pressing the start button on the temperature control unit ( 19 ). Here, the heater ( 5 ) is brought to the base temperature of 800 ° C, at the same time the firing material ( 16 ) is brought to dryness (expelling the residual moisture) to 130 ° C for a period of 7 minutes. The firing ( 16 ) is moved in the direction of the heating ( 5 ) by the lifting / lowering device ( 18 ) until its radiant heat registers at 130 ° C. on the thermocouple ( 17 ). With increasing heating heat (base temperature 800 ° C) the radiation temperature increases, which is registered by the thermocouple ( 17 ) and the firing material ( 16 ) moves down so that the drying temperature of 130 ± 2 ° C is maintained.

The exact object temperature is maintained by slightly raising and lowering the firing material ( 16 ). After drying, the object temperature of 130 ° C is increased at a rate of 55 ° C / minute to a preheating temperature of 550 ° C by moving the lifting device upwards in the direction of the heater ( 5 ). If the temperature of 550 ° C is reached, this temperature is maintained up to ± 2 ° by vertical oscillation. After preheating has ended, a vacuum pump starts until a predetermined vacuum is reached. The object temperature of 550 ° C is maintained until this vacuum is reached. Only after the vacuum has been reached is the object temperature brought from 550 ° C to 930 ° C in 55 ° C / minute by moving the lifting device further towards the heater ( 5 ) and bringing the heater to 1000 ° C. After the object temperature of 930 ° C (± 2 ° C) has been reached, the vacuum pump is switched off and the quartz tube ( 1 ) is flooded with air. The kiln ( 16 ) is then held at 930 ° C for 1 minute. When this time has elapsed, the firing material ( 16 ) moves down and levels off at the cooling temperature I of 850 ± 2 ° C for 3 minutes. A further cooling time II of 2 minutes, at a cooling temperature II of 650 ° C follows the same pattern as in the cooling phase I.

At the end of the cooling phase, the heater ( 5 ) switches off and the material ( 16 ) moves down to the closing plate ( 8 ). The furnace can then be opened.

The method according to the invention has the advantage that the firing material ( 16 ) is moved in parallel with the thermocouples ( 17 ) in a vertical temperature gradient. Due to the bare metal thermal sensor and the small mass of the measuring point, the object temperature is measured with practically no time delay. The real temperature of the material to be burned corresponds to the time delay of the heat transfer difference between the sensor and the metal-ceramic object. It is approximately 20 seconds. This time delay is not relevant for the firing result, since the firing state can be reproduced exactly by specifying the firing program.

Claims (2)

1. A method for firing dental ceramic material in a combustion chamber, which is heated by one or more heating elements controlled by thermal sensors, and in which an adjustable firing tray is installed, on which the metallic support is located, characterized in that in the firing chamber Temperature gradient is generated and the adjustable firing tray is moved along the temperature gradient into the desired temperature zone by means of a thermal sensor built into the firing tray by comparing the actual temperature with the target temperature. 2. Kiln for carrying out the method according to claim 1, consisting of a heat-resistant housing in which there is a heat-insulated combustion chamber which is heated by one or more heating elements controlled by thermal sensors, and in which an adjustable firing tray ( 15 ) is installed, on which the dental part to be veneered ( 16 ) is fastened, characterized in that the heating elements ( 5 ) are irregularly arranged or unevenly heated to form a temperature gradient in the combustion chamber, the firing tray ( 15 ) is provided with a thermal sensor ( 17 ) and along the Temperature gradients can be shifted by means of a mechanical device ( 18 ), the temperature control unit ( 19 ), which is coupled to the thermal sensor ( 17 ) and the temperature controller ( 7 ), comparing the actual and target temperature values and the impulses to the mechanical adjusting device passes on.