The usual casting methods are:
vacuum pressure die-casting
Flame casting is the most traditional casting method and it is probably the most common and less expensive one. This method has been useful to develop casting techniques but it does not fit well with the legal and technical requirements of present-day market. This technique is based solely on the operator’s competence and skill: use of this technique requires ability to control the flame, a good knowledge of metalworking as well as sensitivity and operation carefulness.Although it is true that many operators are true masters of this technique we think that this technique will not guarantee reproducibility and a constant quality level. And if a process, such as this, is completely based on the operator’s skill and competence it is not a flexible process, and flexibility is an essential requirement for modern dental technician laboratories. The process should, indeed, be reproducible regardless of operators’ competence. In addition to this the flame casting method does not allow certification and documenting of the casting process by means of automatic process control systems.
Induction casting has surely represented a breakthrough in the casting sector but despite this the technique has some features that make it impossible to use it in a rational and organized way in the dental technician’s laboratory.The induction system is semi-automatic in nature and the whole process, like flame casting, depends on the operator’s skill.Is a fact that the operator has the task to evaluate whether melting has been correct and to activate the centrifugal device. «Therefore, reproducibility and constant quality level cannot be guaranteed using this technique.Induction casting is very quick. The metal alloy is heated from the inside to the outside. The technical nature of the induction system makes it impossible to stabilise the alloy temperature over time or to block the temperature increase.The centrifugal pressure is unidirectional and many induction casting machines do not feature a vacuum system, therefore the air found in the unit may cause a porous casting.
Vacuum pressure die-casting
The vacuum pressure die casting has always been considered a high-quality casting process, however its popularity remained limited until the mid-90s due to the fact that the temperatures reached by these devices were not suitable for melting and casting of the new dental alloys. A new generation of devices were later developped, that were capable of melting base-metal, semi-precious, Palladian and precious dental alloys.
The Tecno-Gaz pressure die-casting machines feature an excellent melting temperature control, producing the casting in a vacuum and making it possible to carry out multi-directional pressure. All of this ensures great usage flexibility, reproducibility and constant quality and minimises the operator’s impact on the outcome.
How to achieve a good casting
Follow casting temperature requirements
Keeping control over casting temperature is the most important requirement to maintain the metallurgic features of the alloy. Compliance with the casting data and specifi cations is essential to avoid sublimation of the low melting point metals contained in the alloy.
A metal molten at the appropriate temperature will have all the features prescribed by the manufacturing company, otherwise there may be some changes in the metallurgic structure of the metal that may cause changes in technical properties and problems during the subsequent processing phases.
Casting with omnidirectional pressure
Dental alloys are composed of several different metals, each with its own specifi c density. By using centrifugal injection techniques the result will be a mono-directional pressure in which the metals with higher specifi c densities are introduced in the cylinder before the ones with lower densities. Using the Tecno-Gaz pressure die-casting techniques, the metal is introduced statically in the cylinder and then the cylinder is exposed to an omni-directional and constant pressure that allows perfect layering of the metal.
To achieve high mechanical resistance and accuracy the casting shall be carried out in an airfree environment. This ensures a completely non porous alloy casting.
The Tecno-Gaz die-casting system
The Tecno Gaz casting machines represent the logical evolution of traditional die-casting machines. The Tecno Gaz die-casting process is a technologically advanced and well-tested process. All the system and components used have undergone functional and operational tests that lasted for 4 years. The Tecno Gaz casting machines grant automatic control over the whole casting cycle process.
The first step is heating, which is carried out by irradiation: a resistor transmits heat to the crucible, which in turn heats the mass that is being melted. The temperature is constantly monitored and controlled, thanks to a complex system with cross-reference controls on electronics, resistor and thermocouple.
The second step is the vacuum production. After the crucible has been inserted into the melter and the latter has been closed, the casting machine will begin the vacuum production phase, completely controlled and handled by the microprocessor system.
The third step is the inverting and compression, with subsequent falling of the molten metal in the cylinder and automatic controlled compression that will push the metal inside the cylinder. This process produces a vacuum casting, with maximum omni-directional compression that ensures:
• consistant results
• perfect edge closure
• thorough compliance to metallurgic specifi cations
• alloy saving
Fourth step, automatic cooling of metal by forced stopping. Then the muffl e will come back to the initial position.
The advantages of the Tecno-Gaz die-casting system
Compliance with set temperature specifi cations
This is possible thanks to a system that combines control by microprocessor, thermocouple and control logic, carried out with a complex electronic system featuring an infra-red pointer.
Advantages: Maximum accuracy in alloy production with subsequent preservation of metallurgic specifi cations.
Omnidirectional pressure on the metal
Automatic compression produces an uniform and even pressure on the whole cylinder. There is no centrifugal effect of the metals that compose the alloy.
Advantages: Higher alloy compactness, better layering, saving of alloy material (there is no need for extra material to be used for channels and excess cast material)
Melting is carried out in an atmospheric environment
But casting is carried out in an airless environment because the Tecno Gaz casting machines, before overturning, carry out a air free production automatic process.
Advantages: Maximum accuracy, high quality and time saving in fi nishing works.
Maximum operation flexibility
Usability by all laboratory components for there is no human intervention.
Advantages: Usability by all laboratory components.
The process is automatic and features no human intervention.
Advantages: The automatic cycle and absence of human intervention grant a perfect reproducibility of results.
Cost effective management
Overall process management is 100% cost effective: electric energy consumption is low and the consumables are inexpensive.
Advantages: cost effectiveness.
Maximum working temperature 1600°c
Thanks to the exceptional resistance it is possible to reach very high working temperatures.
Advantages: Can melt and cast all types of metals: precious, semi- precious, base, chrome-cobalt, nickel-chrome, steels and metals containing titanium.