Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds

Definitions

• the invention relates to a casting investment material on a ceramic basis for the production of casting molds by the lost wax process for casting titanium, titanium alloys or other metals which react violently with oxygen in the liquid state, which essentially have a basic composition with zirconium oxide and with other thermodynamically stable raw materials and additionally cement and Contains binders.
• a casting investment is described in EP-A-92104283.4.
• the known casting investment material is said to be particularly suitable for the production of casting molds for casting titanium. Due to its good mechanical properties and its biocompatibility, titanium is an almost ideal material for dental restorations. However, the great reactivity of the molten as well as the solid and still glowing titanium has so far been a major problem in casting technology.
• the investment material plays a key role in titanium casting.
• the investment material according to EP-A-92 104283.4 is said to contain quartz (SiO 2 ) and its modifications as a thermodynamically stable, ceramic raw material, mixed with 40-60% zirconium oxide or else aluminum oxide or magnesium oxide. A zirconium oxide content of less than 40% is expressly described as disadvantageous. Monoammonium phosphate (NH 4 H 2 PO 4 ) and magnesium oxide (MgO) are mentioned as binders.
• the investment material according to this document contains at least 40% components that react violently with titanium. To suppress this, the investment mixture should be hardened are stored and shaken in such a way that heavy zirconium oxide diffuses into the vicinity of the casting surface due to gravity.
• the invention is based on the problem of developing a casting investment of the type mentioned at the outset which has all the usual properties of the known phosphate-bound casting investments, but in which reactions between the metal and the material of the casting mold are prevented as far as possible.
• This problem is solved according to the invention in that a maximum of 35% magnesium oxide and a maximum of 50% zirconium oxide or calcium zirconate are provided as thermodynamically stable raw materials, 5-15% hydraulic calcium oxide cement and a maximum of 2% of an alkaline zirconate binder as a binder.
• This problem-solving is based on the knowledge that there are special alkaline zirconate binders outside the ceramic industry, so that hydraulic cements can be used to harden the casting investment material, which are known to harden only in alkaline media.
• the material In the cast investment material according to the invention there are no substances which react with the aggressive titanium. Nevertheless, the material is as easy to process as the previously used silicate and phosphate-containing casting investment materials.
• the zirconate binder required to implement the invention should be alkaline to neutral so as not to adversely affect the hardening of the calcium oxide cement. Depending on the desired processing time, the concentration should be a maximum of 2%.
• the calcium oxide-containing, silicate-free cement ensures the hardening of the cast slip into a hard mold.
• Fast-curing cements with a high CaO content (at least 45%) and the lowest possible Al 2 O 3 content are advantageous.
• the cement content is 5 - 15%.
• the magnesium oxide gives the finished powder mixture a homogeneous structure, improves the flowability of the slip and compensates for the difference between "heavy" zirconium oxide and other "lighter” components of the powder mixture. For this reason, the industrial bulk magnesium oxide powder should be preferred, with a purity of at least 98% being desirable. An optimal effect is achieved from about 20% to 35% MgO. A higher content leads, among other things because of the selected purity, to poorer casting results and a less than optimal behavior of the investment.
• zirconium oxide preference should be given to a fully stabilized electro-melt product with a small surface area, because such powders can be mixed into slurry with a small amount of liquid.
• the grain size should be chosen so that at least 50% of the powder is between 120 to 250 microns.
• the solidification contraction of the cast metal is usually compensated with a corresponding previous volume expansion of the casting mold.
• the contraction of the casting mold must also be compensated for, which occurs from the water outlet at 100 ° C and the sintering shrinkage from approx. 600 ° C.
• Investments of this type can be used with good results for cast titanium, but they are also advantageous at very high temperatures, for example for processing (glass) ceramic materials.
• the spinel formation is only completed at about 1600 ° C, so that the sintering shrinkage of the mold can be constantly compensated for with the increase in volume generated.
• additives can also be added to the investment powder or liquid, e.g. Liquefying agents, agents for achieving a higher gas permeability of the casting mold, dispersing agents, accelerators or retarders of cement hardening etc.
• Liquefying agents agents for achieving a higher gas permeability of the casting mold
• dispersing agents accelerators or retarders of cement hardening etc.
• the preference is always to give burnable or non-phosphate and silicate-containing substances.
• the investment material which is available as a powder and water-containing liquid, is processed similarly to the usual phosphate-bonded investment materials. After mixing the two components, a plastic, flowable slip is created. The wax-up is then cast in. The processing time can be set up to 15 'so that there is enough time for corrections.
• the cement hardening gradually stiffens the casting mold until, after approx. 1/2 - 2 hours - depending on the composition - a sufficiently hard casting mold is obtained. In the event of a fire, a holding level at 150-300 ° C is preferred to allow the water to slowly escape from the ceramic mold.
• the further rise in temperature can basically take place relatively quickly - thanks to the low thermal expansion of the raw materials. However, the overall temperature profile also depends on the expansion medium used.
• the casting mold is preferably subsequently cooled to approximately 450 ° C., annealed and cast with titanium in a casting plant.
• the investment described does not adhere to the casting when devesting and can be removed by hand.
• the cast surface is metallic clean to shiny, with a strongly reduced alpha-case zone, which is only for impurities of raw materials and alumina.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Dental Prosthetics (AREA)
• Dental Preparations (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=7757227

Family Applications (1)

Country Status (2)

Cited By (3)

Families Citing this family (1)

Citations (4)

Family Cites Families (4)

• 1995
  • 1995-03-21 DE DE1995110151 patent/DE19510151A1/de not_active Withdrawn
• 1996
  • 1996-03-20 EP EP96104402A patent/EP0733419A1/fr not_active Withdrawn

Patent Citations (4)

Non-Patent Citations (2)

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