CS233509B1 - Phosphate investment material for casting dental castings - Google Patents

Abstract

New composition of phosphate molding compound intended for the production of molds for casting dental Cr-Co structures of removable partial dentures. Phosphate molding compounds commonly contain about 80% of refractory filler - quartz flour and about 10% MgO and 10% NH^HgPO^ as a binder. To prepare the molds, this powder is mixed with water or SiO^ salts., The advantage of the proposed composition of the molding compound, where instead of the usual equal amount of binding components MgO with NH^HgPO^, an excess of ΝΗ^Η,,ΡΟ^ in a ratio of 1.3 - 2.5 is the high expense of solidification of the molding compound. This expansion reaches up to 2% linearly in these molding compounds dispersed with SiO2 salts, and thus allows to fully compensate for the thermal contraction of Cr-Co castings during cooling from the casting temperature to normal temperature. As a result, volumetrically accurate castings are obtained when using the proposed molding compound.

Description

BACKGROUND OF THE INVENTION The present invention relates to a phosphate investment compound based on primary ammonium phosphate and magnesium oxide with a quartz filler for casting high-melting dental alloys.

For the production of these compositions, fused or sintered magnesium oxide is used in combination with primary ammonium phosphate. As a filler, finely ground quartz powder often serves in combination with sand. These powders are separated by water or a SiO2 sol and solidify by the reaction of powdered MgO, NH4HgPO4 and water by the formation of MgKH2O4.

The problem when casting high-melting alloys is to compensate for the casting death from the solidus temperature to normal temperature. This shrinkage is from 2.5 to 2.8% for Cr-Co alloys and is not generally compensated by the technology used. To compensate for this shrinkage, the solidification and thermal expansion of phosphate investment materials are mainly used. For today's products, this compensation is too low. When mixed with water, the phosphate investment materials have a solidification expansion of about 0.3 to 0.5% and a thermal expansion of 0.8 to 0.9%.

When segregation mass about 30% Si0 ₂ sol it is zvyěuje Expense solidification to about 1%, and achieves a similar thermal expansion value. Phosphate investment materials now have a stable composition of about 8 to 10% MgO, 8 to 10% NH4 HgPO4, 84 to 80% silica filler. Also the mechanical properties, setting time, setting expansion and thermal expansion differ only slightly.

For the production of phosphate investment materials with a high aggregate expansion of 2.5 to 3%, phosphate investment materials can be used according to the invention in which the weight ratio of NH4HgPO4: MgO reaches a value of 1.3-2.5 and preferably mixed with 10-30%. % solo SiOg.

The invention is based on the discovery that the solidification expansion of phosphate investment materials increases sharply with an increasing NH 4 / PO 4 / MgO ratio. Compared to normal phosphate investment materials with the mentioned ratio of about 1, the developed investment materials with a ratio of 1.5 to 2 achieve more than 2x solidification expansion. This is especially important for mixtures mixed with SiOg solo, where the solidification expansion reaches about 2%.

This value together with a thermal expansion of approx. By controlling the ratio of NH ^ ^ HjPO íMgO well as the concentration of SiO ₂ in rozdšlévací expansion fluid can be adjusted for different types of alloys.

Examples

He did

The investment material for casting Cr-Co alloys ae is prepared by mixing the powder with 30% water sol Si0 ₂

Powder composition:

% finely ground quartz% sand 9% NH ₄ H ₂ PO ₄ 6% MgO

NH ₄ H ₂ PO ₄ / MgO = 1.5.

The molding composition has the following properties: mixing ratio of 100 g powder to 12 ml sol, solidification time 8 minutes, solidification expansion 1.85%, thermal expansion 1.05%.

Example 2

The investment material for casting Cr-Co alloys is prepared by mixing the powder with a 15% SiO2 sol.

Powder composition:

% finely ground quartz% sand% MgO io% nh ₄ h ₂ to ₄ NH ₄ H ₂ PO ₄ / UgO ratio = 2.0.

The molding composition has the following properties: mixing ratio of 12 ml of SiO ₂ sol per 100 g of powder, setting time of 8 minutes, solidification expansion of 2.0%, thermal expansion of 1.03%.

Example 3

The investment material for casting Cr-Co alloys is prepared by mixing the powder with a 3055 sol

SiO ₂ .

Powder composition:

% finely ground quartz% sand io% nh ₄ h ₂ to ₄ 7 ° h MgO% finely ground graphite NH ₄ H ₂ PO ₄ / MgO ratio = 1.43.

The molding composition has the following characteristics: mixing ratio of 12.5 ml per 100 g of powder, setting time 6 minutes, solidification expansion 1.94%, thermal expansion 1.07%.

Example 4

Investment material for casting of Ag-Pd and Cr-Co alloys. They are prepared by mixing the powder with water or 10 to 30% SiO2 sol.

Powder composition:

% finely ground quartz 9% NH ₄ H ₂ PO ₄ % MgO

NH ₄ H ₂ PO ₄ / MgO = 1.5.

The molding material has the following properties when mixed with 30% SiO ₂ sol: mixing ratio of 24 ml per 100 g powder, solidification time 6 minutes, solidification expansion 0.6%, thermal expansion 0.7% ·

Claims (1)

An ammonium dihydrogen phosphate and magnesium oxide phosphate investment material for casting dental castings of high-melting alloys for mixing with water or silica sol achieving high solidification expansion, characterized in that the ratio of ammonium dihydrogen phosphate to magnesium oxide in the investment material is 1.3 to 2, 5.