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
  • B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
  • B22C1/08—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives for decreasing shrinkage of the mould, e.g. for investment casting

Definitions

• the invention relates to a non-dusting investment material containing water-soluble phosphates, magnesium oxide and silicon dioxide, mixed with liquids, for the production of precisely fitting castings in dental technology and in the jewelry industry, and to a method for producing such investment materials.
• metallic tooth replacement parts or jewelry parts are generally produced by casting processes.
• the tooth replacement part or jewelery part is modeled in wax, embedded, the wax is removed by melting and the molten alloy is poured into the resulting mold.
• the investment materials used for the production of the casting molds are subject to high demands with regard to the accuracy of fit of the parts produced therein. Due to the expansion of the setting and the thermal expansion of the investment, the contraction of the cast metal part by cooling after casting must be exactly compensated for.
• Phosphate-bonded investment materials containing magnesium oxide and silicon dioxide, since they are resistant to high temperatures and can also serve as a casting mold for high-melting alloys.
• Phosphate-bonded investment materials are mixed with water or a water / silica sol mixture. The addition of the water leads to the setting reaction of the two binder components ammonium phosphate and magnesium oxide.
• DE-PS 37 07 853 describes a powdered investment material which only shows a low level of dust formation. This is achieved by adding 0.5 - 5% of a wetting agent consisting of liquid hydrophobic hydrocarbons, fatty acid esters or fatty acids to the powder mixture of soluble phosphate, magnesium oxide and quartz. Since these liquids have a low vapor pressure, these are always relatively long-chain, organic compounds which lead to an oily grip in the investment materials and reduce the kneadability, so that anionic, surface-active agents must also be added. However, this can have a negative impact on the technical properties of the investment material (low strength, excessive setting expansion, unpleasant smell).
• a wetting agent consisting of liquid hydrophobic hydrocarbons, fatty acid esters or fatty acids
• a liquid to the investment can also be done for other reasons.
• an investment is described in Derwent Abstract 84-003437 / 01, to which an aliphatic alcohol is added in amounts of 0.01 to 0.3% by weight in order to prevent the reaction of the binder material due to the atmospheric humidity, and thus the storage stability increase.
• the amounts added are so small that no freedom from dust is obtained.
• a process for the production of these investment materials should also be developed.
• This object is achieved in that the investment is divided into two components a and b, of which component a contains all of the magnesium oxide and component b all of the phosphate, while the silicon dioxide content either only added to component b or to the two components a and b is distributed, component b containing at least 0.5% by weight of water and component a in the presence of silicon dioxide containing 0.4 to 6% by weight of a hydrophilic aliphatic solvent with a vapor pressure of less than 600 Pa.
• Component a preferably contains the magnesium oxide, part of the silicon dioxide and 0.4 to 6% by weight of a monohydric alcohol having 4 to 7 carbon atoms or a liquid polyhydric alcohol or the corresponding esters.
• component a can also contain hydrophilic carboxylic acids having 3 to 7 carbon atoms or their esters.
• the organic solvent can be dispensed with, since magnesium oxide is less dusty and far less toxic than silicon dioxide.
• the two components a and b can be packed and stored separately in the moist state. They are only mixed together in the correct mixing ratio during processing and mixed with the mixing liquid.
• a polyhydric alcohol such as e.g. Ethylene glycol or glycerin.
• components a and / or b each additionally contain a water-soluble binder, in particular polyvinyl alcohols in amounts of 0.1 to 2% and / or cellulose derivatives in amounts of 0.1 to 5%.
• a water-soluble binder in particular polyvinyl alcohols in amounts of 0.1 to 2% and / or cellulose derivatives in amounts of 0.1 to 5%.
• This agglomeration has the significant advantage that the two components can then be mixed again after drying, without a reaction taking place or a dust load exceeding the legal limit being able to occur.
• the dust-free investment material is produced by dividing the investment material consisting of water-soluble phosphates, magnesium oxide and silicon dioxide into two components a and b, component a, which contains all of the magnesium oxide and, if appropriate, part of the silicon dioxide, in the presence of silicon dioxide with 0.4 to 6% by weight of a hydrophilic aliphatic solvent with a vapor pressure of less than 600 Pa, and component b, which contains the water-soluble phosphate and the remaining part of the silicon dioxide, with at least 0.5% by weight of water is moved.
• the hydrophilic aliphatic solvent used is preferably monohydric alcohols having 4 to 7 carbon atoms, liquid polyhydric alcohols or the corresponding esters.
• components a and / or b optionally with the addition of a water-soluble binder in the form of 0.1 to 2% of a polyvinyl alcohol or from 0.1 to 5% of a cellulose derivative, are agglomerated to form agglomerates of preferably 0.5 to 5 mm in diameter and then dried. This makes it possible to mix the two components again without a setting reaction taking place.
• the refractory components silicon dioxide can be divided arbitrarily between the two components a and b. However, it has proven useful to keep the proportions approximately the same size in order to ensure as homogeneous a mixing as possible during the mixing.
• the amount of liquid required to keep dust-free essentially depends on the grain size of the investment material. The finer the material, the more liquid is required. Since ethylene glycol leads to a reduction in the setting reaction at higher concentrations, it makes sense not to increase the glycol requirement by too much sand or by too fine a grain size. A glycol content of 5% should never be exceeded.
• ethylene glycol butanediol or glycerin, for example, can also be used as the binding liquid for component a.
• the use of water does not have a negative effect on the dental properties of the investment material. Since this is also not quantity-dependent, the water requirement can always be set as required in addition to the a-component due to the fineness of the grain and the amount of sand.
• the handling of the investment material according to the invention can be further improved if the two components are agglomerated separately and mixed together again after drying.
• water-soluble binders can still be dissolved in the liquid used in both components.
• the following have proven suitable, for example: Polyvinyl alcohols, tylose, sugar, gum arabic and soluble starch.
• binders that are usually used in agglomeration processes are also conceivable. Such binders are compiled, for example, in "Chemical Engineering, December 4, 1967".
• the agglomeration of both components takes place in commercially available mixers, with a fine agglomeration of the respective agglomeration liquid leading to a build-up agglomeration.
• a size of approx. 0.5 -5 mm is permitted for the agglomerates.
• the liquid requirement for the desired agglomerate formation is 4 to 60 ml / kg solids for component a and 5 to 200 ml / kg for component b.
• component b is dried by heating to 50-110 ° C., while component a can be left in the moist state. The two components can then be mixed together without impairing the storage stability and the dental properties.
• component a contains only magnesium oxide and no silicon dioxide, it can be agglomerated or tableted without the addition of organic solvents in the form of alcohols, carboxylic acids or esters.
• Such agglomerated investment materials are distinguished from conventional investment materials by significantly reduced dust pollution during processing.
• To measure the dust load a sample of the investment material was mixed in a vessel in a tumble mixer for one minute.
• the vessel was then opened and the dust load was immediately measured using a dust measuring device. It was found that the total amount of dusts released is considerably less than the legally permissible limit values, so that a hazard from inhalable, quartz-containing dusts can be excluded.
• Components a and b were first homogenized in the dry state in a mixer for 3 minutes, then the liquid was added with continuous mixing and mixed again for 5 minutes.
• the setting expansion was determined according to DIN draft 13919, part 2. To determine the accuracy of fit, schematic crown rings were cast and then measured optically. To check the storage stability, repeat measurements were carried out after different storage times.

Landscapes

• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Mold Materials And Core Materials (AREA)
• Dental Preparations (AREA)
• Dental Prosthetics (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)
• Noodles (AREA)
• Analysing Materials By The Use Of Radiation (AREA)
• Silicon Compounds (AREA)
• Refinement Of Pig-Iron, Manufacture Of Cast Iron, And Steel Manufacture Other Than In Revolving Furnaces (AREA)

Applications Claiming Priority (2)

Publications (3)

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• 1990
  • 1990-10-11 DE DE4032254A patent/DE4032254C2/de not_active Expired - Fee Related
• 1991
  • 1991-09-04 ES ES91114886T patent/ES2059004T3/es not_active Expired - Lifetime
  • 1991-09-04 AT AT91114886T patent/ATE108642T1/de not_active IP Right Cessation
  • 1991-09-04 DK DK91114886.4T patent/DK0480171T3/da active
  • 1991-09-04 DE DE59102243T patent/DE59102243D1/de not_active Expired - Lifetime
  • 1991-09-04 EP EP91114886A patent/EP0480171B1/fr not_active Expired - Lifetime
  • 1991-10-07 US US07/771,558 patent/US5250110A/en not_active Expired - Fee Related
  • 1991-10-08 MX MX919101480A patent/MX9101480A/es unknown
  • 1991-10-09 JP JP26161391A patent/JP3242680B2/ja not_active Expired - Fee Related
  • 1991-10-09 ZA ZA918090A patent/ZA918090B/xx unknown
  • 1991-10-10 CA CA002053138A patent/CA2053138A1/fr not_active Abandoned
  • 1991-10-10 BR BR919104393A patent/BR9104393A/pt not_active Application Discontinuation
  • 1991-10-10 AU AU85744/91A patent/AU651137B2/en not_active Ceased
  • 1991-10-10 IL IL9971191A patent/IL99711A/en not_active IP Right Cessation

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