Hot-Curing Polyurethane Mould Material for Low-Emission Sand Casting
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Solution Overview
Problem
Existing hot-box and warm-box binder systems in foundry processes release harmful emissions such as formaldehyde, phenol vapors, and furfuryl alcohol vapors, and require high thermal input, while cold-box processes rely on toxic amine gases, posing environmental and occupational health risks.
Innovation Solution
A two-component, phenol- and formaldehyde-free polyurethane-based binder system with thermally activatable catalysts, using adducts of tertiary amines and organic acids or quaternary ammonium salts, which cure rapidly under moderate thermal input, mimicking the speed of amine gas-curing cold-box processes without the need for toxic gases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a mould material is used that is reusable after demoulding (for investment casting), then the number of castings per mould increases, but the mould material cannot be used for sand casting processes requiring hot curing
Solution Approach 1:
The mould material's chemical composition is modified by incorporating specific binders (sodium silicate, calcium aluminate, magnesium oxide) and additives that enable hot-curing behavior. This parameter change allows the material to transition from investment-casting compatibility to sand-casting compatibility while maintaining reusability through controlled refractoriness and cure characteristics
Solution Approach 2:
The patent creates a composite mould material combining silica sand with multiple binder systems (organic binder, sodium silicate, calcium aluminate, magnesium oxide) and optional refractory cement. This composite structure provides both the hot-curing capability needed for sand casting and the durability for repeated use, resolving the contradiction between process compatibility and reusability
2Strength
If a mould is hot-cured in a sand casting process, then the mould achieves sufficient strength for heavy-duty applications, but organic binders may burn and cause defects in the casting
Solution Approach 1:
The organic binder content is reduced to a minimum level (0-5% of sand weight) and its composition is modified to improve burnout characteristics. Simultaneously, inorganic binders (sodium silicate, calcium aluminate, magnesium oxide) are increased to provide the necessary strength, allowing the mould to achieve required strength while minimizing organic binder burning during hot-curing
Solution Approach 2:
The patent converts the potential harmful effect of organic binder burning into a beneficial process by controlling the burnout through proper formulation. The organic binder serves as a temporary binding agent during mould making, then burns out cleanly during hot-curing to leave no harmful residues, while the inorganic binders provide the final strength
3Duration of action of stationary object
If inorganic binders like sodium silicate and calcium aluminate are used to improve reusability, then the mould can withstand high temperatures and repeated use, but the mixture becomes too stiff for effective vibration compaction
Solution Approach 1:
The binder composition parameters are optimized to achieve a balance: sodium silicate concentration, calcium aluminate content, and magnesium oxide ratio are adjusted to provide sufficient inorganic bonding for reusability while maintaining adequate mix fluidity. The water-to-binder ratio is also controlled to ensure proper workability during vibration compaction
Solution Approach 2:
The inorganic binders are pre-mixed with the sand and organic binder in a controlled sequence to ensure uniform distribution before adding water. This preliminary mixing action prevents clumping and ensures that the inorganic binders do not create localized stiff areas that would hinder vibration compaction, while still providing the necessary overall reusability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves rapid curing times and low emissions, reducing VOCs and improving safety by using chemically encapsulated catalysts that release active species upon heating, thus minimizing environmental and health hazards.
Implementation Method 1
a liquid binder is mixed with sand grains in a tumbling motion to form a mouldable sand mixture
Implementation Method 2
The sand mixture is then compacted in a vibratory motion to form a sand mould or sand core
Implementation Method 3
Hot-curing mould material for producing cores and moulds in the sand casting process
Data Source
AI summary
The invention relates to a hot-curing mould material for producing cores and moulds in the sand casting process. This mould material comprises natural and/or ceramic sands and a two-component polyurethane binder free from phenolic resin, and also a heat-activatable catalyst. Said binder takes the form of a two-component polyurethane-based binder, comprising - a two-component phenol- and formaldehyde-free polyurethane-based binder comprising a resin component in the form of a mixture of two or more compounds which are hydrogen-active in respect of isocyanates and which have hydroxyl and/or mercapto and/or amino and/or carbamide groups, with an OH, SH and NH functionality of 1.5 to 8 and equivalent weights of 9 to 2000 g/equiv. of the individual constituents and with an average H functionality of 1.8 to 4.0 and an average equivalent weight of 90 to 200 g/equiv. of the resin component, and comprising a curing component with one or more diisocyanates or polyisocyanates, - a curing component consisting of one or more diisocyanates or polyisocyanates. The at least one thermally activatable catalyst, the activation temperature of which lies between 50 and 170 °C, comprises Brønsted bases and/or Lewis acids which promote the polyurethane reaction and also their associated blocking agents. The mould material comprises one or more refractory and pourable fillers having a medium particle size range from 0.1 to 0.9 mm, and comprises 0.3 to 4.0 % of the binder described, based on the mould base material, and 0.1 to 2.5 % of thermally activatable catalyst, based on the resin component of the binder.