Material system and process for the production of salt cores for use in the manufacture of hollow composite structures

Abstract

The invention provides a material system and a method for use in the construction of lost cores for composite materials, characterized in that a salt core having a porosity is treated with a silicate solution on the surface.

Description

Summary:

[0001] The invention provides a material system and a method for use in constructing lost cores for composite materials, characterized in that a salt core having porosity is treated with a silicate solution on the surface. Description:

[0002] Technical components fulfill different functions, which are often integrated into a single component. This integration facilitates lightweight construction, and the spatial structure of the component usually becomes more complex. Components that must absorb bending moments and torsion are often hollow structures.

[0003] The hollow structures are usually so complex that a tool part cannot be removed from the interior of the component simply by pulling it out. For this purpose, so-called lost cores are used, which define the cavity and are decomposed by mechanical forces or dissolution processes after the creation of a stable component.

[0004] In the field of fiber-reinforced plastics, such cores are coated with a mixture of fibers and a curable plastic (hereinafter generally referred to as resin, although both chemically and thermally curable plastics are possible). This mixture then hardens to form a thin-walled, usually very lightweight component.

[0005] The core must meet various requirements for such a process, which vary to a greater or lesser extent depending on the process: The core must withstand the process forces. Depending on the process, these may include forces from wrapping fibers or forces from applying a vacuum to wet the fibers without the formation of air bubbles. The vacuum process requires a tight surface to prevent the resin from penetrating the core. The temperature control, usually up to 250°C, requires a certain degree of heat resistance from the core. Last but not least, the core must be able to be removed from the component.

[0006] US 3425982 shows a water-soluble core consisting of sand and a thermoplastic binder. The binder is also water-soluble and can be removed from the core by washing. GB 2586943 shows a different formulation using gypsum and a polymer binder. Like most conceivable formulations, pores are created in the component during molding as part of the manufacturing process. GB 2586943 describes how the pores can be reduced by using a vacuum casting process. This prevents resin penetration and thus enables a safe process.

[0007] Both formulations use a polymer as the basis for bonding inorganic particles. This results in two weaknesses. First, the formulation has limited temperature stability and is therefore restricted for use with special resins. Second, the process is not environmentally friendly simply because it uses polymers.

[0008] Salt cores are used as cores in various processes. Depending on the manufacturing process, more or less porous structures can be expected. Most processes, such as pressing or bonding the particles (see GB 2586943), create pores. Only casting from the melt results in pore-free products. However, this process is costly, and the core is difficult to remove.

[0009] The solubility of the core plays an important role in the dissolution process. Therefore, it is advisable to make the core as soluble as possible while simultaneously preventing resin penetration.

[0010] The invention task is solved by a Material system for use in the construction of lost cores for composite materials, characterized in that a salt core having a porosity is treated with a silicate solution on the surface and a Method for constructing lost cores for composite materials, characterized in that a salt core having a porosity is treated with a silicate solution on the surface solved.

[0011] Salt cores meet the demand for environmentally friendly recycling. The material can be washed out and reused after drying.

[0012] Salt cores can be produced from the melt, as already mentioned above, or from particulate material. If the melt, as described above, is not suitable for an economical process, the component or a preform must be produced from particulate material. For this purpose, the particles in the particulate material must be bonded together. This can be achieved via crystallization, chemical binders, thermal binders, or plasticization under high pressure. This results in the following manufacturing methods: pressing, milling from a block, milling a preform, blocking by exposure to humidity, binding by crystallization, joining salt particles by binders, core shooting, 3D printing or other shaping processes.

[0013] As already described, density and absolute porosity are not a target parameter of the material or the manufacturing process. Rather, it is expedient to select a porosity that optimally accommodates all process steps. However, this varies from material to material (component materials). However, the density of the surface is crucial, so the combination of base material and coating agent as a material system is particularly important.

[0014] According to the invention, the basis for the cores is salt, which has many positive properties for the process and meets the criteria of being environmentally friendly and recyclable. The salt consists, for example, of Anions such as potassium, sodium, calcium, magnesium, iron(II), iron(III), aluminum, ammonium, tetraethylammonium and from cations such as fluorides, chlorides, bromides, iodides, oxides, sulfides, carbonates, sulfates, nitrates, acetates, chromates, permanganates, hexacyanidoferrate(II) These substances form the salt crystals through ionic bonds, which form the basis of the material for the cores. This type of bond makes the cores essentially water-soluble and, compared to other materials, highly temperature-resistant.

[0015] For example, blocks can be pressed from NaCl at high pressures. These blocks exhibit the necessary strength and can be milled into the desired shape with high precision. It is also possible to directly press a special shape. The combination of both processes enables cost-effective production with a high degree of freedom of shape and precision.

[0016] Such cores cannot be used directly due to their residual porosity, which allows for good solubility, as tests have shown. During the production of composite materials, the resin penetrates the core, rendering the component unusable.

[0017] Therefore, a coating must be applied to the core. A variety of materials can be used for this task. Surprisingly, tests have shown that surface treatment with water glass easily meets the above-mentioned process requirements. Compared to other materials, this results in a remarkable range of properties. The salt component can simply be coated with water glass. The water glass is absorbed into the material and solidifies immediately. The material near the surface remains liquid and can be reliably distributed throughout the process. As a result, the surface can be reliably sealed without creating a layer on the component that would change its dimensions.

[0018] The application depends on the manufacturing method of the salt core. Depending on its density, the process may need to be adapted. Cores with very high porosity must not be dissolved by the penetrating water glass. Such cores are coated in several stages.

[0019] Water glass can have various characteristics. In each case, it is possible to control the viscosity and dissolving power of the material through the solid content. Chemically, the water glass types are Sodium water glass, potassium water glass, lithium water glass Available in various blends. The water glass solutions can also be enhanced with viscosity modifiers such as phyllosilicates.

[0020] The material system according to the invention is, as already described, used in an inventive Method for constructing lost cores for composite materials, characterized in that a salt core having a porosity is treated with a silicate solution on the surface used.

[0021] The water glass solution can be Spraying, brushing, applying with cloths, dipping or printing be used up. The above-described property of the inventive combination of salt core and water simplifies the process and makes various application mechanisms reliable. It is particularly noteworthy that manual processes such as brushing do not permanently alter the component's dimensional accuracy and surface texture.

[0022] The inventive method also allows for selective coating of the core surface. This allows the surface portion that comes into contact with the resin to be protected, and the area that supports the core in the mold (above the core mark) can be used for release.

[0023] Drying the component can play a key role in preventing moisture introduced via the water glass from damaging the core. Drying with hot air and infrared heaters immediately after the water glass is applied allows for further process control. Example process chain:

[0024] NaCl salt is pressed into a block at a pressure of 100 MPa. The salt core is milled from this block. The core is then coated with a water glass of the same type in one operation using a brush and dried at room temperature for 4 hours. A pressure test with an overpressure of 0.1 MPa reveals no leaks within the accuracy of the measurement setup. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 3425982

[0006] GB 2586943 [0006, 0008]

Claims

[1] Material system for use in the construction of lost cores for composite materials, characterized in that a salt core having a porosity is treated with a silicate solution on the surface. [2] Material system according to claim 1, characterized in that the salt core is produced by pressing, by milling from a block, by milling a preform, blocking by exposure to atmospheric humidity, binding by crystallization, joining salt particles by binders, core shooting, 3D printing or other shaping processes. [3] Material system according to claim 1, characterized in that the salt core has a porosity in the interior that is determined by the manufacturing process or is specifically adjusted. [4] Material system according to claim 1, characterized in that the salt core consists of a salt of anions such as potassium, sodium, calcium, magnesium, iron(II), iron(III), aluminum, ammonium, tetraethylammonium and cations such as fluorides, chlorides, bromides, iodides, oxides, sulfides, carbonates, sulfates, nitrates, acetates, chromates, permanganates, hexacyanidoferrates(II). [5] Material system according to claim 1, characterized in that the silicate solution is a sodium water glass, potassium water glass, lithium water glass or a mixture of these water glasses. [6] Method for constructing lost cores for composite materials, characterized in that a salt core having porosity is treated with a silicate solution on the surface. [7] Method according to claim 6, characterized in that the silicate solution is used up by spraying, brushing, applying with cloths, dipping or printing. [8] Method according to claim 6, characterized in that the silicate solution is applied selectively. [9] Process according to claim 6, characterized in that the silicate solution is dried using a rapid drying process.