Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
• • 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
  • B22C1/16—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents
  • B22C1/18—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by the use of binding agents; Mixtures of binding agents of inorganic agents
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C7/00—Patterns; Manufacture thereof so far as not provided for in other classes

Definitions

• the present invention relates to lightweight molds, models and tools based on gypsum, which are particularly suitable for the automotive, aircraft and shipbuilding industries, as well as the sanitary and construction sectors, and a method for their production.
• European patent application EP 124 801 A2 describes a process for the production of precision castings using the plaster molding process. This process works in such a way that only forms are created that can absorb moisture and are therefore gas-permeable. These molds are well suited for the production of castings with sharp detail reproduction and high measuring accuracy. However, the mechanical strength of such shapes does not meet the requirements imposed in vehicle and aircraft construction. Even the shapes reinforced with whiskers and glass fibers do not have the required high mechanical strength.
• Glass fiber reinforced gypsum and / or cement laminates are known from EP 203 333 B1. According to this patent, the laminates made of glass fiber reinforced hard plaster and / or glass fiber reinforced cement in Wet-on-wet process. The process is characterized in that at least one base layer of a binder is applied to the model to be molded and provided with a release agent, onto which a glass fiber-reinforced molding composition consisting of 95 to 0% by weight alpha-calcium sulfate hemihydrate, 0 to 95% by weight. % Cement, 0.5 to 8% by weight glass fibers and 0.5 to 4% by weight adjusting agent based on the dry weight, and water is applied and the laminate formed in this way is removed from the mold after setting.
• a glass fiber-reinforced molding composition consisting of 95 to 0% by weight alpha-calcium sulfate hemihydrate, 0 to 95% by weight.
• % Cement 0.5 to 8% by weight glass fibers and 0.5 to
• Another important task was to find a method by which it is possible to variably adjust the wall thickness of the molds, models and tools and thus the mechanical strength of the molds, depending on the requirements.
• Models could be solved, which is characterized in that laminated to the mold surface coated with epoxy resin or plaster, several layers of laminatable reinforcing materials and / or combination of reinforcing materials soaked with a low-viscosity gypsum slurry, and the laminate thus formed after setting and curing is removed from the mold.
• Suitable reinforcing materials are those that are elastic and absorbent, especially nonwovens, and needled glass fiber mats. It is advisable to cut them to the size suitable for this mold before laminating them on the mold surface. This is usually done with the tools known for this.
• Particularly suitable reinforcement materials are nonwovens with a basis weight of 150 to 300 g / m2 and needled glass fiber mats with a basis weight of 200 to 650 g / m2.
• the reinforcement materials are available on the market, e.g. the fleece from Vliesstoffwerke Sandler, 8676-Schwarzenbach, FRG or the glass fiber mat from Syncoglas, in Zele Belgium.
• the epoxy surface resins that can be used here are available on the market, e.g. from Ciba-Geigy, Basel under the brand names SW 404, SV 410 and SV 414 or from Ebalta, Rothenburg o.d.T under the brand name OH 5.
• the procedure is as follows:
• the mold to be molded is provided with a wax as a release agent.
• Several layers of epoxy resin are applied to this mold surface using the wet-on-wet method.
• the reinforcement elements soaked in plaster are laminated onto the last wet layer. It is important that the last epoxy resin layer is still moist so that the reinforcement materials adhere well to the resin-coated mold surface.
• the gypsum slurry for the coating is produced by mixing the powdery components and then adding water. As gypsum, so much water is added to alpha calcium sulfate hemihydrate that an easily spreadable mass is formed. The amount of water added can be, for example, between 26 and 31% by weight, based on the amount of gypsum.
• the process according to the invention produces molds and laminates which are considerably lighter in comparison with conventionally produced ones, but nevertheless have a very high bending tensile strength.
• an adhesion-promoting substance e.g. Apply a filler to the entire surface of the mold with a brush.
• the reinforcing element soaked in plaster is immediately laminated to the still damp surface.
• a model to be molded is carefully separated with release wax.
• a fleece with a basis weight of 150 g / m2, which is pre-cut to the appropriate size, is used as the reinforcing material.
• the mold surface is first covered with a 0.5 mm thick epoxy resin layer. If the epoxy resin layer is gelled, the next resin layer is applied. The last layer of epoxy must be wet when the reinforcing material is applied.
• the gypsum mixture is prepared, namely 100 parts by weight of gypsum powder with 28 parts by weight of water are processed into the low-viscosity slurry. The mixture is expediently stirred in order to obtain a homogeneous, air bubble-free slurry.
• the pre-cut nonwovens are immersed in the freshly made liquid gypsum mixture and left to soak. They are drained a little and immediately placed on the mold. In the same way, two more layers are applied to this layer. It is important that the individual layers are still moist, ie the plaster has not yet set. The adhesion between the individual layers is optimal.
• Example 2 Workflow for the production of a large-area laminate with plaster surface coating and a needled glass fiber mat as reinforcing material
• the model to be molded is separated as in Example 1. Instead of an epoxy resin, a low-viscosity plaster mixture is brushed onto the surface, repeatedly until an approx. 3 mm thick plaster layer is created.
• a large model was taken and the workflow was as follows: After the mold surface is coated with gypsum, wait until it has fully set and has cooled. Then the mold is moistened with a little water and the entire surface of the mold is coated with an adhesion-promoting filler.
• the model or shape is pre-treated with wax as in Example 2.
• the plaster coating is also carried out as in Example 2, only with the difference that the needled glass fiber mat is applied immediately after the plaster coating has been applied to the still moist plaster layer without the use of filler.
• the basis weight of the glass fiber mat is 400 g / m2. Two more layers of glass fiber mat are laminated. After setting, which is completed after 2 hours, the mold is removed.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Laminated Bodies (AREA)

Applications Claiming Priority (2)

Publications (2)

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ID=6410667

Family Applications (1)

Country Status (2)

Cited By (2)

Family Cites Families (4)

• 1991
  • 1991-04-25 EP EP19910106674 patent/EP0467025A3/de not_active Withdrawn
  • 1991-07-19 FI FI913485A patent/FI913485A7/fi not_active Application Discontinuation

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