Molding tool for molten metal or glass

Abstract

A molding tool made of carbon or graphite, namely a casting mold or a casting core for the processing of molten metal or to a molding tool for the processing of molten glass, such as for example a blow mold and a method for producing the molding tool.

Claims

1. A method for producing a moulding die for molten metal or glass, comprising the following steps: a) providing a powdered composition, which consists of carbon particles in a proportion of at least 50 wt. %, b) providing a liquid binder, c) planarly depositing a layer of the powdered composition provided in a), and locally depositing droplets of the liquid binder provided in b) to said layer, and repeating step c) a discretionary number of times, wherein the step of locally depositing the droplets in subsequent repetitions of said step c) is adjusted according to a desired shape of the moulding die to be produced, d) curing or drying the binder and obtaining the moulding die; wherein the carbon particles consist of acetylene coke.

2. The method according to claim 1, wherein the moulding die is heat-treated at least 500° C.

3. The method according to claim 1, wherein the moulding die is heat-treated at least 2,000° C.

4. The method according to claim 1, wherein the moulding die is subject to supplementary densification one or more times, this process comprising the following steps: impregnating with a carbon-delivering medium, and carbonising at a temperature of between 500° C. and 1,300° C.

5. The method according to claim 1, wherein the particles of the powdered composition in the grain size range of d50 have a shape factor (width/length) of at least 0.5 on average.

Description

EXAMPLE 1

(1) Calcined hard coal tar pitch coke was ground and, following grinding and screening at a screen size of from 0.4 mm, had a grain size distribution of d10=130 μm, d50=230 μm and d99=500 μm and an average shape factor of 0.69 (in the grain size range of d50+/−10%). The grain size distribution was determined by means of laser granulometry. 1 wt. % of a liquid sulfuric acid activator for phenol resin, based on the total weight of coke and activator, was first added to the coke, which was then processed by a 3D printing powder bed machine. In this process, a doctor blade unit deposits a thin layer of coke powder (approximately 0.3 mm in height) on a flat powder bed, and a type of inkjet printing unit prints an alcoholic phenol resin solution onto the coke bed according to the desired component geometry. The printing table is subsequently lowered by a degree equal to the layer thickness, a layer of coke is re-applied, and phenol resin is locally printed on again. By means of the repeated procedure, rectangular test specimens having the dimensions 172 mm (length)×22 mm (width)×22 mm (height) were constructed. Once the complete “component” had been printed, the powder bed was introduced into a furnace that had been pre-heated to 140° C., and was kept there for approximately six hours. In the process, the phenol resin cures and forms a dimensionally stable component. Following cooling, the excess coke powder was sucked away, and the component was removed.

(2) Once the binder had cured, the density of the component was 0.83 g/cm.sup.3 (example 1.1). The density was determined geometrically (by weighing and determining the geometry). The component had a proportion of resin of 5 wt. %, which was determined by carbonisation treatment. This process proceeded such that the carbon yield of the used cured resin constituent was determined in advance to be 58 wt. % by means of thermogravimetric analysis (TGA) in the absence of oxygen. On the basis of the loss in mass of the component following the subsequent carbonisation at 900° C. in a protective gas atmosphere for one hour, it was possible to calculate the original resin component in the component.

(3) The carbonised component was subsequently impregnated with phenol resin and carbonised again at 900° C. This increased the density to 1.08 g/cm.sup.3. Within the scope of the present invention, this procedure is described as supplementary densification and is mentioned below as example 1.2.

(4) A selection of the carbonised test specimens was then additionally treated at a high temperature in a protective gas atmosphere. An end temperature of 2,000° C. (example 1.3) was selected in one case, and an end temperature of 2,800° C. (example 1.4) was selected in another. As the temperature rises, the amorphous carbon is converted to the graphite structure. The densities of the test specimens remained approximately constant at 1.1 g/cm.sup.3 in this process. The reason for the slight increase in density is the shrinkage during high-temperature treatment. This shrinkage always occurs if the end temperature of the high-temperature treatment is significantly below the calcination temperature of the coke.

(5) After the test specimens had been produced, they were characterised. The properties are summarised in Table 1.

EXAMPLE 2

(6) Calcined acetylene coke, as delivered and without being ground, was subject to protective screening at a screen size of 0.4 mm. The screened acetylene coke then had a particle size distribution of d10=117 μm, d50=190 μm and d99=360 μm and a shape factor of 0.82. In a first step, 0.35 wt. % of the liquid activator according to example 1 was added to the coke powder, which was then processed so as to form components in the same way as example 1, test specimens being produced in order to determine the isotropy with respect to thermal expansion for all three directions (x, y, z).

(7) The components produced in this way had a proportion of resin of 3.0 wt. %. The density of the test specimens was 0.96 g/cm.sup.3 (examples 2.1x, 2.1y and 2.1z) and was thus significantly higher than for the ground hard coal tar pitch coke from example 1. Some of the test specimens for the X orientation were then impregnated with a phenol resin, this resulting in a density of 1.2 g/cm.sup.3 (example 2.2). The resin-impregnated test specimens were then carbonised at 900° C. in the same way as example 1, this resulting in a final density of 1.09 g/cm.sup.3. All test specimens of this embodiment were characterised. The results are summarised in Table 1.

EXAMPLE 3

(8) Ground synthetic fine-grain graphite powder was screened, the grain fraction of from 0.1 to 0.2 mm being removed. The particle size analysis of the selected screening fraction produced the following result: d10=120 μm, d50=170 μm and d99=250 μm. In a first step, 1 wt. % of the liquid activator according to example 1 was added to the flowable graphite powder, which was then processed, with an increased amount of resin being introduced, so as to form components in the same way as example 1. Once the binder had cured, the density of the test specimens was 1.0 g/cm.sup.3. The proportion of phenol resin was determined to be 10 wt. %, and the test specimens were characterised in line with the above examples (see Table 1).

EXAMPLE 4

(9) Calcined flexicoke, as delivered and without being ground, was subject to protective screening at a screen size of 0.4 mm. The screened flexicoke then had a particle size distribution of dl 0=85 μm, d50=120 μm and d99=220 μm. In a first step, 0.33 wt. % of the liquid activator according to example 1 was added to the coke powder, which was then processed so as to form components in the same way as example 1.

(10) The components produced in this way had a proportion of resin of 7 wt. %. The density of the test specimens was 0.82 g/cm.sup.3. The bending strength, determined in a three-point bending test, was 0.7 GPa. The three-point bending strength was 3.8 MPa. If these values are compared with those for acetylene coke samples (see example 2.1), the superiority of the material based on acetylene coke becomes clear. In spite of a lower resin content, the samples based on acetylene coke have considerably higher strength and stiffness. A lower resin content at the same time as high mechanical strength with acetylene coke as the raw material is particularly advantageous as fewer volatile gases are produced when the moulding die is used, this making it possible to use the moulding die in an environmentally friendly manner.

(11) Analysis

(12) The following table shows a number of physical properties of the test specimens produced:

(13) TABLE-US-00001 TABLE 1 Material characteristic values of the embodiments (averages) Example no. 1.1 1.2 1.3 1.4 2.1 2.2 3 AD 0.83 1.08 1.10 1.10 0.96 1.09 1.0 (g/cm.sup.3) ER 50,000 230 160 45 130,000 1,100 10,000 (Ohmμm) YM 3p 0.3 1.3 0.5 0.3 1.5 0.3 1.1 (GPa) FS 3p 0.4 2.4 1.6 1.3 5.7 1.7 4.0 (MPa) CTE 4.4 3.6 3.2 2.8 5.6 (x 4.7 5.1 RT/ direction) 150° C. 5.6 (y (μm/ direction) (m*K)) 5.5 (z direction) TC 0.5 2.7 20 1.1 (W/ (m*K)) AD (g/cm.sup.3): density (geometric) with reference to ISO 12985-1 ER (Ohmμm): electrical resistance with reference to DIN 51911 YM 3p (GPa): modulus of elasticity (stiffness), determined from the three-point bending test FS 3p (MPa): three-point bending strength with reference to DIN 51902 CTE RT/150° C. (μm/(m*K)): coefficient of thermal expansion, measured at between room temperature and 150° C. with reference to DIN 51909 TC (W/(m*K)): heat conductivity with reference to DIN 51908 Example 1.1: hard coal tar pitch coke, green body having a proportion of resin of 5 wt. % Example 1.2: hard coal tar pitch coke, green body having a proportion of resin of 5 wt. %, additionally impregnated with phenol resin, carbonised at 900° C. Example 1.3: hard coal tar pitch coke, green body having a proportion of resin of 5 wt. %, additionally impregnated with phenol resin, carbonised at 900° C. and treated at a high temperature of 2,000° C. Example 1.4: hard coal tar pitch coke, green body having a proportion of resin of 5 wt. %, additionally impregnated with phenol resin, carbonised at 900° C. and graphitised at 2,800° C. Example 2.1: acetylene coke, green body having a proportion of binder resin of 3 wt. % Example 2.2: acetylene coke, green body having a proportion of binder resin of 3 wt. % and subsequently impregnated with phenol resin, carbonised at 900° C. Example 3: synthetic graphite having a proportion of binder of 10%

(14) As all the examples show, the method according to the invention makes it possible to obtain material data which are in principle suitable for moulding dies and of which some have greater strengths than comparable established sand-based moulding materials.

(15) Furthermore, the density values of all the test specimens are advantageous as they lead to lighter moulding dies.

(16) The test specimens which were subsequently heat-treated demonstrate advantageous electrical conductivity, which opens up the option of resistance heating or inductive heating.

(17) The low values for the modulus of elasticity are particularly advantageous as the thermal shock resistance of the moulding die is thus increased.

(18) The strengths of the test specimens are consistently sufficient for the uses according to the invention. However, noteworthy are the high strengths when the binder content is high and in particular if acetylene coke is used, which strengths even exceed those of corresponding moulding dies made of sand.

(19) Furthermore, the values for the coefficient of thermal expansion are at a low level and can be lowered still by further heat treatment (carbonisation and graphitisation), an extremely low level thus being achieved. It can also be observed in particular that the material is highly isotropic with respect to the coefficient of thermal expansion. This ensures dimensional accuracy, for example during casting, and ensures a constant ratio of the dimensions of the cast part.

(20) Lastly, the values for the thermal conductivity are high in comparison with moulding dies made of sand. Higher thermal conductivities are achieved if graphite and/or high binder contents are selected (see example 3). The thermal conductivity can be increased further still by means of subsequent heat treatment (carbonisation/graphitisation) (see examples 1.3 and 1.4).