MOLD AND METHOD OF MANUFACTURING A MOLD

Abstract: This invention concerns a mold and method for fabricating the mold. The mold in accordance with the invention is essentially comprised of sulfur, into which is mixed a filler material having a particle length of at least 1.5 times the particle thickness. The mold is fabricated by producing the sulfur and filler material into a gel-like molten mix, which is then formed into the desired shape, after which the form-shaped mold of the yet molten mold material is rapidly cooled by its surface in order to solidify the filler-containing sulfur mix. The molten mold material is advantageously produced by heating a mix comprised of sulfur and fine-milled iron slag or wollastonite, with a hydrocarbon fraction such as diesel oil added to it, to a temperature of approx. 115...160 DEG C. The mold in accordance with the invention can be stripped by heating, allowing for the reuse of the mold material.

Description: Mold and method of manufacturing a mold The present invention relates to a mold in accordance with the preamble of claim 1. Furthermore, the invention concerns a method in accordance wit the preamble of claim 10 for manufacturing a mold. According t the method, the mold is fabricated from such an easily shaped material that, after the attainment of the desired shape, can solidified into a dimensionally stable form. Molds have been known since the beginning of the manufacturing art of metals. In later times the use of molds has been expand into the casting of other kinds of materials such clay, gypsum glass, concrete, rubber, elastomers and ceramic materials in general. A plurality of mold applications are known, while only a few methods for manufacturing molds exist. A mold has conventional been fabricated by casting the mold material onto the original to be copied, dividing the mold into parts and reassembling fo a new casting. Molds can also be fabricated by means of the so called melting wax method used in the casting of, e.g., metals In this method the wax filling the casting cavity is subsided the molten metal. In concrete industry molds are conventionally fabricated from plywood or metal material. The most frequently used method is fabricate the mold of a cast concrete element from, e.g., plywood, wherein the manufacturing of the mold takes place entirely manually and consumes expensive materials. Waxes and similar materials are also capable of being used fot prefabricating the mold which is then either cast or, for instance, machined into its final form. Thence, the fabrication technology of molds deals with variou materials and the ways in which they are used. Furtϋer, mold fabrication can be — and today even must be — concerned wit the methods of combining automated production techniques with suitable materials and the ways they in which they are used. Exemplifying the current level of technology, the FI patent publication 71262 deserves to be mentioned disclosing a method in which a polymeric material having a melting point of less than 150 °C is fed in its fluid state into a box-shaped container. After the solidification of the mold material, the material is milled into the desired shape by a milling machine controlled by a computer-stored milling file. Known from SE patent publication 64677 is a casting mold for th fabrication of mold-cast pavement stones, in which mold resin, sulfur and bitumen has been mixed into the molding sand, allow¬ ing the mold surface to be hardened impermeable to water by means of external heating. The mold can be used for producing concrete products with zero shrinkage by virtue of the water- impermeable character of the mold. Release of the cast product from the mold is eased by spraying the mold with soot or talc prior to casting. The mold material disclosed in the SE patent publication 64677 is applicable solely for the fabrication of expendable molds. The goal of the present invention is set as to develop such a novel type of mold material that can be recycled without the disagreeable cost factor of material loss, which is characteristic of the conventional technology. Construction technology uses conventionally molten sulfur in, e.g., certain fixing applications such as the fixing of a metal bolt into a drilled hole or the levelling of concrete test cube ends for compression tests. Sulfur melts at approx. 115 °C and forms an extremely fluid mass. If the temperature is allowed to exceed 160 °C, sulfur undergoes a partial polymerization and turns into a rubbery material. For the purpose of levelling the ends of test cubes, sulfur has conventionally been mixed with fillers such as sand, or more generally, with ground limestone, which is a mineral containing calcium carbonate. This method results in a mixed material with a lower cost than that of mere sulfur, with the added benefit that the sulfur concrete attains the color of a conventional concrete. The most important benefit is, however, that the cooling shrinkage of the concrete can be significantly reduced by way of using filler additives. A sufficient addition of conventional sand and/or ground limestone results in a stiffening of the molten material up to degree that makes even the molten material non-fluid. This effect produces a stiffer material with the use of a higher filler content. Such a stiff molten mix exhibits, however, a Newtonian viscosity behavior. Under the influence of a force t mix will exhibit; the stiffer mix only has a slower flow rate. Because the marker price for sulfur is only about FIM 450...60 per ton, depending on the quality grade, it would be an advantageous material for use in, e.g., molds. The attractive pricing is further enhanced by the reusability of the material By contrast, sulfur brings about disadvantages which so far ha prevented its use as a mold material. For instance, sulfur milling is associated with the same problem that plagues the machining of, e.g., wax, namely that the material melting in t milling process subsequently tends to adhere to the tool. In case of sulfur this problem is accentuated by the utmost tackiness of sulfur onto any material. In addition to the aforementioned problem, milling by itself is a slow and expensive shaping method of materials. An object of the present invention is to overcome the drawbac of conventional mold techniques and to achieve a novel mold material. A further object of the present invention is to achieve such a novel method of mold manufacturing that promot the adaptation of automated and computer-controlled productio technology. In investigations carried out into the use of milled iron sla as a replacement to milled limestone for a filler additive in the molten sulfur mix, it was found that entirely different viscosity characteristics can be imparted to a sulfur mix whe equal weights of either milled iron slag or of sand and limestone are mixed into molten sulfur. In this conjunction it was also found that the use of milled slag and, alternatively, of milled slag complemented with, e.g., fine silica, as an additive achieved such a molten sulfur mix that was not stiff but not fluid either, appropriately described as a gel with eas moldability into any desired shape. According to the invention, such gel-like molten sulfur concrete can be shaped with, e.g., a scraper into all forms most generally required in molding techniques. The present invention is based on the idea that the basic material of the mold is produced by using sulfur as the binder and complementing it with appropriate filler additives, togethe forming a mix appropriately called sulfur concrete. Such additives are used according to the invention for this purpose that avoid the known low viscosity of sulfur concrete, while simultaneously achieving a thixotropic molten mix, i.e., a material with gel-like behavior. This goal is attained by using filler additives whose particle size is characterized by having a length of at least 1.5 times the thickness. Such a filler additive can be achieved by the use of crushing mills which are non-abrasive by their character and can operate but with a minimum of material-against-material abrasion. Examples of such mills are impact mills, jet mills and roll mills. More specifically, the mold in accordance with the invention is principally characterized by what is stated in the characteriz¬ ing part of claim 1. Furthermore, the method in accordance with the invention is characterized by what is stated in the characterizing part of claim 10. According to a preferred embodiment of the invention, the filler additive used is milled iron slag with a fineness of at least 400 m 2 /kg. Preferably the amount of slag is about 2.5 to 5 times the amount of sulfur. According to another preferred embodiment, the filler additive used is milled wollastonite or milled mica. Further, a possible additive in the sulfur mix is an extremely fine-grained filler such as microsilica. The sulfur mix can be plasticized by means of different oils and glycerin. Typical plasticizers used are mineral ils and their fractions such as diesel oil, for instance. All fractio having their boiling point above the temperatures μsed ' are soluble in the molten sulfur. Alternatively, different kinds o liquids known as heat transfer media may be used. These may contain aromatic compounds and glycols or, preferably, glycoethers. By using heat transfer media frothing during heating can be eliminated and, thus, non-porous products are obtained. Sulfur concrete and a filler with sufficiently oblong shape (length > 1.5 x thickness) can easily be cast into solid plan or other shapes, which can then be attached to a mold as a pa of the mold, e.g., as sides of the mold. Such mold sides can melt-jointed to the other part of the mold by conventional methods, for instance, by melt-jointing with molten sulfur. A preferred method for this purpose is, however, electrical melting by using graphite band or braided metal band as the heating element for melting the side part to be joined. This method allows for producing extremely neat joints' quickly and a high level of automation. The power supply used can be a welding transformer or similar apparatus. According to a preferred embodiment, the first layer of the sulfur concrete is casted on a heated base or support. When said base is heated to a suitable temperature of about 70 to 110 C C, the sulfur concrete layer does not bend upon cooling and it is possible to obtain level-casted products in a dimensionally stable form. The mold can be stripped by applying electrical heating in th The mold can be stripped by applying electrical heating in the same manner as used during the assembly, whereby the side planks are detached unbroken, allowing for their reuse. In the case the mold is stripped with the help of electrical heating, it is found that molten sulfur tends to adhere to the surface of the cast concrete product thus forming a homogeneous sulfur layer. This adherence is strong even if mold release oils are used, because such oils themselves are soluble in molten sulfur. Thence, the stripped concrete element is provided for these mold jointing areas with a thin surfacing layer formed of the sulfur mix that can be levelled with a scraper or roller into a layer which is later usable as a jointing layer during the jointing of such concrete elements. Such jointing can advantageously be carried out by means of an electrically conductive layer and electric current applied to it. If the mold has been constructed with a shape having tongued forms protruding into and resulting in grooves in the cast concrete, these grooves will remain, after the stripping of the mold by means of heating following the setting of the concrete, filled with the sulfur concrete mix. Such a groove filled with sulfur concrete can later be advantageously utilized during the jointing of the elements, whereby a joint with a strength of approx. 100 000 N/linear m of joint is achieved for a joint formed by a circular groove joint of 2 cm diameter, which is jointed by means of electrical heating. Furthermore, glass-fiber mat or any other fiber material mat or cloth can advantageously be used as a filler material for sulfur concrete, provided that the melting temperature of the fiber is higher than the temperature of 115...130 °C used in th process. Glass-fiber cloth is applicable with an attractive cost and high strength in conjunction with sulfur concrete or as the only filler in sulfur. The most preferred use of the cloth is i conjunction with sulfur concrete, because molten sulfur alone i too fluid. A glass-fiber cloth of 200 g/m 2 base weight can material with a base weight of 3...5 kg/m 2 is obtained. This material can then be freely shaped by way of local heating so to further obtain from said fiber-reinforced sulfur concrete composite material such edge stiffeners and differently shaped surfaces that during their cooling remain in their formed shap and can be attached to other part of the mold by the simple means of a heat gun or an IR lamp, or electrical heating as well. The invention provides outstanding benefits. For instance, a mold can be formed essentially without the help of machining, simply by using mechanical form-shaping exclusively or" almost exclusively in such a way that principally avoids the removal material, but instead, rather moves the material within the mo area to be shaped. Alternatively, mechanical form-shaping can used for adding material layer by layer to the mold area to be shaped, which is now possible through the fact that the newly applied layers do not exhibit a dripping tendency or shape deformation to a greater degree than that of their cooling shrinkage; all this is achieved by the addition of appropriate fillers that make the mold material sufficiently thixotropic b nature. i Furthermore, it was found that during the setting of the sulfu concrete, particularly in conjunction with the use of the abov described filler materials, the concrete surface hardens to a sufficient degree to locate the cooling shrinkage and resultin cracks principally to the interior of the concrete, thereby avoiding cracking of the surface. This goal is particularly attainable through the modification the sulfur concrete by hydrocarbon fractions, at least part o which must have a relatively high vapor pressure at the proces temperature of 115 °C, one such fraction being diesel oil, fo instance. In this method, the cooling shrinkage produces internal pores into the material, whereby cracks on the surfa are avoided. A mold fabricated and assembled according to the methods described above for the purpose of, e.g., manufacturing concrete elements, can be stripped irrespective of what kind of mold drafts are used, because the mold material can be broken b blows or melting in order to strip the hardened cast free from the mold. In the mutual comparison of sulfur concrete materials produced using milled slag and limestone, respectively, it was found tha the use of slag as the filler material resulted in a remarkably higher bending strength of the sulfur concrete than that obtainable with limestone. Though an exhaustive explanation of the strength and thixotropic behavior of sulfur concrete still remains to be found, it can be assumed that the governing factor will be found in the particle shape of the milled filler material. Microscopic studies reveal that the particle shape of, e.g., milled slag is needle-like and edged, while limestone and sand particles are mostly round and cubic-shaped. Thence, the material used according to the invention must have a glass-like character or such a crystalline form that under non-abrasive milling gives the desired dimensions of the fractured material. The invention is next examined in detail with the help of a fe exemplifying embodiments of nonexhausting character to the implementation of the invention. Example 1 Sulfur concrete mix was produced by adding milled iron slag with a fineness of 450 m 2 /kg into the sulfur according to the following formula: Slag 440 g Fly ash 300 g Sulfur 200 g Glycerin 40 g The mix was heated to a temperature of 125 β C, whereb a mix exhibiting easy form-shaping was obtained, capable of being easily formed into almost vertical wall of 15 cm height. Afte the hardening of the product, no surface cracks *were detectable. Example 2 Sulfur concrete mix was produced according to the following formula: r Slag 600 g Sulfur 250 g Diesel oil 50 g The mix was heated to a temperature of 140 β C under vigorous mixing, whereby a mix exhibiting easy form-shaping was obtain as in the example above. The surface of the hardened product crack-free and hard, while an abundance of round pores with varying diameter were found in the interior of the product. Example 3: Sulfur concrete mix was produced according to the procedure t • of example 2 by using 800 g of slag, 250 g of sulfur and 50 g of diesel oil. The surface of the hardened pro-duct was crack-free and hard. Example 4: Sulfur concrete mix was produced according to the procedure of example 2 by using 800 g of slag, 250 g of sulfur and 50 g of Dowtherm 300 (a heat transfer medium). The mix was heated to 140°C under vigorous mixing and after form-shaping and cooling a smooth-surfaced product was obtained. Practically no pores were found in the interior of the product. Example of reference sample Sulfur concrete mix was produced according to the following formula: Sand, particle size 0...0.6 mm 600 g Limestone, particle size < 0.1 mm 150 g Sulfur 250 g Heating of the mix was to a temperature of 125 °C resulted in a fluid mix of low viscosity, capable of flowing into crevices even narrower than 1 mm and exhibiting a strong adherence to th adjacent walls (concrete) , however, with a shrinkage crack in the middle of the crevice. Any ratio of filler addition failed to make the mix non-flowing and easily form-shaped at the same time. Example 5 A 2 m long level-cast sulfur concrete plane was obtained by casting a sulfur concrete mix produced according to example 3 on a base heated to about 90°C. Onto said plane was jointed a plank of 200 x 3 x 15 cm 3 size, cast in a comparable method from sulfur concrete. The plank surface was precoated with a fine-meshed acid-proof steel net, dimensions 2 x 200 cm 2 which was attached by electrical heating to the surface. The plank was then placed onto said straight sulfur-concrete plane. Cables from a welding transformer were connected to the ends of the steel net with copper clamps, and the transformer output current was set to 40 A, which was found to melt the plank surface in 5 minutes fully cleanly onto the underlying surface of the plane. Finally, current was switched off and the joined parts were allowed to cool jointed together.

Claims: WHAT IS CLAIMED IS: 1. A mold fabricated from a material essentially comprised of sulfur, which mold material has filler materials mixed into sulfur, c h a r a c t e r i z e d in that the filler material has a needle-like shape of particles and that the length of the particles is at least 1.5 times their diameter. 2. A mold in accordance with claim 1, c h a r a c t e r - i z e d in that the filler material is iron slag having a fineness of at least 400 m 2 . 3. A mold in accordance with claim 2, c h a r a c t e r ¬ i z e d in that the ratio of slag to sulfur (w/w) amounts to about 2.5 to 5. 4. A mold in accordance with claim 1, c h a r a c t e r ¬ i z e d in that the filler material is milled wollastonite or milled mica. 5. A mold in accordance with claim 2...4, c h a r a c t e r i z e d in that the sulfur mix further contains an extremely fine-graded filler material such as microsilica. 6. A mold in accordance with any of claims 2...5, c h a r ¬ a c t e r i z e d in that the sulfur mix further contains a hydrocarbon fraction such as diesel oil that has a relatively high vapor pressure at the process temperature of 115 °C. 7. A mold in accordance with any of claims 2...5, c h a r a c t e r i z e d in that the sulfur mix further contains a heat transfer media containing aromatic compounds, glycols or, preferably, glycoethers. 8. A mold in accordance with any of claims 1...7, c h a r ¬ a c t e r i z e d in that at least a part of the mold is comprised of prefabricated elements, which are jointed to eac other using the above-claimed filler-containing sulfur mix. 9. A mold in accordance with any of the foregoing claims, c h a r a c t e r i ze d in that at least a part of fabrication material of the mold is reinforced with fabric material, preferredly with a glass-fiber cloth or mat. 10. A method for manufacturing a mold, according to which metho such an easily form-shaped mold material is used that after the forming to desired shape can be solidified into a stable shape, c h a r a c t e r i z e d in that - the starting materials used in the production of the mold material are elementary sulfur and a complementing filler material with an essentially needle-shaped particles whose external shape is such that the particle length is at least 1.5 times the particle thickness, - the sulfur and filler material are processed into a gel-like and non-fluid molten material, - the molten material is shaped into the desired form of the mold, and - the mold shaped from the molten material is cooled rapidly at least from its surface in order to solidify the filler-containing sulfur mix. 11. A method in accordance with claim 10, c h a r a c t e r ¬ i z e d in that the molten sulfur mix is produced by heating the mix formed of sulfur and fine-milled iron slag to a temperature of approx. 115...160 β C. 12. A method in accordance with claim 10, c h a r a c t e r ¬ i z e d in that the molten sulfur mix is produced by heating the mix formed of sulfur and milled wollastonite or milled mica to a temperature of approx. 115...160 °C. 13. A method in accordance with claim 10...12, c h a r a c ¬ t e r i z e d in that the mix formed of sulfur and a filler material is complemented with microsilica. 14. A method in accordance with any of claims 10...13, c h a r a c t e r i z. e d in that the mix formed of sulfur and a filler material is complemented with a hydrocarbon fraction, preferably diesel oil, or a heat transfer medium, which has at least relatively high vapor pressure at the process temperature of 115 β C. 15. A method in accordance with any of claims 10...14, c h a r a c t e r i z e d in that the first layer of the molten sulfur mix is casted on a base heated to about 70 to 110 °C. 16. A method in accordance with any of claims 10...15, c h a r a c t e r i z e d in that the form-shaped mold of yet molten mold material is cooled by its surface with cold air or cold water. 17. A method in accordance with any of claims 10...16, c h a r a c t e r i z e d in that the mold material is fabricated into separate mold elements, which are attached to each other by placing them abutting at desired points and heating the adjoining jointing areas to a temperature of 115...160 β C, after which the elements are allowed to cool jointed together. 18. A method in accordance with claim 17, c h a r a c t e r i z e d in that the jointing areas are heated electrically by means of heating elements placed on the surfaces of the mold elements and connected to an electrical power supply. 19. A method in accordance with any of claims 10...18, c h a r a c t e r i z e d in that at least a part of the mold is reinforced with a fabric, preferredly a glass-fiber cloth o mat.

Inventors: VIRTANEN PENTTI, VIRTANEN, PENTTI
Applicants: KAUTAR OY
Application year: 1990
Main classification: B28B7
IPC codes: B28B7, C04B28, F02B3