A cement mortar composition and articles produced therefrom

Abstract: The cement mortar composition for producing articles, such as, in particular, dies for shaping plates, comprises in the quantities defined by the following weight percentages: cement 20-50% expanding agent 1-10% dispersing agent 0.5 to 2% de-aerating agent 0.5-1.5% sand 30-70% calcareous filler 1-10% From these compositions it is possible to produce articles, particularly dies for shaping plates, following the preparation of a mixture of water and these cement mortar compositions, the casting of the mixture in a mould corresponding to that of the desired article, and the setting of the mixture.

Description: The present invention relates to a cement mortar composition for producing articles, such as, in particular, dies for shaping plates, for example, of plastics or composite material or metal sheet and to articles produced in this manner. In many areas of industry, and in the motor vehicle industry in particular, dies are used for drawing metal sheets into a desired shape so as to form, for example, bodywork parts and various motor vehicle components. Steel dies are usually used for mass production even though they are very expensive. In fact, they have adequate mechanical strength and their cost is suitably spread over a large number of parts produced. On the other hand, materials other than steel are used for dies used for producing small series of parts and for those used for performing tests, which are modified and/or remade several times, in order to reduce the cost and enable the die to be prepared more rapidly. Among the latter materials there can be listed low-melting metal alloys, thermosetting resins, which may possibly be reinforced, and cement mortars. With respect to the other materials, cement mortars have advantages in terms of cost, ease of working without developing substantial pollutants and the possibility of elimination without harmful consequences for the environment. Cement mortars lend themselves well to this application since they are particularly resistant to the mechanical compressive stresses which are particularly prevalent in a die. Tensile and bending stresses, which are also present in a die, can advantageously be absorbed by providing adequate reinforcement, for example of metal or polymer material. The object of the present invention is to provide a cement mortar composition which is suitable for the production of articles such as, in particular, dies for shaping plates, which is inexpensive and easy to use and, at the same time, permits dies having adequate mechanical strength to be produced. This object is achieved by a cement mortar composition comprising, in the quantities defined by the following weight percentages: cement 20-50% expanding agent 1-10% dispersing agent 0.5 to 2% de-aerating agent 0.5-1.5% sand 30-70% calcareous filler 1-10%. In order to produce a shaped article, such as, for example, a die, from a cement mortar composition according to the invention, a mixture of the latter is prepared with water, the mixture is then agitated for a suitable length of time, it is then poured into a mould which reproduces the shape of the die which is to be produced, and the mixture is left to harden. It has been discovered by experiment that a compressive strength according to the European standard CEN EN 196/1 of at least 50 N/mm 2 is attained using the mortar composition of the invention and this is sufficient for forming operations in conditions which are not extreme. This strength can be attained in a short time (between 1 and 3 days after casting) even at ambient temperature. The composition according to the invention has the particular advantage that, once mixed with water, it assumes high fluidity which is maintained for a length of time sufficient to enable it to be used. The mixture of water and cement mortar according to the invention can thus be cast in complex moulds by filling them sufficiently, without the need to subject it to particular mechanical stresses, such as shaking, vibrations and the like, except in order to expel any air bubbles remaining entrapped against the walls. If the cement mortar according to the invention is used for producing dies comprising a metal reinforcement, it has the further advantages of having a high degree of adhesion to the metal and of not tending to shrink, ensuring optimum cohesion with the frame, once hardened. It is possible to use any type of cement, whether it is based on Portland clinker or is aluminous, in the mortar composition according to the invention. Preferably, a cement of the high-strength type is used, for example of the 42.5 N/mm 2 or 52.5 N/mm 2 type, as defined by the European standard CEN ENV 197/1. The role of the expanding agent is to eliminate hydraulic shrinkage, which, if it is not compensated, can cause flaws and changes in the dimensions of the die. Preferably, a calcium sulphoaluminate or calcium oxide-based product is used for this purpose. The role of the dispersing agent is to reduce the amount of water to be added to the cement mortar composition which, if it is too high, would compromise the mechanical properties of the articles produced from the mixture. Preferably, to this end, a product based on a calcium or sodium salt of naphthalene sulphonate condensed with formaldehyde or based on melamine or on acrylic polymers or copolymers is used. The function of the de-aerating agent is to reduce drastically and, if possible, eliminate the formation of air bubbles when the mortar is mixed with the water and when the mixture is subsequently cast. Preferably, an alluvial siliceous-type sand having granules with a maximum diameter of up to 4 mm and, more preferably, of up to 1 mm is used in the composition according to the invention. This sand has the advantage of being compact and of being formed of rounded granules so as to reduce the amount of water with which it has to be mixed, and of having high resistance to impact and wear. Moreover, the above grain size improves the characteristics of fluidity and cohesion of the fresh mortar. According to another preferred embodiment of the invention the sand is of the alluvial siliceous type with 1 to 50% by weight of granules with a maximum diameter of up to 0.5 mm and 99 to 50% by weight of granules with a diameter comprised between 0.5 and 4 mm. The function of the calcareous filler is to improve the rheological properties of the composition of the fresh mortar, to impart a compact surface to the hardened mortar and possibly to accelerate the development of mechanical strength. The filler preferably consists of powdered calcium carbonate in the form of granules having a maximum diameter of 90 µm, of which at least 50% have a diameter of less than 20 µm. As an alternative to the use of cement and of a calcareous filler as separate ingredients in the composition of the invention, it is possible to use a limestone Portland cement (for example of the type defined by the European standard CEN ENV 197/1) which already contained these two ingredients in a ratio which is within the range defined by the composition of the present invention. A further object of the present invention is an article, in particular a die for shaping plates, produced following the preparation of a mixture from water and a cement mortar composition as indicated above, the pouring of the mixture into a mould corresponding to that of the desired article and the setting of this mixture. Preferably, the above mixture is obtained by mixing 100 parts by weight of cement mortar composition with 8-22, or more preferably 10-17, parts by weight of water. In this manner, articles which can assume a strength of at least 50 N/mm 2 according to the European standard CEN EN 196/1 are obtained at the latest within 3 days after casting and preferably within one or two days after casting. By virtue of their particular composition, the articles produced from the cement mortar of the invention are further free from surface defects and are thus particularly suitable for use as dies. These articles can be produced by casting the mixture of mortar and water into a temporary formwork made of wood, plastic material or metal, or into a permanent metal formwork. The latter facilitates the successive movements of the articles, such as, for example, the anchorage of the press to the frame if dies are involved. The articles produced according to the invention can be formed of one or more parts, possibly reinforced by a continuous metal reinforcement and/or a reinforcement which is diffused with metal, vegetable or polymer fibres buried in the set mortar. Furthermore, the surfaces of the dies produced according to the invention which are intended to be in contact with the plates to be shaped can be covered with a coating layer which is at least 0.1 mm thick and preferably less than 30 cm thick. This coating layer can, for example, be made of metal, reinforced polymer material or a cement material which is different from that of the compositions described above. Further advantages and characteristics of the present invention will become clear from the following embodiments and from the appended sheets of drawings which are provided by way of non-limiting and in which: Figure 1 is a schematic perspective view of a die produced from a cement mortar composition according to the invention; and Figure 2 is a schematic perspective view of a further die produced from a cement mortar composition according to the invention. Example 1 A dry, premixed mortar which is ready for use is prepared and has the following composition given as weight percentages: Portland cement CEM I 52.5R 50.0% DILACON R 5.0% calcareous filler 10.0% naphthalene sulphonate FLUBE R CR 140 2.0% de-aerating additive PDN 1.0% silica having a maximum diameter of 0.5 mm 32.0% DILACON (registered trade mark) is a calcium sulphoaluminate-based expanding agent produced by ENICHEM. FLUBE (registered trade mark) CR 140 is a dispersing agent produced by the Bozzetto company. PDN is a de-aerating agent sold by the Addiment company. Portland cement CEM I 52.5R is produced by Unicem. The mortar having this composition is mixed for four minutes in a high-speed mixer with 20 weight % of water. A homogeneous paste is obtained which is totally depleted ofsegregations, is very fluid, has an only slightly viscous appearance, and which, after 30 minutes, has the same properties almost completely unchanged. The following measurements are taken using standard test methods: spreading (UNI 7044) > 200% density (CEN prEN 1015-6) 2203 kg/m 3 content of air (CEN prEN 1015-7) 0.7% compressive strength after 1 day 41.7 N/mm 2 compressive strength after 3 days 73.0 N/mm 2 The compressive strength is measured on 40x40x160 mm test pieces made and cured according to the provisions of the standard CEN EN 196/1. A die illustrated in Figure 1 is produced with the mortar having this composition. This die consists of three parts, a matrix 10a, a blank holder 12a and a punch 14a respectively, and it can impress a cross shape on a plate in particular a metal sheet. The parts 10a, 12a and 14a have a continuous metal reinforcement, not illustrated in Figure 1 and produced by known methods which imply the use of cages and rods welded to one another. The die is used a number of times, producing a consistent number of impressions each of which is approximately 20 mm deep. The mechanical behaviour of all three parts 10a, 12a, 14a is highly satisfactory. The metal sheet is also drawn in a uniform manner. The surfaces of the die which are in contact with the metal sheet are lubricated with powdered graphite. Various types of metal sheet are used, including 1 mm thick stainless steel sheet. Example 2 A die illustrated in Figure 2 is produced with the same premixed mortar described in Example 1. This die is formed of three parts, a matrix 10b, a blank holder 12b and a punch 14b respectively, and can draw a metal sheet into a shape which faithfully reproduces the parabola of a motor vehicle headlight. The casting process is performed according to the operating procedure described in Example 1. The parts 10b, 12b and 14b have a continuous metal reinforcement not illustrated in Figure 2 and produced by known methods which imply the use of cages and rods welded to one another. When the three parts 10b, 12b, 14b are demoulded, it can be noted that the mortar gives smooth surfaces free from visible defects, as already seen in the die described in Example 1. Numerous forming tests have been performed, following which some examples of parabola have been produced in a satisfactory manner, both from the point of view of the drawing of the metal sheet and of the mechanical behaviour of the die. Example 3 A dry premixed mortar ready for use is prepared according to the following composition given as weight percentages: Portland cement CEM I 52.5 35.0% DILACON R 4.2% calcareous filler 4.9% naphthalene sulphonate FLUBE R CR 140 1.4% de-aerating additive PDN 1.0% silica sand with a maximum diameter of 1 mm 53.5% The mortar having this composition is mixed according to the procedure described in Example 1 with 16.5% of water, obtaining a fresh mortar having rheological characteristics judged suitable for the construction of dies on the basis of the evaluation criteria defined in the preceding examples. The following measurements were taken using the test methods cited in Example 1: spreading > 200% density 2210 kg/m 3 air content 0.5% compressive strength after 1 day 41.3 N/mm 2 compressive strength after 2 days 55.4 N/mm 2 compressive strength after 3 days 61.8 N/mm 2 compressive strength after 7 days 65.2 N/mm 2 compressive strength after 28 days 80.5 N/mm 2 The mortar is used for preparing the three parts 10b, 12b, 14b of which the die according to Figure 2 is composed, according to the procedure described in Example 2. The die is used satisfactorily in repeated metal sheet forming tests and does not give rise to cracking phenomena due to hydraulic shrinkage. Example 4 A dry premixed mortar ready for use is prepared according to the following composition given as weight percentages: Portland cement CEM I 52.5 25.5% DILACON 3.0% calcareous filler 5.0% naphthalene sulphonate FLUBE CR 140 1.0% de-aerating additive PDN 1.0% silica sand with maximum diameter of 0.5 mm 23.0% silica sand with maximum diameter of 4 mm 42.0% By adding to this composition 11% of its weight of water according to the procedure of Example 1, a mortar of suitable rheological behaviour is obtained. The following properties were measured by using the test methods cited in Example 1: spreading 200% air content 1.4% compressive strength after 1 day 43.2 N/mm 2 compressive strength after 3 days 67.4 N/mm 2 compressive strength after 7 days 76.5 N/mm 2 compressive strength after 28 days 83.5 N/mm 2 A die prepared with this mortar performed well in numerous forming tests on metal sheet.

Claims: A cement mortar composition for producing articles, such as in particular dies for shaping plates, comprising, in the quantities defined by the following weight percentages: cement 20-50% expanding agent 1-10% dispersing agent 0.5 to 2% de-aerating agent 0.5-1.5% sand 30-70% calcareous filler 1-10% A composition according to Claim 1, characterized in that the cement is of the type having high strength, of the 42.5 N/mm 2 or 52.5 N/mm 2 type, as defined by the European standard CEN ENV 197/1. A composition according to either of the preceding claims, characterized in that the expanding agent is a calcium sulphoaluminate or calcium oxide-based product. A composition according to any one of the preceding claims, characterized in that the dispersing agent is a product based on a calcium or sodium salt of naphthalene sulphonate condensed with formaldehyde or based on melamine or on acrylic polymers or copolymers. A composition according to any one of the preceding claims, characterized in that the sand is of the alluvial siliceous type and has granules with a maximum diameter of up to 4 mm and preferably up to 1 mm. A composition according to any one of the preceding claims 1 to 4, characterized in that the sand is of the alluvial siliceous type with 1 to 50% by weight of granules with a maximum diameter of up to 0.5 mm and 99 to 50% by weight of granules with a diameter comprised between 0.5 and 4 mm. A composition according to any one of the preceding claims, characterized in that the calcareous filler consists of powdered calcium carbonate in the form of granules having a maximum diameter of 90 µm, of which at least 50% have a diameter of less than 20 µ. An article, in particular a die for shaping plates, produced following the preparation of a mixture from water and those cement mortar compositions according to any one of the preceding claims, the casting of the mixture in a mould corresponding to that of the desired article, and the setting of the mixture. An article according to Claim 8, characterized in that the mixture is obtainable by mixing 100 parts by weight of cement mortar composition with 8-22, preferably 10-17, parts by weight of water, the set mixture constituting the article having a compressive strength of at least 50 N/mm 2 according to the European standard CEN EN 196/1 at the latest within three days after casting and preferably within one or two days after casting. An article according to either of Claims 8 and 9, characterized in that the mixture is cast in a metal formwork which can facilitate the subsequent movement of the article. An article according to any one of the preceding claims 8 to 10, characterized in that it is formed from one or more parts, reinforced with a continuous metal reinforcement and/or a reinforcement diffused with metal, vegetable or polymer fibres buried in the set mortar. An article, in particular a die, according to any one of the preceding Claims 8 to 11, characterized in that its surfaces which are to contact the plates to be shaped are covered with a coating layer which is of at least 0.1 mm thick and preferably less than 30 cm thick. An article according to Claim 12, characterized in that the coating layer is metal, reinforced polymer material or a cement material which is different from that obtained from the composition according to claims 1 to 7.

Inventors: CURCIO FRANCESCO, DE ANGELIS BERNARDO, GALLO ARMANDO, CURCIO, FRANCESCO, DE ANGELIS, BERNARDO, GALLO, ARMANDO
Applicants: UNICEM SPA, UNICEM S.P.A.
Application year: 1995
Main classification: C04B28
IPC codes: C04B28