Process for the Manufacture of Structural Elements

The present invention relates to a process, a product, and a procedure for the manufacture of structural elements by curing molding compositions which are based on thermosetting phenolic resins. The structural elements may be used as building materials, building stones, floor tiles, roofing tiles, sewer pipes and as other molded articles in the construction industry.

The presently most widespread technology for the manufacture of structural elements such as roofing tiles, floor tiles, etc., is based on the well established kiln technology, or on the processing of cement. In both cases the quality of the product depends on the starting materials, and on high quality labor and high energy cost manufacturing methods. In addition, high costs for molds are involved. Frequently, individual items are subject to breakage, resulting in a high reject rate. Furthermore, shortages in the supply of raw material occur.

It is therefore an object of this invention to make available a highly fireproof material, with high compressive strength, and bending strength characteristics, at favorable cost, and based on simple raw materials, such as sand, to which a plastic resin is added and to do so while avoiding or substantially reducing the disadvantages listed above. In addition, relatively simple processing techniques, and independence from cement as a raw material, are further objectives of the invention.

The present invention provides a process for manufacturing structural elements including the steps of mixing minerals as well as low melting metallic substances to form a molding composition based on thermosetting phenolic resins, and then curing the molding composition to form structural elements.

The present invention also provides a product produced in accordance with the novel process.

According to the invention, the above-mentioned objectives are achieved through the use of a molding composition which consists of a combination in minerals, and also comprises low melting metallic substances.

The novel manufacturing procedures, hereinafter described in detail, do not require special raw material grades, nor is a special pretreatment of the inorganic materials a necessity. The manufacturing procedure excludes the use of cement and sodium or potassium silicate solutions (waterglass).

The primary binders used are commercially available organic thermosetting resins, such as, for instance, phenolic resins. Their highest strength characteristics are achieved by curing under controlled temperature conditions of from 40-450.degree. C. To achieve the highest level of mechanical properties of the items produced, up to refractory characteristics at 1300.degree. C., the invention calls for the use of a secondary binder, in the form of low melting metals, which are ground together with a predetermined quantity of inorganic materials, such as, for instance, clay or quartz containing clay. Such a powdery blend is added to the prepared crude molding composition, and mixed in the dry state until a homogenous material is in hand. Once compressed and cured, the resulting article exhibits the exact predetermined strength characteristics, and all the other technical and physical characteristics of the products heretofore used in the building industry.

The high strength characteristics can be achieved due to the fact that the microscopic particles of the low melting metal compounds begin to sinter already at low temperatures and react in sequence. This causes the formation of a monolithic space-lattice structure consisting of these compounds and the oxides. This chemical process, and the curing of the resin, occur completely independent of each other and without influencing each other.

The principal inorganic component is a sand of unspecified chemical composition with a moisture content at the pit of from 5-8%. The procedure according to this invention also applies to other products or structural elements, such as floor tiles of all types, building materials and building stones, and also other structured elements which share a common technological character. Despite the differing final use-areas of the products manufactured from this molding composition, they are all characterized by the following economical advantages:

(a) for the manufacture of these articles, all the common types of sands can be used;

(b) overall production and energy costs are reduced;

(c) capital investment costs are reduced;

(d) substantially lower labor costs; and

(e) increased productivity of the work cycle.

The invention is described in greater detail in the following examples:

In a mechanical mixer the following components are mixed together:

88 parts by weight of moist undried sand which is characterized by an average grain size of from 1.5-0.08 millimeters;

6 parts by weight of a phenolic resole resin with a viscosity of 3300 centipoise, and a combustion residue of 80%,

6 parts by weight of the blend of low melting metals, e.g. Pb--Sn--Al.

This mixture, constituting a homogenous blend, with a residual moisture content of 8%, is then suitable for compression molding at pressures of from 20.degree.-150 Kg/cm.sup.2. The resulting molded articles are then cured according to known procedures in a drying oven, or in heated molds. The temperature required for the curing step depends on the type of phenol resol resin used, and may be from 20.degree.-450.degree. C.

The prepared molding composition, as per the technical description, is ready for shaping and compression. The sintering of the finished parts occurs in stages. During the first stage the resin is cured at temperatures from 20.degree.-450.degree. C., and results in structurally strengthening the molded article. The essential mechanical characteristics achieved during this step, i.e., a bending strength of 210 Kp/cm.sup.2, are already higher than those of conventional building materials. The subsequent sintering is achieved by means of the low melting metal compounds. Therefore, the resulting metal compounds products are dimensionally stable and highly refractory, up to a temperature of 1300.degree. C.

The following components are blended together:

92% by weight of undried sand with a grain size of from 2-0.08 millimeters;

4% by weight of a phenol resole resin with a viscosity of 3500 centipoise at 20.degree. C.;

2% by weight of bonding clay; and

2% by weight of powdered Wood's metal.

Processing is essentially identical to Example I. The molding composition is prepared stepwise. The individual components are added to the continuous blending process. The resin component is heated to about 28.degree.-30.degree. C., and then the bonding clay is added in powdered form. Finally the low melting metals or metal compounds are added and the total composite is well mixed, for example, for a period of 10 minutes. Curing and molding are then carried out in the manner described before.

The following materials are blended in respective amounts:

88% by weight of sand, as described in examples I and II;

3% by weight of a phenol resole resin with a viscosity of 9-11 centipoise at 20.degree. C.;

3% by weight of a phenol resole resin with a viscosity of 3300-3700 centipoise at 20.degree. C.;

1% by weight of toluene sulfonic acid in 65% solution;

2% by weight of bonding clay;

2% by weight of Silumin metal powder; and

1% by weight of powdered tin.

Preparation, blending, processing, molding and curing was done as described in the previous examples.

It is to be understood that the examples only describe certain practical approaches to the invention. The invention is not limited to the practical examples listed.