Feeder inserts and production thereof

0001In foundry technology, it is indispensable to provide feeders for the seal feed of the castings. In principle, these feeders are cavities which are connected to the mold cavity of the casting, are filled with liquid metal by the casting flow and are dimensioned and designed such that the solidification module of the feeder is larger (usually about 20% larger) than that of the Casting. It is advantageous in many respects to provide the feeders with a heat-insulating and / or heat-releasing lining, and numerous types of feeder inserts have already been developed for this purpose. These are molded articles which consist of a mixture of insulating and / or exothermic components bound by a binder and, if appropriate, further additives which influence the properties.

0002Surprisingly, the effort for the production of the well-known and proven feeder inserts is still relatively high. There are essentially three currently carried out processes, namely<ul id="ul0001" list-style="none"><li>1.) The green stand procedure Here, the inserts - usually using a thermosetting binder, for example a phenolic resin - are shaped as "green" molded parts and then dried. This method is particularly prone to errors and requires a lot of experience. A wide range of raw materials and binders is available, but automation to increase productivity is only possible to a limited extent.</li><li>2.) The CO₂-Gassungsverfahren Here is a CO₂ curable binder is used, and gassing results in higher initial strengths than with the green stand method. It is therefore possible to produce relatively dimensionally accurate molded blanks, but here, too, drying has to be carried out afterwards, and the water glass commonly used places increased demands on the choice of minerals and furthermore disrupts the exothermic reaction. The hygroscopicity of the moldings is considerable and difficult to correct.</li><li>3.) The filter slip process Here, a slip is generated from the components and the feeder insert is produced by a filtration process as a shaping process and subsequent drying. The drying of the inserts is complex and the gassing is often immense.</li></ul>

0003All of these processes have in common that the feeder inserts produced have to be subjected to drying before they can be passed on for consumption as finished products. This has numerous disadvantages. Apart from the energy consumption that every drying process inevitably requires, drying is a very complex work process. It has to be meticulous, and the more insulating the material used and the lower the applicable temperature, the more difficult it is. Drying times of 0.5 to 1 hour per centimeter of wall thickness are common, and drying temperatures are very critical, particularly with exothermic materials. The handling of the moldings also requires considerable effort in order to avoid damage or deformation of the moldings which are still very sensitive before drying.

0004This is where the invention comes in. It has the aim of avoiding the drying that was previously necessary in the manufacture of the feeder inserts and achieves this goal by using a polyurethane-based binder for the feeder inserts, the components of which comprise a free OH group-containing phenolic resin and a polyisocyanate as reactant of at least one of which is dissolved in a solvent consisting predominantly or entirely of vegetable oil methyl ester. Both components are preferably completely dissolved in a vegetable oil methyl ester.

0005Polyurethane-based binders in which a free OH group-containing phenolic resin and a polyisocyanate are converted to a cured binder to form urethane are known as such. They are used, for example, in the foundry industry to manufacture molds and cores by mixing the two components with a basic molding material and after shaping (e.g. in a shooting machine) by gassing with a tertiary amine in a matter of seconds to form urethane, i.e. to harden it. Post-drying is not necessary.

0006In the case of binders based on polyurethane, solvents are required in order to keep the components of the system in a sufficiently low-viscosity state. This applies to phenolic resins, which regularly require a solvent due to their higher viscosity, but also applies to polyisocyanates. The two components require different types of solvents, since non-polar solvents are generally well suited for polyisocyanates and less compatible with phenolic resins, while the reverse applies to polar solvents. In practice, therefore, mixtures of polar and non-polar solvents are normally used. High-boiling aromatic hydrocarbons (mostly in the form of mixtures) with a boiling range above about 150 ° C. at normal pressure are preferably used as non-polar solvents, and certain sufficiently high-boiling esters, for example, have been used as polar solvents the "symmetrical" esters described in DE-PS 27 59 262, in which both the acid residue and the alcohol residue have a relatively large number of C atoms (about 6 - 13 C atoms) lying in the same range.

0007There has been no shortage of attempts to use the polyurethane binders known for the production of molds and cores also for the production of feeder inserts in order to quickly achieve a high initial hardness of the shaped bodies with amine gassing and to be able to avoid post-drying. However, these attempts have failed, in particular because excessive soot development or gassing or an undesirably high formation of glossy carbon occurred. It is all the more surprising that the knowledge now found that these disadvantages of the polyurethane binders disappear and that feed inserts with very excellent properties result when methyl methyl ester is used as a solvent for the polyurethane components. Such a success was not predictable and, in retrospect, allows the assumption that the high-boiling aromatics, which could not be dispensed with so far, were partly responsible for the failure of the previous attempts. However, this has not yet been clarified exactly.

0008Overall, the invention thus leads to feeder inserts which can be cured in a matter of seconds to give shaped articles with a sufficiently high initial hardness and require no heating or drying. These moldings are very dimensionally stable, do not require any special care in handling compared to "green" moldings and are ready for use almost immediately. In use, there are no undesirable phenomena such as soot development, gassing or shiny carbon formation, and the selection of the insulating and / or exothermic components of the feeders and the other additives is not restricted, but can be chosen in terms of type, quantity and combination according to the respective need . Particularly noteworthy is the unexpected additional advantage of the low susceptibility to water absorption of the feeder inserts according to the invention.

0009The term "methyl ester of higher fatty acids", or "fatty acid methyl esters" for short, is understood to mean all monomethyl esters which are obtained by transesterification of fats and oils of vegetable or animal origin which are usually present as triglycerides. Rapeseed oil methyl ester is a typical example of such an ester and is a preferred solvent, especially since it is cheaply available in sufficient quantity as diesel fuel. However, the methyl esters of other vegetable oils such as soybean oil, linseed oil, sunflower oil, peanut oil, wood oil, palm oil, coconut oil, castor oil and / or olive oil can also be used. And marine oils, tallow and animal fats can also serve as starting materials for methyl esters which can be used according to the invention. All of these fats and oils, which serve as starting material, can be present in any mixture. You don't have to be fresh and pure natural products either; it can also be hardened or otherwise treated fats and oils. Waste oils and waste fats, such as used cooking oil or frying fat, can also be used as the starting material for the methyl esters which can be used according to the invention. It is therefore a further aspect of the invention that a suitable recycling option is made available for these environmentally harmful waste materials.

0010For reasons of casting technology and also for reasons of environmental protection, 100% replacement of the conventional solvents by fatty acid methyl esters is preferred, because then the advantages of the invention will be fully effective. However, it is also possible to mix these methyl esters with the conventional solvents mentioned above, for example the aromatic hydrocarbons. If such mixtures consist predominantly, that is to say more than 50%, of the methyl esters, the advantages of the invention are also still sufficiently present, albeit to an extent which is gradually weakened as the methyl ester content decreases.

0011The rapeseed oil methyl ester already mentioned as a typical example of the solvents to be used according to the invention is an environmentally friendly and CO₂-neutral natural product. It is high-boiling and sufficiently thin, so it meets the physical requirements for a solvent for polyurethane binder systems. It is also practically odorless and classified as harmless in terms of the workplace. Furthermore, it is not classified as a combustible dangerous good, which considerably simplifies the transport and storage of the solutions produced with it. In addition, it hardly leads to unwanted gaseous fission products during casting, because the numerous double bonds (rapeseed oil mainly contains mono- and polyunsaturated fatty acids) react to form solid, non-outgassing compounds. The maximum tolerable workplace concentrations are not nearly reached when using rapeseed oil methyl ester as a solvent. In addition, rapeseed oil methyl ester also gives an excellent release effect when removing the feeder inserts from the shooting machine, so that the use of additional release agents is not necessary.

0012Analogous statements apply to the other fatty acid methyl esters and fatty acid methyl ester mixtures. The methyl ester of soybean oil should be emphasized because of its unproblematic processability. Particularly good results - in some cases even better than with rapeseed oil methyl ester - were obtained with the methyl ester of linseed oil. Castor oil methyl ester is particularly suitable as a solvent for the phenolic resin, but is less suitable for the polyisocyanates because of its OH group content.

0013The invention is explained in more detail below in exemplary embodiments. Unless otherwise stated, the quantities given are parts by weight.

example 1

0014In a reaction vessel equipped with a cooler, thermometer and stirrer<dl id="dl0001" compact="compact"><dt>385.0 GT</dt><dd>phenol</dd><dt>176.0 GT</dt><dd>Paraformaldehyde and</dd><dt>1.1 GT</dt><dd>Zinc acetate</dd></dl> submitted. The cooler was set to reflux. The temperature was raised continuously to 105 ° C. within one hour and held at this temperature for two to three hours until a refractive index of 1.590 was reached. The condenser was then switched to atmospheric distillation and the temperature was raised to 125-126 ° C. over an hour until a refractive index of approximately 1.593 was reached. This was followed by vacuum distillation up to a refractive index of 1.612. The yield was 82 - 83% of the raw materials used.

0015When the target value was reached, a solution with the following composition was prepared from this phenolic resin:

Resin solution

0016<dl id="dl0002" compact="compact"><dt>55.0 GT</dt><dd>Phenolic resin</dd><dt>25.0 GT</dt><dd>Rapeseed oil methyl ester</dd><dt>17.0 GT</dt><dd>DBE ^(H)<img file="EP0804980A1_D0001.tif" /><img file="EP0804980A1_D0002.tif" /><img file="EP0804980A1_D0003.tif" /><img file="EP0804980A1_D0004.tif" /><img file="EP0804980A1_D0005.tif" /><img file="EP0804980A1_D0006.tif" /><img file="EP0804980A1_D0007.tif" /><img file="EP0804980A1_D0008.tif" /><img file="EP0804980A1_D0009.tif" /><img file="EP0804980A1_D0010.tif" /><img file="EP0804980A1_D0006.tif" /><img file="EP0804980A1_D0011.tif" /><img file="EP0804980A1_D0005.tif" /><img file="EP0804980A1_D0004.tif" /><img file="EP0804980A1_D0012.tif" /><img file="EP0804980A1_D0013.tif" /><img file="EP0804980A1_D0008.tif" /><img file="EP0804980A1_D0014.tif" /><img file="EP0804980A1_D0015.tif" /><img file="EP0804980A1_D0003.tif" /><img file="EP0804980A1_D0006.tif" /><img file="EP0804980A1_D0016.tif" /><img file="EP0804980A1_D0003.tif" /><img file="EP0804980A1_D0017.tif" /><img file="EP0804980A1_D0018.tif" /><img file="EP0804980A1_D0019.tif" /><img file="EP0804980A1_D0020.tif" /><img file="EP0804980A1_D0018.tif" /><img file="EP0804980A1_D0021.tif" />₄<img file="EP0804980A1_D0022.tif" /><img file="EP0804980A1_D0021.tif" />₆<img file="EP0804980A1_D0022.tif" /><img file="EP0804980A1_D0023.tif" /><img file="EP0804980A1_D0005.tif" /><img file="EP0804980A1_D0024.tif" /><img file="EP0804980A1_D0025.tif" /><img file="EP0804980A1_D0017.tif" /><img file="EP0804980A1_D0026.tif" /><img file="EP0804980A1_D0020.tif" /><img file="EP0804980A1_D0018.tif" /><img file="EP0804980A1_D0006.tif" /><img file="EP0804980A1_D0027.tif" /><img file="EP0804980A1_D0010.tif" /><img file="EP0804980A1_D0017.tif" /><img file="EP0804980A1_D0003.tif" /><img file="EP0804980A1_D0018.tif" /><img file="EP0804980A1_D0028.tif" /></dd><dt>3.0 GT</dt><dd>Isophorone.</dd></dl> The following polyisocyanate solution was also provided:

Activator

0017<dl id="dl0003" compact="compact"><dt>85.0 GT</dt><dd>Diphenylmethane diisocyanate <img file="EP0804980A1_D0001.tif" /><img file="EP0804980A1_D0029.tif" /><img file="EP0804980A1_D0011.tif" /><img file="EP0804980A1_D0030.tif" /><img file="EP0804980A1_D0016.tif" /><img file="EP0804980A1_D0003.tif" /><img file="EP0804980A1_D0024.tif" /><img file="EP0804980A1_D0008.tif" /><img file="EP0804980A1_D0018.tif" /><img file="EP0804980A1_D0005.tif" /><img file="EP0804980A1_D0006.tif" /><img file="EP0804980A1_D0007.tif" /><img file="EP0804980A1_D0008.tif" /><img file="EP0804980A1_D0028.tif" /></dd><dt>15.0 GT</dt><dd>Rapeseed oil methyl ester and</dd><dt>0.2 GT</dt><dd>Acid chloride</dd></dl>

Examples 2-4

0018Three different feeder inserts were produced, namely an insulating-exothermic insert (example 2), an exothermic insert (example 3) and an insulating insert (example 4). The effective components of these inserts and the supplements used are given in the table, in parts by weight.<tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row rowsep="1"><entry namest="col1" nameend="col1" /><entry namest="col2" nameend="col2" rowsep="0" align="center">Example 2</entry><entry namest="col3" nameend="col3" rowsep="0" align="center">Example 3</entry><entry namest="col4" nameend="col4" rowsep="0" align="center">Example 4</entry></row><row><entry namest="col1" nameend="col1" align="center"><b>Components</b></entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">Aluminum semolina</entry><entry namest="col2" nameend="col2" align="right">25.0 GT</entry><entry namest="col3" nameend="col3" align="right">31.1 GT</entry><entry namest="col4" nameend="col4" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="right">Cryolite</entry><entry namest="col2" nameend="col2" align="right">2.0 GT</entry><entry namest="col3" nameend="col3" align="right">3.6 GT</entry><entry namest="col4" nameend="col4" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="right">Potassium nitrate</entry><entry namest="col2" nameend="col2" align="right">12.0 GT</entry><entry namest="col3" nameend="col3" align="right">16.1 GT</entry><entry namest="col4" nameend="col4" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="right">sand</entry><entry namest="col2" nameend="col2" align="right">41.0 GT</entry><entry namest="col3" nameend="col3" align="right">45.6 GT</entry><entry namest="col4" nameend="col4" align="right">-</entry></row><row><entry namest="col1" nameend="col1" align="right">Hollow spheres</entry><entry namest="col2" nameend="col2" align="right">20.0 GT</entry><entry namest="col3" nameend="col3" align="right">-</entry><entry namest="col4" nameend="col4" align="right">100.0 GT</entry></row><row><entry namest="col1" nameend="col1" align="right">Iron oxide red</entry><entry namest="col2" nameend="col2" align="right">-</entry><entry namest="col3" nameend="col3" align="right">3.6 GT</entry><entry namest="col4" nameend="col4" align="right">-</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right"><b>total</b></entry><entry namest="col2" nameend="col2" align="right">100.0 GT</entry><entry namest="col3" nameend="col3" align="right">100.0 GT</entry><entry namest="col4" nameend="col4" align="right">100.0 GT</entry></row></tbody></tgroup><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center"><b>binder</b></entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="left">Resin solution</entry><entry namest="col2" nameend="col2" align="right">3.5 GT</entry><entry namest="col3" nameend="col3" align="right">4.0 GT</entry><entry namest="col4" nameend="col4" align="right">6.7 GT</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">Activator</entry><entry namest="col2" nameend="col2" align="right">4.4 GT</entry><entry namest="col3" nameend="col3" align="right">5.5 GT</entry><entry namest="col4" nameend="col4" align="right">8.4 GT</entry></row></tbody></tgroup><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center"><b>Strengths</b></entry><entry namest="col2" nameend="col2" /><entry namest="col3" nameend="col3" /><entry namest="col4" nameend="col4" /></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">immediately</entry><entry namest="col2" nameend="col2" align="right">210 N / cm²</entry><entry namest="col3" nameend="col3" align="right">100 N / cm²</entry><entry namest="col4" nameend="col4" align="right">200 N / cm²</entry></row><row><entry namest="col1" nameend="col1" align="right">after 1 day</entry><entry namest="col2" nameend="col2" align="right">400 N / cm²</entry><entry namest="col3" nameend="col3" align="right">210 N / cm²</entry><entry namest="col4" nameend="col4" align="right">270 N / cm²</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">after 5 days</entry><entry namest="col2" nameend="col2" align="right">420 N / cm²</entry><entry namest="col3" nameend="col3" align="right">250 N / cm²</entry><entry namest="col4" nameend="col4" align="right">290 N / cm²</entry></row></tbody></tgroup></table></tables>

0019In all cases, the constituents and the additives were mixed with the binder according to Example 1, which consisted of the amounts of phenolic resin (resin solution) and polyisocyanate (activator) given in the table.

0020The mass obtained in this way was then shaped into feeder caps by means of a shooting machine and gassed with dimethylisopropylamine. There were molded articles which had the strengths given in the table and were immediately ready for use without drying.

Example 5

0021The feeder caps according to Example 2 were stored in a damp room at 85% relative humidity for 5 days. The water absorption was only 0.1% by weight. For comparison, exothermic caps were produced using the green stand method by<dl id="dl0004" compact="compact"><dt>92.0 GT</dt><dd>Exothermic matrix, containing 25% Al semolina, 12% potassium nitrate</dd><dt>1.5 GT</dt><dd>Spring flour</dd><dt>1.5 GT</dt><dd>Dimethylol urea</dd><dt>5.0 GT</dt><dd>powdered phenol resin of the novolak type</dd></dl> mixed together, mixed with 12% mixing water, shaped and dried at 220 ° C. These comparison caps showed a water absorption of 2% by weight under the same conditions, and other caps made with water glass and CO₂-Gassung were produced, even a water absorption of 10 wt .-%.

Example 6

0022Gassing when heated is a good criterion for assessing the usability of a feeder insert. 1 shows the gas evolution as a function of time for the feeder caps according to Example 2, specifically in comparison with those caps bound with phenolic resin and produced according to the green process, which also served as reference material in Example 5. It can be seen that in the caps according to Example 2, both the absolute amount of gas, represented by the height of the curve in the diagram, and the gas delivery speed, represented by the steepness of the rising curve branch, remain behind the comparison caps. This is good, usable behavior.