DE1239436B - Binding agent for the production of sand cores for foundry purposes - Google Patents

Description

GERMAN 'MTW> PATENT OFFICE

EDITORIAL

German class: 31 b1 -1/20

Number: 1 239 436

File number: Q 652 VI a / 31 b1

1 239 436 filing date: April 11, 1961

Open date: April 27, 1967

The invention relates to binders containing furfuryl alcohol, formaldehyde and an acidic catalyst, for the production of sand cores for foundry purposes.

A casting core can be referred to as a molded part made of sand and binder, which is used as an aid is used to form the inner surfaces of a cast body made of metal. A casting core must have several Requirements are sufficient: it usually has to harden very quickly, in relation to the washing and burning effects to be resistant to a stream of hot metal, to allow gases to escape freely, as an inner body impress its shape on the cast metal, have such a high tensile strength that it during the Handling and its application does not break, and finally after the solidification of the cast body be easily shaken out of metal.

To meet some of these requirements, sand has long been used in metal casting with a Binder used. The part of the casting core composition can be referred to as the binding agent, which causes the adhesion between the sand particles. In the following description, the expression "Binder" or "Binder" used in such a way that all organic constituents of the casting core composition fall under it.

A wide variety of binders are already used for metal casting. One of the oldest known binder is the grain flour kernel oil binder. The main disadvantage of this system is in the required long curing time to be seen. In connection with today's usual, at high speed working automatic systems, however, fast-curing binders are very desirable.

Another type of core binder is made from phenolic resins. Due to the high cost of such Resins, the binder is only used to bind a shell and does not act as a binder within the entire core. Obtained through the use of phenolic resin type binders casting cores that tend not to fall out when vibrating after the metal casting has solidified, especially when it comes to the casting of low-melting non-ferrous alloys. Furthermore, the required hardening time and the tensile strengths of the casting cores formed leave something to be desired left over.

A third type of core binders are the urea-formaldehyde-grain flour binders. With this system it is necessary that water is present in sufficient quantity to give the casting core a sufficient green binding agent for the production of sand cores
for foundry purposes

Applicant:

The Quaker Oats Company,
Chicago, JH. (V. St. A.)

Representative:

Dr. IM Maas, patent attorney,
Munich 23, Ungererstr. 25th

Named as inventor:
Lloyd Hubert Brcwn, Crystal Lake, JU .;
David Derby Watson,
Barrington, JlL (V. St. A.)

Claimed priority:

V. St. v. America July 11, 1960 (41 752)

To give "5 or wet strength" so that it will hold its shape until it is put in an oven. The presence of water in the required quantities increases the hardening time. aside from that a core is formed with these binders, which when in contact with refractory metals, z. B. gray cast iron, disintegrates too easily. Another associated with the cores produced with this binder Difficulty is the lack of moisture resistance. This deficiency leads to the core in loses strength in an atmosphere with high moisture content.

It is therefore the object of the invention to produce a core with improved tensile strength.
The binder according to the invention is characterized by two separately packaged mixtures, the first of which is 5 to 50 parts by weight of furfuryl alcohol and 90 to 35 parts by weight of an unpolymerized aqueous mixture of formaldehyde, urea and the reaction products thereof present at equilibrium, and contains no more than about 15 percent by weight of water, and the second is 1 up to 3 parts by weight of an acidic catalyst and urea sufficient to provide a molar ratio of available urea to available formaldehyde in the combined mixtures of about 1: 1.5 to 1: 2.5, and together for 3000 to 10,000 parts by weight of sand sufficient.

709 577/277

The catalyst contained in the binder is preferably an ammonium salt of a strong acid, especially ammonium chloride.

The molar ratio of available urea to available formaldehyde in the combined mixtures is preferably 1: 2.0 to 1: 2.5.

Furthermore, it has proven to be advantageous if the first mixture contains the furfuryl alcohol in an amount Contains from 25 to 50 parts by weight.

According to one embodiment of the invention, the second mixture also contains 0.5 to 7.0 parts by weight aqueous ammonia, calculated as 29 weight percent ammonia.

In a further embodiment, where the catalyst is ammonium chloride, the second contains Mixture of aluminum stearate in an amount of 1 to 5 percent by weight of the total weight of urea and ammonium chloride in the second mixture.

According to a further embodiment, the second mixture contains 12 to 25 parts by weight of water.

According to British Patent 832 999, furfuryl alcohol polymers are used for core binders and furfuryl alcohol-formaldehyde resins are used. Such substances largely consist of furan rings, which are connected to one another by methylene bridges. The binders according to the invention lead in contrast to urea resins modified with furfuryl alcohol during core production, d. h., that The basic network is built up by condensation polymerization of dimethylolurea. Furfuryl alcohol is built into this network in some way.

Because of this difference, it is possible with the binders according to the invention to use ammonium chloride to use as a catalyst. Substances of the kind used in accordance with the British patent specification are not effectively catalyzed by ammonium chloride, but require strong acids. Both binders according to the invention, ammonium chloride acts as a latent catalyst: it changes the Urea component of the binder practically does not have a catalytic effect at room temperature however, it starts at elevated temperatures. Therefore, the second mixture is that of the present invention Cast core binder can be stored for a long time at normal temperatures without the There is a risk that the mixture as a whole will not harden rapidly in a hot core box. The known resins cure very quickly at normal temperatures and are therefore practically impossible to store and must be manufactured at the time of actual use, what in foundries is quite impractical.

Another considerable advantage of the binders according to the invention over the known ones is to be seen in their excellent properties when pulling out, especially when they are used for lighter ones Metals and alloys are used that have relatively low melting temperatures,

ao like aluminum.

A measure of shudder is the time it takes a core to stand under a given load collapse as a result of the binder burning out. A short breakdown period is in

as is highly desirable, especially when it comes to high-speed production methods acts. (It is assumed here as a matter of course that the other properties meet the minimum requirements.)

With the known resins, the breakdown time is unduly long, especially at the lower temperatures used with low melting point metals.
It is assumed that formaldehyde, urea and the reaction products formed therefrom at equilibrium, as are present in aqueous urea-formaldehyde mixtures (hereinafter referred to as aqueous H.-F. mixtures), can be expressed by the following equilibrium formulas:

NH ₂ CONH + HCHO = ^ = NH ₂ CONHCH ₂ OH Nh ₂ CONHCH ₂ OH + HCHO HIGH ₂ NHCONHCH ₂ OH HIGH ₂ NHCONHCH ₂ OH + HCHO HIGH ₂ NHCON (CH ₂ OH) ₂ high ₂ NHCON (CH ₂ OH) ₂ + HCHO =? = (HIGH ₂ ) ₂ NCON (CH ₂ OH) ₂

The above equations illustrate the term used, "an unpolymerized aqueous Mixture of formaldehyde, urea and reaction products from them present at equilibrium «. Those urea molecules in the equilibrium mixture that have more than one methylol group are sometimes called polymethylolureas. It's difficult between different polymethylolureas in the aqueous H.-F. mixtures. For this The reason is the composition of the aqueous H.F. solution as weight percent urea and Formaldehyde. A typical analysis of such a mixture gives 59 percent by weight formaldehyde, 26 percent by weight urea and a maximum of 15 percent by weight water.

The total amount of urea and formaldehyde present in the finished mixture (the combination of the first and the second mixture) is given as a molar ratio. The number of in the Second mixture introduced urea parts fluctuates with the analysis of the respective aqueous H.-F. mixture, that is used for the first mixture. The number of parts of powdered urea contained in the second mixture can be introduced, with the help of the mentioned molar ratio in consideration the analysis of the respective aqueous H.F. mixture can be determined.

The term "available urea" refers to both free urea and urea Urea containing methylol groups as shown in the equations above. The designation "Available formaldehyde" refers to both free formaldehyde and formaldehyde which has entered into a connection with urea according to the above equations.

The amount of acid catalyst used in the second mixture varies within that specified Range depending on the type of sand used and the hardening properties that are achieved should be. Sands with a high clay content can have a high acidity requirement and more require acid catalyst. In general, any acidic catalyst can be used, e.g. B. Am-

monium chloride, ammonium trichloroacetate, ammonium dihydrogen phosphate, ammonium sulfate and Ammonium nitrate.

3000 to 10,000 parts of molding sand are used for about 100 parts of binder. The one in the next The sand used in the examples given below was a clean inland sand with a fineness number of about 83. However, any of the commonly used molding sands are suitable.

The fineness number («) is dimensionless and is calculated using the following formula:

η -

JSj ₁ + 5 j ₂ + IOs ₃ + 20 j ₄ + 30j ₅ + 40j ₆ + 50 j ₇ + 70 j ₈ + IOOj ₉ + 140 j ₁₀ + ZOOj ₁₁ + 300 s _v

S ₁ + s ₂ 4- j ₃ + j ₄ 4- j ₅ + j ₆ + j ₇ + s _s + j ₉ + j ₁₀ + j ₁₁ + j

A sieve analysis is carried out with a weighed sample to determine η. In the above formula:

j
j,
j.

s,
j ₁

S.

⁵ 8 =

⁵ 9 = ⁵ IO ⁼

j ₁ i =

Sieve residue in percent by weight on test sieve with a mesh size of 3.36 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 1.68 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.84 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.59 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.42 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.297 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.210 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.149 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.105 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.074 mm Sieve residue in percent by weight on test sieve with a clear mesh size of 0.053 mm Passage in percent by weight of the test sieve with a clear mesh size of 0.053 mm

Various other constituents can be added to the urea and the catalyst in the second mixture can be added. The aforementioned addition of ammonia leads to a considerable improvement the shelf life with little loss of cure speed. Through the The addition of aluminum stearate mentioned above prevents the powdered urine from sticking together. The mentioned addition of water leads to an improved catalyst distribution.

The following examples illustrate the invention without restricting it.

example 1

By mixing 17.8 parts of a H.-F. mixture with 9 parts of furfuryl alcohol, a first mixture made. 6 parts of urea powder were mixed with 0.30 parts of ammonium chloride and then mixed with 1000 parts of sand to form a second mix. Then became the first Mixture to the second mixture to achieve a finished mixture of all of the constituents mentioned added. This finished mixture contained 30 parts of furfuryl alcohol in the binder portion. on four other finished mixtures with 10, 20, 40 and 50 parts of furfuryl alcohol, respectively, were made in the same way produced in the binder content. The formaldehyde to urea molar ratio in these five finished blends was 2. 25 g samples of the finished mixes were molded three times with a Dietertram mashed that were trained like dog biscuits. This gave samples 6.35 mm thick, molded directly onto aluminum plates. These samples were based on the aluminum plates A hot plate is placed in an oven at about 218 ° C, where it is placed for various periods of time cured and tested at 5-second intervals. The time after which the samples were hard when they were removed from the oven than the normal curing time written down. The following results were obtained:

sample Share furfuryl alcohol
in the binder Curing time
(Seconds at 218 ° C,
425 ° F) 1 10 25th 2 20th 25th 3 30th 30th 4th 40 30th 5 50 30th

From the above, it can be seen that the effect of changing the furfuryl alcohol concentration on the curing time of the core binder is only short.

Additional samples made from the above five finished mixes were tested during the hardened times given above. Tensile strength tests were then carried out. The specified Strength values represent mean values of five tests in each individual case get the following results:

sample Share furfuryl alcohol
in the binder tensile strenght
of the casting core
(normal curing time)
kg / cm ² 6th 10 21.35 7th 20th 30.8 8th 30th 37.8 9 40 41.3 10 50 40.6

The strength of the cores subjected to the heat treatment was increased by replacing 20% by weight of the resin in the binder is increased to about twice as much by furfuryl alcohol, and the strength is increased increased linearly when up to 30 weight percent furfuryl alcohol was used.

Claims (8)

In the manufacture of casting cores, the cores with thicker bodies often require more intensive hardening in order to achieve sufficient hardening of the inner parts. This can result in the surface becoming excessively hardened. In order to determine the effects of excessive cure on the compositions obtainable according to the invention, additional samples were cured according to the procedure outlined above for 20 seconds beyond the normal time. The following results were obtained: Sample parts of furfuryl alcohol in the binder Tensile strength of the casting core (excessively hardened) kg / cm21110141220133029.4144038.5155040.6 15 A comparison of the tensile strengths of the cores with normal hardening time and those with excessive hardening shows that at higher concentrations of furfuryl alcohol ( 40 to 50 parts) the 20 seconds longer hardening has little effect in terms of lowering the tensile strengths. Accordingly, if the risk of excessive hardening is reduced by adding larger amounts of furfuryl alcohol, a larger amount of heat can be applied to effect hardening through the entire core body. Example 2 The procedure described in Example 1 for the preparation of the finished mixtures was repeated with the exception that the parts of furfuryl alcohol were kept constant at 20 parts, while the molar ratio of available formaldehyde to available urea was different in each of the four finished mixtures. In addition, 0.18 parts of aluminum stearate was added to the urea and ammonium chloride in the second mixture. The following tensile strengths were obtained for the casting cores: Sample molar ratio of formaldehyde to urea → Tensile strength of the casting cores kg / cm211.2517.8521.5024.531.7531.542.030.8 50 These data show that with an increase in the molar ratio of formaldehyde to urea up to 1.75 an increase the tensile strength of the casting core was connected. Patent claims: 1. Binder containing furfuryl alcohol, formaldehyde and an acidic catalyst for Manufacture of sand cores for foundry purposes, characterized by two separated packaged mixtures, the first 5 to 50 parts by weight of furfuryl alcohol and 90 to 35 parts by weight of an unpolymerized, at most aqueous mixture of formaldehyde and urea containing about 15 percent by weight of water and the reaction products present therefrom at equilibrium and their second 1 to 3 parts by weight of an acidic catalyst and contains so much urea that a molar ratio of available Urea to available formaldehyde in the combined mixtures of about 1: 1.5 up to 1: 2.5 is present and which together are sufficient for 3,000 to 10,000 parts by weight of sand. 2. Binder according to claim 1, characterized in that the catalyst is an ammonium salt a strong acid. 3. Binder according to claim 2, characterized in that the second mixture also 0.5 to 7.0 parts by weight of aqueous ammonia, calculated as 29 percent by weight ammonia, contains. 4. Binder according to claim 1, characterized in that the molar ratio 1: 2.0 to Is 1: 2.5. 5. Binder according to claim 1, characterized in that the first mixture is the furfuryl alcohol contains in an amount of 25 to 50 parts by weight. 6. Binder according to claim 1, characterized in that the catalyst is ammonium chloride is. 7. Binder according to claim 6, characterized in that the second mixture is aluminum stearate in an amount of 1 to 5 percent by weight of the total weight of urea and ammonium chloride in the second mixture contains. 8. Binder according to claim 6, characterized in that the second mixture 12 to Contains 25 parts by weight of water. Considered publications:
British Patent No. 832 999.