DE1215872B - Process for producing a cast core binder - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. Cl .:

BlZJfC-

German KL: 31c -1/03

Number: 1215 872 ^ ₃

File number: Q 651VI a / 31 c

Filing date: April 11, 1961

Opening day: May 5, 1966

21 -N

The invention relates to a method of production a core binder using furfuryl alcohol and formaldehyde.

A casting core can be referred to as a molded part made of sand and binder, which is used as an aid serves to form the inner surfaces of a cast metal body. A cast core binder can be used as the Part of the casting core that causes the adhesion between the sand particles. The properties of a casting core are determined to a large extent by the properties that are given to it by the binders used are imparted. Certain requirements must be placed on a casting core become: He has to withstand the washing and burning effects of a stream of hot metal, the unhindered Allow gases to escape, imprint its shape on the cast metal body as the inner body, have such a high tensile strength that it does not break during handling and use, and finally collapse and fall out after the cast metal body has solidified.

The most varied of binders have been used in foundries with varying degrees of success. One of the oldest known binders is the grain flour kernel oil binder. The main one associated with it The disadvantage is its long hardening time. In high-speed automatic systems a fast setting binder is highly desirable.

Another type of core binder is made from phenolic resins. Because of the high cost of With such resins, the binder only serves to bind a shell and not for the whole Core. The use of phenolic resin binders leads to cores which, especially when casting low-melting non-ferrous alloys, tend to to withstand shaking after solidification of the metal casting. Further disadvantages of phenolic resin binders are the extended curing times Cores and tensile strengths that do not meet the requirements.

A third type of core binders are the urea-formaldehyde-grain flour binders. The cores produced with the help of this binding agent collapse too quickly on contact with refractory metals and lose some of their strength in an atmosphere with a high moisture content. A solvent is required to make these binders to prevent crystallization or gel formation. Water has been used as such a solvent, but it has certain undesirable effects such as a prolonged process for making one
Cast core binder

Applicant:

The Quaker Oats Company, Chicago, JU.

(V. St. A.)

Representative:

Dipl.-Chem. Dr. rer. nat. I. M. Maas,

Patent attorney, Munich 23, Ungererstr. 25th

Named as inventor:

Lloyd Hubert Brown, Crystal Lake, JIL;

David Derby Watson, Barrington, JU. (V. St. A.)

Claimed priority:

V. St. v. America July 11, 1960 (41728) - -

Curing time and excessive shrinkage of the casting core after curing. In addition, water leads since it is not a reactive solvent, it does not improve the urine-formaldehyde resin inherent weaknesses.

The disadvantages of the known binders are caused by the process according to the invention obtained binder eliminated.

The process according to the invention is characterized in that a solution is prepared from an unpolymerized, aqueous mixture of formaldehyde, urea and reaction products present therefrom at equilibrium, which contains at most about 15 percent by weight water, furfuryl alcohol and, if necessary, so much additional urea that the molar ratio of total available urea to available formaldehyde is in the range from 1: 1.75 to 1: 3.0 and the furfuryl alcohol is present in an amount such that it constitutes 15 to percent by weight of the solution that the solution is brought to pH adjusts in the range from 5.0 to 6.5, ^{heated to reflux at 95 to 105 0} C until it has a viscosity in the range from 350 to cP / 25 ° C, and then the pH of the solution to a value in the range of 6.5 to 8.5.

609 567/414

The molar ratio of total available urea to available formaldehyde is preferably in the range from 1: 2.0 to 1: 2.5.

It has proven advantageous to use a solution containing 25 to 40 percent by weight of furfuryl alcohol to use.

The pH of the solution is preferably adjusted to 5.5 to 6.0 before refluxing. It is particularly useful when refluxing is maintained until a viscosity in the range from 400 to 1500 cP / 25 ° C is reached.

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

Due to this difference, ammonium chloride is possible with the binder obtainable according to the invention to use as a catalyst. Substances of the type used in accordance with the British patent specification Kinds are not effectively catalyzed by ammonium chloride, but require strong acids. Both In binders prepared according to the invention, ammonium chloride acts as a latent catalyst: it catalyzes the binder very slowly at room temperature, but its catalytic effect jumps at elevated temperatures. Therefore, the core binder obtained according to the invention is in the presence the catalyst can be stored for a long time at ordinary temperatures without the risk is that rapid hardening does not occur in a hot core box. The known resins harden at

5 'normal temperatures very quickly, are therefore practically not storable and have to be used in each case Date of actual use.

Another considerable advantage of the binder obtained according to the invention over the known can be seen in its excellent properties when shaken out, especially when it is used for lighter metals and alloys, which have relatively low melting temperatures, such as aluminum. A measure of the shaking is the time it takes a core to under a given load as a result of the burning out of the Collapse binder. A short breakdown time is highly desirable especially when it comes to high-speed production methods. (Here It is taken for granted that the remaining properties meet the minimum requirements suffice.) With the known resins, the breakdown time is excessively long, especially with the lower temperatures, such as those used for low-melting metals.

It is believed that the formaldehyde, urea and those present at equilibrium Reaction products from it, as they are in aqueous urea-formaldehyde mixtures (hereinafter referred to as aqueous H. F. mixtures) are present, can be expressed by the following equilibrium formula can:

NH ₂ CONH ₂ + HCHO

NH ₂ CONHCH ₈ OH + HCHO

HIGH ₂ NHCONHCh ₂ OH + HCHO

HIGH ₂ NHCON (CH ₂ Oh ₂ + HCHO NH ₂ CONHCH ₂ OH
HIGH ₂ NHCONHCh ₂ OH
HIGH ₂ NHCON (Ch ₂ OH) ₂
(HIGH ₂ ) ₂ NCON (CH ₂ OH) ₂

The above formulas explain the statement “an unpolymerized, aqueous mixture Formaldehyde-urea and reaction products from it present at equilibrium «. Those of the urea molecules shown in the above equations that carry more than one methylol group, are sometimes referred to as polymethylolureas. It's difficult to choose between the different To differentiate between polymethylolureas in aqueous H.F. mixtures. Because of this, the composition the aqueous H.F. mixtures best defined by the 'weight percent Indicating urea and formaldehyde. According to a typical analysis, an aqueous H.F, mixture contains 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 contained in the solution according to the invention described is given in terms of a molar ratio. The separately added amount of urea (im In contrast to that in the aqueous H.F. mixture contained urea) fluctuates with the analytical composition of the applied aqueous H. F. mixture. For example, the amount of urea to be added separately can be determined on the basis of the molar ratio mentioned and the analysis of the aqueous H.F. mixture used in each case will.

The term "available urea" refers to free urea and methylol groups containing urea according to the equations given above. The term "available formaldehyde" refers to free formaldehyde as well as to formaldehyde, as in those reproduced above Equations shown associated with urea.

The end point of the reflux treatment can be determined by either measures the refractive index or the viscosity of the solution. The measurement of viscosity is however preferred for determining the end point of the reflux treatment. The refractive index as well as the Viscosity are indicators of the resinification level of the solution. The resinification level is of particular importance as the binder

solution is unstable if the resinification is insufficient. If, on the other hand, the degree of resinification exceeds one In addition to a certain point, the high viscosity of the binder solution prevents the formation of a complete mixing of the binder with the sand in the foundry.

The following examples illustrate the invention without restricting it. The amounts given in parts relate to the weight, unless otherwise stated. The specified percentages of binding agent relate to the weight of the molding sand. The stated percentages of the binder components (e.g. furfuryl alcohol, catalyst and water) relate, unless otherwise stated, to the total weight of the binder. The tensile strengths are given in kg / cm ² .

example 1

In 2710 parts of an aqueous H.F. mixture there were 2025 parts of furfuryl alcohol and 645 parts Urea mixed in. The pH of the solution obtained was made more aqueous by adding 50% strength Phosphoric acid adjusted to 5.7. This solution was then put into a thermometer with a stirrer and a three-necked flask equipped with a reflux condenser. The solution was on for an hour Heated to 100 ° C. and then refluxed for a further 2 hours at approximately the same temperature. The degree of resinification was determined by checking the viscosity at regular time intervals tracked. As soon as a sample of the solution has a viscosity of 380 cP / 25 ° C (measured with a Brookfield Viscometer), the reflux was stopped and 28 parts became Sodium phosphate (in 125 parts of water) was added, adjusting the pH to 8.08. After cooling, the resulting binder composition was a slightly cloudy, light amber color Liquid.

40 Example 2

To demonstrate the importance of adding furfuryl alcohol to the aqueous HF mixture, binders were prepared essentially as described in Example 1, but with varying amounts of furfuryl alcohol. The binders obtained in this way were then used to manufacture casting cores. To produce the casting cores, the binders were mixed with sand and catalyst in the proportions given below and the mixtures formed were rammed into core containers with the dimensions 28.575 × 50.8 mm. The obtained cores were removed from the core boxes and cured in an oven at 218 ° C. for 5 minutes. The hardened cores were then held in a Dietert Thermolab dilatometer at 816 and 1370 ° C. for 5 minutes. A compressive load was applied. The hot strength at break was determined in kg / cm ^a . The following results were obtained for three cores using 1.5% binder:

core

° / o furfuryl alcohol
in the binder

0 25th 40

Hot strength
816 ⁰ CI 1370 ° C

3.78 (54)
4.48 (64)
5.04 (72)

0 (0)
0.28 (4)
1.47 (21)

The following results were obtained for three cores using 2.0% binder:

core

% Furfuryl alcohol
in the binder

25th
40

Hot strength
816 ⁰ CI 1370 ° C

3.57 (51)
6.23 (89)
9.1 (130)

0 (0)
1.26 (18)
4.13 (59)

From the above results it can be seen that by adding furfuryl alcohol to the Binder the hot strength is increased considerably.

Claims (5)

Patent claims: 1. A method of making a cast core binder using furfuryl alcohol and formaldehyde, characterized in that a non-polymerized, aqueous mixture of formaldehyde, Urea and the reaction products that result from it at equilibrium, which contain a maximum of about 15 percent by weight of water, as well as of furfuryl alcohol and so much additional urea makes a solution that the molar ratio of the total available Urea to available formaldehyde is in the range of 1: 1.75 to 1: 3.0 and the Furfuryl alcohol is present in such an amount that it makes up 15 to 50 percent by weight of the solution, that the solution is adjusted to a pH in the range from 5.0 to 6.5 at 95 to 105.degree heated under reflux until it has a viscosity in the range from 350 to 3000 cP / 25 ° C and then adjust the pH of the solution to 6.5 to 8.5. 2. The method according to claim 1, characterized in that there is a ratio of total urea to formaldehyde in the range of 1: 2.0 to 1: 2.5. 3. The method according to claim 1, characterized in that there is a 25 to 40 percent by weight Furfuryl alcohol-containing solution is used. 4. The method according to claim 1, characterized in that the pH of the solution is before adjusts the reflux to 5.5 to 6.0. 5. The method according to claim 1, characterized in that when boiling under reflux holds until a viscosity in the range of 400 to 1500 cP / 25 ° C is reached. Considered publications:
British Patent No. 832 999. 609 567/414 4.66 © Bundesdruckerei Berlin