DE2205214A1 - PROCESS FOR MANUFACTURING LARGE AREA, COMPLICELY DESIGNED FOUNDRY CORES, IN PARTICULAR CORES FOR HEATING BOILERS - Google Patents

Description

VJSB Chemische ί, '/ erke Cottbus Gottbus, November 23, 1971

22052H

inventor

Bastian, Hans
Chroszcz, Leo
Dr. Schumann, Hans

Process for the production of large, complexly designed foundry cores , in particular barrows for boilers

The invention relates to a method for the production of large, complicatedly designed foundry cores, especially cores for cast iron boiler members, these after Hot-box procedures as completely nonexistent with or without air cannulas getting produced·

As is known, cores of this type have hitherto been produced manually using conventional methods, predominantly with oven-drying oil core binders or with synthetic resin core binders using the thermal shock process. In each case, half-cores are manufactured, which are glued together afterwards or during a two-stage hardening process. The production of two heap cores to be connected is necessary in order to be able to create interconnected channels in the core, which are used for gas discharge during the casting process. or solid cores with a few channels using the hot box method, although such attempts have already been made many times.

The processes that have hitherto been customary in foundry technology have different methods Lack of

With the old ülsand method, a high physical load is the Recorded core makers due to core size. In addition, the kernels require two hours of drying time. That

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The procedure is therefore very time, transport and manpower and requires large drying chambers.

The thermal shock treatment offers the possibility of machine core production, but requires a long continuous furnace in which the short-term hardening (thermal shock) of the cores takes place, tfenn the joining of the core halves during the The hardening process is to be carried out twice through the oven, otherwise an additional work step, the gluing of the halves of the joint after hardening, is required. Included there is always the risk that the glue joint is not tight and liquid iron penetrates into the gas discharge channels

Heavy drying bowls are required for both methods, on which the none lie during the clearing process. These have to be transported and warmed up, as is the case with both The process of inserting reinforcing wires into the interior of the core is customary or required.

Attempts have also been made to cut the gas discharge ducts through the core Map inserting foam. Apart from the fact that core halves are also blown or shot in the two-stroke process need to be, this procedure has not proven itself in technology let introduce.

In order to make core production more economical, attempts have also been made to produce the core halves using the hot box method and immediately after removal from the core box with the help of the heat contained in them to stick together hot or after cooling. It had to be observed, however, that an absolutely secure closure of the very long glue joints could not be achieved, because the kernels warped unevenly during the cooling process. Flawless casts cannot be made with these cores. because even minor leaks in the glue line cause iron to run into the gas discharge ducts. A far larger committee is created but when using such cores, the fact that stresses occur in the core due to the pressure applied during gluing, which cause the core to grow unevenly during the casting process. This results in uneven wall thicknesses in the casting or even core breakthroughs.

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The purpose of the invention is to eliminate the deficiencies listed and thereby, a more rational core production even with such core assortments, as they are designed as large and complex, z. B. exist as boiler cores to enable.

The invention is based on the object of developing a method which allows large, complexly designed foundry cores, especially cores for boiler sections as full cores without or with a few gas discharge channels and without reinforcement to manufacture on hot-box masciiineu and thereby the waxing of the To make cores consistent and determinable during casting »

It has been found that it is possible to use a mixture of synthetic resin core binders such as phenol-formaldehyde resins, toluenesulfonic acids as hardening accelerators and highly gas-permeable ^f ^ uarzsand, which in heated core boxes Ddt a temperature of 240 ··. 300 ⁰ C is blown in or shot in, large-area, complicated cores, in particular boiler section cores, to be produced as full cores without or with few gas discharge channels and thus to cast perfect castings

As the synthetic resin core binder preferably phenol-formaldehyde resins are used, the ... 70 ⁰ G, followed by distillation up to a solids content typically of 70 ·. · 73% obtained by cautious alkaline condensation of Pheaol and formaldehyde predominantly in the temperature range of 40. The hydroxides of the alkali and alkaline earth metals are preferably used as condensation agents. In order to give the condensation mixture sufficient flowability, the binder is ^{adjusted to a viscosity (25 0} O) of 400 + 100 cP. The pH-i7ert should not exceed 7 »0 ... 8.5i, preferably 7i5i ·

The selection of a suitable hardening accelerator is essential for success. It has been found that of the known hardening accelerators, the toluenesulfonic acids are the most suitable are. In contrast to the generally accepted procedure of

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However, using dilute acids has been found to be one so high acid concentration must be chosen that with low The amount of hardener in the sand mixture has a pH value of 3. ·· 3.5 exactly can be adjusted. In this way, the sand mixture receives a particularly good flowability, which is good for blowing or Shooting large, intricate cores is vital. In addition, the mixture retains this fluidity over several hours when the pH -. * / ert of 3 in the sand mixture is not exceeded. Compliance with the pH-inert 3 ··· 3 »5 on the other hand, ensures fast and even hardening of the cores to the inside of different core cross-sections. But this is an essential prerequisite for large area none during the casting process a defined, small and

Growth to be taken into account when dimensioning the core box exhibit.

The toluenesulfonic acids are used in a concentration of 55 ··· 65 % t, preferably 60 % _y . It is advantageous, the curing agent 10 ... 20%, preferably 15% _t A'thylenglykol, glycerol or similar di- or TrioIe add *

In addition to the selection of a suitable Ker-nbinder-Harter system for success the use of a high gas permeability

g the use of a highly gas permeable sand necessary. This should be mixed with the binder system have a minimum gas permeability of 250. It may however, the grain size should not be so coarse as to create an unclean cast surface.

Depending on the sand quality, an iVüsci.jung of 97 .. · 98 % resin sand and 2 ... 3 % synthetic resin core binder is used for the production of the cores. Before adding the binder, 1 ... 2 ml of a hardener consisting of aqueous-alcoholic toluenesulfonic acid (55-65%, preferably 60 %) per kilogram of resin sand are premixed. The core sand mixture has a pH value of 3 ... 3.5 and a gas permeability of at least 250.

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This Kernaandgemisch is blown into heated core boxes, with a temperature of 240 ⁰ C or 300 ··· injected * The core box are arranged horizontally, and the sand mixture is introduced through the head box. For boiler sectional cores of the order of magnitude 700 χ 1600 mm with a mass of 66 kg, a maximum "dwell time of the cores in the heated core box of 3 minutes" is required After cooling, the core hardness tester can determine that the core hardness in all cross-sections of the core is about p: slightly high.

O-

Are phenol-formaldehyde resin core binders with minor amounts If concentrated hardener and quartz sand are mixed, they result in cores with a low gas number after hardening, i.e. H. they develop at thermal decay during the casting process little gas. Contrary to previous experience, it was surprisingly found that that an appropriately selected, highly gas-permeable <iuarzsand has sufficient porosity to prevent the when pouring large, complex cores, preferably boiler section cores, those made with such binding systems; are arising discharge gases through the core brand. With many cores, the introduction of gas discharge channels can be completely. Komiaen in Portfall. With some complicated assortments you can facilitate the evacuation of gas by before filling the Keimbox air skewers of approx. 8 mm in diameter inserted, which one pulls out immediately after filling. The remaining holes in the Core outside the core brands can be made with small core plugs close.

It was further found that the binder-hardener system described Surprisingly, causes a slight, constant, to be determined growth of the cores during the casting process, which only of the cross-sectional sizes and shapes in the spatial coordinates depends. This allows the necessary undersize, Radii of curvature and positional deviations of the model opposite determine the desired cavity of the casting and take it into account when designing the core box.

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By using the procedure described, for the first time Large, complex cores, preferably cores for boiler sections, manufactured as full cores in one operation, so that the physical loads are reduced compared to the previously usual types of production and by the elimination of the Core reinforcement and shortening of the drying process the profitability of the core production is increased significantly · In addition This process guarantees cores that are perfectly dimensionally stable, so that the quality of the castings is improved.

The invention is to be described in more detail below by means of a few examples explained.

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example 1

100 kg of dried quartz sand (mean grain size 0.35 mm ι degree of uniformity 72% _t 0.2% slurries) were with 100 ml of hardener (60 ^ oige toluenesulfonic acid with 15 % ethylene glycol) and 2500 g of acid-hardenable alkali condensed phenol-formaldehyde resin (pH 7t5i viscosity at 25 ⁰ G 400 cP) mixed. This mixture resulted in curing in. heated core box at 300 ⁰ G the following flexural strengths:

Hardening time warm cold ^r kp / cm ² : ■ kp / cm ² , ί 7.5 6th 23 i ^ 11 37 '30 21 50 • 60 ■ 33 60 120 33 80;

The gas permeability of an uncured standard test piece of 50 mm diameter was 270 with 9 rams, with 6 and 4 Ramrn strokes 290 or 300

The specific gas number (weight loss on coking in the covered quartz crucible within 6 min at 1000 ⁰ G (based on the amount of binder in the core)) was for cores with a curing time of 60 s

Example 2

A Kex * nsäule 60 ram in diameter, was cast around 350 mm Gußlänge and 8 mm wall thickness with cast iron of I35O ⁰ C temperature · The growth in length of the core was measured during the casting and then to solidify in the mold, with an inductive lAfegaufnehmer ·

If the procedure according to Example 1 was used for the production of the core, this resulted in a curing time of 3 minutes an increase in the length of the core until the iron solidifies

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0.3 mm, b -.;, I 5 lan liar te time 0.6 mm. With a usual xiern length from 1600 this corresponds to the equivalent of 1.6 mm or 3 »2 mm. These ratios proved to be constant and could with dec core box dimensioning must be taken into account. In the In practice, castings were obtained with tight wall thickness tolerances.

If other synthetic resin lter systems were used for the production of the "far away", in which the inner part was not fully hardened to the optimum strength or had insufficient strength overall, the total core length of 1600 ωά calculated a growth in length of 10 ... 15 mm and more, these greatly fluctuated Ws.te at several attempts Aiit such cores could be in the I ³ taxis no uniform iVatidstärken the castings Qs Kielt. Likewise, such Langen wax could not turn in the core box dimensioning be compensated.

Example β

Large cores for the yawing of heated boiler members jiner max. length of 15ΟΟ mm and a weight of 55 ka from an opening according to Example 1 by means of a blower

^w 2

machines manufactured. The blowing pressure was 0.5 kgf / cm, the Jilas time 12 s, the curing temperature in the heated gas under and Oberkernkasben duiOhschnittlich 270 ⁰ G. 2.5 min after _Beöndi-: '' un _ä 'of Ulaszeit was the full core without Lult ducts dug out of the core box with pins and canceled to cool. iTach α; After using it, it was placed in a green sand mold and poured without any further treatment. The casting obtained was free of gas bubbles and other defects, and the required wall thickness of 8 mm was present with low tolerances in all of the sections.

Example 4

Large cores for pouring heating kes. members with a maximum length of 1600 and a weight of 66 kg, which were more structured than the beads according to Example 3, v. were in the same ./eise as described in Example 3 hor ^ e

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But before blowing the sand mixture into the Core box in length one and in the cjuere two air skewers inserted. These crossed in the two core binary marks. oofort After you had filled the remote box, the air bubbles were pulled out. While awake in the curing period, the cores were removed from the box dug out with pens and put down to the cold. While the next core was cast and hardened, it was time in place to plaster the core and the four leading to the outside Close the hole with small core plugs. The Gießvorä'arig proceeded as in example 3 »the casting was just as dimensionally accurate and had no gas bubbles.

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Claims (2)

22052U Pa te η t ans or iic he 1. A method for the production of large, complicated Jie ^ ereikernen, in particular cores for cast-iron hot boiler members, characterized in that a (jemi sch of synthetic resin core binders such as phenolic innaldehydhar ze η, toluenesulfonic acids as hardening accelerators, which iithyleneglycol, glycerine or similar di- or . triols are added and hochgasdurchlässigem ^ uarzsand in core box heated to a temperature of 240 ... ⁰ 3OO G wirdi eingeblpsen or injected with the Keinsandgelüiaoh by the addition of small amounts of a flärtungsbeschleuniger pIMV'e.'t of 3 ··· 3 » 5 and has a permeability of at least 250 2. The method according to claim 1, characterized in that is used for making the core and ge Irish a resin core binder which is by means of a airtungsbeschleunigers in the position, in the temperature range of 2 ^z j0 .. 3OO ⁰ G quickly and evenly cure as well as in Pouring with liquid metal does not exceed a specific gas number of 45 fo (coking number); Preferably, the core binder should consist of an alkaline condensed phenol-formaldehyde resin, which is mainly produced in the temperature range of 40 ... 70 ⁰ G and subsequent distillation up to a solids content of 70 ... 75% with alkalis or jirdalkaiien as a condensation medium has a pH value of 7 ··· 8.5 »preferably 7» 5i · 3 · Process according to claims 1 and 2 _3, characterized in that the hardening accelerator is a high-percentage aqueous-alkali solution of toluenesulphonic acids with 55-65 % toluenesulphonic acid, which can also contain 10 ... 20% diols or triols * 309822/0707 72057H Method according to claims 1 to 3 »characterized in that a mixture of
97 ··· 98% ^ uarzGand and 2 *. * 3% resin core binder is used, wherein nbinders before dei Zutaischung of Kei
1 ··. 2 ml hardening accelerator is added to each kilo of granules of sand 309822/0707