FR2461538A1 - SELF-CURING MIXTURE FOR THE MANUFACTURE OF FOUNDRY MOLDS AND CORES - Google Patents

Abstract

THE INVENTION CONCERNS THE FOUNDRY. THE SELF-CURING MIXTURE WHICH IS THE OBJECT OF THE INVENTION IS OF THE TYPE INCLUDING A REFRACTORY CHARGE, ORTHOPHOSPHORIC ACID, A MATERIAL BASED ON DEADLY COOKED MAGNESIA, AND WATER, AND IS CHARACTERIZED IN THAT THE MATERIAL A DEATH-COOKED MAGNESIA BASE IS A SPINEL-TYPE COMPOUND OF MAGNESIUM, CALCINATED AT A TEMPERATURE OF 1600 TO 1900C FOR 40 TO 1600H. THE COMPOSITION OF THE SAID MIXTURE IS AS FOLLOWS (PARTS BY WEIGHT): ORTHOPHOSPHORIC ACID, 2 TO 10; MAGNESIUM SPINEL-TYPE COMPOUND, 2 TO 20; WATER, 0.5 to 6.0; REFRACTORY CHARGE, THE BALANCE. THE MIXTURE IN QUESTION CAN BE USED FOR THE PRODUCTION OF STEEL, CAST IRON AND NON-FERROUS METALS.

Description

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  The present invention relates to the field of foundry and particularly relates to a self-hardening mixture

  for making molds and cores.

  Said self-hardening mixtures are generally used to make the cores and molds used in the production of steel castings, cast iron castings and castings.

non-ferrous metals.

  A self-hardening blend is known to the manufac-

  cation of molds and cores, comprising a

  fractary, ground metallurgical magnesite and orthophosphoric acid (Japanese Patent Application No. 52-23882, Cl, 11A212, published June 28, 1977). This mixture is characterized by a reduced duration of use, insufficient mechanical strength in the state

  hardened and low resistance + crumbling.

  Also known is a self-hardening mixture for the manufacture of molds and foundry cores, comprising a refractory filler, orthophosphoric acid, water and a magnesia material cooked to death, namely, a magnesia powder. or metallurgical chromite-magnesia. This mixture is characterized by an excessive reactivity of magnesia or metallurgical chromite-magnesia with orthophosphoric acid, which complicates the adjustment of the duration of use and the rate of hardening of the mixture, expressed by an increase in the mechanical strength of the mixture in the necessary range, and adversely affects the mechanical strength of the molds and foundry cores. This mixture is characterized by a duration

  from 5 to 8 seconds and a mechanical resistance

  than 2.5 kg / cm2 at the end of 0.5 hours and 22 kg / cm2

after 24 hours.

  It has therefore been proposed to widen the range of adjustment of the duration of use of the self-hardening mixture and of its curing speed, as well as to increase the mechanical strength of the molds and foundry cores, by a more appropriate choice. magnesia-based material

cooked to death.

  This problem is solved thanks to a self-hardening

  for the manufacture of molds and foundry cores, of the type comprising a refractory filler, orthophosphoric acid, a dead-burnt magnesia material and water, in which, according to the invention, the dead-burned magnesia material is a magnesium spinel compound, calcined at a temperature of 1600 to 1900 ° C. for 40 to 1600 hours, the composition of said mixture being the following (parts by weight): orthophosphoric acid ... ... 2 to 10 magnesium spinel compound .................. 2 to 20 water ................

  ......... 0,5 to 6,0..DTD: refractory load ............ the balance.

  The use of said spinel type compound of

  magnesium makes it possible to widen the range of

  2 to 3 times, widen the range of curing rates from 2 to 4 times and increase the mechanical strength at the initial and final curing stages

from 1.5 to 2 times.

  It is recommended that said magnesium spinel compound in the composition of the self-hardening mixture be a product obtained by grinding spent magnesia-chromite bricks from the vault.

  refractory steelmaking equipment.

  It is advantageous, in order to increase the initial curing speed and the overall mechanical strength of the mixture, that said spinel type compound of

  magnesium component of the self-hardening

  a product obtained by grinding the active part,

  previously separated from said used magnesia bricks

  chromite. The self-hardening mixture for the production of molds and foundry cores, subject to

  the invention is prepared in the following manner.

  The refractory filler, for example quartz sand or any other filler used in a foundry, is

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  mixed with magnesium spinel compound powder, calcined at a temperature of 1600 to 1900 C

  during 40 to 1600 h. Then add the orthophosphoric acid

  phoric and water and stirring continues for 1 to 2 minutes.

  The self-hardening mixture subject of the invention

  It contains from 2 to 20 parts by weight of magnesium spinel compound. Lowering the amount of this compound to less than 2 parts by weight does not provide a mixture of necessary strength, and its increase above 20 parts by weight is irrational because the rate of hardening of the mixture

becomes excessive.

  The magnesium spinel compound is calcined beforehand at a temperature of 1600 to 1900 ° C for 1600 hours. At this calcination regime a magnesium spinel structure is formed. If the temperature

  is less than 1600 C and the calcination time inferior to

  at 40 h, said structure is not formed. Calcination

  at a temperature above 1900 C and a longer duration

  1600 hours are irrational, since quantitative and qualitative phase and chemical

  already reached their optimum values.

  The self-hardening mixture according to the invention

  contains 2 to 10 parts by weight of orthophosphoric acid.

  An amount of orthophosphoric acid of less than 2 parts by weight does not provide a mixture of necessary mechanical strength, and increasing this amount above 10 parts by weight does not influence

  sensitive on the technological properties of the mixture.

  The ideorophosphoric acid can be used as a soluti nsaq.e.s of different caoatraticms. The total amount of acid, counted as undiluted acid, is between 2 and 10 parts by weight. To use an acid concentration of 40 to 80%, it is added to the concentrated acid

0.5 to 6.0 parts by weight of water.

  In the mixture forming the subject of the invention, the magnesium spinel-type compound used is a

  product obtained by grinding spent chromite bricks

  magnesia or magnesia-chromite, originating from the refractory vault of steelmaking apparatus and having the following chemical weight composition magnesium oxide ......... eu. 30 to 94% iron (III) oxide ........... 2.0 to 40.0% iron oxide (II) ............... 0.01 to 11.0% chromium (III) oxide ............... 1.0 to 13.0% silicon oxide (IV) .......... 2 0 to 8.0% aluminum oxide ............... 2.0 to 19.0% calcium oxide .............

  . 0.5 to 8.0% It is evident that the formation of a magnesium spinel structure is dependent on the starting materials used. During the calcination of magnesia-chromite bricks and chromitemagnesia, DTD is formed: a spinel-periclase structure.

  It is advantageous to use a mixture containing a product obtained by first separating spent bricks from their active part located on the laboratory side of the steelmaking apparatus and by grinding it, said active part having, for example, the chemical weight composition. following magnesium oxide .......... o * o70,26% iron oxide (III). .. 7, 51% iron oxide (II) ... 1.96% chromium (III) oxide .. 8.98% silicon oxide (IV) ...... 6.78% oxide of iron aluminum., ............. 3,4% calcium oxide ................ 1,0% losses during calcination .. 0 In this last case, in the phase composition of the material, the part of the ferro-magnesian compounds of the wustite or magnesium iron type is increased, while that of the periclase is lowered, and the chemical composition is characterized by an increased quantity. of iron oxide and a reduced amount of manganese oxide compared to the composition of the powders obtained by grinding the entire

mass of bricks.

  The bricks are crushed using the material

  standard used in the preparation of materials

  powder mills, ball mills, jet mills, vibratory mills and others. The specific surface of the product obtained after the grinding of used bricks is between 500 and 5000

  cm 2 / g, preferably between 1200 and 3000 cm 2 / g, the determination of

  natbn taking place by the Kozeni-Karmann method. The table below gives the compositions and the properties of the mixture according to the invention, compared with those of the known mixture which is the subject of the author's certificate.

USSR 605,364.

  I. Composition of mixtures Designation of constituents Quartz sand

Orthophosphoric acid

that Water

Brick of magnesia-

chromite, active part

Brick of magnesia-

  Chromite Magnesite-chromite Content of constituents, parts by weight Mixture according to the mixture known to the invention (Certif. No. 605 364 Ir metallurgical - II.

I 2 3 4

Resistance to the com-

  pressure, kg / cm2: after 0.5 hours after 1 hour after 4 hours 9, 5 12.5 16.5 6.2 17.3 22.5 2.5 13.0 16.5

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  II. properties of the mixtures (continued)

1 2 3 4

  at the end of 24 h 19.0 27.0 22.0 Clear,%: after 24 h 0.1 0, 1 0.4 Operating time min 15 16 5 to 6

  The table shows that the mechanical resistance

  that mixtures are greater than that of the known mixture, both in the initial period and in the final stage of hardening. It should be noted that the mixtures according to the invention retain their high mechanical strength properties even when the contents of constituents are minimal, and that when these contents are maximum, the mechanical strength of the mixtures is greater than that of the known mixture. at all stages of hardening. Moreover the crumbling of the mixture decreases significantly. The duration of use of the mixture which is the subject of the invention can be varied between 9-10 and 20 minutes, by modifying the composition within the limits indicated. Compared to the known mixture, the curing rate of the mixture according to the invention, characterized by its mechanical strength 0.5 h after its preparation, is much higher, the duration of use remaining at the same time sufficient for the performance of all manufacturing operations of molds and cores. On the other hand, together with the high curing speed at the initial stage, the mechanical strength continues to increase in the following periods and, after 24 hours, it reaches high values, while the known mixtures have a speed relatively low curing and low mechanical strength after 24 hours. To better fix the ideas, several concrete but non-limiting examples of embodiment of the invention are

described below.

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Example 1

  81 parts by weight of quartz sand are mixed with 10 parts by weight of the product obtained by grinding (specific surface area 1900 to 2100 cm.sup.2 / g) of the active part, separated beforehand, of used magnesia-chromite bricks. Stir the mixture for 1 to 2

  mn, then 5 parts by weight of orthoacid

  phosphoric material with a density of 1.58 to 1.60 g / cm3 and 3 parts by weight of water. The mixture is stirred again for 1 to 2 minutes. With the obtained mixture, specimens for the determination of the compressive strength are prepared in the form of

  cylinders 50 mm in diameter and 50 mm in height.

  The compressive strength is determined by the

standardized method.

  The resulting mixture has the following properties Compressive strength, kg / cm2 at the end of 0.5 h ............ 9.5 at the end of 1 hr ... 19 , After 4 hours .... 26.0 after 24 hours .... 30.0 Duration of use ....

  ............. 15mn Crumbling at the end of 24 hours ... 0, 1% Example 2 The mixture is prepared in the same manner as in Example 1. 5 parts by weight of quartz sand, 2 parts by weight of product obtained by grinding the active part of magnesia-chromite bricks having the same specific surface area as in Example 1, 2 parts by weight of orthophosphoric acid (density of 1.58 to 1.60 g / cm 3) and 0.5 parts by weight of water. The resulting mixture has the following properties: Compressive strength, kg / cm at the end of 0.5 h .... 6.0 at the end of 1 h.12.5 at the end of 4 h ............ 16,5 at the end of 24 hours .......... 19,0 duration of use ......... 18 mn - Crumbling at the end of 24h 0.15%. DTD: Example 3

  The mixture is prepared in the same manner as in Example 1. 64 parts by weight of quartz sand, 10 parts by weight of orthophosphoric acid (density of 1.58 to 1.60 g / cm 3), 5 parts are mixed. by weight of water and 20 parts by weight of product obtained by grinding the active part of bricks of magnesia-chromite, analogous

to that of Example 1.

  The resulting mixture has the following properties: Resistance-to compression, kg / cm2: at the end of 0.5 h .......... 12 at the end of I h ..... ...... 24.5 at the end of 4 h ...... 32.0 at the end of 24 h ....... 43.0 Duration of use ... ........ 12 mn Cracking after 24 h ...... 0.1%

Example 4

  The mixture is prepared in the same manner as in Example 1. 81 parts by weight of quartz sand are mixed, 10 parts by weight of product obtained by grinding magnesium-chromite spent bricks (specific surface area 1900 to 2100 cm 2 / g), 6 parts by weight of orthophosphoric acid (density of 1.58 to 1.60 g / cm3)

and 3 parts by weight of water.

  The resulting mixture has the following properties: compressive strength, kg / cm 2 at the end of 0.5 h ....... 6.2 at the end of 1 h ...... 17.3 at the end of 4 hours .......... 22.5 after 24 hours .......... 27.0 Duration of use ..

  ............ 16 min Cracking after 24 h ....... 0.1% .. DTD: Example 5

  The mixture is prepared in the same way as in

example 1o

  86.25 parts by weight of quartz sand 10 parts by weight of products obtained by grinding of the

  active part of used magnesia-chromite bricks

  specific surface of 1900 to 2100 cm2 / g), 3 parts by weight of orthophosphoric acid (density of 1.58 to 1.60 g / cm3

and 0.75 parts by weight of water.

  The resulting mixture has the following properties Compressive strength, kg / cm2 at the end of 0.5 h .... o ....... 0 14 at the end of 24 h ..... ......... 21 Duration of use ................... 9 10 mn

Example 6

  The mixture is prepared in the same way as in

the example lo

  81 parts by weight of quartz sand are mixed with 10 parts by weight of product obtained by grinding the active part of magnesium bromide bricks, analogous

  to that of Example 5, 6 parts by weight of orthoacidic acid

  phosphoric acid (density of 1.58 to 1.60 g / cm3) and 3 parts

by weight of water.

  The resulting mixture has the following properties Resistance to compression, kg / cm2y at the end of 0.5 h ............ 9.5 at the end of 24 h .... .... 0 ... 0. 30.0 Duration of use .................. 15 mn

Example 7

  The mixture is prepared in the same way as in

Example 1

  75.5 parts by weight of quartz sand 10 parts by weight of product obtained by grinding the active part of magnesium bromide bricks, analogous

  5.9 parts by weight of orthoacidic acid are

  phosphoric acid (density of 1.58 to 1.60 g / cm3) and 5.5 parts

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by weight of water.

  The resulting mixture has the following properties Compressive strength, kg / cm2: at the end of 0.5 h..vooeoo.ooo 7.6 at the end of 24 h ... Oo ...... ... 38 Duration of use .................... 20 mn

Example 8

  The mixture is prepared in the same way as in

Example 1

  81 parts by weight of quartz sand (average grain size of 0.16 to 0.20 mm), 10 parts by weight of product obtained by grinding of spent chromite-magnesia bricks, 6 parts by weight of orthophophoric acid are mixed. (density of 1.58 to 1.60 g / cmn) and 3

parts by weight of water.

  The resulting mixture has the following properties: Compressive strength; kg / cm2: at the end of 0.5 h .... 6.0 at the end of 1 h .............. 15.5 at the end of 4 h. 20.0 at the end of 24 hours .............. 25.5 Duration of use b 15 mn Crumbling at the end of 24 hours ........ .. 0.15% Of course, the invention is not limited to the embodiments described and represents that have been given as an example. In particular, she

  includes all means constituting technical equivalents

  the means described, as well as their combinations, if they are carried out according to his spirit and

  implemented in the context of protection as claimed.

1 1

R E V E N D I C AT I 0 N S

  lo Self-hardening mixture for the manufacture of molds and foundry cores of the type comprising a refractory filler, orthophosphoric acid, a dead-burnt magnesia material, and water, characterized in that the material based on burned magnesia is a magnesium spinel compound, calcined at a temperature of 1600 to 1900 C for 40 to 1600 h, 2. Self-hardening mixture according to claim 1, characterized in that it contains (parts by weight) : orthophosphoric acid ..... 000 .. 2 to 10 composed of magnesium spinel type ............... Èc..o 2 to 20 water ooooo..oo..o ..... o..O 0.5 to 5.0 refractory charge ... 0000 .... the balance

  3o self-hardening mixture according to one of the claims

  1 and 2, characterized in that the magnesium spinel type compound used in its composition is a

  product obtained by grinding used magnesia bricks

  chromite from the refractory lining of steelmaking equipment.

  4. Self-hardening mixture according to one of the

  cations 1, 2 and 3, characterized in that the magnesium spinel type compound used in its composition is a product obtained by grinding the active part,

  previously separated from said used magnesia bricks

chromite.