DD158090A1 - METHOD FOR STRENGTH CONTROL OF INORGANIC MATERIALS BASED ON ALKALISILICATE SOLUTIONS - Google Patents

Abstract

Process for the strength regulation of inorganic molding materials, in particular of core and mold molding materials based on alkali silicates. The aim of the invention is to consciously and safely influence the strength properties - increase of the primary strength or reduction of the residual strength - of the bound and hardened core and mold molding material. According to the invention, the object is achieved by dissolving dissolved or pulverulent phosphates having a monomeric, dimeric, cyclic or chainlike anion structure with stirring into the water glass solution having a molar ratio of SiO 2: M deep 2 O = 1.5 to 4.0 (M = Na, K) are introduced with a SiO 2 depth of 15 to 35% by weight and that including the binder, stored for a certain time and then mixed with foundry-specific granules. The invention is applicable to mold and core manufacturing in foundry technology.

Description

•1 . Application of the invention: ^{w β} ~ ^ <£ »^ #

The invention relates to a method for regulating the potting properties of core molding materials based on aqueous alkali metal silicates, which affords favorable strengths in the molding process of casting production.

2. Object of the invention

The aim of the invention is to achieve the simplest possible gesielt an increase dor primary strength or a reduction in the residual strength of the bonded and cured core and Formej molding material. , , ,

Characterization of the known technical solutions

Inorganic binders based on aqueous alkali silicate solutions have been used for a long time in the mold-making process for casting production. The hardening of the water-glass mixtures is effected by chemical, physical or physicochemical methods. The economic and hygienic advantages, the environmental friendliness of the process and the sufficient availability of Wasserglaslösungen face as lachteile especially the very high residual strength of the cured Formstcffes. Characteristic of the water glass -Forms t off ν he f ehren is the opposite organic. Forms open unsatisfactory disintegration property of Formst offs _e This requires an increased energy expenditure when separating the used sand from the casting and at the moment crucially limits the scope of application of the process. The reduction of the residual strength of wasserglasgebimdenem Fonnstoff after thermal stress according to the current state of the art by the addition of organic or inorganic disintegration conveyor is still koine 'optimal' solution. Since both primary and secondary strength of the cured waterglass-sand mixture decisively from the sinter point-lowering Alkali part of SiIicatlosung is affected, a reduction in the binder content with the addition of the conventional disintegration promoter is not. possible. On the contrary, it is often necessary, especially with finely ground inorganic additives such as bauxite, to increase the binder content, in order to ensure sufficient primary fulgence. Thus, this decay-promoting addition of the additive is in some cases reversed or "reduced".

Neither the specialist literature nor existing patents disclose processes which provide for the use of monomeric or condensed phosphates for the purpose of regulating the strength of inorganic form. The use of hexa-sodium tetraphosphate, mentioned in RO-PS 51 778, incorporated herein by reference Waterglass Cement Forming is said to improve the flowability of molding compounds only in combination with an alkylaryl sulfone tergent «,

In DD-PS 140213 a process for the controlled solidification of inorganic molding material binder is described, which is characterized in that by addition of Natriummonophosphat'en, preferably UaH ₂ PO ^ H ₂ O (or 2H ₂ O) _- and Na ₂ HPO ₄ '12H ₂ O or Aikalisilicatlösung used by phosphorus pentoxide, i ^ O-iQ »binder ^{to 0} ^ ³ can be set a desired Brstarrungsint interval of Formst offbinders. In this case, a premature solidification of the mold material before pouring is, besides the prevention of "an increased mold block stability _s then observed a reduction in the compressive strength. However, the invention in claim exclusively comprises the Verzögerung.der solidification of molding materials. It is used in DD-PS 140213 in the exposition expressly pointed out that the tertiary, monomeric or, for example, condensed phosphates used in the invention do not show the desired strength-regulating effect representing the object of the present invention.

3 "statement oF ₁₁ ^ essence of the invention

The invention is based on the technical object, in the formation of core and mold materials from aqueous alkali metal silicate solutions with foundry-specific granules, the proportion of Silicatlö.sung in the mixture, 'while increasing the Primärfestigkei.t after hardening and lowering the residual strength after thermal stress of form, off, to reduce decisively.

According to the invention, the strength regulation of inorganic molding material on the basis of Aikalisilicatlösung is achieved by introducing dissolved or powdered phosphates with stirring in the Aikalisilicatlösung, and / then that the binder is stored for a certain time before it. in another process?

sche granules, especially quartz sand and chamotte, is mixed. '·

It is expedient to use a sodium silicate solution with a molar ratio SiO ₂ : M ₂ O = 1.5 to .4.0 with a SiO ₂ content of 15

up to 35% by mass, of a density of 1150 to 1550 kg / m 2

- 3 -1

Surface tension of 72 to 77 · 10 -I ¹ Tm and a viscosity of 1 to 2000 mPa * s at a mass ratio of water glass solution to phosphate of 100 to 0.1 to 20 to use «, It is also advantageous to use phosphates, with respect their structure are mono- or dimer, cyclic or chain-shaped,. , · For example, trisodium monophosphate, Ha ^ PO ,, pure, commercial, tetrasodium diphosphate 12-hydrate, pantanesodium triphosphate 6-hydrate, ^ Q ₂ trisodium cyclotriphoaphate, ITaoPoOg and. Depending on the desired strength regulation (primary or secondary strength), the binder may be left to stand for between 5 minutes and 24 hours before it is preferably treated with pouring of specific granules within 3 minutes in a snow-running blade mixer.

The advantage of using the inventive method be st EIIT _it's that so is able Pestigkeits features hardened or thermally loaded Y / asserglas molded materials targeted and siche.i? adjust. The economic advantages in the application of the method according to the invention result from a saving of binder or use of a much cheaper to produce alkali silicate solution and a Arbeitsaeiteinsparung by reducing the energy and time required to separate the core and J ^ Orrnenf ormst of f it from Gußkorper « Furthermore, the phosphates used as binder additives are non-hazardous and non-toxic, as well as harmless to the environment in terms of the small amounts used and may therefore be handled without any special measures of preservation and environmental protection.

s guide s i spi ele

The invention will be explained below by two embodiments. , ·

Example 1. ·

.Rezeptur; 97 $ O Maase-% Quartz Sandy Dry

average grain size 0.24 mm Degree of uniformity 73. % loss on ignition O, 11 % .

Sludge content O ₉ 2% pH of the aqueous extract 5.4 3.0% by mass of binder

Mass ratio of water glass solution too

.'Phosphate 100; 2 leave the glass solution σ

SiO ₉ »content 25.05% by mass

C.

Molar ratio SiO ₂ : IJa ₂ O = 3.47 density 1310 kgm ^-3

Viscosity 28 mPas

- 3 -1

JHM

Surface tension 75 · 10 Phosphate: Ua-iPO ^, pure, commercially available ". (Not carbonate free)

• preparation, processing:

The phosphate is stirred into the waterglass solution for 30 minutes. The preparation time of quartz sand and binder is 3 min. _C The mixture is ready for processing for 20 min.

Result: .

Standard test specimens according to TGL 14317 are prepared from the mold material and tested for their strength. After a drying time of 1 h at 378 K, the stated strength is found in comparison to test specimens prepared without addition of phosphate

Compressive strength increases from 6.10 JiTPa to 8.24 MPa = 35 %

Increase Bending strength increases from 2.64 MPa to 3.65 MPa = .38 %

• · - Increase «

The residual strength changes from 0, -54.MPa to O _? 61 MPa * This corresponds, based on the compressive strength, a change of 8.86 % without Phosphatzusatz'auf 7.40 % with PhosphatzusatZj cL'h. , the relative residual strength increased in the latter case 17 % .

Example 2 '

'Formulation; 97.5% Masa quartz edge, as in Example 1. '2.5 mass- binder

Mass ratio of water glass solution

Phosphate 100: 1.6 water glass solution

25.6% by weight. , .

Molar ratio SiO ₂ ϊ Na ₂ O = 3.33: 1 density 1 340 kg m ~

Viscosity 27 mPa s. .

- 3 -1

Surface tension 75 _S 5 * 10 ^ Im

Phosphate: trisodium cyclotriphosphate PoOg, anhydrous

Preparation, processing: as' Example 1

Residuality of the binder · during processing 2 _s 0 h

Result;

Standard test specimen heating and testing - as in Example 1 Curing of the mixtures as in Example 1 Result in comparison with analogous test specimens prepared without addition of phosphate:

Compressive strength: from 5.42 IiPa to 6.48 IvIPa = 19 % increase

Flexural strength: from 0.51 MPa to 0.96 MPa = 88 % increase

Residual strength; from 0.36 MPa to 0.27 MPa = 34 % decrease in

relative residual strength

Claims (1)

/ C ^f i 'j iss; j A method for resistance regulation inorganic molding materials based on alkali silicate solution for the mold, and cores for the Gußkörperbildungspro.zeß, characterized in that j that dissolved or powdered phosphates with monomeric, diraerer _s cyclic, or · catenate anion structure with a weight ratio water glass solution au phosphate with a racemic, dimeric, cyclic or chainlike anionic structure of 100; (0.1 to 20) while stirring in the waterglass solution with a molar ratio SiO ₂ t M ₂ O = 1.5 to 4 _? 0 (M = Ka, K) with a SiCU content of 15'-35% by mass, a density of 1/150 to 1 ^ 550 kg »/ m ^J and a viscosity of 1.0 to 2000 mPa« s introduced and then that the binder is stored for a certain time and then mixed with foundry-specific granules, in particular "quartz sand and chamotte"