SU933179A1 - Method of preparing sand-clay mixture for producing casting moulds - Google Patents

Description

one

The invention relates to the field of foundry production, namely -,: to methods for preparing sandy-clay (sandy-bentonite) mixtures used to make casting molds;

The bulk density (bulk density) of the mixture has a significant effect on the quality of the raw sandy-clay forms, especially when using models of complex forema and with elements that differ significantly in height. As the bulk density decreases, the hardness and strength of the mold decrease. However, the existing methods of mixing do not allow to obtain a sufficient value of the bulk weight and flow for a given strength of the forms.

A known method of preparing sand-clay mixture for the manufacture of casting molds, according to which dry powdered clay in a content of 15-25% by weight of previously introduced clay lj is additionally introduced into the mixture 2-10 seconds before the end of the mixing.

This method is associated with an additional increase in binder consumption, which impairs its economic performance.

The closest to the proposed invention to the technical essence and the achieved result is

10 method of preparing sand-clay mixture for the manufacture of casting molds, which consists in mixing the dry ingredients of the mixture (refractory filler, clay binder)

15 with liquid (mainly water) until the electrical conductivity of the mixture reaches a maximum, which indicates the best mutual distribution of ingredients 2J.

20

However, this method does not provide improvement of such technological properties as bulk density and fluidity of the mixture without deteriorating the strength properties. If it is necessary to increase the strength of the form, the indicated properties (bulk density, flowability) will deteriorate, which can lead to different density and strength of 5 shape sections.

The aim of the invention is to increase. the bulk density of the mixture and the ability to even compaction at a constant consumption of clay binder - 10.

 To achieve this, a method is proposed ... for preparing a forest-clay mixture for the manufacture of casting molds, which includes mixing 15 dry ingredients with a liquid, characterized by ot known for first preparing a preliminary mixture by mixing dry ingredients .; in the amount of 50-85. OB. X from their full

volume with a liquid ingredient until it is evenly distributed, then the remaining volume of dry ingredients is added and the mixture is stirred until a bulk volume is reached. weight greater than the bulk density of the pre-mixture at 6-35.

The pre-mix is prepared by mixing part-dry ingredients (50-85% of their total volume with the liquid ingredient, for example, water, taken mostly full of 1 dose, and mixing is carried out in runaways using rollers create a squeezing force, i.e. putting pressure on the mixture

with simultaneous averaging. When this occurs, the intensive alignment of moisture in the mixture.

Then, the obtained preliminary mixture (with evenly distributed moisture) is mixed with the remaining volume of dry ingredients (sand, clay

without the use of squeezing pressures, which is achieved by mixing the paddle stirrer, or by using compressed air or using vibration. At the same time, there is no leveling of the moisture content: a mixture is ready consisting of alternating wet and dry zones or zones that have a. several times less moisture, due to this, wet particles are covered with a dry composition.

In order to provide the required properties of the mixture, the volume of dry and 55 graded ingredients in the preliminary mixture should be 50-85 vol. from their full volume. When kept dry

ingredients less than 50 vol. a substantial increase in the bulk density is achieved, however, the crumbling rate does not correspond to the normative values, and with a content of more than 85% by volume, the achieved increase in the bulk density is of little importance.

The mixing time of the pre-mix with the remaining volume of dry ingredients in the mixer, which does not create squeezing, should be no more than a few minutes, preferably no more than 3 minutes. In this case, the ready mix consists of alternating wet and dry microzones (microvolumes), evenly distributed throughout the volume. Between dry and wet microzones, there should not be a quick leveling of their moisture content, since then fluidity will not be ensured (flowability of the mixture.

In the process of compaction, for example, by pressing, moisture moves from wet microzones to dry, i.e. its gradual alignment takes place in the volume of the mold, which allows to obtain the required physicomechanical characteristics of the mixture. At the same time, an increase in the flowability and bulk density of the mixture contributes to a better filling of the e-bridge of the forming tool, a more uniform compaction of the form, a decrease in the pressing pressure, especially at high models. The method nq of the invention also makes it possible to regulate the bulk density and to increase the strength of the areas of the moldj remote from the press plate.

When the maximum pressing pressures are reached, the change in the fluidity of the mixture is already insignificant, since the mixture turns into usual in the usual way, however, at the initial moments of pressing, the flow improves significantly, which is especially noticeable when forming according to complex models.

The proposed method allows, if necessary, to increase the average moisture content of the mixture without lowering the flowability (flowability J below the norm.

In order to strengthen the surface layer of the form, it is advisable to moisten the surface of the model. For the same purpose, hygroscopic additives can also be used. The moisture content of the dry composition should not exceed 30% of the average moisture content of the goat / togo mixture. The described method can also be applied in the preparation of fluid mixtures containing various organic additives and oils. In this case, the pre-mix contains part of the volume of dry ingredients evenly mixed with organic liquid o in the runners, after which the remaining part of the dry ingredients is added and mixed in the body mixture that does not create squeezing effort. to dry The bulk density of the mixture prepared by the proposed method exceeds the bulk weight of the pre-mix by 6-35%. Exceeding less than 6% does not allow to justify the costs of implementing the described method, and than 35%. impractical due to increased shedding of the form. Example. The control composition was prepared in a known manner by successively mixing dry ingredients (90 o6. Of quartz sand and tO OBT of bentonite) in runners with water to obtain a mixture with a total moisture content of 3%. Three other compositions were prepared by the method of the invention. For this, 90 vol.% Of quartz sand and 10 lb.% of bentonite were mixed in runners, after which the dry mix was removed from the runners and the same amount of water was added to ensure the total; mixtures of 3% Chvklyucha, and 15 50% vol. removed. However, due to the total volume of dry ingredients in the runners, the moisture content of this pre-mix was 3.53-6.00% .i This wet pre-mix was mixed in the runners for 5 minutes, after which it was removed from the runners. The pre-wet, s-mixture was mixed with the remaining dry ingredients (15 50 rbd in a paddle mixer. For the mixtures to be compared, the following properties were determined. The bulk weights were determined by the specific weight of the mixture, with a diameter of 50 mm and a height of 120 mm, with filling it is through screens of 2,, 5 mm cells. Other properties were determined with the help of samples obtained by compacting the control of a given amount of the mixture inside this: “tube case.” The results of the tests are given in the table. As can be seen from the test 4I involved in the table of results, the method according to the invention allows an increase in bulk density by an average of 4.3 times and turnover on average by 1.1, times, and also contributes to a slight increase in strength and gas permeability (amosti. Due to the an increase in bulk density, an improved ability to uniformly compaction of the mixture is observed. Despite a slight increase in crumbling, it remains within acceptable limits. The proposed method should be used to obtain forms of compression under high pressure. The method can also be applied to facilitate the transport of the mixture.

The ratio of the volume of dry ingredients in the preliminary composition to their remaining volume,%

Humidity,%:

pre-mix

85:15

75:25

4.00

3.53

t

added remaining portion of dry ingredients

The average moisture content of the mixture, i,

Bulk weight of the mixture (in non-compacted state),

Fluidity,% Compressive strength in wet condition,

eight

933179 Continuation of the table

0.72 0.68

0.89 7 ", 6 68.9

Claims (1)

The claims of ' _Λ . 1 35 A method of preparing a sand-clay mixture for the manufacture of foundry molds, including mixing dry ingredients with liquid, about t and h and to? ni and D to I in that ₄₀ to increase the bulk weight of the mixture and its ability to uniform compaction at a constant flow rate of the clay binder is first prepared by pre-blend .., dry mixing the ingredients in an amount of about 50-85 Λ of their total volume with liquid ingredient until they are evenly distributed, and then add the remaining ¹ volume of dry ingredients and mix the mixture until the bulk weight is reached, which exceeds the bulk weight of the preliminary mixture by 6-35%.