BG4185U1 - Composition for making low grain-size distribution quartz sand casting molds for prototyping ductile iron parts using 3d machining - Google Patents

Abstract

This utility model relates to compositions for making low grain-size distribution quartz sand casting molds for prototyping ductile iron parts using 3D machining. The first composition includes includes 55% refractory concrete, 35% low grain-size distribution quartz sand from 0.04 to 0.063 mm and 10% quartz sand 0.25 mm with silicazole binder in an amount of 9% of the weight of the dry mix. The other composition contains 55% refractory concrete, 35% low grain-size distribution quartz sand from 0.04 to 0.063 mm and 10% quartz sand of 0.25 mm with a water glass binder in an amount of 8 % of the weight of the dry mix.

Description

(54) COMPOSITION FOR MAKING FOUNDRY MOLDS FROM LOW GRAIN QUARTZ SAND FOR PROTOTYPING DIGITATED IRON PARTS USING 3D PROCESSING

Field of technique

The main objective of the utility model is the production of ductile iron prototypes in a shorter time, at a lower cost and with comparable and better quality compared to classical manufacturing methods and to the latest 3D sand mold printing methods. The method is intended for obtaining cast iron castings with increased strength characteristics for the production of parts operating under conditions of high loads, in machine building, the automotive industry, railway transport, etc., for the production of body parts, gears, crankshafts, pumps and others. The utility model is suitable for obtaining complex and thin-walled castings.

Prior art

Various methods are known for making molds for ductile iron castings:

1. Manual and machine production of casting molds from sand bentonite mixtures. This is the classic casting technology developed since ancient times using two half molds of quartz sand, bentonite binder with added water and solid graphite powder. The most common methods for machining molds are: pressing, snapping, sandblasting compaction, sandblasting compaction, pulse compaction, etc. In compaction by pressing, the making of the casting mold is carried out by a single pressing and shaking of the molding mixture previously poured into the casting box between two pressing plates. On one of them is mounted the sub-model plate (the so-called "model blank") with immovably fixed to it, usually metal or plastic models. Depending on the location of the models in relation to the pressing plate, two main pressing options are realized - upper and lower - differing in the distribution of the degree of compaction of the molding mixture along the height of the casting case.

2. Making molds from quick-hardening mixtures based on water glass and organic resins. The use of synthetic organic resins as binders accounts for the existence of the largest group of molding and core compounds. A large part of the synthetic resins used in foundry production are patent or production secrets, therefore they can only be listed in principle. The most famous of them are: phenol-, urea- and urea-phenol-formaldehyde resins; furan resins obtained from them by modification with furyl alcohol or furfural; polyurethane resins. The mold is made by pouring the mixture on a sub-model plate with models mounted on it and a pouring system. The mold is compacted on a vibrating table.

3. Vacuum forming is one of the modern methods for making casting molds. The most characteristic of this method is that the mold is made of pure sand, without a binder. By means of the heating device, a plastic sheet is heated to obtain maximum plasticity. In a vacuum chamber (the mold box), a plastic sheet adheres tightly to the surface of the model and the submodel plate. Sand is poured into the chamber and compacted by vibrating and pressing 2. The mold remains strong until its vacuum is terminated. Two half-molds are made and after pairing, they are filled with metal.

4. Casting on fusible patterns. In this method, the mold is produced as a refractory coating on a meltable model. The most commonly used modeling materials are wax, paraffin, stearin and rosin. After the model is melted, burned or dissolved, a cavity is formed in the mold, into which, after firing the mold (in the form of a refractory ceramic shell), the liquid metal is poured. In this way, both the shape and the pattern are used only once.

5. Casting by gasifying models. Styrofoam is most often used to make the models in this casting method. Unlike the above methods, here the model is not removed from the mold when it is poured with melt, but remains in it. When the liquid metal enters the mold, under the influence of the high temperature, the model is gasified and the space freed in this way is filled with melt.

All of the above methods require the use of complex, expensive and pre-made tooling - models, core boxes, molds for evaporation and melting models. Some of the mold making methods require expensive and complex equipment.

6. The most modern method of building molds is additive manufacturing. 3D printers are used to produce the mold and cores from quartz sand and binders. 3D printing builds the details, adding layer by layer. The result is dense, hard and strong parts that can be processed and used for casting molds. The method has not entered the foundry industry en masse, due to the high cost of production equipment. The price of 3D printers for sand molds starts from 200,000 euros for those with a working area of 200x200x150 mm and reaches over 1,500,000 euros for the largest machines 2000x1500x1000 mm. The method is suitable for rapid prototyping, but is currently available only to the largest foundries and research and scientific centers.

Technical nature of the utility model

The mold assembly for the rapid prototyping of ductile iron parts using 3D processing of low-grain quartz sand heat-resistant solid molds is aimed at producing ductile iron prototypes in a shorter time, at a lower cost and with commensurate and better quality compared to classic manufacturing methods and to the latest methods of 3D sand printing molds.

With the developed composition, casting mold blanks with special characteristics (hardness, heat resistance and strength) are produced, which are mechanically processed on a CNC milling machine according to a set program until the required mold for pouring is achieved. Depending on the complexity of the part, a 3-axis, 4-axis or 5-axis machine is used. It is not necessary to divide the mold into two parts, as with classic machine molding technologies (vertical or horizontal), but it can be optimized to a greater number of segments according to the geometry of the part, the presence of casting "shadows" and reducing the number of required hearts.

With the new composition for the production of casting molds, the mandatory methods listed from item 1 to item 5 are avoided - constructive and technological development and production of complex casting tooling, which can be used for manual or machine production of casting molds. When compared to item 6, it can be seen that the new mold composition is different from 3D printing materials and the way of use is opposite to additive manufacturing and the desired shape is achieved by removing material from the blank.

The task of the utility model is to create a mold with increased strength characteristics, hardness suitable for mechanical processing and to provide at the same time the necessary gas permeability.

The task is solved by an appropriate selection of materials for production.

Composition of the dry molding mixture for mold blanks:

1. Refractory concrete - 55%

2. Quartz sand with low grain size - 0.04 mm/0.063 mm - 35%

3. Quartz sand PK 0.25 mm - 10%

Two types of components can be used for a binder:

Water glass Na2SiO - 8%, or

Silicasol with chemical formula mSiO2.xH2O - 9%.

The three main components are mixed in a mixer at 60 rpm. The binder (water glass or silicasol) is added in a thin stream and mixing continues for 15 min. The mixture is distributed evenly and placed in a pre-prepared form with a rectangular, square or round section. The mixture is compacted in the mold with a vibrating table. In casting molds where the ratio of liquid metal to mold weight is less than 1:2.25, metal fibers are added to the mixture to strengthen the mold and increase tensile strength.

The main component of the casting mold is corundum concrete with a granulation of 0 mm - 0.25 mm - 55%. Tabular alumina is produced from aluminum hydroxide. The volume stability at high temperatures and good resistance to thermal shocks of tabular Al ₂ O ₃ are due to the large crystals with closed spherical pores remaining included in the recrystallization of submicron α-Al ₂ O ₃ in the rapid sintering process.

Chemical composition and properties of refractory concrete - tabular corundum A1 ₂ O ₃

FIRE RESISTANT CONCRETE

PROPERTIES MEASURE VALUE 1. Maximum temperature of application °C 1800 2. Main component corundum tabular AliOj 3. Grain composition mm 0-0.25 4. Contents of A1;Oz % >95 5. Compressive strength MPa >45 6. Contents of FcjOj >0.03 7. Laying method casting, vibration casting

Two types of components can be used as a binder.

• Water glass - KagBYuz - (8%) • Silicasol - with chemical formula mSKKxI GO - 11%

Water glass is an aqueous solution of sodium silicate (NaCl) with hydrated silicon oxide (S1O2.XH2O). This material is obtained by autoclaving a sodium silicate melt. The composition of quartz sand with soda (sodium sulfate) is used in the melt, carrying out this process in electric furnaces at a high temperature of over 1500°C. After the melt is formed, it cools quickly and breaks into pieces that are greenish-mint in color, which is called a silicate block. Dissolution in water involves hydrolysis of sodium silicate. This forms a colloidal solution of silicic acid as well as alkali hydroxides. One of the important characteristics of water glass is its density and modulus.

Technical characteristics of water glass:

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Indicators Water glass used in foundry Appearance Syrupy consistency without mech. inclusions Density at 20°C g/cm3 1.45 — 1.50

Silica content ΞϊΟι 23.5%-29% FfcCb and ALOj content not more than 0.7% Content of CaO is more than 0.5% 8Oz content no more than 0.2% Contents iiaNaQ ] 1%- 12% Module 2.1 - 2.6

The water glass modulus is determined by the ratio between the number of gram moles of S1O2 and that of NaO:

M = S1O2 % / NaO % x 1.032 (the ratio of molecular masses of sodium and silicon oxide).

Silicasol is a stable colloidal solution of amorphous silica S1O2 usually in an aqueous medium, which is non-toxic, odorless and tasteless. Due to its low viscosity, silicasol can penetrate materials like water and mix very well with other substances. Upon evaporation of the water contained in the silicasol, the colloidal particles bind firmly to the surface of the material as well as to each other, forming Si-O bonds. Due to its high binding strength, high fire resistance and heat resistance, silicasol is used as a binding agent for various refractory materials. In the developed method - silicasol increases the strength of the forms and improves the surface characteristics of the final products.

BG 4185 UI

Technical characteristics of silicasol:

Indicator Value Content of silicon dioxide SiO3, in % 40.0-42.0 HaNa;O content, in % 0.4 pH 9.0 — 10.5 Viscosity (25'С), mPa. s-1 25 Density (2 5 °C), g/cm3 1.28-1.30 Average particle diameter - mm 10-20

At temperatures below 10°C in the working rooms, the forms must be hardened using CO2. Blowing with carbon dioxide CO2 reduces the drying time of the mold. In order for the form to be frozen with carbon dioxide, holes are made with a clearance of 2 mm. These clearances also play a role in ventilation of the mold by removing the resulting gases during subsequent pouring in order to eliminate gas pores and a better appearance of the casting.

At temperatures below 0°C, the forms are tempered in a furnace in the following mode:

- Heating for 2 h at 50°C per hour.

- Hold at 100°C for 1 h.

- From the third hour, the temperature increases by 100°C per hour.

- At 400°C, hold for 1 h.

- After this delay, the furnace is turned off and the forms are allowed to cool together with the furnace.

After this treatment, the forms are ready for storage in a dry place for 6 months.

Advantages of the new composition for making casting molds:

- Shortening of the preparation cycle and the total time to receive a finished product (samples) in a short period of 2-3 days.

- High accuracy and dimensional stability of castings.

- Ability to produce prototypes of complex and thin-walled castings with a wall thickness of 3-5 mm.

- Very good surface quality and low roughness.

- Minimal mechanical processing of the resulting castings.

- Reduction of harmful effects on the environment. After use, the molds are crushed in a ball mill and the waste product can be used as a filler in bentonite molds.

- The ability to work with more than two half molds provides different levels of casting feed in critical areas prone to porosity and prevents casting defects.

- The casting forms of the new composition are made with high precision by a CNC machine, and this applies not only to the models, but also to the elements of the casting system - filters, slag traps, exothermic sleeves and "dead" heads.

Disadvantages:

- Mold cracking due to improper compaction or transportation.

- Difficult removal of the gases that occurred during the filling of the mold due to incorrect clearance.

- If the tempering temperature regime is not observed, there is a risk of retention of residual moisture and gas porosity.

- At higher temperatures than those specified in the regime, a decrease in tensile strength is observed, which may lead to the mold bursting when pouring with liquid metal.

At temperatures below 0°C, it is necessary to temper the forms in a furnace, which is related to the consumption of natural gas or electricity.

Example implementation of the utility model

After receiving a prototyping order and receiving a part drawing, a 3D model of the casting is constructed, accounting for the shrinkage of the cast iron. Machining and casting allowances are placed and casting technology is developed. According to the technological development, the number and type of half-forms, hearts, exothermic sleeves, nippers, filters and dead heads are determined.

A complex detail was developed in which several dividing planes distributed in different directions in space were used. This development demonstrates a modern and innovative approach to the casting of details with complex geometry.

Dry molding mixture for mold blanks is prepared:

1. Refractory concrete - 55%

2. Quartz sand with low grain size - 0.04 mm/0.063 mm - 35%

3. Quartz sand PC 0.25 mm - 10%

Silicasol 9% is used as a binder. The components are mixed in a mixer with a capacity of 250 kg at 60 rpm. The binder (silicasol) is added in a thin stream and mixing is continued for 15 min. The mixture is distributed evenly and placed in previously prepared boxes according to the size of the individual forms. The mixture is compacted in the molds with a vibrating table.

For faster hardening, the blanks are annealed in an electric furnace in the following mode:

- Heating for 2 h at 50°C per hour.

- Hold at 100°C for 1 h.

- From the third hour, the temperature increases by 100°C per hour.

- At 400°C, hold for 1 h.

- After this delay, the furnace is turned off and the molds are allowed to cool with the furnace.

The prepared blanks are processed on a CNC router to achieve the required shape. A router with a maximum revolutions of 24000 per minute is used. Special cutting tools for concrete are used to process the forms. The processing program is created with the software product Siemens NX 12. The processed forms go through quality visual control and checking for dimensional compliance with a 3D scanner.

All the individual elements of the mold are assembled into a single unit using the pre-set centering pins.

The mold is poured with liquid metal and left to cool gradually. After the finished prototype is knocked out of the mold, the casting is separated from the casting system with a hydraulic hammer and undergoes shot blasting.

Application of the utility model

The new composition for making casting molds serves for the rapid prototyping of parts from ductile iron. Outside of this narrowly specialized area, it can find applications in the foundry industry for prototyping, small series production, and spare parts in steel and aluminum. Using 3D processing of low-grain, heat-resistant quartz sand solids 8 achieves order fulfillment in a shorter time, at a lower cost and with commensurate and better quality compared to classical production methods and compared to the most - the new methods for 3D sand printing of shapes.

Claims (2)

Composition for making low grain size quartz sand molds for prototyping of ductile iron parts using 3D machining, characterized in that it includes 55% refractory concrete, 35% low grain size quartz sand from 0.04 to 0.063 mm and 10% quartz sand 0.25 mm with silicazole binder in an amount of 9% by weight of the dry mix Composition for making low grain size quartz sand molds for prototyping of ductile iron parts using 3D machining, characterized in that it includes 55% refractory concrete, 35% low grain size quartz sand from 0.04 to 0.063 mm and 10% quartz sand 0.25 mm with water glass binder in an amount of 8% by weight of the dry mix