RU2818101C1 - Composition for making gasified casting patterns - Google Patents

Abstract

FIELD: foundry.

SUBSTANCE: composition for making gasified cast patterns contains polypropylene, polymethyl methacrylate and a foaming agent. Polypropylene and polymethyl methacrylate are taken in ratio of 75:25 wt.%, respectively. Foaming agent is taken in amount of 0.5–5.0 wt.% over 100 wt.%.

EFFECT: ensures the production of cast iron castings of high quality in structure, mechanical properties, surface defects and gas porosity without deteriorating working conditions.

1 cl, 1 tbl

Description

The invention relates to foundry production, namely to the production of machine parts blanks from cast iron by casting using gasified models.

A distinctive feature of the technological process of casting using gasified models is the direct contact of the metal melt with a disposable casting model, in which the material of the model is “gasified” under the influence of the thermal energy of the metal poured into the mold.

It is known to use expanded polystyrene foam as a material for gasifying models [1].

Its main disadvantages include intense gas release upon contact with a metal melt, as well as a high probability of surface defects appearing on castings due to the deposition of a large amount of coke residue on the mold walls, resulting from gasification of the model. In addition, studies of the interaction of a metal melt with polystyrene foam [2-4] have proven the selective nature of thermal destruction and gasification of the model material and the thermal stability (up to 2000 ° C) of the benzene ring of polystyrene, on the basis of which an undesirable inherited structure of pearlite “granules” - glomeroblasts - is formed in cast iron castings , ultimately worsening the performance characteristics of products.

There is a known composition for the manufacture of gasified models, including polystyrene foam and special additives, which differs in that in order to regulate the degree of surface carburization of castings, the composition contains carburization inhibitors as special additives in an amount of 0.5 - 30 wt. hours per 100 weight. including polystyrene foam [5]. In this case, iron oxide, calcium carbonate, potassium carbonate or antimony pentoxide are used as inhibitors.

The disadvantages of the composition are the presence of defects of gas origin in the castings, as well as contamination of the casting body with solid products of thermal destruction of carburization inhibitors, namely, oxides of iron, calcium, potassium and antimony.

A model composition for casting using gasified models is known, including polystyrene, a blowing agent - volatile hydrocarbons, peroxide compounds, characterized in that in order to increase the rate of melting and gasification of the model material when filling molds with liquid metal, mercaptans - hydrogen sulfide derivatives containing hydrocarbon radicals, are introduced into it. associated with the sulfhydryl group, at a certain ratio of components [6].

The main disadvantage of the model composition is the low environmental friendliness of its use due to the fact that mercaptans are characterized by the second hazard class. In addition, mercaptans have a very strong odor even at low concentrations. All this ultimately significantly worsens the working conditions of production personnel.

Dow Chemical (USA) proposed using a copolymer of styrene and acrylonitrile as a material for gasified models [7].

This material is characterized by the amount of coke residue formed as a result of gasification of the model, which is more than 1.5 times greater compared to expanded polystyrene.

In Japan, a material has been developed for disposable foundry gasified models, which is a copolymer of cyclopentane oxide, cyclohexane oxide and cyclopentane oxide or isobutylene oxide [7].

Its main disadvantages are the complexity of production and, as a consequence, high cost and scarcity.

There is a known composition for the production of gasified models based on polymethyl methacrylate [7].

However, it is not free from shortcomings. Models made from this composition are characterized by low mechanical strength and are easily deformed under load, so the density of the models is forced to increase 2-3 times, which leads to an increase in the volume of gas release when pouring the mold with a metal melt, as well as increased deposition of soot free carbon on the walls of the mold and, as consequence, surface defects of the casting.

It is known to use a composition consisting of a copolymer of polystyrene and polymethyl methacrylate in various ratios for the manufacture of foundry disposable gasified models [7].

Its disadvantages include the difficulty of choosing the composition of the optimal composition, as well as the need to use special equipment for making models.

The closest thing to the invention is the use of polypropylene foam as a foundry material for disposable gasified models [7].

The disadvantages of the prototype include the high chemical inertness and heat resistance of the material, which significantly complicates the assembly of casting models by gluing individual parts and fragments, as well as heating their contact surfaces until softening and subsequent compression. In addition, the material is destroyed when exposed to ultraviolet rays and is characterized by low resistance to mechanical shock at low temperatures, which does not contribute to its long-term storage and increases the risk of breakage of casting models during transportation and molding. All this ultimately negatively affects its manufacturability.

These shortcomings are eliminated by the proposed solution.

The objective of the proposed solution is to ensure the quality of iron castings produced by casting using gasified models.

The technical result is a composition composition for the manufacture of gasified models, which does not contain scarce and expensive components, is characterized by high manufacturability, allows one to obtain models in a short time with minimal labor intensity and ensures the production of high-quality castings in terms of structure, mechanical properties of cast iron, surface defects and gas porosity without deterioration working conditions of production personnel.

The technical result is achieved by the fact that in the composition for the manufacture of foundry gasified models, which contains polypropylene, polymethyl methacrylate and a foaming agent, polypropylene and polymethyl methacrylate are taken in a ratio of 75:25%, wt. respectively, and the foaming agent - in an amount of 0.5–5.0% in excess of 100%, wt.

Polypropylene (PP) is a linear hydrocarbon thermoplastic polymer of propylene (propene), belongs to the family of polyolefins, is characterized by low mass density (900-910 kg/ ^m3 ) with high tensile strength (40-60 MPa) and bending strength (80- 100 MPa), insoluble in water, alcohols, hydrocarbons, resistant to solutions of alkalis, acids, salts. Begins to soften at a temperature of at least 140 °C. The melting point reaches 175 °C. Burns out at temperatures of 325–390 °C. This material lends itself well to casting, including rotational casting, as well as injection molding on injection molding machines with foaming, welding, cutting, and drilling. To produce products from this polymer, specialized or non-standard equipment is not required. Non-toxic and chemically inert, has low frost resistance (up to -5 ° C). Under the influence of UV radiation it is destroyed.

Polymethyl methacrylate (PMMA, acrylic, plex, plexiglass, plexiglass, acrylic glass) is a linear thermoplastic polymer of methyl methacrylate, an ester of methacrylic acid and methanol, with high transparency and weather resistance. It has a mass density of 1100-1150 kg/ ^m3 , tensile strength is about 30-40 MPa, and bending strength is 100-120 MPa. It is highly soluble in carboxylic acids, esters, including its own monomer, ketones, aromatic hydrocarbons, resistant to acids, alkalis, light and oxygen, oil- and water-resistant. When heated to about 105-110 °C, polymethyl methacrylate softens, melts at 160 °C, and burns out at 405-410 °C. It is characterized by a combination of high hardness with impact resistance and flexibility. Due to its thermoplasticity and relatively low softening point (less than 110 °C), it can be easily machined, extruded, injection molded, welded and thermoformed. It has high frost resistance (up to –60 °C). Has high resistance to UV radiation.

Both polymers (PP and PMMA) are produced by industry in Russia and friendly countries in sufficient quantities and are characterized by low cost. As part of the composition, PP and PMMA functionally complement each other, ensuring the manufacturability of the material for the gasified foundry model and eliminating the shortcomings of the prototype. When in contact with molten cast iron, PP and PMMA are completely or partially gasified in a short period of time, depending on the degree of oxygen access to the contact zone.

The most probable chemical reactions of thermal destruction:

1) polypropylene (PP):

under conditions of access (excess) oxygen

(C ₃ H ₆ ) _n + 4.5n O ₂ = 3n CO ₂ ↑ + 3n H ₂ O↑,

in conditions of lack of oxygen (anaerobic heating)

(C ₃ H ₆ ) _n + 3n O ₂ = 3n CO↑ + 3n H ₂ O↑,

(C ₃ H ₆ ) _n + 1.5n O ₂ = 3n C + 3n H ₂ O↑;

2) polymethyl methacrylate (PMMA):

under conditions of access (excess) oxygen

(C ₅ H ₈ O ₂ ) _n + 6n O ₂ = 5n CO ₂ ↑ + 4n H ₂ O↑,

in conditions of lack of oxygen (anaerobic heating)

(C ₅ H ₈ O ₂ ) _n + 4.5n O ₂ = 5nCO↑ + 4n H ₂ O↑,

(C ₅ H ₈ O ₂ ) _n + 2n O ₂ = 5nC + 4n H ₂ O↑.

The linear nature of the structure of the PP and PMMA polymers and the absence of a benzene ring in it, found, for example, in polystyrene, traditionally and widely used as a material for foundry gasified models, prevents the formation of glomeroblasts in cast iron castings.

The foaming agent in the composition through liquid-phase foaming ensures the production of casting models with a porous structure from it, thereby making it possible to controllably reduce the mass density of the model material and the mass of the gasified casting model, as a consequence, reducing gas emission when filling the mold with a metal melt and minimizing the risks of the formation of surface defects in castings. the reason for the deposition of sooty coke residue on the walls of the mold. In this case, the mass density of the model material is adjusted by dosing the foaming agent in the composition.

In order to test the effectiveness of the proposed solution, a complex of experimental work was carried out under existing production conditions.

In the work, for the manufacture of casting models, we used low-pressure polypropylene grade 21020-02, grade 1, GOST 26996-86 in granules 2.0-5.0 mm in size and polymethyl methacrylate grade “Dacryl-8” TU 2216-243-05757593-2000 in granules measuring 3.0-5.0 mm. A concentrate of foaming polyethylene grade 107-OVAS TU 6-05-2001-85 in granules measuring 2.0-5.0 mm was used as a foaming agent.

Models for casting “Case” with a wall thickness from 5.0 to 20.0 mm were chosen as test ones. The models were manufactured on a horizontal injection molding machine BJ90-V6/S6 from PowerJet Plastic Machinery (China) using high-precision injection molding technology with foaming, which is used to reduce the weight of products and can significantly improve the shape of the part and dimensional stability when stress is removed during injection at while reducing the compression force. All components of the composition in the required quantity were placed through a loading funnel into an extruder, where they were mixed with a screw mixer and heated to a temperature of 190-200 °C, at which a flowing polymer melt was formed within a short time and foaming took place simultaneously with the melt moving to the nozzle of the machine for injection into the mold. After holding in the mold to complete foaming and final hardening, the finished model was removed and the cycle was repeated. At the same time, the duration of the production cycle did not exceed 1.5-2.0 minutes.

At the first stage, the optimal amount of foaming agent was determined in a composition including PP and PMMA in a ratio of 50:50%, wt. It was experimentally established that when the foaming agent content in the composition was less than 0.5% over 100%, wt., the number of pores in the casting models was very small, which did not allow them to significantly reduce their weight, and the excess of the foaming agent content in the composition was above level 5 .0% over 100%, wt. led to a deterioration in the quality of the surface of the models due to the appearance of open pores, protrusions and depressions (“waviness”) on it and, as a result, created problems for uniform coloring of the models before molding.

At the second stage, the ratio of the content of PP and PMMA in the composition was varied at a fixed optimal foaming agent content of 0.5-5.0% in excess of 100%, wt. We produced several experimental batches of 10 pieces. casting models, each from a composition with a different ratio of PP and PMMA, as well as a control batch (10 pieces of casting models) from a composition including only PP (100%, wt.), according to the prototype.

Foundry models of experimental and control batches were used to produce “Corpus” castings from cast iron grade SCh20 GOST 1412-85 weighing 3.5 kg into vacuum-sealed sand molds using the casting method using gasified models. Cast iron was smelted in a GW 0.45-500-1 induction crucible furnace. Models of the gating system were assembled manually using ERGOMELT-275 hot-melt adhesive rods based on ethylene vinyl acetate produced by ERGOTEK LLC (Perm) and a glue gun. At the same time, it took more time to assemble the model blocks of the control batch compared to the model blocks of the experimental batches due to insufficient initial adhesion of the glue to the contact surfaces. After assembly, a water-based non-stick coating of grade PPU-1 TU 4191-001-151102120-2012 was applied to the model blocks with a brush in two layers. Each layer was dried in a dead-end dryer in a stream of hot air at a temperature of 55-60 °C for 3 hours. After this, molding was carried out. To make the molds, calcined quartz sand of grade 1K ₂ O ₂ 02 GOST 2138-91 was used. The molds of the experimental and control batches were filled with metal from the same heat. The temperature of pouring the cast iron melt into the mold was 1375-1450 °C.

The structure, mechanical properties (tensile strength, hardness) of cast iron were monitored, as well as gas release when pouring molds and the quality of castings in terms of geometry, the presence of surface defects and gas porosity. The structure and mechanical properties were determined on samples poured together with castings from experimental and control batches (one sample per mold). Gas emission during mold filling was assessed using a chemical multicomponent gas detector of the GKhK-PV-1 brand produced by CJSC "Christmas+" (St. Petersburg).

In the cast iron of the control and all experimental batches, the structure of pearlite “granules” - glomeroblasts - was not found. There were no significant differences in the mechanical properties of cast iron, as well as gas emissions when pouring molds between the experimental and control batches. The results of comparing the quality of castings from the control and experimental batches are presented in Table 1.

As can be seen from Table 1, the absence of defects on the castings was recorded in experimental batch No. 3, corresponding to the content of PP and PMMA in the composition, taken in a ratio of 75:25%, wt.

Thus, the tests carried out showed the effectiveness of the proposed technical solution in comparison with the prototype and confirmed the declared technical result.

Table 1

Batch number Ratio of PP and PMMA, wt.% Defects found in castings Castings with defects, % / pieces Castings without defects, % / pieces PP PMMA 1 25 75 warping, sooty blockages on the surface 40 /4 60 / 6 2 50 50 sooty clogs on the surface 20/2 80 / 8 3 75 25 No 0 / 0 100 / 10 4 (prototype) 100 - waviness, gas porosity, cuts in places where fragments of the model and the gating system are glued together 50 / 5 50 / 5

Note: the number of castings in each of the experimental and control batches was 10 pieces.

Information sources

1. Casting using gasified models: fundamentals of theory and technology / Yu.A. Stepanov [and others] - M.: Mashinostroenie, 1976. - 224 p.

2. Gurulev, S.A. Substitution phenomena in melts // DAN USSR. –1978-238. – No. 1. – pp. 203-206.

3. Gurulev, S.A. The process of carburization of iron and steel castings during casting using gasified models / S.A. Gurulev // Foundry production. – 1980. – No. 6. – pp. 21-22.

4. Gurulev, S.A. Traces in cast iron / S.A. Gurulev // Chemistry and life. – 2007. – No. 6. – pp. 18-19.

5. Copyright certificate of the USSR No. 500870, B22 C7/02, 1976.

6. Copyright certificate of the USSR No. 426742, B22 C7/02, 1974.

7. Shulyak, V.S. Casting using gasified models / V.S. Shulyak. – St. Petersburg: Professional, 2007. – 408 p. – prototype.

Claims (1)

Composition for the manufacture of foundry gasified models containing polypropylene, polymethyl methacrylate and a foaming agent, characterized in that polypropylene and polymethyl methacrylate are taken in a ratio of 75:25 wt.%, respectively, and the foaming agent is in an amount of 0.5-5.0 wt.% over 100 wt. .%.