CN111375725A - Core making process capable of reducing hindered shrinkage - Google Patents
Core making process capable of reducing hindered shrinkage Download PDFInfo
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- CN111375725A CN111375725A CN202010481942.1A CN202010481942A CN111375725A CN 111375725 A CN111375725 A CN 111375725A CN 202010481942 A CN202010481942 A CN 202010481942A CN 111375725 A CN111375725 A CN 111375725A
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- sand
- core
- thermal expansion
- negative thermal
- casting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C1/00—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds
- B22C1/02—Compositions of refractory mould or core materials; Grain structures thereof; Chemical or physical features in the formation or manufacture of moulds characterised by additives for special purposes, e.g. indicators, breakdown additives
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22C—FOUNDRY MOULDING
- B22C9/00—Moulds or cores; Moulding processes
- B22C9/10—Cores; Manufacture or installation of cores
Abstract
The invention relates to the technical field of casting, in particular to a core making process for reducing hindered shrinkage.
Description
Technical Field
The invention belongs to the technical field of casting, and particularly relates to a core making process for reducing hindered shrinkage.
Background
The shrinkage of the cast alloy generally comprises liquid shrinkage, solidification shrinkage and solid shrinkage, wherein the main factors which have great influence on the forming quality of the cast part are the solidification shrinkage and the solid shrinkage. In the common sand casting, a casting mold and a sand core are required to have certain deformability, the shrinkage resistance of casting alloy is reduced, a casting is biased to freely shrink, if the casting is hindered from shrinking, casting stress is easily generated, the casting is deformed, cracked and the like, the precision and the strength of the casting are reduced, and the casting is scrapped and cannot be used due to serious deformation and cracking.
In order to solve the above technical problems, in the prior art, flammable and volatile substances such as wood chips, carbon powder and the like are generally added into casting sand, or a foam plate is buried in a casting mold, and the substances are combusted and volatilized through high temperature during casting to form a cavity so as to improve the deformability of the casting mold and a sand core, but nowadays, the method obviously has the following defects: (1) wood dust, carbon powder, foam and the like can generate a large amount of gas during combustion or volatilization, the pouring environment is poor, and the defects of air holes, insufficient pouring and the like of a casting are easily caused; (2) is not easy to be fully combusted, and can generate gases such as carbon monoxide and the like harmful to human bodies and the environment; (3) the wood chips, the carbon powder, the foam and the like are all disposable, so that the cost is increased; (4) the combustion and volatilization of the substances can generate a large amount of gas, and if the gas cannot be discharged in time, the gas can obstruct the filling of molten metal, and the defects of insufficient pouring, cold shut and the like are generated.
Disclosure of Invention
The present invention is directed to solving the problems and deficiencies of the prior art described above and to providing a core making process that reduces hindered shrinkage by adding negative thermal expansion particles without using disposable materials such as wood chips, foam, and the like.
The technical scheme of the invention is as follows: a core making process for reducing hindered shrinkage is characterized in that negative thermal expansion particles are added into casting sand, the negative thermal expansion particles are made of negative thermal expansion materials, the initial temperature of the negative thermal expansion characteristics of the negative thermal expansion materials is lower than the solidification temperature of casting alloys, and the decomposition temperature of the negative thermal expansion characteristics is higher than the pouring temperature. The sand core comprises a surface sand layer, a yielding layer and a back sand layer, and the core making process comprises the following steps:
(1) mixing the mixture by a sand mixer according to the volume ratio of 1: 1, uniformly mixing the common casting sand and the negative thermal expansion particles for later use;
(2) uniformly covering common casting new sand on a core box to form a surface sand layer with a certain thickness;
(3) filling the mixed sand containing the negative thermal expansion particles obtained in the step (1) to form a yielding layer with a certain thickness;
(4) and finally, filling a core box with the recycled and regenerated used casting sand serving as the back sand to form a back sand layer, and taking out the sand core after the sand core is hardened.
The core making process for reducing the hindered shrinkage is characterized in that the casting sand is water glass sand or furan resin sand.
According to the core making process for reducing the hindered shrinkage, the negative thermal expansion material is monoclinic zirconium dioxide.
According to the core making process for reducing the hindered shrinkage, the negative thermal expansion material is zirconium tungstate.
According to the core making process for reducing the hindered shrinkage, the thickness of the surface sand layer is 30-50 mm.
The invention has the beneficial effects that: (1) by utilizing the self thermal shrinkage and cold expansion characteristics of the negative thermal expansion material, the negative thermal expansion particles are subjected to volume shrinkage at the high temperature of the molten metal, a space is reserved, the deformability is improved, no gas is generated, and the negative thermal expansion material is very friendly to workers and the environment; (2) the negative thermal expansion particles shrink at high temperature, the temperature of the casting is reduced after the casting is solidified, and the negative thermal expansion particles gradually recover to the original size, so that the negative thermal expansion particles can be recycled for multiple times, and the cost is saved; (3) the sand core is divided into three layers totally, the surface sand is new sand, the surface quality of the casting is guaranteed, the yielding layer guarantees the shrinkage of the casting and can save the used sand, the back sand utilizes the old sand, the using amount of the new sand can be greatly reduced, and the sand core is very environment-friendly.
Drawings
Fig. 1 is a schematic illustration of the sand core assembly of the invention.
Fig. 2 is a sectional view of the sand core of example three.
In the above drawings, the names corresponding to the symbols are as follows:
1-surface sand layer, 2-yielding layer, 3-negative thermal expansion particles, 4-back sand layer, 5-cavity and 6-casting mold.
Detailed Description
The present invention will be further described with reference to the accompanying drawings and examples, in which it is apparent that the described embodiments are some, but not all embodiments of the invention, and that all other embodiments obtained by a person of ordinary skill in the art on the basis of the embodiments of the present invention without inventive faculty are within the scope of the present invention, and that the features of the following embodiments may be combined with each other without conflict.
As shown in fig. 1, the core making process for reducing hindered shrinkage of the present invention comprises the steps of firstly weighing a material with a volume ratio of 1: 1, pouring the common casting sand and the negative thermal expansion particles 3 into a sand mixer to be uniformly mixed for later use; then, uniformly covering common casting new sand on the core box to form a surface sand layer 1 with the thickness of 30-50 mm; filling the uniformly mixed sand containing the negative thermal expansion particles 3 to cover the surface sand layer 1 to form a yielding layer 2 with a certain thickness; and finally, filling a core box with the recycled and regenerated used sand serving as the back sand to form a back sand layer, and taking out the sand core after the sand core is hardened. And (4) after the sand core is taken out, assembling the sand core into the casting mold 6, wherein the sand core and the casting mold 6 together form a cavity 5, and then waiting for pouring.
The first embodiment is as follows: when a steel casting made of ZG20Mn is produced, monoclinic zirconium dioxide particles with a certain volume are weighed, sodium silicate sand with the same volume is weighed, and the monoclinic zirconium dioxide particles and the sodium silicate sand are poured into a sand mixer to be uniformly mixed; when in modeling, new sodium silicate sand is filled firstly, so that the sodium silicate sand is uniformly covered on a core box, and the thickness of a surface sand layer is 30-50 mm according to the size of a casting; then filling the uniformly mixed sodium silicate sand containing the monoclinic zirconium dioxide particles, wherein the thickness of the filling yielding layer is determined according to the size of the casting; filling the rest of the core box with recycled and regenerated sodium silicate sand, after the sodium silicate sand is hardened, disassembling the core box, taking out the sand core, assembling the sand core into a casting mold and pouring. The above-mentioned sodium silicate-bonded sand can be replaced by furan resin sand.
The zirconium dioxide is in a monoclinic crystal form below 1200 ℃, when the temperature exceeds 1200 ℃, the crystal form of the zirconium dioxide is transformed from the monoclinic crystal form to a tetragonal crystal form, and then the volume is shrunk by about 7-9 percent; when the temperature is reduced to about 1000 ℃, the crystal form of the zirconium dioxide is changed from a tetragonal crystal form to a monoclinic crystal form, and the volume is slowly recovered. When the steel casting of ZG20Mn is produced, because the temperature line of beginning solidification of ZG20Mn is about 1510 ℃, the pouring temperature is at least 1540 ℃, which is higher than the crystal transformation temperature of zirconium dioxide, molten metal enters a cavity during pouring, the temperature of a yielding layer is also rapidly increased, at the moment, the volume of zirconium dioxide particles is reduced, gaps are reserved, the yielding property of a sand core is improved, and the stress is reduced for the contraction of the molten metal; when the temperature of ZG20Mn liquid is reduced to be about 1471 ℃, the liquid steel is almost completely solidified, and the zirconium dioxide particles still keep a tetragonal crystal form and are in a small-volume state; and (3) when the temperature is continuously reduced to about 1000 ℃, the zirconium dioxide particles are changed into monoclinic crystal form, the volume is slowly recovered, finally the zirconium dioxide particles fall into a box for sand removal, and the zirconium dioxide particles are recovered for the next use.
Example two: when an aluminum casting made of ZL114A is produced, a certain volume of zirconium tungstate particles are weighed, then furan resin sand with the same volume is weighed and poured into a stirrer to be uniformly mixed, and the rest steps are the same as those in the first embodiment and are not described.
Zirconium tungstate has negative thermal expansion characteristics in a temperature range of-272.7 ℃ to 777 ℃, the solidification range of ZL114A is about 560-620 ℃, and the pouring temperature is about 700 ℃; the molding is generally completed at room temperature, when zirconium tungstate particles are added into a sand core to form a yielding layer, the temperature of the whole sand core is increased during casting, the volume of the zirconium tungstate particles is shrunk relative to the room temperature, gaps are generated in the sand core, and the hindered shrinkage of molten metal is reduced; as the molten metal is solidified, the temperature of the sand core is reduced, but the volume of the zirconium tungstate particles is still smaller than that at room temperature, so that the filling resistance in the solidification process is ensured to be smaller, and the molten metal is convenient to shrink; and after the casting is solidified for a certain time, the casting falls out of the box and is cleaned, and zirconium tungstate particles are recovered for subsequent use.
Example three: as shown in figure 2, monoclinic zirconium dioxide particles with a certain volume are uniformly mixed with furan resin sand with the same volume, new furan resin sand is uniformly covered on a core box to form a surface sand layer with the thickness of 40 mm, the mixed sand of the zirconium dioxide particles and the furan resin sand is filled to form a 120 mm yielding layer, and finally, the used sand of the reclaimed and regenerated furan resin sand is used as back sand to fill the core box to prepare the sand core with the total radius of 300 mm and the height of 600 mm.
The total volume of the sand core was calculated to be about 16.96 × 107mm3Wherein the volume of the surface sand layer is about 4.22 × 107mm3The volume of the yielding layer is about 9.05 × 107mm3The volume of the back sand layer is about 3.69 × 107mm3Since the volumes of the zirconia grains and the furan resin sands in the concentrative layer were the same, the total volume of the fresh sands was 8.74 × 107mm3About 51.56% of the total volume of the sand core, it can be seen that the amount of new sand can be greatly reduced by the process, the amount is about half of that of the common process, secondly, because the zirconium dioxide is subjected to crystal form transformation at high temperature and generates volume shrinkage of 7% -9%, a yielding layer can be totally vacated by about 0.36 × 10 under the casting state7mm3The size of the sand core is increased, so that the concessional performance of the sand core is improved, and convenience is provided for the contraction of the casting.
Claims (6)
1. A core making process for reducing hindered shrinkage is characterized in that negative thermal expansion particles are added into casting sand, the negative thermal expansion particles are made of negative thermal expansion materials, the initial temperature of the negative thermal expansion characteristics of the negative thermal expansion materials is lower than the solidification temperature of used casting alloys, the decomposition temperature of the negative thermal expansion characteristics is higher than the pouring temperature, a sand core comprises a surface sand layer, a yielding layer and a back sand layer, and the core making process comprises the following steps:
(1) mixing the mixture by a sand mixer according to the volume ratio of 1: 1, uniformly mixing the common casting sand and the negative thermal expansion particles for later use;
(2) uniformly covering common casting new sand on a core box to form a surface sand layer;
(3) filling the mixed sand containing the negative thermal expansion particles obtained in the step (1) to form a yielding layer;
(4) and finally, filling a core box with the recycled and regenerated used casting sand serving as the back sand to form a back sand layer, and taking out the sand core after the sand core is hardened.
2. A core making process with reduced hindered shrinkage as claimed in claim 1 wherein said foundry sand is water glass sand.
3. A core-making process for reducing hindered shrinkage as set forth in claim 1 wherein said foundry sand is furan resin sand.
4. A core making process with reduced hindered shrinkage as claimed in claim 1 wherein said negative thermal expansion material is monoclinic zirconia.
5. A wickmaking process for reducing hindered shrinkage as claimed in claim 1 wherein said negative thermal expansion material is zirconium tungstate.
6. A core-making process for reducing hindered shrinkage according to claim 1 wherein the facing sand layer has a thickness of 30 to 50 mm.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202010481942.1A CN111375725B (en) | 2020-06-01 | 2020-06-01 | Core making process capable of reducing hindered shrinkage |
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| CN202010481942.1A CN111375725B (en) | 2020-06-01 | 2020-06-01 | Core making process capable of reducing hindered shrinkage |
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| CN111375725A true CN111375725A (en) | 2020-07-07 |
| CN111375725B CN111375725B (en) | 2021-01-19 |
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| CN202563117U (en) * | 2012-04-25 | 2012-11-28 | 李群星 | Anti-radiation high-temperature compensation optical fiber |
| CN104550756A (en) * | 2014-12-26 | 2015-04-29 | 中核苏阀横店机械有限公司 | Sand core of pipe mould |
| CN104630685A (en) * | 2015-01-28 | 2015-05-20 | 河北钢铁股份有限公司 | Zero-expansion coefficient metal ceramic composite powder transition layer material |
| CN104907123A (en) * | 2015-05-29 | 2015-09-16 | 芜湖银海机械制造有限公司 | Lining of conical crusher and casting process of lining |
| CN106424577A (en) * | 2016-08-16 | 2017-02-22 | 浙江省机电设计研究院有限公司 | Sand core device and method for preventing hot cracks during steel casting iron mold sand covering casting production |
| CN107052254A (en) * | 2016-11-30 | 2017-08-18 | 安徽应流集团霍山铸造有限公司 | It is a kind of to strengthen a kind of technique device of its core sand deformability and collapsibility |
| CN107059780A (en) * | 2016-12-28 | 2017-08-18 | 上海蓝坤环境科技有限公司 | Disappear for navigable river and fall the multilayer materials and processing method of section ecological revetment |
| CN108213324A (en) * | 2018-02-11 | 2018-06-29 | 常州中车汽车零部件有限公司 | A kind of high-accuracy cast precoated sand and preparation method thereof |
| CN110666107A (en) * | 2019-09-30 | 2020-01-10 | 北京百慕航材高科技有限公司 | Sand core, preparation method thereof and casting mold |
-
2020
- 2020-06-01 CN CN202010481942.1A patent/CN111375725B/en not_active Expired - Fee Related
Patent Citations (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101773984A (en) * | 2010-03-30 | 2010-07-14 | 晋西铁路车辆有限责任公司 | Process design method for sand core print and core print seat for casting |
| CN202563117U (en) * | 2012-04-25 | 2012-11-28 | 李群星 | Anti-radiation high-temperature compensation optical fiber |
| CN104550756A (en) * | 2014-12-26 | 2015-04-29 | 中核苏阀横店机械有限公司 | Sand core of pipe mould |
| CN104630685A (en) * | 2015-01-28 | 2015-05-20 | 河北钢铁股份有限公司 | Zero-expansion coefficient metal ceramic composite powder transition layer material |
| CN104907123A (en) * | 2015-05-29 | 2015-09-16 | 芜湖银海机械制造有限公司 | Lining of conical crusher and casting process of lining |
| CN106424577A (en) * | 2016-08-16 | 2017-02-22 | 浙江省机电设计研究院有限公司 | Sand core device and method for preventing hot cracks during steel casting iron mold sand covering casting production |
| CN107052254A (en) * | 2016-11-30 | 2017-08-18 | 安徽应流集团霍山铸造有限公司 | It is a kind of to strengthen a kind of technique device of its core sand deformability and collapsibility |
| CN107059780A (en) * | 2016-12-28 | 2017-08-18 | 上海蓝坤环境科技有限公司 | Disappear for navigable river and fall the multilayer materials and processing method of section ecological revetment |
| CN108213324A (en) * | 2018-02-11 | 2018-06-29 | 常州中车汽车零部件有限公司 | A kind of high-accuracy cast precoated sand and preparation method thereof |
| CN110666107A (en) * | 2019-09-30 | 2020-01-10 | 北京百慕航材高科技有限公司 | Sand core, preparation method thereof and casting mold |
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