CN113102731B

CN113102731B - Use method of pressed borax in copper-steel bimetal casting process

Info

Publication number: CN113102731B
Application number: CN202110430902.9A
Authority: CN
Inventors: 尹延国; 刘凌峰; 吴玉程; 曹刚; 李蓉蓉; 张钰辉; 刘聪
Original assignee: Hefei University of Technology
Current assignee: Hefei University of Technology
Priority date: 2021-04-21
Filing date: 2021-04-21
Publication date: 2022-04-26
Anticipated expiration: 2041-04-21
Also published as: CN113102731A

Abstract

The invention discloses a method for using pressed borax in a copper-steel bimetal casting process. In the method, the borax can play a role in removing oxidation, preventing oxidation, preserving heat and constructing sequential solidification conditions, and the volume of the borax is reduced and the dependence on the size of a steel matrix is reduced by pressing the borax.

Description

Use method of pressed borax in copper-steel bimetal casting process

Technical Field

The invention belongs to the field of bimetal composite forming, and particularly relates to a use method of pressed borax in a copper-steel bimetal casting process.

Background

The copper-steel bimetal has the advantages of excellent tribological property of copper alloy and mechanical and machining properties of steel, so that the copper-steel bimetal has wide application in various mechanical parts, particularly key application in shaft sleeves, bushings, key parts of plunger pumps, large and medium stamping die guide parts and the like. There are many methods for forming copper-steel bimetal, and the methods widely used in production at present mainly include: rolling composite method, powder sintering method, casting composite method, electromagnetic continuous casting method, fusion casting method, etc. The rolling composite method and the powder sintering method generally have the problems that the limitation of low bonding strength is difficult to stably operate under high load, and the casting and electromagnetic continuous casting have complex operation, expensive equipment and the like.

The method for preparing the copper-steel bimetal composite material by adopting the fusion casting method has the advantages of convenience and rapidness in operation, simplicity in device and capability of obtaining the copper-steel bimetal material which has higher bonding strength and can stably run under high load. However, during the casting process, there is a risk that the freshly treated surface is oxidized again, as in the case of stainless steel: in the air dried at room temperature, the oxide film with the thickness of 10 angstroms can be produced on the fresh surface for 1min and is kept stable, thereby influencing the mutual diffusion of copper and steel elements. In the process of putting the bimetal casting sample into the furnace, the high heat is radiated by convection due to the overhigh temperature of the hearth, and the oxidation process is also aggravated in the process of putting the sample into the furnace. Meanwhile, the casting is faced with common casting defects such as shrinkage porosity and shrinkage cavity after the casting is finished.

Disclosure of Invention

Based on the defects of the prior art, the invention provides the use method of the pressed borax in the copper-steel bimetal casting process, and aims to design the use method of the borax so that the borax can play the roles of deoxidation, oxidation resistance, heat preservation and structural sequential solidification conditions.

In order to realize the purpose of the invention, the following technical scheme is adopted:

a method for using pressed borax in a copper-steel bimetal casting process is characterized by comprising the following steps: after carrying out dehydration treatment and particle refinement on borax, mixing the borax with potassium fluoride and sodium carbonate, and then pressing the mixture into borax blocks; the borax blocks are used in the copper-steel bimetal casting process. The method specifically comprises the following steps:

step 1, heat preservation is carried out on borax for 20-40min at the temperature of 350-plus-400 ℃ to remove crystal water, and then grinding or ball milling is carried out until the particle size is 100-plus-200 meshes.

Step 2, uniformly mixing the borax treated in the step 1 with potassium fluoride and sodium carbonate; pressing the obtained mixed powder to obtain a borax block; in the mixed powder, the mass percent of potassium fluoride accounts for 5-10%, the mass percent of sodium carbonate accounts for 5-10%, and the balance is borax; the pressing pressure is 30-200MPa, the dwell time is 1-10min, and the density of the obtained borax block is 40-90%.

Step 3, placing the copper alloy, the borax block and the steel matrix in the order of the copper alloy, the borax block and the steel matrix from top to bottom; putting the placed sample into a heating furnace, and taking nitrogen with the purity of not less than 99.999 percent as a protective gasProtecting gas, namely firstly heating up to the temperature (880 ℃) at which the borax can be melted and decomposed to obtain acid oxides at the speed of 10 ℃/min and preserving heat for 20-30min, then heating up to the casting temperature (1050-; the thickness of the borax layer after melting is more than 1 mm; in the fusion casting process, when the copper alloy is melted, the density difference (borax density 2.75 g/cm)³Less than 8.913g/cm of density of copper alloy³) The borax layer floats the carried oxide to the surface of the copper alloy, and the liquid copper alloy and the steel matrix are subjected to inter-atomic diffusion, so that a bonding layer with certain strength is formed, and the connection of copper and steel bimetal is realized;

and 4, after casting is finished, taking out the sample and cooling the sample from the bottom of the steel matrix by using cooling water, wherein the heat preservation effect of the boron sand layer enables the sequential solidification condition of solidification of the bottom of the liquid copper alloy firstly and solidification of the upper surface finally to be constructed in the cooling process.

The invention has the beneficial effects that:

1. in the method, the borax is pressed into the borax blocks with certain strength, so that the borax powder volume is greatly reduced, the dependence on the depth of the steel matrix groove is reduced, and the material is saved.

2. In the method, the temperature is kept for 10-30min when the borax is molten, acidic oxides can be decomposed after the borax is molten, the surface oxides of the steel matrix can be fully removed, and the condition that the copper and steel atoms are blocked by the oxidation of the steel matrix is avoided.

3. In the method, the borax molten layer floats to the surface of the copper alloy, so that the contact between air and the copper alloy can be isolated, and a certain heat preservation effect is achieved, so that the sequential solidification condition of solidification of the bottom of the liquid copper alloy and solidification of the upper surface at last is formed during cooling solidification, and various casting defects in the solidification process are avoided.

4. The components of the borax block of the invention comprise borax, potassium fluoride and sodium carbonate, wherein the borax has large viscosity and poor fluidity below 800 ℃, the potassium fluoride can improve the film removing capability and reduce the melting point and surface tension of the borax, so that the fluidity of the borax becomes good, and the sodium carbonate can increase the solubility of oxides.

Drawings

FIG. 1 is a schematic diagram of a fusion casting process of a steel matrix, a copper alloy and a borax block;

FIG. 2 is a surface state diagram of a copper layer after wire-cutting of the sample obtained in example 1;

FIG. 3 is an SEM image of the binding face of the sample obtained in example 1;

FIG. 4 is a microscopic view of the binding surface of the sample obtained in example 1, in which (a) and (b) are at different magnifications;

FIG. 5 shows the shear strength at different locations on the bonding surface of the sample obtained in example 1.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. The following disclosure is merely exemplary and illustrative of the inventive concept, and those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Example 1

A use method of pressed borax in a copper-steel bimetal casting process comprises the following steps:

step 1, adding borax into a graphite crucible, installing the graphite crucible on an induction heating furnace, and keeping the temperature at 400 ℃ for 30min to remove crystal water; then ball-milling borax to the particle size of 100-200 meshes.

And 2, uniformly mixing the borax treated in the step 1 with potassium fluoride and sodium carbonate to obtain mixed powder. In the mixed powder, the mass percent of potassium fluoride accounts for 5%, the mass percent of sodium carbonate accounts for 5%, and the balance is borax;

and pressing the obtained mixed powder, wherein the pressing pressure is 50MPa, the pressure maintaining time is 5min, and the mass of pressed borax is 9.14g, so that a borax block with the density of 56% is obtained.

And 3, cleaning the steel substrate (the diameter of the groove of the 45# steel is 46mm, the thickness of a 9.14g molten layer of borax in the groove is 2mm) and the copper sample (ZCuPb10Sn10) by using absolute ethyl alcohol in an ultrasonic vibration cleaning machine for 5 min. As shown in fig. 1, the copper alloy, the borax block and the steel matrix are placed in the order of the copper alloy, the borax block and the steel matrix from top to bottom; putting the placed sample into a heating furnace, taking nitrogen with the purity of 99.999% as protective gas, firstly heating to 880 ℃ at the speed of 10 ℃/min and preserving heat for 30min, then heating to 1050 ℃ at the speed of 5 ℃/min and preserving heat for 30 min.

And 4, after the heat preservation is finished, taking out the sample, rapidly cooling the sample from the bottom of the steel matrix by using cooling water, and removing the upper surface part of the copper layer and borax by wire cutting after solidification is finished.

FIG. 2 shows the state where the position of the copper layer of 3mm remained after wire cutting, and no defects such as shrinkage cavity were observed. Fig. 3 is an SEM image of the copper-steel junction surface, the upper side is steel and the lower side is copper, and it can be seen that the copper-steel bimetal junction surface is in a good state and no shrinkage porosity occurs. FIG. 4 is a microscopic view of the junction surface, the upper side is copper and the lower side is steel, no shrinkage cavity is formed on the junction surface, and lead is distributed uniformly. The shear surface size of FIG. 5 is 2X 15mm, and it can be seen that the shear strength of the bimetal bonding surface is about 200 MPa.

Example 2

and pressing the obtained mixed powder, wherein the pressing pressure is 40MPa, the pressure maintaining time is 5min, and the mass of pressed borax is 6.85g, so that a borax block with the density of 48% is obtained.

And 3, cleaning the steel substrate (the diameter of a 45# steel groove is 46mm, the thickness of a 6.85g borax molten layer in the groove is 1.5mm) and the copper sample (ZCuPb10Sn10) by using absolute ethyl alcohol in an ultrasonic vibration cleaning machine for 5 min. As shown in fig. 1, the copper alloy, the borax block and the steel matrix are placed in the order of the copper alloy, the borax block and the steel matrix from top to bottom; putting the placed sample into a heating furnace, taking nitrogen with the purity of 99.999% as protective gas, firstly heating to 880 ℃ at the speed of 10 ℃/min and preserving heat for 20min, then heating to 1100 ℃ at the speed of 5 ℃/min and preserving heat for 30 min.

And 4, after the heat preservation is finished, taking out the sample, rapidly cooling the bottom of the steel matrix by using cooling water, and removing the upper surface part of the copper layer and borax by wire cutting after the solidification is finished.

The characteristics show that the bimetallic joint surface of the sample obtained in the embodiment has good state and high shear strength, and no shrinkage porosity occurs.

The present invention is not limited to the above exemplary embodiments, and any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A use method of pressed borax in a copper-steel bimetal casting process is characterized by comprising the following steps: after carrying out dehydration treatment and particle refinement on borax, mixing the borax with potassium fluoride and sodium carbonate, and then pressing the mixture into borax blocks; the borax blocks are used in the copper-steel bimetal casting process; the method specifically comprises the following steps:

step 1, heat preservation is carried out on borax for 20-40min at the temperature of 350-plus-one 400 ℃ to remove crystal water, and then grinding or ball milling is carried out until the particle size is 100-plus-one 200 meshes;

step 2, uniformly mixing the borax treated in the step 1 with potassium fluoride and sodium carbonate; pressing the obtained mixed powder to obtain a borax block;

step 3, placing the copper alloy, the borax block and the steel matrix in the order of the copper alloy, the borax block and the steel matrix from top to bottom; putting the placed sample into a heating furnace, taking nitrogen as protective gas, firstly heating to the temperature at which borax can melt and decompose acid oxides, and preserving heat for 20-30min, then heating to the melting and casting temperature, and preserving heat for 20-40 min; in the casting process, after the copper alloy is melted, the oxide carried by the boron sand layer floats to the surface of the copper alloy due to the density difference, and the liquid copper alloy and a steel matrix are subjected to interatomic mutual diffusion, so that the connection of copper and steel bimetal is realized;

and 4, after the casting is finished, taking out the sample and cooling the sample from the bottom of the steel matrix by using cooling water.

2. Use according to claim 1, characterized in that: in the mixed powder in the step 2, the mass percent of potassium fluoride accounts for 5-10%, the mass percent of sodium carbonate accounts for 5-10%, and the balance is borax.

3. Use according to claim 1, characterized in that: in the step 2, the pressing pressure is 30-200MPa, the pressure maintaining time is 1-10min, and the density of the obtained borax block is 40-90%.

4. Use according to claim 1, characterized in that: in step 3, the temperature at which the borax can melt and decompose the acidic oxide is 880 ℃.

5. Use according to claim 1, characterized in that: in step 3, the thickness of the borax layer after melting is more than 1 mm.

6. Use according to claim 1, characterized in that: in step 3, the fusion casting temperature is 1050-.