CN114226693B

CN114226693B - Preparation method of flexible gradient porous metal

Info

Publication number: CN114226693B
Application number: CN202111586940.XA
Authority: CN
Inventors: 徐治国
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2021-12-23
Filing date: 2021-12-23
Publication date: 2022-11-01
Anticipated expiration: 2041-12-23
Also published as: CN114226693A

Abstract

A flexible gradient porous metal preparation method, through pouring into casting sand and making the porous metal mould in the polystyrene foam of gradient, inject the molten liquid of the metal with smaller hardness into the porous metal mould, form the original gradient porous metal skeleton; then fixing the casting sand on a vibration table for vibration, so that a gap is formed around the framework in the casting sand; and further pouring molten liquid of metal with higher hardness to obtain the flexible gradient porous metal with different specifications. The flexible gradient through-hole porous metal is prepared by repeatedly using the investment casting method, so that the production cost is greatly reduced, the preparation speed is improved, and the flowing boiling heat exchange performance can be greatly improved.

Description

Preparation method of flexible gradient porous metal

Technical Field

The invention relates to a technology in the field of composite materials, in particular to a preparation method of flexible gradient porous metal.

Background

The gradient through hole porous metal has a dense metal framework, a winding complex communication channel is arranged in the gradient through hole porous metal, the heat exchange specific surface area is large, the relative density is small, the porosity or the pore density of the gradient through hole porous metal has a gradient change trend, the gradient through hole porous metal has a unique physical structure, and the market application prospect in the fields of environmental chemical engineering, energy conservation, emission reduction and the like is very bright. However, when gradient porous metal is used in the tube to enhance the flow boiling heat transfer, the flow resistance is increased, the pumping work is increased, and the energy consumption is increased due to the existence of the metal skeleton perpendicular to the flow field direction. If bionic design is carried out on the gradient porous metal framework by referring to the bamboo section structure, the inner part adopts a metal material with lower hardness, the outer part adopts a metal material with higher hardness, and the flexible gradient porous metal can be prepared. Therefore, during flowing boiling heat exchange, in a high flow velocity area close to the central axis of the pipeline, the skeleton of the flexible gradient porous metal inclines in the flow direction as wind blows over the treetops, and the inclination degree of each part of the flexible gradient porous metal is in direct proportion to the flow velocity of the cross section. The flexible gradient porous metal reduces the flow resistance on one hand, and is more favorable for the escape of bubbles moving along the inclined direction on the other hand, thereby greatly strengthening the flow boiling heat exchange capacity.

Disclosure of Invention

Aiming at the defects that the preparation process is complex, the cost is high and the preparation method cannot be popularized to the preparation of the flexible gradient porous metal with a complex structure in the prior art, the invention provides the preparation method of the flexible gradient porous metal, and the flexible gradient porous metal with the through holes is prepared by repeatedly using an investment casting method, so that the production cost is greatly reduced, the preparation speed is improved, and the flowing boiling heat exchange performance can be greatly improved.

The invention is realized by the following technical scheme:

the invention relates to a flexible gradient porous metal preparation method, which comprises the steps of pouring casting sand into gradient polystyrene foam to prepare a porous metal mold, and injecting molten liquid of metal with lower hardness into the porous metal mold to form an original gradient porous metal framework; then fixing the casting sand on a vibration table for vibration, so that a gap is formed around the framework in the casting sand; and further pouring molten liquid of metal with higher hardness to obtain the flexible gradient porous metal with different specifications.

The gradient polystyrene foam is obtained by pre-foaming and curing polystyrene beads in advance, then performing compression molding, and finally connecting polystyrene foam adhesives with different specifications.

The metal with lower hardness is as follows: aluminum, tin or lead.

The metal with higher hardness is as follows: copper, steel or nickel.

The injection is as follows: and in an argon environment, heating the metal with lower hardness in a muffle furnace until the metal is completely melted, injecting the metal into a porous metal mold, and naturally cooling to form the original gradient porous metal.

The vibration refers to: fixing the original gradient porous metal containing the casting sand on a vibration table to vibrate in small amplitude in the front-back, up-down and left-right directions, and forming gaps around a metal framework in the casting sand.

The small amplitude refers to that: maximum amplitude of vibration less than 2 cm

The frequency and time of the vibration are as follows: the vibration frequency was 10 Hz, and the vibration time was 20 minutes.

The porosity of the voids is preferably 0.88 to 0.98.

The flexible gradient porous metal framework has the metal wire with smaller hardness accounting for 90-95% and the metal wire with smaller hardness accounting for 5-10%.

The number of the through-hole foam layers is 2-4.

The invention relates to the flexible gradient-density through-hole porous metal prepared by the method, the pore density of the porous metal is changed in a gradient manner, namely the porosity is the same, and the pore density is increased along a certain direction; or the pore density is the same, the porosity increases in a certain direction. The porous metal has a skeleton in which a metal having a relatively low hardness is disposed and a skeleton in which a metal having a relatively high hardness is disposed.

The pore density ranges from 5PPI to 130PPI.

The internal metal of the framework is as follows: aluminum, tin or lead, and the metal outside the framework is copper, steel or nickel.

Technical effects

Compared with the disclosed rigid gradient porous metal, the flexible gradient porous metal prepared by the invention has greatly improved flexibility, and can obviously reduce flow resistance, increase heat exchange coefficient and improve critical heat flux density when being used for forced convection heat exchange in a pipe.

Drawings

FIG. 1 is a schematic diagram of the effect of example 1;

FIG. 2 is a schematic diagram of the effect of example 2.

Detailed Description

Example 1

The preparation process of this example is as follows:

firstly, pouring casting sand into gradient polystyrene foam to form a mould.

And secondly, heating the mixture to 250 ℃ in a muffle furnace in an argon environment to melt the tin into liquid, and then injecting the liquid tin into a gradient polystyrene foam mold. Cooling to form the original gradient tin foam.

And thirdly, vibrating the gradient tin foam in a small amplitude from left to right, from front to back, from top to bottom, and forming gaps around a tin wire framework in the casting sand.

And fourthly, heating to 670 ℃ in a muffle furnace in an argon environment to melt the aluminum into liquid, and then quickly injecting the liquid aluminum into gaps around the original gradient tin foam skeleton. Cooling to form the flexible aluminum tin gradient porous metal with the porosity of 0.98 and the pore density gradient of 20PPI-60 PPI. As shown in fig. 1.

Simulation calculation shows that under the same wall surface superheat degree, the flow boiling heat exchange coefficient of the flexible aluminum-tin gradient porous metal with the same shape and appearance parameters is improved by at least 20% compared with that of rigid gradient aluminum porous metal, and the critical heat flux density is improved by 30%.

Example 2

The preparation process of this example is as follows:

firstly, pouring casting sand into gradient polystyrene foam to form a mold.

And secondly, heating the mixture to 350 ℃ in a muffle furnace in an argon environment to melt the lead into liquid, and then injecting the liquid lead into a gradient polystyrene foam mold. Cooling to form the original gradient tin foam.

And thirdly, vibrating the gradient aluminum foam in a small amplitude from left to right, front to back, up to down, and forming gaps around the aluminum wire framework in the casting sand.

And fourthly, heating the copper to 1100 ℃ in a muffle furnace in an argon environment to melt the copper into liquid, and then quickly injecting the liquid copper into gaps around the original gradient lead foam skeleton. Cooling to form the flexible copper-lead gradient porous metal with the porosity of 0.98 and 20PPI-60 PPI. As shown in fig. 2.

Simulation calculation shows that under the same wall surface superheat degree, the flow boiling heat exchange coefficient of the flexible copper-lead gradient porous metal with the same shape and appearance parameters is improved by at least 10% compared with that of rigid gradient copper porous metal, and the critical heat flux density is improved by 20%.

Compared with the prior art, the performance indexes of the flexible gradient porous metal prepared by the preparation method are improved as follows: flow boiling heat transfer coefficient and critical heat flux density.

The foregoing embodiments may be modified in many different ways by those skilled in the art without departing from the spirit and scope of the invention, which is defined by the appended claims and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A flexible gradient porous metal preparation method is characterized in that casting sand is poured into gradient polystyrene foam to prepare a porous metal mold, and molten liquid of metal with lower hardness is poured into the porous metal mold to form an original gradient porous metal framework; then fixing the casting sand on a vibration table for vibration, so that a gap is formed around the framework in the casting sand; then further pouring molten liquid of metal with higher hardness to obtain flexible gradient porous metal with different specifications;

the flexible gradient porous metal refers to: the inner part adopts metal material with lower hardness, and the outer part adopts metal material with higher hardness.

2. The method as claimed in claim 1, wherein the gradient polystyrene foam is prepared by pre-foaming and curing polystyrene beads in advance, then press-molding, and finally connecting polystyrene foam of different specifications.

3. The method for preparing a flexible gradient porous metal as claimed in claim 1, wherein the injecting is performed by: and in an argon environment, heating the metal with lower hardness in a muffle furnace until the metal is completely melted, injecting the metal into a porous metal mold, and naturally cooling to form the original gradient porous metal framework.

4. The method for preparing flexible gradient porous metal according to claim 1, wherein the vibration is: fixing the original gradient porous metal framework containing the casting sand on a vibration table to vibrate in small amplitude in the front-back, up-down and left-right directions, and forming gaps around the metal framework in the casting sand.

5. The method as claimed in claim 4, wherein the small amplitude is: the maximum amplitude of vibration is less than 2 cm; the vibration frequency was 10 Hz, and the vibration time was 20 minutes.

6. A flexible gradient porous metal is characterized by being prepared by the method of any one of claims 1 to 5, wherein the porous metal has gradient pore density, namely the porosity is the same, and the pore density is increased along a certain direction; or the pore density is the same, and the porosity is increased along a certain direction; the inner part of the framework of the porous metal is a metal with lower hardness, and the outer part of the framework is a metal with higher hardness; the pore density of the porous material is in the range of 5PPI to 130PPI.