CN111390115B

CN111390115B - Wear-resistant part shell mold casting method

Info

Publication number: CN111390115B
Application number: CN202010253524.7A
Authority: CN
Inventors: 邢振国; 申海斌; 邢万里; 常连波; 张学志; 武世旭
Original assignee: Handan Huiqiao Composite Material Technology Co ltd
Current assignee: Handan Huiqiao Composite Material Technology Co ltd
Priority date: 2020-04-02
Filing date: 2020-04-02
Publication date: 2021-05-14
Anticipated expiration: 2040-04-02
Also published as: CN111390115A

Abstract

The invention discloses a shell type casting method of a wear-resistant part, which is applied to the field of shell type casting. The method comprises the steps of sand box molding and vibration pouring, wherein the sand box molding comprises the steps of upper and lower box molding, box assembling, covering of an insulating layer and the like; firstly, a shell mould and a sealing box shell with the thickness not more than 3mm are manufactured in a metal mould, the upper metal mould is removed and replaced by a box body, the shell mould is checked, the local unformed part is repaired by using precoated sand, and the sand box is ensured to be vacuumized and airtight. Adding steel shots into the box body, covering an agricultural film, vacuumizing, and demolding from the lower metal mold to finish the molding of the upper box and the lower box; and covering quartz sand or heat-insulating cotton layers on the top surface and the periphery of the sand box after the box is closed. And (3) when pouring, the sand box is in a vacuum state, the vibration is immediately carried out after pouring, and the vibration is stopped before the vacuum is removed. By adopting the method for molding, the usage amount of the precoated sand is greatly reduced, as-cast crystal grains of the wear-resistant part are refined, cracks generated by temperature stress are avoided, and the energy consumption of heat treatment of the wear-resistant part is also greatly reduced.

Description

Wear-resistant part shell mold casting method

Technical Field

The invention is applied to the field of casting, provides a thin-wall shell type casting method, and is particularly suitable for casting production of wear-resistant parts.

Background

The method for obtaining the casting by pouring molten metal is shell mold casting. The precoated sand is formed and crusted in a metal template preheated to about 280-320 ℃, the shell is divided into two layers under normal conditions, the surface layer is a thin shell which can make the surface of a casting smooth, and the second layer is a reinforcing layer which can increase the strength of the shell. And buckling the two half shells, putting the half shells into a sand box, adding steel shots around the half shells for fixing, pouring molten metal, and cooling to form a casting. At present, the shell mould is made into a layer for improving the productivity, and the thickness is generally not less than 5mm for ensuring the molding strength. During mass production, a sand-coated iron mold is adopted, a layer of molding sand is coated on an inner cavity of the preheated metal mold, and the shell mold is combined with the metal mold, so that a white structure can be avoided.

The two shell molding processes are both beneficial to the rapid solidification of molten metal and the reduction of as-cast structure, and have two main defects, namely, the shell is thick, the expensive precoated sand is large in material and high in production cost, and the metal mold or steel shot outside the shell is fast to cool, especially a wear-resistant casting, because of more carbides and high brittleness, the casting needs to be slowly cooled after solidification, especially after phase change is completed, cracks generated by temperature stress and structure stress are prevented, so that the shell needs to be increased in thickness to slow down the cooling speed, but the increase of the shell thickness brings the contradiction that the cooling speed of the molten metal is slow and the using amount of the precoated sand is large.

Disclosure of Invention

The technical problem solved by the invention is as follows: the shell casting method of the wear-resistant part is provided, and under the conditions of reducing the thickness of the shell and increasing the solidification speed of molten metal, the cooling speed of a high-temperature solid casting is slowed down, and cracks are prevented from being generated.

The technical scheme adopted by the invention is as follows: the casting method of the wear-resistant part shell mold comprises the following steps of sand box molding and pouring: 1) and (3) performing upper box molding, sending the precoated sand into a horizontally placed metal mold cavity by high-pressure air, and performing heating and hardening to form an upper shell mold and a box sealing shell, wherein the thicknesses of the upper shell mold and the box sealing shell are not more than 3mm for reducing the using amount of the precoated sand, and the minimum thickness of the metal mold in molding is the best. And then removing the upper metal mold, replacing the upper metal mold with an upper box body, checking the shell mold, repairing the local unformed part of the upper shell mold or the box sealing shell by using precoated sand, and ensuring that the sand box is vacuumized and airtight. And positioning a pouring gate shell mold on an inner pouring gate, adding steel shots into the upper box body, scraping the upper opening of the upper box body after the steel shots are filled, covering an agricultural film, vacuumizing the upper box, demolding from the lower metal mold and removing to finish the molding of the upper box. 2) And (3) molding the lower box, sending the precoated sand into a horizontally placed metal mold cavity by high-pressure air, and heating and hardening to form a lower shell mold and a box sealing shell, wherein the thicknesses of the lower shell mold and the box sealing shell are not more than 3mm for reducing the using amount of the precoated sand, and the minimum thickness of the metal mold in molding is the best. And removing the upper metal mold, replacing the upper metal mold with a lower box body, checking a shell mold, repairing the local unformed part of the lower shell mold or the box sealing shell by using precoated sand, and ensuring that the sand box is vacuumized and airtight. And adding steel shots into the lower box body, scraping the upper opening of the lower box body after the steel shots are filled, covering a lower agricultural film, vacuumizing the lower box, demolding from the lower metal mold and removing to finish the modeling of the lower box. 3) Closing the box, namely overturning the lower box and flatly placing the lower box on a vibration pouring table, and positioning the upper box to buckle the lower box; for hollow castings, core setting operation is required when the box is closed. 4) Covering the heat-insulating layer; and quartz sand or heat-insulating cotton heat-insulating layers are covered on the top surface and the periphery of the sand box. Pouring is finished on the vibration pouring table, the sand box is in a vacuum state during pouring, vibration is carried out immediately after pouring, and vibration is stopped before vacuum removal. The vibration adopts low-amplitude high-frequency vibration, the amplitude is not more than 5mm, and the frequency is 100-200 Hz.

The invention has the beneficial effects that: the thickness of the shell mold is reduced by about half, and the using amount of the precoated sand is reduced by half. The method solves the contradiction between the increase of the solidification speed and the reduction of the cooling speed of the casting, refines the cast crystal grains, and avoids the cracks generated by temperature stress and tissue stress. The method has great influence on the heat treatment of the casting, and greatly reduces the energy consumption of the heat treatment.

Drawings

FIG. 1 is a schematic view showing the construction of a flask according to example 1;

FIG. 2 is a schematic view showing the fabrication of the upper shell of example 1;

FIG. 3 is a schematic illustration of the sand addition to the upper tank in example 1;

FIG. 4 is a schematic view showing the construction of a flask according to embodiment 2;

FIG. 5 is a schematic illustration of the flask filling and sand feeding in example 2;

wherein: 1-quartz sand, 2-upper agricultural mold, 3-steel shot, 4-sprue, 5-upper shell mold, 6-upper box body, 7-lower box body, 8-lower agricultural film, 9-lower shell mold, 10-box sealing shell, 11-vacuum interface, 12-upper metal mold, 13-lower metal mold and 14-sand core.

Detailed Description

Example 1.

The high-chromium grate bars are wear-resistant wearing parts which are commonly used by sintering machines and are resistant to thermal fatigue, and the attached drawing 1 is a schematic structural diagram of a high-chromium grate bar shell mold casting sand box which is formed by combining an upper box and a lower box, wherein one box is two or four. The lower opening of the upper box body 6 is covered by the upper shell type 5 and the box sealing shell 10 at the bottom of the upper box body, the thickness of the upper shell type 5 and the box sealing shell 10 is not more than 3mm, and the minimum thickness of the mould forming is preferably used. The upper box top is covered by upper agricultural film 2 and is gone up the mouth of box 6, and the inside of going up box 6 is filled shot 3, has designed vacuum interface 11 on last box 6, and runner 4 draws the grid section die cavity out the upper box top, is used as the gating system, and the shell mould thickness of gating system is not less than 5mm, guarantees to go up box 6 internal addition shot occasionally sufficient intensity. The top of the lower box is covered by a lower shell 9 and a box sealing shell 10, the upper opening of the lower box 7 is covered by the lower shell 9 and the box sealing shell 10, the thickness of the lower shell 9 and the box sealing shell 10 is not more than 3mm, and the minimum thickness of the die forming is better. The bottom of the lower box is covered by a lower agricultural film 8 at the lower opening of the lower box 7, the lower box 7 is filled with steel shots 3, and the lower box 7 is also provided with a vacuum interface 11. The vacuum ports 11 of the upper box and the lower box are connected with a vacuum pump, and the vacuum state of the upper box and the lower box is kept in the processes of box assembling and pouring of the upper box and the lower box, so that the box collapse is prevented. If the upper box body 6 and the lower box body 7 are made of steel, the quartz sand 1 covers the periphery of the whole sand box and the top surface of the upper box, and if the upper box body 6 and the lower box body 7 are made of wood sand boxes, the quartz sand 1 only covers the top surface of the upper box.

When the high-chromium grate bar molten metal is poured, the high-chromium grate bar molten metal enters the grate bar cavity through the ingate by the pouring gate 4, the shell mold of a pouring system is thick, the heat preservation effect can be achieved, the shell mold of the grate bar cavity is thin, the molten metal can be rapidly solidified, steel shots 3 surrounding the cavity can rapidly absorb heat, the supercooling degree of the molten metal is increased, solidification nucleation is facilitated, crystalline grains are reduced, and thick cast-state dendritic crystals are prevented. After the molten metal in the grid section cavity is solidified, the upper box and the lower box can be evacuated. The periphery of the sand box is surrounded by poor heat-conducting objects, such as quartz sand and wood, so that the cooling speed of the high-temperature solid grate bar is slow. The sand box structure ensures the quick solidification and slow solid cooling of the grate bars, and avoids cracks generated by temperature stress and structural stress while ensuring fine as-cast grains.

The manufacturing of the high-chromium grate upper shell mold 5 is shown in figure 2, a cavity between an upper metal mold 12 and a lower metal mold 13 is the upper shell mold 5 and a box sealing shell 10, coated sand is sent into the cavity by high-pressure air, and after the coated sand is heated to the temperature of 280 ℃ and the temperature of 320 ℃ and hardened, the upper metal mold 12 is removed and replaced by an upper box body 6. And (4) checking the quality of the shell mold, and if a local shell mold is not formed, quickly supplementing precoated sand and hardening by utilizing the preheating of the lower metal mold 13. The upper box is shaped as shown in figure 3, a pouring gate 4 shell type is positioned on an inner pouring gate, and steel shots 3 are added into an upper box body 6. After the steel shot 3 is filled in the upper box body 6, the upper opening of the upper box body 6 is scraped off, and the agricultural film 2 is covered. And connecting a vacuum port 11 of the upper box with a vacuum pump, vacuumizing, demoulding and removing the upper box from a lower metal mold 13, and finishing the operation of the upper box.

When the upper box is filled with steel shots, the shell mold with a thin wall thickness is supported by the lower metal mold 13 in a conformal manner, and cannot be damaged by pressure due to insufficient strength. The upper box is vacuumized to integrate the steel shots without flowing, and the upper shell type 5 and the box sealing shell 10 are smoothly released from the lower metal mold 13 under the action of negative pressure. Generally, the height of the upper box is not higher than 700mm, the downward pressure of the steel shots 3 on the shells is lower than the upward pressure of the atmosphere, and the upper box as a whole cannot collapse under the condition that the agricultural film 2, the upper shell type 5 and the box sealing shell 10 are completely airtight. The height of the upper box of the present embodiment is less than 100mm, and the risk of box collapse is avoided during the demolding and moving processes.

The high-chromium grate lower box is the same as the upper box in shape, and has two main differences, namely, a pouring gate shell type is not needed, the lower box body 7 is used for replacing the upper metal mold 12 and then directly adding the steel shot 3, and the lower agricultural film 8 is covered. Secondly, the box turning operation is needed, the box feeding and steel shot adding before demoulding is consistent with that shown in the attached drawing 3, and the box needs to be turned over by 180 degrees and laid flat after vacuumizing demoulding, as shown in the lower box of the attached drawing 1.

Because the sizes of the upper box body and the lower box body of the high-chromium grate bar are smaller, the consumption of steel shots is less, and the strength of the wood sand box can meet the requirement. The wooden sand box has good heat preservation, after the upper box and the lower box are combined, a layer of quartz sand is spread on the top surface of the upper box, the thickness of the quartz sand layer is not less than 50mm, the quartz sand layer mainly plays a role in heat preservation, and simultaneously the quartz sand layer also plays a role in protecting the upper agricultural film 2 and preventing high-temperature metal liquid from scalding the upper agricultural film 2 in the pouring process, so that the vacuum degree of the upper box is ensured, and the thinner shell mould is ensured not to collapse.

If the precoated sand is not well filled in the metal mold and the shell mold is defected in forming, the precoated sand is used for repairing after the upper metal mold 12 is demoulded and before steel shots are added, and the air leakage is ensured. Therefore, the thickness of the shell mold is reduced as much as possible in terms of reducing the amount of precoated sand and increasing the solidification rate of molten metal. The molding method hardly generates shell type waste products on the premise of reducing the wall thickness of the shell type and greatly reducing the using amount of the precoated sand, so that the cost of the precoated sand material is reduced by 1/2-2/3 compared with the original cost.

After the high-chromium grid-section sand box is combined, the high-chromium grid-section sand box is placed on a vibration pouring table, molten metal is poured quickly, when a pouring gate is full of molten metal, a vibration motor is started, and cast dendrites of the molten metal are vibrated to be broken under high-frequency low-amplitude vibration to form a core, so that grains are further refined. The vibration amplitude is not more than 5mm, and the vibration frequency is 100-200 Hz.

The high-chromium grate bar produced by the method can be directly used in an as-cast state without heat treatment, and the service life of the grate bar is equivalent to that of a heat treatment state. Compared with the production cost of the high-chromium grid section of the clay sand, the modeling cost is increased, but the heat treatment process with high energy consumption is omitted, so that the production cost is reduced, the surface quality is obviously better than that of the clay sand, and the method has obvious competitive advantage.

Example 2.

The bucket tooth is the wear-resisting piece that the quantity was the biggest on the excavator, and fig. 4 is bucket tooth shell mould casting sand box structure sketch map, and the sand box is formed by upper box and lower case mould assembling equally, and there are two points with embodiment 1's difference, and first the bucket tooth is hollow structure, and the design has the bolt hole, so install psammitolite 14 in the bucket tooth shell mould die cavity, and second upper and lower box all adopts the steel material, and quartz sand 1 heat preservation covers the top surface of upper box except, still covers the sand box all around, prevents that the steel sand box from dispelling the heat to all around.

FIG. 5 is a schematic illustration of sand addition to a bucket tooth shell mold casting drag. After the lower shell mold 9 is formed by the upper and lower metal molds, the upper metal mold is removed and replaced by the lower box body 7, the quality of the lower shell mold 9 and the box sealing shell 10 is checked, if a local shell mold is not formed, precoated sand can be quickly supplemented, and preheating and hardening of the lower metal mold 13 are utilized, so long as the sand box is vacuumized and is not airtight. The steel shot 3 is added into the lower box body 7, and the steel shot 3 is strickled off after being filled up and covered with the lower agricultural film 8. When the box is closed before pouring, the vacuum interface 11 is connected with a vacuum pump, vacuum pumping is carried out, the lower box is demolded and removed from the lower metal mold 13, and then the lower box is horizontally placed by rotating 180 degrees, so that the operation of the lower box is completed.

The upper box molding was identical to the upper box operation of example 1, except that the core setting step was added during the box closing operation. And after the lower box is stably placed on the vibration pouring table, the sand core 14 is placed, and then the lower box is closed. And covering quartz sand heat-insulating layers on and around the sand box, and pouring. In the processes of box closing and pouring, the upper box and the lower box are kept vacuumized, and the vacuum can be removed after the molten metal is solidified.

And (3) quickly pouring molten metal after the bucket tooth shell mold is closed, starting a vibration motor when the pouring gate is full of molten metal, and vibrating off cast-state dendrites of the molten metal under high-frequency low-amplitude vibration to form a core so as to play a role in refining cast-state grains. When the vibration is carried out, the amplitude is not more than 5mm, and the frequency is 100-200 Hz.

The excavator bucket tooth produced by the molding and vibration pouring method has the advantages of refined grains, good toughness and long service life of products under the same hardness condition. The bucket teeth of the excavator are mostly made of medium-low carbon alloy steel, three heat treatment processes of annealing, quenching and tempering are needed after casting, and the bucket teeth produced by the method can be cleaned and then subjected to high-frequency quenching, so that the energy consumption of heat treatment is greatly reduced.

The two embodiments adopt quartz sand for heat preservation, and can also adopt other heat preservation measures such as heat preservation cotton, and although the heat preservation effect of the heat preservation cotton is good, the material cost is higher.

Claims

1. A wear-resistant part shell mold casting method comprises sand box molding and pouring, and is characterized in that: the molding of the sand box comprises the following steps:

1) and (3) upper box modeling: sending the precoated sand into a horizontally placed metal mold cavity by high-pressure air, heating and hardening to form an upper shell mold (5) and a box sealing shell, removing an upper metal mold (12), replacing the upper metal mold with an upper box body (6), positioning a pouring gate (4) shell mold on an inner pouring gate, adding steel shots (3) into the upper box body (6), scraping the upper opening of the upper box body (6) after the steel shots (3) are filled, covering an agricultural film (2), vacuumizing the upper box, demolding and removing from a lower metal mold (13), and finishing upper box molding; the thickness of the upper shell type (5) and the box sealing shell is not more than 3 mm;

2) molding the lower box: sending the precoated sand into a horizontally placed metal mold cavity by high-pressure air, heating and hardening to form a lower shell mold (9) and a box sealing shell, removing an upper metal mold (12), replacing the upper metal mold with a lower box body (7), adding steel shots (3) into the lower box body (7), scraping the upper opening of the lower box body (7) after the steel shots (3) are filled, covering a lower agricultural film (8), vacuumizing the lower box, demolding and removing from a lower metal mold (13), and finishing the modeling of the lower box; the thickness of the lower shell type (9) and the box sealing shell is not more than 3 mm;

3) assembling the box: the lower box is overturned and horizontally placed on the vibration pouring table, and the upper box is positioned and buckled with the lower box;

4) covering with a heat insulation layer: covering quartz sand or heat-insulating cotton heat-insulating layers on the top surface and the periphery of the sand box;

and the pouring is finished on the vibration pouring table, the sand box is in a vacuum state during pouring, the sand box vibrates immediately after pouring, and the vibration stops before the vacuum is removed.

2. The method of casting a shell of a wear part of claim 1, wherein: and in the step of mould assembling, finishing the core setting operation.

3. The method of casting a shell of a wear part of claim 1, wherein: and in the upper box molding and lower box molding steps, before the steel shot (3) is added, the local unformed parts of the upper shell mold (5), the lower shell mold (9) or the box sealing shell are repaired by coated sand, so that the sand box is ensured to be vacuumized and airtight.

4. The method of casting a shell of a wear part of claim 1, wherein: the amplitude of the vibration is not more than 5mm, and the frequency is 100-200 Hz.