CN115365454A

CN115365454A - Casting method of headstock

Info

Publication number: CN115365454A
Application number: CN202211077818.4A
Authority: CN
Inventors: 王海涛; 王秦阳
Original assignee: Qingdao University of Technology
Current assignee: Qingdao University of Technology
Priority date: 2022-09-05
Filing date: 2022-09-05
Publication date: 2022-11-22

Abstract

The invention discloses a method for casting a headstock, which solves the problems that in the prior art, the inner hole grooves of a casting of the headstock are numerous, shrinkage cavities, shrinkage porosity and other defects are easily generated in the casting process, and the casting efficiency is low, and has the following beneficial effects: a method of headstock casting comprising determining the pouring position: pouring with vertical bottom pouring, wherein the end surface of the sealing ring groove of the headstock is positioned at the bottommost part; selecting a horizontal plane in which the center of a bearing hole of a part is located as a parting plane; designing a sand core: the device comprises a main body core, wherein the main body core is manufactured by adopting a core disassembling and assembling mode, an exhaust passage is arranged in the sand core, a positioning core head is arranged on the sand core, and a core frame is added in the main body core; designing a pouring system: adopting a semi-closed pouring system, wherein the sectional area of an ingate is less than that of a sprue and is less than that of a cross gate, adopting one box for pouring, and designing a model: a sand mold is manufactured by adopting a two-box molding, namely an upper box and a lower box.

Description

Casting method of headstock

Technical Field

The invention relates to the technical field of headstock casting, in particular to a headstock casting method.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

The machine tool headstock is an important part of a machine tool, is mainly used for arranging a machine tool working main shaft, a transmission part and a corresponding additional mechanism thereof, transmits power to the main shaft through transmission gears and transmission shafts at various positions in the headstock, enables the main shaft to obtain set rotating speed and direction, and can be assembled and installed by the headstock.

The existing headstock is mostly manufactured in a casting mode, the casting structure of the headstock is complex, the inner hole grooves are numerous, the complexity of different casting steps is different, and the defects of shrinkage cavities, shrinkage porosity and the like are easily generated in the casting process, so that the existing headstock is low in casting efficiency and poor in casting quality.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for casting a headstock, which solves the technical problems that the structure of a casting of the headstock is complex, the number of internal holes and grooves is large, the casting efficiency of the headstock is low, and the casting quality is poor in the prior art.

In order to achieve the purpose, the invention is realized by the following technical scheme:

a method of headstock casting comprising:

determining a pouring position: pouring with vertical bottom pouring, wherein the end surface of the sealing ring groove of the headstock is positioned at the bottommost part;

determining a parting surface: selecting a horizontal plane in which the center of a bearing hole of a part is positioned as a parting plane;

designing a sand core: the sand core comprises a first sand core as a main body core, wherein the first sand core is manufactured in a decomposition and core assembly mode, an exhaust passage is arranged in the sand core, a positioning core head is arranged on the sand core, and a core bone is added into the main body core;

designing a pouring system: adopting a semi-closed pouring system, wherein the sectional area of an ingate is less than that of a sprue and less than that of a cross gate, adopting a box for pouring one by one, and arranging the cross gate in two sections;

designing a pattern: adopting two-box molding, namely an upper box and a lower box, setting a draft angle in the demolding direction of the pattern, and manufacturing a sand mold;

pouring: fixing the sand core, closing the box, placing a pouring cup and pouring molten metal.

According to the method for casting the headstock, the sand core further comprises a second sand core, a third sand core and a fourth sand core, wherein the second sand core, the third sand core and the fourth sand core are provided with positioning core heads, the second sand core and the third sand core are used for forming square holes of castings, and the fourth sand core is used for forming grooves in the tops of the castings.

In the above method for casting the headstock, when designing the pattern, the pattern draft of 0 ° 30' is set in the pattern stripping direction, the pattern is set according to the casting shrinkage rate of 0.9%, and the sand mold is manufactured according to the shape of the pattern.

In the above described method for casting a headstock, the cross-sectional area of the sprue: cross-sectional area of runner: ingate cross-sectional area = 1.1.

According to the method for casting the headstock, the sprue pit is arranged below the sprue, the runner pit is arranged at the end part of the runner, and the ingate is perpendicular to the runner and parallel to the sprue.

According to the casting method of the head box, the pouring cup is placed at the top of the sprue, and the iron spacer is arranged at the joint of the pouring cup and the sprue.

According to the method for casting the headstock, the top of a casting is provided with the blind riser before pouring, the root of the blind riser is necked down, and the gas outlet rod is pre-buried in the upper box.

According to the method for casting the headstock, the plurality of plate-type chills are arranged at the hot spot part on the inner side of the bearing hole before pouring, and the plate-type chills are uniformly distributed on the circumference.

According to the method for casting the headstock, after the sand mould is manufactured, the second sand core, the third sand core and the fourth sand core are fixed on the upper box, the first sand core is fixed on the lower box, and after the sand cores are fixed, the upper box is closed and fastened.

In the above method for casting a headstock, the sand core is made of furan resin sand.

The beneficial effects of the invention are as follows:

1. the invention adopts a vertical pouring mode, can ensure that the bearing hole surface is positioned at the middle lower part of the whole body, ensures the casting quality, adopts a bottom pouring mode, can completely fill the cavity with molten metal, ensures that the casting is solidified without the phenomena of insufficient cast-in-place and cold shut, has complete casting and clear corners, can directly vertically pour the casting by selecting the horizontal plane where the center of the largest bearing hole of the part is positioned on the parting surface, and is convenient for manufacturing the core head positioning groove at the bearing hole of the sand mold.

2. The pouring basin sets up the spacer, and the spacer begins to separate pouring basin and sprue when the molten metal pouring, and when pouring basin liquid level was poured certain degree of depth, the iron spacer was melted and is worn, plays good dross and hinders the sediment effect, guarantees simultaneously that the sprue is full of the state.

3. The cold iron is matched with the risers for use, so that the sequential solidification condition of the casting can be enhanced, the tail end area formed by the cold iron is utilized, the feeding distance and range of the risers are enlarged, the number or volume of the risers is reduced, the cooling of a hot spot part is accelerated, the whole casting is close to simultaneous solidification, the risers are designed on the basis of post-feeding and graphitized expansion self-feeding of a gating system, and when liquid shrinkage is terminated or volume expansion is started, pressure is built in the casting by utilizing all or part of graphitized expansion, so that self-feeding is realized. A dead head with a dark atmospheric pressure at the top is adopted, so that the heat insulation effect is good, the feeding pressure is constant, no vacuum exists, and a feeding channel is smooth and has no resistance; in order to solidify the molten metal at the hot spot at the same time, direct external chill was used. The cold iron material is selected from graphite cold iron with high refractoriness and large heat conductivity coefficient, so that the defects of shrinkage cavity and shrinkage porosity at the hot spot part of the bearing hole are overcome.

4. The horizontal plane at the center of the bearing hole of the selected part is a parting surface, the vertical molding is adopted, the vertical casting process is immediately performed, the damage to the sand mold caused by carrying and overturning in the molding operation is reduced, the sand core is used for making the core head positioning at the bearing hole of the sand mold, the upper sand box and the lower sand box are buckled and tightly pressed, and the floating dislocation of the sand core in the casting process can be prevented.

5. Using a semi-closed bottom-pouring gating system, sigma A _{Inner part} :∑A _{Horizontal bar} :∑A _{Straight bar} 1.5, the maximum cross-sectional area is at the cross gate, the flow speed of molten metal in the cross gate is reduced, no turbulent flow, no splash and no coil are generatedThe gas and scum slag blocking effect is good, the filling is stable, the scouring of the molten metal to the cavity is greatly reduced, and the quality of the casting is obviously improved.

6. The pouring system adopts a novel ceramic tube forming process, and the designed and formed sprue, cross gate and ingate are buried in sand during the molding process and directly used as the pouring system, so that the molding is convenient, the working efficiency is improved, the molding process is simplified, the mold structure is simplified, and the mold manufacturing cost is reduced.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are included to illustrate an exemplary embodiment of the invention and not to limit the invention.

Fig. 1 is a schematic view of the overall structure of a headstock in the embodiment of the present invention.

Fig. 2 is a schematic axial structure diagram of the headstock in the embodiment of the invention.

Fig. 3 is a schematic view of the pouring position of the headstock in the embodiment of the present invention.

Fig. 4 is a schematic structural view of a parting plane of a headstock in an embodiment of the invention.

FIG. 5 shows example 1 of the present invention ^# Sand mold, 2 ^# Sand mold, 3 ^# Sand mold 4 ^# And (4) a structural schematic diagram of the sand mold.

FIG. 6 shows example 1 of the present invention ^# Schematic diagram of horizontal positioning core heads on the left side and the right side of the sand core.

FIG. 7 shows examples 1-1 of the present invention ^# 、1-2 ^# 、1-3 ^# Sand core combination 1 ^# And (4) a structural schematic diagram of the sand core.

FIG. 8 shows example 2 of the present invention ^# The core head structure of the sand core is shown schematically.

FIG. 9 shows example 3 of the present invention ^# The core head structure of the sand core is shown schematically.

FIG. 10 shows example 4 of the present invention ^# The core head structure of the sand core is shown schematically.

FIG. 11 shows example 1 of the present invention ^# The core skeleton structure of the sand core is shown schematically.

FIG. 12 is a schematic illustration of a sand core venting arrangement in an embodiment of the present invention.

FIG. 13 is a schematic view of a bottom-pouring gating system in an embodiment of the present invention.

FIG. 14 is a schematic view of a tundish iron spacer in an embodiment of the present invention.

FIG. 15 is a schematic view of the structure of the sprue cup and the runner cup according to the embodiment of the present invention.

Fig. 16 is a schematic structural diagram of the installation of the atmospheric blind riser in the embodiment of the invention.

Fig. 17 is a schematic diagram of a chiller arrangement in an embodiment of the present invention.

FIG. 18 is a schematic view of a gas stick arranged on the top of a casting during pouring in the embodiment of the invention.

FIG. 19 is a schematic view of an embodiment of the invention showing an unforeseen core print positioning pattern for a casting.

FIG. 20 is a schematic view of an overall pattern for positioning a core print for a casting design according to an embodiment of the present invention.

FIG. 21 is a schematic view of a pattern of a foundry cope flask in an embodiment of the present invention.

FIG. 22 is a schematic view of a pattern of a drag flask for castings according to an embodiment of the present invention.

Fig. 23 is a schematic diagram of the structure of the upper sand box in the embodiment of the invention.

Fig. 24 is a schematic view of the structure of a lower box sand mold in the embodiment of the invention.

FIG. 25 shows the molding, core setting and mold assembling process flow of the embodiment of the present invention.

In the figure: the spacing or size between each other is exaggerated to show the location of the portions, and the illustration is merely for illustrative purposes.

Wherein: 1.1 ^# Sand core, 2.2 ^# Sand core, 3.3 ^# Sand core, 4.4 ^# Sand core, 5 bearing hole, 6 core head, 7.1-1 ^# Sand core, 8.1-2 ^# Sand core, 9.1-3 ^# The casting mold comprises a sand core, 10 parts of a core rod, 11 parts of an iron spacer, 12 parts of a straight pouring gate pit, 13 parts of a cross pouring gate pit, 14 parts of a blind riser, 15 parts of a chill and 16 parts of an air outlet rod.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

As introduced by the background art, the invention provides a method for casting a headstock, which aims to solve the technical problems that in the prior art, the structure of a casting of the headstock is complex, the inner hole and the inner groove are numerous, the complexity of different casting steps is different, the defects of shrinkage cavity, shrinkage porosity and the like are easily generated in the casting process, the casting efficiency is low, and the quality of the casting is poor.

Examples

In an exemplary embodiment of the invention, and with reference to fig. 1-25, there is provided a method of casting a headstock:

firstly, determining the pouring position of a headstock casting according to the structural shape of the headstock casting: adopting a pouring mode of vertical bottom pouring, wherein the end surface of the sealing ring groove of the headstock is positioned at the bottommost part;

then determining a parting surface according to the structure of the headstock: selecting a horizontal plane in which the center of the part bearing hole 5 is located as a parting plane;

and then designing a sand core: comprising as a main body core 1 ^#

Sand core

1,1 ^# The sand core 1 is manufactured by adopting a core disassembly and assembly mode, an exhaust passage is arranged in the sand core, and a positioning core head is arranged on the sand core 1 ^# Adding a core rod into the sand core; the sand core also comprises a positioning core head 2 ^#

Sand core

2, 3 ^#

Sand cores

3 and 4 ^#

Sand core

4,2 ^# Sand core and 3 ^# Sand cores for forming square holes in castings, 4 ^# The sand core is used for forming a groove at the top of the casting.

Then, designing a pouring system: adopting a semi-closed pouring system, wherein the sectional area of an ingate is less than that of a sprue and less than that of a cross gate, adopting a box for pouring one by one, and arranging the cross gate in two sections;

then, carrying out pattern design: the method comprises the steps of adopting two-box molding, dividing the two-box molding into an upper box and a lower box, setting a 0-degree 30' drawing slope in the mold stripping direction of the mold, setting the mold according to the casting shrinkage rate of 0.9% lofting, and manufacturing a sand mold according to the shape of the mold.

And finally, pouring: fixed sand core, 2 ^# Sand core, 3 ^# Sand core and 4 ^# The sand core is fixed on the upper box 1 ^# The psammitolite is fixed in the lower box, and the back is fixed to the psammitolite, and the mould assembling is fastened, lays the pouring basin, and the pouring basin is laid in the sprue top, and pouring basin and sprue junction set up the iron spacer, and the pouring molten metal sets up the blind riser at the foundry goods top before the pouring, and the necking down of blind riser root sets up the venthole in last case. Before casting, a plurality of plate-type chills are arranged at the hot spot part at the inner side of the bearing hole, and the plate-type chills are uniformly distributed on the circumference.

The method of casting the headstock will be described in detail below:

1. determining a pouring position:

the pouring position refers to the state (posture) and position of the casting in the casting mold during pouring. The pouring position of the headstock has horizontal type in various directions and vertical type in various directions.

By analyzing the advantages and the disadvantages of various pouring positions of the casting, the upright pouring position shown in figure 3 is adopted, the end face of the seal ring groove is positioned at the bottommost part, and the bearing hole is positioned at the middle lower part, so that the quality of the material of an important processing surface is ensured. The vertical casting mode is favorable for controlling the solidification of the casting, ensures the quality of the important bearing cylindrical surface and the sealing end surface, and has the advantages of small internal stress, small hot cracking tendency, small deformation and uniform and consistent metallographic structure. The liquid metal pouring pressure head is large, the mold filling is smooth, shrinkage cavities are reasonably arranged at hot spots of the middle bearing hole through a chill, defects of top hot spots and collapse are eliminated through a riser, and the internal quality of the casting is guaranteed.

The defects of the on-site headstock casting are difficult to eliminate due to unreasonable selection of the casting position, the headstock is horizontally placed for casting, the headstock sealing ring groove is upwards cast in an upright mode, the defects of castings are more, and the rejection rate is high, so that the upright mode that the end face of the sealing ring groove is positioned at the bottommost part is adopted in the embodiment.

2. Determining a parting surface:

and analyzing a mold splitting and parting scheme from the appearance overall structure of the casting, wherein the contact surface of the two half molds after mold splitting is a parting surface. Because the casting adopts vertical pouring, the vertical molding is adopted, namely, the vertical pouring process is immediately carried out, so as to reduce the damage of carrying and overturning to the sand mold in the molding operation. Meanwhile, in consideration of the positioning of the sand core, a core head positioning groove needs to be manufactured at the position of the sand mould bearing hole, the sand core is buckled and pressed by the upper sand box and the lower sand box, and the sand core can be prevented from floating and dislocating in the pouring process, so that the mold splitting and parting scheme shown in the figure 4 is determined, and the horizontal plane where the center of the part bearing hole is located is selected as a parting plane.

This embodiment selects the die joint in 5 center departments of dead eye, need not overturn, but direct vertical casting, and the foundry goods dead eye 5 department makes the core head constant head tank in order to utilize 6 location psammitolites of core head in the sand mould of being convenient for, and the sand box lock compresses tightly the psammitolite from top to bottom, prevents that the pouring in-process psammitolite from floating the dislocation.

The analysis of the structure of the headstock of the embodiment is similar to typical structural components such as a headstock and a gearbox of a machine tool, is suitable for casting gray cast iron, and has the outline dimensions of 487mm multiplied by 400mm multiplied by 345mm and the total volume of 20366.8cm ³ The total weight of the finished casting is 147.59Kg. The minimum wall thickness of the casting is 20mm, most wall thickness is 20-30mm, local wall thickness is 35-50mm, the casting is a hot spot part of the casting, and shrinkage porosity and shrinkage cavity are generated by solidification. The casting is complex in structure and various in hole and groove, and the molding of the internal hole and groove is completed by manufacturing a sand core and filling the core.

3. Sand core design

(1) Sand core structure design

The internal hole and groove of the casting are completed by designing a sand core, and the hole and groove structure design 1 of the casting of the headstock is designed ^# 、2 ^# 、3 ^# 、4 ^# Sand core as shown in fig. 5. Wherein 2 ^# 、3 ^# The sand core is manufactured independently and placed independently if the square hole sand core is manufactured independently, the position is not well mastered, and the sand core is easy to shift. So 2 ^# 、3 ^# The sand core needs the manufacturing of three square hole core block connecting bodies, the whole core is arranged, the operation is convenient, the efficiency is high, and the core arrangement dislocation is also prevented.

1 ^# The sand core is positioned by adopting a horizontal core head, and the core heads are positioned at the left side and the right side, as shown in figure 6.

1 ^# The sand core has a complex structure and cannot be integrally manufactured,the core is needed to be disassembled and connected for assembly. According to 1 ^# The structure of the sand core 1 is decomposed into 1-1 ^# Sand core 7, 1-2 ^# Sand core 8, 1-3 ^# The sand cores 9, as shown in FIG. 7, are separately made and finally combined to form 1 ^# And (6) a sand core.

2 ^# Sand core, 3 ^# Sand core, 4 ^# The core takes the positioning in the sand mold into consideration, the core head is designed, a certain gradient is reserved in the mold stripping direction of the mold sample and the core box for the convenience of mold stripping, the mold stripping gradient is determined to be 0 degrees and 30' of mold stripping gradient according to the mold stripping height, the surface roughness and the molding (core) method of the mold sample, as shown in figures 8, 9 and 10.

(2) Sand core manufacturing and core box design

The sand core is made by adopting a furan resin sand manual cold box. The core box is a special craft for manufacturing the sand core, and the quality and the molding efficiency of the sand core are influenced to a great extent if the size precision and the structure of the core box are reasonable or not. And (4) carrying out structural design on the core box by analyzing the structure of the sand core. And (4) folding and molding each sand core through the left core box and the right core box, and hardening the sand cores at room temperature for later use.

(3) Core design

The first sand core, namely the 1# sand core, is large in volume, so that the core rod 10 needs to be added inside, and the strength is increased. The core material Q235 is formed by welding a delta 10mm steel plate and phi 20 and phi 30 steel bars, and is shown in figure 11. And (5) casting, cooling, shakeout, cutting and taking out.

(4) Sand core exhaust

During the casting pouring process, the high-temperature molten metal vaporizes the water in the sand core, and the organic matters are volatilized, decomposed and combusted to generate a large amount of gas in a short time. These gases, once introduced into the molten metal, can cause porosity in the casting. Therefore, in order to ensure that the gas generated in the sand core can be timely discharged from the core head so as to ensure the exhaust of the sand core, an exhaust passage is arranged in the sand core during the core making. The sand core adopts a wax embedding line to open a sand core exhaust channel, as shown in figure 12. And melting the wax wire during pouring, and discharging sand core gas through the channel. When the core is placed, care should be taken not to block the air outlet hole of the core head.

4. Designing a pouring system:

the gating system is a general term for the passage of liquid metal in the mold into the mold cavity. It is composed of pouring cup, straight pouring channel, horizontal pouring channel and internal pouring channel. Whether the gating system is designed correctly or not greatly influences the quality of the casting, and 30% -40% of casting waste is caused by improper gating system.

In order to facilitate the modeling, improve the working efficiency and simplify the modeling process, the pouring system of the headstock casting adopts a novel ceramic tube modeling process, and the designed ceramic tube modeling is buried in sand to be directly used as the pouring system in the modeling process. Each set of ceramic tube pouring system is disposable, and the metal of the ceramic tube pouring system is recycled after the casting is cast and cooled and is broken. The cross sections of a sprue, a cross runner and an ingate of the formed ceramic tube type pouring system are all round tube type.

(1) Type of gating system

The casting system can be divided into closed and open casting systems according to the full state of metal liquid flow in the casting system, and the casting of iron castings usually adopts the closed casting system in the liquid flow full state, and is characterized in that the sectional area sigma A of a sprue is _{Straight bar} Maximum, ingate cross-sectional area ∑ a _{Inner part} Minimum, cross-runner cross-sectional area ∑ a _{Horizontal bar} Between them, i.e. Σ a _{Straight bar} >∑A _{Straight bar} >∑A _{Inner part} 。

The cross gate has the largest cross section, better slag resistance effect and stable filling. The sprue pit is arranged below the sprue, so that the scouring of molten metal on the bottom sand mold of the sprue is reduced, the buffer effect is achieved, and meanwhile, the local resistance coefficient and the head loss of the molten metal at the sprue-cross runner are reduced. The transverse pouring gate nest is arranged at the end part of the transverse pouring gate, the ingate and the transverse pouring gate are vertically arranged and are arranged in parallel with the straight pouring gate, and the total area of the ingate is the minimum and is the flow choking area position of the pouring system.

The closed casting system is divided into a fully closed casting system and a semi-closed casting system, the flow resisting section of the semi-closed casting system is on an inner pouring channel, the section of a transverse pouring channel is the largest, and Sigma A _{Straight bar} >∑A _{Inner part} ，∑A _{Horizontal bar} >∑A _{Straight bar} ，∑A _{Horizontal bar} >∑A _{Inner part} . During the pouring process, the pouring system can be full, but later than the closed pouring systemThe cross runner has the largest cross section area, so that the flow speed of molten metal in the cross runner is reduced, and the filling stability and the scouring force to a cavity are superior to those of a fully-closed pouring system.

Multiple field tests are carried out, a semi-closed pouring system is selected for the head box casting, sigma A _{Inner part} :∑A _{Horizontal bar} :∑A _{Straight bar} ＝1:1.5:1.1。

A top pouring type pouring system, an injection type pouring system and a bottom pouring type pouring system can be designed according to the opening position of an inner pouring gate, the characteristics of the headstock casting are comprehensively analyzed, and the bottom pouring type pouring system is adopted for reducing the adverse factors such as turbulence, splashing, entrainment, slag inclusion and sand mold scouring in the molten metal pouring process, as shown in figure 13.

By adopting a bottom pouring type pouring system, the cross gates are divided into two sections, and four ingates are arranged, so that the cross section areas of the sprue, the cross gates and the ingates can be calculated.

And a bottom pouring type pouring system is adopted, so that molten metal can be smoothly filled in a mold, and the speed is high. The molten metal filling type is injected from the bottom, is stable and orderly and is in a laminar flow state, and each layer surface has no turbulent flow and no splashing phenomenon. The metal liquid can completely fill the cavity in the pouring mode, and the phenomena of insufficient cast-in-place and cold shut cannot occur when the casting is solidified. Comprehensively considering, the optimized pouring mode of the headstock casting adopts a bottom pouring mode, the top shrinkage and collapse and the internal shrinkage cavity and shrinkage porosity of the headstock casting are eliminated by adopting a cold iron and riser mode, and the casting quality is improved.

(2) Gating system computing

Firstly, calculating the flow-resisting area of the pouring system, and calculating the semi-closed pouring system sigma A of the headstock casting _{Inner part} :∑A _{Horizontal bar} :∑A _{Straight bar} 1.5, and a flow-blocking area thereof at the ingate. And then calculating the cross-sectional area of each pouring gate according to the proportion of the cross-sectional areas of the pouring system.

τ＝2.31G ^0.5

In the formula, A resistance-pouring system flow resistance area (cm) ² ) Rho-molten metal density (Kg/cm) ³ ) G-total mass (Kg) of poured metal, τ -filling time(s), G-acceleration of gravity (cm/s) ² )，H _p Filling type average calculation pressure head (cm), H ₀ The metal pressure head (cm) above the flow-resisting section, C the total height of the casting, namely the height (cm) of the die cavity, and P the height (cm) of the die cavity above the flow-resisting section.

HT200 Density rho is 7.25g/cm ³ The total mass of the poured molten metal comprises a casting and a pouring system, wherein the casting has a mass of 150Kg, and the reference is made to an actual measurement pouring system weight of 28Kg simulated by ProCAST, so that the total mass of the poured molten metal is 178Kg. The net height of the casting is 487mm, and the machining allowance is considered and calculated according to 50 cm. The mold filling height spans 50cm of the whole casting, the sand eating quantity at the top of the sand box is 7cm, and the height of the sprue cup is 14cm, then:

H ₀ ＝14+50+7＝71cm

τ＝2.2G ^0.5 ＝29.4s

G＝178Kg，ρ＝0.00725Kg/cm ³ ，τ＝29.4s，μ＝0.48，g＝980cm/s ²

a resistance =5.8cm ²

A _{Resistance device} ＝∑A _{Inner part} The cross-sectional area ratio Sigma A of the semi-closed pouring system _{Inner part} :∑A _{Horizontal bar} :∑A _{Straight bar} 1.1, obtaining:

∑A _{inner part} ＝5.8cm ²

∑A _{Horizontal bar} ＝8.7cm ²

∑A _{Straight bar} ＝6.4cm ²

The ingate is manufactured by embedding a circular ceramic tube in a sand mold, and a casting is generally cast by adopting a plurality of ingates, so that the sectional area of each ingate is the average area of the flow blocking area of the total ingate. Four ingates are provided in this embodiment.

The pouring mode of end pouring, divide 2 sections in the cross gate, 4 are seted up to the ingate, calculate sprue, cross gate, ingate cross sectional area:

D _{inner part} ＝1.37cm(13.7mm)

D _{Horizontal bar} ＝2.35cm(23.5mm)

D _{Straight bar} ＝2.85cm(28.5mm)

The sprue is also made by embedding a circular ceramic tube in a sand mold. The diameter of the ball of the sprue pit of the embodiment is 1.5 times of the diameter of the bottom of the sprue. Because a semi-closed type pouring system is adopted, the sprue is designed to have a certain taper to ensure that the sprue is fully filled with molten metal and in a closed state, and the taper is designed to be 0-degree 25' according to a standard design.

The cross gate is also formed by adopting a ceramic tube type forming gate and is molded by embedding a tube, the cross gate is divided into two sections, and the sectional area of a single cross gate is half of the total cross gate sectional area Sigma A cross gate. The cross gate nest is designed at the tail end of the cross gate, so that slag collection, slag blocking and turbulence prevention are achieved, and the ball diameter of the cross gate nest is 1.5 times of the diameter of the cross gate.

(3) Pouring cup

The pouring cup adopts a pool type pouring cup, the pool depth of the pouring cup is 14cm, the connection part of the pouring cup and the sprue is in the form of an iron spacer 11, an iron spacer 11 with the thickness of 3mm is filled between the bottom of the pouring cup and the cope flask, as shown in figure 14, the iron spacer 11 begins to separate the pouring cup from the sprue during molten metal pouring, when the liquid level of the pouring cup is poured to a certain depth, the iron spacer is melted through, the good slag-blocking effect is achieved, the sprue filling state is guaranteed, and the effect of a closed pouring system is achieved.

(4) Straight pouring gate nest and cross gate nest

The straight pouring channel and the horizontal pouring channel are both made of circular ceramic tubes embedded in the sand mould. A straight pouring gate nest 12 is designed below the straight pouring gate, so that the scouring of molten metal to the sand mold at the bottom of the straight pouring gate is reduced, and a buffering effect is achieved; meanwhile, the local resistance coefficient and the head loss of molten metal at the sprue-cross runner are reduced. The transverse runner nest 13 is designed at the tail end of the transverse runner to play a role in collecting slag, blocking slag and preventing turbulence. The diameter of the ball of the straight pouring channel pit is 1.5 times of the diameter of the bottom of the straight pouring channel, namely 42.8mm. The runner nest ball diameter is taken to be 1.5 times the runner diameter, i.e. 35.3mm. The straight gate nest and cross gate nest design is shown in fig. 15.

(5) Riser design

The riser is a cavity used for storing molten metal in the casting mould, supplies metal in the casting solidification process, and has the functions of preventing shrinkage cavity, shrinkage porosity, exhausting and collecting slag.

The gray cast iron eutectic solidification is a layer-by-layer and pasty intermediate solidification mode, is similar to an 'endogenous shell-shaped solidification mode', is different from cast steel, and has the self characteristics of feeding.

Graphite is separated out in the cast iron solidification process, and the cast iron has the characteristic of self-feeding along with phase change expansion. Therefore, the process design is carried out on the head box casting feeding based on the feeding after the gating system and the stony desertification expansion self-feeding. When liquid shrinkage is stopped or volume expansion is started, pressure is built in the casting by using all or part of graphitization expansion amount, and self-feeding is realized. The eutectic expansion of the cast iron forms internal pressure, liquid is forced to flow to the position where shrinkage cavity and shrinkage porosity are formed, and the vacuum degree of the casting in the solidification period is prevented, so that the defects of shrinkage cavity and shrinkage porosity are avoided.

The riser of the head box casting is designed according to a feeding liquid amount method, and the diameter D of the riser _{Cap with heating means} Is the sum of the diameter D of the feeding ball and the wall thickness T of the feeding part D _{Cap (A)} = d + T, then riser height H _{Cap (A)} ＝(1.15-1.8)D _{Cap (A)} 。

Wherein v is the volume of the part of the casting to be fed, epsilon is the shrinkage rate of the metal liquid solidified body of the casting, epsilon v is the total volume of the metal liquid feeding ball, and the actually measured shrinkage cavity volume epsilon v is 119.35cm by referring to the ProCAST simulation ³ . D =6.11cm (61.1 mm), feeding site wall calculatedThickness T =30mm, riser diameter and height were calculated:

D _{cap (A)} =61.1+30=91.1mm (take 100 mm)

H _{Cap with heating means} ＝1.3D _{Cap (A)} ＝130mm。

The riser is arranged at a boss part which is thick at the top and easy to generate defects, and the specific position is determined by performing multiple pouring simulation through ProCAST. The blind riser is adopted for good heat insulation effect, and the atmospheric pressure riser is adopted for preventing the blind riser 14 from feeding to form vacuum, so that the molten metal in the riser can be smoothly fed. In order to facilitate the later cutting and cleaning of the riser after the casting is solidified, a free-cutting riser with a necking root is adopted.

The design and position of the casting riser are shown in figure 16.

(6) Chiller design

The chiller 15 is a chilled material placed on the surface or inside of the casting to increase the local cooling rate of the casting. The method prevents shrinkage cavity and shrinkage porosity at the position where riser feeding is difficult, prevents cracks from being generated at the joint part of wall thickness and the position with rapid change, can strengthen the sequential solidification condition of the casting when being used together with the riser, utilizes the tail end area formed by chill to enlarge the feeding distance and range of the riser, reduces the number or volume of the riser, accelerates the cooling of the hot spot part, and enables the whole casting to be close to simultaneous solidification. The reasonable use of the chill can prevent the casting from deforming, improve the process yield of the casting, improve the local metallographic structure and mechanical property of the casting, refine the matrix structure, improve the surface hardness and wear resistance of the casting and reduce the component segregation in the thick-wall casting.

In the process, direct external chill is used in order to ensure the quality of the casting and obtain good cooling effect of the hot spot part. The graphite chilling block with high refractoriness and large heat conductivity coefficient is selected and used as the chilling block material. The cost of the graphite chilling block is between that of a copper alloy chilling block and that of an iron alloy chilling block, the copper alloy chilling block is high in price and low in melting point and is not suitable for casting of steel castings, and the graphite chilling block is superior to the iron alloy chilling block in the effect of eliminating casting defects and is beneficial to improving the qualified rate of the castings.

The thickness of chill can be confirmed according to the thermal node circle diameter, and this embodiment respectively lays 6 plate type chills at the big dead eye inboard thermal node position in both sides, and the circumference equipartition, thickness delta are 20mm.

Specifically, the thickness of a chilling block delta = (0.25-0.5) T is selected, the T is the diameter of a hot spot circle of the casting, 38mm is taken, and delta =20mm is taken.

And (3) calculating the area of the chilling block:

in the formula V ₀ Required chill volume of the casting, ac-chill surface area, M ₀ Casting modulus, M ₁ -chill equivalent modulus.

To effect sequential coagulation, M ₁ =0.89Mp (thermal node modulus) and Mp ≧ 0.67M ₀ 。

Calculated to obtain the total area of the chilling block of 126.5cm ² 。

And (3) repeatedly testing the placing positions and the quantity of the chills by ProCAST pouring simulation, and finally obtaining the optimized cooling solidification effect of basically eliminating shrinkage cavities and shrinkage porosity. The chilling blocks are arranged as shown in figure 17, 6 plates of chilling blocks are respectively arranged at the hot spot positions at the inner sides of large bearing holes at two sides, the chilling blocks are uniformly distributed on the circumference, and the thickness delta is 20mm.

(7) Exhaust of a gating system

The total exhaust area of the pouring system is not less than the sectional area of the sprue, and the sprue is 6.4cm ² Therefore, 5-6 vent holes are needed according to the

diameter phi

12, 6 vent holes are needed, and as the cores are arranged on the upper, lower, left, right, front and back surfaces of the casting to be in direct contact with the sand mold, part of gas can be discharged through the cores and the sand mold.

During modeling, the gas outlet rods 16 of the forming ceramic tubes are arranged at the positions of the top of the upper box, which are contacted with the bosses at the top of the pattern, and are uniformly distributed, as shown in figure 18. One of the air bars 16 is connected to the blind riser 14 and also serves as a riser atmospheric pressure riser vent. Some air vents are arranged at the hole cavity of the mold core in contact with the molding sand, some air vents are arranged at the contact position of the molding sand and the casting, and the casting blank at the position is provided with an air vent rod which needs to be cut off and cleaned.

5. Design of pattern

The pattern was made according to the structure and parting plane of the sand core, the unfired holes and grooves were filled in the headstock by the machining allowance, and the pattern was made by setting out the pattern according to the shrinkage (0.9%) and applying the draft (0 ° 30'), as shown in fig. 19.

Considering the positioning of the sand core, a core head positioning die head needs to be designed at a corresponding position in the pattern, such as the integral casting pattern manufactured according to various process parameters such as core head design and the like in fig. 20.

The casting adopts a two-box model, and the whole wood pattern needs to be decomposed into upper and lower box wood patterns from a parting surface, as shown in figures 21 and 22. And performing sand mold molding on the two sand boxes through the two wood mold patterns, then placing sand cores in the sand molds, and pouring metal liquid to form castings according to spaces between the sand molds and the sand cores.

The base casting sand box adopts cast iron with low cost, convenient manufacture and higher strength and rigidity. And (5) determining a casting pouring mode through ProCAST multiple times of simulation, and finishing the optimal design of a pouring system and a riser. Designing and decomposing the wood pattern of each box by combining sand mold sand consumption analysis, and finally determining the size of the inner frame of the cope box to be 700mm (length) multiplied by 550mm (width) multiplied by 490mm (height); the size of the inner frame of the drag box is 700mm (length) multiplied by 550mm (width) multiplied by 300mm (height).

And (4) performing resin sand hand molding in the upper box and the lower box respectively according to the wood pattern. During molding, the upper box sprue, the atmospheric pressure riser and the gas outlet rod of the molded ceramic tube are buried in the upper box filled with sand. And (4) burying a cross pouring channel, an inner pouring channel and a lower box sprue of the formed ceramic tube in the lower box.

6. Moulding, core setting and mould assembling process flow

(1) Moulding

And (4) manually molding furan resin sand in the upper box and the lower box respectively according to the wood pattern.

During molding, the upper box sprue, the atmospheric pressure riser and the gas outlet rod of the molded ceramic tube are buried in the upper box filled with sand. And burying a cross pouring channel, an inner pouring channel and a lower box sprue of the formed ceramic pipe in the lower box.

The completed cope and drag molds are shown in fig. 23 and 24.

(2) Core setting and mould assembling box

The reasonable core setting sequence and the accurate positioning are powerful guarantee of the size precision of the casting. The specific operation is as follows:

1) Placing the upper and lower box sand molds with parting surfaces upward on a molten iron casting field stably;

2) Respectively combine 2 ^# Sand core, 3 ^# Sand core, 4 ^# The sand core is accurately placed by aiming at the core head groove of the upper box, and the sand core is firmly bonded with the sand mould by using a bonding agent;

3) Will be assembled 1 ^# The sand core is aligned with a core print slot of a lower box sand mold and is accurately positioned and placed;

4) The case is gone up in the upset, goes up lower case lock, notices and can not collide with the psammitolite that has installed, does not miss and bumps the sand mould, arouses to fall the sand, prevents that the foreign matter from falling into the sand mould, goes up the case and passes through the accurate location lock of pin. The upper box sand core headstock and the upper box sand core are accurately positioned and matched;

5) The upper box and the lower box are fastened by bolts, the diagonal fastening is noticed, the fastening is carried out in a symmetrical sequence, the force is uniformly applied, and the parting surfaces of the upper box and the lower box are prevented from being buckled untight and even deformed and uneven;

the dislocation of the sand boxes is a direct reason for producing casting waste products, and the positioning of the sand boxes is strictly controlled to prevent the dislocation of the sand boxes. When the box is closed, the two pins with the opposite angles and the diameter of 20 are used for positioning.

The sand box needs to be fastened after being positioned, otherwise, the sand box can expand and run out in the process of pouring the molten metal, and waste products and safety accidents are easily caused. The molding box of the sand box is fixed by 2M 20 bolts at each side, and the total number of the M20 bolts is 8. During modeling, a plurality of forming ceramic tube air outlet rods are arranged at positions of bosses at the top of the upper box, which are in contact with the top of the pattern, the number of the forming ceramic tube air outlet rods is determined according to specific conditions, and the positions are uniformly distributed.

6) And placing a pouring cup, paying attention to the fact that an outlet at the bottom of the pouring cup is aligned with an inlet of a sprue gate of the upper box, placing a weight, completing a box closing process, and waiting for molten iron pouring of the next process.

The process flow of shaping, core setting and mould assembling is shown in figure 25.

And after the casting is poured for about 1.5 hours, the temperature is reduced to be within 400-450 ℃ for boxing, and then the casting is lifted to a vibration shakeout machine for shakeout treatment.

And after the shakeout treatment, a dead head cutting system, a pore cast iron needle, flash, rough edges and the like are cut by gas cutting.

And further polishing the scars and burrs cut by the gas cutting through an angle grinder.

And performing shot blasting and sand cleaning treatment on the sand adhered to the surface of the casting through shot blasting equipment. In the cooling process of the casting, the surface cast iron sheet belongs to a chilling structure, has high hardness and more sand grain impurities, and is difficult to process. The surface stress concentration can be eliminated through the surface shot blasting and sand cleaning treatment, the surface tissue structure is improved, the hardness is uniform, and the subsequent processing treatment is facilitated. The shot blasting machine adopts steel shots with the granularity of 2-3mm, the throw amount is 250-300Kg/min, the shot blasting speed is 60-70m/s, and the shot blasting and sand cleaning speed is improved.

7. Cast iron smelting process

The quality of molten iron is a main factor determining the quality of castings. The chemical composition, purity, contents of oxygen, hydrogen and other gases, impurities and impurities, and temperature are three main quality indexes of molten iron.

Pure furnace burden is selected in the smelting process, and a medium-frequency induction furnace is adopted for heating and smelting. The method adopts overheating purification treatment and adopts a process of 'high-temperature tapping and low-temperature pouring', the tapping temperature of molten iron reaches 1450-1470 ℃, effective deoxidation is carried out, oxide impurities are removed, the matrix structure is refined, graphite is refined, and the matrix strength is improved.

The overheating purification of the iron liquid is followed by inoculation treatment. The inoculation treatment adopts FeSiSr inoculant containing silicon, calcium, aluminum and strontium, and the ingredients are shown in the table 1.

TABLE 1FeSiSr inoculant compositions (% by weight)

The inoculation needs to control the particle size of the inoculant, the inoculant is too large in particle size and is not fully melted, and the inoculant is too small in particle size and is easily wrapped with the slag, so that the inoculation effect is reduced. Multiple inoculation can prevent inoculation recession, improve the uniform distribution degree of graphite in the casting, reduce the supercooling tendency of iron liquid, obtain A-type graphite, promote the increase of the number of non-spontaneous crystal nuclei, refine crystal grains, strengthen a matrix and improve the strength and the performance of cast iron. The adoption of instantaneous inoculation can effectively improve the inoculation effect of the molten iron, reduce the chilling tendency caused by the use of external chill and reduce the possibility of generation of D and E type graphite. The grain size of the inoculant is controlled to be 3-8 mm, the inoculation process adopts twice stokehole inoculation and once instant sprue cup inoculation, and the pouring temperature is controlled to be 1340-1360 ℃.

Before pouring the molten iron, routinely using a triangular test piece to detect the quality of the molten iron in front of the furnace.

8. Casting heat treatment process

And (4) carrying out aging treatment for eliminating casting stress, and adopting a mechanical vibration mode for aging treatment for saving time. The excitation frequency is 80-100 Hz, the dynamic stress is large, the effect is good, and the aging time is saved.

Annealing after rough machining, stress relief annealing, heating the iron casting to the elastic and plastic temperature range of the material, preserving heat, eliminating, relaxing or homogenizing residual stress, and then slowly cooling to eliminate casting thermal stress, structural stress and structural stress generated by graphitization annealing.

The annealing process is shown in Table 2:

TABLE 2 stress relief annealing process for headstock casting

For some defects on the casting, such as air holes, slag inclusion, sand inclusion, shrinkage porosity, small cracks and the like, the defects can be removed through gas cutting and an angle grinder, and then the defects are welded, filled and reworked and repaired.

For detected defects such as air holes, slag inclusion, sand inclusion, shrinkage porosity, small cracks and the like, a welding repair method adopted after excavation is a cold welding process, the welding part is preheated to 100-150 ℃ through gas cutting flame, a nickel-based non-cast iron welding rod is adopted, small current welding is adopted, natural air cooling is carried out after welding, the white cast tendency is reduced, and the cracks are prevented from being generated.

And (4) repairing the defects of the machined part by welding, and then repairing the machined part again, polishing and finishing the surface of the non-machined part by using an angle grinder, and performing smooth transition with the adjacent surface.

The dry sand mold is preferably selected for the selection of molding materials of the headstock casting to prevent the casting from having defects such as air holes, cold shut and the like, and the furan resin sand mold is particularly selected for molding and core making, has high strength, good heat resistance, small resin viscosity, convenient sand mixing, good resin sand hardness and permeability and high old sand regeneration rate.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or 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 method of casting a headstock, comprising:

determining a parting surface: selecting a horizontal plane in which the center of a bearing hole of a part is located as a parting plane;

designing a pouring system: adopting a semi-closed pouring system, wherein the cross section of an ingate is smaller than that of a sprue and is smaller than that of a cross gate, pouring by one box, and arranging the cross gate in two sections;

pouring: fixing the sand core, closing the box, placing a pouring cup and pouring metal liquid.

2. The method of casting a headstock of claim 1 wherein the sand cores further comprise a second sand core, a third sand core and a fourth sand core having a locating core, the second sand core and the third sand core being used to form a casting square hole and the fourth sand core being used to form a casting top recess.

3. The method for casting the headstock according to claim 1, wherein the pattern is designed such that a draft of 0 ° 30' is provided in a pattern drawing direction, the pattern is set at a casting shrinkage of 0.9%, and the sand mold is manufactured according to a shape of the pattern.

4. The headstock casting method according to claim 1, wherein the cross-sectional area of the sprue is: cross-sectional area of runner: ingate cross-sectional area = 1.1.

5. The method of casting a headstock according to claim 4, wherein a sprue pocket is provided below the sprue, a sprue pocket is provided at an end of the runner, and the ingate is provided perpendicular to the runner and parallel to the sprue.

6. The method for casting the headstock according to claim 1, wherein the pouring cup is placed at the top of the sprue, and an iron spacer is arranged at the joint of the pouring cup and the sprue.

7. The method for casting the headstock according to claim 6, wherein a blind riser is arranged at the top of the casting before pouring, the root of the blind riser is necked down, and an air outlet rod is pre-buried in the upper box.

8. The method of claim 7, wherein a plurality of plate-type chills are circumferentially and uniformly distributed in the hot spot inside the bearing hole before pouring.

9. The method for casting the headstock according to claim 2, wherein after the sand mold is manufactured, the second sand core, the third sand core and the fourth sand core are fixed to the upper box, the first sand core is fixed to the lower box, and after the sand cores are fixed, the box is closed and fastened.

10. The method of casting a headstock of claim 2 wherein the sand core is made of furan resin sand.