Dry sand negative pressure molding process for lost foam

Abstract

The invention relates to the technical field of full mold casting, and provides an evanescent mode dry sand negative pressure molding process, EPS particles are doped with nanometer silane modified silicon dioxide with the mass percentage being 0.5% of that of the EPS particles, so that the strength of a foam model is improved by 20%, the heat deformation temperature is increased to 80 DEG C, and deformation in the molding and pouring process is reduced. The coating of the bottom layer of the model adopts 20% of bauxite and 5% of carbon fibers to be matched with a water-based binder, so that the air permeability is enhanced, and the coating of the surface layer of the model adopts 60% of emery and 10% of silica powder to be matched with a water-based binder, so that the fire resistance is improved. Pre-jolt ramming and main jolt ramming are carried out after sand filling, so that the compactness uniformity of dry sand is improved to 95% or above; sealing is carried out, main vacuumizing and auxiliary vacuumizing are carried out, the vacuum degree sealing performance during pouring is guaranteed, then pouring forming is carried out, and the vacuum degree is monitored in the pouring process, so that the stability of the vacuum degree in the pouring process is guaranteed; and finally cooling and releasing negative pressure to obtain the casting.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of real type casting technology, and particularly relates to a lost foam dry sand negative pressure molding process. BACKGROUND

[0002] Traditional lost foam casting is generally divided into resin sand and dry sand negative pressure casting process, and there are three core problems in actual production: first, the foam model joint of complex castings is easy to deform, resulting in size deviation of the castings; second, the traditional resin sand and dry sand molding process is manually dropped, and there are problems such as unpractical sand burying or single vibration direction of the dry sand vibration table, uneven vibration, and "virtual sand" in complex cavities, which causes sand eye defects of the castings, even chemical sand sticking, and brings troubles to subsequent casting cleaning, and then affects the quality of the castings; third, the vacuum degree fluctuates greatly during pouring, and the model gasification gas is not discharged smoothly, causing casting porosity problems. Therefore, a molding process suitable for complex lost foam is needed to solve the above problems. SUMMARY

[0003] Therefore, the present application aims to provide a lost foam dry sand negative pressure molding process to solve the problems in the background art.

[0004] In order to achieve the above purpose, the present application provides a lost foam dry sand negative pressure molding process, which comprises the following steps: Step one, select EPS particles as raw materials, add 0.5% of nano-silica modified silicon dioxide to the EPS particles, mix them evenly, and then add them to a foaming machine for high-pressure foaming, and then mature; Step two, each part of the complex model is formed through a mold, and the matured particles are added to the forming mold to form each part of the lost foam model; Step three, a hot melt groove is processed at the joint of the obtained model, and the hot melt grooves of each part of the model are bonded and spliced into a complete lost foam model by injecting low-melting hot melt glue; Step four, the surface of the model is coated with paint, and then baked at 80 DEG C for 2h; Step five, the model is placed in a sand box, and the sand is filled in a layered filling manner, and the thickness of each layer of sand is controlled to be 200-300 mm; Step six, then pre-vibrate using high frequency and low amplitude, and then main-vibrate using low frequency and high amplitude; Step seven, seal the sand box, and then vacuumize, vacuumize the sand box using a main vacuum pump at high speed for basic vacuumization, and using an auxiliary vacuum pump at low speed for auxiliary vacuumization; Step eight, pouring forming, pouring the molten metal into the sand box to form a casting, the pouring temperature is 1350-1550 DEG C, and the pouring speed is 8-12 kg / s; Step nine, after the casting is cooled to below 150 DEG C, open the sand box to release the negative pressure, remove the casting, machining.

[0005] Preferably, the step three hot melt groove depth is 0.5mm.

[0006] Preferably, the step four model bottom layer coating is added to the coating 20% bauxite + 5% carbon fiber with water-based binder, the model surface layer coating is added to the coating 60% corundum sand + 10% silicon powder with water-based binder.

[0007] Preferably, the coating layer of the coating is 1.2-1.5mm.

[0008] Preferably, the step six pre-vibration frequency is 150Hz, and the amplitude is 3mm.

[0009] Preferably, the step six main vibration frequency is 80Hz, and the amplitude is 6mm.

[0010] Preferably, the step seven main vacuum pump speed is 500m³ / h, and the vacuum degree of the sand box base is extracted to 0.04-0.06MPa.

[0011] Preferably, the step seven auxiliary vacuum pump speed is 200m³ / h, and the vacuum degree is 0.055MPa.

[0012] Preferably, the step eight pouring process monitors the vacuum degree of the pouring area in real time, and when the fluctuation exceeds ±0.005MPa, the extraction is supplemented to ensure that the gasification gas is quickly discharged in a directional manner.

[0013] The beneficial effects of the present application: the present application is in the EPS particle doping mass percentage of EPS particle 0.5% of nano-silica modified silicon dioxide, through high pressure foaming forming, the strength of the foam model is improved by 20%, the thermal deformation temperature is increased to 80 DEG C, and the deformation in the process of modeling and pouring is reduced.

[0014] By dividing the complex lost foam into multiple parts and forming separately, the model splicing part is connected by opening a hot melt groove and injecting a low-melting-point hot melt adhesive for hot melt curing, and the strength reaches 1.2MPa, solving the problem of insufficient strength of traditional binders.

[0015] The model bottom layer coating uses 20% bauxite + 5% carbon fiber with water-based binder, which enhances the air permeability, and the model surface layer coating uses 60% corundum sand + 10% silicon powder with water-based binder, which improves the fire resistance, and the total thickness of the coating is 1.2-1.5mm, the air permeability reaches 50-80m³ / (m²·h), and the requirements of anti-sticking sand and exhaust are met.

[0016] After filling sand, pre-compact at a frequency of 150 Hz and an amplitude of 3 mm, and then main compact at a frequency of 80 Hz and an amplitude of 6 mm, the dry sand compactness uniformity is improved to more than 95%, the "virtual sand" caused by traditional single vibration is effectively avoided, the phenomenon of sand occupation is effectively prevented, the secondary cleaning of the appearance of the castings in the later stage is facilitated, and the appearance quality of the castings is improved.

[0017] Then, the sand box is sealed and vacuumized, the base vacuumization of the sand box is performed by a main vacuum pump at a pumping speed of 500 m3 / h to a vacuum degree of 0.04-0.06 MPa, the vacuumization of the sand box is performed by an auxiliary vacuum pump at a pumping speed of 200 m3 / h to ensure that the vacuum degree is 0.055 MPa, the vacuum degree sealing during pouring is ensured, then, the sand box is poured into a shape, the vacuum degree during pouring is monitored to ensure the stability of the vacuum degree during pouring, and finally, the castings are obtained after cooling and negative pressure release. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below with specific examples.

[0019] It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the present application should be understood as the general meaning understood by those skilled in the art to which the present application belongs. The terms "first", "second" and the like used in the present application do not represent any order, number or importance, but are only used to distinguish different components. The terms "include" or "contain" and the like mean that the elements or objects before the terms cover the elements or objects listed after the terms and their equivalents, and do not exclude other elements or objects. The terms "connect" or "connected" and the like are not limited to physical or mechanical connection, but can include electrical connection, whether direct or indirect. The terms "up", "down", "left", "right" and the like are only used to represent relative positional relationship, and when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] The present embodiment provides a dry sand negative pressure molding process for lost foam, which comprises the following steps: S1, selecting EPS particles as raw materials, adding 0.5% of nano-silica modified silicon dioxide in mass percentage to the EPS particles, mixing the two uniformly, adding them to a foaming machine, foaming by high pressure, and then aging; the strength of the foam model is improved by 20%, the thermal deformation temperature is increased to 80℃, and the deformation in the molding and pouring processes is reduced; S2, each part of the complex model is separated and molded by a mold, and the particles after aging are added to the molding mold to obtain each part of the lost foam model; S3, the splicing of the obtained model is processed into a hot melt groove with a depth of 0.5 mm, and the hot melt grooves of the various parts of the model are bonded by injecting low-melting hot melt glue to splice into a complete lost foam model; the strength reaches 1.2 MPa, solving the problem of insufficient strength of traditional binders; S4, the surface of the model is coated with paint, 20% bauxite + 5% carbon fiber is added to the paint coated on the bottom layer of the model to match the water-based binder, and 60% corundum sand + 10% silicon powder is added to the paint coated on the surface layer of the model to match the water-based binder, and then dried at 80°C for 2h; this improves the refractoriness, the total thickness of the coating is 1.2mm, and the air permeability reaches 60m³ / (m²·h), which meets the requirements of anti-sticking sand and exhaust.

[0021] S5, the model is placed in the sand box, and the sand is filled in a layered filling manner, and the thickness of each layer of sand is controlled to be 250 mm; S6, then pre-compact at a frequency of 150Hz and an amplitude of 3mm, and then main-compact at a frequency of 80Hz and an amplitude of 6mm; in this way, the uniformity of the dry sand compactness is improved to more than 95%, effectively avoiding the "virtual sand" caused by traditional single vibration, effectively preventing the phenomenon of sticking sand, which is beneficial to the secondary cleaning of the appearance of the castings in the later period, and improves the appearance quality of the castings; S7, seal the sand box, then vacuumize, use the main vacuum pump to perform basic vacuumization on the sand box at a rate of 500m³ / h to a vacuum degree of 0.05MPa, use the auxiliary vacuum pump to perform auxiliary vacuumization on the sand box at a rate of 200m³ / h to ensure the vacuum degree is 0.055MPa; in this way, the vacuum degree sealing during pouring is ensured, then pouring forming is performed, and the vacuum degree during pouring is monitored to ensure the stability of the vacuum degree during pouring; S8, pouring forming, pouring the molten metal into the sand box to form a casting, the pouring temperature is 1350-1550°C, and the pouring speed is 8-12 kg / s; the vacuum degree of the pouring area is monitored in real time during pouring, and when the fluctuation exceeds ±0.005MPa, the vacuum is supplemented to ensure that the gasification gas is quickly and directionally discharged; S9, after the casting is cooled to below 150°C, the sand box is opened to release the negative pressure, the casting is taken out, and machining is performed.

[0022] The size tolerance of the casting prepared in this embodiment is controlled to be ±0.08mm, the surface roughness Ra is ≤10μm, and the defect rate is reduced by more than 60%. Efficiency optimization: the production cycle of complex castings is shortened by 25%, and the dry sand reuse rate is improved to 98%.

[0023] The process breaks through the bottleneck of traditional lost foam process by the synergy of material-equipment-process, and is especially suitable for batch production of complex castings such as automobile engine cylinder block, wind power gear box, machine tool main shaft box, transmission seat, automobile die trolley, inclined wedge sliding block and insert, small convex die and the like, and has significant technical and economic benefits and industrialization prospect.

[0024] Those skilled in the art should understand that the above discussion of any embodiment is only exemplary and is not intended to imply that the scope of the present application is limited to these examples; the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in details for the sake of brevity. Any omission, modification, equivalent replacement, improvement and the like within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A process for lost foam dry sand negative pressure molding, characterized in that, The method comprises the following steps, Step one, select EPS particles as raw material, add 0.5% nano-silicon modified silicon dioxide to the EPS particles, mix them evenly, and then add them to the foaming machine for high-pressure foaming, and then mature; Step two, separate each part of the complex model and form it through the mold, add the matured particles into the forming mold to form each part of the lost foam model; Step three, process the hot melt groove at the joint of the obtained model, and bond and splice the hot melt grooves of each part of the model into a complete lost foam model by injecting low-melting hot melt adhesive; Step four, coat the surface of the model with paint, and then dry it at 80℃ for 2h; Step five, put the model into the sand box, and fill the sand in a layered manner, with the thickness of each layer controlled at 200-300mm; Step six, then pre-compact using high frequency and low amplitude, and then main-compact using low frequency and high amplitude; Step seven, seal the sand box, and then vacuumize it, which is achieved by using a main vacuum pump at high speed to perform basic vacuumization on the sand box, and using an auxiliary vacuum pump at low speed to perform auxiliary vacuumization on the sand box; Step eight, pouring forming, pour the smelted metal liquid into the sand box to form a casting, with the pouring temperature being 1350-1550℃ and the pouring speed being 8-12 kg / s; Step nine, after the casting is cooled to below 150℃, open the sand box to release the negative pressure, take out the casting, and machine it.

2. The process according to claim 1, characterized in that, The depth of the hot melt groove in step three is 0.5mm.

3. The process according to claim 1, wherein The paint added to the bottom layer of the model in step four comprises 20% bauxite + 5% carbon fiber + water-based binder, and the paint added to the surface layer of the model comprises 60% corundum sand + 10% silicon powder + water-based binder.

4. The process according to claim 3, wherein The coating of the paint is 1.2-1.5mm.

5. The process according to claim 1, wherein The frequency of the pre-compact in step six is 150Hz, and the amplitude is 3mm.

6. The process according to claim 5, wherein The frequency of the main-compact in step six is 80Hz, and the amplitude is 6mm.

7. The process according to claim 1, wherein The suction speed of the main vacuum pump in step seven is 500m³ / h, and the basic vacuumization of the sand box is performed to a vacuum degree of 0.04-0.06MPa.

8. The process according to claim 7, characterized in that, The suction speed of the auxiliary vacuum pump in step seven is 200m³ / h, and the vacuum degree is ensured at 0.055MPa.

9. The process according to claim 8, characterized in that, The vacuum degree of the pouring area is monitored in real time during the pouring process in step eight, and the suction is supplemented when the fluctuation exceeds ±0.005MPa, so as to ensure the directional and rapid discharge of the gasification gas.