CN111761032B - Method for casting cold core box sand core of complex camshaft of large diesel engine body - Google Patents
Method for casting cold core box sand core of complex camshaft of large diesel engine body Download PDFInfo
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- CN111761032B CN111761032B CN202010748151.0A CN202010748151A CN111761032B CN 111761032 B CN111761032 B CN 111761032B CN 202010748151 A CN202010748151 A CN 202010748151A CN 111761032 B CN111761032 B CN 111761032B
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- B22—CASTING; POWDER METALLURGY
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- B22C9/00—Moulds or cores; Moulding processes
- B22C9/10—Cores; Manufacture or installation of cores
Abstract
The method for casting the complex camshaft cold-box sand core by using the large diesel engine body utilizes the cold-box core of the core shooter to make the core, and has the advantages of low gas forming amount of core sand, good fluidity, easiness in molding and compaction, difficulty in deformation of the core box, high size precision of the sand core, smooth surface, collapsibility and good deformability, and the whole positioning of key size elements of different functional parts of the engine body is realized on the side surface of an outer die; according to the specific shape, position and size of the camshaft part, an inner chill and an outer chill are adopted to balance the thermal junctions of the thick and large isolated parts; the air channels in the cold core box sand core are connected to form a net, and the air channels in the sand core are connected with the air outlet hole in the side surface of the upper sand box, so that the air in the sand core is led out, and the size precision and the internal and external quality of the machine body are improved.
Description
Technical Field
The invention belongs to the technical field of casting, and particularly relates to a manufacturing method of a complex camshaft cold core box sand core of a large diesel engine body.
Background
A certain type of diesel engine body belongs to a large-scale complex nodular iron casting, and the maximum outline dimension of the engine body is as follows: 4895 × 1536 × 1287, casting deviation is required to be performed according to CT10 in ISO8062, the machine body structure is complex, the number of cavities and lugs is large, the wall thickness is greatly different, and the requirement on dimensional accuracy is high.
The camshaft hole is one of three important holes of a diesel engine body, a two-layer structure is arranged in a camshaft cavity, a lower layer mainly adopts a tappet jacking structure, an upper layer mainly adopts the camshaft hole structure, the internal shape structure is complex, the quantity of lugs is large, the wall thickness difference is great, and the diameters of the tappet jacking structure and the cylinder cover bolt lug position reach about 100. The requirements for ultrasonic flaw detection, magnetic powder inspection and the like are high, and the requirements for internal and external quality are high.
The existing wood mold is low in strength and rigidity, greatly influenced by temperature and humidity, unreasonable in arrangement of a chill, unsmooth air outlet in a sand core and the like, so that the size control difficulty of a camshaft cavity of a machine body is high, the quality problem is high, and casting defects such as thin wall of an observation window, drill-through of a lug, deviation of a drilled hole from a center, a cylinder cover bolt hole, a camshaft jacking hole, a camshaft hole, shrinkage porosity and the like often occur after processing. There is therefore a need for improvements.
Disclosure of Invention
The technical problems solved by the invention are as follows: the invention provides a manufacturing method of a complex camshaft cold box sand core of a large diesel engine body, which solves the casting defects of high size control difficulty, multiple quality problems, thin camshaft and crankshaft observation window walls, lug drilling, deviation of a drilling hole from a center, shrinkage porosity of a thick part, pores of a camshaft shaft hole and the like after processing, and has stable mass production quality and greatly improved size precision and surface quality of the engine body by a combined structural method of a complex core shooting machine cold box, discrete core making, unified positioning, internal and external chillings, balance hot spots, drilling networking and internal and external air guiding.
The technical scheme adopted by the invention is as follows: a manufacturing method of a large diesel engine body complex camshaft cold box sand core is characterized in that a core shooter cold box is used for making a core, and the whole positioning of key size factors of different functional parts of the engine body is realized on the side surface of an outer die; according to the specific shape, position and size of the camshaft part, an inner chill and an outer chill are adopted to balance the thermal junctions of the thick and large isolated parts; connecting an internal gas channel of the cold core box sand core to form a net, and connecting the gas channel of the sand core with a side gas outlet hole of an upper sand box to realize external guiding of gas in the sand core;
the method specifically comprises the following steps:
the first step is as follows: dividing the cold core box sand core;
the cold core box sand core mold is divided along the bottom plane of the tappet jacking structure and is divided into an upper layer cam shaft sand core and a lower layer cam shaft sand core, the lower layer cam shaft sand core structure is mainly based on the tappet jacking lug, and the upper layer cam shaft sand core structure is mainly based on the cam shaft hole structure;
the second step: positioning a cold core box sand core;
all cold core box sand cores adopt a unified positioning reference at the bottom and the side of the outer mold, so that a box matching reference, a marking reference and a design reference of a machine body are unified, a lower layer camshaft sand core structure adopts a camshaft jacking hole conformal core head to position at the bottom of the outer mold, and an upper layer camshaft sand core and a lower layer camshaft sand core respectively position at the side of the outer mold along a camshaft observation window to outwards eject the core head;
the third step: manufacturing a cold box sand core;
establishing a three-dimensional model, reasonably dividing loose pieces in a cold core box sand core, processing by adopting an NC technology according to the three-dimensional solid model, and measuring the shape and position dimensions of a mould by adopting a three-coordinate measuring instrument;
the fourth step: cold iron setting;
the inner side and the end surface of a camshaft hole and the outer side surface of a cylinder cover bolt hole lug are chilled by adopting external cold irons, a tappet jacking structure part of the camshaft adopts the external cold irons to break a hot spot part, and the inner part of the jacking hole lug adopts inner cold irons to directly impact the central part of the hot spot, so that the hot spot of the thick part of the camshaft is eliminated;
the fifth step: a core making process;
1) Preparing: checking and setting a core box, a tool, a gas path, raw sand control, a resin component distribution ratio, sand shooting pressure and air blowing pressure;
2) The process comprises the following steps:
the method is implemented according to the process steps of material preparation, sand mixing, resin sand blowing into a core box, core solidification, ammonia odor removal and mold opening and core taking;
and a sixth step: an air outlet channel;
drilling a hole to a preset depth of a key part in the cold core box sand core along the direction of the core head of the cold core box sand core, communicating an air outlet channel in the cold core box sand core, and connecting the part on the side surface of the core head of the cold core box sand core with an air outlet hole on the side surface of an upper sand box through a nylon rope to realize the outward guiding of air in the sand core;
the seventh step: and (3) storing the cold box sand core: storing in a dry place, wherein the storage time is not more than 48 hours when the air relative humidity RH is more than 80%, and the storage time is not more than one week when the air relative humidity RH is less than 80%;
the eighth step: coating;
the sand core is coated with alcohol-based zircon powder coating with the Baume degree of 60-65 for the first time by using the alcohol-based coating, then the mixture is ignited, and after the sand core is extinguished, the surface of the sand core is cooled to room temperature and then is polished to be flat; secondly, coating alcohol group zircon powder coating with the Baume degree of 40-45, then igniting, thirdly coating alcohol group zircon powder coating with the Baume degree of 40-45, and paying attention to the fact that the head of the sand core cannot be coated with the coating, wherein no flow mark exists on the surface of the casting mould after coating;
the ninth step: and (3) drying the sand core: the drying temperature of the cold box sand core is 160-180 ℃, and the heat preservation time is 2 hours;
the tenth step: and (5) preparing a box and pouring.
In the first step, the structure of the cold core box sand core is as follows:
1) A sand shooting position;
the sand shooting surface of the lower camshaft sand core is selected to be downward from the bottom plane of the tappet jacking lug, and the sand shooting surface of the upper camshaft sand core is selected to be downward from the plane of the crankshaft cavity;
2) A sand shooting nozzle;
the quantity and arrangement of the sand shooting nozzles are based on the trend of the air flow, so that the sand flow is fully filled in the sand shooting process, the whole sand core is ensured to be compact, and the catalyst can uniformly reach each part of the sand core and is properly positioned;
calculating the area of the sand shooting nozzle:
sand jet nozzle area S Shooting device = kg (core weight) x 2.2 pounds per kg x (minimum area) square inch per pound.
Area minimum law: large, heavy sand cores require at least 0.2 square inches per pound of sand.
3) Air intake and exhaust;
the quantity and arrangement of the air inlet and exhaust plugs are ensured to ensure that the whole sand core is compact, and the catalyst can uniformly reach each part of the sand core; the exhaust hole is arranged at the sand flow intersection, the deep recess and the deepest part of the core box at proper positions so as to achieve the purpose of obtaining a complete sand core; the area of the exhaust hole is smaller than that of the air inlet hole, and the exhaust plug is far away from the air inlet hole and cannot be arranged right below the sand shooting nozzle;
calculating the areas of the air inlet and the air outlet:
air inlet area S Go into = kg (core weight) x 2.2 lb/kg x (minimum area) square inch/lb;
area S of exhaust port Row board = (core weight) kg × 2.2 lb/kg × (minimum area) square inch/lb × factor;
area minimum law: the air inlet area of the large sand core is at least 0.25 square inch per pound, the exhaust area is smaller than the air inlet area and is 60-80% of the air inlet area;
in addition, the reasonable design of sealing structure, drawing inclination, machining allowance, process correction and mud core clearance is carried out on the sand core of the cold core box.
In the fourth step, the external chill is made of cast iron, the working surface is required to be smooth and flat without pore defects, shot blasting is carried out before use, and a certain drawing slope is arranged around the working surface to ensure the stability of the chill in the sand core;
1) External chill:
the calculation process of the thickness dimension T of the external chilling blocks at different positions is as follows:
T＝t·T heat node ；
In the above formula, t is the thickness coefficient, t is more than or equal to 0.3 and less than or equal to 1.0 Heat node The wall thickness or the diameter of the thermal knuckle circle of the casting;
according to the specific positions, shapes and sizes of different hot spot positions in the camshaft cavity, the arrangement of the chilling blocks of each core box is carried out:
2) Internal chill:
the material of the internal chill is low-carbon steel, rust removal is carried out in hydrochloric acid after processing meets the requirements, tinning treatment is carried out after cleaning with clear water, and the internal chill is stably placed at the corresponding position of the sand core in the box matching process;
the calculation process of the size d of the internal chill is as follows:
d＝p·T heat node ；
In the above formula, p is a thickness coefficient, p is more than or equal to 0.3 and less than or equal to 1.0 Heat node The wall thickness of the casting or the diameter of the thermal knuckle circle.
Compared with the prior art, the invention has the advantages that:
1. the scheme follows the machine body design integration principle, the cold box is adopted to separately make cores at different functional parts of the camshaft cavity of the machine body, and the core outlet head of the side window of the machine body, the sand core of the main body of the machine body and the like are utilized to jointly position on the side surface of the outer die by adopting a unified reference, so that the integral positioning of key size elements of the different functional parts of the machine body is realized, and the size precision and the surface quality of the machine body are improved;
2. according to the scheme, for the large isolated hot spot of the tappet jacking structure existing at the camshaft part, the method that the external chill divides the hot spot from the middle part and the internal chill directly hits the central part of the hot spot is adopted to eliminate, so that the dense and defect-free interior of the thick and large isolated hot spot at the key part of the camshaft of the engine body is realized;
3. the scheme is characterized in that the structure is complex, the whole size is large and the sand core is relatively isolated from the outside, a large amount of gas generated after molten iron is coated cannot be discharged out of a cavity in time, a large-power pistol drill and a lengthened drill bit are adopted for drilling, the internal gas channel of the thick and large cold box sand core is connected into a net, a nylon rope is laid upwards on the side face of the core head of the sand core along an external mold, a casting mold is led out through the gas outlet hole on the side face of an upper sand box, internal gas leading-out of the bottom complex sand core of a large machine body is realized, and the problem of gas hole quality existing in the shaft hole part of a camshaft after the cold box sand core is adopted is solved.
Drawings
FIG. 1 is a schematic view of the arrangement structure of a cold box sand core in a machine body mold according to the present invention;
FIG. 2 is a sectional view of the structure taken along line B-B in FIG. 1 according to the present invention;
FIG. 3 is a cross-sectional view of the structure of FIG. 1 taken along line C-C;
FIG. 4 is a sectional view of the structure of FIG. 1 taken along line D-D.
Detailed Description
Embodiments of the present invention are described below with reference to fig. 1-4.
A manufacturing method of a complex camshaft cold box sand core of a large diesel engine body utilizes a core shooting machine cold box to make a core, and the core sand has the advantages of low gas evolution, good fluidity, easiness in molding and compaction, difficult deformation of the core box, high size precision of the sand core, smooth surface, collapsibility and good deformability, and realizes the integral positioning of key size elements of different functional parts of the engine body on the side surface of an outer die; according to the specific shape, position and size of the camshaft part, an inner chill and an outer chill are adopted to balance the thermal junctions of the thick and large isolated parts; the air channels in the cold core box sand core are connected to form a net, and the air channels in the sand core are connected with the air outlet hole in the side surface of the upper sand box, so that the air in the sand core is led out, and the size precision and the internal and external quality of the machine body are improved. The present embodiment is specifically described by taking a core making method of a certain type of diesel engine as an example, and specifically includes the following steps:
the first step is as follows: dividing the cold core box sand core;
the camshaft cavity is an important part of a machine body, the profile of the die is large, the dimensional control requirement precision is high, the internal shape is complex, the structural form of the die is advanced, reliable and reasonable while the strength, rigidity and appearance quality of the die are ensured, and the die has good service performance, safety, maintainability and certain production efficiency.
The cold core box sand core mold is divided along the bottom plane of the tappet jacking structure 2 and is divided into an upper layer cam shaft sand core 3 and a lower layer cam shaft sand core 4, the lower layer cam shaft sand core 4 mainly adopts a tappet jacking lug, and the upper layer cam shaft sand core 3 mainly adopts a cam shaft hole structure 5;
1) A sand shooting position;
the sand shooting surface of the lower camshaft sand core 4 is selected to be downward from the bottom plane of the tappet jacking lug, and the sand shooting surface of the upper camshaft sand core 3 is selected to be downward from the plane of the crankshaft cavity;
2) A sand shooting nozzle;
the quantity and the arrangement of the sand shooting nozzles are according to the trend of the air flow, so that the sand flow is sufficient during sand shooting, the whole sand core is guaranteed to be compact, the catalyst can uniformly reach each part of the sand core, and the position is proper. The abrasion of the convex part of the cold core box is prevented, and the sand flow is prevented from directly rushing to the convex part of the cold core box, the inclined plane of the core box and the core drawing rod.
A large nozzle with a straight-through large inner diameter of 5/8-5/4 inches is usually adopted, and the sand blowing pressure, the sand speed, the abrasion and the cleaning are low, so that the service life of a core box is prolonged, and the compactness of the sand core is improved.
Calculating the area of the sand shooting nozzle:
sand jet nozzle area S Shooting device = kg (core weight) x 2.2 pounds per kg x (minimum area) square inch per pound.
Area minimum law: large, heavy sand cores require at least 0.2 square inches per pound of sand.
For the diesel engine of the type in this embodiment,
the minimum area is actually selected: 0.25 square inches per pound of sand.
Lower camshaft psammitolite 4: (45 kg):
the area of a sand nozzle required by the lower camshaft sand core 4 is as follows: s. the Downward shooting ＝45×2.2×0.25＝24.8，
Actually selecting: 20 φ 5/4 "with an area of 24.5.
Wherein, the core head position sand shooting mouth phi 5/4' is divided into two rows, each row has 5, totally 10.
The sand shooting nozzles phi 5/4' are arranged in the mold, and are divided into two rows, 5 sand shooting nozzles are arranged in each row, 10 sand shooting nozzles are arranged in total, and the sand shooting nozzles are uniformly arranged according to specific shapes.
Upper camshaft sand core 3: (55 kg):
the area of the sand nozzle required by the upper layer of camshaft sand core 3 is as follows: s Upward-emitting ＝55×2.2×0.25＝30.3，
Actually selecting: 25 φ 5/4 "with an area of 30.7.
Wherein, the core head is provided with sand shooting nozzles phi 5/4' which are divided into three rows, and each row is provided with 5 sand shooting nozzles, and the number of the sand shooting nozzles is 15.
The sand shooting nozzles phi 5/4' are arranged in the mould, and are divided into two rows, 5 sand shooting nozzles are arranged in each row, and 10 sand shooting nozzles are arranged uniformly according to specific shapes.
3) Air intake and exhaust;
positive pressure is required in the core box cavity to promote ammonia gas to permeate into the mixture of the sand, one side of the sand core is fully filled with catalyst gas, and the size and the position of the exhaust holes are reasonably arranged to ensure that the gas uniformly passes through the sand core. The number and arrangement of the air inlet and exhaust plugs are to ensure that the whole sand core is compact and that the catalyst can uniformly reach each part of the sand core.
The air exhaust is the key of the cold core box, and is the key for determining the molding and appearance quality of the sand core, and the position of the air exhaust hole is appropriate to be placed at the sand flow intersection, the deep recess and the deepest part of the core box as far as possible to achieve the purpose of obtaining the complete sand core. The area of the exhaust hole is smaller than that of the air inlet hole, and the area of the exhaust hole is 60-80% of that of the air inlet hole. The air vent plug is far away from the air inlet and cannot be arranged under the sand shooting nozzle, so that the situation that the sand core cannot be effectively hardened due to the fact that the flow path of triethylamine is short through the core sand is avoided.
Calculating the areas of the air inlet and the air outlet:
air inlet area S Go into = (core weight) kg x 2.2 pounds/kg x (minimum area) square inch/pound
Area S of exhaust port Row board = (core weight) kg × 2.2 lb/kg × (minimum area) square inch/lb × coefficient
Area minimum law: the large sand cores must have an air intake area of at least 0.25 square inches per pound, and the air exhaust area must be less than the air intake area, typically 60 to 80 percent of the air intake area.
For the diesel engine of the type in this embodiment,
actually selecting: the minimum inlet area is 0.25 square inches and the exhaust hole area is 60% of the inlet hole area.
Lower camshaft sand core 4 (45 kg):
the air inlet area required by the lower camshaft sand core 4 is as follows: s. the Advancing downwards ＝45×2.2×0.25＝24.8mm 2 ，
Actually selecting: 20 phi 5/4' with an area of 24.5mm 2 。
Wherein, the core head is provided with air inlet holes phi 5/4' and is divided into two rows, 5 air inlets are arranged in each row, and the total number of the air inlets is 10.
The inner position of the model is provided with air inlet holes phi 5/4' which are divided into two rows, each row comprises 5 air inlet holes, the number of the air inlet holes is 10, and the specific position of the air inlet holes is the same as that of the air inlet nozzle.
The lower camshaft sand core 4 needs the exhaust area: s. the Lower row of ＝24.5×0.6＝14.7mm 2 ，
Actually selecting: the diameter of the exhaust plug is phi 20mm, the number of the exhaust plugs is 30, and the area of the exhaust plug is 14.6mm 2 。
And (3) upper camshaft sand core 3: (55 Kg):
the required air inlet area of the upper layer camshaft sand core 3 is as follows: s. the Upper inlet ＝55×2.2×0.25＝30.3mm 2 ，
Actually selecting: 25 phi 5/4' with an area of 30.7mm 2 。
Wherein, the core head position air inlet hole phi 5/4 ", divide into three rows, 5 of each row, 15 totally.
The inner part of the model is provided with air inlet holes phi 5/4' which are divided into two rows, each row is provided with 5 air inlet holes, the number of the air inlet holes is 10, and the specific positions of the air inlet holes are the same as those of the air inlet nozzle.
The exhaust area required by the upper camshaft sand core 3 is as follows: s Upper row ＝30.7×0.6＝18.4mm 2
Actually selecting: the diameter of the exhaust plug is phi 20mm, the number of the exhaust plugs is 38, and the area of the exhaust plug is 18.5mm 2 。
In addition, the gap between the ejector rod and the ejector rod hole is also the main part of air exhaust, the gap (single side) between the ejector rod and the ejector rod hole is 0.10-0.15 mm, the size of the gap of the air exhaust plug is smaller than the diameter of sand grains and generally does not exceed 0.3mm, so that the core sand is prevented from entering the gap to cause blockage, and the gap is cleaned in time in the continuous core making process so as to avoid local sand core defects.
Designing parameters (a sand shooting position, a sand shooting area, an exhaust position, an exhaust area and the like) of a cold box sand core 1;
4) Sealing;
the sealing of the cold core box sand core 1 is the key for determining the sand core forming and the appearance quality, each core cavity is respectively sealed except the nozzle and the box surface, and the positioning pin and the reset rod are also required to be separately sealed.
5) Drawing the slope: the inclination of the drawing die is 7 degrees at the bottom core head part, the inclination of the drawing die is 3 degrees at the side core head part, and the inclination of the drawing die is 0 degree 30-1 degrees at other parts.
6) And (4) machining allowance: the bottom surface of the casting is 10mm, the side surface of the casting is 12mm, the inner hole of the camshaft is transited from 12mm to 15mm, and the rest inner holes are transited from 10mm to 12mm.
7) And (3) process correction: in order to prevent the position deviation of the drilled lug of the casting, the process correction amount around the drilled lug is 3mm. In order to prevent the dimension error of the width direction of the casting, the process correction amount of the plane on the inner side of the observation window is 2mm.
8) Clearance of the sand core: the clearance between the sand cores at the horizontal position is 1mm respectively, the clearance between the sand cores at the vertical position is 2mm at the lower part, the clearance between the sand cores and the bottom surface of the outer mold is 1mm at the outer mold, the clearance between the sand cores and the side surface of the outer mold is 2mm at the outer mold, and the sand filling surface of the sand core is provided with a core splitting negative number of 2mm. Considering the influence of the coating, the thickness of the unilateral coating layer of the sand core is 0.5mm. A sand collecting groove 6 with the size of 2 multiplied by 2mm is arranged at the bottom of the matching part of the external mold and the core print.
The second step is that: positioning a cold core box sand core;
the unification of the box matching reference, the scribing reference and the design reference is realized, and the key for the successful manufacture of the large complex machine body mold is realized. All cold core box sand cores adopt unified positioning reference at the bottom and the side of the external mold, so that the matching reference, the scribing reference and the design reference of the machine body are unified, the structure of the lower-layer camshaft sand core 4 adopts a camshaft jacking hole conformal core head to be positioned at the bottom of the external mold, and the upper-layer camshaft sand core and the lower-layer camshaft sand core respectively adopt outward core heads along a camshaft observation window to be positioned at the side of the external mold. And the inner cavity sand cores including the cam shaft, the main body, the cylinder hole, the air cavity and the like are uniformly positioned at the bottom and the side surface of the outer die, so that the integral positioning of key size elements of different parts of the machine body is realized, and the accuracy of the integral size is ensured.
1) A lower camshaft sand core;
aiming at a certain diesel engine in the embodiment, a positioning core head with the bottom surface of a camshaft (phi 114mm increases the machining allowance) of phi 90mm and communicated phi 90mm splayed holes with the following shape height of 30mm and the inclination of 7 degrees is positioned at the bottom of an outer die, the outer die is provided with a matching core seat, and the gap of the matching surface is 1mm. The side surface of the camshaft forms a core print with the length of 100mm along with the shape of the observation window of the camshaft. Wherein, the length of the positioning part on the side surface of the external mold is 50mm, the width of the positioning part on the side surface of the external mold is 140mm (the center of the core print is 70mm towards two sides respectively), and the three matching surfaces of the positioning part and the core print seat are inclined by 3 degrees. The external mold is provided with a matched core print, the clearance between the external mold and the three matching surfaces of the core print is 2mm, and the edge of the core print is provided with a sand collecting groove 6.
2) An upper camshaft sand core;
the side surface of the camshaft forms a core print along with the shape of a camshaft observation window, wherein the length of the positioning part and the side surface of the outer die is 50mm, the width of the positioning part and the side surface of the outer die is 140mm (the center of the core print is 70mm towards two sides respectively), and the three matching surfaces of the positioning part and the core print seat are inclined by 3 degrees. The outer die is provided with a matched core seat, and gaps of 2mm are formed between the outer die and the three matching surfaces of the core head.
The third step: manufacturing a cold box sand core;
and establishing a three-dimensional model, reasonably dividing the movable block in the sand core, processing by adopting an NC technology according to the three-dimensional entity model, and measuring the form and position dimensions of the die by adopting a three-coordinate measuring instrument.
Cold box mould structure: frame construction to reduce deformation, material: ZL107. The type of the core shooter matched with the core shooter: 100 liters.
The dimensional deviation of the working surface of the core box is manufactured according to GB/T1800.3-1998 tolerance and IT11 level precision in fit. The size deviation of the working surface of the core box is generally a negative value, the convex part is a positive value, the center distance of the lug boss is less than or equal to 500mm, and the size deviation is +/-0.15 mm. The center distance is more than 500mm, and the size deviation is +/-0.20 mm.
The surface roughness of the working surface, the parting surface and the loose piece matching surface of the die is Ra3.2um, the surface roughness of the positioning pin hole of the die is Ra1.6um, and the planeness of the parting surface of the die is less than 0.12mm. The thickness reserve of the coating layer is made according to the requirement of 0.5mm.
The sand shooting opening and the vent plug are required to ensure that the shooting core is compact, and the deformation of the mould is less than or equal to 0.2mm after the mould is used for one year.
The fifth step: setting a cold iron;
the chilling block plays an important role in accelerating the cooling speed of the hot spot part of the casting, increasing the temperature gradient of the surface and the center of the casting, balancing the temperature field of the whole casting and improving the utilization degree of graphitization expansion.
The inner side and the end face of the camshaft hole disassembly structure 5 and the outer side face of a cylinder cover bolt hole lug are chilled by adopting external cold irons, the hot spot part of the tappet jacking structure 2 of the camshaft is broken by adopting the external cold irons, and the hot spot at the thick part of the camshaft is eliminated by directly impacting the central part of the hot spot by adopting internal cold irons in the jacking hole lug.
The outer chill is made of cast iron, the working surface is required to be smooth and flat without pore defects, shot blasting is carried out before use, and in order to ensure the stability of the chill in the sand core, a certain pattern drawing slope is arranged around the working surface.
1) External chill:
the calculation process of the thickness dimension T of the chilling block at different parts is as follows:
T＝t·T heat node ；
In the above formula, t is the thickness coefficient, t is more than or equal to 0.3 and less than or equal to 1.0, and the T thermal node is the wall thickness of the casting or the diameter of the thermal node circle.
According to the specific positions, shapes and sizes of different hot spot positions in the camshaft cavity, the arrangement of the chilling blocks of each core box is carried out:
(1) 1# conformal chill 8: t is 1 ＝t 1 ·T Heat node 1 ，t 1 ＝0.75，T Heat node 1 =35, then T 1 =26.3, round, T 1 =25, the area is 80 multiplied by 80, and the number of the blocks is 1, and the blocks are placed at the side part of the upper layer camshaft hole;
(2) 2# conformal chill 9: t is 2 ＝t 2 ·T Thermal segment 2 ，t 2 ＝0.75，T Thermal segment 2 =35, then T 2 =26.3, round T 2 =25, the area is 80 multiplied by 80, and the number of the blocks is 1, and the blocks are placed at the side part of the upper layer camshaft hole;
(3) 3# Fan-shaped chiller 10: t is 3 ＝t 3 ·T Thermal segment 3 ，t 3 ＝0.75，T Thermal segment 3 =35, then T 3 =26.3, round T 3 =25, width 35, included angle 50 °, 2 pieces in number, placed at the side part of the upper cam shaft hole;
(4) No. 4 conformal chill 11: t is a unit of 4 ＝t 4 ·T Thermal segment 4 ，t 4 ＝0.75，T Thermal segment 4 =35, then T 4 =26.3, round T 4 And 4 blocks of =25, with an area of 60 × 50, are placed on the side surface of the upper cam shaft hole.
(5) No. 5 conformal chill 12: t is 5 ＝t 5 ·T Heat node 5 ，t 5 ＝0.50，T Heat node 5 =58, then T 5 =29, round T 5 =30, area 40 × 40, number 2, placed at the side tab position of the upper camshaft observation window.
(6) 6# conformal chill 13: t is a unit of 6 ＝t 6 ·T Heat node 6 ，t 6 ＝0.40，T Heat node 6 =75, then T 6 =30, area 85 × 65, number 2, and is placed at the side of the lug of the lower camshaft jacking structure.
(7) 7# conformal chill 14: t is 7 ＝t 7 ·T Thermal segment 7 ，t 7 ＝0.35，T Thermal segment 7 =95, then T 7 =33, round T 7 And the cam nut is placed on the side surface of a bolt hole lug 7 of a lower camshaft cylinder cover, wherein the area is 90 multiplied by 80, and the number of the cam nut is 1.
(8) No. 8 conformal chill 15: t is 8 ＝t 8 ·T Heat node 8 ，t 8 ＝0.35，T Heat node 8 =95, then T 8 =33, round T 8 And the camshaft is placed at the side part of a lug bolt hole lug of a lower camshaft cylinder cover, wherein the area is 90 multiplied by 40, and the number of the camshaft is 1.
(9) No. 9 conformal chill 16: t is 9 ＝t 9 ·T Thermal segment 9 ，t 9 ＝0.35，T Thermal segment 9 =95, then T 9 =33, round T 9 And the camshaft is placed at the side part of a lug bolt hole lug of a lower camshaft cylinder cover, wherein the area is 90 multiplied by 35, and the number of the camshaft is 1.
2) Internal chill:
the material of the internal chill is low-carbon steel, rust removal is carried out in hydrochloric acid (HCL) after processing meets the requirements, tinning treatment is carried out after cleaning with clear water, and the internal chill is stably arranged at the corresponding position of the sand core in the box matching process.
The calculation process of the size d of the internal chill is as follows:
d＝p·T heat node ；
In the above formula, p is a thickness coefficient, p is more than or equal to 0.3 and less than or equal to 1.0 Heat node The wall thickness of the casting or the diameter of the thermal knuckle circle.
Inner chill 17: d = p · T Heat node ，p＝0.25，T Heat node 1 =104, then d =31.2, rounded, d =30, then a diameter Φ 30mm, length 165mm, wherein the core head portion is 60mm long, 2 pieces in number.
Placing positions: the lower layer camshaft sand core jacking hole core head is inserted into the lower layer camshaft sand core jacking hole core head before box preparation, the insertion depth is 60mm, looseness is avoided, and the distance between the top surface of the inner chill and the top surface of the mud core is 10mm.
The fifth step: a core making process;
the general requirements of the cold box core making process control are as follows: the method takes the control of moisture hazard as a main consideration, and comprehensively controls the factors such as temperature, pressure, time, tooling, gas circuit and the like.
The cold box process air blowing solidification is the main process in the whole process, namely, under the conditions of certain temperature and pressure, the catalyst is atomized, and the whole cavity is filled and uniformly distributed after a certain period of time, so that the adhesive force is formed between sand grains and resin in the cavity, and two processes of sand shooting and air blowing are reasonably arranged, thereby being the key for ensuring the stable quality of the core making process.
1) Preparing;
(1) Core box and tool inspection: whether the inside of the core box is clean or not; whether the release agent is sprayed or not; whether the sand shooting class, the space between the upper core plate (ammonia blowing plate) and the upper core box and the lower core box are sealed or not and whether the sealing rings are aged or not; whether the sealing nozzle of the sand shooting nozzle is defective or not;
(2) Gas circuit inspection: whether a tail gas treatment system is normal or not and whether compressed air is dry or not, wherein the air leakage point under normal pressure is less than or equal to minus 45 ℃; the triethylamine generator is preheated to 90-110 ℃ (the gasification point of triethylamine is 87-89 ℃).
(3) Raw sand control: drying type scouring sand, granularity: 40/70, the content of SiO2 is more than or equal to 90 percent, the content of mud is less than or equal to 0.3 percent, the water content is less than or equal to 0.3 percent, and the content of micro powder is less than or equal to 0.5 percent. The sand temperature is required to be 0-40 ℃, the ideal temperature is 20-30 ℃, and the sand temperature is controlled to be 30-35 ℃ in winter. The sand temperature effect follows the 10 ℃ principle, i.e. every 10 ℃ increase in sand temperature will increase the resin reaction by 1 time, and likewise every 10 ℃ decrease in sand temperature will decrease the resin reaction by 1 time. And adjusting the addition of the resin according to the sand temperature.
(4) The proportion of resin components is controlled;
the cold box resin comprises a component I and a component II, wherein the component I is the cold box resin, and the main component of the cold box resin is formaldehyde-based phenolic resin; the component II activating agent comprises the main component of poly-iso-urethane, and the two components are both liquid, wherein the component I is light yellow, and the component II is dark brown. The resin should be stored in a shade place, and the component II should be strictly prevented from being mixed and contacted with water. The component I is increased, the initial strength is increased, and the toughness is reduced. The component II is increased, the medium strength is increased, the gas forming amount is increased, and the component I: the component II is (60-40)%: (40-60)% of the total weight of the composition.
(5) Sand shooting pressure;
in order to ensure the sand shooting to be tight, different sand shooting pressures are adopted, generally 0.2-0.5 MPa, and preferably 0.25-0.35 MPa. The lower sand shooting pressure can reduce the consumption of compressed air, reduce the abrasion of the core box, prolong the service life of the core box, reduce the number of core box venting plugs and reduce the manufacturing cost and the maintenance cost of the core box. Meanwhile, the stable filling of the core sand can keep the density and the size of the core sand consistent and prolong the service life of the core sand.
(6) Blowing pressure;
the ammonia blowing hardening is divided into two steps, ammonia is blown at low pressure, ammonia is introduced for hardening at 0.15-0.3 MPa, air is blown at high pressure, and exhaust cleaning is carried out at 0.2-0.3 MPa. When the catalyst is introduced, the core is not solidified, if the pressure is too high, the surface of the core is concave, and the pressure is too high and is maintained for enough time along with the solidification of the core, so that the catalyst penetrates through the section of the core to fully solidify the core, and on the one hand, the redundant catalyst is discharged from a cavity to obtain the core with a good surface.
2) The process comprises the following steps:
(1) Preparing materials;
raw sand: big forest sassafras scouring sand, granularity: 40/70, the content of SiO2 is more than or equal to 90 percent, the content of mud is less than or equal to 0.3 percent, the water content is less than or equal to 0.3 percent, and the content of micro powder is less than or equal to 0.5 percent. The sand temperature is 20-30 ℃.
Component i (phenolic resin): an HA resin 5388 which is a mixture of a plurality of resins,
component ii (isocyanate): an HA-activating agent (5828) is,
additive: VL14000.
(2) Sand mixing;
mixing raw sand, a component I, a component II and an additive, wherein the component I and the component II are mixed according to the proportion of 1:1, adding 1.2-1.5% of raw sand and 5% of additive, mixing for 30-60 s, and discharging.
(3) Blowing resin sand into the core box;
the sand shooting pressure of the lower camshaft sand core is 0.3MPa, and the sand shooting time is 3s; the sand shooting pressure of the sand core of the upper layer of the camshaft is 0.3MPa, and the sand shooting time is 3.5s.
(4) Curing the core: atomizing triethylamine, mixing with compressed air, and blowing gaseous ammonia for curing;
the ammonia blowing pressure of the lower camshaft sand core is 0.2MPa, the final pressure reaching time is 6s, and the ammonia blowing time is 5s; and the ammonia blowing pressure of the upper layer camshaft sand core is 0.2MPa, the final pressure time is 5s, and the ammonia blowing time is 6s.
(5) Removing ammonia odor: blowing compressed air for washing to purify residual air;
the air blowing pressure of the lower camshaft sand core is 0.3MPa, and the air blowing time is 10s; the air blowing pressure of the upper camshaft sand core is 0.3MPa, and the air blowing time is 15s.
(6) Opening the mould and coring.
Cold box core making technological parameters:
the rest core boxes are used for manual core making by resin sand, and the outer mold is molded by adopting a resin sand process.
The reaction process of the component I and the component II is cured in the first and the last stages, the gas-out intensity formed by rapid curing under the action of the catalyst only accounts for 50-75% of the whole final intensity, and 25-50% of the intensity needs to be formed in the later stage, so that the coating time, the drying temperature, the storage time, the temperature and the humidity need to be controlled in order to ensure that a formed mold core is not damaged and the final intensity is smoothly formed.
And a sixth step: an air outlet channel;
the large diesel engine body is a large complex iron casting, the inner cavity is complex, particularly, the camshaft is divided into an upper layer structure and a lower layer structure, a partition plate, a jacking structure, a camshaft shaft hole and the like are arranged in the camshaft, and the problem can be solved by pricking an air hole and embedding a nylon rope in manual core making. However, after core shooting by a core shooter, because the mud core has a complex structure, a large integral size and is relatively isolated from the outside, a large amount of air is generated after the molten iron is coated and cannot be effectively discharged out of a cavity to cause air blocking, so that the camshaft hole of the casting has air hole defects.
The air outlet channel inside the cold core box sand core is communicated by adopting an ultralong drill bit to drill to a preset depth (30-50 mm away from the outer surface of the important part of the sand core) of the key part inside the sand core along the direction of the core head of the sand core, the side part of the core head of the cold core box sand core is connected with the side air outlet hole of an upper sand box through a nylon rope 18, the periphery of the air outlet of the core head is sealed by mud strips, and the internal air outlet of the complex camshaft sand core of the core shooter of a large diesel engine body is led out.
An electric tool;
the model is as follows: JIZ-FF03-13B, a 13mm drill, 220V,800W,550r/min.
Drilling a bit: the drill bit is lengthened by a straight shank with the diameter of 12mm and the length of 500mm.
1) The lower camshaft sand core air outlet channel;
the method comprises the steps of horizontally placing the core head of the sand core, selecting the side surface of a cam shaft to position the geometric center of the core head, clamping a lengthened drill bit with the diameter of 12mm by using a 13mm electric drill, drilling inwards in parallel along the direction of the core head of the sand core with the depth of 165-170 mm, and then respectively inclining 35 degrees towards two sides in parallel along the direction of the core head of the sand core with the drilling depth of 205-210 mm.
The lower outlet passage 20 of the lower camshaft sand core is shown in fig. 4.
2) An air outlet channel of the upper layer camshaft sand core;
the head of the sand core is placed horizontally, a 13mm electric drill is used for clamping a lengthened drill bit with the diameter of 12mm, the center of a shaft hole of a camshaft is selected, and drilling is conducted inwards in parallel along the direction of the center of the shaft hole of the sand core until the shaft hole of the sand core is drilled through. Selecting the side surface of the camshaft to position the geometric center of the core print, and drilling inwards in parallel along the direction of the core print of the sand core with the depth of 365-370 mm. The core head of the sand core is parallel and deviated from the side with larger depth of the camshaft hole by 20 degrees, and the drilling depth is 390-395 mm. The side with smaller depth of the camshaft hole is parallel and deviated by 25 degrees along the direction of the core head of the sand core, and the drilling depth is 405-410 mm. After the air outlet channels are communicated with each other through compressed air inspection, the shaft hole of the camshaft is plugged by using molding sand, and the depth is about 30mm.
The upper layer air outlet channel 19 of the upper layer camshaft sand core is shown in figure 3.
The seventh step: storing the cold box sand core;
the cold core is easy to absorb moisture and should be stored in a dry place.
When the air relative humidity RH is more than 80%, the storage time is not more than 48 hours, and when the air relative humidity RH is less than 80%, the storage time is not more than one week.
The eighth step: coating;
the sand core is coated with alcohol-based coating, alcohol-based zircon powder coating with the Baume degree of 60-65 is coated for the first time and then ignited, and after the sand core is extinguished, the surface of the sand core is cooled to room temperature and then polished to be flat; the second time of painting alcohol group zircon powder coating with the Baume degree of 40-45, then igniting, the third time of painting alcohol group zircon powder coating with the Baume degree of 40-45, and after painting, the surface of the casting mould should not have flow marks. Note that the core head of the sand core cannot have paint.
The ninth step: drying the sand core;
drying in a drying kiln at 160-180 deg.c for 2 hr.
The tenth step: preparing a box and pouring;
before the lower-layer camshaft sand core 4 is assembled, a groove with the width of 20mm and the depth of 15mm is formed in the core head position on the side face of the lower-layer camshaft sand core 4 along the height direction, a nylon rope 18 with the diameter of 10mm is inserted into the core head position of the lower-layer camshaft sand core 4 by 60mm, the nylon rope is reserved by 800mm, and the nylon rope is expected to extend out of a middle sand box by 50-70 mm. The nylon rope 18 is fixed in the groove of the core head part by an iron nail, and then red mud is used for sealing treatment, so that iron liquid is prevented from drilling into the air outlet of the sand core in the pouring process.
And (2) inserting internal chill 17 with the diameter phi of 30mm and the length of 165mm into a core head of a jacking hole of the lower camshaft sand core 4, wherein the depth of the inserted core head is 6mm0, and the internal chill 17 is not loosened, and the top surface of the internal chill is 10mm away from the top surface of the mud core.
And a lower-layer camshaft sand core 4 is matched, and phi 4mm mud strips are laid on the core head part of the side surface of the lower-layer camshaft sand core of the outer die, so that on one hand, a certain gap is reserved between the sand core and the outer die, and the sand inclusion defect caused by sand core collapse is avoided. On the other hand, the air outlet part of the core head is sealed, so that molten iron is prevented from drilling into the air outlet hole of the sand core. Positioning is carried out in the corresponding core print on the bottom surface of the external mold by using a positioning core print with the following height of 30mm, the inclination of 7 degrees and the clearance of 1mm, and the side surface of the sand core is positioned at the position of the positioning core print with the length of 50mm, the width of 140mm, the inclination of 3 degrees and the clearance of 2mm on the side surface of the external mold and the position of the positioning core seat of the external mold. The side surface of the sample plate sand core and the wall thickness of the cylinder hole are 12mm, and the level of the core head of the sand core is checked by a level gauge.
Before the upper layer camshaft sand core 3 is matched, a groove with the width of 20mm and the depth of 15mm is formed in the core head position on the side face of the upper layer camshaft sand core along the height direction, a nylon rope with the diameter of 10mm is inserted into the core head position of the upper layer camshaft sand core by 60mm, the nylon rope with the diameter of 600mm is reserved outside, and the nylon rope is expected to extend out of a middle sand box by 50-70 mm. The nylon rope 18 is fixed in the groove of the core head part by an iron nail, and then red mud is used for sealing treatment, so that iron liquid is prevented from drilling into the air outlet of the sand core in the pouring process.
And matching the upper layer camshaft sand core 3, laying phi 4mm mud strips on the core head part on the side surface of the lower layer camshaft sand core, simultaneously sealing the air outlet part of the core head part, and positioning the positioning core head with the side surface of the sand core at the side surface of the external mold, wherein the positioning core head is 50mm in length, 140mm in width, 3 degrees in inclination and 2mm in gap, and the positioning core seat part of the external mold. The side surface of the sample plate sand core and the wall thickness of the cylinder hole are 12mm, and the level of the core head of the sand core is checked by a level meter.
And (3) sealing the air outlet parts of the upper and lower cam shafts by using mud strips in the process of falling into the main sand cores, leading the air outlet ropes of the upper and lower cam shafts out of the casting mold (extending 50-70 mm outwards) from the air outlet holes on the side surface of the middle sand box 21 before the middle sand box 21 is sleeved with the sand, filling the sand between the core heads on the side surfaces of the casting mold and the middle sand box 21 and leveling the sand, and closing the cover box after all the sand cores are assembled.
In order to prevent the loam core and the casting mold from getting damp and prevent the surface of the chilling block from absorbing moisture and influencing the quality of the casting, hot air is blown into the casting mold for drying before pouring, the hot air blowing time is 12 to 16 hours, and the casting mold temperature is 70 to 90 ℃.
In the pouring process, a torch is used for igniting the outward air outlet of the upper and lower cam shaft cavities at the middle sand box part, so that the air in the sand core can be smoothly discharged after the upper and lower cam shafts are coated with molten iron, and the defect of air holes caused by air blocking is avoided.
The invention solves the casting defects of thin wall of a camshaft and a crankshaft observation window, drill through of a lug, deviation of a drill hole from a center, shrinkage of a thick large part, air holes of a camshaft shaft hole and the like after processing, and has stable mass production quality, and greatly improves the size precision and the surface quality of the engine body.
The above-mentioned embodiments are only preferred embodiments of the present invention, and should not be used to limit the scope of the present invention, so that all equivalent changes made by the contents of the claims of the present invention should be included in the scope of the claims of the present invention.
Claims (2)
1. The method for casting the complex camshaft cold core box sand core by using the large diesel engine body is characterized by comprising the following steps of: the cold box of a core shooter is used for core making, and the whole positioning of key size factors of different functional parts of the machine body is realized on the side surface of the outer die; according to the specific shape, position and size of the camshaft part, an inner chill and an outer chill are adopted to balance the thermal junctions of the thick and large isolated parts; connecting an internal gas channel of the cold core box sand core to form a net, and connecting the gas channel of the sand core with a side gas outlet hole of an upper sand box to realize external guiding of gas in the sand core;
the method specifically comprises the following steps:
the first step is as follows: cold box core division
The cold core box sand core mold is divided along the bottom plane of the tappet jacking structure and is divided into an upper layer cam shaft sand core and a lower layer cam shaft sand core, the lower layer cam shaft sand core structure is mainly based on the tappet jacking lug, and the upper layer cam shaft sand core structure is mainly based on the cam shaft hole structure;
the second step is that: cold box sand core positioning
All cold core box sand cores adopt a unified positioning reference at the bottom and the side of the external mold, so that the matching reference, the scribing reference and the design reference of the machine body are unified, the lower layer camshaft sand core structure adopts a camshaft lifting hole conformal core head to position at the bottom of the external mold, and the upper layer camshaft sand core and the lower layer camshaft sand core respectively outwards extrude the core head along a camshaft observation window to position at the side of the external mold;
the third step: cold box sand core manufacturing method
Establishing a three-dimensional model, reasonably dividing loose pieces in a cold core box sand core, processing by adopting an NC technology according to the three-dimensional solid model, and measuring the shape and position dimensions of a mould by adopting a three-coordinate measuring instrument;
the fourth step: chill arrangement
The inner side and the end surface of a camshaft hole and the outer side surface of a cylinder cover bolt hole lug are chilled by adopting external cold irons, a tappet jacking structure part of the camshaft adopts the external cold irons to break a hot spot part, and the inner part of the jacking hole lug adopts inner cold irons to directly impact the central part of the hot spot, so that the hot spot of the thick part of the camshaft is eliminated;
the fifth step: core making process
1) Preparing: checking and setting a core box, a tool, a gas path, raw sand control, a resin component distribution ratio, sand shooting pressure and air blowing pressure;
2) The process comprises the following steps:
the method is implemented according to the process steps of material preparation, sand mixing, resin sand blowing into a core box, core solidification, ammonia odor removal and mold opening and core taking;
and a sixth step: an air outlet channel: drilling a hole to a preset depth of a key part in the cold core box sand core along the direction of the core head of the cold core box sand core, communicating an air outlet channel in the cold core box sand core, and connecting the part on the side surface of the core head of the cold core box sand core with an air outlet hole on the side surface of an upper sand box through a nylon rope to realize the outward guiding of air in the sand core;
the seventh step: and (3) storing the cold box sand core: storing in a dry place for not more than 48 hours when the air relative humidity RH is greater than 80%, and not more than one week when the air relative humidity RH is less than 80%;
eighth step: coating: the sand core is coated with alcohol-based zircon powder coating with the Baume degree of 60-65 for the first time by using the alcohol-based coating, then the mixture is ignited, and after the sand core is extinguished, the surface of the sand core is cooled to room temperature and then is polished to be flat; secondly, coating alcohol group zircon powder coating with the Baume degree of 40-45, then igniting, thirdly coating alcohol group zircon powder coating with the Baume degree of 40-45, and paying attention to the fact that the head of the sand core cannot be coated with the coating, wherein no flow mark exists on the surface of the casting mould after coating;
the ninth step: and (3) drying the sand core: the drying temperature of the cold box sand core is 160-180 ℃, and the heat preservation time is 2 hours;
the tenth step: preparing a box and pouring;
in the first step, the structure of the cold core box sand core is as follows:
1) Sand shooting position
The sand shooting surface of the lower camshaft sand core is selected to be downward from the bottom plane of the tappet jacking lug, and the sand shooting surface of the upper camshaft sand core is selected to be downward from the plane of the crankshaft cavity;
2) Sand shooting nozzle
The quantity and arrangement of the sand shooting nozzles are based on the trend of the air flow, so that the sand flow is fully filled in the sand shooting process, the whole sand core is ensured to be compact, and the catalyst can uniformly reach each part of the sand core and is properly positioned;
calculating the area of the sand shooting nozzle:
sand jet area S Shooting device = core weight kg x 2.2 lb/kg x minimum area square inch/lb;
area minimum law: large, heavy sand cores require at least 0.2 square inches per pound of sand;
3) Air intake and exhaust
The number and arrangement of the air inlet and exhaust plugs are ensured to ensure that the whole sand core is compact, and the catalyst can uniformly reach each part of the sand core; the exhaust hole is arranged at the sand flow intersection, the deep recess and the deepest part of the core box at proper positions so as to achieve the purpose of obtaining a complete sand core; the area of the exhaust hole is smaller than that of the air inlet hole, and the exhaust plug is far away from the air inlet hole and cannot be arranged right below the sand shooting nozzle;
calculating the areas of the air inlet and the air outlet:
air inlet area S Into = core weight kg x 2.2 lb/kg x minimum area square inch/lb
Area S of exhaust port Row board = core weight kg × 2.2 lb/kg × minimum area square inch/lb × coefficient
Area minimum law: the air inlet area of the large sand core is at least 0.25 square inch per pound, the exhaust area is smaller than the air inlet area and is 60-80% of the air inlet area;
in addition, the reasonable design of sealing structure, drawing inclination, machining allowance, process correction and mud core clearance is carried out on the sand core of the cold core box.
2. The method for casting by using the large diesel engine body complex camshaft cold core box sand core as claimed in claim 1, wherein the method comprises the following steps: in the fourth step, the external chill is made of cast iron, the working surface is required to be smooth and flat without pore defects, shot blasting is carried out before use, and a certain drawing slope is arranged around the working surface to ensure the stability of the chill in the sand core;
1) External chilling:
the calculation process of the thickness dimension T of the external chilling blocks at different positions is as follows:
T＝t·T heat node
In the above formula, t is a thickness coefficient, t is not less than 0.3 and not more than 1.0 Heat node The wall thickness or the diameter of the thermal knuckle circle of the casting;
according to the specific positions, shapes and sizes of different hot spot positions in the camshaft cavity, the arrangement of the chilling blocks of each core box is carried out:
2) Internal chill:
the material of the internal chill is low-carbon steel, rust removal is carried out in hydrochloric acid after processing meets the requirements, tinning treatment is carried out after cleaning with clear water, and the internal chill is stably placed at the corresponding position of the sand core in the box matching process;
the calculation process of the size d of the internal chill is as follows:
d＝p·T heat node
In the above formula, p is a thickness coefficient, p is more than or equal to 0.3 and less than or equal to 1.0 Heat node The wall thickness of the casting or the diameter of the thermal knuckle circle.
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