CN1265914C - Integral easting method of cast steel supporting roller - Google Patents

Abstract

The invention relates to an integral casting process of cast steel support rolls, in particular to an integral casting method of cast steel support rolls. The present invention adopts advanced gating system design principles, iron mold sand-coating technology, tangential inner gate rotary filling method, thermal insulation riser technology; it uses computer simulation technology to reasonably design metal molds, and uses iron mold sand coating And thermal insulation riser technology realizes the sequential solidification of castings, and adopts a new gating system and tangential ingate rotary filling to prevent entrainment and inclusions, and through the control of key process parameters, the product quality of large-scale roll castings is guaranteed , Produced high-quality cast steel backup rolls without defects, which are suitable for the overall casting process of various types and specifications of cast steel, cast iron backup rolls, and work rolls, making it possible to localize large cast steel backup rolls.

Description

Integral Casting Method of Cast Steel Backup Roll

technical field

The invention relates to an integral casting process of cast steel supporting rolls, in particular to an integral casting method of cast steel supporting rolls. It is suitable for the overall casting process of various types and specifications of cast steel, cast iron backup rolls and work rolls.

Background technique

At present, the metallurgical industry is developing rapidly, and the demand for various steel products is increasing day by day. my country's steel output has already ranked first in the world. The rolling process has achieved large-scale, high-speed and continuous production. The quality of the roll, the largest consumable in the rolling production line, directly affects the efficiency and cost of rolling. There are many hot rolling production lines and cold rolling production lines in China, which consume a large number of work rolls and backup rolls every year.

There are forged steel rolls and cast steel rolls for the active work rolls and back-up rolls in the steel rolling production line. Back-up rolls made of traditional materials are difficult to meet the requirements of high strength and high wear resistance. The newly developed low-alloy chromium steel overcomes this difficulty. For example, Anshan Iron and Steel's 1780 hot-rolled strip steel production line uses chrome steel backup rolls.

The increase of chromium content in the alloy brings many difficulties to casting. The key technology of large cast steel backup rolls, especially the cast steel backup rolls with a Cr content of 4% or more than 4%, has not yet been broken through. Therefore, the large cast steel backup rolls used online all rely on imports, or use forging instead of casting. The back-up roll produced by the forging method has a long production cycle and high cost, which increases a lot of expenses.

The Davy Roll Co., Ltd., Sheffield Roll Factory in the UK and the Midland Roll Factory in the United States all use the integral casting process to produce 40Cr4 large cast steel backup rolls. Japan, South Korea, and Germany have also developed

related technologies.

In this case, the development of integral casting technology for cast steel backup rolls will undoubtedly be welcomed by manufacturers and users, and the localization of large cast steel backup rolls will be realized.

Contents of the invention

The object of the present invention is to provide an integral casting method of a cast steel backing roll which can guarantee the quality and improve the performance and service life of the casting.

The present invention is an integral casting technology for cast steel backup rolls, and its main contents include: computer simulation, iron mold covered with sand, tangential inner gate rotary filling, thermal insulation riser technology; using new pouring system design principles and sequential solidification principles to carry out Gating system design and casting mold design; determination principles of key process parameters.

(1) Computer simulation technology: In the actual pouring process, it is difficult for us to observe the details of the pouring process. Using computer to simulate the filling process, the movement state of molten metal at different times can be observed. The computer simulation results show that the new gating system is used to fill the runner with the molten metal during the filling process without creating voids. The tangential inner gate bottom pouring is adopted, and the molten metal rises steadily without turbulent flow. The simulation software is View Cast software.

The numerical simulation of the solidification process can observe the temperature field, solid fraction field, etc. of the casting. According to the simulation results of the temperature field, the solidification sequence of the castings can be determined, and whether the feeding channel is unblocked; the shrinkage sequence of the castings can also be determined according to the thickness of the shell. According to the simulation results of the temperature field, the appropriate insulation material and the corresponding dosage can be selected. The numerical simulation of the stress in the solidification process can observe the stress-strain field of the casting, the shrinkage of the casting, etc. According to the stress simulation results, the tendency of hot cracking of castings during solidification can be predicted. Using these simulation results for process design reduces the blindness of work.

(2) Tangential inner gate rotary filling: The molten metal enters the cavity in a tangential form and rotates continuously in the cylindrical cavity. Due to centrifugal force, inclusions with lighter density gather toward the center and float up with the rise of molten metal. Finally, all the inclusions float into the riser, which ensures the purity of the molten metal in the casting. Utilizing this ingate for pouring significantly reduces the probability of inclusions in the casting.

(3) Iron mold sand-coating technology: the inner surface of the lower roll neck and roll body iron mold is covered with 10-30mm thick chromite sand. The surface of the iron mold of the roller body is covered with chromite sand, which can not only ensure a sufficient depth of the surface columnar grain structure working layer, but also reduce the thermal impact of the molten metal on the iron mold and increase the service life of the iron mold. The surface of the lower roll neck is coated with chromite sand, mainly to increase the concession and reduce the crack tendency of the casting. At the same time, it also reduces the thermal fatigue on the surface of the iron mold.

(4) Insulation riser technology: The insulation riser has a strong feeding effect. The common riser with the same feeding capacity is 20-40% larger than the thermal insulation riser, and the large riser is not conducive to the retreat of the casting when it solidifies and shrinks. The thermal insulation riser can properly reduce the volume, increase the feeding capacity, and reduce the possibility of shrinkage cavity and porosity of the casting. The upper part of the riser retracts inward, its taper is 1-5%, the diameter of its root is the same as that of the top of the upper roll neck, and the height-to-diameter ratio of the riser is 1.4:1-1.7:1. The riser is surrounded by insulation boards, and after the pouring is completed, the upper surface is covered with a heating insulation agent, and the thickness is between 100 and 300mm.

(5) Design of iron mold: The wall thickness of the iron mold is different, and the chilling capacity is different. In order to ensure the sequential solidification of castings from bottom to top, the iron mold is required to be gradually thinned from bottom to top. Using computer simulation technology to determine the iron mold thickness of each part between 120mm ~ 500mm, to ensure the sequential solidification of castings. Simulation software can use View Cast software.

(6) Determination principles of key process parameters:

(1) Determination of pouring temperature. The pouring temperature of large steel castings is set with reference to the liquidus temperature of the alloy. If the pouring temperature is too high, the molten metal will be seriously oxidized; if the pouring temperature is too low, harmful impurities in the molten metal will not easily float. Therefore, when setting the pouring temperature, generally the superheat degree selected for large parts is relatively small, and the superheat degree selected for small parts is relatively large. The degree of superheat is generally 50-80°C.

(II) Selection of pouring speed. If the pouring speed of large castings is too fast, defects such as air entrainment and inclusions may occur, especially for tall castings such as rolls, if the pouring speed is too fast, it will cause severe erosion to the mold wall; if the pouring speed is too slow, there will be insufficient pouring, and cold Defects occur at intervals. Since the inner cavity of the cast steel support roller is relatively high, if the pouring speed is too slow, it will inevitably cause the molten metal to bake the mold wall for a long time, especially the sand covering on the iron mold. disintegrate and crumble. So pouring too slowly is dangerous. Considering the influence of various factors comprehensively, the pouring speed is 8-10 tons/min.

(III) Control of mold temperature. The temperature of the mold plays a big role in the pouring process of the casting. If the temperature is too high, the mold will not have a chilling effect on the molten metal. Especially in the production process of cast steel backup rolls, it is necessary to control the mold temperature, because the outer layer of the cast steel backup roll body only has a certain depth of columnar crystal structure, in order to ensure a sufficient depth of the working layer after heat treatment. If the mold temperature is too high and the chilling capacity is not enough, too many coarse equiaxed grains will be formed, which will deteriorate the casting structure. In the subsequent heat treatment process, the outer layer of the roll body will not be able to obtain a sufficiently thick hardened layer. If the mold temperature is too low, it will cause the sand mold to absorb moisture, and it is easy to generate gas during pouring, forming pore defects. Sometimes when the pouring temperature is low, defects such as cold shut and insufficient pouring may also occur due to the insufficient temperature of the mold. Therefore, it is also very important to ensure that the mold has an appropriate mold temperature before pouring. After the molding of each part is completed, preheat the kiln uniformly. The preheating temperature of the mold is 50-100°C. After the mold is preheated to the temperature, it is assembled;

(IV) Boxing time. Different castings have different boxing time and different boxing temperature. Some castings need to be boxed at high temperature, and some castings need to be boxed at low temperature. The rolls are generally boxed at high temperature, and the boxing time can be calculated according to the formula: the shortest boxing time (h)t=D×2.8%-3, the longest boxing time (h)t=D×3.2%-3, where D is the cast steel backup roll diameter (mm).

The present invention has following beneficial effects:

1. The present invention adopts advanced gating system design principles, iron mold sand-covering technology, tangential ingate rotary filling method, and thermal insulation riser technology; the casting mold is designed by applying computer simulation technology, and the sequential solidification of castings is realized. The key process parameters are reasonably determined, and high-quality cast steel backup rolls without defects are produced, which are suitable for the integral casting process of cast steel and cast iron rolls of various types and specifications, making it possible to localize large cast steel backup rolls.

2. The present invention adopts computer simulation technology, which increases the rationality of design, shortens the production cycle of castings, and improves productivity.

3. The present invention adopts the advanced gating system design principle to keep the molten metal in the gating system in a full state all the time, preventing air entrainment and inclusion.

4. The invention adopts the tangential inner gate rotary casting technology, the molten metal rotates smoothly in the cavity, and the inclusions gather toward the center due to the centrifugal effect. The inclusions can neither adhere to the surface of the casting nor stay in the center of the casting, and the inclusions finally float up into the riser smoothly. Therefore, both the surface quality and the core quality of the casting are guaranteed.

5. The casting of the present invention adopts the iron mold sand-coating technology, and the surface of the casting mold is covered with chromite sand, which can not only prevent cracks in the casting, but also obtain a dense working layer with a certain thickness. While adjusting the cooling capacity of the mold, the service life of the mold is increased and the production cost is reduced.

6. The invention fully realizes the sequential solidification of castings, eliminates defects such as cracks and porosity, and improves the performance and service life of castings.

7. In the present invention, iron molds are used for the lower roll neck and roll body, and sand molds are used for the upper roll neck and riser to realize sequential solidification and eliminate defects such as shrinkage cavities, looseness, and cracks.

Description of drawings

Fig. 1 schematic diagram of traditional process;

Among them: 1-lower roll neck iron mold 2-roller 3-roll body iron mold 4-sliding roll neck pad iron 5-sliding roll neck 6-upper roll neck iron mold 7-riser box 8-electric heating riser box Grounding steel plate 9-tapered sprue cup 10-sprue 11-sand 12-sprue

Fig. 2 process schematic diagram of the present invention;

Among them: 13-Iron mold 14-Roll 15-Sand 16-Insulation board 17-Heating insulation covering agent 18-Sprue cup 19-Stop rod 20-Sprue 21-Transition arc between sprue and runner 22 - Sprue arc brick 23- Cross sprue 24- Drum turn 25- Boss 26- Sprue cup outlet

Fig. 3 Flow field simulation result diagram during mold filling process;

Fig. 4 temperature field simulation result diagram during solidification;

Fig. 5 simulation results of shrinkage cavity distribution;

Fig. 6 adopts the back-up roller blank photograph of casting of the present invention's new pouring system design process method;

Fig. 7 adopts the photo of the cast steel backup roll after machining produced by the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in Fig. 2, the schematic diagram of the casting process of the cast steel backup roll of the present invention. Among them, the pouring system mainly includes the sprue cup 18, and the sprue 20 and runner 23 connected thereto. , the sprue cup 18 is equipped with a plug rod 19 corresponding to the sprue cup outlet 25, and the outlet has a boss 25 protruding from the inner bottom of the sprue cup 18, which can ensure a good fit between the plug rod 19 and the sprue cup outlet 26 , when the molten metal is filled to the height of 1/2~1/3 of the sprue cup, open the stopper rod, the sprue 20 is a streamlined structure with a large top and a small bottom, and the corner of the sprue 20 and the runner 23 is a direct pouring The transition arc 21 between the runner and the runner, the fillet radius of the arc transition between the sprue 20 and the runner 23 is at least twice the diameter of the runner 23, and the arc is formed by the sprue arc brick 22 Formed, the barrel brick 24 that the outlet of the runner 23 communicates with the cavity is connected in a tangential manner. During the pouring process, control the stability of the filling and reduce the filling speed; keep the molten metal in the pouring system in a full state at all times to prevent the gas and oxide film from being involved in the molten metal, causing cracks and loose defects. According to the principle of equal flow , to design the size of the runner in the gating system. In addition, the outside of the riser on the roll 14 is followed by a thermal insulation board 16, sand 15, and iron mold 13, and a conventional heating and heat preservation covering agent 17 is placed on the top of the riser.

Example 1

The material of this embodiment is 40Cr4, and the liquidus temperature of this material is 1470°C. The pouring temperature is 1550°C, the weight of the molten metal is 50 tons, and the pouring speed is 10 tons per minute. Its casting process is as follows:

1) Design the sprue cup and pouring system according to the principle of smooth filling, and use tangential ingate rotary pouring.

2) The sprue and runner are formed with chromite sand. The diameter of the sprue inlet is 130mm, the outlet diameter is 75mm, and the diameter of the runner is 75mm.

3) Both the roll body and the lower roll neck iron mold are covered with chromite sand, and the thickness of the sand layer is 10-30mm. The thickness of the iron mold at different parts is 120-500mm; the taper of the upper roll neck is 2%.

4) The thermal insulation riser should be surrounded by thermal insulation board 16, its root diameter is 1050mm, the upper part of the riser is retracted inward, the taper is 1%, and the height-to-diameter ratio of the riser is 1.4:1.

5) After the molding of each part is completed, preheat the kiln uniformly, and the preheating temperature is 100°C.

6) After the mold is preheated to the temperature, assemble it. Metal molds in different parts are positioned by seams and assembled together. After the pouring is completed, the upper surface is covered with a heating and thermal insulation covering agent with a thickness of 100mm.

7) The boxing process is a hot boxing process. The roll body diameter of the poured roll is 1435mm, and the boxing is done 42 hours after the casting.

The first pouring was successful, and the produced cast steel back-up rolls were mechanically processed and then ultrasonically tested, and there were no defects in the rolls, which fully met the relevant national standards. However, there are a few things to be aware of in practice. The surface quality of the lower roll neck casting is not very good, and it is difficult to box the riser box.

Example 2

The material is 40Cr4, the pouring temperature is 1520°C, the weight of the molten metal is 48 tons, and the pouring speed is 9 tons per minute. Its casting process is as follows:

1) The sprue cup and gating system are designed according to the principle of smooth filling, and the tangential ingate rotary pouring technology is still used.

2) Both the sprue and the runner are formed with shaped refractory bricks, and the base cavity is also formed with shaped barrel bricks 24, which form a tangential ingate with the runner. The diameter of the shaped barrel brick 24 is 350mm, and The height is 350mm. The diameter of the sprue inlet is 120mm, the outlet diameter is 70mm, and the diameter of the runner is 70mm.

3) Both the roll body and the lower roll neck iron mold are covered with chromite sand, and the thickness of the sand layer is 15-30mm. The thickness of the iron mold at different parts is 120-500mm; the taper of the upper roll neck is 2%.

4) The thermal insulation riser should be surrounded by thermal insulation boards, with resin sand as the back sand, the root diameter is 1000mm, the upper part of the riser is retracted inward, the taper is 3%, and the height-to-diameter ratio of the riser is 1.5:1.

5) After the molding of each part is completed, preheat the kiln uniformly, and the preheating temperature is 80°C.

6) After the mold is preheated to the temperature, assemble it. Metal molds in different parts are positioned by seams and assembled together. After the pouring is completed, the upper surface is covered with a heating and thermal insulation covering agent with a thickness of 150mm.

7) The boxing process is a hot boxing process. The roll body diameter of the poured roll is 1435 mm, and the boxing is performed 38 hours after the casting.

After pouring, it is easy to box the riser, and the surface quality of the lower roll neck has been significantly improved. Castings are of good quality.

Example 3

The material is 40Cr4, the pouring temperature is 1540°C, the weight of the molten metal is 47 tons, and the pouring speed is 8 tons per minute. Its casting process is as follows:

1) The sprue cup is designed according to the principle of smooth filling, and the tangential inner gate rotary pouring technology is still used.

2) Both the sprue and the runner are formed with shaped refractory bricks, and the base cavity is also formed with shaped barrel bricks 24, which form a tangential ingate with the runner. The diameter of the shaped barrel brick 24 is 350mm, and The height is 350mm. The diameter of the sprue inlet is 120mm, the outlet diameter is 65mm, and the diameter of the runner is 65mm.

3) Both the roll body and the lower roll neck iron mold are covered with chromite sand, and the thickness of the sand layer is 15-30mm. The thickness of iron molds in different parts is 120-500mm.

4) The thermal insulation riser should be surrounded by thermal insulation boards, and resin sand should be used as the back sand for the thermal insulation riser. The diameter of the root of the thermal insulation riser is 950mm, and the upper part of the riser is retracted inward, and its taper is increased from the original 1% to 5%. The height-to-diameter ratio of the riser is 1.7:1.

5) The taper of the upper roll neck is increased. Increased from the original 2% to 4%.

6) After the molding of each part is completed, preheat the kiln uniformly, and the preheating temperature is 50°C.

7) After the mold is preheated to the temperature, assemble it. Metal molds in different parts are positioned by seams and assembled together. After the pouring is completed, the upper surface is covered with a heating and thermal insulation covering agent with a thickness of 300mm.

8) The boxing process is a hot boxing process. The roll body diameter of the poured roll is 1435 mm, and the boxing is performed 40 hours after the casting.

After pouring, it is easy to unbox the riser, and it is also easy to unbox the upper roll neck. The quality of the upper roll neck has been significantly improved. The surface quality of the casting is good (see Figure 6). Adopt the cast steel supporting roller (referring to Fig. 7) after the machining of the production of the present invention.

Working process and result of the present invention:

When the invention is applied to casting cast steel support rolls, during the pouring process, the molten metal is always in a full state in the runner, leaving no space for gas, so defects such as gas entrainment and oxide film will not be formed. Castings achieve sequential solidification. Therefore, the large integral casting cast steel support roller produced by the present invention does not produce cracks and loose defects. The tangential inner gate is used for pouring, and the inclusions float up sufficiently, so there are no defects such as inclusions inside the casting. The flaw detection results are in full compliance with national standards.

The present invention can use a computer to simulate the filling process, and the simulation software uses View Cast software. Figure 3 shows the flow field simulation results during the filling process; Figure 4 shows the temperature field simulation results during the solidification process; Figure 5 shows the shrinkage cavity distribution simulation results.

comparative example

As shown in FIG. 1 , it is a schematic diagram of a traditional cast steel roll 2 integral casting process. The conical sprue cup 9 adopts a conical design, and the sprue 10 adopts steel pipe bricks with the same upper and lower diameters. A right-angle transition is adopted at the junction of the sprue 10 and the runner 12. There are two runners 12 with equal diameters. Brush the paint on the surface of the iron mold 3 of the roller body. The upper and lower roll neck iron molds 6 and 1 are covered with sand of 80-100mm, and the electric heating riser box 7, the grounding steel plate 8 of the electric heating riser box, the sliding roll neck pad iron 4, and the sliding roll neck 5 are used.

The disadvantages of this design are:

(1) The gating system cannot be filled, and there is a large space left for the molten metal to flow in the runner, which is easy to cause air entrainment and inclusion. The gas or inclusions involved can easily form the source of cracks in the casting. When the casting is under stress during cooling or heat treatment, it is likely to crack at the source of the crack.

(2) The mold design does not fully consider the sequential solidification problem. During the solidification process of the casting, it is easy to form stress concentration at the thermal junction of the upper and lower roll neck corners, resulting in crack defects.

Sliding roll neck technology is used both at home and abroad, but this technology needs to remove the sliding roll neck pad iron in a timely manner during the pouring process, so there are relatively large human factors in the operation. In actual operation, sometimes the horn cannot be removed.

Claims (10)

1. A method for integral casting of steel backup rolls, characterized in that the specific steps are as follows: 1) The sprue cup and pouring system are designed according to the principle of smooth filling, so that the molten metal is always in a full state in the pouring system, and the tangential inner gate is used for bottom pouring, and the molten metal is introduced in a tangential form. Rotate and rise in the cavity; 2) Casting mould: the lower roll neck and roll body are made of iron mold, the upper roll neck and riser are made of sand mold, the roll body and the lower roll neck iron mold are covered with chromite sand, the thickness of the sand layer is 10-30mm, different The thickness of the iron mold at the part is 120-500mm, and the wall thickness of the iron mold gradually decreases from bottom to top to achieve sequential solidification; 3) The thermal insulation riser should be surrounded by thermal insulation boards, its root diameter is the same as that of the top of the upper roll neck, the upper part of the riser is retracted inward, the taper of the riser is 1-5%, and the height-to-diameter ratio of the riser is 1.4:1-1.7:1 ; 4) After the molding of each part is completed, preheat the kiln uniformly, and the mold preheating temperature is 50-100°C; 5) After the mold is preheated to the temperature, assemble it; 6) The superheat of molten metal is 50-80°C, and the pouring speed is 8-10 tons/min; 7) The boxing process is a hot boxing process, and the boxing time is calculated according to the following formula, the shortest boxing time, the unit is h, t=D×2.8%-3, the longest boxing time, the unit is h, t=D ×3.2%-3, where D is the diameter of the cast steel backup roll, in mm. 2. The integral casting method for steel backup rolls according to claim 1, characterized in that: in said step 2), the thickness of the iron mold at each part is determined by computer simulation technology, and the thickness of the iron mold is between 120 mm and 500 mm. 3. The integral casting method for steel backup rolls according to claim 1, characterized in that in said step 5), metal molds at different positions are positioned by notches and assembled together. 4. The integral casting method for steel backup rolls according to claim 1, characterized in that: in the step 6), after the pouring is completed, the upper surface is covered with a heating and heat-preserving covering agent with a thickness of 100-300mm. 5. According to the integral casting method of steel backup rolls according to claim 1, it is characterized in that: in the step 6), computer simulation is used to simulate the filling and solidification process in the pouring process, and the solidification sequence of the castings is determined according to the simulation results of the temperature field Sequence, whether the feeding channel is smooth; determine the solidification sequence of the casting according to the thickness of the shell; select the appropriate thermal insulation material and the corresponding amount according to the simulation results of the temperature field; The state of motion in the mold, as well as the filling speed and filling time of the molten metal; observe the stress-strain field of the casting according to the stress numerical simulation of the solidification process, and predict the hot cracking tendency of the casting during the solidification process according to the stress simulation results. 6. The integral casting method for steel backup rolls according to claim 1, characterized in that: the taper of the upper roll neck is 2%-4%. 7. The integral casting method for steel backup rolls according to claim 1, characterized in that: in said step 1), the gating system includes a sprue cup (18), a sprue (20) and a horizontal sprue connected to it Road (23), the sprue cup (18) is an eccentric structure, the sprue cup (18) outlet is biased to the side of the sprue cup (18) center, and the sprue cup (18) is equipped with a device corresponding to the sprue cup outlet. The stopper rod (19), the sprue (20) is a streamlined structure with a large top and a small bottom, and the corner of the sprue (20) and the runner (23) is the transition arc between the sprue and the runner ( 21), the fillet radius of the arc transition between the sprue (20) and the runner (23) is at least twice the diameter of the runner (23), and the outlet of the runner (23) is connected to the cavity Ingate, the ingate is connected to the cavity in a tangential way. 8. The integral casting method for steel backup rolls according to claim 7, characterized in that: the sprue cup outlet (26) has a boss (25) protruding from the inner bottom of the sprue cup (18). 9. The integral casting method for steel backup rolls according to claim 7, characterized in that: when the molten metal is filled to 1/2-1/3 of the height of the sprue cup, the stopper rod (19) is opened. 10. The integral casting method for steel backup rolls according to claim 7, characterized in that: the cavity of the base is formed with shaped barrel bricks, and forms a tangential ingate with the runner.

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