Process control method for improving thread steel negative tolerance technology

Abstract

The invention discloses a process control method for improving a deformed steel bar negative tolerance technology, and belongs to the technical field of bar rolling, and the control method comprises the steps of small-specification slitting rolled finished product size optimization, small-specification slitting line difference fluctuation optimization, small-specification double-length head and tail size fluctuation optimization and large-specification deformed steel bar negative tolerance and inner diameter optimization. The method aims at the technical bottlenecks that in existing deformed steel bar negative tolerance rolling, the inner diameter of a small-specification slitting rolled finished product is prone to exceeding the standard, the slitting line difference fluctuation is large, the double-length head and tail size difference is obvious, the large-specification negative tolerance is small, and the inner diameter is prone to exceeding the standard. According to the method, negative tolerance improvement is achieved through multi-dimensional collaborative optimization, the base circle size of a small-specification finished hole pattern is optimized, the rolling mill assembly precision is controlled, a pre-segmentation hole pattern is iteratively adjusted, a precise guide and guard beam is applied, electrical parameters are optimized, a rolling control system is upgraded, and large-specification finished hole pattern parameters are iterated for multiple rounds; and after application, the market competitiveness and management and delivery benefits of products are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bar rolling, in particular to a process control method for improving the negative tolerance technology of threaded steel, which surrounds the negative tolerance control bottleneck of the theoretical weight delivery mode of threaded steel, maximizes the negative tolerance level through multi-dimensional process optimization, and is suitable for the production process of small-specification cut rolling and large-specification threaded steel. BACKGROUND

[0002] Under the theoretical weight delivery mode, the negative tolerance control level of threaded steel directly determines the economic benefit of the enterprise: the more mature the negative tolerance rolling technology, the higher the theoretical yield, the more products that meet the theoretical weight can be produced under the same raw material consumption, and higher profits can be created; if the negative tolerance control level is low, not only will the yield be reduced, but also customer complaints and returns may be caused due to the product size exceeding the allowable range of the national standard, significantly weakening the product market competitiveness; however, the existing threaded steel negative tolerance rolling process has the following key technical bottlenecks, which are difficult to meet the demand for maximizing the benefit of theoretical weight delivery; small-specification threaded steel is mostly cut and rolled, and due to unreasonable finished product pass design, when pursuing large negative tolerance, the finished product inner diameter size is easy to exceed the lower limit of the national standard, resulting in unqualified products.

[0003] In order to realize the maximum benefit of the theoretical weight delivery of straight bar threaded steel, the negative tolerance control level of threaded steel becomes more and more important; the key control point of improving the negative tolerance rolling level is to make the size parameters of threaded steel as small as possible under the premise of meeting the national standard.

[0004] On this basis, through retrieval, application No. CN202510235080.7 discloses a material shape control method for improving the negative tolerance of three-cut threaded steel;

[0005] However, the above method lacks effective emergency solutions for the problem, and the existing technology mostly adopts single-dimensional improvement, such as only optimizing the pass or adjusting the rolling mill, without forming a systematic solution, which cannot fundamentally break through the above bottleneck; therefore, a multi-dimensional collaborative optimization process control method is needed to significantly improve the negative tolerance level of threaded steel.

[0006] In view of the above problems, a process control method for improving the negative tolerance technology of threaded steel is proposed. SUMMARY

[0007] The present application aims to provide a process control method for improving the negative tolerance technology of threaded steel, which addresses the problem that the traditional technology mostly adopts single-dimensional improvement, such as only optimizing the pass or adjusting the rolling mill, without forming a systematic solution, which cannot fundamentally break through the above bottleneck, therefore, a multi-dimensional collaborative optimization process control method is needed to significantly improve the negative tolerance level of threaded steel.

[0008] To achieve the above object, the application provides the following technical scheme: a negative tolerance technology for lifting threaded steel, comprising the following steps:

[0009] Step one: size optimization of small-specification split-rolled finished products: in view of the problem that the inner diameter size is prone to exceed the standard in the split-rolling of small-specification threaded steel, the finished product pass base circle size optimization and rolling mill assembly precision control are carried out; the finished product pass base circle size optimization is to reduce the base circle radius and design the side wall slope at the pass fillet; the rolling mill assembly precision control is to select a fifth-generation finished product rolling mill with anti-channeling device, and the rolling mill axial channeling amount is less than 0.2 mm;

[0010] Step two: small-specification split-line difference fluctuation optimization: in view of the problem that the size difference between the middle line and the two side lines in the split-rolling of small-specification threaded steel, pre-split pass parameter iterative optimization and precision guide beam application are carried out; the pre-split pass parameter iterative optimization is to adjust the pass arc radius and height so that the lengths of the lines after splitting are consistent; the precision guide beam is a worm and gear control type, which is used at the inlet of K3 / K4 rolling mill to ensure the uniformity of pre-splitting;

[0011] Step three: small-specification double-length head and tail size fluctuation optimization: in view of the problems of small-specification threaded steel double-length head steel drawing, small size and longitudinal rib flattening, the precision rolling loop control program, rolling line transmission control system and motor steel biting speed drop compensation parameters are optimized, and the rolling control system is upgraded to a system with micro-tension control and self-adaptive adjustment function;

[0012] Step four: large-specification threaded steel negative tolerance and inner diameter optimization: in view of the problems of small negative tolerance and easy exceeding of the standard of the inner diameter of large-specification threaded steel, multi-round iterative optimization of finished product pass parameters is carried out, the pass parameters include base circle inner diameter, transverse rib spacing, α angle and side wall slope, and by adjusting the parameter combination, the negative tolerance of large-specification threaded steel is greater than-3.0% and the minimum surface size meets the national standard.

[0013] Preferably, in step one, when the small-specification threaded steel is Φ20 screw, the finished product pass base circle radius is reduced from R9.6 to R9.55, and the side wall slope at the pass fillet is matched with the base circle radius adjustment to increase the minimum inner diameter size.

[0014] Preferably, in step two, when the small-specification threaded steel is Φ16 screw three-split, the pre-split pass parameter iterative optimization process is: first, adjust the pass arc radius from R10.15 to R10.05 and the height from 20.3 mm to 20.1 mm; then keep the height of the two side passes unchanged, and adjust the two side pass arc radius from R10.05 back to R10.15 to make the lengths of the three lines consistent.

[0015] Preferably, in step two, after the application of the precision guide beam, the four-split line difference is less than 1%, and the two-split line difference is less than 0.5%.

[0016] Preferably, in the step three, the upgraded rolling control system is a rolling control system of Beijing Metallurgical, after the system is put into operation, the size difference of the head and tail of the double-length is less than 1%, and the longitudinal rib cutting phenomenon of the head of the double-length is eliminated.

[0017] Preferably, in the step four, when the large-size threaded steel is Φ36 screw, the multi-round iterative optimization process of the finished product pass parameter is as follows: in the first optimization, the base circle inner diameter is reduced from 35.00 mm to 34.70 mm; in the second optimization, the base circle inner diameter is kept unchanged, the transverse rib spacing is adjusted from 15.5 mm to 16 mm, and the alpha angle is adjusted from 55° to 50°; in the third optimization, the pass width is adjusted from 34.70 mm to 35.00 mm, and a 76° side wall slope is added; in the fifth optimization, the base circle inner diameter is adjusted back to 34.70 mm, the pass width is adjusted to 35.2 mm, and the side wall slope is adjusted to 73°, and after the optimization, the negative tolerance can reach-3.5%.

[0018] Preferably, in the step four, when the large-size threaded steel is Φ40 screw, the finished product pass parameter optimization includes: the base circle inner diameter is reduced from 38.70 mm to 38.40 mm, the transverse rib spacing is adjusted from 15.5 mm to 16 mm, the alpha angle is adjusted from 55° to 50°, and a 77° side wall slope is added, and after the optimization, the negative tolerance can reach-3.5% and the minimum face size meets the national standard.

[0019] Preferably, in the step four, when the large-size threaded steel is Φ28 screw or Φ32 screw, the finished product pass parameter optimization includes:

[0020] Φ28 screw: the base circle inner diameter is reduced from 27.20 mm to 26.90 mm, the pass width is set to 27.20 mm, and a 73° side wall slope is added;

[0021] Φ32 screw: the base circle inner diameter is reduced from 31.00 mm to 30.70 mm, the pass width is set to 31 mm, and a 75° side wall slope is added; after the optimization, the average negative tolerance of the two is greater than-3.2% and the minimum face size meets the national standard 。

[0022] Compared with the prior art, the beneficial effects of the present application are as follows:

[0023] 1. The purpose of the present application is to overcome the technical bottlenecks of small size inner diameter exceeding standard, large cutting line difference, significant double-length fluctuation and low large size negative tolerance in the existing screw steel negative tolerance rolling process, provide a process control method for improving the negative tolerance technology of screw steel, significantly improve the negative tolerance level and the theoretical yield rate under the premise of ensuring that the size of screw steel meets the national standard, and finally realize the benefit maximization of rational calculation delivery; the present application breaks through the technical bottleneck of the existing screw steel negative tolerance rolling through multi-dimensional collaborative optimization, has the following remarkable beneficial effects, firstly, the quality is improved, ensures that the size parameters of screw steel meet the national standard, solves the problems of inner diameter exceeding standard, large line difference, double-length fluctuation and the like, and the product qualified rate is high; secondly, the benefit is remarkable, the negative tolerance level is improved compared with before the implementation of the project, and the corresponding theoretical yield rate is improved; for example, the competitiveness is enhanced, the small size cutting line difference and double-length fluctuation are controlled at the industry leading level, and the competitiveness of the product in the rational calculation delivery market is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 A process control method flow chart for improving the negative tolerance technology of screw steel. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0026] In order to further understand the content of the present application, the present application will be described in detail with reference to the drawings.

[0027] In combination with Figure 1 A process control method for improving the negative tolerance technology of screw steel, comprising the following steps:

[0028] Step one: small size cutting rolling finished product size optimization: in view of the problem that the inner diameter size of small size screw steel cutting rolling is easy to exceed the standard, the finished product pass base circle size optimization and rolling mill assembly precision control are carried out; the finished product pass base circle size optimization is to reduce the base circle radius, and the side wall slope is designed at the pass fillet; the rolling mill assembly precision control is to select the fifth generation finished product rolling mill with anti-channeling device, and the rolling mill axial channeling amount is less than 0.2mm;

[0029] Step 2: Optimization of Small-Diameter Cutting Line Difference Fluctuation: To address the issue of dimensional differences between the center line and the two side lines in the cutting and rolling of small-diameter rebar, iterative optimization of pre-cutting pass parameters and application of precision guide beams are carried out. The iterative optimization of pre-cutting pass parameters involves adjusting the radius and height of the pass arc to ensure consistent lengths of all lines after cutting. The precision guide beam is a worm gear controlled type, used at the inlet of the K3 / K4 mill to ensure uniformity of pre-cutting.

[0030] Step 3: Optimization of head and tail dimension fluctuations in small-size multiple-length rebar: To address the issues of steel pulling, undersized dimensions, and flattened longitudinal ribs at the head of small-size multiple-length rebar, the control program of the finishing rolling looper, the rolling line drive control system, and the motor bite speed reduction compensation parameters are optimized, and the rolling control system is upgraded to a system with micro-tension control and adaptive adjustment functions.

[0031] Step 4: Optimization of negative tolerance and inner diameter of large-size rebar: In response to the problem of small negative tolerance and easy over-standard inner diameter of large-size rebar, multiple rounds of iterative optimization of the finished product hole parameters were carried out. The hole parameters include the base circle inner diameter, transverse rib spacing, α angle and side wall slope. By adjusting the parameter combination, the negative tolerance of large-size rebar is made to be greater than -3.0% and the minimum surface size conforms to the national standard.

[0032] The present invention will be further described below with reference to embodiments.

[0033] Research revealed that temperature differences exist between the height and width of the finished product rolled from the finished pass, resulting in varying shrinkage rates of the inner diameter of the finished product's height and width. The inner diameter of the surface corresponding to the height of the finished product has a smaller shrinkage rate than that of the surface corresponding to the width, ultimately leading to the presence of a maximum and a minimum surface on the finished product. The maximum surface dimension is the height dimension of the finished product, while the minimum surface is located near the longitudinal rib of the finished product. Therefore, due to factors such as the design of the finished pass and the misalignment of the finished mill rolls, the phenomenon of the inner diameter of the finished product exceeding national standards is prone to occur during the production process of improving the negative tolerance rolling level. The following optimization and improvement work on the finished pass was carried out.

[0034] (I) Optimization of the dimensions of small-diameter slitting and rolling finished products (applicable to Φ12~Φ20 screws)

[0035] Due to factors such as the design of the finished product pass and the misalignment of the mill rolls, large negative tolerance control during the single-bar splitting rolling process can easily lead to the finished product's inner diameter exceeding national standards. Therefore, optimization research is needed in terms of finished product pass dimensional parameters and mill assembly standards.

[0036] Optimization of the base circle size of the finished hole:

[0037] To solve the problem of different inner diameter shrinkage caused by temperature difference of finished product, the base circle radius of finished product pass is reduced and the side slope is designed at the pass fillet. Take Φ20 screw as an example, the base circle radius of finished product pass is reduced from R9.6 to R9.55, and the side slope is adjusted according to the base circle size. The minimum inner diameter size is increased while the negative tolerance is ensured, which effectively prevents the inner diameter from exceeding the standard caused by slight roll misalignment.

[0038] Roller assembly precision control:

[0039] The fifth generation of finished product rolling mill with anti-channeling device is selected to ensure the product quality from the nature of the equipment. The roll assembly is strictly carried out according to the standard to ensure that the axial displacement of the rolling mill is less than 0.2mm, avoiding the size of the finished product exceeding the standard caused by roll misalignment.

[0040] (2) Optimization of small size slit line difference fluctuation

[0041] Through long-term tracking and research of the research group, the main problems affecting the slit line difference are as follows: first, the size difference between the middle line and the two side lines exists due to the influence of pre-cutting and cutting pass; second, the size difference between the two side lines exists due to the inaccurate adjustment.

[0042] Pre-cutting pass parameter iterative optimization:

[0043] For the size difference between the middle line and the two side lines after cutting, take Φ16 screw three-cutting as an example for iterative optimization: under the initial pass, the three lines are short in the middle and long on both sides.

[0044] First optimization: adjust the pre-cutting pass arc radius from R10.15 to R10.05 and the height from 20.3mm to 20.1mm, and the three lines become long in the middle and short on both sides.

[0045] Second optimization: keep the height of the two side passes unchanged, and adjust the two side pass arc radius from R10.05 to R10.15, and finally realize the same length of the three lines.

[0046] Application of precision guide beam: in the process of cutting, in order to ensure the uniformity of pre-cutting, the centering of pre-cutting guide beam is required to be very high. When the centering of guide beam is not good, it is easy to cause uneven cutting. In the past, we used ordinary guide beam with screw rod device in pre-cutting rack. The horizontal movement of guide beam is driven by screw rod, which is not precise and has large error, leading to the phenomenon of not in place or over-adjustment during adjustment, resulting in large line difference between the two sides during production, affecting the negative tolerance control level.

[0047] The new precision guide and guard beam adjusting mechanism is controlled by a worm gear, and compared with a transmission guide and guard beam, it is more precise in workmanship, more accurate and faster in adjustment, and can better ensure the adjustment accuracy, and has obvious effect on the control of the slit line difference; the traditional screw control ordinary guide and guard beam is replaced by the new precision guide and guard beam controlled by a worm gear at the inlet of a K3 / K4 rolling mill. The guide and guard beam is precise in workmanship, accurate and fast in adjustment, can effectively ensure the pre-cutting centering, and significantly reduce the slit line difference, and after application, the four-cut slit line difference is less than 1%, and the two-cut slit line difference is less than 0.5%.

[0048] (Three) Optimization of Small-Scale Multiple Head-Tail Size Fluctuation

[0049] The influence of the multiple head-tail size difference is mainly affected by the rolling line loop response speed, the precision of the electrical transmission device, and the inherent defects of the rolling line control system, etc., resulting in a large size difference of the multiple pass bar, and a serious steel drawing phenomenon within 1.5 meters of the head, and a small size.

[0050] Optimization of electrical parameters:

[0051] The electrical professional optimizes the finishing mill loop control program, the rolling line transmission control system and the motor steel biting speed reduction compensation parameters, improves the small size of the multiple head and the longitudinal rib flattening phenomenon, and for example, the head negative tolerance fluctuation and the longitudinal rib height deviation are significantly reduced.

[0052] Upgrading of rolling control system:

[0053] The original Jinanming rolling control system is upgraded to the rolling control system of Metallurgical Jinan, the new system has faster response speed, can be put into micro-tension control and self-adaptive adjustment function, can automatically learn and optimize the rolling parameters, further reduces the size difference of the multiple head and tail, and after upgrading, the size difference of the multiple head and tail of each specification is less than 1%, and the head longitudinal rib flattening phenomenon is completely eliminated.

[0054] (Four) Optimization of Large-Scale Threaded Steel Negative Tolerance and Inner Diameter (Applicable to Φ28-Φ40 Screws)

[0055] In view of the problems of small negative tolerance and easy over-standard of inner diameter of large-scale threaded steel, a multi-round iterative optimization of the finished pass parameters is carried out, and the specific methods are as follows:

[0056] Optimization of Φ36 screws:

[0057] First time: the inner diameter of the base circle is changed from 35.00 mm to 34.70 mm, the negative tolerance is increased to-2.8%, and the risk of over-standard inner diameter still exists;

[0058] Second time: the base circle is kept unchanged, the horizontal rib spacing is changed from 15.5 mm to 16 mm, and the α angle is changed from 55° to 50°, the negative tolerance reaches-3.0%, and the risk is not eliminated;

[0059] Third time: hole width 34.70 mm changed to 35.00 mm, 76° side wall slope added, Φ36 screw effect not obvious;

[0060] Fourth time: base circle inner diameter 34.70 mm changed to 34.60 mm, side wall slope 76° changed to 74°, negative tolerance reduced to -2.7%, risk increased;

[0061] Fifth time: base circle inner diameter 34.60 mm changed to 34.70 mm, hole width 35.00 mm changed to 35.2 mm, side wall slope 74° changed to 73°, negative tolerance reached -3.5%, risk eliminated.

[0062] Φ40 screw optimization:

[0063] First time: base circle inner diameter 38.70 mm changed to 38.40 mm, negative tolerance -2.8%, risk of exceeding standard;

[0064] Second time: horizontal rib spacing 15.5 mm changed to 16 mm, α angle 55° changed to 50°, negative tolerance -3.0%;

[0065] Third time: 77° side wall slope added, negative tolerance reached -3.5%, risk eliminated.

[0066]

[0067] Table 1 Threaded steel finished hole parameter improvement

[0068] Φ28, Φ32 screw synchronous optimization:

[0069] Φ28 screw: base circle inner diameter 27.20 mm changed to 26.90 mm, hole width 27.20 mm, 73° side wall slope added;

[0070] Φ32 screw: base circle inner diameter 31.00 mm changed to 30.70 mm, hole width 31 mm, 75° side wall slope added;

[0071] After optimization, the average negative tolerance of both is greater than -3.2%, and there is no risk of exceeding the inner diameter standard.

[0072] Example 1:

[0073] Φ20 screw small size cutting rolling optimization

[0074] Hole type adjustment: the finished hole type base circle radius is machined from R9.6 to R9.55, and a matching side wall slope is milled at the hole type fillet;

[0075] Rolling mill assembly: the fifth generation finished rolling mill with anti-channeling device is selected, and after assembly, the axial channeling amount is detected to be 0.15 mm (less than 0.2 mm);

[0076] Effect: The minimum inner diameter size of the finished product is increased by 0.12mm, and when there is a slight roll deviation, the inner diameter does not exceed the standard, and the negative tolerance is stably maintained at-2.9% to-3.1%.

[0077] Example 2:

[0078] Φ16 screw tri-segment line difference optimization

[0079] Pre-cutting segment hole type adjustment: first turn the hole type arc radius R10.15 into R10.05, and the height is ground from 20.3mm to 20.1mm; then the arc radius on both sides is adjusted back to R10.15;

[0080] Guide beam replacement: install a precision guide beam controlled by a worm and gear at the inlet of the K3 / K4 rolling mill, and the adjustment accuracy is controlled within ±0.05mm;

[0081] Effect: The three-line length deviation is reduced from the original 0.8mm to 0.2mm, and the segment line difference is stably maintained at 0.4%(less than 0.5%).

[0082] Example 3:

[0083] Φ36 screw large specification negative tolerance optimization

[0084] Hole type iterative adjustment: process the hole type according to the fifth optimization parameters, the base circle inner diameter is 34.70mm, the hole type width is 35.2mm, the side wall slope is 73°, the cross rib spacing is 16mm, and the α angle is 50°;

[0085] Rolling control: adopt the control system of Metallurgical Jingcheng, and put into micro tension and adaptive function;

[0086] Effect: The finished product negative tolerance is stably maintained at-3.4% to-3.5%, the minimum face size is larger than the national standard lower limit by 0.08mm, and there is no risk of exceeding the standard.

[0087] In summary, the working principle is: a process control method for improving the negative tolerance of threaded steel, which effectively solves the several bottleneck problems in the production process of large specification threaded steel thread cutting threaded steel low negative tolerance, greatly improves the negative tolerance control level, creates greater economic benefits, and also improves the market competitiveness of the company's products.

[0088] It should be noted that the above-mentioned electrical elements are provided with power supplies, and their control modes are prior art, which are uniformly described herein in order to avoid tedious description. The present application mainly serves to protect mechanical equipment, and therefore the control mode and circuit connection are not explained in detail herein. In this document, relational terms such as first and second and the like can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0089] While embodiments of the present application have been shown and described, it is to be understood that the embodiments described are merely divergences, modifications, replacements, and variations of the embodiments, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A process control method for improving the negative tolerance technology of rebar, characterized in that, Includes the following steps: Step 1: Optimization of finished product dimensions in small-specification slitting and rolling: To address the issue of easily exceeding the inner diameter limit in small-specification rebar slitting and rolling, optimization of the finished product pass base circle size and control of mill assembly accuracy are carried out; the finished product pass base circle size optimization involves reducing the base circle radius and designing sidewall slopes at the fillet corners of the pass; the mill assembly accuracy control involves selecting a fifth-generation finished product mill with an anti-slip device, and ensuring that the axial movement of the mill is less than 0.2mm; Step Two: Optimization of Small-Diameter Cutting Line Difference Fluctuation: To address the issue of dimensional differences between the center line and the two side lines in the cutting and rolling of small-diameter rebar, iterative optimization of the pre-cutting pass parameters and the application of precision guide beams are carried out. The iterative optimization of the pre-cutting pass parameters involves adjusting the radius and height of the pass arc to ensure consistent line lengths after cutting. The precision guide beam is a worm gear controlled type, used at the inlet of the K3 / K4 mill to ensure uniform pre-cutting. Step 3: Optimization of head and tail dimension fluctuations in small-size multiple-length rebar: To address the issues of steel pulling, undersized dimensions, and flattened longitudinal ribs at the head of small-size multiple-length rebar, the control program of the finishing rolling looper, the rolling line drive control system, and the motor bite speed reduction compensation parameters are optimized, and the rolling control system is upgraded to a system with micro-tension control and adaptive adjustment functions. Step 4: Optimization of negative tolerance and inner diameter of large-size rebar: To address the issue of small negative tolerance and easy over-standard inner diameter of large-size rebar, multiple rounds of iterative optimization of the finished product die parameters were carried out. The die parameters include the base circle inner diameter, transverse rib spacing, α angle and sidewall slope. By adjusting the parameter combination, the negative tolerance of large-size rebar was made greater than -3.0% and the minimum surface size met the national standard.

2. The process control method for improving the negative tolerance technology of rebar according to claim 1, characterized in that: In step one, when the small-specification rebar is Φ20, the base circle radius of the finished hole is reduced from R9.6 to R9.55, and the side wall slope at the rounded corner of the hole is adjusted to match the base circle radius to increase the minimum inner diameter.

3. The process control method for improving the negative tolerance technology of rebar according to claim 1, characterized in that: In step two, when the small-specification rebar is Φ16 rebar cut into three sections, the iterative optimization process of the pre-cutting hole shape parameters is as follows: first, adjust the arc radius of the hole shape from R10.15 to R10.05 and the height from 20.3mm to 20.1mm; then, while keeping the height of the hole shape on both sides unchanged, adjust the arc radius of the hole shape on both sides back from R10.05 to R10.15 so that the lengths of the three lines are consistent.

4. The process control method for improving the negative tolerance technology of rebar according to claim 1, characterized in that: In step two, after applying the precision guide beam, the difference between the four bisector lines is less than 1%, and the difference between the two bisector lines is less than 0.5%.

5. The process control method for improving the negative tolerance technology of rebar according to claim 1, characterized in that: In step three, the upgraded rolling control system is the MCC Jingcheng Rolling Control System. After the system goes online, the difference in the head and tail dimensions of multiple-length rolls is less than 1%, and the phenomenon of flattening the longitudinal ribs at the head of multiple-length rolls is eliminated.

6. The process control method for improving the negative tolerance technology of rebar according to claim 1, characterized in that: In step four, when the large-diameter rebar is Φ36, the multi-round iterative optimization process of the finished hole profile parameters is as follows: First optimization: the base circle inner diameter is reduced from 35.00mm to 34.70mm; Second optimization: keeping the base circle inner diameter unchanged, the transverse rib spacing is adjusted from 15.5mm to 16mm, and the α angle is adjusted from 55° to 50°; Third optimization: the hole width is adjusted from 34.70mm to 35.00mm, and a 76° sidewall slope is added; Fifth optimization: the base circle inner diameter is returned to 34.70mm, the hole width is adjusted to 35.2mm, and the sidewall slope is adjusted to 73°. After optimization, the negative tolerance can reach -3.5%.

7. The process control method for improving the negative tolerance technology of rebar according to claim 1, characterized in that: In step four, when the large-size rebar is Φ40, the optimization of the finished hole profile parameters includes: reducing the base circle inner diameter from 38.70mm to 38.40mm, adjusting the transverse rib spacing from 15.5mm to 16mm, adjusting the α angle from 55° to 50°, and adding a 77° sidewall slope. After optimization, the negative tolerance can reach -3.5% and the minimum surface dimension meets the national standard.

8. The process control method for improving the negative tolerance technology of rebar according to claim 1, characterized in that: In step four, when the large-diameter rebar is Φ28 or Φ32, the optimization of the finished thread profile parameters includes: Φ28 screw: The base circle inner diameter is reduced from 27.20mm to 26.90mm, the hole width is set to 27.20mm, and a 73° sidewall slope is added; Φ32 screw: The base circle inner diameter is reduced from 31.00mm to 30.70mm, the hole width is set to 31mm, and a 75° sidewall slope is added; after optimization, the average negative tolerance of both is greater than -3.2% and the minimum face size conforms to the national standard.

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