Rolling Forming Technology for Super Large Ring Forgings and Cylinder Forgings

This article mainly introduces a new process for producing large ring forgings and large cylinder forgings – radial and axial rolling technology. It introduces the equipment capacity of the world’s most giant ring rolling machine today and the rolling and forming process of oversized rings with a diameter of 15.45m and cylinders with a diameter of 6m.
Ultra-large ring forgings and cylinder forgings are critical components for large equipment and have wide applications in offshore wind power, nuclear power, hydropower, petroleum refining, aerospace, and other fields. With the rapid development of China’s equipment manufacturing industry, the contradiction between supply and demand for large ring forgings and cylinder forgings is increasingly apparent due to the limitations of domestic manufacturing technology and capacity. Some equipment manufacturers have to turn their attention to imports.
Large ring forgings with a diameter of more than 10m are mainly produced using segmented welding or casting processes. For example, large concrete rotary kiln tires are mainly produced using casting processes. Due to the large diameter of the workpiece, it is necessary to set multiple gating risers, which reduces the material utilization rate and makes it challenging to avoid casting defects such as sand holes, shrinkage holes, and cold shuts. However, the segmented welding process for large ring forgings has significant defects that the microstructure of the weld and the body need to be more consistent.
Large cylinder forgings with a diameter of more than 4m in China are produced mainly by free forging. The leading manufacturers include China First Heavy Industries, Second Heavy Industries, Shanghai Heavy Industries, CITIC Heavy Industries, and other large forging enterprises. In 2015, CITIC Heavy Industries forged a super large cylinder with a diameter of 6.72m, a height of 3.95m, and a weight of 202t using a 185MN oil press. Due to restrictions such as the clearance height of the oil press and the opening size, the cylinder forgings of this size have reached the limits of the equipment.
In addition, the forging time of sizeable open die forgings is generally long, and the initial and final forging parts’ forging temperature and deformation amount must be uniformly consistent. Therefore, the forgings‘ internal structure and grain size may vary greatly, especially for forgings such as austenitic stainless steel that cannot be refined through subsequent heat treatment; the difference is even more significant.
In producing large ring forgings and cylinder forgings, there are typical problems such as low production efficiency, poor homogeneity, and high material consumption, regardless of the tailor welding process, casting process, or free forging process.

What is radial and axial rolling technology?

Radial, axial rolling technology (ring rolling) is an internationally recognized advanced manufacturing technology for near net forming, which applies to forming ring, disk, and barrel forgings. Compared with traditional free forging processes, it has the characteristics of energy saving, high efficiency, and high material utilization. Moreover, the internal structure of the rolled workpiece is dense, with refined grains and complete flow lines, which is of great significance for improving the strength, wear resistance, and fatigue life of the workpiece

(a) Large cast rings

(b) Free-forging cylinder
Figure.1 Large Cast Rings and Free Forged Cylinders
The RAW2500/1250-16000/3000 ring rolling machine is the giant radial and axial ring rolling machine in the world today, with a radial rolling force of 2500t; Axial rolling force of 1250t; The maximum rolling diameter is 16m, the maximum rolling height is 3m, and the rolling billet weight reaches 200t. It can produce ultra-large seamless rings with a diameter of 16m and cylindrical forgings with a height of 3m. This can solve large ring and cylindrical forgings’ current production and manufacturing problems, providing a solid guarantee for the R&D and production of large equipment in China.

This equipment has a sizeable rolling force and an accurate control system (Figure 2), which has a multifunctional and accurate ability to execute user expectations. It can automatically set rolling variables, automatically control rolling processes, automatically monitor the workpiece growth process, and has advanced special-shaped rolling functions. High precision control improves the appearance quality of forgings and can further reduce the forging allowance and material consumption.

Figure.2 Automatic Control Panel
In May 2018, the ring rolling mill and its supporting 135MN oil pressure machine, heat treatment equipment, and machining equipment were put into production throughout the line, successively producing large ring forgings with a diameter of 15.45m and cylindrical forgings with a diameter of 6m and a height of 3m, as described below.
Rolling of super large annular forgings
The target size of the ring: outer diameter 15.45m, wall thickness 285mm, height 645mm, material Q345E, steel ingot weight 105t. The hydraulic press is used for blank opening, with dimensions of 5300mm outer diameter, 3400mm inner diameter, and 850mm height.

Process flow: ingot rounding – elongating – blanking – upsetting – punching – reaming – first heat rolling – second heat rolling – cooling after forging (Figure 3).

(a) Upsetting and punching

(b) Reaming

(c) First heat rolling

(d) Second heat rolling

(e) Blank size measurement

Figure 3 Rolling Process of Super Large Ring Forgings
Ring forgings with a diameter of 15.45m are rolled from 5.3m to 7m in the first heat, and the rolling takes only 7 minutes; The second heat rolling is from 7m to 15.45m, taking 10 minutes and 32 seconds, and the final rolling temperature is not lower than 900 ℃. After rolling the ring, the blank was measured, and the measurement results are listed in Table 1. The data in Table 1 shows that the outer diameter of the blank is elliptical 58 mm; The inner diameter is oval 54mm, and the flatness is ≤ 5mm. The appearance of the forging is flat, without defects such as grooves, pits, and folds.

Table.1 1.5.45 m Ring Forging Blank Dimension Measurement Results Unit (mm)

Target size	Position	Outer diameter	Inner diameter	Height	Ovality
		15450	14880	645
Measured dimension	0°	15415	14731	645	Outer diameter: 58 Inner diameter: 54
	30°	15421	14739	646
	60°	15473	14785	645
	90°	15445	14781	645
	120°	15435	14750	646
	150°	15428	14741	645

Rolling of large cylinder forgings

The target size of the cylinder: outer diameter: 6000 mm; Inner diameter of 5500mm; Height of 3000mm; Material: Q345E, steel ingot weight 158t. Forging blank size: outer diameter 4290mm; Inner diameter 3500mm; height is 3035mm. Process flow: ingot rounding – elongation – blanking – upsetting – punching – mandrel elongation – reaming – rolling – cooling after forging. (Figure 4)
Rolling a large cylinder with a diameter of 6m and a height of 3m took 4 minutes and 52 seconds. The dimensional inspection results of the cooled blank are listed in Table 2. The data in Table 2 shows that the cylinder is well rolled and formed, with an ovality of ≤ 20mm, an upper and lower taper of ≤ 12mm, and excellent appearance quality.

Table.2 Measurement Record of Cylinder Blank Size Unit (mm)

Target size	Position	Outer diameter (upper/middle/lower)	Inner diameter (upper/middle/lower)	Height	Ovality	Taper
		6000	5500	3000
Measured dimension	0°	5997/5995/5990	5460/5455/5450	2995	15	12
	45°	5994/5990/5983	5460/5462/5448	2997
	90°	5997/5590/5986	5459/5450/5450	2995
	135°	5982/5987/5970	5445/5448/5435	2996

Figure.4 Rolling Process of Large Cylinder Forgings

Performance testing of rolled ring forgings

In June 2018, our company undertook the manufacturing task of the support ring for a project’s integral bolt tensioning machine. The product is made of 30Cr2Ni2Mo and has an outer diameter of 5262mm; Inner diameter of 4210mm; A height is 371mm, a weight of the steel ingot is 41t, and performance testing requires sampling from three bolt holes P1, P2, and P3. The positions of the three bolt holes are separated by 120 °. The shape and sampling requirements of the finished product are shown in Figure 5.

(a) Finished product

(b) Sampling requirements
Figure.5 Bolt Tensioner Support Ring

Manufacturing process flow: ingot rounding – hot cutting water riser – blank forging – ring rolling – post forging heat treatment – rough machining – UT testing – quenching and tempering treatment – sampling testing – finishing (Figure 6). The mechanical property test results are listed in Table 3:

(a) Ingot rounding

(b) Reaming

(c) Rolling ring

(d) Blank
Figure.6 Process Flow of Support Ring

Table.3 Test Results of Mechanical Properties of Support Ring Forgings

Material quality	Status	Test direction		Rm	Rp0.2	A	Z	Test	AKv
				MPa		%			J
Technical requirement				≥830	≥700	≥12	≥50	Room temperature	≥45
30Cr2Ni2Mo	Quenching and tempering	P1 Landscape		977	777	19.5	63	Room temperature	69.8
		P1 axial direction		944	739	19	62		151.6；56.0
		P2 Landscape		967	770	18.5	65		125.8
		P2 axial direction		955	767	20	63		154.9；48.4
		P3 Landscape		971	745	19.5	63		156
		P3 axial direction		939	738	20	61		80.1；149.3
Hardness test results
Technical requirement			Detection location		Measured value
					P1		P2		P3
HB250-302			Upper		286；286；288		292；290；292		285；283；285
			Medium		280；280；278		283；282；280		278；277；278
			Lower		290；288；288		288；288；286		283；276；283

From the data listed in Table 3, it can be seen that the mechanical properties of rolled ring forgings after heat treatment meet the technical requirements. The test results at P1, P2, and P3 show a difference of 10 MPa in transverse tensile properties and 16 MPa in axial tensile properties. The hardness difference between the surface layer and the forging center is only 16 HB. The properties of each part of the forging are uniform, with little difference. Thoroughly verify the forging penetration ability of large ring rolling machines, reflecting the homogenization characteristics of rolled ring forgings.

Conclusion

The radial and axial rolling process is a unique forming process for ring forgings, which is recognized for its high forming accuracy, small margin, and high production efficiency. European and American countries have widely applied barrel-rolling technology to key energy equipment fields such as petrochemical and nuclear power.

Author: Ren Xiufeng, Niu Yugang, Qu Zaiwen