Special steel mills from Primetals Technologies are specifically designed for the rolling of stainless steel, electrical steel and other special-purpose steels. The most common configuration is the single reversing mill. Various mill designs are offered that include 6-high UCMs (Universal Crown Control Mill), ZR mills and 12-high cold-rolling mills with small-diameter work rolls for the efficient rolling of materials of high hardness.
20Hi ZR Mill, HZ Mill
The ZR mill uses ultra-small diameter work rolls to efficiently roll high-hardness materials such as stainless steel, electrical steel strip, and phosphor bronze.
To the original high rolling reduction capacity of the mill, we have added the double AS-U (shape control mechanism) originally developed by our company. This provides superior shape control over that of an ordinary ZR mill. A further modification has created the HZ mill. In the HZ mill the housing is split into an upper and lower section enabling a large roll gap to be created for strip threading. This mill has been particularly well evaluated for rolling electrical steel strip materials.
The ZR mill is a mill for cold rolling of hot-rolled coils of stainless steel and other hard materials to the designated product thickness and strip shape accuracy. The ultra-small diameter rolls are firmly supported in a 20Hi roll cluster arrangement.
With a conventional ZR mill, the roll bending mechanism for the backing bearing shafts that control the shape (the AS-U system) contains only two shafts (shafts B & C) of the four upper backing bearing shafts (shafts A, B, C, D). As a result, the strip shape control capability is insufficient, and there are problems which make high-speed rolling with high rolling reduction difficult. To resolve this, we developed the KZR mill. This mill is equipped with a double AS-U system one for the two upper backing bearings shafts A and B, and the other for bearing shafts C and D. The KZR mill also includes effective automatic shape control. Because the KZR mill is capable of high-speed rolling with high rolling reduction, it can deliver a boost to productivity for rolling stainless steel and other hard materials.
HZ Mill (Advanced Split Housing ZR Mill )
Because the housing is split into upper and lower sections, a large gap between the upper and lower work rolls can be achieved. This makes strip threading easier and also, in the event of a cobble, strip cutting for removal. In contrast, in a conventional ZR mill, the 20Hi rolls are supported in a cluster arrangement contained inside a mono-block housing. Although this structure is compact, the gap between the upper and lower work rolls is small, and extra work is required for threading and to cut strip should a cobble need to be cleared.
For this reason, we developed an advanced split housing ZR mill (HZ mill) which splits the mono-block housing into an upper and lower section, supported by two outer housings. Also, unlike the mono-block ZR mill, the work rolls can be used to nearly their full diameter range regardless of the diameter of the intermediate rolls, so providing greater operating time.
12Hi CR Mill
The 12Hi cold roll (CR) mill was developed independently by Primetals Technologies to roll stainless steel, copper alloys, and nickel alloys. Compared with a ZR mill, the number of rolls is less and it provides greater shape control. In addition, the work roll diameter range is significantly broader, allowing high accuracy rolling of a greater range of materials, soft, medium, and hard.
The upper and lower backup roll frame is split, enabling automatic work roll changing. This also provides good strip threading performance and ease of maintenance. It is also possible to modify the housing of an existing 4-high mill to convert it to 12-high. Also, a shift function has been added to the intermediate roll, preventing the backup roll contact mark being transferred to the strip so enabling this mill to be used to roll materials which have strict surface requirements.
- 12-roll arrangement (Work roll x 2, IMR x 4, BUR x 6)
- Split-type BUR
- Exceptional shape control
- Small-diameter work rolls provide high rolling reduction.
- Modification of a conventional mill using the existing housing is possible.
Plant productivity and product quality are substantially depending on the quality of plant automation, process control, and available process optimization functions.
To get the best performance out of a plant, Primetals Technologies provides add-on specific optimization solutions for further improvement of production efficiency and strip quality, besides standardized high performance automation system.
Excellent Strip quality with:
- REC - Roll Eccentricity Compensation for uniform and accurate strip thickness
- CECO - Coil Eccentricity Compensation for uniform and accurate strip thickness
- AFC - Model based Automatic Flatness control
- ChatterMon / Mill Chatter Monitoring with automatic process speed adaptation
For Reversing cold mills a highly optimized solution is available matching all kind of mill stand configurations. According to the complexity of production a look-up table or rolling model based mill setup can be chosen.
As a result of the application of the Advanced 20Hi Split Housing ZR-Mill (HZ-Mill) to plants rolling hard metals such as electrical steel strip, high-strength steel strip and others, its performance has been highly evaluated by customers. A total of 20 HZ-Mills have been delivered or are under construction to date as shown in this figure. Three HZ-Mills are currently under construction. Additional sales are also expected in response to the growing demand for high value-added products in recent years.