Replacing backing bearings in a Sendzimir Z-Mill is not simply a matter of finding a bearing with the same nominal diameter. Backing bearings operate as precision support elements in multi-roll cold rolling mills, where dimensional consistency, rolling accuracy and load distribution directly affect mill performance.
When ordering replacement backing bearings, the original bearing number, boundary dimensions, bearing structure, precision requirements and matching conditions should all be checked. This is particularly important when replacing imported bearings or sourcing an alternative manufacturer.
This guide explains the key information required to specify replacement backing bearings for Sendzimir Z-Mills and other multi-roll rolling mills.
1. Start With the Original Backing Bearing Number
The original bearing number is usually the best starting point for a replacement project. A complete bearing designation can provide important information about the bearing series, dimensions, row configuration, sealing arrangement and other design characteristics.
However, the original part number should not be used as the only criterion for interchangeability. Different manufacturers may use different designation systems for dimensionally similar backing bearings.
For example, Sendzimir mill backing bearings may be specified using original equipment or bearing manufacturer part numbers, while replacement suppliers may offer corresponding BN, NNCF or other equivalent designs.
2. Confirm the Bearing Dimensions
If the original bearing number is unavailable, the bearing dimensions become especially important. At minimum, three main dimensions should be confirmed:
Bore Diameter (d)
The bore must match the mandrel or shaft arrangement used in the backing assembly.
Outside Diameter (D)
The outside diameter determines the working and support geometry of the bearing assembly.
Width (B)
Bearing width must correspond to the available axial space and backing assembly configuration.
Measuring only the bore and outside diameter is not always sufficient. The total bearing width, shoulder dimensions, chamfers, internal configuration and other interface dimensions may also be important for proper installation.
3. Identify the Sendzimir Mill Model
The Sendzimir mill model provides useful information about the rolling mill configuration. Sendzimir 20-high mills commonly use ZR designations, such as ZR21, ZR22, ZR23, ZR24 and ZR32.
The ZR designation describes the mill section and is associated with the dimensions of components such as the backing bearings and work rolls. For example, Sendzimir documentation lists a backing bearing diameter of approximately 225 mm for a ZR23 mill section.
However, the mill model should be treated as supporting information rather than a direct bearing part number. Different mill configurations, modifications and bearing arrangements may require different bearing specifications.
4. Check the Bearing Row Configuration
Backing bearings for Sendzimir and other multi-roll mills are specialized cylindrical roller bearing designs. Depending on the application, double-row and triple-row configurations are commonly used.
The number of roller rows affects the load-carrying capacity, internal geometry and overall bearing dimensions. A replacement bearing should therefore have the correct row configuration rather than simply matching the outside diameter.
Some backing bearing designs also use an eccentrically or specially thickened outer ring. The outer ring functions as the working support surface in the backing assembly and therefore requires high dimensional accuracy and surface quality.
5. Specify Precision and Running Accuracy
Precision is one of the most important considerations when replacing backing bearings in a Sendzimir Z-Mill.
Backing bearings are installed in groups and work together to support the rolls. Small differences in bearing geometry can influence load distribution, rolling stability and strip quality.
Depending on the mill and application requirements, precision grades such as P4 or P2 may be specified. The required tolerance should be confirmed from the original bearing documentation, mill drawings or customer specifications.
- Outside diameter accuracy
- Outer ring roundness
- Roller diameter consistency
- Radial clearance
- Axial clearance
- Running accuracy
- Surface finish of the working surface
6. Pay Attention to T-Value Matching
T-value matching is particularly important for backing bearing sets used in multi-roll mills. Multiple bearings are installed together, so the individual bearings need to maintain consistent working dimensions.
If the bearings in one set have excessive dimensional variation, the load may not be distributed evenly. This can increase localized loading, vibration and wear.
For replacement projects, customers should therefore specify whether the bearings need to be supplied as a matched set and provide the required T-value or matching tolerance when available.
Why T-Value Matching Matters
- Helps maintain consistent bearing working height
- Improves load distribution between bearings
- Reduces localized overload
- Supports stable rolling performance
- Helps maintain strip thickness and surface quality
7. Confirm Clearance and Lubrication Requirements
Clearance should also be checked before ordering replacement backing bearings. The correct clearance depends on the bearing design, operating conditions, assembly arrangement and mill requirements.
Lubrication is another important consideration. Sendzimir backing bearings may operate under demanding lubrication conditions, and some designs are available with different sealing or lubrication configurations.
When replacing an existing bearing, it is advisable to keep the same lubrication arrangement unless the mill manufacturer or bearing engineer has approved a change.
8. Check the Original Manufacturer and Equivalent Design
Replacement backing bearings are often required when the original imported bearing is no longer readily available, has a long delivery time or is too expensive for routine maintenance.
In these cases, the original manufacturer and bearing designation should be recorded. Common international backing bearing designs include products from manufacturers such as SKF, NSK and FAG.
A replacement manufacturer can then evaluate the original specification and determine whether a dimensionally interchangeable bearing is available.
The objective should not be to match the brand name alone. The replacement should be evaluated according to dimensions, internal design, precision, clearance, load capacity and matching requirements.
9. Information to Provide When Requesting a Replacement
To reduce quotation time and avoid incorrect bearing selection, provide as much of the following information as possible:
| Information | Example / Requirement |
|---|---|
| Original bearing number | Complete manufacturer part number |
| Mill model | ZR21, ZR22, ZR23, ZR24, ZR32, etc. |
| Bore diameter | d |
| Outside diameter | D |
| Bearing width | B |
| Row configuration | Double row or triple row |
| Precision grade | P4, P2 or other specified tolerance |
| Clearance | Original or specified clearance |
| T-value requirement | Matched set requirements, if applicable |
| Quantity | Individual bearings or complete matched sets |
If the original bearing is available, photographs of the bearing marking can also be useful. A bearing drawing, old inspection report or dimensional measurement can provide additional information when the original designation is unclear.
10. Can a Replacement Backing Bearing Be Made From a Drawing?
Yes. When the original bearing number cannot be identified, a replacement backing bearing can often be specified using a drawing and dimensional requirements.
For non-standard or obsolete bearings, the drawing should ideally include the complete bearing envelope dimensions, internal geometry requirements, precision class, clearance and any special requirements for the outer ring or assembly.
This approach is especially useful for older Sendzimir mills where the original bearing designation may no longer be available.
For more information about how backing bearings are manufactured and how dimensional accuracy and matching requirements are controlled, see our Backing Bearing Manufacturing guide.
Replacement Backing Bearings for Sendzimir Z-Mills
JYHY Group supplies backing bearings for Sendzimir Z-Mills and other multi-roll rolling mill applications. The product range includes double-row and triple-row cylindrical roller backing bearings, including BN-series and NNCF-series designs.
Available specifications can include high-precision grades, controlled clearance and matched bearing sets according to the application requirements. Replacement bearings can also be evaluated based on original bearing numbers, drawings or dimensional requirements.
You can view the available models on our Backing Bearings product page.
Need a Replacement Backing Bearing?
Send us the original bearing number, mill model, dimensions or drawing. Our engineers can check the specification and recommend a suitable replacement backing bearing for your Sendzimir mill.
Conclusion
Specifying a replacement backing bearing for a Sendzimir Z-Mill requires more than matching one dimension. The original bearing number, mill model, bore, outside diameter, width, row configuration, precision, clearance and T-value matching requirements should all be considered.
For critical rolling mill applications, the safest approach is to compare the complete bearing specification with the original design before confirming interchangeability. Providing the original bearing number or drawing allows the replacement manufacturer to evaluate the application more accurately and reduce the risk of an incorrect selection.