Deep Hole Drilling for Industrial Rolls: Paper Mill Dryers, Steel Mill Work Rolls, and Rubber Roll Cores

Industrial rolls — paper machine dryer rolls, steel mill work rolls and backup rolls, rubber rollers for printing and textile processing — share a common manufacturing requirement: a precisely bored central hole or network of cooling passages that run the full length of the roll body.

The function of the bore varies by application. In paper machine dryer rolls, the bore carries steam for heating the roll surface to dry the paper web. In steel mill work rolls, a pattern of longitudinal and radial holes circulates coolant to remove heat generated during rolling. In large backup rolls, a center bore removes forging defects detected by ultrasonic inspection. In rubber rollers, the bore is simply the core onto which the rubber covering is applied.

This guide covers the deep hole drilling operations required in industrial roll manufacturing across these industries.

Paper Machine Dryer Rolls

Paper machine dryer rolls are large, steam-heated cylinders that dry the paper web after the press section. A typical dryer roll may be 1,500 mm in diameter and 6,000–10,000 mm long. The roll shell is heated by steam admitted through a bore in the journal at one end; condensate is removed through a bore at the opposite end.

Materials

Paper machine dryer rolls are manufactured from:

Bore Requirements

Manufacturing Sequence

1. Casting or forging of the roll shell
2. Heat treatment — stress relief annealing
3. Rough turning of OD
4. BTA drilling of center bore
5. Fine boring of bore to final diameter
6. Journal machining — turning, threading, keyway
7. Dynamic balancing
8. Hydrostatic pressure test — typically 1.5× working pressure

Drilling Configuration

For rolls longer than approximately 5,000 mm, the bore is drilled from both ends with a meeting point at the center. The BTA machine typically rotates the roll while the drill tube feeds from the tailstock end. Counter-rotation (roll and tool rotating in opposite directions) provides the best straightness.

The machine requirements for paper roll drilling include:

• Workpiece rotation capability (rolls are heavy — up to 30 tons)
• Chuck clamping on both ends with runout < 0.02 mm
• Steady rests for long roll support
• High-pressure coolant system (30–50 bar, 400–800 L/min)

Steel Mill Work Rolls

Steel mill work rolls require cooling passages drilled into the roll body to remove the intense heat generated during hot or cold rolling. The passages circulate coolant (typically water or emulsion) through the roll to maintain surface temperature within the operating range.

Cooling Passage Design

Two types of cooling holes are used in work rolls:

Longitudinal passages:

• Drilled parallel to the roll axis
• Spaced evenly around the roll circumference
• Diameter: 10–30 mm
• Number of holes: 8–48 depending on roll diameter
• Length: full roll body length

Radial connecting passages:

• Drilled at an angle from the bore surface to connect the longitudinal passages
• Diameter: same as longitudinal passages
• Position: near each end of the roll body
• Angle: typically 30–60° from the roll axis

The cooling passages form a circuit: coolant enters through one end of the roll, flows through the longitudinal passages, reverses at the opposite end, and returns through alternating passages.

Work Roll Materials

Drilling Parameters for Steel Rolls

Work roll materials are significantly harder than paper roll materials and require adjusted parameters.

Manufacturing Sequence for Work Rolls

1. Forging — ingot forged to near-net shape, forging ratio ≥ 3
2. Electro-slag remelting (ESR) — for premium rolls to minimize inclusions
3. Heat treatment — quenching and tempering to final hardness
4. Rough turning of OD
5. Center bore drilling — BTA or gun drilling of central hole
6. Longitudinal cooling passage drilling — spacing and depth per design
7. Radial passage drilling — connecting longitudinal passages to center bore
8. Plugging — radial passage openings at the surface are plugged before final assembly
9. Final turning and grinding of roll OD
10. Ultrasonic inspection — verification of passage integrity and wall thickness

Tolerances for Cooling Passages

Backup Rolls

Backup rolls in steel mills support the work rolls and are significantly larger. Large backup rolls (exceeding 2,000 mm diameter and 150 tonnes weight) often require a center bore to remove forging or casting defects.

Center Bore for Defect Removal

The purpose of the backup roll center bore:

• Remove centerline porosity and shrinkage defects detected by ultrasonic inspection
• Provide access for internal ultrasonic inspection during service life
• Reduce weight (significant for large rolls)

Backup Roll Materials

Drilling Parameters for Backup Rolls

Backup roll drilling is typically performed on large BTA machines with workpiece rotation.

Multi-Piece Backup Roll Design

For very large backup rolls that exceed forging capabilities, a multi-piece design is used:

• A main part with a large-diameter center bore (to remove defects)
• End parts with no bore or a smaller-diameter bore
• Parts joined via form-fit joints (locating spigot, key, and bolts)
• Bore diameter of the main part can be 0.5–1.5× the smallest OD of the end part

Rubber Rollers

Rubber rollers for printing, textile processing, and material handling have a steel or aluminum core that is bored to accept bearings and journals.

Core Materials

Core Manufacturing

The core manufacturing process:

1. Tube selection — seamless or welded steel/aluminum tube
2. BTA drilling or boring — to achieve uniform ID and remove weld seam (welded tube)
3. End preparation — counterboring for bearing housings
4. Journal fitting — welding or shrink-fitting of end shafts
5. Surface preparation — shot blasting for rubber-to-metal bonding
6. Rubber covering — extrusion or molding, followed by vulcanization
7. Grinding — CNC grinding to final OD tolerance and surface finish

Bore Tolerances for Rubber Rollers

Machine Requirements for Roll Drilling

Dedicated BTA drilling machines for industrial roll manufacturing have specific capabilities:

For related reading, see the Energy and Power Generation Deep Hole Drilling Guide, the Deep Hole Drilling 4140 and 4340 Alloy Steel Guide, and the Deep Hole Drilling Equipment Guide.