Paper Mill Roll and Press Component Deep Hole Drilling

In 2017, a suction roll shell in a Scandinavian paper mill catastrophically failed during operation at 1,200 m/min, sending fragmented shell sections across the machine hall. Metallurgical investigation revealed that fatigue cracks had initiated from multiple blind-drilled holes where inadequate deburring had left sharp-edged burrs exceeding 0.15 mm. The burrs acted as stress concentration sites under cyclic nip loading. After approximately 60 million nip cycles, the cracks propagated through the ligament between adjacent holes, causing complete shell fracture. The incident caused EUR 15 million in damage and 4 months of production downtime, leading to revised industry standards for suction roll hole edge conditioning.

Paper Mill Roll and Industrial Press Component Deep Hole Drilling Overview ​

Paper mill rolls and industrial press components represent a specialized category of deep hole drilling where the drilled hole pattern directly determines the functional performance of the component.

Paper machine suction rolls and blind drilled press rolls require thousands of precisely positioned radial holes drilled through the roll shell or into its rubber cover. These holes enable water removal from the paper web as it passes through the press nip. The hole diameter, spacing, pattern, and edge quality directly affect water removal efficiency and roll fatigue life.

Industrial hydraulic press columns and tie rods require axial deep hole drilling for weight reduction, hydraulic fluid passages, or pre-stressed bolt construction. These long, slender components demand exceptional straightness and surface finish.

Suction Roll Shell Drilling ​

Suction rolls are among the largest components requiring deep hole drilling in industrial manufacturing. A typical suction roll measures 600–1,500 mm diameter with 3,000–8,000 mm face length and shell thickness of 30–80 mm. The shell is drilled with 10,000–100,000 radial holes arranged in a precise pattern.

Suction roll hole pattern specifications:

The hole pattern uses a triangular offset arrangement where each hole is positioned at the center of an equilateral triangle formed by the three surrounding holes. This pattern maximizes open area while maintaining minimum ligament width for structural integrity.

Modern suction roll drilling is performed on multi-spindle CNC drilling machines capable of drilling 20–50 holes simultaneously. The Safop Drillmatic system is one example of a dedicated machine platform for this application.

BTA Drilling for Large Suction Roll Shells ​

For thick-walled suction roll shells (40–80 mm wall thickness) in large-diameter rolls, BTA drilling is sometimes used for the through-holes. The BTA process provides the necessary penetration rate and hole quality for these deep radial bores.

BTA drilling parameters for roll shell materials:

Research by Haddag et al. (2020) on BTA drilling of low-alloy steels (18MND5, similar to roll shell materials) demonstrated that feed rate has a proportional effect on axial force, while cutting speed has a minor effect. Recommended parameters for BTA drilling in this material class are cutting speed of 95 m/min with feed of 0.145 mm/rev for larger-diameter BTA tools.

Blind Drilled Press Rolls ​

Blind drilled press rolls feature holes drilled part-way through the rubber or polyurethane cover, rather than through the entire shell. These holes trap water under nip pressure and release it by centrifugal force after the nip.

Blind drill roll specifications per US Patent US4366025 (Beloit Corp):

Blind holes are arranged in rows between through-hole rows. Each blind hole is positioned at the center of a triangle formed by three adjacent through holes. The offset between adjacent through-hole rows defines an angle of 20–40°. Blind holes at two different depths (6 mm and 10 mm) are used alternately to avoid shear planes in the cover.

The drilling process for blind drilled rolls uses short, stiff carbide drills with positive rake geometry. The rubber or polyurethane cover is typically 15–40 mm thick with hardness of 70–90 Shore A. Drilling is performed before the final grinding of the roll cover diameter.

Blind drilling parameters for roll covers:

Industrial Hydraulic Press Column Deep Hole Drilling ​

Industrial hydraulic presses use columns or tie rods to contain the pressing force. These components range from 150–500 mm diameter with 2,000–8,000 mm length, typically manufactured from 4140, 42CrMo4, or C45E steel.

Column types requiring deep hole drilling:

• Solid columns with axial bore: 150–300 mm diameter with 30–80 mm central bore for hydraulic fluid return or sensing lines
• Tie rods with through-bore: 50–150 mm diameter with 15–40 mm central bore for pre-stress bolt installation
• Prestressed column assembly: Multiple concentric layers with drilled passages for hydraulic tensioning

The axial bore in press columns serves multiple functions: hydraulic oil return passages in double-acting presses, temperature control fluid circulation, and weight reduction for large moving assemblies.

BTA Drilling of Press Columns ​

BTA drilling is the primary method for producing axial bores in press columns. The process must maintain straightness within 0.1–0.3 mm per 1,000 mm over the full column length.

BTA drilling parameters for press column steels:

Straightness control is critical for long press columns. Double-rotation BTA systems, where the column rotates while the BTA tool also rotates, achieve the best straightness for columns exceeding 4,000 mm length. Typical straightness deviation with counter-rotation: 0.05–0.10 mm per 1,000 mm.

Gun Drilling of Tie Rod Hydraulic Passages ​

Tie rods in hydraulic presses often require small-diameter axial bores for hydraulic tensioning systems. These bores allow hydraulic fluid to reach the tensioning nut at the opposite end of the rod.

Gun drilling parameters for tie rod bores:

The entry and exit of the gun drill must be carefully controlled. A pilot bushing with 0.003–0.008 mm clearance is essential at the entry. At breakthrough, feed must be reduced by 50% for the last 10 mm to prevent exit burr formation.

Heat Plate and Extrusion Press Component Drilling ​

Industrial heat plates for presses and extrusion press components require deep hole drilling for heating/cooling channels and hydraulic passages.

Heat plates used in laminating presses and rubber vulcanizing presses feature networks of drilled passages for steam heating or water cooling. These passages are typically 10–25 mm diameter × 2,000–6,000 mm length, arranged in serpentine patterns within the plate.

BTA drilling is used for the main passages, while gun drilling produces the interconnecting cross-passages. The drilling sequence must account for intersection points where vertical and horizontal passages meet.

Extrusion press container bores require large-diameter BTA drilling for the container bore (100–500 mm diameter × 1,000–3,000 mm length) in H11 or H13 hot-work tool steel at 40–48 HRC. BTA drilling of hardened tool steels for extrusion containers demands cutting speeds of 15–30 m/min with carbide grades designed for high-temperature applications.

Gang Drilling and Multi-Spindle Systems ​

High-volume drilling of paper machine rolls requires gang drilling systems capable of producing thousands of holes efficiently. These systems use multiple spindles operating simultaneously across the roll face.

Gang drill specifications for paper rolls:

The hole pattern is indexed by rotating the roll and traversing the gang drill head axially. Modern CNC systems manage the indexing sequence automatically, compensating for roll taper and camber.

Hole quality requirements for suction rolls:

• Diameter tolerance: ±0.05–0.10 mm
• Position tolerance: ±0.15–0.30 mm
• Burr height: ≤ 0.05 mm (deburred)
• Edge radius: 0.1–0.3 mm
• Surface finish inside hole: Ra ≤ 1.6 µm

Tooling for Roll and Press Component Drilling ​

Tool selection varies significantly between paper roll drilling (small diameter, high volume) and press column drilling (large diameter, deep penetration).

Paper roll drilling tooling:

For through-hole drilling in roll shells, solid carbide circuit board drills or gun drills with TiAlN coating provide the best combination of tool life and hole quality. Drill diameter tolerance of h6 or better is required to maintain hole size consistency across tens of thousands of holes.

Tool life in stainless steel roll shells: 500–2,000 holes per edge. In bronze shells: 2,000–5,000 holes per edge.

Press column BTA tooling:

For large-diameter BTA drilling of press columns (30–150 mm), indexable carbide insert tooling with TiAlN or AlTiN coating is standard. The BTA drill head features 2–3 staggered cutting inserts with 2 guide pads.

Quality Standards and Inspection ​

Paper mill rolls and industrial press components are manufactured to dimensional and surface quality standards that ensure reliable operation under cyclic loading.

Paper roll standards:

• TAPPI TIP 0402-34: Suction Roll Shell Condition Assessment
• ISO 1101: Geometrical Product Specifications
• Roll dynamic balance per ISO 1940 G2.5–G6.3

Press component standards:

• ISO 4413: Hydraulic Fluid Power — General Rules
• ASME B30.1: Hydraulic Press Safety Requirements
• EN 12418: Hydraulic Press Safety

Inspection requirements for deep drilled bores:

Non-destructive testing for roll shells includes ultrasonic thickness measurement between holes, magnetic particle inspection of ligament areas, and eddy current inspection for surface cracks. Press columns are inspected by ultrasonic and magnetic particle methods after BTA drilling and final machining.

FAQ ​

1. How many holes are drilled in a typical paper machine suction roll? A large suction roll (1,200 mm diameter × 6,000 mm face) contains 50,000–100,000 holes. The exact number depends on hole diameter, spacing, and open area requirement (typically 20–25% of roll face area).

2. What is the purpose of blind drilled holes in press rolls? Blind drilled holes in the roll cover trap water under nip pressure and release it by centrifugal force. They improve water removal efficiency and reduce rewetting of the paper web.

3. What cutting speed is recommended for BTA drilling of press column steel? For 4140/42CrMo4 at 300 HB, recommended cutting speeds are 50–80 m/min for diameters 30–80 mm and 40–70 m/min for diameters 80–150 mm.

4. How is straightness controlled in long press column BTA drilling? Double-rotation (counter-rotation) BTA systems achieve the best straightness. The workpiece rotates in one direction while the BTA tool rotates in the opposite direction, canceling out lateral cutting forces.

5. What causes suction roll shell fatigue cracking? Fatigue cracks initiate from burrs at hole edges, inadequate edge radius (< 0.05 mm), or surface damage from debris in the nip. Cracks propagate through the ligament between adjacent holes under cyclic nip loading.

6. What is the typical through-hole diameter in a suction roll? Standard through-hole diameter is 2.5–4.0 mm. The diameter must balance water removal capacity against structural integrity of the shell.

7. Can gun drilling be used for hydraulic press tie rod bores? Yes, gun drilling is the standard process for tie rod axial bores of 6–25 mm diameter × 1,000–6,000 mm depth in 4140 steel at 280–350 HB.

8. What coolant pressure is required for drilling press columns? BTA drilling of press columns requires 20–45 bar coolant pressure depending on diameter and material. Gun drilling of tie rods requires 60–120 bar.

9. How are hole edge burrs removed from suction rolls? Deburring is performed by mechanized brushing, abrasive flow, or electrochemical methods. Burr height must be reduced to ≤ 0.05 mm with 0.1–0.3 mm edge radius to prevent fatigue crack initiation.

10. What is the typical material for large hydraulic press columns? C45E/#45 steel for standard columns (up to 500 ton), 4140/42CrMo4 for high-strength columns (500–2,000 ton), and 4340 for ultra-high-pressure presses above 2,000 ton capacity.

Summary Table ​

Paper mill roll and industrial press component deep hole drilling encompasses a wide range of applications from small-diameter high-volume pattern drilling to large-diameter precision boring. The common thread is the requirement for consistent hole quality, controlled edge condition, and process reliability across thousands or tens of thousands of holes per component.