Appearance
A paper machine suction roll 6 metres long with 30,000 precision-drilled holes removes 1,200 litres of water per minute from the forming web — every hole must be within 0.1 mm of its true position, or the dewatering pattern becomes uneven and the paper tears. In roller manufacturing, deep hole drilling is not secondary machining; it is the process that defines functional performance.
Roller Types and Their Drilling Requirements
Paper and printing machines use several distinct roller types, each requiring a different deep hole drilling approach:
| Roller Type | Industry | Drilling Purpose | Hole Count per Roll | Typical Dimensions |
|---|---|---|---|---|
| Suction roll | Papermaking | Radial through-holes for vacuum dewatering | 5,000–50,000+ | Ø0.3–1.5 m × 3–10 m length |
| Press roll (blind drilled) | Papermaking | Blind holes in rubber cover for water removal | 10,000–100,000 | Ø0.5–2 m × 3–10 m length |
| Chill roll / cooling roll | Printing, coating | Axial cooling channels for temperature control | 10–40 per roll | Ø0.2–1.5 m × 2–8 m length |
| Printing cylinder | Flexo, gravure, offset | Ink passages, thermal control bores | 1–20 | Ø0.1–1 m × 1–6 m length |
| Central impression cylinder | Flexographic printing | Spiral cooling channels for temperature uniformity | 1–2 channels, spiral path | Ø1–3 m × 2–4 m length |
| Calendar roll | Paper, plastic film | Central bore for heating/cooling fluid | 1 (large bore) + 10–30 axial channels | Ø0.3–1 m × 2–8 m length |
Note: Anilox rollers (flexographic printing) use laser engraving for ink cell creation, not deep hole drilling. The deep hole drilling process is applied to the roller core or cooling channels, not the surface ink-carrying layer.
Suction Roll Drilling
Suction rolls are rotating perforated shells in the forming and press sections of paper machines. A vacuum box inside the roll draws water through the holes, dewatering the paper web.
Hole Pattern and Geometry
| Parameter | Typical Value | Notes |
|---|---|---|
| Hole diameter | 2.5–4.0 mm | Larger holes for higher drainage; smaller for finer paper grades |
| Shell thickness | 25–75 mm | Determines drilling depth (through-hole) |
| Hole spacing (circumferential) | 8–15 mm | Determines open area ratio |
| Hole spacing (axial) | 10–20 mm | Staggered pattern for uniform dewatering |
| Open area ratio | 20–30% | Critical for dewatering capacity |
| Drilling angle | 0–20° from radial | Angled holes reduce water throw from centrifugal force |
The open area ratio is the key design parameter. A typical suction roll with 3 mm holes on 12 mm staggered spacing achieves approximately 25% open area — meaning one quarter of the roll surface is open hole.
Drilling Process
Suction roll shells are drilled using multi-spindle gang drilling machines:
- Setup: The roll is mounted on a heavy-duty indexing system that rotates it in precise circumferential increments
- Gang drill: A row of 10–50 drill spindles, spaced to match the axial hole pattern, advances radially into the shell
- Indexing: After drilling one row of holes, the drill head indexes axially by one row spacing, or the roll rotates for the next circumferential row
- Through-hole detection: Each drill breaks through the inner shell surface — drill feed length confirms full penetration
- Pattern completion: The process repeats until the full roll surface is drilled
Tip: For suction rolls requiring millions of holes over the production lifetime, multi-spindle drilling reduces cycle time from weeks to days. A 50-spindle gang drill can complete one suction roll in 3–5 days versus 3–4 weeks for single-spindle drilling.
| Drilling Method | Spindle Count | Typical Cycle Time per Roll | Best For |
|---|---|---|---|
| Single-spindle | 1 | 3–4 weeks | Low volume, prototype rolls |
| Multi-spindle gang drill | 10–20 | 1–2 weeks | Medium production |
| Multi-spindle gang drill | 30–50 | 3–5 days | High-volume production |
| On-machine drilling | 5–15 | In-situ (no removal) | Roll remains in paper machine |
On-Site Drilling Technology
Several patents (US 6,361,254; US 6,789,984; US 5,344,259) describe apparatus for drilling paper machine cylinders without removing them from the machine frame:
- A multi-spindle drilling head is supported on adjacent cylinders using fastening belts and adjustable frames
- Separate motors drive spindle rotation and feed movement
- Drill guides contact the cylinder face to maintain position
- Air blast nozzles clear chips from drilled holes
This is particularly valuable for re-drilling or pattern modification on existing paper machines where roll removal would require weeks of downtime.
Suction Roll Materials
| Material | Application | Drillability | Wear Resistance |
|---|---|---|---|
| Bronze (SAE 64, 660) | Traditional suction rolls | Excellent | Good |
| Stainless steel (316L, 17-4 PH) | Corrosion-resistant rolls | Moderate | Excellent |
| Duplex stainless steel | High-strength, corrosive environments | Moderate-difficult | Excellent |
| Alloy steel (Ni-Cr-Mo) | High-load press rolls | Moderate | Very good |
| Rubber or polyurethane cover | Blind drilled press rolls | Soft, easy | Cover wear limits life |
Warning: Stainless steel and duplex stainless steel suction rolls require rigid drill guidance and pecking cycles to prevent work-hardening at the hole entry point. Cobalt HSS drills or carbide-tipped drills are recommended for production quantities.
Press Roll Blind Drilling
Press rolls in paper machines combine a steel core with a rubber or polyurethane cover (15–40 mm thick). Blind drilled holes in the cover carry water away from the press nip:
| Parameter | Typical Value |
|---|---|
| Blind hole diameter | 2–3 mm |
| Blind hole depth | 7–15 mm (cover thickness minus ~5 mm) |
| Hole pattern | Staggered, typically 25–30% open area |
| Cover material | Polyurethane (20–25 mm typical), rubber |
| Core material | Cast steel or stainless steel |
The blind holes are drilled radially into the roll cover after the rubber or polyurethane has been applied and ground to finished diameter. Multi-spindle drills with depth stops control penetration — the drill must not contact the steel core.
BTA Trepanning for Large Roller Bores
Heavy paper machine rolls (calendar rolls, press rolls, large drying cylinders) require a large central bore for:
- Weight reduction
- Heat transfer fluid circulation
- Mounting and shaft assembly
BTA trepanning is the preferred method because it produces a precision bore while recovering a solid core that can be used for other components.
Process Parameters
| Parameter | BTA Trepanning | BTA Solid Drilling |
|---|---|---|
| Bore diameter | 50–250 mm | 40–120 mm |
| Max depth | 16 m | 16 m |
| Depth-to-diameter | Up to 100:1 | Up to 100:1 |
| Coolant pressure | 2.5 MPa | 2.5 MPa |
| Coolant flow | 800 L/min | 800 L/min |
| Core recovery | Yes — solid bar recovered | No — material becomes chips |
| Typical roll OD | 100–670 mm | 100–670 mm |
Working Modes
For large paper rolls, three working modes are available on BTA machines such as the Premach T2150/T2250 series:
| Mode | Workpiece Rotation | Tool Rotation | Feed | Best For |
|---|---|---|---|---|
| 1 | ✓ Rotates | ✓ Rotates | Reciprocal | Largest rolls, highest straightness |
| 2 | ✓ Rotates | — Stationary | Reciprocal | Moderate length, simpler setup |
| 3 | — Stationary | ✓ Rotates | Reciprocal | Rolls that cannot be rotated (assembled rollers) |
Mode 1 (counter-rotation) produces the straightest bore because rotational errors from both the workpiece and tool cancel out. This is the preferred mode for calendar rolls and large press rolls where bore straightness directly affects roll balance.
Trepanning vs. Solid Drilling
| Factor | BTA Trepanning | BTA Solid Drilling |
|---|---|---|
| Material waste | Low (core recovered) | High (all chips) |
| Power required | Lower | Higher |
| Bore straightness | Excellent | Excellent |
| Equipment cost | Higher (trepanning head) | Standard |
| Typical bore size | > 60 mm | < 120 mm |
Cooling Channels for Chill Rolls and Printing Cylinders
Temperature-controlled rollers — chill rolls for extrusion coating, cooling rolls for film processing, and printing cylinders — require precision axial channels for heat transfer fluid circulation.
Channel Configurations
| Configuration | Description | Temperature Uniformity | Complexity |
|---|---|---|---|
| Single large bore | One central channel with inserted coolant pipe | ±5–10°C | Low |
| Multiple axial bores | 10–40 parallel gun-drilled channels near periphery | ±1–3°C | Medium |
| Spiral channel | Helical path machined or formed in roll shell | ±1–2°C | High |
| Supply/return pairs | Channels grouped in pairs with end-connected mixing chambers | ±1°C | High |
Multiple axial bores are the most common approach for precision temperature control. The process:
- Gun drill 10–40 parallel channels through the roll body, spaced evenly around the circumference
- Channels are typically 6–20 mm diameter, located 10–30 mm below the roll surface
- End caps or manifolds connect alternating channels into supply/return circuits
- Coolant flows through one set of channels and returns through the adjacent set
Gun Drilling Parameters for Cooling Channels
| Parameter | Typical Value |
|---|---|
| Channel diameter | 6–20 mm |
| Channel length | 2,000–8,000 mm |
| Number of channels per roll | 10–40 |
| Radial position tolerance | ±0.5 mm from nominal |
| Surface finish inside channel | Ra 1.6–3.2 μm |
| Coolant type | Water, thermal oil, or glycol mixture |
| Temperature uniformity target | ±1°C across roll face |
Tip: For chill rolls in extrusion coating, a temperature variation of just ±3°C across the roll face produces visible coating thickness variation. Gun-drilled cooling channels positioned close to the roll surface (10–15 mm) with high coolant velocity (3–5 m/s) achieve the best uniformity.
Spiral Cooling Channels
Modern flexographic printing central impression cylinders use spiral flow channels for temperature control:
- Research on satellite flexographic press cylinders (2024) shows that spiral channels with optimized rectangular cross-sections achieve axial temperature differences as low as 2.46°C
- Channel cross-section aspect ratio (height/width) significantly impacts heat transfer — a ratio of 0.6 produces optimal uniformity
- Spiral channels are typically machined or cast rather than gun-drilled, but they connect to axially gun-drilled supply and return passages
Printing Cylinder Manufacturing
Printing cylinders (for flexographic, gravure, and offset printing) require deep hole drilling for:
| Application | Drilling Requirement | Process |
|---|---|---|
| Cylinder shaft bore | Precision axial through-hole for mounting | Gun drilling or BTA |
| Ink supply channels | Small-diameter axial or radial passages | Gun drilling |
| Temperature control | Axial cooling channel arrays | Gun drilling |
| Lightweight construction | Large central bore | BTA trepanning |
| Journal bores | Precision concentric bores at each end | Gun drilling or boring |
Industry suppliers like Hole Specialists Inc. and Hone-All Precision provide gun drilling and deep hole drilling services specifically for printing industry rollers. Key requirements include concentricity within 0.05 mm and surface finishes of Ra 0.4–0.8 μm for bearing surfaces.
Machine Specifications Comparison
| Machine Series | Process | Max Bore Ø | Max Depth | Coolant | Application |
|---|---|---|---|---|---|
| Premach T2150/T2250 | BTA trepanning, drilling, boring | 250 mm (trepan), 500 mm (bore) | 16 m | 2.5 MPa, 800 L/min | Large paper rolls |
| Multi-spindle gang drill | Radial drilling | 2–6 mm (per spindle) | 75 mm | Emulsion mist | Suction rolls |
| Horizontal gun drilling machine | Gun drilling | 1–40 mm | 8 m+ | 5–10 MPa | Cooling channels |
| On-site drilling apparatus | Radial re-drilling | 2–6 mm | Shell thickness | Air blast | Roller maintenance |
Quality Requirements
Dimensional Accuracy
| Parameter | Suction Roll | Chill Roll | Printing Cylinder |
|---|---|---|---|
| Hole position tolerance | ±0.2–0.5 mm | ±0.5 mm (axial position) | ±0.1 mm |
| Hole diameter tolerance | ±0.05–0.1 mm | ±0.02–0.05 mm | ±0.02 mm |
| Bore concentricity | — | ±0.05 mm | ±0.02–0.05 mm |
| Surface finish Ra | — | 1.6–3.2 μm (channel ID) | 0.4–0.8 μm |
| Open area tolerance | ±1% | — | — |
Inspection Methods
| Inspection | Method | Frequency |
|---|---|---|
| Hole position | Coordinate measuring machine (CMM) or optical template | First-off + spot check every 10th row |
| Hole diameter | Plug gauge or air gauge | 100% for suction rolls |
| Bore straightness | Laser alignment system | Every roll |
| Channel pressure test | Hydrostatic test at 1.5× working pressure | 100% |
| Roll concentricity | Dial indicator during rotation | Every roll |
| Surface temperature | Thermal camera or contact thermocouple array | Calibration run |
Manufacturers and Service Providers
Deep Hole Drilling Machine Builders
| Manufacturer | Machine/Service | Key Capability |
|---|---|---|
| Premach (China) | T2150/T2250 BTA series | Trepanning up to 250 mm Ø × 16 m |
| MWN Niefern (Germany) | Suction roll manufacturing | 800+ suction rolls, 3,500+ covers |
| TBT (Germany) | Deep hole drilling machines | Precision BTA and gun drilling |
| Mollart (UK) | Accubore deep hole drilling centre | 7-axis, multi-process capability |
Contract Drilling Services
| Service Provider | Specialization | Certifications |
|---|---|---|
| Hole Specialists Inc. | Printing industry components | Precision gun drilling |
| Hone-All Precision | Thin-wall rollers, packaging industry | Specialised in complex geometries |
| Various Chinese manufacturers | Blind drill press rolls | Cast steel + rubber coated |
FAQ
Why do paper machine suction rolls need so many drilled holes?
Suction rolls dewater the paper web by vacuum — each hole acts as a drainage channel. A typical roll with 25% open area and 3 mm holes requires approximately 25,000–50,000 holes to achieve the water removal capacity needed for modern paper machines running at 1,500+ m/min.
What is BTA trepanning and why is it used for roller bores?
BTA trepanning cuts an annular groove around a solid core, producing a precision bore while recovering the centre material as a usable solid bar. It is used for large roller bores because it produces excellent straightness, minimises material waste, and handles the 100:1 L/D ratios typical of paper machine rolls.
What is the difference between a suction roll and a blind drilled press roll?
Suction rolls have through-holes drilled completely through the shell, with internal vacuum pulling water through. Blind drilled press rolls have shallow holes 7–15 mm deep in a rubber or polyurethane cover — these holes compress and release in the press nip, mechanically squeezing water out.
How are cooling channels made in chill rolls?
Axial cooling channels are gun-drilled parallel to the roll axis, typically 10–40 channels spaced around the circumference. End caps or manifolds connect them into supply/return circuits. Channel diameter is 6–20 mm, drilled up to 8,000 mm deep.
Can printing cylinders be re-drilled on site?
Yes. Specialised on-site drilling apparatus can be mounted on adjacent cylinders in the paper machine or printing press. Multi-spindle drilling heads with adjustable spacing and guide jigs allow hole pattern modification or re-drilling without removing the roll.
What materials are used for paper machine suction rolls?
Bronze (traditional, excellent drillability), 316L stainless steel (corrosion resistance), 17-4 PH stainless steel (high strength), duplex stainless steels (aggressive environments), and alloy steels (Ni-Cr-Mo for high-load applications).
What is the typical open area of a suction roll?
20–30% of the roll surface area. Higher open area increases dewatering capacity but reduces shell strength. The optimal ratio depends on paper grade, machine speed, and roll diameter.
How is hole position accuracy maintained across 50,000 holes?
Multi-spindle gang drills with precision indexing systems maintain hole position within ±0.2–0.5 mm. The roll rotates on a computer-controlled rotary axis, and the drill head indexes axially between rows. Laser or mechanical templates verify pattern accuracy at regular intervals.
What is the temperature uniformity requirement for printing chill rolls?
±1°C across the full roll face width is the standard for high-quality printing. Achieving this requires multiple gun-drilled cooling channels (10–40) with optimised flow distribution and end-connected supply/return circuits.
Can deep hole drilling create spiral cooling channels?
Spiral channels are typically machined or cast rather than deep-hole drilled. However, spiral flow paths can be created by drilling axial channels and connecting them with cross-drilled holes at the ends, or by inserting baffles into gun-drilled channels.
Conclusion
Deep hole drilling serves three distinct functions in paper and printing roller manufacturing: dewatering hole creation in suction and press rolls, large bore generation through BTA trepanning for lightweight and thermally controlled rollers, and precision cooling channel drilling for temperature-critical chill rolls and printing cylinders. Each application requires a different drilling process — multi-spindle gang drilling for radial through-holes, BTA trepanning for large central bores, and gun drilling for small-diameter axial cooling channels — but all share the requirement for precision, repeatability, and process control. Modern multi-spindle drilling technology has reduced suction roll drilling cycle time from weeks to days, while gun-drilled cooling channels enable the ±1°C temperature uniformity that high-speed printing and coating processes demand. The deep hole drilling processes described here are not peripheral to roller manufacturing; they are the core manufacturing operations that determine functional performance.