In wire and cable production, the "rod breakdown machine" process for copper rod and aluminum rod is the first critical step in conductor forming. The quality of the drawn wire directly affects the subsequent processes of intermediate drawing, fine drawing, annealing, stranding and even the final cable’s acceptance rate. Many cable plants encounter several typical problems in actual production:
· Drawing speed cannot be increased, limiting output.
· Wire surface is dull, scratched, or even retains oxide scale.
· Excessively long downtime when changing specifications or dies.
· Mechanical properties of the drawn copper/aluminum wire are not ideal, and remain unstable even after annealing.
To solve these problems, simply “buying a more expensive Copper / Aluminum RBD Machine” is not enough. One must understand the technical fundamentals of the drawing machine’s capstan drive system, cooling & lubrication design, annealing integration mode, and take-up type. This article approaches from a process perspective, sharing key control points in copper / aluminum RBD machine, hoping to provide practical reference for cable industry technical colleagues.
I. Deformation principle of RBD machine: why not “draw in one pass”?
Copper rod (normally 8.0mm diameter) or aluminum rod (normally 9.5mm diameter) must be reduced to around 2.0–3.5mm through multiple passes. In each pass, the wire passes through a drawing die with progressively smaller bore, undergoing plastic deformation under the pull of the drawing capstan.
Core constraints:
· Reduction per pass cannot be too large (otherwise wire breakage or die damage).
· Adequate cooling and lubrication must be provided.
· Tension between passes must be continuous and stable.
Therefore, modern Copper / Aluminum RBD Machine generally adopt a “multi-capstan, multi-die” continuous drawing configuration.
II. Drive types: single-motor drive vs. split-drive vs. individual-motor drive
The drive method of RBD machine directly determines speed adjustability, die change efficiency, tension stability and final wire quality. Currently there are three main technical routes in the industry, each suitable for different applications.
| Type | Single-motor (central) drive | Split independent drive (typical: independent finish capstan + one motor for the rest) |
Individual-motor drive (one independent motor per drawing capstan) |
|---|---|---|---|
| Configuration | One main motor drives all drawing capstans through a gearbox, belt or chain. The speed ratios between capstans are fixed | · The first several drawing capstans are driven by one shared motor· The last drawing capstan (finish capstan) is driven by a separate independent motor· Tension between the two sections is closed-loop controlled via a tension sensor | Each drawing capstan (including the finish capstan and all preceding ones) is driven by its own independent AC servo motor or inverter-duty motor. All motors are synchronised in real time via a high-speed fieldbus |
| Advantages | · Simple construction, low manufacturing cost· Low control system requirements, easy maintenance | · Finish capstan independently controls final line speed, giving more stable outlet speed· The front section retains good synchronisation with its shared drive· Die change only requires adjusting the overall speed ratio of the front section, faster than single-motor drive· Moderate complexity, controllable cost | · Each pass tension independently closed-loop controlled – different pass reduction distributions can be set for different materials (copper, aluminum, copper clad aluminum), minimising breakage risk · Near-zero downtime for die change – simply modify speed ratio values on the HMI; no gear changing or mechanical realignment · Slip approaches zero – each capstan’s line speed precisely matches the die outlet speed, greatly reducing surface scratching · One machine, multiple uses – easily switch between copper rod, aluminum rod and even copper clad aluminum; also enables special processes such as “backward drawing” · Energy optimisation – individual motors can be stopped when a pass is temporarily unused, reducing no load losses |
| Disadvantages | · Tension in each pass cannot be adjusted individually; only mechanical ratio wheels or slip compensation is possible· When changing dies, the speed ratios of all passes must be recalculated, resulting in long line downtime· Wire tends to slip on the capstans, affecting surface quality· Poor adaptability to different materials (copper vs. aluminum) | · The capstans within the front section still have fixed speed ratios; individual pass reductions cannot be optimised separately· When producing special wires (e.g. high strength aluminum alloy, high elongation copper wire), tension distribution is still not fine enough | · Higher initial investment (more motors, drives, control system components)· Higher technical requirements for electrical commissioning and subsequent maintenance personnel· Larger electrical cabinet volume and increased heat dissipation needs |
| Applicable scenarios | Small-scale production, long-term single-specification production, budget-limited retrofit projects | Most conventional cable conductor production, balancing efficiency and flexibility | · Cable plants that frequently change wire specifications or materials· High end power cables, aerospace wires, electronic wires and other products with extremely demanding surface quality and elongation· Smart factories aiming for full digitalisation and traceable production |
III. The key to surface quality: oxide removal and cooling/lubrication
Copper and aluminum rods develop an oxide film on their surface during storage or prior processing. If not effectively removed during drawing, this film can be drawn into the wire or pressed onto the surface, leading to:
· Dark, dull wire, affecting appearance.
· Difficulty in subsequent welding or tinning.
· Increased contact resistance.
Effective process measures of Copper / Aluminum RBD Machine:
· Inlet cleaning section – before the first die, use felt pads or spray devices to initially remove loose oxide scale.
· Enhanced coolant supply at the die area – coolant (emulsion or drawing oil) not only carries away heat but also creates a high-pressure zone at the die inlet, flushing away tiny oxide particles from the wire surface while providing lubrication.
· Die box design – the flow channel shape and coolant outlet angle affect the flushing effect. With optimised design, the wire emerges with a bright, metallic colour, eliminating the need for additional pickling or mechanical polishing.
Technical point: For aluminum rod, the oxide film is harder and more brittle. Adequate coolant flow and pressure must be ensured, otherwise “aluminum dust” adhesion easily occurs, causing die damage and wire scratching.
IV. In-line annealing: how “continuous drawing + continuous annealing” improves performance
Many cable plants perform drawing and annealing separately: first draw to hard wire, then anneal in a separate furnace or annealer. This has two problems:
· Hard wire left for too long ages naturally, leading to non-uniform annealing results.
· Two handling steps (take-up and pay-off) increase labour and scrap.
In-line annealing means annealing the wire continuously after the last drawing capstan, before take-up. Key technical points include:
· Annealing voltage/current interlocked with line speed – the faster the speed, the higher the heating power must be synchronised
· Annealing tube length matched with cooling section – ensures the wire completes recrystallisation in a protective atmosphere (or steam)
· Uniform cooling after annealing – affects final elongation and resistivity
With “continuous drawing + continuous annealing” integration, Copper / Aluminum RBD Machine obtain:
· Stable elongation of 20%–30% or more (depending on material).
· Conductivity meeting or exceeding IEC requirements.
· Elimination of intermediate annealing steps, reducing work-in-process inventory.
V. Take-up options: double-wheel spooler vs. basket coiler
Many people overlook the impact of the take-up stage on wire quality. Uneven take-up tension leads to uneven tightness on the spool, even causing indentation or tangled wire.
Technical characteristics of the two mainstream take up methods:
| Take-up type | Double-wheel spooler | Basket coiler |
|---|---|---|
| Structure | Two active wheels alternate take-up; spool change without stopping | Large, shaftless basket; wire coils naturally |
| Suitable wire size | Mainly medium-fine wires (for direct use after heavy drawing) | Long-length, heavy-weight wires for subsequent stranding |
| Advantages | Short changeover time, suitable for continuous operation | Large coil weight; shaftless design avoids spool deformation damage |
| Cautions | Must precisely control tension spike during changeover | Requires attention to bending radius; careful with aluminum wire |
Suggestion: Choose according to downstream processes. If heavy-drawn wire goes directly to intermediate drawing or stranding, a double-wheel spooler is more efficient. If the wire needs long-distance transport or long-term storage, a basket coiler is more reliable.
Conclusion
Copper / aluminum RBD machine is not a mystery. It is a balanced integration of multiple subsystems: transmission, lubrication, cooling, annealing and take-up. LINT TOP’s experience with the RBD machines shows that split independent drive + optimised cooling + optional in-line annealing + flexible take-up can effectively cover the mainstream requirements of today’s cable factories for conductors.
If you are struggling with efficiency, quality or changeover flexibility in your rod breakdown process, start by examining the above technical points against your existing equipment. You are also welcome to exchange ideas with our process engineers, and together explore a drawing solution better suited to your product mix.
LINT TOP – speaking with technical details, building the drawing equipment that cable plants need.