Galling in wire drawing: why it happens and how to prevent it
A capstan that starts marking the wire, a pulley with bright, torn patches, a batch coming off the line with longitudinal scores always in the same place: these are the classic symptoms of galling, a form of damage caused by direct contact between two metal surfaces sliding against each other under load.
Unlike abrasive wear, which removes material gradually and predictably, galling works by tearing: it takes hold in moments, leaves deep marks and damages the component and the quality of the wire at the same time. In the drawing of ferrous and non-ferrous wire, resistance to galling is therefore a technical requirement on a par with hardness and wear resistance.
| Are you finding torn areas or transferred material on your capstans? Ask our specialists for a technical assessment and identify the cause before it happens again. |
| YOU MIGHT ALSO LIKE▸ Capstan and pulley recovery: how to regenerate worn components on your wire drawing line▸ Wolside® vs Kerblack®: which coating should you choose for your wire drawing line |
What galling actually is
Galling is cold welding on a microscopic scale. When two metal surfaces press against each other and slide, real contact does not occur across the whole apparent area but on the microscopic peaks of the profile. On those peaks local pressure becomes extremely high, the lubricant film thins out and the two metals bond as if they had been welded together.
The motion, however, continues. The junctions that have just formed break apart and, as they break, tear material from one surface and transfer it to the other. This is the mechanism behind the build-ups, bright patches and grooves typically found on the pulling band of capstans, the part of the component where the wire wraps and slides.
The difference from abrasion is substantial: abrasive wear removes material slowly and evenly, and can be planned for; galling is sudden, localised and tends to get worse on its own, because every asperity it creates becomes the trigger point for the next one.
| Find out more about Paganoni, a division of Mario Nava S.p.A., specialised since the 1970s in anti-wear coatings for the wire drawing industry. |
The conditions that raise the risk
Galling does not strike at random: it appears when a number of operating conditions add up. Recognising them is the first step to knowing where to act.
- Dry drawing. With powder-soap lubrication the lubricant film is less continuous than in a liquid bath, and direct contact between wire and component becomes more likely.
- Metallurgical affinity between the materials in contact. Similar metals bond easily. Copper and aluminium in particular are ductile materials that readily adhere to the surface they run on.
- High pressures and speeds. The greater the load on the pulling band and the higher the line speed, the more heat friction generates — and heat encourages surfaces to bond.
- High surface roughness. A high Ra value means more pronounced peaks, so fewer contact points but far higher local pressure: exactly the condition in which cold welding takes hold.
- Geometry altered by wear. A component that has lost its original profile distributes load poorly and concentrates stress on narrow areas.
| For a guide by wire material, see Which coatings to choose for different metal alloys. |
What galling costs in production
The damage spreads across three fronts and adds up quickly.
On the wire: longitudinal scores, transferred material, surface defects that later passes do not correct but extend along the whole coil. In many applications wire finish is a supply requirement, so the defect turns into scrap or a downgraded batch.
On the component: the torn surface loses its original finish and, with it, the geometry of the pulling band. From that point on friction rises, heat rises and degradation accelerates. The capstan, cone or pulley reaches the end of its service life far earlier than planned.
On the line: unplanned interventions, early replacements, downtime. The largest cost is almost never the spare part, but the production lost.
| Do you have recurring stoppages on the same component? Talk to our technical team for an analysis of your line. |
| YOU MIGHT ALSO LIKE▸ Kersint®: the sintered technical ceramic for wet wire drawing and acid baths▸ Coldside®: the tungsten carbide coating for ribbed wire drawing |
Why a technical coating breaks the mechanism
An anti-wear coating does more than make the surface harder: it acts on the cause of galling, which is the affinity between the materials in contact.
The first lever is chemical. By placing a layer of oxides or carbides between wire and component, contact is no longer metal on metal: the affinity that lets the two surfaces bond disappears, and cold welding simply does not start.
The second lever is geometric. Coatings developed for wire drawing are finished to very low roughness values: fewer peaks mean load spread over a larger area, lower local pressures and less frictional heat. The wire’s coefficient of friction on the surface drops appreciably, and the risk of adhesion drops with it.
The third lever is stability over time. A super-compact, porosity-free deposit keeps its finish through long working cycles, whereas a porous surface degrades and gradually restores the original conditions.
| Want to know which solution suits your process? Request technical advice. |
Anti-seize solutions in the Paganoni range
Each product in the range answers a different combination of process, wire material and working environment. The choice starts from these three variables.
- Kerblack® — the chromium-oxide coating is regarded as the best anti-wear and anti-seize coating currently known, nationally and internationally, for dry drawing of ferrous and non-ferrous metals. It drastically reduces the wire’s coefficient of friction on the surface and eliminates galvanic corrosion and passive currents. It is also suited to aluminium parts.
- Wolside® — super-compact hard metal, hot-fused with HIP (Hot Isostatic Pressing) technology and based on tungsten carbides. It combines anti-seize protection with high impact resistance: suited to rings and cones, dancers, wire guide rollers, return pulleys, pulling capstans and roughing dies, both dry and wet.
- Coldside® — also tungsten-carbide based, it stands out for its high resistance to friction and to wire slippage. It is the choice for capstans used in drawing ribbed wire for reinforced concrete, and it can be applied to already finished or worn parts.
- Kersint® — sintered ceramic based on zirconium oxide. It is not a deposit: the part is ceramic throughout its volume, so there is no interface with an underlying metal. It requires and maintains very low roughness, and resists corrosion in acid baths such as those of copper-plating tanks.
- Niksint® — a coating obtained by depositing nickel, with anti-wear and anti-corrosion functions, used on the tubes and components of furnaces for the in-line annealing of copper wire.
Prevention, inspection and recovery of damaged parts
Protection against galling is maintained with the same care with which it is achieved. The dimensional and roughness checks set by Paganoni’s internal standards, together with dynamic balancing and the final inspection certificate, exist precisely to verify that the component works under the conditions it was designed for.
When the damage has already occurred, replacing the part with a new but uncoated component means restarting the very same cycle. The more effective route is recovery: restoring the original geometry and depositing Kerblack®, Wolside® or Coldside® on the pulling band gives the part a surface with a low Ra value and no affinity with the wire. The regenerated component is far superior to a new, uncoated capstan, with a clear economic advantage over buying new.
The service also includes cleaning the inside of the capstan, removing scale deposits and applying a product that slows their re-formation: a drum that cools properly runs at lower temperatures, and temperature is one of the factors that encourage surfaces to bond.
| Do you have parts already marked by galling? Consider the capstan and pulley renovation service or contact us for a technical analysis. |
| Hai particolari già segnati dal grippaggio? Valuta il servizio di recupero di cabestani e pulegge oppure contattaci per un’analisi tecnica. |
