Titanium wire is normally drawn through a flooded die rather than a dry die, because the metal seizes against almost any counterface once the surface film is disrupted. In wet drawing, wire passes through a circulating oil-in-water emulsion that cools the die, carries part of the drawing load on a lubricating film and flushes metal fines out of the contact zone. When that emulsion drifts out of specification, the outcome is predictable: discoloured wire, rapid die wear, breakage, scratches and burrs.
Why Wet Drawing Is Preferred for Titanium Wire
Heat removal – titanium conducts heat poorly, so friction heat concentrates at the die. Flood cooling holds the contact zone at a workable temperature.
Galling control – titanium has a strong tendency to pick up on steel and cemented carbide; a stable emulsion film keeps the metal separated from the die.
Surface quality – clean, bright wire reduces the pickling load and gives the uniform finish expected of wire for medical, dental and jewellery applications.
Fine gauges – wet multi-die machines draw wire from 0.1 mm to 5.0 mm with good dimensional control and reasonable die life.
Productivity – higher drawing speeds are possible because the die and the wire are cooled continuously.
Emulsion and Lubricant Control
Emulsion performance is measured, not judged by eye. The four numbers below should be logged every shift, because most drawing defects trace back to one of them moving out of range.
| Parameter | Typical range | What goes wrong | Action |
|---|---|---|---|
| Concentration | 8 – 15 % by volume | Low concentration gives a weak film, discolouration and die wear | Top up with concentrate at the correct ratio |
| Emulsion temperature | 35 – 45 °C | Too cold starves the film, too hot promotes oxidation and microbial growth | Adjust heating or cooling to hold the band |
| pH value | 8.5 – 9.5 | Falling pH signals bacterial activity and attacks the wire surface | Add alkali and a suitable biocide, then re-check |
| Water quality | Softened or demineralised | High hardness and dissolved salts cause precipitates and stratification | Change the make-up water source |
| Filtration | 20 – 50 µm | Metal fines and chips scratch the wire and clog the die holes | Service filters, skim the tank surface, keep the overflow running |
Keep the inlet and outlet free of contamination from machine oil and hydraulic leaks. A small amount of tramp oil is enough to break the emulsion film and to emulsify the lubricant system into a state that no dosing can recover.
Diagnosing Surface Discolouration
Discolouration of drawn wire is an oxidation effect. The usual causes, in order of frequency, are an emulsion concentration that has fallen below the working range, an emulsion temperature outside the 35 to 45 °C band, an excessive oil load carried in on the incoming wire, poor make-up water quality, and ingress of foreign oil from the machine itself.
Bring the concentration back to the specified value and re-check with a refractometer corrected for the emulsion type.
Restore the emulsion temperature to the working band and verify with a calibrated probe at the die box, not at the tank.
Check that the emulsion overflows at the exit die; a weak overflow lets fines and heat build up along the wire path.
Remove tramp oil with a skimmer or separator and repair any leaking seals or hoses.
Reduce drawing speed if the wire still discolours after the emulsion is back in specification; the contact zone may simply be running too hot.
Die Wear, Breakage and Surface Defects
Two root causes account for most die wear: the machine is not set up correctly, or the lubricant is not doing its job. Misalignment between the capstan, the guide and the die axis loads the die on one side, while an incorrect reduction schedule forces the die to do work that should be shared across several passes.
Check alignment of guide, die and capstan before every run, and confirm that the die angle matches the reduction being taken.
Control reduction per pass; excessive single-pass reduction causes die ring wear and wire breakage.
Use dies of the right material and finish for titanium wire, and record die life against the weight drawn.
Maintain adequate lubrication: insufficient film allows direct metal-to-metal contact, which produces scratches and torn surfaces.
Filter out metal chips and replace emulsion that has aged; contaminated emulsion carries debris straight into the die.
Inspect for burrs at the point of a break, which usually indicate a clogged die hole or lubricant breakdown rather than a material fault.
Routine Maintenance and Troubleshooting Matrix
| Symptom | Probable cause | Corrective action |
|---|---|---|
| Wire surface discoloured | Low concentration, wrong temperature, tramp oil, poor water | Restore concentration and temperature, remove tramp oil, change water |
| Rapid die wear | Misalignment, wrong die schedule, weak lubricant film | Realign the line, revise reduction steps, check emulsion strength |
| Scratches and burrs on broken wire | Metal chips, clogged die hole, aged lubricant | Improve filtration, clear dies, replace the emulsion charge |
| Emulsion stratification or heavy precipitate | Microbial attack, low pH, hard water, high temperature | Dose biocide and alkali, switch make-up water, cool the system |
| Wire breakage at high speed | Drawing too fast for the lubricant film, die wear | Reduce speed, inspect and change worn dies |
Frequently Asked Questions
Q: What emulsion concentration should be used for titanium wire wet drawing?
Most wet drawing lines run between 8 and 15 % by volume, with the exact figure set by the lubricant supplier and the pass schedule. Confirm the number on the product data sheet and verify it with a refractometer every shift.
Q: Why does titanium wire discolour during drawing?
Discolouration is oxidation in the contact zone. It usually comes from an emulsion temperature above or below the working band, a concentration that has fallen too low, oil carried in on the wire, or contaminated make-up water. Correct all four before adjusting the machine.
Q: How can die wear on titanium wire be reduced?
Correct alignment, a reduction schedule matched to the die angle, clean emulsion and an adequate lubricating film do more for die life than any single change. Record die life per die so that wear trends show up before quality suffers.
Q: What causes scratches and burrs on drawn titanium wire?
Metal chips in the emulsion, a partly clogged die hole, aged lubricant and a film too weak to separate wire from die are the common causes. Better filtration, clean dies and a fresh emulsion charge normally remove the defect.
Q: What causes emulsion stratification or heavy surface precipitate?
Microbial growth, a pH that has drifted low, hard water with a high dissolved salt content, and an emulsion running too warm. Add biocide and alkali as required, change the make-up water and cool the system back into range.
Q: How often should wet drawing emulsion be changed?
Change it on measurement rather than on a fixed calendar. Track concentration, pH, conductivity and bacterial count; top up and partially replace as trends move, and discharge the whole charge once several parameters can no longer be held in range.
