The mould is the last tool that touches the strip before it becomes a tube. Its bore sets the seam-to-gauge gap, its surface sets the mark left on the OD, and its keyway sets how it seats on the shaft.
When a new tube size comes in with ovality, seam mismatch or scuffing, the mould is the first suspect.
So the right way to specify tooling is to work backwards from the finished pipe: decide the family, then the steel grade, then the hardness and tolerance class, and only then talk price.
What decides accuracy and surface
Three table attributes determine what the finished tube looks like — steel grade, hardness and tolerance — and the key dimensions are the checks that confirm them before shipping. The table gives the first three per row, so a buyer can name a class instead of a vague request.
Key dimensions are 100% inspected — raw material, arc precision, hardness, thickness, base diameter, bore and keyway — which is the list to think about when writing a purchase spec.
Two families on the size envelope
YH makes two mould families, and the size range decides which one applies before anything else does.
Laser welding moulds cover round pipe Φ5–630 mm and square or special-shaped tube from F10×10 to F400×400. Steel grade is Cr12MoV, SKD11 or D2, heat treated to 60–65 HRC. Round moulds are specified on roundness; square and shaped moulds on flatness.
High frequency (HF) welding moulds cover round pipe Φ5–711 mm and square tube from 10 to 1000 mm. Steel grade is Cr12MoV alloy steel, heat treated to 60–66 HRC. Round moulds are specified on arc; square moulds on diagonal.
There is also a third row for cold-forming profiles with custom sections in high-Cr MoV alloy, tolerance per drawing, 60–66 HRC. That row is not a size band — it is for structural profiles where the section is drawn by the customer.
Overlap matters. A round tube from Φ5 to Φ630 mm sits inside both laser and HF ranges, so size alone does not pick the family. The welding process on the line does.
If you are still choosing the line, the laser welding tube mill and high-frequency tube mill pages describe each process; the mould set should follow the process, not the other way around.
Above Φ630 mm round, or above F400×400 square, only the HF family is in range.
Tolerance classes: how to translate a pipe requirement
The table uses different tolerance terms per family, and that is the point a buyer usually misses.
Laser mould rows state roundness ±0.05 to ±2.0 mm for round pipe and flatness ±0.05 to ±2.0 mm for square and shaped.
That is a band, not a single figure: the tolerance stated in your order should sit inside it and be matched to the wall thickness and the pipe's end use. A thick-wall structural tube and a thin-wall sanitary tube do not need the same end of that band.
HF mould rows state arc ±0.02 mm for round pipe and diagonal ±0.02 mm for square. These are single figures rather than bands. The category summary describes tolerances of "from ±0.02 mm".
The practical translation: if your finished-pipe drawing calls out ovality or roundness, it maps to the laser roundness figure; if it calls out squareness or equal diagonals, it maps to flatness (laser) or diagonal (HF); if it calls out wall uniformity around the circumference, it maps to the arc figure on HF moulds.
Ask the supplier to confirm which figure the quoted mould is held to. A quote that just says "precision mould" has not answered the question.
How a mould is made and checked
Every YH mould follows an 11-step flow: mould raw material → rough machining → drilling → CNC precision machining → polishing → marking → heat treatment → bore grinding → finish machining → keyway cutting → final inspection.
Two steps carry most of the buyer's risk. Polishing is where the working surface reaches a mirror-grade finish, which is what keeps the mould from scuffing the strip. Heat treatment follows it and is where the 60–66 HRC figure is set.
In the flow as listed, bore grinding and keyway cutting come after heat treatment, so the bore and keyway are finished at final hardness. Final inspection is where the 100% key-dimension check happens.
When you receive a set, the same list is the one to check against the packing sheet: hardness, arc precision, thickness, base diameter, bore, keyway. Request the inspection record with the shipment — it is the document that ties the delivered mould back to the row you ordered.
Service life and the honest limit
YH states stable rolling over thousands of tons of steel with a service life above 5,000 hours. That is the figure the source gives, and it is a useful order-of-magnitude for planning.
What the source does not give is a regrinding interval or a replacement schedule. We will not invent one. Hardness (60–66 HRC), strip grade, line speed and whether the mould is high-chromium-molybdenum-vanadium on a high-wear design all move service life, and no single number can cover every combination.
So the buyer should build the interval from their own records. On each mould set, log:
- the tube size and shape it runs;
- the strip grade and thickness;
- the metres or hours run between changes;
- the reason for the change: wear, scuffing, dimension drift or damage.
After two or three change cycles the pattern usually separates a mould life problem from a line-setting problem. That data also makes the next order easier to specify — you can tell the supplier which row you are replacing and why.
Stating the requirement before ordering
A mould requirement that can be quoted without follow-up questions looks like this:
- Family: laser or HF, matching the line.
- Shape and size: round Φ___ mm, or square F___×___ mm.
- Steel grade: Cr12MoV, SKD11 or D2 for laser; Cr12MoV alloy for HF. If you run high-wear strip, say so and ask about the high-Cr MoV variant.
- Hardness: 60–65 HRC for laser rows; 60–66 HRC for HF rows.
- Tolerance: the specific term (roundness, flatness, arc or diagonal) and the figure — within the row's band on laser rows, at the stated single figure on HF rows.
- Inspection: ask for the key-dimension record with the shipment.
If the size is new to your line, YH develops custom moulds for new pipe sizes and profiles, including tooling for other mill brands. For the full tooling catalogue, including roller sets and wear parts, see tooling and spare parts.
For the laser and HF lines the moulds run on, see the laser pipe welding line and the HF carbon steel pipe mill.
Next step
Send your tube size (round or square, with the dimension), your mill model and your strip grade through the contact page. You will get back the matching mould row — family, steel grade, hardness and tolerance term — before any price discussion.
If you already run a mould set that is wearing early, include the change log described above; it is the fastest way to find which of those four variables is off.