PLC Automatic Tube Mill for Round and Square Pipe

The forming, welding and sizing train is shared; what changes is how much of the sequence the PLC and drives run without an operator at the panel.

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Technical Specification Table

Model steps and OD coverage (mm), HG32 through HG630: HG32 Φ10–32 HG50 Φ16–50.8 HG76 Φ12.7–76 HG89 Φ32–89 HG114 Φ45–114 HG165 Φ60–165 HG219 Φ114–219 HG273 Φ114–273 HG325 Φ165–325 HG426 Φ165–426 HG508 Φ219–508 HG630 Φ325–630 Section shapes: round, square, rectangular — most HG steps run all three. The table below is the same table a buyer would build from our model list, because the automation grade does not move any of these boundaries. Twelve model steps cover the outside-diameter range, and a line is quoted against one of them.

Welding: high-frequency induction welding across the whole series, using skin and proximity effect to concentrate current at the seam. Automation grade: semi-automatic, or full-automatic under PLC control. Welder power: stepped with diameter across 150–1500 kW. Material yield: 93% or better by line design.

Forming technology: conventional roll forming, or direct forming square.

Line Configuration and Scope of Supply

1. Uncoiler with a pneumatically expanding four-link mandrel, fed by a coil car, which tensions the coil so it neither wanders nor slackens.
2. Five-roller leveller, which flattens the strip before forming. Strip flatness is the precondition for everything downstream.
3. Automatic shear-welder, which crops the irregular head and tail of each coil and butt welds one coil to the next.
4. Spiral accumulator, which stores strip so the mill keeps forming while the next coil is being joined. This is the unit that makes non-stop running real rather than nominal.
5. Forming and sizing mill, the core unit: rolls bend the flat strip progressively into an open tube shape, and after welding the sizing stands bring it to final diameter.
6. High-frequency induction welder, sized to the pipe range.
7. Flying saw, cutting to length while pipe is still being delivered at speed.
8. PLC and variable-frequency control system, which ties line speed, sequence timing and cut length into one controller.

The process the units perform is the same in either grade: rolls form the strip step by step; high-frequency current concentrates at the open edges through skin and proximity effect and heats them to welding temperature; squeeze rolls press the two edges together to form a continuous seam; the tube is then cooled, sized and straightened.

The eighth unit is where the automation grade actually lives. On the full-automatic grade the PLC and variable-frequency drives hold line speed and repeat the cut length without the operator trimming settings between cuts; control stability is what keeps speed from drifting and length from wandering.

Ten factors decide whether a line holds quality across a production run, and all ten are listed below rather than left to be discovered on site.

1. Incoming strip — grade, thickness tolerance and flatness — checked on arrival; when it is wrong the symptoms are forming wander, seam inclusions and uneven wall.
2. Roll material and heat treatment, which govern how long shape stability holds.
3. High-frequency power, frequency and welding speed, which govern seam fusion.
4. Squeeze amount and seam alignment, which govern weld offset, edge mismatch and burr.
5. Sizing and straightening, which set final dimension and straightness.
6. Impeder and induction-coil condition, which decides how tightly weld energy stays focused at the seam.
7. Control and servo stability, which keeps line speed and cut length repeatable — the one factor the full-automatic grade addresses head on.
8. Operator setup and changeover practice, which decides how much scrap a size change costs.
9. Final inspection as a stage in its own right, with UT and eddy-current testing on API builds.
10. Post-weld cooling matched to welding speed, which stabilises seam structure.

Five of the ten sit inside the mill and are engineered into it; three are operational and respond to training; two — strip quality and the discipline of replacing wear parts on time — sit on the buyer’s side of the line. Saying which is which before a line is quoted is more useful to a plant manager than a blanket assurance covering all ten.

Ultrasonic and eddy-current testing are worth naming precisely: in-line UT and ECT belong to the API line-pipe configuration, where medium-frequency annealing, straightening, end facing, hydrostatic testing, UT and ECT are added on top of the high-frequency mill.

Final inspection on a standard HG line is a stage in its own right; in-line UT and ECT belong to the API build.

A tube mill is bought as a sequence of units, and the automation grade changes how they are driven rather than which ones are present. Eight units make up the standard train:

Size Change, Roll Wear and Running Cost

On a direct-forming square build, a combined die set is adjusted by servo instead, and the roll saving is above 90% because contact is point contact rather than full-face. Running cost on a tube mill is dominated by two things a specification sheet rarely shows: how long a size change takes, and how fast the rolls wear. There is one exception: making 100 × 100 mm tube needs the upper roll on the final open stand changed.

Rolls are machined in-house on our own CNC equipment, which is the reason replacement rolls stay available years after handover rather than becoming an obsolescence problem.

Size change behaves differently depending on the forming technology quoted with the line. On a conventional roll-forming build, a size change means changing rolls.

Setting up after a size change is also an operator variable: quick changeover and trained change crews are what keep scrap during commissioning of a new size down.

Forming and sizing rolls are the first determinant of shape accuracy, roundness and squareness, edge definition and dimensional consistency. Roll material and heat treatment govern how long that accuracy holds; when either is wrong, the symptoms are early wear, diameter drift, uneven corner lines and repeated re-machining at every size change.

• Impeders and induction coils, wear parts replaced against welding hours; their condition directly affects how tightly weld energy stays focused.
• Cooling water and emulsion, and hydraulic oil and grease — specifications supplied by us, purchased locally by the buyer.
• Forming and sizing rolls as replacement wear items, backed by in-house CNC capacity. Wall thickness, line speed and shift output are confirmed against your pipe size, material grade and cut length at quotation. Send us those three and we will state the figures.

Applications and Output Examples

What those buyers measure is weld pass rate, diameter and wall coverage, non-stop coil change, and energy and yield per tonne. Two application families account for most enquiries.

Structural and scaffolding tube: structural-tube plants produce square, rectangular and round sections for load-bearing steelwork, scaffolding and general machinery parts. Here the measures shift to corner definition and straightness on square and rectangular sections, changeover efficiency, and electricity per unit.

Two further applications are served by the same line capability rather than by separate machines: electrical wiring conduit and agricultural pipe are both round carbon-steel sections within the HG diameter range.

Responsibility for the result splits cleanly, and stating it early prevents the common argument later. The mill controls weld power, seam alignment and squeeze; sizing and straightening set dimensional accuracy and straightness; line design supports material yield above 93%.

Incoming strip grade, thickness tolerance and flatness, and day-to-day operation, remain the buyer’s side — the line offers levelling and incoming checks, but it cannot compensate for out-of-spec strip.

Fluid transport pipe: pipe plants run HG lines continuously to produce carbon-steel welded pipe for oil and gas transport, municipal water and drainage, gas distribution, and chemical and heating pipework.

Delivery, Installation and Training

Lead time is 50–90 days.

Training is not optional on this line, and specific steps require it. Coil loading and strip threading need operator training. Shear-welding a coil join in time with the accumulator needs operator training. Setting a new size — roll change on a conventional build, servo adjustment on a direct-forming build — needs a trained change crew.

Setting welder power, welding speed and squeeze, then running and watching the process, needs process-level training. Cutting and collecting is routine operation.

After handover, support is a first reply through a single named point of contact, all-hours online support, on-site dispatch when needed, and direct spare-part shipment.

The engineering side behind that is a team of twenty averaging twenty years each, working from an owned production base that is open to factory audit.

Certification: GB/T 19001-2016 / ISO 9001:2015 (quality management system, certificate No. 18524Q11269R2S). Product standards applicable to the pipe produced depend on the destination market and the buyer’s product specification; the equipment itself follows destination-market machinery-safety rules and the product standard the pipe is made to.

Export packing is specified per item rather than generically. Control cabinets, impeders and induction coils, forming rolls and cutting tools travel in moisture-protected wooden cases with a spare-parts pack; heavy large-diameter frames ship bare, braced on cradles with designated lifting points and rust protection.

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