What gets marked on pipes
Pipes are marked along their length so that every cut piece still carries its identity. Typical data includes the brand, the size and wall thickness or pressure class, the material grade, the applicable standard and licence details where the product is certified, a heat or batch number and the production date and time. Plastic pressure pipes often carry metre marks as well, and copper tubes for air conditioning and plumbing carry their size and type. Stainless pipes for process lines usually carry heat numbers so that a mill test certificate can be traced back to the pipe.
Because pipes come off the mill or the extruder continuously, the mark is normally applied on line as the pipe moves, at a fixed pitch, with a time stamp or counter that updates automatically. Off-line marking of cut lengths is mostly used for small batches and fittings.
Which laser marking machine suits pipes
For metal pipes, a fiber laser is the practical choice. On mild steel and stainless steel it makes a dark mark or a light engraving, and on copper tube it marks well once focus and settings are right. On GI pipe the laser removes the zinc layer locally, which gives good contrast but leaves the marked spot without zinc protection, so keep the mark small and clear of areas that will be wet in service. NMB's On-line Fiber Laser is built for flying marking, where the laser marks a moving product using an encoder signal for line speed.
Plastic pipes are different. Black HDPE pipe can be laser marked on line in some plants, but the result depends on the compound and the line speed, so it needs trials on your own pipe. Many plastic pipe makers use continuous inkjet (CIJ) instead, because it prints at extrusion speed on most plastics in a contrasting ink colour, and NMB deals with Markem-Imaje CIJ printers for this. PVC is a special case. Laser marking PVC releases chlorine compounds that form hydrochloric acid with moisture, which is harmful to people and corrodes equipment, so PVC pipes must not be marked with a general purpose laser marker. Some large extrusion plants run dedicated laser coders on PVC with high-volume fume extraction, but for most plants CIJ is the safer and simpler route.
When CIJ is the better choice
For plastic pipes, and always for PVC pipes, continuous inkjet is usually the better choice. It prints at extrusion speed on most plastics in a contrasting ink colour and creates no laser fumes. A laser makes sense mainly on metal tube lines or on plastics that have passed a trial.
Setting up the job
On-line marking needs a firm head mount close to the pipe and an encoder that tells the controller the line speed, so the text does not stretch or squeeze as speed changes. A product sensor or a timer triggers each mark at the chosen pitch. Pipes can roll or wander on a run-out table, so add guide rollers just before the marking point to hold the pipe at a steady distance from the lens or print head.
For laser marking on pipes coming off an extrusion line, mark where the pipe is cool and dry. Keep the text short enough to finish within the time the pipe takes to cross the marking window at full line speed; long texts at high speeds may need a larger field or a second head. On welded steel tube, decide whether the mark goes on the seam side or away from it, and keep it clear of ends that will be threaded or welded later.
What to check before you buy
- Pipe material and coating. List each material you run, such as MS, SS, GI, copper, HDPE and PVC, because it decides between fiber laser and CIJ.
- Line speed. Give your maximum line speed and text length, as these set whether an on-line laser can finish each mark in time.
- Diameter range. Check that the mounting lets the head be adjusted for your smallest and largest pipe sizes.
- Variable data. Confirm the controller can add date, time, shift and a running metre or piece count automatically.
- Encoder and trigger. Ask how the marker connects to your line encoder and product sensor, and whether mark spacing stays even when the line slows.
- Fume handling. Laser marking coated or plastic pipe produces fumes, so plan extraction at the marking point.
- No PVC under the laser. If any of your lines run PVC, plan CIJ for those lines rather than sharing a laser marker between them.
- Shop conditions. Tube mills are hot and dusty, so check the enclosure and cooling arrangement of the marker.
Laser marking on pipes in Tamil Nadu
Pipe and tube work in Tamil Nadu ranges from steel tube and fabrication units in Chennai's industrial belt and BHEL-linked fabrication around Trichy, which handles boiler tubing and pressure parts, to plastic pipe extruders supplying the farm and building markets. Coimbatore's pump industry creates steady demand for pipes in agricultural water supply. For these plants, laser marking on pipes is most useful on metal tube lines and for marking cut lengths and fittings, while CIJ remains the common choice on plastic pipe lines.
NMB Enterprises in Poonamallee, Chennai, distributes IndoForeign Technologies laser systems including the On-line Fiber Laser, and deals with Markem-Imaje coding systems. Call or WhatsApp 098417 60722 with your pipe material, diameter range and line speed for a recommendation on laser marking on pipes or a CIJ setup.