Short answer
- Controlling pipe thickness by cutting a sample now and then leaves almost all production unmeasured, forces you to extrude with extra wall and warns you late.
- The solution is to measure in line, continuously and at several points around the circumference, with alarms at the moment and a record of every pipe.
- That is what an ultrasonic thickness gauge installed on the extrusion line does.
1 to 4 simultaneous channels, pipes from 20 to 250 mm in diameter and walls from 0.5 to 200 mm, in HDPE, PVC or GRP. Configured to suit each line.
Problem 1: measuring by sampling
The symptom: a piece of pipe is cut every so often and measured in the lab. Between one sample and the next, metres and metres go out unchecked.
Why it matters: a process variation —temperature, haul-off, resin flow— can produce an out-of-tolerance section that doesn't coincide with any sample, and is discovered on site.
How it is solved: by measuring non-stop, on the line itself, as the pipe moves.
With the QST: it measures in real time, around 8 times per second per channel, 100% of production.
Problem 2: extruding with extra wall
The symptom: to guarantee the minimum thickness of the standard or the customer, the line runs with a generous safety margin.
Why it happens: if you don't know precisely what thickness is coming out at each moment, the only way not to fall short is to overshoot. And every extra tenth of a millimetre is resin paid for and given away.
How it is solved: by seeing the real thickness continuously, so the extruder can be set as close as possible to the required minimum, without going below.
With the QST: each channel's continuous reading lets you adjust resin consumption with data, not margins.
Problem 3: the wall isn't even around the circumference
The symptom: the average thickness is right, but one side of the pipe comes out thinner than the other.
Why it happens: die centring, gravity on the still-hot material or uneven cooling push the wall to one side. A single measuring point doesn't see it.
How it is solved: by measuring the wall at several points around the pipe at the same time.
With the QST: up to 4 simultaneous channels; the manufacturer recommends 4 to cover the circumference.
Problem 4: finding out too late
The symptom: the defect is found at the end of the shift, when there are already many metres of pipe to reject.
How it is solved: with minimum and maximum limits that warn the instant the thickness goes out.
With the QST: visual alarms and a relay output to connect an external warning on the line.
Problem 5: proving what thickness each pipe had
The symptom: a customer complains, and there is no way to know what thickness that pipe had, which resin batch it came from or who was on the line.
How it is solved: by recording every measurement with its position along the pipe and the production data.
With the QST: logging by time or distance, with an input for a length encoder, and dmq DataCenter software, which stores date and time, pipe position, resin or batch and operator. Bluetooth and RS232 communication.
Problem 6: every line is different
The symptom: a standard system doesn't fit the line's diameters, thicknesses or layout.
How it is solved: by configuring the system to measure: number of channels, transducers for the diameter and thickness, and mounting to suit the line.
With the QST: it is built to order and installed on site. It uses fixed single-crystal transducers: 2 MHz for thick walls and large pipes, 5 MHz for thin walls and small to medium pipes, with cable extensions to fit the line.
What the QST doesn't do
- Outside diameter or ovality: it measures wall thickness, not outside dimensions.
- Spot measurements by hand, off the line or on installed pipe: that is what the portable QS gauge is for (see also the corroded pipes guide).
- Metal pipe: ask us about the application.
Source: DEMEQ, QST series page and brochure.
