Diameter Difference Measurement Sensor

What is the difference in measurement to determine weather to change the barrel or not?

The allowable tolerance (maximum) is 0.6mm on either side (radially) and hence an increase in barrel diameter or decrease in screw diameter of 1.2mm calls for replacement or rework. Since dismantling, cleaning, measuring screw / barrel is a difficult process we need a method to measure diameter difference (absolute or relative) over entire barrel length.

As I understand it you are wanting to measure the diameter of the barrel along the entire length of 3 meters, if so I would suggest a laser measuring curtain. Measuring along the entire length is going to be difficult. You will need to have the measuring device slide along the length while while measuring. If the barrel expands or shrinks uniformly you can take a single point measurement.

I would suggest a laser measuring system, there are many different manufacturers. Determine what your requirements are then shop around.

I do not think an ultra sound device would function quite as well as you require.

If you could elaborate on how you plan to measure I may be able to provide a better idea.

This isn't going to work as the OP wants to do it without dismantling the device. Your laser curtain would only work inside the barrel wouldn't it? Plus the centre rotor has to be measured as well; to get the difference.

I am overwhelmed by the response we have here for this issue that I have with my clients. Anything that does should consider two factors, as already indicated. The screw-barrel assembly should not be dismantled from machine since it might consume as much as 24 hours. And, there will be some plastic material inside since it is not possible to clean them out. But if we use any method that only takes into consideration the metal and not non-metal, would that not be helpful? The LC frequency meter is quite a good idea but I am thinking how to do on-site. Does it not sound kind of "laboratorical?"

Hi,

if your injection molding machine is filled with molten material then ultrasound will work, may be you have to play a bit with frequencies and intensities as the reflection from steel to plastic is very strong, so only a little bit of the wave is entering the plastic, then reflected and coming back.

If it is not filled with molten material then there are two possibilities:

a. capacitive distance sensing if you can insert a 1 cm diameter capacitive probe into the wall of the machine (Lion-precision has some good ones)

a1. use the barrel as one side of a capacitive sensor and the screw as the other side: most simple but requires electrical insulation of screw to barrel and this is usually not possible (depending on bearings and gears).

and

b. use your barrel-screw as UHF oscillator. The screw to barrel acts as capacitance and the path along barrel and screw as inductance, so this is an LC oscillator. As the gap grows the capacitance is going down and frequency up.

Estimated resonant frequency for 1 m screw length will be near 50MHz. If plastic inside then the dielectric constant of the molten material will change this a bit, especially damping will be much higher if material is non PE or similar low loss material.

Get an RF-frequency generator and an oscilloscope and try.

RHABE