Re: String Line Rip Detector
They are reasonably effective. If you wish a more precise definition, then you need to observe the geometry.
A series of string lines are placed in between the impact idlers as far forward as possible such that the foreign object penetrating the belt has little space where it cannot be detected. The idea is that the idler is the reaction point which stops the penetrants forward motion carried by the belt.
The string engages the penetrant between idlers, for each and every idler that may see the penetrant. There is a small zone where the string line cannot engage the penetrant that is located between the string line and next idler downstream of the belt's flow direction. IF the penetrant punctures the belt in this zone, it may come to a stop against this downstream idler, ripping the belt without annunciation.
The string line needs to be close to the belt's bottom cover to catch the penetrant that pierces the belt's bottom cover. Here again, there is a zone where the belt is punctured but not annunciated if the protrusion is not sufficiently long to engage the string.
Often we see must application of the string line where the installer is not aware of its proper function and misplaces it.
The internal rip detectors coils/antennas are superior but much more costly. Do your risk and benefit assessment.
There are other methods that do enhance the string line which I will leave for others to comment on. ■
String Line Rip Detector
I agree with Larry, it is all about how well they are set up and designed and overall there effectiveness is fair. Given the cost differentials between alternates they are not a bad investment. They can unfortunately be damaged in high impact applications and also can be subject to giving false alarms also in high impact applications. They were originally developed in the '70's by a maintenance engineer who worked for then Mt. Newman Mining (now BHP Billiton Iron Ore) and as a consequence are now extensively used at both major iron ore operations in the West Australian Pilbara. I would have no hesitation recommending them as a relatively cheap piece of protection providing the client is aware that they are not fail safe but much better than nothing.
Col Benjamin ■
String Line Rip Detector
How effective are they? Dollar wise , they seem like a good investment on a system subject to potential belt tear. But do they work? Where should they be best located ? What about the return strand?
Comments appreciated , Neil Kinder ■