Measurement of friction is done using various types of measuring instruments. Tribometer is an instrument which is used to measure parameters like friction and wear. Even though I have seen enough literature I would like to know more about the advantages and disadvantages of POD on the reciprocating rig.
A pin-on-disc system allows travel in one direction for an unlimited time at a range of linear velocities depending only on position of the pin from the center of the disc. A reciprocating system allows for a wider wear track because the "pin" can be formed in to a flat. A ball-on-spindle system allows for configurations closer to bearing loads.
A pin-on-disc system allows travel in one direction for an unlimited time at a range of linear velocities depending only on position of the pin from the center of the disc. A reciprocating system allows for a wider wear track because the "pin" can be formed in to a flat. A ball-on-spindle system allows for configurations closer to bearing loads.
In fact, let us see it this way, Pin-on-disc tribometer may be used to model wear and lubricant behavior when the actual parts are having a linear relative velocity which is fairly constant like shaft in bush. Whereas, reciprocating tribometer may be used to model tribo-behavior of the components which are having reciprocating motion like piston ring in cylinder. Only point that should be considered that reciprocating motion by cam and by slider crank mechanism, may or may not be same. For better results it is preferable that reciprocating motion of actual assembly and the tribometer should be same eg simple harmonic motion.
The POD scheme has some disadvantage due to that pin's edge might burrow inside the counterpart disk and thusly influence on the sliding conditions. Also this scheme requires long time for runing-in especially when hard materials are used for experimenting. Therefore this scheme is used only to evaluate sliding wear in laboratory conditions.
Reciprocal sliding may be used on a tribometer too but in this case it you have to be careful when measuring the friction coefficient since depending on the pin run frequency a parasite peaks may appear on its time dependence.
I have some of my views in this regard .. I would like to know about their correctness
1) Reciprocating Tribometer could not be used for high speed tests where as POD could be used for high speed tests (up to 5m/s).
2) Seizure is a major concern in Reciprocating tribometer... May not be incase of POD
3) Reciprocating tribometer is well suited for the evaluation of properties of the lubricants ... But POD may not be...
This is an interesting tread and a good discussion. To echo some of the points above, a reciprocating wear tester is probably more suited to low-load micro/nano applications as both side of the track should see the same forces and therefore should have a consistent profile and wear features. This is useful when examining the fracture of a coating at the edge of a wear track. Most nano-film mechanical testing will be carried out using a reciprocating tester; with multiple tracks side by side under the same or differing conditions (load, #cycles, speed).
This is harder to do with POD samples as changing the track width has to be coupled with a change in rpm to ensure constant linear speed. The pin will also see a longer travel distance when the radius of the track is increased so if you are wearing your pin during testing, it isn't as easy to do direct comparisons for multiple tracks on the one sample. POD testing is better suited for high load and longer run times needed for hard and/or low friction surfaces.
Apart from aforementioned points trapping of heat and trapping of debris also chage the tribological response of tribocouple.
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