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Why hard material wear when slid aginst soft one?

Why hard material wear when slid aginst soft one?

Why hard material wear when slid aginst soft one?

When cotton fibre runs against steel, steel components wear out, e.g. steel or plastic components used in the textile industry. My question is " Why does a hard surface such as hardened steel wear when a soft material such as cotton fiber runs on it?"

I think cotton fiber is not abrasive. It is a natural fiber. Is cotton fiber corrosive? Are there any other dust or dirt particles mixed in the yarn? Please explain.

RE: Why hard material wear when slid aginst soft one?

Why not?  Even water erodes rocks.

Don't forget that you're running miles per day of cotton against a single spot on the metal.  


RE: Why hard material wear when slid aginst soft one?

IRstuff, thanks for your consideration and reply.

I am interested in the micromechanism/s of wear between cotton fiber/yarn and steel.

I agree with you on the fact that the same spot of steel is exposed to miles and miles of cotton fiber. I do not however understand why and how it happens.

Water erodes rock by many mechanisms. One of them is abrasive wear mechanism (cutting, plowing, chipping, etc.)due to erosion by the abrasives (stones/sand) present in the flow. There may be involvement of some kind of corrosive wear mechanism, depending on the pH and other chemical species present in water.

Could any body direct me to a good source of reference for this subject - wear of materials by fibers?

RE: Why hard material wear when slid aginst soft one?

You might try posting this in the Sharp Tool Engineering forum: Forum924, are there are some well-known blade sharpening approaches using soft materials such as leather, paper, etc.


RE: Why hard material wear when slid aginst soft one?

Could static discharges on high voltages per mm2 be one cause ?

RE: Why hard material wear when slid aginst soft one?

Against a conductive blade?  

Leather is not well known as a high static generator in any case.


RE: Why hard material wear when slid aginst soft one?

It is known that the transitory separation of surfaces (a good conductor from a poor conductor) by a very thin air film in a sliding process is supposed to cause arcing by a dielectric breakdown with an average duration of a few milliseconds.

It reminds me of the buildup of a static charge when placing two different materials in a tumble drier, or walking across a rug, or removing a sweater. The clinging of fabrics and sometimes the appearance of audible sparks are the result of static charge build-up.

This is only an hypothesis from applying some lateral thinking. As IRstuff insinuates I may be totally wrong.


RE: Why hard material wear when slid aginst soft one?

Have you checked the hardness of the cotton fiber? Even though it feels soft, the hardness, coefficient of friction, and number of contact areas may cause the material erosion. There probably is some level of dirt in the fiber, and yes it can be corrosive to metal if moist. Just lay a wet rag on clean steel and check later.

RE: Why hard material wear when slid aginst soft one?

If the softer material is moving faster than the harder material, the harder material will be removed. This is why you can polish diamonds. Some polishing wheels are made of cloth.
From Marks' Standard Handbook for Mechanical Engineers "The nature of the polishing process has been debated for a long time. Two mechanisms appear to play a role: One is finescale abrasion, and the other is melting of surface layers. In addition to removal of material by abrasive particles, the high temperatures generated because of friction soften the asperities of the surface of the workpiece, resulting in a smeared surface layer. Furthermore, chemical reactions may also take place in polishing whereby surface irregularities are removed by chemical attack."

The rate of removal would depend on the RPM of roller and the diameter. The amount of dirt in cotton will affect rate.

RE: Why hard material wear when slid aginst soft one?

As we produced synthetic fibers the problem with wear was several orders of magnitude greater than with cotton and pursuant to same information posted by aviat, we had to attack the problem from several different angles.

We used hard chrome plating on hardened metal guides, ceramic guides, sapphire inserts, and ceramic coatings on larger guides and rollers.

As we had both mechanisms mentioned at work at the same time one of the most significant methods of preventing wear was have the thread line dance or move around on a guide or roll. This didn’t do much for the abrasive wear but help with the heating problem.   

It get very complicated where a threadline crosses a guide when you take into account the thread material, addiatives, finishes, and guide material.

RE: Why hard material wear when slid aginst soft one?

Thanks to all of you for your valuable posts. My job now is to get evidence from the worn steel surfaces for any or all the mechanisms discussed (no particular order).
1. Abrasion of steel by cotton itself
2. Abrasion of steel by dirt, sand and other plant materials present in cotton fibers
3. Melting of steel surface asperties due to frictional heating
4. Softening of steel surface asperties due to frictional heating
5. Plastcic deformation of asperities (smoothening)
6. Discharge of static electricity through arcing, causing arc craters
7. Corrosion of steel by cotton fiber, especially when humid or wet
8. Any other theory?

My question to EdDanzer:
How can I measure hardness of cotton fiber? I can get hardness values for synthetic materials from plastics handbooks.

I do sincerely appreciate your thought-provoking posts.

RE: Why hard material wear when slid aginst soft one?

Try finding a collage that does MEMS work. In the thin film industry they appear to have methods of testing the hardness of small areas.
Microscopic viewing of the fiber will also allow you to size and number of points on the fibers, these could be penetrating the soft areas and voids in the surface of the metal, pulling small pieces of metal from the surface, then abrading the rest of the surface more.
The corrosion may be accelerated by additional static electricity, particularly for some elements in the metal being contacted. If you stain the metal to show the grain structure, take a several 100X picture, then run the fiber over it and take another micrograph, you may see where the erosion starts.

RE: Why hard material wear when slid aginst soft one?

The simple answer is high coefficient of friction. Steel is not a wear surface.  Rub on it long enough with any fiber (soft or hard) and you will eventually see wear.  A thermo-plastic UHMW Polyethylene will outwear steel 15/1 and is a very low coefficient of friction.  The film is skived in 3 mil. and up and is available with a pressure sensitive adhesive.  The meat and packing industry lines all of their shutes and stainless steel trays with UHMW to keep the product from hanging up and everything slides across the surface and cleans up easily.  It is also FDA approved for direct food contact. If you can, consider lining the surface of the steel with a UHMW film tape. We produce this in 24" in wide rolls in black and clear with a permanent adhesive and liner for bonding and mounting.

RE: Why hard material wear when slid aginst soft one?

TaperDr, can you use this film on knife edges?

RE: Why hard material wear when slid aginst soft one?

You can but it needs to be in block form, similar to guide rails or cutting board type of sheet.  There a few variations of the UHMW.  I was talking about a skived film in the previous post. The knife edges will cut into the UHMW, film or solid form, and it all depends on the force that is used.   We produce in both solid form skived film. The black verson has black carbon fiber added to the UHMW prior to manufacturing. It is also known as Poor Mans Teflon as it is a viable low cost alternative to PTFE where temp and and a superior wear surface is desired.

RE: Why hard material wear when slid aginst soft one?

I had the same question about three years ago, but it was how does a seal cut into and wear a shaft. The closest answer I could find that made any sense was that the softer material (seal or cotton in your case) would wear away the surface by removing the oxides from the surface, and could possibly be picking up the oxides and become abrasive. But I'm convinced that oxide removal is the reason why.

RE: Why hard material wear when slid aginst soft one?

"If the softer material is moving faster than the harder material, the harder material will be removed. This is why you can polish diamonds. Some polishing wheels are made of cloth."
This is an amazing statement that appears to turn the world of material removal on its head.
A "soft" carbon steel part is turned at high speed against a static HARD tungsten cutting tip and the SOFT CS part wears away the HARD tungsten edge?
In your dreams.
A tungsten cutting edge will eventually dull over but not before a hell of a lot of steel is removed.
Cotton is NOT naturally abrasive. However it is a very strong material. Just as importantly it will carbonise before it melts. Therefore, under the "wrong" conditions it is known to wear carbon and stainless steel significantly. The wear process occurs as the surface of the material (in this case cotton)breaks down as it is pyrolized against the steel sliding surface. This is caused by continuous intense localised heat and pressure. However, the cotton that wears away is continuously replaced with fresh material so appears not to suffer. The surface of the affected steel part appears rough like a file. As far as coating a steel part affected this way, any attempt to remedy the problem using UHMWPE or similar thermo-plastic is a complete waste of time.
My suggestion would be to consider ceramics.


RE: Why hard material wear when slid aginst soft one?

To boomerang, the article is valuable in summarizing various types of wear. However, it doesn't mention all of the wear mechanisms listed by CdotS.

RE: Why hard material wear when slid aginst soft one?

The soft material in this case is always under some tension and there would be a measureable coefficient of friction.  

That shows that there are atomic interactions, since the wear would otherwise result in a smooth surface.

It may be arguable that any friction must result in wear.


RE: Why hard material wear when slid aginst soft one?

IRstuff, I think you're on to something.
There could be at least two wear mechansims here.
1)   Cotton essentially is cellulose fibre and some decomposition begins around 130 deg.C (266 deg.F) It really gets going around 200 deg. C (392 DEG.F). Now, as the cotton decomposes, it releases hydrocarbons, CO2 & H2O right at the sliding surfaces. None of these appear to be particularly corrosive to steel (H2O would be vapour) but the hydrocarbons may react with the protective metal oxide. At the same time because there is surface contact, the now carbon rich cotton line is able to present carbon to the steel surface. As carbon is soluble in steel the melting point of the steel will be lowered by any increase in carbon. All the while fresh cotton is sliding right on past and is clearing away debris so fresh surface is always exposed.

2)   At high speed with sliding surfaces running dry, surface rubbing temperatures can go way past 200 deg. C and once past its comfort threshold, a weaker material will either melt (thermo-plastic synthetic fibre)or decompose (cotton fibre). When the fibre does not melt it is conceivable that carbon steel (and I'm talking about right at the mating surface)could reach its own plastic temperature. What's that now, 690 deg.C (1274 deg. F ?)It could reach that while the cotton is still mecahanically intact because fresh material is continuously being presented at high speed.The result of this would be to draw fine "fingers" or fine acicular protrusions of steel resulting with the rough texture that I described earlier.

RE: Why hard material wear when slid aginst soft one?

I am in the process of analyzing the surface of a steel component that was exposed to cotton fibres. From the preliminary results, I have observed the following:
They do show some plastic protrusions due to deformation of the surface asperities by cotton fibres. I have also observed abrasion marks (grooves) generated by sharp hard surfaces, possibly sand particles that are present in cotton fibre feed. In fact, I have a photo showing a sand particle embedded on the wearing surface.

Any corrosion mechanism present will play a minor role. Abrasion and sliding (plastic deformation) seem to dominate.

I am not sure very sure about the concept of melting of cotton fibre and diffusion of carbon into steel at these speeds. At 200C (I am not sure about the interface temperature), there will be not noticeable happening in terms of diffusion.

This very similar to shaving blades that encounter human hair. Shaving blades do wear (maybe low speed, unless somebody is in a hurry!) while cutting human hair. I need read about the mechanisms of shaving blade wear. Another situation similar to this would be knives. They also seem to go after harder surfaces such as tungsten carbide-cobalt cermets or PVD based carbide coatings on steels.

RE: Why hard material wear when slid aginst soft one?

At 200 C cotton will decompose and I agree if the surface temp of the steel was 200 C very little C would infuse into it. However, if the cotton travels fast enough and exerts sufficient tension the nett effect is high speed and compression around the steel part. It is possible to consider a few molecules of the otherwise unaffected cotton fibre to surface decompose at 200 C as well as micro parts of the steel surface to reach its plastic temp at the same point of time. This is possible because the steel part is "passive" to the moving cotton. While the cotton is able to cool as it passes the contact point, the steel surface cannot so is continuously heated with more cotton. Under these conditions, carbon could transfer from cotton to steel.

RE: Why hard material wear when slid aginst soft one?

What I described in my earlier post certainly does not apply to shaving a beard! In this circumstance the wear is "normal" in that velocity and pressure are within both materials (steel & hair fibre) heh heh, comfort zone.
As far as cutting edges keeping their edge I think some hard materials like tungsten carbide and diamond hold their edge better or worse with different materials.
For example on one hand, tungsten carbides work great with steel yet fail miserably machining a simple composite such as resin filled with silica. On the other hand, diamond is not used for HS cutting steel yet lasts a very long time indeed cutting a composite heavily filled with silica. It is well worth trying different combinations to see what works best both in terms of materials that cut best against other materials as well as materials that resist other materials.
One suggestion for your cotton application is to hard chrome plate one of the parts and see how it does. Chrome oxide is very hard and chemically stable so may resist better than steel. I earlier suggested ceramic as a possible excellent wear surface but that may be difficult and expensive to implement.

RE: Why hard material wear when slid aginst soft one?

Shaving a beard with the resulting in loss of cutting ability of the blade is mainly due to corrosion not wear.
The reason that WC2 isn’t good from some materials is that loosely consolidated small abrasive particles can rapidly remove the binder for the carbide.

Now back to cotton and wear.  
The original machines handling cotton had very slow filament speeds and all the materials were plain steels or cast iron.  As the speed of the threadline increased next came the hardenable steel and the ability to flame hardened cast iron.  The next step in the progression was that someone realized that if the relative speed of the threadline vs guide could be decreased by the use of roller guides, spinning rings with  guides, etc. These were used first where there was a relative high angle of attack of the threadline vs guide or change in direction of the threadline.  These rolls were made from various materials, some of which were CI, Case Hardened steel, even basalt.  

The evolution of a particular guide first used in cotton mills called a “balloon guide” started out as plain CS progressed to hardenable steel, then to case hardened, then to carburized and then to case hardened and carburized,  then to 1095 CS which in turn was case hardened and carburized.  With the introduction of hard chrome plating all steel textile guides were immediate candidates for plating.

With the advent of Nylon the guide problem became more acute.  Unadorned Nylon fiber causes extreme wear on anything it crosses or touches.  This problem was attacked by the use of the hard chrome plate, the used of ceramics mainly “AlSiMag”for all pin small pin (convergence) guides, as the process for improved larger and larger guides were made from ceramics.  Next came the thermal sprays including the CrO, “Polymet”.  Thermal spray also allowed the roll to be made from steel which in turn allowed another speed increase and a repeat of the wear problem.  Today we have synthetic sapphire and diamond coating.  To add to discussion of static electricity nylon fiber under the right conditions will become a VanDeGraaff generator.

Back to cotton, if the threadline speed is below a certain threshold it will not wear guides to any extent.  But as stated above as the speed increases the contact stresses increase to a point where the application of a finish or lubricant will decrease or prevent wear on the same guide.  Finishes were usually made  behind closed doors and were proprietary information of the highest order.  Finishes for cotton soon had became generic and available off the shelf.  The finishes again went underground when they started treating the cotton fiber to enhance it’s properties.  Some of these properties allowed an increase in speed of the threadline and the contest to combat wear of guides began anew.
These finishes presented other problems as some were corrosive to certain materials until dry.  Some contained waxes, fats, and oils which each in it’s own way affected the choice of guide materials.
The wear of a steel guide is affected by the threadline material, guide material , cleanliness of thread line, speed of the threadline, contact pressure on the guide, whether it is lubricated or not. All of these are common to wear problems.                

If the above wasn’t windy enough this will be.  
I have in my hand an extremely fine, several thousandth’s,  Cu wire plated with diamonds. This is analogous to the “Angel Hair” of storied fame.   The diamond particles are so small that the wire feels smooth but will cut just about anything going.  The secret in cutting with this wire is that it has to move to cut without wearing out.  If you rotate the part the wire tends to wear.

Just the opposite.
In another wear situation we had a 2" dia shaft made from “Vasco Jet 1000" hardened to 60 RHc rotating at less than 100 RPM @ 600°F we had an insulator/mechanic wrapped a single strand of 1/16" SS tie wire around the shaft.  The initial load on the wire was in the order of several pounds tension, but would have went to essenitally nothing quickly.  After about 100 days an unscheduled outage allowed the shaft and wire to be exposed.  The SS wire had cut a 5/16" deep by exactly 1/16" wide, using the wire as a feeler gauge, groove in the shaft.   The precision of this groove would be hard to duplicate.  The most amazing part of the event was that it took an electron microscope to see any effect on the SS wire.  The apparent abrasive media, none was seen embedded in the wire, was a small amount of the expanded calcium silicate dust from the insulation.   This event occurred on another machine that ran for one year but wasn’t cut, only a very slight polish.  The difference was temperature.  The shaft temperature in this case was approximately 150°F instead of 600°F.

There has been a tremendous amount of work done on wear of guides both in the natural and synthetic fiber business.  I know a considerable amount is still considered proprietary but enough  has been published to keep from reinventing the wheel.  Sometimes one has to take the Edisonian  approach to get a starting point then start making incremental improvements until a problem becomes manageable.  This is especially true with wear and the textile industry.   

RE: Why hard material wear when slid aginst soft one?

This is one of a number of interesting points you raised.
..."With the advent of Nylon the guide problem became more acute.  Unadorned Nylon fiber causes extreme wear on anything it crosses or touches."....
I have not found this with virgin nylon. As a bearing material used wet, dry, with grease or with oil I have never found it naturally abrasive to steel. (I am not a proponent of nylon, just stating what are my observations.)
Although we occaisionally manufacture highly specialised bearing materials for the textile industry I cannot say I have a deep knowlege of that industry beyond the narrow field our products operate so I found your comments about nylon interesting. The fact you state with nylon threadline there is extreme wear gives weight to 25362's remarks about static electricity.
Nylon is an excellent insulator and in normal air will easily hold a static charge compared to cotton. Change a dry nylon shirt in the dark and see the sparks. Doesn't happen with cotton. Cotton is also an excellent electrical insulator but unlike nylon, moisture must be completely absent.
If the nylon line, travelling at high speed and charged with static electricity continuously discharged (earthed) against a metal wear part I imagine it would wear away that part in relatively short time.

RE: Why hard material wear when slid aginst soft one?

In practice there is a difference in chemical composition of Nylon fiber and Nylon polymer used for bearing components.  Both are made from the same starting nylon salt solution and each has a different additive package with fiber having the most initially.   Some of the additives are metallic salts, again much more so in the fibers.  Both products have silicone added as an antifoam agent.
These additive are known to affect the performance of the Nylon in subsequent processing.

Nylon fiber is very abrasive from the moment it changes from a liquid polymer to solid fiber, air quenched.   At this point everything the fiber touches has to be wear resistant or turning roll guides plus the immediate application of a finish to enhance it’s processing qualities. The finish also protects the Nylon fiber from surface damage.   Guides, surface finish of the guide, finish solutions on the fiber, and line speed are very critical to Nylon fiber as the fiber has to drawn, stretched or reduced in diameter,  to be very useful.  This draw ratio, based on length, can be from less than 1 to over 4.  In every case the fiber or guide is moving relative to each other.  Nylon fibers have a propensity to be more abrasive/agressive as the diameter decreases and the relative speed between the guide and threadline increases.   There have been numerous studies, more unpublished than published, on this effect mainly dealing with what could you do to mitigate the damage.  I seen Thermography, High Speed Photography, IR, Mechanical, and numerous other testing done on fiber thread lines.  I’ve never seen much changed from what was known by empirically derived improvements.
An older process for Nylon used a modified machine from the cotton mills to do a secondary operation on Nylon.  The only thing changed on the machine was that the guides were chrome plated, or changed to chrome plated or ceramic coated rollers.

Nylon molding resin polymer has to be treated in the same way except it's is water quenched due to it's heat capacity.  Size reduction, dicing or chopping, is nearly always carried out underwater. This is true both for a batch process or continuos process material.    
A 1/8" dia. Nylon molding resin extrusion running over a guide bar is very abrasive whereas Nylon pellets (1/8"x1/8") cut from the same bar aren't abrasive as they are convey by air both is SS and Al tubes, screened with SS wire mesh, and stored in Al silos with no problems.   One of the external inspection points is to verify the grounding strap on the Al silos are functional.

The static electricity problems in our facility were handled by the normal grounding methods. plus the manufacturing area used conditioned air with a very high humidity to help keep the static down.  Whether this help with the wear problems I can't say.  The control of the air in the manufacturing area was job critical.  The cotton mills that I’ve visited just keep it hot with the high humidity.  

The worn parts we observed in our lab appeared to be mainly abrasive wear  combined with polishing action.  We never saw any surface effects that could be attributed to arc damage.  For reasons I can’t divulge at the present time we were well aware of the surface effects of small arcs on metal.  Nearly all additions of solid additives to molten Nylon by any method had a detrimental effect on the wear problem.   There was an interesting effect noted in that there was some point in the additive concentration at which the effect of the additive became exponential as it pertains to wear.  On some of the more agressive components the results were truly dramatic, the wear problem backed
into the molten state.

You got me thinking that in my 42 years involved in and around Nylon and other synthetics I’ve only seen pure Nylon (66) one time in the research lab. It was in a very small quantity for use in deriving some physical properties.  Nylon doesn’t behave very well without the additives.

RE: Why hard material wear when slid aginst soft one?

I understand virgin nylon to be nylon product made from original resin, as against re-cycled.
I agree about additives. Mostly beneficial and neccessary to achieve a desired result.
We make a grade of bearing material that is re-enforced with woven nylon and is definetly not abrasive.

RE: Why hard material wear when slid aginst soft one?

We used a lot of your sleeve type bearings on our equipment.  

Your mention of rework reminded me that we noticed a significant difference in the behavior of reworked vs virgin Nylon.  When reworking local Nylon waste from our process we almost had to treat it as a different material based on several changes in physical parameters.  One being it's ability to cause wear problems.  We had to make several mechanical changes to the equipment for handling the rework.  In fact it was essentially reworked on a separate line, FCM, Extruder Screw, and Dicer, due to the excessive wear problems.  We only used reprocessed Nylon as compounding additive as it was extremely hard mechanically process as a fiber or monofilament.

As this Forum has pointed out the simple act of running almost any type thread line over a round guide can create a set of conditions that creates wear to the guide or damage the fiber filament.  

I do know that having the tools of today, specifically the modeling and the basics of nanotechnology, I would like to get back and look at some things I noted in the macro world.

Though there are some specific conditions known to avoid, I've never seen one being able to offer a specific remedy for a every set of conditions.  I think CdotS will have to find a solution to his specific conditions and then look back on the basic problem of wear.  

It would be most interesting if all the work on wear by everyone in the fiber business was published as compendium, with links, to where it could be data-mined if nothing else.  

RE: Why hard material wear when slid aginst soft one?

UHMW Thermplastic Film Has 15 times the wear surface of steel. Unless there is something very sharp in the cotton fibers you will not be able to wear it out very easily.  Of course that will depend on the heat generated.  The coefficient of friction is much higher on the steel vs. the very low coefficient of friction on the UHMW film surface, which will not build up heat which is created by constant friction moving across a high surface energy substrate such as steel.  

RE: Why hard material wear when slid aginst soft one?

The comment by TapeDr again brings to mind the subject of static charging. From what I've learnt from reading specialized books, UHMW PE and PTFE, as well as all conventional plastics, can be charged electrostatically whenever the conductivity is smaller than 10-9 S/cm and the relative humidity lower than ca. 70%, either by rubbing two surfaces against each other (triboelectric charging) or by contact of a surface with ionized air.

Static charging can indeed be diminished by incorporation of conducting fillers such as carbon black or metal powders (internal antistatics).

External antistatics reduce surface resistivities by increasing the polarity of the surface by application of humidity-absorbing additives or by reducing friction through lubricants or coating with PTFE or UHMW PE, as TapeDr said. However, external antistatics wear out and have to be renewed from time to time.

RE: Why hard material wear when slid aginst soft one?

Threadline speeds can be extremely fast, and where thread changes direction there is pressure placed on the bearing material. Conditions where high surface speed & pressure are present rapidly translate to conditions where high temperature and pressure exist and unfortunately that is no place for thermoplastic materials like UHMWPE.

RE: Why hard material wear when slid aginst soft one?

Cdots issue is why does the steel surface wear when cotton fibre runs against it? We can agree that the steel surface is a high coefficient of friction which produces frictional resistance and will eventually wear. This is in direct proportion to the velocity or speed of the cotton material running or dragging across the steel surface and amount of constant force or pressure the cotton fibre has against the steel surface while in motion. Most would engineer this application where the wear surface posseses as low coefficient of friction or by a lubrication material that can be applied or coated to create the desired wear surface, paying special attention to possible high temperatures created by the shear speed of the cotton fibre line.  I would disagree with rnd2 in that thermoplastics do have a place in higher temperature applications, including UHMWPE.  With added polymers patent ingredients UHMWPE Special Formuation High Temperature UHMWPE can perform at a constant temperatures of 275F without melting or loosing its wear properties. Used extensively in chemical wash wear surface environments and many other harsh environments and high temperature applications. Straight UHMWPE skived or extruded) will not be able to handle 275F without the added components of oil-filled nylons, nylon 6, nylon mds, Acetol and Teflon®.

RE: Why hard material wear when slid aginst soft one?

There is a very simple explanation for why soft materials wear away harder ones. The world is a dusty place and all surfaces will have some dust particles on them. Cotton fiber especially are grown in dirt, after all. These particles are abrasive and there is a tremendous amount of contact with a fiber guide. This is why most fiber guides are made of very hard alumina or other ceramic.

The process for lapping steel uses bronze or other soft metal with an abrasive slerry. The abrasive particles will get embedded into the soft metal and wear away the harder metal with litle wear to the soft metal.

RE: Why hard material wear when slid aginst soft one?

I can accept an explanation that soft materials wear away hard materials because they contain or support abrasive particles. However, it is not correct to say a soft material is therefore the cause of wear. In this specific instance, without doubt the wear mechanism is the hard abrasive material doing the material removal, not the soft copper or bronze material, which is merely the carrier. Substitute the soft copper or bronze with a water jet or even air jet to carry the abrasive particles and the abrasion continues.

RE: Why hard material wear when slid aginst soft one?

You don't even have to have abrasives in water if the pressure is high enough.  I think the threshold pressure for efficient cutting metals without abrasives is 77,000 psi, though 55,000 will do a pretty good job.
Abrasives just make the process economical, less wear and tear on the equipment.  

RE: Why hard material wear when slid aginst soft one?

Hi All

I could not believe the growing interest in this subject after I hhave posted the first post so many weeks ago. I have done scanning electron micrscopic (SEM) work on some wornout steel components used in the textile fibre processing industry. Some of the mechanisms discussed previously by others are possibile reasons for wear.

Predominantly, abrasive wear in very minute scale (less than microns - nano scale perhaps)is one of the prime mechanisms (Polishing wear due to dust?).

Then there is plastic deformation of the surface asperities due to frictional forces. This si similar to UncleSyd's water cutting without abrasives. Just force on the metal to deform. In the same line, there is plastic delamiation due to repetetive application of force, resulting in laminar particle. Refer to N.P. Suh's delamination theory of wear. If yu are not familar with this theory, refer to a god text book on wear (e.g. book by Ian Hutchings).

I will post more when I do some more SEM work in the near future.

Thanks to all for keepig this thread alive and interesting.

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