Bite mark repair for plastics

[cuteline]

I have a 1930's sheaffer Pencil (grey marble with red vein), most likely made of celluloid. It has numerous light bite marks at the end. I heard that heating can cure these marks, but tried hair drier for 5 minutes without success. I am wondering how high the temperature do I need to go for this task? I probably will go grab a heat gun for the job. Thanks for the help.

[Ron Z]

No set temperature - but I must caution you that the line between removing the tooth marks and having a flambe' is very thin indeed. The first sign that you have overheated the pen is the puff of smoke when celluloid toasts.

 

Not all plastics respond well to heat, and you need to know your materials. Some will melt or blister before the marks pop out. The plastic on some Sheaffers (like OS Balances in particular) will also shrink with heat without the marks coming out.

 

I usually encourage folks to try repairs themselves, but this is one procedure for which I recommend sending the pen to a qualified repair person rather than try it yourself.

[Guest PeteWK]

No set temperature - but I must caution you that the line between removing the tooth marks and having a flambe' is very thin indeed. The first sign that you have overheated the pen is the puff of smoke when celluloid toasts.

 

Not all plastics respond well to heat, and you need to know your materials. Some will melt or blister before the marks pop out. The plastic on some Sheaffers (like OS Balances in particular) will also shrink with heat without the marks coming out.

 

I usually encourage folks to try repairs themselves, but this is one procedure for which I recommend sending the pen to a qualified repair person rather than try it yourself.

 

 

Even as someone who uses open flame on occasion with great success (I know Ron disapproves but we all have our style), I wouldn't do that. I try not to purchase pens with bite marks but I wouldn't take them out if I had them short of some buffing.

 

PeteWK

[eckiethump]

I removed an engraving on a Parker Thrift pen, using this method, and the more in depth instructions given by SMG on another thread, threads around here somewhere.

Resuts were very pleasing, the variety of quality in plastics, hard rubber and celluloid when you are "bringing them back to lfe" are I find quite astounding.

 

Sould be noted, I did practice and fail on some scrap pieces, before trying the method on a pen, I intended to save as a pen.

 

All the pens I have are users, think if I wanted something to just look at, I'd collect stamps. Whoops, called myself a collector there, more a user and messer about with.

 

et

[Ron Z]

Even as someone who uses open flame on occasion with great success (I know Ron disapproves but we all have our style), I wouldn't do that. I try not to purchase pens with bite marks but I wouldn't take them out if I had them short of some buffing.

 

PeteWK

 

It's not a matter of style, it's a matter of safety, especially for the guy who's new to doing repairs. The process was developed before safer tools/methods were available. I simply don't see the need to take the risk today. When you have had one piece of celluloid burst into flame, I can assure you, there won't be another.

 

Interesting side effect of sanding and buffing to remove tooth marks. You sometimes have to take off a lot of material, and some folks give up. So when you heat the pen, you can end up with reverse tooth marks, which you then have to remove. Rather funny to see when it happens.

[antoniosz]

Interesting side effect of sanding and buffing to remove tooth marks. You sometimes have to take off a lot of material, and some folks give up. So when you heat the pen, you can end up with reverse tooth marks, which you then have to remove. Rather funny to see when it happens.

 

Actually this is quite expected, if you know about viscoelasticity

Viscoelasticity is the return to the original configuration a "long" time after the load that caused the mark is removed.

 

In fact this suggested an interesting variant in this technique.

In viscoelasticity, the time-temperature superposition is applicable.

Time-temperature equivalence means that the behavior of the material at high temperature and short time is equivalent to

the behavior at low temperature and long time. This means that the marks will disappear eventually (maybe in few centuries - or faster if global warming continues :ltcapd: ). Seriously now, you may want to try a lower temperature treatment but hold the sample under temperature for longer times.

For example if the temperature that heals the marks is 55C and the ignition point is at 60C, then you might be able to get the same result

by exposing the part to 40C for, say, one hour (numbers are for the sake of argument only). Of course this requires controlled continuous heating,

but reduces the chance of getting a pen flambee

Edited July 15, 2007 by antoniosz

[HLeopold]

Even as someone who uses open flame on occasion with great success (I know Ron disapproves but we all have our style), I wouldn't do that. I try not to purchase pens with bite marks but I wouldn't take them out if I had them short of some buffing.

 

PeteWK

 

It's not a matter of style, it's a matter of safety, especially for the guy who's new to doing repairs. The process was developed before safer tools/methods were available. I simply don't see the need to take the risk today. When you have had one piece of celluloid burst into flame, I can assure you, there won't be another.

 

snip

 

My mother used to collect celluloid items, combs, things like that. She kept some of them in the kitchen on some open quarter shelves above the counter. One day during breakfast we had a close up look at what happens when celluloid meets too much heat, our toaster was below the shelves (at least a good foot and a half) and the resulting flash/smoke and scorching of the woodwork were quite educational. I think one of the combs went off first and set off most of the others including a good sized hair brush that was solid celluloid. The shelve never again looked quite right, very deeply burned in places.

 

I really would not want something like that going off in my hands or near my face even with protective glasses and gloves.

 

Right now I really wish we still had that hair brush though, nice color and quite large enough to have made a large fountain pen out of. Hmm, should check on the possibility next time I go garage sale shopping.

[cuteline]

Very interesting theory. Just not sure if the relationship between the time and temperature is exponential or polynomial, or if there is a critical-transition (like ice to water). But may worth a try just for the fun of it. Of course, I'll use a cheap pencil, with a big bucket of water on site.

 

Jun

 

 

Interesting side effect of sanding and buffing to remove tooth marks. You sometimes have to take off a lot of material, and some folks give up. So when you heat the pen, you can end up with reverse tooth marks, which you then have to remove. Rather funny to see when it happens.

 

Actually this is quite expected, if you know about viscoelasticity

Viscoelasticity is the return to the original configuration a "long" time after the load that caused the mark is removed.

 

In fact this suggested an interesting variant in this technique.

In viscoelasticity, the time-temperature equivalence is applicable.

Time-temperature equivalence means that the behavior of the material at high temperature and short time is equivalent to

the behavior at low temperature and long time. This means that the marks will disappear eventually (maybe in few centuries - or faster if global warming continues :ltcapd: ). Seriously now, you may want to try a lower temperature treatment but hold the sample under temperature for longer times.

For example if the temperature that heals the marks is 55C and the ignition point is at 60C, then you might be able to get the same result

by exposing the part to 40C for, say, one hour (numbers are for the sake of argument only). Of course this requires controlled continuous heating,

but reduces the chance of getting a pen flambee

 

[antoniosz]

Very interesting theory. Just not sure if the relationship between the time and temperature is exponential or polynomial, or if there is a critical-transition (like ice to water). But may worth a try just for the fun of it. Of course, I'll use a cheap pencil, with a big bucket of water on site.

It can be derived by considering the deformation of the material as a thermally activated Debye-process.

One model is the WLF equation (e.g., check here).

In principle, it should be applicable above the glass transition point, but I have seen it applied over the whole range of temperatures.

[MYU]

It can be derived by considering the deformation of the material as a thermally activated Debye-process.

If you're not careful, it can easily become the Byebye-process.

 

 

 

 

 

 

 

Sorry, couldn't resist.

 

Yikes, those equations remind me of how much I've forgotten about mathematics. Rather confusing to the uninitiated as to what to plug into the variables... even the nomenclature. What's "1000 h"? (maybe I shouldn't ask)

[antoniosz]

If you're not careful, it can easily become the Byebye-process.

:roflmho:

 

Yikes, those equations remind me of how much I've forgotten about mathematics. Rather confusing to the uninitiated as to what to plug into the variables... even the nomenclature. What's "1000 h"? (maybe I shouldn't ask)

Actually there is nothing in that page that is not taught in early high school. It isa matter of attitude .

1000 h means 1,000 hours What it says is that a deformation that takes 1 minute (~0.01 hour) at 112oC it will take 1,000 hours at 100oC.

Another example that illustrates the same principle is when plastic shelves warp under the weight of books, this model tells us that much of the deformation occurs during hot days than during cold days...

 

 

[belfast-popeye]

Check other topics on this, another much safer method is to fill the tooth marks in then buff and polish back, still got to get round to this myself

[Buzz J]

For example if the temperature that heals the marks is 55C and the ignition point is at 60C, then you might be able to get the same result

by exposing the part to 40C for, say, one hour (numbers are for the sake of argument only). Of course this requires controlled continuous heating,

but reduces the chance of getting a pen flambee

 

But if you are trying to remove a personalization imprint but not the maker imprint close by, you want to hit the sweet temperature quick without heating the entire barrel like a slow cooker would.

 

[eckiethump]

For example if the temperature that heals the marks is 55C and the ignition point is at 60C, then you might be able to get the same result

by exposing the part to 40C for, say, one hour (numbers are for the sake of argument only). Of course this requires controlled continuous heating,

but reduces the chance of getting a pen flambee

 

But if you are trying to remove a personalization imprint but not the maker imprint close by, you want to hit the sweet temperature quick without heating the entire barrel like a slow cooker would.

 

Therein lies another minefield, funnily enough the pen that I removed an engraved name from, I couldn't see the Geo. Parker until after I had done the work.

 

et

 

 

[artaddict]

Yay! The hair dryer trick worked on one of my pens! The marks are much shallower now, & I'm afraid to go any further. I keep imagining puffs of smoke.