Does Bakelite/ Catalin expand with age?

at

I have found that many of the pot metal castings used for metal parts on old radios, turntables, etc. have expanded over time.

I was astonished to learn that metal can do that in a timescale measured in decades.

I'm sure that bakelite and other plastics can change dimension over time too. Those I have a much easier time understanding, since the evaporation (sublimation?) rate of the organic chemicals is always something that I've associated with a timescale of years or decades, and I know from my experience living in southern california that exposure to ozone and intense sunlight can accelerate the process incredibly.

My gut feeling is that just like different pot metal mixes exhibit the expansion at different rates probably based on whatever they had to throw in the pot that day, that plastics can vary based on detail of manufacture too.

Tim.

that

I have found that many of the pot metal castings used for metal parts on old radios, turntables, etc. have expanded over time.

I was astonished to learn that metal can do that in a timescale measured in decades.

I'm sure that bakelite and other plastics can change dimension over time too. Those I have a much easier time understanding, since the evaporation (sublimation?) rate of the organic chemicals is always something that I've associated with a timescale of years or decades, and I know from my experience living in southern california that exposure to ozone and intense sunlight can accelerate the process incredibly.

My gut feeling is that just like different pot metal mixes exhibit the expansion at different rates probably based on whatever they had to throw in the pot that day, that plastics can vary based on detail of manufacture too.

Tim.

+++++

The one this week was where the bakelite closure, top panel, was recessed into the steel back body, so either metal had shrunk or the bakelite had expanded over 70 years

Bakelite typically uses wood flour as a filler, which is hygroscopic and could swell with age.

Catalin shrinks, as the entrained water evaporates.

Alan

As many of us have experienced through situations like screw holes that are no longer aligned with the chassis, and back covers that somehow have become larger than the opening they are covering.

at

Catalin shrinks as Alan suggests - for two reasons. First, the water entrained when froming the piece dissipates - this happens pretty quickly. Then additional water and formaldehyde starts to outgas, this is a gradual process taht depends on climate and temperature, but is continuous to a greater or lesser degree until ultimately the material will crumble altogether.

Bakelite uses a much different process although it is essentially the same material as catalin (thermosetting phenolic resin) but it is twice-formed and uses some sort of aggregate including colorants, wood flour (again as Alan suggests), carbon-black, glass powder and fibers and any of many other sorts of things. *Depending on the aggregate* it is very dimensionally stable over time and under most conditions, hence its favor for electrical parts exposed to harsh conditions, and so forth.

White metal will expand, crumble or crack over time depending on its composition and environment. Most other pure metals or alloys are diminsionally stable excepting expansion and contraction for due to temperature - although some alloys of steel will expand under certain kinds of radiation - which if they exist in your home to that extent, you are dead already. Some types of glass will turn purple with age, some say due to ultra-violet, some say due to cosmic rays as it will turn purple whether inside or out. Pick whichever you choose.

Peter Wieck Melrose Park, PA

that

Catalin shrinks as Alan suggests - for two reasons. First, the water entrained when froming the piece dissipates - this happens pretty quickly. Then additional water and formaldehyde starts to outgas, this is a gradual process taht depends on climate and temperature, but is continuous to a greater or lesser degree until ultimately the material will crumble altogether.

Bakelite uses a much different process although it is essentially the same material as catalin (thermosetting phenolic resin) but it is twice-formed and uses some sort of aggregate including colorants, wood flour (again as Alan suggests), carbon-black, glass powder and fibers and any of many other sorts of things. *Depending on the aggregate* it is very dimensionally stable over time and under most conditions, hence its favor for electrical parts exposed to harsh conditions, and so forth.

White metal will expand, crumble or crack over time depending on its composition and environment. Most other pure metals or alloys are diminsionally stable excepting expansion and contraction for due to temperature - although some alloys of steel will expand under certain kinds of radiation - which if they exist in your home to that extent, you are dead already. Some types of glass will turn purple with age, some say due to ultra-violet, some say due to cosmic rays as it will turn purple whether inside or out. Pick whichever you choose.

Peter Wieck Melrose Park, PA

++++

So wood pulp filler could lead to expansion but if a mineral was used ,as a filler, then dimensionally stable bakelite would result ?

Catalin shrinks as Alan suggests - for two reasons. First, the water entrained when froming the piece dissipates - this happens pretty quickly. Then additional water and formaldehyde starts to outgas, this is a gradual process taht depends on climate and temperature, but is continuous to a greater or lesser degree until ultimately the material will crumble altogether.

Bakelite uses a much different process although it is essentially the same material as catalin (thermosetting phenolic resin) but it is twice-formed and uses some sort of aggregate including colorants, wood flour (again as Alan suggests), carbon-black, glass powder and fibers and any of many other sorts of things. *Depending on the aggregate* it is very dimensionally stable over time and under most conditions, hence its favor for electrical parts exposed to harsh conditions, and so forth.

White metal will expand, crumble or crack over time depending on its composition and environment. Most other pure metals or alloys are diminsionally stable excepting expansion and contraction for due to temperature - although some alloys of steel will expand under certain kinds of radiation - which if they exist in your home to that extent, you are dead already. Some types of glass will turn purple with age, some say due to ultra-violet, some say due to cosmic rays as it will turn purple whether inside or out. Pick whichever you choose.

Peter Wieck Melrose Park, PA

At the risk of sounding gross, what is the type of plastic that smells like......vomit?

Paul P

not

And while at it , what glue, or whatever, breaks down over decades to give the small of rotted horse manure, not fresh, maybe referred to as a "caproic" (goaty) smell . You open up some kit and there is that small that can saturate the workroom for hours before it dissipates.

a

Not pulp - well, OK... derived from pulp but not the same. The wood flour that is used is very nearly pure lignin - that part of wood that lends strength and is also hydrophobic - so that big oak tree out there does not dissolve in the rain.

So, to the extent that the wood flour used is contaminated with other wood components, it might expand when exposed to moisture. But the material is heated (twice) and formed under great pressure. Most of the water created by the initial chemical reaction is dissipated in first heating, the last done under great pressure and greater heat completes the thermosetting process - but most of the water is already long-gone. And any non-lignin components remaining were mostly burnt off in the first go as well.

The smelly plastic is Cellulose Acetate - which goes to vinegar and a few other smellies. And there are several other materials that use Cellulose Acetate in their formulations to a greater or lesser extent

- which decay similarly with similar smells.

Peter Wieck Melrose Park, PA

Oh, yeah. I've got an old Philips bakelite radio that has one of those schemes where the tuning and volume are on the same shaft. The metal used in the construction of this gizmo has expanded enough that the tuning only moves as far as the volume control, and turning either one makes both of them move. I can't even extract the chassis to try to fix this because the knob is literally fused to the shaft from the expansion. I haven't figured out how I'm going to deal with that yet, so the set is a shelf queen.

-Scott

that

not

Faced with a similar situation some years ago and wanting to save the knob and so knobs. I found a piece of steel or Al round bar, drilled through axially on a lathe, 1/8 inch hole. Mounted co-axially over the knob held there with Jubilee / hose clip and some padding. Then 1/8 inch drilled into the knob and into the shaft. Saved the bakelite dust to mix with epoxy to make good afterwards. Luckily the 1/8 inch drilling was enough to loosen the knob and filled the shaft with epoxy as well, in the end. Otherwise it would have been a matter of drilling larger holes until freed

that

I asked an industrial chemist about this and he suggested it was Caproic or Hexanoic Acid and I would suggest it was from use of rendered down horse bones for horse glue in plywood making or cabinet joining before PVA glues came in.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Cellulose acetate butyrate, which breaks down releasing butyric acid (which incidentally hastens the breakdown of the remaining plastic, so sealing the item in an airtight enclosure is a bad idea).

Alan

Not pulp - well, OK... derived from pulp but not the same. The wood flour that is used is very nearly pure lignin - that part of wood that lends strength and is also hydrophobic - so that big oak tree out there does not dissolve in the rain.

So, to the extent that the wood flour used is contaminated with other wood components, it might expand when exposed to moisture. But the material is heated (twice) and formed under great pressure. Most of the water created by the initial chemical reaction is dissipated in first heating, the last done under great pressure and greater heat completes the thermosetting process - but most of the water is already long-gone. And any non-lignin components remaining were mostly burnt off in the first go as well.

The smelly plastic is Cellulose Acetate - which goes to vinegar and a few other smellies. And there are several other materials that use Cellulose Acetate in their formulations to a greater or lesser extent

- which decay similarly with similar smells.

Peter Wieck Melrose Park, PA

Celluloid is either cellulose acetate or cellulose nitrate, both were used as photographic film base and neither is stable. The acetate smells of vinegar when its decomposing and nitrate often smells of camphor although other substances were used as plasticizers. Both shrink, distort, and disintegrate with age. Acetate does not support flame while the nitrate is nearly impossible to extinguish once ignited since it supplies its own oxygen. The latter is the main reason cellulose nitrate was discontinued for film base in 1951. Probably most plastic dial windows on old radios are cellulose acetate.

--

--
Richard Knoppow
Los Angeles
WB6KBL
dickburk@ix.netcom.com

Plastics can absorb moisture (the universal solvent) over time. Additionally, steel does in fact shrink with a shrinkage rate of about

1 part in 10^8 per year. Invar expands with about the same magnitude, which is why such alloy rods were abandoned as length standards in the 1960s.

... what a job... measuring the same rod four times a year for decades.

David A. Smith

Bryce wrote in news:gs0kr3$nku$2 @news.motzarella.org:

You did what? Do you imagine that others see the same thread and posting preceding yours?

You posted on Usenet. People read Usenet using various methods. Some use Google, some use various Usenet readers, some use other methods. FYI, Usenet postings propagate at different speeds and some postings never propagate along some paths. Other readers may never see the text to which you are responding. Others may see your comment before they see the material to which you responded.

You should ALWAYS properly 'quote' the material [proper means to give the source AND format the quoted material so that it can not be mistaken for your comments] and add your comments, removing extraneous [not related to your comment] original material.

--
bz

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

bz+spr@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap

Oh, MY!!

He did - expand with age.

Peter Wieck Melrose Park, PA

Yes, I expanded. Alas, in so doing I became (more) ignorant and neglected proper newsgroup etiquette. Sorry.