Date   

Re: Weighing Freight Car Models with Liquid Gravity

Peter Ness
 

HI Dave,

 

The gain in density will likely be rather minimal in most cases, and it may even reduce the density.  This is a very common observation in soil science -- things like dune sands usually have higher (dry) densities than do other soils that have a range of particle sizes

 

I think the statement you are substantiating here regarding reduced density is true because the material is non-homogeneous. I am not a dirt guy, but to me I see this saying sand has a different density than potting soil, which I expect may be true even if I chose poor examples.

 

If you start mixing smaller spheres in with bigger ones, then the little ones can get in the way of the dense packing of the big ones.

 

Not true in general for homogenous materials which behave very much in agreement with physics.  The condition you are defining is when the small particle interferes with the direct contact points of the larger particle with adjacent larger particles and the area surrounding this point contact that is less in distance than the diameter of the smaller particle. 

 

Overall, this is a very small percentage of the surface area and, since most commercial particles are within a range of particle sizes and not perfectly uniform, the percentage decreases from theoretical. 

 

This does not apply if the larger and smaller particle sizes are similar (i.e. 5 micron and 2.5 micron) because the range of particle sizes in both powders will probably overlap in the tails of the particle size distribution.  Also, if some new high falutin’ technology is used that does create extremely uniform particle size with minimal or no distribution this does not apply as well.

 

Going to 0.1 mm spheres is only going gain you something on the order of one or a few percent (maybe), hardly worth worrying about.

 

True enough for us in this group, but still a relative statement. Not so true if you are making a space shuttle tile, turbine blade or ceramic gun barrel liner. :D

 

Peter Ness   

 

From: main@RealSTMFC.groups.io [mailto:main@RealSTMFC.groups.io] On Behalf Of Dave Parker via Groups.Io
Sent: Tuesday, October 30, 2018 9:45 PM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Weighing Freight Car Models with Liquid Gravity

 

Tim:

My comments on this have always included the caveat that spheres the have to small enough to achieve something at least close to idealized spherical packing.

If you had a center-sill space with a 1 x 1 cm cross-section, and you carefully filled it with 1-cm diameter spheres, you would indeed have about 52% sphere and 48% void space (just the ratio of the volume of a sphere and a cube of the same size).  Obviously, if the spheres are say 0.75 cm in dia, then you can't pack them in there efficiently, and you'll get less weight.

But if the spheres were say 1 mm, or even 2, then you are going to get something at least close to idealized packing (74-26).  Going to 0.1 mm spheres is only going gain you something on the order of one or a few percent (maybe), hardly worth worrying about. 

Concerning Tony's comment, I agree but only in theory.  If you start mixing smaller spheres in with bigger ones, then the little ones can get in the way of the dense packing of the big ones.  The gain in density will likely be rather minimal in most cases, and it may even reduce the density.  This is a very common observation in soil science -- things like dune sands usually have higher (dry) densities than do other soils that have a range of particle sizes.

Dave Parker
Riverside, CA


Re: Weighing Freight Car Models with Liquid Gravity

Tony Thompson
 

Peter Ness wrote:

For the second part of the statement; If one has two identical cavities and fills one volume with Lead shot and the other with Lead powder, the cavity filled with Lead powder will have more mass than the one filled with shot. Why? The smaller the particle, the higher the surface area and among homogenous material, the smaller the interstitial spacing – all to say there is more mass of powder in the cavity than mass of shot in the other cavity.

       If you use powder, with a range of particle sizes and shapes, sure, no argument. Then you would pack little ones between big ones, and odd-shaped ones into spaces. But if you use actual spheres, the size CANNOT matter. That's all I said.

Tony Thompson             Editor, Signature Press, Berkeley, CA
2906 Forest Ave., Berkeley, CA 94705         www.signaturepress.com
(510) 540-6538; e-mail, tony@...
Publishers of books on railroad history






Re: Weighing Freight Car Models with Liquid Gravity

Peter Ness
 

Hi Tony,

 

Of course, if you have a range of sizes of spheres, the little ones pack between the big ones. But if they are all the same size, using smaller ones changes nothing.

 

I may not be reading this the way you intended, so apologies in advance if that is the case.  Not quite correct or true to my understanding and experience:

 

The first part of the statement is true - smaller particles fill the interstitial space.  Assume we are talking about a homogenous material – meaning it’s either all Lead spheres or all Tungsten spheres and for purposes of clarity spheres means a round if not uniformly so (i.e. not a perfect sphere) particle geometry.

 

So, using a range of particle sizes that includes what we may term shot or powder, because, as you state, the little ones pack between the big ones, will increase the mass (weight) contained inside the identical volumetric space (cavity). To be clear, if one fills the cavity with Lead shot and then adds Lead powder to fill the spaces, the mass (weight) of the loaded cavity will increase.

 

For the second part of the statement; If one has two identical cavities and fills one volume with Lead shot and the other with Lead powder, the cavity filled with Lead powder will have more mass than the one filled with shot. Why? The smaller the particle, the higher the surface area and among homogenous material, the smaller the interstitial spacing – all to say there is more mass of powder in the cavity than mass of shot in the other cavity.

 

Back in my day when working with metal powders of varying particle size, the key physical property that applies here was tap density and there was/is an ASTM standard to quantify this material property. Similar to specific gravity, tap density is a measurement of mass per unit volume. The smaller the particle size, the greater the tap density and the closer this value approaches the theoretical density or specific gravity of the material.

 

So in both cases, using powder to fill the space between shot or using a uniform small particle size powder, will increase the mass – weight- of that part. And if the cavity is filled with a 2 micron average diameter particle size powder rather than a 15 micron average diameter particle size powder, the mass of the part will be greater as well.

 

Again, if I misunderstand your statement, apologies.  Now, my head hurts from digging back more than 20 years in memories, so with permission I’ll go back to modeling freight cars.

 

Peter Ness

 

From: main@RealSTMFC.groups.io [mailto:main@RealSTMFC.groups.io] On Behalf Of Tony Thompson
Sent: Tuesday, October 30, 2018 8:11 PM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] Weighing Freight Car Models with Liquid Gravity

 

Dave Parker via Groups.Io wrote:



This was also discussed previously and, unless the shot are sufficiently large to preclude close packing in the available space, the weight you can gain does not depend on the diameter of the spheres, only on the density of the metal.  See post #139844.

 

     Or to put it another way, the proportion of space occupied by spheres, even in the closest packing, is independent of the size of the spheres.

      Of course, if you have a range of sizes of spheres, the little ones pack between the big ones. But if they are all the same size, using smaller ones changes nothing.

 

Tony Thompson             Editor, Signature Press, Berkeley, CA

2906 Forest Ave., Berkeley, CA 94705         www.signaturepress.com

(510) 540-6538; e-mail, tony@...

Publishers of books on railroad history

 

 



 


Re: Poultry Cars

Daniel A. Mitchell
 

Kristen:

I think 2800 is “well over 2000”.   :-)

I have one Ambroid car assembled and in use on my model railroad. I bought it partly assembled, and completed it as best I could on the info available at the time. Unfortunately, as is often the case, the mesh sides were already installed and I didn’t think it wise at the time to cut it open and install the interior decks. Now I wish I had. Here’s the car on an unfinished part of my layout …


Obviously I now know some of the problems with this model, but it’s It’s still an attention-getter. Perhaps someday I’ll rebuild it (see below). 

And, after searching for several years, I finally found an unbuilt kit for the half poultry-half refrigerator car version. For whatever reason these are far harder to find than the all-poultry-car version. I’ve been looking forward to building it, but now I think I’ll wait a while since you seem to have stirred up a lot of interest in the subject. Perhaps better construction options will result in the not distant future.

There’s also a small electronic sound unit that makes chicken noises. It could be hidden in the car’s center section. Then one could attempt to deal with the smell ...

I very much enjoyed your presentation at the Chicagoland RPM meet. It’s been very effective at getting many people interested in the subject. A good poultry car would be an excellent subject for a mixed resin and photo-etch kit.

Thanks,

Dan Mitchell
==========

On Oct 30, 2018, at 5:56 PM, Kristin Dummler <kbdummler@...> wrote:

Dan,

2800+ cars were in operation at their most popular.

The Ambroid kits are still out there. I have several that I have purchased to build in the last year. They are hard to come by, but around. The idea all along has been to develop a kit for building these cars. Whether laser cut wood, mixed medium, 3D printed, resin, etc.. etc.. they will not be a simple model. Especially not if truly prototypical.

Kristin D.


On 10/30/2018 4:05 PM, Daniel A. Mitchell wrote:
A Photo-Etched side might well prove the best of the several options.

The mesh will probably need to be a bit coarser than scale to avoid optical problems and still achieve adequate transparency.

The best thing about this approach is etching the entire side in one piece, slots and all. 3D etching, or a multi-layer etch could also represent the ends of the deck boards protruding through the slots. That would greatly simplify building such a model. 

One question is how many of the old Ambroid cars are still around in salvageable form? A better one might be … if the PE sides become available, would one of the resin builders market a new car kit that uses them? I think there may indeed be a market for such. It seems well over 2000 of these cars were in service at one time, pretty much all over the country. They were NOT all that rare.

Dan Mitchell
==========
On Oct 30, 2018, at 3:38 PM, Bill Welch <fgexbill@...> wrote:

A known and skilled "photo-etcher" was present for Kristin's second presentation and he signed on to consult and help her.

Bill Welch




Re: Weighing Freight Car Models with Liquid Gravity

Dave Parker
 

Tim:

My comments on this have always included the caveat that spheres the have to small enough to achieve something at least close to idealized spherical packing.

If you had a center-sill space with a 1 x 1 cm cross-section, and you carefully filled it with 1-cm diameter spheres, you would indeed have about 52% sphere and 48% void space (just the ratio of the volume of a sphere and a cube of the same size).  Obviously, if the spheres are say 0.75 cm in dia, then you can't pack them in there efficiently, and you'll get less weight.

But if the spheres were say 1 mm, or even 2, then you are going to get something at least close to idealized packing (74-26).  Going to 0.1 mm spheres is only going gain you something on the order of one or a few percent (maybe), hardly worth worrying about. 

Concerning Tony's comment, I agree but only in theory.  If you start mixing smaller spheres in with bigger ones, then the little ones can get in the way of the dense packing of the big ones.  The gain in density will likely be rather minimal in most cases, and it may even reduce the density.  This is a very common observation in soil science -- things like dune sands usually have higher (dry) densities than do other soils that have a range of particle sizes.

Dave Parker
Riverside, CA


Re: Weighing Freight Car Models with Liquid Gravity

Tim O'Connor
 

Tony and Dave

There HAS to be a flaw in this logic. Although Tony has expressed that size
DOES matter. Let me explain.

I think the flaw is to assume perfect packing that yields the magic 26% open
space regardless of the size of the spheres. That level of packing would only
occur if the dimensions of the space were an INTEGRAL multiple of the diameters
of the sphere, and if there were no wasted space above the spheres!

Think of the case of a POWDER - essentially very very tiny spheres, packed into
a 100x100 format (i.e. their diameters are 1/100 of the dimension of the space)
versus large spheres in a 1x1 format. CLEARLY you're going to get more stuff into
the space with the powder.

In other words, in a 1x1 format, the "empty space" is actually 1.00 - 4.19/8.00 =
.47625 or 47% empty space! The 26% empty space is a BOUNDARY CONDITION of maximally
packed spheres.

In any case, it is subject to experiment to determine whether this is true, or not.

Tim O'




  Or to put it another way, the proportion of space occupied by spheres, even in
  the closest packing, is independent of the size of the spheres. Of course, if you
  have a range of sizes of spheres, the little ones pack between the big ones. But
  if they are all the same size, using smaller ones changes nothing.
  Tony  Thompson

--
Tim O'Connor
Sterling, Massachusetts


Re: Weighing Freight Car Models with Liquid Gravity

Tony Thompson
 

Dave Parker via Groups.Io wrote:

This was also discussed previously and, unless the shot are sufficiently large to preclude close packing in the available space, the weight you can gain does not depend on the diameter of the spheres, only on the density of the metal.  See post #139844.

     Or to put it another way, the proportion of space occupied by spheres, even in the closest packing, is independent of the size of the spheres.
      Of course, if you have a range of sizes of spheres, the little ones pack between the big ones. But if they are all the same size, using smaller ones changes nothing.

Tony Thompson             Editor, Signature Press, Berkeley, CA
2906 Forest Ave., Berkeley, CA 94705         www.signaturepress.com
(510) 540-6538; e-mail, tony@...
Publishers of books on railroad history






Re: Monon Decals

Bill Welch
 

I used the kit ladders but replaced the rungs w/0.010 styrene rod for Plastruct.

Bill Welch


Re: Monon Decals

steve_wintner
 

Bills presentation leaves me a bit unclear on the ladders he used for this car, but I note Yarmouth's etched 16" 7 rung stiles look about right.

Steve


Re: Weighing Freight Car Models with Liquid Gravity

Dave Parker
 

Peter Weiglin wrote:

"Given that the smaller the shot, the denser the lead weight,"

This was also discussed previously and, unless the shot are sufficiently large to preclude close packing in the available space, the weight you can gain does not depend on the diameter of the spheres, only on the density of the metal.  See post #139844.

Dave Parker
Riverside, CA


Re: Poultry Cars

Kristin Dummler
 

Dan,

2800+ cars were in operation at their most popular.

The Ambroid kits are still out there. I have several that I have purchased to build in the last year. They are hard to come by, but around. The idea all along has been to develop a kit for building these cars. Whether laser cut wood, mixed medium, 3D printed, resin, etc.. etc.. they will not be a simple model. Especially not if truly prototypical.

Kristin D.


On 10/30/2018 4:05 PM, Daniel A. Mitchell wrote:
A Photo-Etched side might well prove the best of the several options.

The mesh will probably need to be a bit coarser than scale to avoid optical problems and still achieve adequate transparency.

The best thing about this approach is etching the entire side in one piece, slots and all. 3D etching, or a multi-layer etch could also represent the ends of the deck boards protruding through the slots. That would greatly simplify building such a model. 

One question is how many of the old Ambroid cars are still around in salvageable form? A better one might be … if the PE sides become available, would one of the resin builders market a new car kit that uses them? I think there may indeed be a market for such. It seems well over 2000 of these cars were in service at one time, pretty much all over the country. They were NOT all that rare.

Dan Mitchell
==========
On Oct 30, 2018, at 3:38 PM, Bill Welch <fgexbill@...> wrote:

A known and skilled "photo-etcher" was present for Kristin's second presentation and he signed on to consult and help her.

Bill Welch



Re: Weighing Freight Car Models with Liquid Gravity

Peter Weiglin
 

Given that the smaller the shot, the denser the lead weight, I reasoned that lead powder might offer the greatest density.
And I found that lead powder was indeed available from a golf supply house.  Seems they use lead powder to weight golf clubs.

Not available or shippable to California, I was told.  So we moved to Ohio.  (Well, there were other reasons.)

Handle with care -- but it does fill the nooks and crannies in hopper cars, etc.

Peter Weiglin


Re: Weighing Freight Car Models with Liquid Gravity

Ed
 

You also might try golf supply stores for the pourable shot they use in golf clubs.

Ed Robinson


Re: Poultry Cars

Daniel A. Mitchell
 

A Photo-Etched side might well prove the best of the several options.

The mesh will probably need to be a bit coarser than scale to avoid optical problems and still achieve adequate transparency.

The best thing about this approach is etching the entire side in one piece, slots and all. 3D etching, or a multi-layer etch could also represent the ends of the deck boards protruding through the slots. That would greatly simplify building such a model. 

One question is how many of the old Ambroid cars are still around in salvageable form? A better one might be … if the PE sides become available, would one of the resin builders market a new car kit that uses them? I think there may indeed be a market for such. It seems well over 2000 of these cars were in service at one time, pretty much all over the country. They were NOT all that rare.

Dan Mitchell
==========

On Oct 30, 2018, at 3:38 PM, Bill Welch <fgexbill@...> wrote:

A known and skilled "photo-etcher" was present for Kristin's second presentation and he signed on to consult and help her.

Bill Welch


Re: Roof Query

Tim O'Connor
 


A DESPATCH roof is quite different from a Milwaukee welded roof as applied to
the Milwaukee rib sided box cars. They are easily distinguishable.

I'm not familiar with those Southern box cars, but don't confuse the DESPATCH
and Milwaukee roofs!

Tim O'Connor



As Ben Hom mentioned, Branchline made a Despatch roof in its undecorated boxcar kits that is similar to, if not indistinguishable from, the Murphy welded roof. Others have suggested a roof from a Milwaukee ribside box car that also is quite similar if not identical.

Richard Townsend
Lincoln City, OR


-----Original Message-----
From: mike turner <yardcoolie1968@...>
To: main <main@RealSTMFC.groups.io>
Sent: Mon, Oct 29, 2018 9:16 pm
Subject: Re: [RealSTMFC] Roof Query

Just confirmed Murphy Welded Roof on SOU drawing SF-5210.

Thx for the replies.

Now to try and find an HO roof of this flavor.

Mike Turner

MP-Z35

On 10/29/2018 9:43 PM, David via Groups.Io wrote:
> Murphy Welded Roof, as shown on pp. 411-412 of the 1940 CBC. The
> panels were welded together, but the roof as a whole was riveted to
> the carbody. Milwaukee did use it on their ribside boxes.
>
> David Thompson

--
Tim O'Connor
Sterling, Massachusetts


Re: Poultry Cars

Bill Welch
 

A known and skilled "photo-etcher" was present for Kristin's second presentation and he signed on to consult and help her.

Bill Welch


Re: Poultry Cars

Denny Anspach <danspachmd@...>
 

Poultry Car in Petaluma: Petaluma was and has been famed as the “egg capital" of the San Francisco Bay region. In this regard, the poultry car was most probably full of inbound layers raised elsewhere. The car would have arrived on the light jointed-rail tender mercies of the NWP via either the SP via Schellville, or more gently over the waves by Santa Fe car barge via Tiburon.

Before 1937, Petaluma was also effectively isolated from principal egg-market San Francisco itself by the pre-bridge Golden Gate. As a result, Petaluma’s egg production went to market by gentle river boat, a series of night freight boats, PETALUMA I, II, OR III that loaded in Petaluma in the evening traversed Petaluma River to the Bay (under the two (2) NWP lift bridges) and then on to San Francisco to unload, reload with machinery, etc. to arrive back in Petaluma in the morning. This was the very last of the many such San Francisco Bay river boats, lasting at least into the 1960s, I believe. I recall seeing the last PETALUMA paddling it way across the bay several times in the fifties, the last, finished with engines, in terminal layup tied up to the C&H Crockett Carquinez Straits sugar refinery. When seen, the PETALUMA was always popularly pointed-out as being “full of eggs”.

I am having some difficulty attempting to fact-check my memories about river boat shipping, etc., so corrections, additions etc. are welcome!

H-mmm…excuse me now: my morning egg (probably from Petaluma) is just now….perfectly….done, ready to enjoy.

Denny

Denny S. Anspach MD
Sacramento CA


Re: CNJ boxcars in LA circa 1947?

bill stanton
 

thanks very much for the info




From: main@RealSTMFC.groups.io <main@RealSTMFC.groups.io> on behalf of brianleppert@... <brianleppert@...>
Sent: Sunday, October 28, 2018 1:55 PM
To: main@RealSTMFC.groups.io
Subject: Re: [RealSTMFC] CNJ boxcars in LA circa 1947?
 
There is a color photo of CNJ 21675 in the Steamscenes' 2002 Southern Pacific calender, month of September.  The 1923 ARA proposed design box car is directly behind a cab forward steam locomotive crossing the Carquinez Straits bridge near Martinez, CA.  The car has the larger "Statue of Liberty" herald.  Photographed by Donald Duke, so of coarse it's undated.

Brian Leppert
Carson City, NV


Re: Poultry Cars

Dennis Storzek
 

Reading through this discussion, I'm surprised no one has suggested photo etching. The bands of mesh could be done, complete with the frames, and depending on how the junction with the end and center compartment work out, possibly all the bands for the side could be one piece, properly spaced. Biggest problem is this is likely not a do-it-yourself etching project, as getting the mesh fine enough is going to take some technical expertise and good process control. I know there have been vent panels for "chicken wire" F units etched with acceptable results.

Dennis Storzek


Re: Roof Query

Dennis Storzek
 

The big problem with the MILW roofs is the rib side cars don't have Z bar eaves, so the roof is the full width of the body, wider than on a typical car.

Dennis Storzek

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