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Frosty Type

Started by Jason, June 24, 2022, 03:31:24 AM

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Jason

I suppose this would have been a better topic while I was casting 72pt type (I spent a good part of today stripping the caster to pull my large-type mould/pump/etc. and replace it to cast 18pt), but despite plenty of attempts, all of the 72pt type came out frosty.

Some of what I attempted to improve things:
  • raised and lowered metal temperature
  • increased and decreased speed
  • increased and decreased main pump spring pressure (from around 2" to close to 4")
  • engaged the nozzle-seating timer mechanism to hold nozzle seating until the last second
  • increased and decreased water flow
  • used compressed air to cool mat, and then didn't
  • adjusted number of pump plates at top and bottom of post
  • adjusted position of crossblock on injection (moving it slightly forward/back)

As you can see, I tried pretty much everything I could think of as a variable, but no matter what I was getting frost/pitting on the face. Best casts were the first casts of the day (which suggests cooler mould/mat).

This was a thick, narrow sans-serif, so lots of surface area to the face. Middle of the sort was good (solid, smooth, no frost), but the frost appeared at the top and bottom of the letter.

This image is lit and shot macro, so it exaggerates the situation, but as you can see, the frost is significant.



Any and all feedback & suggestions welcome!

Jason




KPMartin

It almost looks like the metal is entering the mould cavity as a spatter or spray rather than a smooth stream. This sticks to the matrix as a pattern of small circles, and the heat of the bulk metal is insufficient to re-melt this to smooth the face out.

It is mostly on the top of the face of the type; how does this relate to the jet position in the mould?

Maybe a dirty or damaged nozzle? Misaligned jet/crossblock? Pump sucking back too much air into the nozzle on the return stroke? On the comp caster this might be having the type carrier driven by the wrong pin position on the cam lever, or using the wrong crossblock coupler.
-Kevin

Dan Jones

60 and 72 pt. type on the Super Caster can be a challenge, like Kevin says the nozzle is spitting. Metal has to go through the narrow slot where the type trimmer travels, and then expand out. And the effect you are seeing will only get worse with larger set widths.

First, I suggest to figure out what the lowest temperature is to consistently run the type; because as the temperature gets higher, I believe the alloys start to separate when you cast and spitting just makes it worse.

Second, do you know what your metal content is? With larger type, I get better results if I lower the alloy content, i.e. more lead percentage. That being said, more Tin improves the flow of the metal. And Tin has a relatively low melting point (around 450 degrees F). So that points to Antimony. I believe too much Antimony can mess things up in larger type, it has a very high melting point (around 1167 degrees F) and probably starts to freeze up quickly (difficult to prove, but you are looking for options).
 
Third, when was the pump and piston cleaned? Note that there is no "top hat" device in the large Super Caster pump body, so sucking back on metal in the nozzle might not be a big issue.

Fourth, maybe run the cycle faster. These are aluminum mats? They can stand a little heat. Metal at 600 degrees is hitting a matrix at what, 150 degrees? It freezes instantly, like water from a Zamboni onto ice. Give the metal a fraction of a second more time to flow against the matrix before it freezes up.

I had this issue with some Giant Caster mats and was able to turn the mat around in the holder, it can make a small  difference. Some Giant Caster mats will not fit this way in the Super Caster.

I use bottom plates as required, and add top plates carefully. These can also delay the pump timing, so be aware.

If all else fails, and if this type is just for your own use, you could run the casts through a Ludlow Super Surfacer (or similar), large Ludlow mats can cast similar faces and Ludlow designed the machine to cleaned up cast face. Then use packing.


Jason

Hmmm, this raises another issue. I have two pistons for large type, but only one pump body. The piston I've been using feels quite loose in the pump: when I pull it up, it seems to "slip", as in I don't feel much of a vacuum as I pull it up. If it's pushed to the bottom, there's good tension to about halfway up, then it just sort of slips up the rest of the way. I wonder if I'm getting a lot of air in there, which might cause the spitting?

My other piston is quite scarred, which is why I haven't been using it.

Yesterday I took the good piston apart and cleaned it thoroughly, and snugged up the piston head (it was fairly sloppy), and the pump body is clean. I should try it again now that I've cleaned and snugged up the piston head assembly.

My fear is that my pump body bore is worn and thus the piston might be loose in there. I'll clean and try the second piston to see if it's a better fit.

Am I right that there should be tension/vacuum the entire time I lift the piston? And resistance all the way down?

Jason

John Cornelisse


Dan Jones

Jason, it looks to be filling the mould OK, so the piston is doing it's job. Try measuring the bore and diameter, and Monotype made oversize pistons so that a worn pump could be repaired.

Dave Hughes

There's some great advice on this thread. Many thanks to @KPMartin and @Dan Jones for trying to sort Jason's problem out.

I did have to Google a "Canadian" reference though!

Dan said:

QuoteIt freezes instantly, like water from a Zamboni onto ice.

I'm guessing you have a lot more Zambonis than we do here in the UK.


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Jason

I was running a No.5 nozzle, as indicated for 42-72pt type. The pump body was clean, and the nozzle freshly drilled out, so I don't think the pump body or nozzle were an issue.

I just took apart all three of my large-type pistons. The actual piston head on one is in great shape, the other two not so much, see photo of one of the bad ones:

large-piston-head.jpg

Rest assured that my good piston is actually in good shape, not like that one. However, if anyone has a spare large-type piston head (especially an oversized one as mentioned above), please let me know (I have a substantial list of stuff available for trades).

I also found that in the good piston (the one I was using), the slotted washer inside the piston was completely stuck to the bolt: no movement at all. So, I cooked it in the pot, wire-brushed it, eventually managed to move the washer down to the threads and then took a brass wire-wheel on a rotary tool to the bolt post to get all the crud off. I also took a very thin file to the slots to clean them out. Nice and clean and easy movement of the washer now. I also cleaned out the inner areas of the piston head, ran a tap & die on the bolt, handle end, and the lock nut. Everything is now nice and clean, but I've already switched to cast 18pt, so will have to wait a while to see if any of this will help with the frost.

Thanks for all of the feedback from everyone. I'm not sure I'm any closer to a solution, but I'm hoping the cleaned piston will help.

Jason

Dan Jones

The outside diameter of a piston meant for the 1 1/4" pump body appears to be about 1.124", i.e. one thou less than the bore of the pump. I never measured this before, it seems very tight.

KPMartin

Jason,
That's one nasty looking piston. That looks like rust pitting to me, and it is likely beyond being usable.

Have you ever had a chance to inspect the bore of the pump for similar pitting, especially higher up towards the top of the piston head motion?

It sounds like you have to disassemble and clean all the parts of the piston head. The metal enters the pump through the bore of the piston. The piston has a bit of vertical play on the rod; during the pumping stroke, the piston pushes up and seals against the cone nut. On the return stroke when the pump rod is moving up, the piston moves down on the rod so a gap opens up around the cone nut, admitting metal to the center bore of the piston head. At the bottom, the piston is tight against the slotted washer, and the slots allow the metal to pass from the piston bore into the main pump chamber.

You should feel a bit of resistance when manually pulling up the piston (I suggest you seal the nozzle when trying this to avoid suck-back confounding the issue) since the metal must pass through some small passages to fill the pump chamber.

It may be that the upper section of your pump chamber is more worn than the lower section, possibly because of a long life of casting smaller type (which does not use the entire stroke), or possibly due to corrosion.

However, as others have mentioned, you seem to have plenty of metal volume. You should cut one of those types with a saw to evaluate the trapped air pockets. If these are small it means that your pump is also producing plenty of pressure. Low pressure would be the main symptom of a poorly-fitting piston since it would not really affect refilling of the chamber.

Even if air is somehow entering the pump chamber, it would be the last thing forced out the nozzle, but your problem is spitting/spattering of the first metal coming out of the nozzle.

I don't know what the specification is for piston clearances. I would need access to the drawings for the pump body and pistons to see how they are toleranced. Also knowing what oversize piston heads were available would give a hint to this (for instance if they were, say, 0.010" and 0.020" oversize this would imply that a (IMHO) loose fit of 0.009" would be considered acceptable). I also expect that oversize piston heads cannot be installed without first reaming and/or honing the pump bore first to remove uneven wear.

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