PVC Tube Casting vs Flat Molds

[Pjohnson]

I have been casting PR for 3-4 years with good results.
Something I noticed just recently was the difference in the blank when it is cast in a PVC tube vs a flat mold. I do not use a pressure pot - after pouring I place the mold near my boiler for some conveyance of heat.

Using the exact same formula PR & MEK - the blanks from the PVC tube have a smoother cut on the lathe. The ability to achieve ribbons is quick and much less chippy. When using a flat mold the blank has more of a glassy affect and stays chipy until the final stages.

Could this be caused by the amount the resin is exposed to air flow?

PVC tube casting has its advantages and for me this appears to be one of them. The disadvantage is the ability to "control' the swirl - specifically if I am looking for a veining affect.

Please share your thoughts -- Thanks ... PJ

 

[BSea]

That's interesting. I primarily cast in PVC, and I've found (and been told) that the blanks turn very easily. I've only done a few casts using PR in flat molds, and to be honest, I didn't notice any difference. But I really haven't done enough flat pours to know for sure.

 

[Jim Burr]

Hmmmm...I've been casting organic stuff lately and stayed away from verticals because of the sinking/floating problem. May be worth a try if it cuts better.

 

[panamag8or]

I've noticed that, as well. I wonder if it is that the pvc blank generates less heat while curing than a block does, and is therefore less brittle.

 

[Sylvanite]

I wonder if it is that the pvc blank generates less heat while curing than a block does, and is therefore less brittle.

I think that's exactly right. The larger mass of a block, especially if it's thicker, will lead to a hotter cure (it's a temperature sensitive exothermic reaction), which is in turn produces a more brittle result.

Regards,
Eric

 

[BSea]

I wonder if it is that the pvc blank generates less heat while curing than a block does, and is therefore less brittle.

I think that's exactly right. The larger mass of a block, especially if it's thicker, will lead to a hotter cure (it's a temperature sensitive exothermic reaction), which is in turn produces a more brittle result.

Regards,
Eric

I think that's true. Awhile back I did some 1" PVC pours, and I was told they were a little chippy. Maybe the 1" size made them cure hotter.

 

[79spitfire]

I wonder, I tried some in 1/2" PVC to make some mechanical pencils. They took much longer than usual to set, they also had a severely wrinkled surface. I understand that is from the center curing faster than the outside. I should be able to turn one tomorrow. If anything interesting happens, I'll let you know.

 

[PSNCO]

I can easily demold a 3"x5" block in 2-3 hours. A pvc mold might take 6-12 hours. I've started to decrease the amount of MEKP in the block molds. My son has more blowouts drilling the blanks from a block. The block molds use more PR, but I feel I get a bit more control over the swirls on a block mold.

 

[79spitfire]

I had to redo the 1/2 ones, the wrinkles were way too deep. It had nothing to do with the mold it self, they had gotten heated un-evenly. After re-doing them and letting them sit (no external heat) they came out fine.

 

[Mondo]

That's interesting. I primarily cast in PVC, and I've found (and been told) that the blanks turn very easily. I've only done a few casts using PR in flat molds, and to be honest, I didn't notice any difference. But I really haven't done enough flat pours to know for sure.

Bob don't you change a thing. My son and myself love your blanks!

 

[BSea]

That's interesting. I primarily cast in PVC, and I've found (and been told) that the blanks turn very easily. I've only done a few casts using PR in flat molds, and to be honest, I didn't notice any difference. But I really haven't done enough flat pours to know for sure.

Bob don't you change a thing. My son and myself love your blanks!

LOL, don't worry. I won't fix what isn't broken. And thank you!

 

[znachman]

I've noticed that, as well. I wonder if it is that the pvc blank generates less heat while curing than a block does, and is therefore less brittle.

This is the reason long curing time.

 

[znachman]

I have been casting PR for 3-4 years with good results.
Something I noticed just recently was the difference in the blank when it is cast in a PVC tube vs a flat mold. I do not use a pressure pot - after pouring I place the mold near my boiler for some conveyance of heat.

Using the exact same formula PR & MEK - the blanks from the PVC tube have a smoother cut on the lathe. The ability to achieve ribbons is quick and much less chippy. When using a flat mold the blank has more of a glassy affect and stays chipy until the final stages.

Could this be caused by the amount the resin is exposed to air flow?

PVC tube casting has its advantages and for me this appears to be one of them. The disadvantage is the ability to "control' the swirl - specifically if I am looking for a veining affect.

Please share your thoughts -- Thanks ... PJ

Try to cure the mold far away "YOUR BOILER"...:yawn::yawn:

 

[redneckmedic]

I wonder if the fact that the PVC blanks start off round is a variable as well as slower curing time.

 

[mvande21]

I might be getting off the original topic here. But I used both kinds of molds, although I had alumilite. But what do u use on the "capped" side of the PVC tube?? I would like to try to get more into the pvc castings, since it creates less waste and less waste means more profit!! Is there any tips or tricks of the trade. Do you also do embedment's in the pvc molds??

 

[BSea]

I use silicone stoppers, but others use blue painters tape. I've never done any embedded materials in a PVC tube.

 

[Pjohnson]

I use a cork and wax paper.