Disclaimer: I am relatively new to Petrobond. I am casting flask sides for another set of aluminum flasks for casting in green sand iron 18" straight edges. The wood flasks are about 28" long and 10.5" wide inside and are constructed from recycled grooved 3/4" plywood . Since I have limited Petrobond, I made wood flasks "as small as possible" not really knowing what "possible" is when using Petro. I think I made them too thin for good function as the flasks are 2" deep for the drag and 2.75 deep for the cope. On packing the flasks I found that the drag wanted to dropout when I tried to reassemble the drag onto the cope. I noted that the sand was not losing its grip on the flask sides but was sagging across the span. So, I tried installing 1/4" every 6" bars to support the Petro. It worked remarkably well. I had the opportunity to "torture test" the drag when I screwed up the opening of the flask the first time through. Several pretty sharp inverted taps of the drag did not result in dropout and when I finally did abuse the drag enough to cause the sand to fallout, substantial sand was held back by the bars. In summary, It made a big positive difference. The bars are secured in their holes by friction. I intentionally mis-aligned the holes a bit when I used a hand drill to bore the 1/4" holes. So, the pins were knocked home with a few light taps from a hammer. That is enough to prevent them from falling out when the flask is empty. The bars did not seem to interfere with mold ramming, BTW. I'd be interested to hear what strategies others have used in a similar circumstance. FWIW, Denis
Pretty hard to beat the simplicity of the bars if they are working for you. I've seen a number of schemes over the years. My favorite was 1/8" slats that slid into vertical slots in the flask sides. The slats had holes in them for sand retention. The benefit was you could install them wherever it didn't hit the pattern and/or profile a slat for clearance if needed. -Just made it more adaptable to different patterns. I don't recall any mechanism for locking the slats in the slot. Probably just used a backing board. It was easy to recover them after shake out. Best, Kelly
So, those slats just dropped into open slots that would be made just by cutting a kerf across the cope-facing edge of the drag? I can see how they would stiffen the sand and the sand itself would prevent them from dropping out. A disadvantage would be effectively reducing the height of the drag flask side and thus reducing its vertical stiffness some. But an idea worth tucking away. Denis
nothing at all wrong with what your are doing, just an FYI, large wooden flasks, will sometimes need/have threaded rods ran through them, similar to what you have done, to prevent the sides of the flask from bowing out during ramming . you might need this on a longer flask . one of the down sides of petrobond, is it just doesn't have the green strength of greens sand, and will often need supports in the flask especially in larger sizes. this is seldom an issue for hobbiests, even I dont like working with anything over about 16 inches Well done V/r HT1
I did stiffen the long sides with added strips of 3/4 ply screwed to the outside of the flask as I was pretty sure 3/4 ply itself on a span of 30” would be too springy. They did hold up to pretty firm ramming, though. The petro seems gummier than green sand and may tend to spread sideways with ramming somewhat less than green. So, it may put a little less pressure on the flask sides than a similar span of green. (Lots of supposing in this statement;-). ) Denis
not a sand term I have heard, but I understand Petro will stick to the flat of your hand, and can be hard to get off, while green sand brushes right off. jus so you know, this seems to lessen with use Petrobond is odd to any other sand, in that brand spanking new, it's just not as good as sand that has been used , I assume , the heat changes the properties of the clay some , we all know old or cold petrobond, has poor green strength and can be "crumbly" V/r HT1
Nice solution Denis. On my steel moulding boxes, I have welded a strip of flat bar into the inside, so that they sit above the pattern. The bars are typically 25mm wide, in a box with 60mm high sides. On timber boxes, same deal with strips of wood, Cheers Charlie
So, let's see if I visualiz this right. You attach bars to the inside of the flask lengthwise so that cross-bars of metal or wood can be laid in place crosswise to form what would look like a ladder? Sounds pretty slick. I can see how it would be very quick and easy to place and remove the bars, but they would be held securely by a combination of sand and the lengthwise strips. I am visualizing the rungs maybe being maybe 12mm thick and, as you say, 25mm wide. Nice! Thanks. Worth tucking that one away for future use. Denis
I've noticed in a lot of the casting videos where the molder is squatting and working on the ground that their copes have a metal matrix built in. I would think that would create some ramming issues, but then I watch them walk on the mold barefoot to "finish ram" the sand instead of using a rammer. Pete
Strange idea: when making your (wood?) flasks, cut one retention groove deeper than the others, and give it a squarish cross-section (in contrast to using, say, a core-box bit to give a full-radius groove). Cut cross-pieces/gaggers (recall reading about this term years ago in one foundry book or another) such that they can be wedged into that deeper retention groove. (Put a radius on their ends to make this easier to do.) https://www.google.com/url?sa=t&sou...FjANegQIBRAC&usg=AOvVaw2gRPrQ_CXFBRDYpN6xQKc2
I like the idea of grooving the flask sides and inserting cross bars as you suggest. I think the term gagger refers to hook like devices hung in the sand to reinforce it. Hand Tool # 15. Gagger: A gagger is used for reinforcing the moulding sand in the cope part of the moulding box. These are the iron rods or thick wires bent at one or both the ends. The bottom end of the gagger must be kept 5 to 8 mm away from the embedded pattern Fig. 4.1 (o). Denis
I thought that one called the cross-bars gaggers, actually. I knew they were used to reinforce sand. I wonder how big the flask can be before these pieces are required? I doubt they're needed on, say, an 8×10 (inch) outside dimension flask... Or are they?
I will claim no special knowledge of foundry terminology. But here is a patent from the 30's that seems to use cross bars and gaggers to describe a reinforcement method. https://patents.google.com/patent/US1948867A/en Regardless of the names for the cross bars, your suggested idea is a good one. I do not think folks on this forum use gagggers or crossbars often. But I have a couple of patterns that do require them as the shape of the pattern divides the sand up in a way that is very prone to droput without them. I'd like to get more experience with them and learn from someone who has used them a lot as I think gaggers can be pretty simple in design (from what I hear) and still be effective. I think mine have been overbuilt. They work, but may be needlessly complex. Denis
Probably need them for running those straight-edges, or similar parts - like, say, the bed for a *Deathtrap Wood-Lathe.* Note: said lathe is a fictional implement.
Yes By vertical stiffness do you mean resistance to drop out? ....and don't the bars reduce the effective flask height in the same respect? The slats could be inserted in the slots where needed and profiled on the pattern side for pattern clearance as needed. On long narrow flask like the one you showed, sometimes they just used a couple slats toward the center even though they had kerf slots all along the flask side and this was sufficient to prevent drop outs yet easily adaptable to different patterns. Best, Kelly
Ya, I was referring to the vertical strength (resistance to deflection) of the flask side. For example, if your flask side vertical height were originally 3.5" and you kerf it an inch deep at 6" intervals, it now is effectively 2.5 inches high and a bit springier vertically than it was prior to kerfing. Probably not a major problem. Interestingly, Dennis' solution above would not reduce the vertical strength much at all. It is interesting that a simple bar in a kerf you describe would reduce dropout. But that is consistent with my observation that sand can visibly sag if making a long span, but it may or may not actually fallout. A couple/few bars like you describe could easily make the difference I now understand. Anyhow, I am finding it very informative to be kicking these various ideas around. Denis
That, and a (woodworking) duffer like me can cut those grooves on a router table! On a more-serious note, one could simply cut a dado at the very bottom of the flask, and then attach, say, a piece of angle iron to provide the bottom wall of the slot. Use a fair number of screws to attach the metal parts, and this will have less impact on the depth of the flask - and its bending strength, also.
From C.W. Ammen's sand casting handbook: cope bars and gaggers. Not to say that someone else might not use different terms, or use these terms differently. Note the grippy grooves on the cope bars. Also bars that are contoured to avoid the pattern. For even bigger molds, crossbars across the crossbars too, which he calls chucks. Jeff