Cast the Timing Cover, Oil Pan, and Bell housings today, two each. Not a single fail since that first valve cover, which I suppose was to be expected on that one. With the more generous gating, I also backed off on the pour temp. Still very hot at 1450F but not stupid hot. 1/2ATM vacuum on the flask. Here's a video reviewing the fruits of this morning's casting session. Best, Kelly
I had some ideas for further refinements for the valve covers. So I made 5 more patterns to incorporate them. First, on an unrelated trip to Home Depot, I noticed they had some Owens Corning Foamular 250 (pink XPS insulation board) on the shelf. 250 is supposed to be 1.5 lb/ft3 and 150 1.3lbs/ft3. In the past I have noticed the slightly denser board machines marginally better. I primarily use 150 and that was all I had on hand so I went and bought the sheet of 250. When I weighed it, it was only 1.25lb/ft3....Argggh! I used it any way. If anything, I would say it was actually softer than the lot I had been using. I made some further refinements to the machining program. The graphics/fonts were slightly better and the grooves/ribs much better. They're the best quality patterns so far. I previously poured the 3 successful valve covers at 1600F and 1/2ATM vacuum. That is stupid hot for aluminum. I added more generous gating to the other (non-valve cover) parts I poured after those VCs and managed to successfully pour them at 1450F. So I Increased the cross section of the feed system and sprue, and made it from very low-density EPS. The idea being to fill that feed system very rapidly, and since it is fairly massive compared to the pattern itself, it should provide hotter melter sooner to the pattern extremities. -We shall see. I'll try the first one at 1400F and 1/2ATM. The vacuum is essential for the fine detail and very thin walled casting. Without, the very low mass and high surface area of the casting just loses heat to the mold too fast and prematurely freezes. The vacuum also creates a ~7psi pressure differential above the sprue, pulls air out through the coating and draws the metal into the detail.......similar to vacuum block investment casting. This is only the second project in 6 years where I've needed to use vacuum. I did the initial development work back on this experiment: Saucer Cup & Spoon – The Lost Foam Edition | The Home Foundry I spent some time sanding the exterior to improve the surface finish and then applied a thin coat of paste wax with a soft bristle brush. After it dried I buffed with a paper towel. It definitely improved the surface finish. I suppose the paste wax does a little filling too, but looking at it under magnification, what it mostly does is cause the micro-burrs/foam fur to lay down on the surface and in the cell voids. The wax repels water more strongly than even the foam. I dipped them in my home brew surfactant, (Dawn dishwashing soap and water) and the water beaded in many places, so I lightly brushed the entire surface with a soft chip brush to break the surface tension and then used the end of the brush to gently stab the refractory coating into the fine graphics details, work out bubbles, then dipped and hung them to dry as usual. Subsequently I applied an additional coat of refractory with brush to the ribbed and graphics area with brush. Best, Kelly
I had to escape to the sunshine for while but got back last night and cast the 5 valve covers this morning. Here's how they came out of the sand. Here they are cleaned up. ....and a short video reviewing the resulting castings. Time to move on to the block and heads...... Best, Kelly
