There must be something going on with the flask blow out described in the posts.<\/p>\n
I have invested and cast flasks from 2 \u00bd inches to 6 inches for thirty years.\u00a0 I have had only two blow outs that I can remember.\u00a0 Something in the steps I take prevents blowouts or the casting gremlins are busy elsewhere when I cast.<\/p>\n
The frustrating thing about casting is that what works for one may not work for others.\u00a0 Knowing this I risk telling what I do in investing and casting my flasks.\u00a0 Some of the techniques will probably leave casters thinking \u201cNO WAY THAT WON\u2018T WORK.\u201d\u00a0 However I have had success following these steps.<\/p>\n
Maybe these steps will lead to clues as to why blow outs happen.<\/p>\n
I try to follow the rule of allowing \u00bc inches of investment above the wax for every 1 inch of flask diameter.\u00a0 Note I said I try to follow the rule.\u00a0 Some times on smaller flasks I violate this rule.
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\nThis wax is a little less than 3 \u00bd inches in diameter.\u00a0 It is placed in a 4 inch diameter flask.\u00a0 As indicated there will be about 1 \u00bd inches of investment above the wax.<\/p>\n
I do not worry about the distance between the wax and the flask on most of my waxes as long as the wax does not touch the flask.\u00a0 On the larger pieces of pottery I try to provide at least \u00bc of an inch between wax and flask.\u00a0 The only investment holding the top of the investment to the bottom of the investment is the ring between the flask and the wax.<\/p>\n
I do not use tap water but use only water bought from local water treatment stores.<\/p>\n
Both the investment and water are at room temperature.<\/p>\n
I use Ransom and Randolph investment.\u00a0 I store the investment in my house.\u00a0 I have had investment sit for many months between usages.<\/p>\n
Weight out 5 pounds of investment and measure the recommended amount of water.\u00a0 I pour the recommended amount of water into the mixing bowl.\u00a0 Pour the investment into the water.\u00a0\u00a0 Mix the investment with an electric mixer on high speed for 1 min 15 seconds.<\/p>\n
Place the mixing bowl under a bell jar and pull a vacuum.\u00a0 The vacuum is maintained for 1 minute after the investment pancakes.<\/p>\n
Place the flasks to be invested on the rubber pad and pour the investment through a kitchen strainer into the flasks.\u00a0 I find the strainer will sometimes strain our improperly mixed investment.<\/p>\n
Five 2 \u00bd inch flasks can be invested at a time.<\/p>\n
Maintain a vacuum for one minute after the first bubble appears in the investment.<\/p>\n
If all goes well I will have enough time to invest a second set of flasks with the remains of the first 5 pounds of investment.\u00a0 I try to complete all the investing within a seven minute period.<\/p>\n
Let the flasks sit for three hours.<\/p>\n
I scrape the top of the investment with a curved trowel.\u00a0 This gives a slight concave shape to the investment.\u00a0 I believe the vacuum will be more uniformly distributed across the entire face of the flask.\u00a0 The slight curve in the investment might, and I am just guessing, give the investment a little more strength.<\/p>\n
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\nMy oven holds 16-2 \u00bd inch flasks on the first level.\u00a0 I will add additional flasks if they are short.\u00a0 The oven will handle flasks up to seven inches tall.\u00a0\u00a0 The taller flasks should be placed in the center and front of the oven.\u00a0 There is a danger of overheating the heating coils if tall flasks are placed against the back and side walls.\u00a0 If I cast very large flasks I place them in the center of the oven.
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\nI scratch the flask number on the investment so that I can identify which flask\u00a0 id being poured.<\/p>\n
I normally do not cast unless I have a full oven.<\/p>\n
Place flasks in the burnout oven and increase the temperature from room temperature to 250 degrees and hold for 2 hours.\u00a0 Increase the temperature by 300 degrees per hour until the temperature of 1350 is reached.\u00a0 If the oven is really packed the oven may not be able to increase 300 degrees per hour.<\/p>\n
I maintain the burnout temp of 1330 for 8 hours.\u00a0 I have found it takes 8 hours to completely remove all the wax in the full oven.\u00a0 Then cool the flask down to 860 degrees if silver is to be poured.\u00a0 The flasks are allowed to sit for at least one hour before pouring the first flask.<\/p>\n
The silver is melted in an electro melt furnace at around 1370 degrees.<\/p>\n
The flask is placed on the pad when the system is set to pull a vacuum.\u00a0 It might be safer to place the flask on the pad then increase the vacuum to the flask.<\/p>\n
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\nThis sketch shows the convex surface of the investment.<\/p>\n
Pour the silver.<\/p>\n
Place the hot flask immediately on to a wax covered pad.\u00a0 Throw wax on the sprue and cover the flask with a larger flask then place a solder pad on top of the cover flask.\u00a0 This if my way of preventing fire scale on the silver casting.\u00a0 The process is better described in Orchids \u201cTips from the jeweler\u2019s bench.\u201d<\/p>\n
Allow the melt furnace to stand for around 5 minutes before a second pour is made.\u00a0 This allows the upper ring of the graphite crucible to heat up to pouring temperature.\u00a0 If the ring is not heated up again before pouring the silver will chill as it flows over the ring.<\/p>\n
I quench the smaller flasks in about 7 minutes after pouring and around 15 to 20 minutes for the very large flasks.<\/p>\n
Note:\u00a0 The gripping tongs normally used to hold the flasks do not work well on the 4, 5 and 6 inch flasks.\u00a0 To solve this problem I scrape some investment away form the top and bottom edge of the flask so that I can grip the flask with vice clamp pliers.\u00a0 The flask is removed from the oven by clamping the pliers on the non sprue end.\u00a0 The flask is placed on a flat surface and the pliers are moved to the sprue end.\u00a0 The pliers are left clamped to the flask as the silver is poured.\u00a0 The flask and head of the pliers go under the surface of the quench water when quenching.
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\nNow that I have said all that the casting gremlins will probably cause some blow outs when I cast four 4 inch flasks this coming Friday.<\/p>\n
I have written a rather lengthy paper on vacuum casting.\u00a0 It is free to anyone who can receive an attachment on their e-mail.<\/p>\n","protected":false},"excerpt":{"rendered":"
There must be something going on with the flask blow out described in the posts. I have invested and cast flasks from 2 \u00bd inches to 6 inches for thirty years.\u00a0 I have had only two blow outs that I can remember.\u00a0 Something in the steps I take prevents blowouts or the casting gremlins are […]<\/p>\n","protected":false},"author":22,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"open","ping_status":"open","template":"","meta":[],"_links":{"self":[{"href":"https:\/\/userblogs.ganoksin.com\/leessilver\/wp-json\/wp\/v2\/pages\/5"}],"collection":[{"href":"https:\/\/userblogs.ganoksin.com\/leessilver\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/userblogs.ganoksin.com\/leessilver\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/userblogs.ganoksin.com\/leessilver\/wp-json\/wp\/v2\/users\/22"}],"replies":[{"embeddable":true,"href":"https:\/\/userblogs.ganoksin.com\/leessilver\/wp-json\/wp\/v2\/comments?post=5"}],"version-history":[{"count":0,"href":"https:\/\/userblogs.ganoksin.com\/leessilver\/wp-json\/wp\/v2\/pages\/5\/revisions"}],"wp:attachment":[{"href":"https:\/\/userblogs.ganoksin.com\/leessilver\/wp-json\/wp\/v2\/media?parent=5"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}