Casting Defects

Timothy L. Donohue and Helmut F. Frye have posted an excellent paper "Characterization and Correction of Casting Defects" (http://www.platinumguild.com/files/pdf/V5N2W_characterization.pdf).

They show cartoon images of the defects and discuss various causes. Highly recommend reading through the entire document before fixing on one defect as there are many and sometimes the differences are subtle.

Investment Flask Facts

The wax (art piece + sprue system + pour cup) determines the size of the investment flask. Since the flask is a cylinder (technically a right circular cylinder), the total volume is determined using the height (H) and diameter (D) or radius (R) (D = 2 * R) in the equation Volume = pi * R^2 * H = pi * (D/2)^2 * H, where pi = 3.14159265... is half the circumference of a circle with radius 1.

Here are some simple rules relating the height (h) and diameter (d) of the wax and the flask height (H) and diameter (D):

1. Because the flask will have a 2-3 inch cap to seal the bottom before filling, H = h + 2. Large flasks (diameter > 20 inches may need larger caps depending on the shape of the wax).
2. 2 inches between the widest points on the wax and the flask wall are ideal, so D = d + 4.

The flask's total volume (measured in cubic inches or in^3) is given in the first row of each cell in the table below.

Since the flask is filled using 5 US gallon buckets of wet investment material, in order to estimate the number of buckets needed to fill a flask, one needs to divide the total volume by 231, the number of cubic inches in 5 US gallons. The second row of each cell in the table below gives these values. Note that these are full buckets and it will take more "partially filled" buckets, so treat these values as lower bounds (minimum).

Finally, the third row of each cell provides estimates of the flask's total wet weight. These are based on the weights of water, sand, and plaster mixed in the proportions of 1/3, 4/9, and 2/9 (resp.). For a 5 US gallon bucket these weights are roughly 14, 22.3, and 7.9 lbs (resp), putting a 5 US gallon bucket of investment at 52 lbs. Note that actual full buckets have been weighed and come very close to this value.

Diameter and Height combinations shaded in green are "doable" with a few assistants to move the finished flask. Those in red are "challenging", and white is "beyond reason".

Volume (in^3) # Buckets Weight (lbs)		Flask Height (inches)
		10	12	14	16	18	20	22	24	26	28	30	32	34	36
Flask Diameter (inches)	10	785 0.6 35	942 0.8 42	1099 0.9 49	1256 1 56	1413 1.2 63	1570 1.3 70	1727 1.4 77	1884 1.6 84	2041 1.7 91	2199 1.9 99	2356 2 106	2513 2.1 113	2670 2.3 120	2827 2.4 127
	12	1130 0.9 50	1357 1.1 61	1583 1.30 71	1809 1.5 81	2035 1.7 91	2261 1.9 101	2488 2.1 112	2714 2.3 122	2940 2.5 132	3166 2.7 142	3392 2.9 152	3619 3.1 162	3845 3.3 173	4071 3.5 183
	14	1539 1.3 69	1847 1.5 83	2155 1.8 97	2462 2.1 110	2770 2.3 124	3078 2.6 138	3386 2.9 152	3694 3.1 166	4002 3.4 180	4310 3.7 194	4618 3.9 207	4925 4.2 221	5233 4.5 235	5541 4.7 249
	16	2010 1.7 90	2412 2 108	2814 2.4 126	3216 2.7 144	3619 3.1 162	4021 3.4 181	4423 3.8 199	4825 4.1 217	5227 4.5 235	5629 4.8 253	6031 5.2 271	6433 5.5 289	6835 5.9 307	7238 6.2 325
	18	2544 2.2 114	3053 2.6 137	3562 3 160	4071 3.5 183	4580 3.9 206	5089 4.4 229	5598 4.8 252	6107 5.2 274	6616 5.7 297	7124 6.1 320	7633 6.6 343	8142 7 366	8651 7.4 389	9160 7.9 412
	20	3141 2.7 141	3769 3.2 169	4398 3.8 198	5026 4.3 226	5654 4.8 254	6283 5.4 282	6911 5.9 311	7539 6.5 339	8167 7 367	8796 7.6 396	9424 8.1 424	10052 8.7 452	10681 9.2 480	11309 9.7 509
	22	3801 3.2 171	4561 3.9 205	5321 4.6 239	6081 5.2 273	6842 5.9 308	7602 6.5 342	8362 7.2 376	9122 7.8 410	9883 8.5 444	10643 9.2 479	11403 9.8 513	12163 10.5 547	12924 11.1 581	13684 11.8 616
	24	4523 3.9 203	5428 4.7 244	6333 5.4 285	7238 6.2 325	8142 7 366	9047 7.8 407	9952 8.6 448	10857 9.4 488	11761 10.1 529	12666 10.9 570	13571 11.7 611	14476 12.5 651	15380 13.3 692	16285 14.1 733
	26	5309 4.5 239	6370 5.5 286	7432 6.4 334	8494 7.3 382	9556 8.2 430	10618 9.1 478	11680 10.1 525	12741 11 573	13803 11.9 621	14865 12.8 669	15927 13.7 717	16989 14.7 764	18051 15.6 812	19112 16.5 860
	28	6157 5.3 277	7388 6.3 332	8620 7.4 388	9851 8.5 443	11083 9.5 498	12314 10.6 554	13546 11.7 609	14777 12.7 665	16009 13.8 720	17240 14.9 776	18472 15.9 831	19703 17 887	20935 18.1 942	22166 19.1 997
	30	7068 6.1 318	8482 7.3 381	9895 8.5 445	11309 9.7 509	12723 11 572	14136 12.2 636	15550 13.4 700	16964 14.6 763	18377 15.9 827	19791 17.1 891	21205 18.3 954	22618 19.5 1018	24032 20.8 1081	25446 22 1145
	32	8042 6.9 362	9650 8.3 434	11259 9.7 506	12867 11.1 579	14476 12.5 651	16084 13.9 724	17693 15.3 796	19301 16.7 868	20909 18.1 941	22518 19.4 1013	24126 20.8 1086	25735 22.2 1158	27343 23.6 1231	28952 25 1303