a. Design the accessories so that the casting will air-conditioned as analogously as possible, and so that abbreviating takes abode sequentially.
b. Avoid designs (like alternating blubbery and attenuate cross-sections), which tend to arrest admixture breeze during solidification.
c. Avoid astute angles and shapes, which can about-face abbreviating admonition abruptly.
d. All angles (inside and outside) should accept fillets or circuit with radii according to bisected the array of the section. Sharp angles account "hot spots" and apply accent points. Caution: Fillets with too ample a ambit may account shrink- age and weakness.
e. Avoid "X" blazon intersections. In- stead, alternate abutting accoutrements for more good breeze of metal, and to abate the all-embracing aggregate of metal at anniversary junction.
f. Avoid acicular capacity and attenuate edges, area possible, back they may not ample completely.
g. Design accessible holes so that they are no best than four times the aperture diameter. Blind holes should not be added than alert the hole’s diameter.
2. Selection of casting alloys
As a accomplishment jeweler you accept abounding alloys from which to choose, so your best charge be a accurate one, Factors to accede accommodate fluidity, hardness, calefaction treatability, temperature range, and abandon from porosity and reproducibility.
Karat ascendancy is additionally of abundant importance, and should accommodate a amount of believability that is accurate by assays. The admixture you baddest should accept a accurate almanac of performance, accurate by analysis abstracts and by assembly recommendations, which any alembic can follow.
The arrangement of fresh metal to remelt banal will alter widely, according to the casting technique. As a accepted rule, 60 % fresh gold with 40 % remelt will accord acceptable after-effects for chicken golds; for white golds the arrangement should be about 70 % fresh to 30 % remelt. These accommodation assignment best back the alloys accept had deoxidizers added by the producer. If, afterwards several casting cycles, the admixture becomes darker, the allotment of fresh admixture should be aloft until the botheration disappears.
3. Specific casting techniques
a. The accumulated weight of the sprues, copse and button should according or beat the weight of the commodity to be cast.
b. The cross-sectional breadth of the sprue should be according to, or greater than, the array of the commodity at the point of juncture.
c. The sprues should be continued abundant to position the accessories abroad from any pools of heat, which generally advance abreast the timberline or base. d. Whenever possible, the sprue should accommodated the commodity at its heaviest section. This is a analytical application back casting white golds.
e. Light rings or bezels can adhere anon from the button. For added intricate pieces, position the timberline amid the sprue and button.
f. Where a timberline is used, its cantankerous area should be at atomic alert as abundant as that of the alone sprue.
g. With high-temperature karat golds (primarily the white, nickel- address alloys), abstain absolute approximation of the aqueous metal adjoin the investment. Where possible, use a sprue, absorbed to the timberline at a bottomward angle, abroad from the administration of the metal flow.
h. Allow for able addict time, as recommended by the architect of the advance materials.
4. Porosity – the above problem
Porosity is accustomed as the best accepted birthmark in articles fabricated by absent wax advance casting. As a basic guide, the afterward advertisement presents the above causes of porosity in adjustment of their accident in the casting process.
a. Abnormal construction/spruing of model.
b. Air bubbles in wax pattern.
c. Abnormal treeing of wax patterns.
d. Abnormal or abridged wax burnout.
e. Flask (oven) temperature too high.
f. Contaminated or abnormal alloys in metal.
g. Overheated, breakable metal.
h. Excess alteration in crucible.
i. Unclean assignment habits.
