Patterns Full size model of shrink rule measurements

Patterns • Full size model of shrink rule measurements used to produce a mold cavity

# of castings to be made from pattern determines pattern type of material • wood ‑ soft or hard - mostly pines and mahogany • metal ‑ superior to all ‑ used for shell molding (heat) - all types • plaster • plastic ‑ injected into a mold • styrofoam / wax • composites ‑ laminates (wear resistance and strength)

pattern layout ‑ made full size ‑shrinkage and taper allowance is added • contraction is volumetric ‑ correction allowance is expressed linearly • 1/8 to 1/4" per foot ‑ • Linear shrinkage allowances in Table 2‑ 1 (p. 18)

Shinkage depends on: • 1. casting design 2. type of metal 3. pouring temp 4. resistance of the mold to normal contraction of the casting

Taper • Taper of 1/16" per foot for vertical walls on patterns drawn by hand • machine drawn patterns require about 1 degree taper • for pockets or cavities in the pattern, more taper needed

Machining allowance • when locations on the castings surface will be machined, excess material must be left for machining. This allowance is called "finish” • when possible, surfaces to be machined should be in the drag (bottom) side of the mold. – a. provides a cleaner casting surface on the bottom because impurities float to top b. Most shrinkage is on top

Table 2‑ 2 (p. 19) for machine finish allowances

Pattern Configurations:

1. single or loose pattern: • for single copy of pattern • for hand molding • gates and risers cut by hand or loose pieces used • pattern is drawn from sand by hand

2. Matchplate pattern: • used for large quantities of small castings • cope and drag mounted to opposite sides of wood or metal plate • runners and gates mounted to plate • used to increase productivity

Matchplate (Cont. ) • usually use a molding machine • Flask slips off after mold making and slip jacket used to prevent movement of the mold during pouring

3. Cope and drag patterns: • • Larger castings cope half mounted on cope plate drag half mounted on drag plate 2 molders working on opposite sides of line • one makes drags • one makes copes

4. Special devices: • loose patterns with irregular parting lines • follow board or pattern bed (match) is used

5. Two Dimensional Sweep Pattern - For Loam molding • rotate 2 -D shape about an axis ‑ creates a complex 3 -D shape

Color markings for wood patterns: by AFS • 1. Black ‑ body of casting unfinished 2. Red ‑ surfaces to be machined 3. Yellow ‑ core prints and seats for loose core pints 4. Red stripes on yellow background ‑ seats of and for loose pieces on the pattern 5. Black stripes on a yellow background ‑ stop offs ‑

Stop off • portion of a pattern which produces a mold cavity that is later filled with sand so it doesn’t become filled with metal during pouring and appear on the casting. • A stop off may be a reinforcing member on a frail pattern the mold impression of the reinforcing member being filled in by a core

Should use fillets to avoid shrinkage cracks and stresses at intersections in patterns