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