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FACTOR #4 DESIGN SIMPLICITY

It is well known that the simplest design is the best design. It is also the most economical. A healthy compromise between contour simplicity and uniform stress distribution usually requires less expensive pattern equipment and few or no cores. The construction and maintenance of pattern and core boxes and core-making itself all contribute to product cost. Again, talk to the foundry.

The effect of large differences in section size on casting soundness was briefly discussed earlier. Heavy bosses or walls adjoining thin sections require special treatment on the part of the foundry (risers, chills). This means additional cost and is detrimental to casting yield. The impact of casting yield on foundry production economy is the most important of all variables including the material selected and heat treatment. The freezing pattern and feeding requirements are also influenced by the geometry of the design. More on this later.

PRINCIPLE NO. 4-

DESIGN FOR CASTING SOUNDNESS

Thanks to the volumetric expansion which occurs during part of the solidification process, a sound, pressure tight casting is easier to produce from Ductile Iron than from any other metal or alloy except ordinary gray cast iron. Still, feeding requirements vary with casting shape and size; variables under the control of the designer. Unlike steel, brass and most other alloys, the designer and foundry processes for Ductile Iron should aim at simultaneous solidification of the whole casting. This requirement is opposite to the desire for directional solidification which applies to steel.

Design aimed at simultaneous solidification minimizes and sometimes eliminates the need for risers with corresponding improvement of casting yield. Conversely, parts of a Ductile Iron casting which cool much slower than the rest may become defective unless the foundryman provides extra (and expensive) feeding. Some examples of such isolated "hot spots" are as follows:

  • Cast-on heavy bosses
  • Cast-on heavy test coupons
  • Sharp internal corners
  • Joints between equally thick walls
  • Multiple joints (2 is better than 3, 3 is better than 4, etc.)
  • Joints at acute angles (90° is best)
  • Isolated heavy sections.

Which could be lightened without reducing load carrying capacity.

 

SCAFFOLD FITTING

One advantage of using castings is the clear marking of names, direction of rotation, etc. Even the date, or heat, or production hour can be easily marked on the surface.

Courtesy: Metallgesellschaft, A.G. Germany

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