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Planning the runner system layout

Posted by admin on July 31st, 2012
2649 Views
Planning the runner system layout
Basic layouts There are three basic runner system layouts typically used for a multi-cavity system. These layouts are illustrated in Figure 1 below. Standard (herringbone) runner system “H” bridge (branching) runner system Radial (star) runner system FIGURE 1. Basic runner system layouts Balanced vs. unbalanced layouts Balanced layouts The R......Read more

Determining the number of cavities

Posted by admin on July 31st, 2012
1911 Views
Determining the number of cavities
Factors involved The number of cavities depends on the available production time, product quantity required, machine shot size and plasticizing capacities, shape and size of the moldings, and mold costs. Formulas Following are simple formulas for determining the number of cavities. Use the minimum value derived from the following formulas. Product quantity ......Read more

Runner systems

Posted by admin on July 30th, 2012
2178 Views
Runner systems
Helping the melt flow A runner system directs the melt flow from the sprue to the mold cavities. Additional pressure is required to push the melt through the runner system. Shear (frictional) heat generated within the melt while the material is flowing through the runner raises the melt temperature, also facilitating the flow. Runner size considerations Alt......Read more

Design for assembly

Posted by admin on July 30th, 2012
321801 Views
Design for assembly
Molding one part vs. separate components A major advantage of molding plastics parts is that you can now mold what were previously several parts into one part. These include many of the functional components and many of the fasteners needed to assemble the molded part to other parts. However, due to the limitations of the mold and the process, functional re......Read more

Boosting structural integrity with ribs

Posted by admin on July 29th, 2012
2637 Views
Boosting structural integrity with ribs
Structural integrity: the goal of every design The major component of designing for structural integrity, in many cases, is to design the structure to be stiff enough to withstand expected loads. Increasing the thickness to achieve this is self-defeating, since it will: Increase part weight and cost proportional to the increase in thickness. ncrease molding......Read more

Cycle time increases with thickness

Posted by admin on July 29th, 2012
2897 Views
Cycle time increases with thickness
Injection-molded plastic parts have to be cooled sufficiently before being ejected from the mold to avoid deformation due to ejection. Parts with thick wall sections take longer to cool and require additional packing. Theoretically, Cooling time is proportional to the square of the heaviest part wall thickness or the power of 1.6 for circular features. Ther......Read more

Designing for extreme temperatures

Posted by admin on July 25th, 2012
2302 Views
Designing for extreme temperatures
You’ll need to design parts to accommodate the changes in temperature they’ll be exposed to. The following suggestions should help. Use the proportional limit Use the proportional limit for the expected exposure temperature in design calculations to avoid permanent distortion of the part. Allow differential expansion and contraction Do not rigid......Read more

Loading at extreme temperatures

Posted by admin on July 25th, 2012
1652 Views
Loading at extreme temperatures
Storage, shipping, and usage temperatures can easily exceed or go below the normal room temperature range of 20º to 30ºC. Following are examples of conditions under which a part will need to withstand temperatures above or below the ambient room temperature. Above room temperature Plastics parts stored or operated in these conditions will need to accommodat......Read more

High velocity and impact loading

Posted by admin on July 25th, 2012
1782 Views
High velocity and impact loading
High velocity loading refers to velocities greater than one meter per second, while impact loading refers to velocities greater than 50 meters per second. Avoid high velocity and impact loading on areas that are highly stressed from residual and/or assembly stresses. When designing a part that must withstand these types of loading conditions, keep the follo......Read more

Repeated loading

Posted by admin on July 25th, 2012
2510 Views
Repeated loading
When parts are subject to conditions of repeated loading, you need to consider the number of loads that part will be expected to withstand over its life span. The table below gives examples of types of repeated loads. The corresponding numbers are the expected number of times the loading may occur. Read through the following suggestions if the part youR......Read more