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The actual losses in efficiency are due to the difference in heat transfer from scale and the mold base material. Therefore, the more conductive the tool steel, the more the scaling will diminish cooling. So, for example, a 420-SS mold base will not be as greatly affected by scale as a BrCu core would be affected. In general, the excessive scaling will drop the efficiency 10-25% for steel.

Some people look at a 15% drop in cooling efficiency as a minor change. In most processes, this can result in a 10% increase in overall cycle time, resulting in a 5-10% drop in overall productivity, efficiency, and plant capacity. In today’s market where every penny counts, this is an avoidable drop in productivity which most companies cannot afford to bear.

-Andy

It is preferable to use a 1st stage fill which provides a ~90% filled part. This provides a good representation of how the part will perform during production.

If you have a product which require a profiled 1st stage injection, it may be a useful exercise to perform such a test at each stage in the profile. This will help you ensure the final fill balance is optimal.

For more blog entries on cavity imbalance, please feel free to review the following:

Correcting for Cavity Imbalance…

Adjusting Hot Runner Systems…

-Andy

Actually, the focus should not be on the machine inputs, but the actual process outputs. this is a little more complicated, but below are some examples:

Generally speaking, the feed zone of the screw should be at least 1.5 times the total injection stroke. This allows the material in front of the feedthroat to properly convey to the transition zone with a low likelihood of blow-back.

When processing materials which tend to melt better with conductive heating such as ABS, PP, and Nylon, the feed zones are often longer to allow more material heating to take place before reaching the transition (compression) zone. An ABS screw, for instance, typically has a feed zone approximately half the overall length of the screw.

-Andy

Basically, hydrolysis is the process of breaking the water molecule into a positive hydrogen (H+) atom and a negative hydroxide (OH-) molecule. These powerful ions can react with the atoms of many different polymer chains. When these ions attack the polymer chains, they often cause the chains to breakdown, resulting in degradation of the polymer. In other cases, these ions attach to the polymer chains and interfere with the inter-molecular forces between the chains. In either case, the hydrolysis causes a reduction of the polymer strength and often affects the appearance of the molded part.

-Andy