From global corporations to small manufacturers across all of North America, we’ve spoken to and sold Haitian machines into many different types of shops. This has allowed us to see a broad evolution of how North America manufacturers its products, as well as general patterns in how our industry often makes new purchasing decisions. When we look back, a lot has changed for the positive! Still, machines have a long life and we see lots of instances where purchasing practices of the past continue to have their effect on molding operations today. From our perspective, here is one of the longest lingering purchasing practices in our industry:
“Just select the biggest injection unit … because we never know what parts and molds we may need to run in the future.”
Focusing on the injection unit size skews the priority of the shot weight in the direction of specifying a larger screw, barrel, and shot capacity than would be typical today. In the past a higher percent of molding was performed with commodity resins, on relatively thick walled parts, at relatively low injection and hold pressures.
Today’s range of high performance material (engineered polymers) are often more sensitive to residence time. Too much time in the heated barrel can actually result in degradation of the enhanced properties the material is being used for in the first place. Also, reducing material usage by designing products with thinner wall often results in the need for additional pressure to maintain fill rates through the thinner flow channels.
Finally, older machines are more likely to be hydraulic (especially in the larger tonnage range). For a hydraulic machine, a small shot size relative to the machine capacity tends to translate into less precise control and more shot to shot variability.
These things together tend to shift the appropriate selection toward a shot size that balances shot weight, injection pressure, and injection speed, versus just focusing on getting the biggest shot size. In addition, L/D ratios, screw geometry (optimized for dedicated applications), and abrasion and corrosion resistance (particularly for glass filled materials and materials that generate corrosive chemistry - such as PVC and Actel) are all things that should be considered.
If you add the business parameters that should be considered (price, delivery, and aftermarket support) you may find yourself yearning for the simplicity of the old days (just buy the big one). But spending time upfront will reap years of benefit.
Need help choosing the right machinery? Get in touch with our team at firstname.lastname@example.org or 508-459-5372.