Plastic Injection: Start Up Checklist

Start-up is one of the most important factors affecting your plant's production efficiencies. Low scrap, cycle times and standardization are key components of any plastic injection facility. The following article outlines many of the key components in a successful plastic injection start-up. Thorough, standardized set up and repetitive start up procedures utilize historical response/ avoidance

Other factors will certainly come into play, but this article will outline many of the key fundamentals that define what variables are most important when sizing up your approach as a processor. Processors face the task of analyzing machine/ mold/ material set up and processing variables. It is up to the molder to establish how to best set up his press, identify and avoid potential causes of scrap, anticipate and plan quick changeovers and develop quick responses to defects and system failures.

A successful molder establishes consistent processes that quickly stabilize. A stable process is best defined as being optimized (fast and consistent cycle), low to zero scrap ratio, repetitive in successful set-up, start-up and is easily maintained despite changes in mold/ material/ machine/ manning.

The following points are broad and are certainly not bullet-proof. Nonetheless, they are a basic checklist of key variables that can assure solid start ups, low scrap rates, reduced down times and solid efficiencies:

• Cleaning Your Mold

  Processing issues can often stem from tooling that is dirty. Vents should be clean, moving parts should be lubricated and cavitation should be inspected for wear, buildup and damage. Using a blue penlight can help to spotlight gas buildup unseen to the naked eye.

• Correct watering/ Water is On

  In the era of quick changeovers, it is easy for a set up crew to water a tool improperly. It is important to make sure that water circuits have been correctly identified and that the water has been turned on. Hoses should be routed avoiding potential pinches and rubbling. Thermolator actual temps should match setpoints, and pressure to and from your mold should show only a mild drop in water pressure. Molds running at high temperatures should be heat soaked with mold halves touching to allow even heat transfer.

• Clamp Adjustment

  It is important that the clamp has been set up for optimum efficiency. The clamp should be dry-cycled.. inspecting for fast closing and opening without "lunging". Mold close/ open slow setpoints should allow safe exit and entry onto guidepins. Clamp lockover position ( " mold safe" ) should be verified to assure tooling is protected against abnormal lock up conditions. Low pressure close should be set as low as possible for added protection against tool damage.

• Material Set up

  Material is key to any successful start up. Equipment conveying materials should be cleaned properly according to changes in resin base and color. The first 20 pounds should be drained from the hopper to assure Material loaded for start up is dry. Moisture content should be checked to prevent using material that is still wet . The press should be purged thoroughly to allow the screw to heat soak using back pressure. This should occur just prior to press start up.If using a hot runner mold, it may be beneficial to purge through the tool to heat up the hot runner and skin a new color.

• Nozzle Tip

  The nozzle tip should be correct for the material being used, and the tip orifice should be 1/16" smaller than the bushing orifice

• Initial Start Up

  Hold and pack pressure should be set at zero to prevent overpacking. Parts produced in this state should be 95-98% filled out.. with small shorts at end of fill or a "sink" appearance. A light coating of mold release may need to be applied to prevent parts sticking. The press should be started in semi to establish part ejection is properly established. After a couple of shots, hold and pack are stepped up until parts are full and free of sinks.

• Process Monitoring

  At this point, it is important to compare current running variables to previous runs. By replicating past run conditions, you assure that the process being established mimics historical production runs.