TABLE OF CONTENTS Blow moulding by its nature will generate a certain amount of flash. In some parts flash can be up to 100% of the total part weight. It is an economic must that this flash be recovered as regrind.
In order for this regrind to be used for finished product it must be kept clean. Foreign material can harm surface appearance and degrade the properties of the part or resin. Foreign material may also hang up in the head and cause additional foreign material build-up. All material should be covered and all material handling equipment (grinders, boxes, loader) should be clean.
The amount re-grind used in a given product is determined by several factors.
Many times testing of physical properties is required to determine a maximum or optimal amount of re-grind in the finished product. Reprocessing material tends to reduce these values.
For some materials, re-grind levels above 50% can have a negative affect on hang strength and die swell. Parison length consistency will also be a problem.
Some resins will lose important physical characteristics at high re-grind levels. Most resin suppliers recommend that a re-grind have no more that three heat histories. Parts, which need to withstand impact or repeated stress, should be produced with precisely controlled levels of re-grind.
Quantities of flash can be reduced by keeping the mould as close to the head as possible and by using the proper size head tool for the job.
Regrind...
