Friday 11 August 2023

Achieving the Optimal Residence Time in Injection Moulding incl. New Online Calculator

Achieving the Optimal Residence Time in Injection Moulding incl. New Online Calulator

Hello and welcome to this blog post on how to achieve the optimal residence time in injection moulding. 

Let us start with a brief recap on melt residence time.

How to calculate the residence time? 

The total time the resin is in molten state, from the time it is completely melted, leaving the barrel, entering the mould runner system into the cavity is defined as melt residence time. Figure 1 shows how it can be calculated and this formula is used later in my calculator tools too. A detailed post with all calculations can be found here .

Try out my tool right here below or in this section of my blog

What are recommended residence times (at melt temperature) of engineering and high performance polymers?

In the following, the recommend residence times of selected polymers are shown which can serve you as a guideline: 

  • Polyamide 6 (PA 6): 10 minutes
  • Polyamide 6 with glass fibers (PA 6-GF): 10 minutes
  • Polyamide 6.6 (PA 6.6): 15 minutes
  • Polyamide 6.6 impact modified (PA 6.6): 10 minutes
  • Polyamide 6.6 with 30 wt% glass fibers (PA 6.6-GF30): 15 minutes
  • Polyamide 6.6 with 25 wt% glass fibers  and flame retardant (PA 6.6-GF25 FR): 10  minutes
  • Polyphthalamide (PPA): 4 minutes
  • Polyketone (PK): 10 minutes
  • Polyethylene terephthalate with 30 wt% glass fibers (PET-GF30): 8 minutes
  • Polybutylene terephthalate (PBT): 8 minutes
  • Polybutylene terephthalate with 30 wt% glass fibers (PBT-GF30): 8 minutes
  • Polycarbonate (PC): 6 minutes
  • Polycarbonate (PC) / Polybutylene terephthalate (PBT) blend: 6 minutes
  • Polysulfones (PSU): 5 minutes
  • Polyethersulfone (PESU): 5 minutes
  • Polyphenylsulfone (PPSU): 5 minutes
  • Polyphenylene sulfide (PPS): 5 minutes 
  • Polyetheretherketone (PEEK): 5 minutes
  • Liquid crystal polymer (LCP): 1.5 minutes (max. 4 minutes)

How to achieve the optimal residence time in injection moulding?

An extensive melt residence time will result in degradation of the molecular weight of the and as a consequence your plastic part will not have the desired chemical resistance and thermal stability. It is crucial to keep the molecular weight as close to the virgin material as possible. Degradation is not always visible at first sight, however it can backfire once the part is in use. 

Optimal residence time is achieved by having a good mould design, together with optimal part design (minimum wall thickness), and an efficient running moulding process. 

Let us dig deeper into the running of the moulding process. Apart from the temperature, and cycle time, the biggest impact on the residence time is the size of your plasticizing unit and its optimal selection. If you have a high metering stroke, residence time is low. If you have only a small metering stroke, residence time will be up and you have to check if you are not above the maximum residence time of the polymer. It can encounter this by using an increasing temperature profile on your plasticizing unit.

How about extrusion residence times?

Yes, also there I have you covered. The extrusion residence time can be approximately be calculated by building the quotient of the volume of the extruder filled with melt and the volume flow of the melt. This is the background of the online calculation tool shown below. 

Thanks for reading and #findoutaboutplastics



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