Some molders needlessly spend hours purging. For some, it takes multiple shifts.
Shaving seconds off of cycle times can generate a significant boost in profits, so why have your machines down for hours when you don’t have to?
Purging compounds—especially the right type for your application—shrink purge times to minutes from hours, recapturing hundreds of hours of productivity, and saving tens of thousands of dollars every year.
When to Use High-Grade Purging Compound
If purging takes you longer than 30 minutes, it’s time to upgrade from your current brand.
Slide purging compounds are not for every situation, but can reduce purging time from several hours – or multiple shifts – to just minutes, especially under challenging circumstances like these:
- You are using nasty, gas emitting resins or temperature sensitive resins – perhaps flame retardants like Delrin or Acetal
- You have to send a purge squeezing through hot runner manifolds with gates that are less than 0.30 microns in diameter
- You are switching from dark (black, blue, red) to light resins (clear, white), particularly after a long period of use
- You are using a large machine especially if it’s an older model
Case Study: Molder Saves $79,000/year by Switching to Slide
For years, a molder of closures took two hours to run 100 pounds of an inexpensive purging material each time they cleaned the hot runner and barrel between color changes. After the barrel was clean and the new resin color was in place, the molder still had to mold at least 50 "test" parts before quality control approved the next production run.
A Slide Products Factory Sales Rep calculated the following as the difference between the old purging compound and KLENZ from Slide:
- Old: 2 hours of labor + resin for 50 test parts + 100 pounds of purging compound = $428.50 per purge
- KLENZ: 0.3 hours of labor + resin for 7 test parts + 35 pounds of purging compound = $271.54 per purge
Tip: remember to purge the barrel first, then purge through the mold to ensure that any garbage pulled out of the barrel will not contaminate the mold and hot runner areas.
The Purging Case Study that Didn’t Happen: Cost per Purge vs. per Pound
Some molders see the clear productivity benefits of using more effective purging compounds and even a cheaper cost-per-purge. However, they can’t make the switch because of a purchasing department veto when the better compound costs slightly more per pound.
The production manager at a medium-sized injection molding plant tested different products to eliminate streaking and shorten purge times. He used 33 pounds of purging compound, which took 3 hours and required over a dozen shots to be reviewed by quality assurance before he could get his machine back into production.
After working with a factory expert to test a purging compound from Slide Products, the production manager:
- Eliminated streaking
- Reduced the amount of purging compound to 9 pounds from 33
- Reduced purging time to 20 minutes from 3 hours
- Now requires only 6 shots to restart full production – instead of 12
He went to purchasing and requested to switch to the Slide purging compound but was denied. The problem: the old purging compound was $1.49/pound cheaper even though it cost $47.07 more per purge when wasted resin and time were calculated into the full cost to purge!
- Old purging compound: $2.52/pound x 33 pounds/purge = $83.16/purge
- Slide purging compound: $4.01/pound x 9 pounds/purge = $36.09/purge
- A switch to Slide purging compound would have saved $36,000 per year
Tip: make sure to include the purchasing agent early in the process if you’re planning to switch purging compounds.
Case Study: Molder Saves $25,000/year by Switching to Slide
A molder of small snaps and connectors made with polypropylene in a rainbow of colors needed hours of purging time to clear out the color to prevent streaking and specks when switching to white or clear resin. The process generated a significant amount of wasted resin.
A factory expert from Slide Products came to the plant and spent 3.5 hours testing alternatives to their purging process. Using NPT Purging Compound on a 300-ton machine using polypropylene resin, the changeover to a new color only took 10 minutes instead of 60 minutes, with no resin waste or scrap. And only a fraction of the amount of NPT was required compared to the compound they were previously using.
In total, the molder now saves $190 per purge, which saves them approximately $25,000 every year.
3 Types of Purging Compounds: Mechanical, Chemical & Liquid
- Mechanical: relies on shear force and the differences in viscosity to clean with no chemical reaction and no soak time
- Chemical: mechanical purges may not be effective in parts of the barrel, screw and manifolds where there is low pressure; a chemical purge is a better choice because a chemical reaction takes place when the purge contacts the resin or carbon
- Liquid: usually a surfactant, liquid purging compounds reduce the tension of the liquid in which they are dissolved, kind of like a hybrid between a mechanical and chemical purge
Selecting the Right Purging Compound
Picking the right purging compound for your various applications requires a little research and testing. It’s best to start by contacting an expert, such as a factory expert from Slide Products. With multiple purge types, and years of experience tackling tough purging applications, our experts can help you zero in on the right options after just a few minutes discussing your problem.
Slide Products offers trial quantities for testing a purge and often will send a technician to help processors fine tune the purging process and trim even more time off the purge cycle.