Purging Tip of the Week: #20
If heats are raised while purging and the flow of material is slowed or stopped, be sure that high throat temperatures don’t lead to premature melting of the purging material. This can cause causing...
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Polymers Go Nuts!
The latest item from the bio-polymers front is the announcement by NEC (described in this Design News article) of a material prepared from cellulose and cardanol. Cardanol is a phenol derived from...
View ArticlePurging Tip of the Week: #21
Clear polycarbonate and clear acrylic are prone to post-purge hazing or cloudiness if the purging compound in use is polyolefin-based. To avoid this issue, make sure that the purging products you use...
View ArticlePurging: Observations of an Expert
The September issue of Plastics Technology magazine landed in my "In" basket today with a feature article by noted extrusion expert Chris Rauwendaal, titled "Optimize Product Changeover & Purging."...
View ArticlePurging Tip of the Week: #22
System temperatures are important in purging. Changes in temperature cause movement of metal parts (due to the metal’s coefficient of thermal expansion) and this can dislodge contaminants. Increased...
View ArticlePurging Tip of the Week: #23
If the purging process calls for changes in system temperatures, great care is needed if the production material is heat-sensitive. You could degrade residual production resin and badly contaminate the...
View ArticlePolymer Cleaning (of a Different Sort)
A firm in England, Xeros, Ltd., has developed a "nearly" waterless washing machine where the process involves tumbling soiled clothes with Nylon pellets (and just a bit of water). (They look like...
View ArticlePurging Tip of the Week: #24
Certain high-temperature materials (notably polyether-imides’s such as Ultem®) will adhere very tenaciously to internal machine surfaces if allowed to cool below the melt range of the material. To...
View ArticlePurging Tip of the Week: #25
Plunger-type molding machines are old designs and have become quite rare but a few are still in service. Purging procedures for these machines are similar to those for reciprocating screw machines...
View ArticlePlastic Plantations?
There would seem to be no reason for the polymer industry to discriminate among feedstocks. Hydrocarbons are hydrocarbons, and any viable source of same will serve our purposes. It is as yet "early...
View ArticlePurging Tip of the Week: #26
On small extruders or molding machines it is usually easiest to load purging material directly into the throat after unbolting and setting aside the hopper. For larger systems it will often be...
View ArticlePurging Tip of the Week: #27
Purging compounds are available in several basic classes – chemical, mechanical (sometimes referred to as physical) and hybrid. Chemical purging compounds actually affect the polymer molecules of the...
View ArticleThings May Not Be As They Seem
Since we are hearing of late so much about bioplastics in their various forms, it's interesting to contemplate a recent study by Dr. Amy Landis and her colleagues at the University of Pittsburgh. Dr....
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Purging Barrier Screws
An email from "Mike" asks, "Color changes on a machine using a barrier screw are always very difficult. Why is this?"Here's our theory of what's happening, Mike. In a barrier screw design (like the one...
View ArticlePurging Tip of the Week: #28
Here are some hints for purging high temperature resins (those processed at more than 600ºF (315ºC) – including polysulfone, PEEK, poly-ether-imide, many fluoropolymers and others).Never let them drop...
View ArticlePurging Tip of the Week: #29
Occasionally, it can be difficult to find a way simply to introduce a purging compound into the production system. Especially in large equipment, the feed system may be fully closed from the supply...
View ArticleThe Sage of Omaha says: "Plastics!"
In case you're bearish about the prospects for the plastics processing industry, be advised that Warren Buffett would appear to disagree. It seems that Berkshire-Hathaway (via its CTB, Inc. subsidiary)...
View ArticlePurging Tip of the Week: #30
Many mechanical purging compounds increase effectiveness by incorporating fillers or abrasive resins. These ingredients cover a range from quite gentle “polishing” agents to quite aggressive scouring...
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Is the Giant Pacific Plastic Garbage Patch Imaginary?
Were we to give credence to the media reports describing the purported pollution of the North Pacific Gyre by plastic debris, we'd probably think you could walk from Oregon to Japan on the trash. But...
View ArticlePurging Tip of the Week: #31
When purging extruders that normally run with screen packs in place, be sure to discuss with your purging compound supplier whether the purging material will be able to pass through the screen mesh...
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