Full Version: Acrylic drinkware cracking
From: Dave Jones (DAVERJ) [#4]
19 Apr 2007
To: Carl (CSEWELL) [#3] 19 Apr 2007
I was just thinking that the area around the engraving would have been affected by the heat of the laser, and it was the heat stress that caused the solvents to cause crazing and cracking. I think the solvents didn't cause the crazing/cracking on acrylic that wasn't heat stressed.
But I am just guessing here.
From: RALLYGUY (RALLYGUY1) [#5]
19 Apr 2007
To: Dave Jones (DAVERJ) [#4] 19 Apr 2007
I think you might have nailed it on this one Dave.
The problem described is typicaly a problem that you find with acrylic with flame polished edges. Anytime you get a solvent near the heat exposed area, you run the risk of crazing. We experienced this with screen printing in the past, and had to adjust how close to the flame polishing we could print to eliminate the problem. Any solvent (yes even alcohol can cause this problem. Just because the manufacture recommends the solvent for cleaning, doesn't mean that they understand what you're doing to the product with your process......
I'm betting it's the alcohol.......or some other solvent exposure that's causing the problem.
From: Carl (CSEWELL) [#6]
20 Apr 2007
To: Dave Jones (DAVERJ) [#4] 20 Apr 2007
I put isopropyl alcohol (91%) in a marked acrylic stemware and left it overnight. This morning, it was severely cracked all the way around the stemware and the alcohol had drained. There were higher concentrations of cracks away from the marked area. There are definite, repeating patterns in the curved portion (near the stem) suggesting material flow during molding may have changed the material properties in this area. Surprisingly, none of the cracks propagated to the rim of the drinkware AND only the extreme lower portion of the marked area cracked while cracks in other places propagated above the height of the engraving. If the engraving had introduced heat affected zones, crazing, and/or stress concentrations, wouldn't you expect the opposite to be true?
I did the same with an UNMARKED stemware this morning and it cracked in the same manner after a few hours. At the same time, I used another marked stemware (same type, may not be from the same lot) containing isopropyl alcohol and it has NOT cracked over the same time frame. Before I finished writing this, this other marked stemware cracked but NO WHERE near the marked area.
I also used a different acrylic drinkware (14 oz square) that was deeply engraved and had also been used to soak parts in mineral spirits (for days) and it cracked through the base (and the gate) after two hours. The crack started (or ended?) on part of the engraving. An unmarked, new, drinkware of the same type has not cracked over the same time period.
A third type (28 oz round), deeply engraved around the entire periphery of the drinkware, has not cracked over the same time frame. The material flow in this product has less drastic changes in material density as compared to the stemware and square drinkware.
Time to add another caveat to acrylic drinkware: don't dishwash and don't drink while drinking!!! Or, if you are going to drink, drink fast and immediately hand wash the drinkware.
From: Stunt Engraver (DGL) [#7]
20 Apr 2007
To: Carl (CSEWELL) [#6] 20 Apr 2007
I don't know why I've read this entire thread without remembering a set of acrylic tumblers I bought, that looked very much like colored glass.
There was a warning label that specifically said not to use alcoholic beverages in the drinkware.
Your last post jogged my memory. :-$
From: Carl (CSEWELL) [#8]
20 Apr 2007
To: Stunt Engraver (DGL) [#7] 20 Apr 2007
From: http://www.devicelink.com/mpb/archive/96/01/001.html
Acrylic is resistant to a wide range of chemicals including salts, bases, aliphatic hydrocarbons, fats and oils, most common gases and inorganic chemicals, dilute mineral and organic acids, and dilute and concentrated solutions of most alkalis. It is attacked by strong acids, chlorinated and aromatic hydrocarbons, ketones, alcohols, ethers, and esters. Of course, the chemicals and other materials to which a molded part will be exposed should be carefully considered before selecting any thermoplastic.
Isopropyl alcohol tends to promote crazing in acrylic, as it does in many transparent plastics. Some acrylic grades are more alcohol-resistant than others: resistance is typically a function of the molecular weight of the polymer, with higher molecular weight providing better alcohol resistance. Diluted solutions of isopropyl alcohol can be used to wipe down acrylic without adverse reaction. Acrylic copolymers, particularly those with styrene, offer improved chemical resistance but do not transmit light as well as 100% PMMA.
Consistency is the key; any changes in thickness should be gradual, and feature radiused edges. Vertical walls should be the same thickness as the rest of the part to avoid pressure variations on the flow front, which can lead to stressed areas and voids caused by trapped air. Moderate residual stress does not affect part performance, but high levels of stress can reduce impact strength and resistance to chemical or heat crazing, and can undermine the dimensional stability of the molded part.
EDITED: 20 Apr 2007 by CSEWELL
From: Dave Jones (DAVERJ) [#9]
20 Apr 2007
To: Carl (CSEWELL) [#6] 20 Apr 2007
From: PenTrophy (PENINSULATROPHY) [#10]
20 Apr 2007
To: Carl (CSEWELL) [#1] 20 Apr 2007
From: Carl (CSEWELL) [#11]
20 Apr 2007
To: PenTrophy (PENINSULATROPHY) [#10] 20 Apr 2007
From: PenTrophy (PENINSULATROPHY) [#12]
20 Apr 2007
To: Carl (CSEWELL) [#11] 20 Apr 2007