Full Version: Acrylic drinkware cracking
From: Carl (CSEWELL) [#1]
19 Apr 2007
To: ALL
I've done quite a few acrylic drinkware, and get pretty good results with monograms and simple images. I recently sold a set of (4) (Huang Acrylic - H1110 12 oz all purpose stemware) with a single letter monogram (laser 'frosted', no depth). The thickness of the acrylic is about 1/8".
The customer brought two of them in yesterday that were cracked in the area that I monogrammed. These weren't surface cracks. They went all the way through, and it didn't look like they started or ended on the monogram, but they were only in the area of the monogram. She said that she may have been a little rough with them while washing them in the sink. She told me that she hesitated to tell me about them because she didn't want me to replace them. I told her I would replace them and appreciated her feedback. Hopefully, she'll accept the replacements and if she doesn't, I'll ask her if she'll be so kind as to run additional testing for me!
I know the acrylic drinkware will craze after repeated dishwasher washings, and I tell my customers that dishwashing will eventually damage them, but this was different. The cracks started in the middle of the glass, and do not extend to the edges.
I took an old sample that I had and mercilessly beat the monogrammed area on the corner of a metal table and I could not get it to crack AT ALL! I also held it under extremely hot, running, water for several minutes without cracking. I even placed it in the freezer after that! And back under hot water after it had been in the freezer for an hour. I've had several different styles of acrylic drinkware in the dishwashers at home and at work on a continuous basis and haven't seen this type of failure.
I only use Novus #1 as a post-laser cleaner, and I'm not exposing them to any solvents. The Novus MSDS only lists isopropyl alcohol (1 to 5% by weight).
I'm stumped. What could have caused the cracking? Any ideas at all?
From: Dave Jones (DAVERJ) [#2]
19 Apr 2007
To: Carl (CSEWELL) [#1] 19 Apr 2007
From: Carl (CSEWELL) [#3]
19 Apr 2007
To: Dave Jones (DAVERJ) [#2] 19 Apr 2007
I guess I can fill one with alcohol and see what happens. I guess it is possible that when they were drinking wine out of them, the alcohol spilled on the outside......
I had one in the freezer for several hours and then hit the monogram area against the corner of a concrete block very hard (relative, I know). The drinkware fractured from the strike point out to the edges. I would consider my test extremely severe, though.
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