7

My fridge shelves cracked and broke, and although I tried a repair mentioned in a previous question, it eventually failed as expected.

broken shelf

Since it seems that replacement shelves are no longer sold for this fridge model (Daewoo ERF-384/385/387/388 M/A), I looked for metal bar stock as suggested in the linked QA, but it seems that aluminium bar stock of the suggested width and thickness would be more expensive than purchasing a sheet of plastic. There are vendors who (e.g.) sell 'universal' replacement shelves, and those who sell plastic cut to size as replacement for shelves. Both of these are examples, but both list the thickness of the acrylic/Perspex/Plexiglass sold as 5mm.

I contacted a local plastic supplier who can supply cut cast acrylic sheets (among others) for advice, but they were unable or unwilling to make a recommendation as to material. Is there a difference between cast acrylic, Perspex, and Plexiglass? If not, is 5mm a suitable thickness for reasonable, everyday domestic fridge shelf use? My local supplier can make sheets up to 10mm if thicker is better.

The measurements of the replacement shelf are shown below:

fridge CAD

(dimensions in mm)

The shelf seems to be very slightly tapered and so is trapezoidal, being 10mm shorter along the rear edge where the arc is. I am hoping the local plastics supplier can cut accordingly but if not I assume (hope) the plastic can be filed/abraded to fit.

My intention is to duplicate the top-down ("2d") shape of the shelf, rather than trying to mimic the "3d" shape of it with grooves and retaining stops etc- ie end up with something flat.

I would prefer to keep the fridge, rather than replace it for want of a couple of shelves!

bertieb
  • 267
  • 2
  • 11
  • 1
    Can your plastic supplier identify what your shelf is made of if you bring it to them? If so, get a replacement of the same material. Note that your existing shelf has some bends and ridges so it can be made of thinner material but still be strong enough to meet the weight support called for in the fridge design. If you can't get your shelf made with those bends/ridges, you'll want to use thicker plastic to get the same strength. – FreeMan Jun 22 '22 at 16:53
  • @FreeMan No idea if they could/would identify the material- when I enquired what they would recommend I got a polite-but-blunt "we are plastics sheet manufacturers and distributors. We suggest that you get in touch with a contractor", which is fair enough. Good point re the overall shape- I wasn't going to duplicate it exactly, with all the ridges/grooves and retaining points; just the top-down 2d shape of it! – bertieb Jun 22 '22 at 17:09
  • I meant to include something about the shape of the replacement in OP, which I've updated now- thanks for the reminder! :) – bertieb Jun 22 '22 at 17:13
  • Fwiw, I just added a couple of 1/4” (6mm) shelves in bog standard plexi (would have chosen lexan if it was easy to get), and it works fine. My span was only about 14”, so in your case, a slightly thicker than 5mm shelf might seem prudent. – Aloysius Defenestrate Jun 22 '22 at 18:43
  • I had some 8mm polycarbonate sheets cut to size to replace some shelves in our fridge about ... 8 years ago. Still going strong. – Moo Jun 23 '22 at 04:01

5 Answers5

11

It's Polystyrene, according to the label (like all fridge shelves).

enter image description here

Is there a difference between cast acrylic, Perspex, and Plexiglass?

Poly(methyl methacrylate) (PMMA) belongs to a group of materials called engineering plastics. It is a transparent thermoplastic. PMMA is also known as acrylic, acrylic glass, as well as by the trade names and brands Crylux, Plexiglas, Acrylite, Astariglas, Lucite, Perclax, and Perspex,

ie, they're all the same. It's tougher than polystyrene but more expensive.

It should work alright. They make airplane windows out of this stuff, so it should withstand the environment inside a fridge. I'd pick something like 8mm so it doesn't flex when putting bottles on it.

You'll probably need to mill notches or retaining points in the sides like the original so it locks in the fridge and doesn't pull out.

Polycarbonate (Lexan) is tougher, but don't put it near your food, as it contains Bisphenol residues.

bobflux
  • 8,484
  • 22
  • 28
  • 1
    Ooh, nice spot on the manufacturing mark! I think going thicker is a good idea. I think the plastics supplier are happy to drill holes on request, but I wondered how close to the edge they could get without causing problems? Ideally, they would be about 10-20mm in from the edge, as if I had access to a 3d printer I'd print myself a retaining piece. But you say it's a thermoplastic, which means it can be melted and shaped... I wonder about putting small 'wings' on he outside edges and heating+curving them vertically as retainers... tho that's probably another question :) – bertieb Jun 22 '22 at 19:30
  • 1
    I don't think you need to drill holes, just cut notches in the sides so it grabs the retainers in the fridge... should not be difficult to do with a dremel or similar tool – bobflux Jun 22 '22 at 19:38
  • Aye, there's probably a way of doing it like that :) Hard to explain without seeing the retaining parts in the fridge -- which I did take a photo of -- but that's really getting into separate question territory. Cheers for your answer! – bertieb Jun 22 '22 at 19:59
  • 8
    Bpa or bps in polycarbonates is typically more problematic when the plastics are heated. Personally I wouldn't put something on my fridge shelf that isn't in a package and eat it without washing - maybe a piece of citrus fruit but then you don't eat the peel so I don't think I'd worry about a shelf that contains BPA. – Fresh Codemonger Jun 22 '22 at 20:42
  • As an alternative top making the whole thing thicker, make the main shelf thin enough to fit in place, and attaching both retaining pieces and stiffening ribs. You can solvent-weld with a suitable solvent for the plastic you're buying (probably acrylic), or screw with countersunk machine screws and nuts on the bottom (you can even recess the nuts into a counterbore, though that's harder to drill nicely. You can also bend up the back edge, using heat to soften the material, and clamping the sheet between wooden battens ("line bending") – Chris H Jun 23 '22 at 08:10
  • 3
    I'd choose acrylic over polycarbonate for this, having cut and line-bent both. Polycarbonate may be tougher, but acrylic is stiffer, which is what you want here - bending will be more of an issue than impact. Acrylic is also easier to line-bend if you do want to bend it to form a back edge rib (a wider temperature band between softening and scorching.) – Chris H Jun 23 '22 at 08:13
  • @FreshCodemonger I'm inclined to agree, but note that citrus zest is used, and it's not unreasonable to wash a whole pack of lemons (or peppers, or many other veg) then put some back in the fridge, open so that they're not sitting in water. – Chris H Jun 23 '22 at 08:15
  • @ChrisH what material would you recommend for the reinforcing material? Cost is my primary concern here; or secondary if you count "would it work at all" as primary ;-P – bertieb Jun 24 '22 at 11:32
  • With limited tools I'd either use more acrylic underneath (solvent-bonded or bolted) , or some L-section /angle section aluminium extrusion along the back edge (probably bolted) and maybe front edge if it wouldn't stick out too much downwards. You should be able to pick up offcuts or short pieces pretty cheap. With my tools I'd line bend a lip at the back edge, but I'm well equipped. I'd still look for front reinforcement – Chris H Jun 24 '22 at 12:02
9

Been there, done that.

About 10 years ago I had 2 broken shelves when my wife placed a too heavy casserole dish (cast iron skillet) on the top shelf and it crashed through that shelf and the one below.

I had a couple of 5 mm thick acrylic sheets (couldn't easily source anything thicker) cut to the outer dimensions of the original shelves.
Then I used a Dremel with a burr bit to shape the cutout going into the back of the fridge and to taper the sides. (My shape was almost identical to yours. I also had to create rounded corners at the back.)

I used a burr bit because I was a bit worried that cutting into the acrylic would splinter the material. (Or scorch through overheating. It is easier to control the heat with a burr bit.)

Last, but not least. I got a piece of aluminum U-profile, 5 mm wide and 12 mm high that I slid (and glued) over the front edge of each shelf to give it more resistance against bending under weight.
The sides and back are well-supported by the ridges on which the shelves rest, but the front obviously not.
The aluminum strip gives that extra support and it looks a lot nicer than the bare edge of the acrylic.

Both shelves are still in fine shape. (I gave the fridge to my cousin a few years ago and he is still using it with my DIY replacement shelves.)

Tonny
  • 735
  • 4
  • 10
  • 2
    In my experience, cutting acrylic can be done using all the same tools as wood. There are different feeds and speeds, and some different techniques to prevent acrylic from cracking, but the the tools themselves are the same. I would have thought that .2" acrylic would be a bit thin for a fridge shelf, but if it works, it works. I can still see it warping with heavy loads, though. Acrylic also won't be affected by hot pans, like glass, and it's less likely to shatter than glass because it's flexible. – computercarguy Jun 23 '22 at 15:21
  • 1
    Really useful to have an answer based on practical experience and encouraging to hear they're still going strong- makes me think a replacement along the lines of what you did would outlast the fridge itself (as it's getting on in years) – bertieb Jun 24 '22 at 11:30
  • @computercarguy it depends how hot - but you shouldn't be putting really hot stuff in the fridge anyway. Acrylic will soften quite readily at temperatures you could expect in a kitchen. I've used my oven set really low to prewarm before line bending with a heat gun - a hot oven allows direct forming (I keep meaning to build a vacuum former) – Chris H Jun 24 '22 at 12:06
  • @ChrisH, yes, it'll deform, but it won't shatter like glass. I use acrylic in laser cutters and I've been wanting to build a vacuum former as well as a bender for years, too. – computercarguy Jun 24 '22 at 14:52
  • @computercarguy I had visions of a shelf with a large hot pan (probably inspired by Tonny's answer) softening and deforming enough to sag out of its mounts and drop. Getting glass cut for replacement would be problematic, but the vast majority of fridges I've owned and used have had glass shelves - temepered of course – Chris H Jun 24 '22 at 14:58
  • @ChrisH, imo, cleaning up a mess after an acrylic shelf deformed, but is still in one piece, is better than cleaning up a mess after tempered glass turned into pea gravel. I've looked at getting a piece of tempered glass about the size of a fridge shelf, years ago for a chessboard, and it was $50+. Going to a shop that builds things with acrylic, you can get a scrap piece that big for < $15. I get what you're saying, but I think the risks of acrylic outweigh the risks of glass. Most of the reasons fridges use glass shelves are aesthetic, rather than practical. – computercarguy Jun 24 '22 at 15:06
  • @computercarguy if DIYing a replacement I'd definitely go for but there's no reason for glass to shatter. Tempered glass can take heat better than most plastics (I have several worktop protectors/oversized trivets made of it) and is pretty good against impact too (I once dropped a hammer onto on of those worktop protectors from a height of about a metre). Aesthetics count though - the polystyrene meat drawer and veg box in my fridge have aged far worse than the glass shelves: surface damage as you can't scrub them without causing scratches if something gets stuck or packaging print transfers – Chris H Jun 24 '22 at 15:12
  • @ChrisH, tempered glass deals well with impacts, which is why it's used often in tables, windows, and other places. But it's still not good with [thermal shock](https://www.nytimes.com/wirecutter/blog/tempered-vs-borosilicate-glass/). It's better than standard glass, but it'll still shatter from a hot pan regardless how big the pan is. Acrylic will deform around 300F (160C), but that's localized, not over the whole sheet, especially when the fridge is constantly cooling the shelf. The cold helps acrylic defend against a hot pan, while the cold causes tempered glass to fail with a hot pan. – computercarguy Jun 24 '22 at 15:23
  • @computercarguy as I said, I imagined a pan nearly as big as the shelf from another answer - almost all the shelf would deform. But only an idiot would go straight from the oven to the fridge with a pan for many reasons, and tempered glass at room temp can take an oven-hot dish - at least 200°C, for a ΔT of 180°C. So even if someone was perverse enough to put a dish of boiling water straight into a fridge, with ΔT around 100°C, it would still be fine. The other food that got warm from the heat of the dish might not be OK. – Chris H Jun 24 '22 at 15:41
  • @ChrisH, but a fridge shelf is at ~40F (4c), so a temp difference of over 200C, and 200C is the limit for thermal shock of tempered glass. Also, most people don't have pans the size of a shelf. You have to take into account thermal transfer when consider acrylic softening, and that transfer is going to be really bad between a pan and the shelf. You can put a very hot pan on acrylic and the surface will melt before it deforms because the heat transfer is so bad. Acrylic is a bad heat conductor, which is why it laser cuts so nicely. https://en.wikipedia.org/wiki/List_of_thermal_conductivities – computercarguy Jun 24 '22 at 16:01
  • @ChrisH, now you are stating an opinion about people, rather than sticking to facts. Also, it's better to put hot foods in the fridge, rather than let them cool too long in ambient temps. https://www.allrecipes.com/article/is-it-safe-to-put-hot-food-in-fridge/ And just because you have a pan that large, it doesn't mean everyone or anyone else has one. I know I don't. If I use your logic, I would assume that because I don't own one, no one owns one. – computercarguy Jun 24 '22 at 20:39
  • The advice there is still ideally to let it cool a bit, and anyway, that's advice based around big powerful fridges. Most (small, efficient) domestic fridges in most of the world will take hours to recover from a few litres of near-boiling liquid being put in there - "large amount" in the article has to be with respect to the size of the fridge. But I'm out of here - have a nice day – Chris H Jun 24 '22 at 20:53
7

Polystyrene, and similar acrylic (Perspex and Plexiglass are brand names) are quickly attacked by solvents such as acetone and methyl ethyl ketone (MEK), found in nail-polish remover. Put a little nail-polish remover, acetone or MEK (all are flammable!) on a small piece of paper towel and let it sit on the damaged shelf -- if the shelf softens or gets a crazed ("frosted") appearance at that spot, it's most likely made of acrylic.

BTW, polycarbonate is a far tougher and stronger plastic, though more expensive. There are grades of polycarbonate suitable for food contact, though I don't know if it needs to be "food grade" for use as a shelf. It would be a personal choice if the extra strength were worth the cost, though.

DrMoishe Pippik
  • 5,427
  • 13
  • 18
  • +1 for getting right to the point and saying they're all the same. I _think_ you can see frosting from where I used the solvent weld in the previous question (middle of lower portion) so I expect you're right :) – bertieb Jun 22 '22 at 19:24
  • 3
    Polystyrene and PMMA (Perspex, etc) are different plastics – bobflux Jun 22 '22 at 20:08
2

Well, since it's polystyrene, it is thermoplastic and can be melted and re-formed with solvent appropriate for polystyrene. You know what else is made of polystyrene? Airplane/boat/car models that kids (of ALL ages) put together. And do you know how you glue those? "Model airplane cement" which is acetone, really.

PVC "gluing" works the same way (with a different solvent though). Everyone assumes it's a sandwich of

  plastic | magic glue | plastic

But it's not gluing at all, it's welding. The solvent dissolves (liquefies) both pieces of plastic in the mate area, causing them to inter-flow, then the solvent dries away and you are left with

  plastic

and that's it. It's one piece of plastic now.

Note that neither type of cement can bridge a gap. If someone is desperate they might try

 plastic | cement | AIR GAP | cement | plastic

And that is not going to work. Fit and clamping will be everything.

All that to say, it may be possible to sand off all that incompatible PVC crud and have another go using polystyrene sheets. But they should really reinforce.

Remember that tray is a structure, exactly like a bridge. The top is in compression, the bottom is in tension. Reinforce accordingly and don't spare the material.

As far as a replacement piece, special attention will need to be paid to how the shelf docks on the side. I don't think 5mm (3/16" will be strong enough, but you are constrained by what will fit in the slots the shelf fits into. You should measure both the old shelf and the fridge itself. Measure twice, cut once LOL.

Harper - Reinstate Monica
  • 276,940
  • 24
  • 257
  • 671
  • Thanks for weighing in Harper, invariably good answers from you :) I was just thinking this would be a decent answer on the previous linked QA... and I see you've answered there too. Unfortunately I missed bridge-building classes in primary school, so I was hoping the replacement would have sufficient strength as a single sheet/slab of acrylic lol AFAICT the shelf sits on top of the retaining 'slots' (I have a picture but was going to save that for a follow-up QA) – bertieb Jun 24 '22 at 11:21
2

In general, No. The original shelf has features that make it rigid that are going to be difficult to replicate. My suggestion is to make two identical copies of the shelf. One cut by the plastic shop from food-safe polycarbonate and the other by a glass fabricator out of 10mm glass. Laminate the two together with clear 3M VHB or similar. (A strong tape, just put small discs cut from VHB about an inch from the corners and one or two in the middle. ala #5 on dice). The glass will be rigid and the policarbonate will tolerate getting dinged. Put the polycarbonate sheet on top. Many fridges have glass shelves only and that can certainly work. BUt they will usually have a plastic edge protection to keep a small chip from turning into a catastrophic fail.

Aaron K
  • 146
  • 1
  • Hi Aaron, thanks for the answer. Fair points about the original's 3d construction / features. Ideally a 1:1 replacement would work as well as the original (by definition lol), but I don't think it'd be economical; I'm tightly constrained by budget- have held off replacing this at all after it broke a while ago for that reason! Currently using a piece of stiff cardboard, which just about holds a small bag of parsley... – bertieb Jun 24 '22 at 11:27