Archive for the ‘UHMW’ Category

There are a lot of outdoor enthusiasts who are interested in food-grade plastic cutting boards. But it for an outdoor kitchen to something exotic like a fish cleaning station on a boat. The applications might seem different; however, the same family of plastic, polyethylene, is almost always used. But which plastic to use? What concerns are there?

Both UHMW (ultra high molecular weight) polyethylene and HDPE (high density polyethylene) in their “white” or more correctly, “natural” grades are FDA and CFIA approved for direct contact with food. HDPE, even though it’s less expensive, is preferable because unlike UHMW, it will not dull knives over time. If you have UHMW lying around it’s certainly a good option though and is probably worth the trade-off vs. buying a whole new sheet of HDPE. UHMW is commonly available in 4′ x 10′ sheets but many plastic companies will send you a partial piece of that sheet (with a nominal cutting fee included). HDPE is commonly available in 4′ x 8′ sheets though many companies also stock it in 4′ x 10’s.

Cutting the plastic to size is easy: household power tools such as drills and saws will easily cut it. Having a 40 grit sandpaper on hand would be good to deburr the cut edges. The plastics glue very poorly so if you’re installing a blacksplash, for example, attached to the cleaning station or cutting board you will need to screw it in. 3/16″ or 1/4″ self-tapping screws 6-12″ apart should be fine. The plastics are soft enough that your drill will countersink the heads slightly.

The problem with these natural grade plastics is that they are not UV-stable. You should expect some cracking of your cleaning station if exposed to the sun in about two years depending on exposure. The board surface should be seen as a “sacrificial” surface which will need replacement every few years – just part of the gig. The surface will become brittle and crack which isn’t good because it allows bacteria to hide in the crevices but otherwise this degradation does NOT make the plastic toxic.

If you need assistance or a quote on either of these food-safe plastics, please contact Redwood Plastics and Rubber.

 

One of the most common questions the DIY community has is trying to figure out what type of plastic they have or need. Maybe you have an old part or sample and you forget what it is? Perhaps the two plastics people most want to differentiate between are acetal and UHMW (or other polyethylene). But they both come in white and black and they kind of look similar, so what to do? Well, if you’re familiar with the two plastics UHMW or HDPE will feel different: more waxy and lighter than the acetal which almost feels like more of a metal than anything.

There’s another way to identify polyethylene though as long as you can disfigure the sample. Take a sharp knife, such as a steak knife, and start scraping the plastic, give it some gusto with long strokes. If the plastic shaves off in curls then you have polyethylene. Acetal and other plastics will not do this, an example of polyethylene with this type of shaving is pictured here:

 

For those not very familiar with plastics, it is sometimes difficult to tell the plastics apart. A plastic rod feels like, well, just plastic and we don’t consider sometimes the nuances of each material. One major consideration for those of us in the DIY community is how a material is fabricated or machined. Acetal is a very hard plastic and machines very well and can be held to tight tolerances (+/- 0.005″) whereas realistically (+/- 0.05″) is the best you can get out of UHMW in a DIY setting. UHMW is much softer and less dimensionally stable; however, it is slicker and more economical.

A short video on YouTube we found shows both plastics being machined and offers a comparison, take a look below:

Sick of cracked, rotten, and unstable wooden jack pads for your RV? Want to do a little project that will make you feel accomplished and provide a long-lasting solution? The good news is making your own plastic jack pads is an incredibly easy project that virtually any member of the “DIY” community can do! Fabrication of a couple pads for your RV should take 15 minutes or less.

What you will need to start:

-(1) 12″ x 24″ x 0.75″ (thick) piece of UHMW black-reprocessed plastic.

-(2) pieces of rope 1/2″ in diameter 12″ long.

-Table saw

-Power drill with 3/4″ bit. The bit should be at least 1.25″ long.

Instructions:

  1. Measure with a colored marker or tape the halfway point on the UHMW plastic. You want to simply cut it in half to obtain two 12″ x 12″ pieces. One of the pieces may be undersized but that is not important for this application.
  2. Cut the UHMW in half.
  3. Find the midpoint on each pad again. Mark it.
  4. On either side of your mid-mark, 1″ in, make two points 2.5″ on either side of that line.
  5. Drill thru-holes with your 3/4″ bit in those two marks.
  6. stick a piece of rope through the holes. Tie knights on each end wide enough that the rope cannot get pulled back through the drilled holes.
  7. *Optionally you can then cut the corners off the pads.

There you go, you have two jack pads that should last as long as you have your RV! Estimated cost per pad would be $35.00 including materials but they would likely retail around $70.00+ for an equivalent pad were you to buy them.

For members of the public PTFE (polytetraflouroethylene) and UHMW (ultra-high molecular weight polyethylene) seem to be very similar materials. They’re both white, soft, food-safe, and widely available from plastic companies. But are they that different? Oh yes they are! The first thing you would notice is the price. PTFE is literally in another category of plastics called the “high performance” plastics. This means the cost is going to be much higher than UHMW. So when do you need PTFE?

It would be an application where slickness is important above all other factors. UHMW, while less expensive, will outwear, outbear, and outperform PTFE in tough mechanical applications like homemade bushings, cutting board, etc. PTFE is very soft, so soft in fact it suffers from something called “cold flow”. This means that PTFE slowly creeps like a semi-solid liquid almost just sitting at rest in room temperature doing nothing. What PTFE does have in addition to outstanding slickness (low coefficient of friction) is that it takes very high temperatures up to 500 degrees Fahrenheit. UHMW does poorly in high temperatures and cannot handle more than 180 degrees Fahrenheit.

To be honest, in most DIY applications that call for a white plastic with balanced properties UHMW is going to be your go to. It’s too available, too cheap, and too balanced to go with PTFE. But in certain situations where very low friction is required (telescope mounts for example) or high heat will be encountered – PTFE may be your only choice.

For more assistance with your application please contact Redwood Plastics and Rubber.

UHMWPE (Ultra-High Molecular Weight Polyethylene) often abbreviated as “UHMW” is one of the most popular and well known industrial plastics. UHMW is seen as a “Jack of All Trades” in many applications while being more available and less expensive than other plastic options. While this is true to a degree, UHMW has limitations that means it will not solve all problems in all situations. In fact, it has some properties which make it deficient and the “DIY” community should keep this in mind.

When to use UHMW:

UHMW excels at taking impact and it is virtually unbreakable, it’s also very slick and the colder the operating temperature is, the better it performs. This is why UHMW is so popular in applications such as toboggans or as rails on sleds: impact + cold + slickness are all important to the application, and it does really well in this application. UHMW is also easy to work with as it drills, saws, and lathes well. It functions as wear pads, sliding blocks, fenders, and in other impact absorbing applications.

When NOT to use UHMW:

The main application we here at Redwood Plastics see UHMW incorrectly used in is bearing applications. UHMW is a poor choice as a bearing for two reasons:

1.) it is difficult to machine to tight tolerances (+-) 0.02″ are the best you can usually hope for and

2.) UHMW has low load bearing capabilities (500-800PSI). In a DIY bearing application nylon or Tuffkast will be superior.

The issue with tolerances is important to hit home: UHMW is not a dimensionally stable material. Not just compared to metals but even compared to many other plastics. We regularly receive drawings and requests for UHMW parts where we cannot quote based off the requested tolerances (or have to get a written waiver for acceptable tolerances). This lack of dimensional stability extends to thermal expansion and contraction which is why it is so hard to guarantee tolerances: if the part is manufactured in 30 degree weather but used in 90 degree heat the dimensions of the UHMW will drastically change!

We hope this points you in the right direction if UHMW is or isn’t right for your project. But if you have questions, or might be wondering what an alternative material could be, please contact us and we’d be glad to help!

UHMW polyethylene has countless applications for the DIY community but as we head into winter there is one simple application that we have to highlight on this blog. That is the UHMW plow blade for snow plows. Let’s not over-complicate things: this is just a UHMW strip with some holes drilled in. But in order to get what you need, you need to know what to ask for! First of all know that the material you likely want is the reprocessed-black UHMW grade. While being less expensive than the natural grade, the cross-linking in its production actually improves wear properties. A nice bonus when you’re also saving some money.

You also need to know what thickness of blade you want. In general, the blades are almost always 1″, 1.5″ or 2″ thick with 1.5″ being the most common. If you don’t know what you need, pick 1.5″. Many plastic companies will pre-drill holes for you if you need them for a fee (usually about $80.00) but we would recommend you do not. Firstly to save money, secondly you need to remember that UHMW is not a dimensionally stable plastic. Changes in temperature may expand the blade from when the holes were drilled meaning by the time you get it – the holes don’t line up! To avoid disappointment we recommend you do the drilling if at all possible.

If you have questions about UHMW snow plow blades please contact us.

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