Identifying material

[lwalker]

I just won some material at auction and I don't know what it is. The description was "two boxes of plastic blocks." It's an online auction and my bid was low enough (about $10) that I didn't bother to drive over there to preview it before pickup. Since it's from a CNC shop I'm hoping it's Delrin (slabs of sawn black plastic shown in the photos). My question is how can I test it to positively identify it as Delrin? I'll probably be picking up my "winnings" later this week.

[tattoomike68]

Plastic comes in 1,000's of types, no way can you tell for sure.

If you know the name of the shop or can find out the name you could call them.

There is no such thing as cheap (as in low quality) plastic anymore all of it is formulated for an application and does that well.

[gellfex]

I don't know if this would be positive, but delrin has a formaldehyde smell when burned (yeah, I should slow down on my table saw cuts). I just googled to be sure and came up with this cool website:

http://www.modernplastics.com/how_to_identify_plastics.htm

[Rich Carlstedt]

If it has black waves in the plastic ie....light/dark/light.
It would be Nylatron..a graphite impregnated Nylon (nice stuff)
If it is solid black and soft. it could be polyethylene
If light black, almost gray and very soft and slick, it's reformulated Teflon
If black and hard, it could be PVC (check smell) or ABS..
If black and very hard, and brittle, it could be a Vespel ($$$$$$$$) which goes for about 50 bucks per cubic inch

Rich

[outback]

Delrin usually does not soften when machined. PVC and nylon soften quickly when being drilled. I also know Delrin burns with a faint blue glow and emitts very little soot. The fumes from burning delrin are very strong and offensive.

Delrin is also one of the harder plastics which makes it better to machine.

Jim

[Evan]

Wait a minute guys.

First, graphite filled nylon is graphite filled nylon, not nylatron.

In this pic the left item is Nylatron. Nylatron is often called "black nylon" even though it isn't black but gray instead. Nylatron is filled with molybdenum disulfide.

In the center is graphite filled nylon, sometimes called Ballistic Nylon.

On the right is natural nylon.




One way to identify Delrin or acetal thermoplastic is to turn it in the lathe. At slow speed it will make a continuous and very strong chip. However, as the feed rate and the speed are cranked up at some point it will begin to chip break on its own regardless of the shape of the tool. When that happens it will throw bits all over the shop. It has to be cut hard to do that but I don't know of another plastic that does it.

Delrin usually does not soften when machined.

Sure it does. It has a relatively low melting point and will melt easily, especially when drilling it.

[Rich Carlstedt]

" Nylatron is filled with molybdenum disulfide"

I agree..must have had a brain fart
Rich

[lwalker]

I picked up my auction stuff this morning on my way in to work. There's about 50lbs of the plastic!!! Not bad for $12 and I have a project that can use some right away.

It is black and the unmachined sides of it are glossy and have a sheen that makes it look like there are metal particles embedded in it. I'll do the flame test as soon as I can.

I'm typing this at work over lunch and I can't see Evan's pics: I think IT blocks that server, so I'll have to look at them when I get home.

Right now I'm a bit more excited about the "looks new" Te-Co clamping set I also got at the auction. That's something I really need.

[gellfex]

Sure it does. It has a relatively low melting point and will melt easily, especially when drilling it.

Huh? I've drilled a gazillion holes in delrin and almost never melt it, no matter what size or how aggressively I go. Nylon is as you describe however, and I rarely use it.

[Evan]

The melting point of acetal homopolymer, trade name Delrin, is 175C or 347F. Nylon 6, the most commonly used type, is 220C or 428F. That's a big difference. If you are in fact using acetal copolymer instead of Delrin the melting point is 200C which is still lower than Nylon.

[edit]

I use both materials extensively and both materials will pose problems with drilling and tapping. Plastics are lousy heat conductors and will quickly build up heat when drilled. As the heat is not well conducted it causes the ID of the hole being drilled to expand inward and grab the bit. One way to deal with this, especially for larger holes, is to use a spade bit when drilling. This produces much less friction and gives plenty of room for chip clearance.

[gellfex]

The melting point of acetal homopolymer, trade name Delrin, is 175C or 347F. Nylon 6, the most commonly used type, is 220C or 428F. That's a big difference. If you are in fact using acetal copolymer instead of Delrin the melting point is 200C which is still lower than Nylon.

[edit]

I use both materials extensively and both materials will pose problems with drilling and tapping. Plastics are lousy heat conductors and will quickly build up heat when drilled. As the heat is not well conducted it causes the ID of the hole being drilled to expand inward and grab the bit. One way to deal with this, especially for larger holes, is to use a spade bit when drilling. This produces much less friction and gives plenty of room for chip clearance.

Wow, we have such different perceptions of the same stuff. I view Delrin as the easiest stuff in the world to drill, mill or tap, it's the miracle material! My only issue with it is when reaming, its elastic enough to expand around the ream without actually being cut. I keep oversize reams for this reason.

As for melting, maybe melting pint isn't all there is to it whether something gums up from machining, perhaps delrins rigidity combined with it's low coefficient of friction keeps it from melting. All I know is I drill from #60 to 1 1/2 in delrin happily. I also find forstners work better than spades. I use them in UHMW polyethylene too.

[lwalker]

So far the flame test looks closer to Nylon than Delrin (burns with blue flame, but no discernible smell). I'll see if I can get one of the mech. engineers at work to find me a small piece of Delrin scrap so I can compare them.

Machines nicely though. Regardless of what it is, I can use it.

[Evan]

There is no question that delrin is easy to machine. I normally use acetal as it has slightly different properties. Where is causes the most trouble is drilling and tapping. I made acetal lead screw bearings for my mill and tried to run the acme tap through under power. That didn't work as it simply melted the material and ripped out the threads.

As for spade bits I resharpen them to a slight positive rake with no spurs on the OD. They do a nice job on nylon which is harder to drill than acetal because of binding.

This hole in Nylatron was drilled with a spade bit.

[tdmidget]

While you're ID ing stuff Evan, what was the shaft you asked about?

[lwalker]

...and a week later, I found some pieces with partial labels.
It's High density polyethylene plate.