Why no commercially made open wire spreaders on the market?

[k4kyv]

I must have mis-read.  I could have sworn he said polycarbonate, but Frank says it is polypropylene.

Even polycarbonate has to have UV protection.  I notice in the catalogues for plastic products it states whether or not it is protected on one side or both.  But I have heard numerous stories of antenna insulators made from Lexan lasting in the sun for years.  Apparently the UV protection is applied to the surface.  In that case, whenever it is cut, unprotected plastic is exposed.

Maybe some products have UV protection built into the material.

Plexiglass is inherently UV resistant.  It was developed during WW2 as a shatter resistant material for use in aircraft windows. Interestingly, it still shattered upon severe impact, such as bullet hits.  Small pieces sometimes embedded in the eyes of personnel on the planes, but it was discovered that years later, the embedded shards of plastic had caused no ill effects from the body trying to reject the foreign material, so plexiglass was successfully used to make artifical lens implants following cataract surgery. 

I'm not sure if the same material is still in use, since to-day's surgery uses a flexible plastic lens that is rolled up into a cylinder, inserted through a tiny incision, and fully deployed inside the eye, kind of like building a model ship inside a bottle. Before installing the implant, the clouded natural lens is pulverised and then sucked out through a hollow needle.

[ZS6TMV]

Maybe some products have UV protection built into the material.

I'm trying not to drift too far off topic here, but I'm sort of guessing that the material properties of ladder line spreaders and other mechanical parts could be considered relevant. :-)

To keep a long story short, almost all plastics are susceptible to degradation over time. This is, in a nutshell, mainly due to three factors.

The first is inherent chemical instability in the material itself, which causes the molecule to break down into smaller fractions over time. Good quality plastics do not exhibit this property to any appreciable degree, but bad ones might. In some cases this property is even considered desirable, e.g. when materials have to be bio-degradable.

The second is the influence of chemicals. Well-known examples are rubber and plastic washers that crumble when exposed to engine oil, or polycarbonate (and, to a lesser degree, poly-ethylene-therephtalate) that may start to crumble when exposed to gasoline for several days. Because plastics consist of organic compounds, it will generally be organic chemistry (e.g. petrochemicals, especially volatile solvents) that are able to attack them.

The third, and perhaps most important one in this discussion, is exposure to UV. To be exact, this is not really a factor per sé, but UV rather acts as a catalyst that speeds up material degradation due to the first factor above (inherent long-term instability causing the molecule to break down) dramatically, by a factor of tens or hundreds. In other words, if a plastic might take 100 years to break down while kept in the dark and in an inert atmosphere, exposure to UV could speed up that process to take one or two years, or even less, and harmful chemicals would speed up the process even more.

There are two ways to combat this. The most popular ones used in the plastics industry are 1.) to improve chemical stability, and 2.) to prevent UV from wreaking havoc on the material in the first place. Option 1 is difficult, and essentially requires that a plastic be synthesized that exhibits excellent long-term stability even under adverse conditions. Examples of this are Perspex (which is very stable compared to other plastics, albeit still not 100%) and oil and solvent resistant rubbers and plastics for applications that involve petrochemicals.

The second option is the most popular one, and takes the form of a UV blocker or UV absorber. A UV blocker is a pigment that prevents UV from entering all but the topmost surface layer of the material. (That's why black cable ties stand up to UV so much better than the white or semi-transparent ones.) A UV absorber is a dye that absorbs UV and re-radiates it on different wavelengths (usually in the infra-red) similar to fluorescent paints and inks, and the powders with which the inside of a florescent tube has been coated.

Some materials, including plastics (to return to the start of this over-long diatribe) exhibit one or both of these properties naturally. Chemicals that are inherently part of the material's composition may block or absorb/re-radiate UV naturally, which does away with the need to add substances to achieve this. Some have better long-term stability than others. And some have a bit of both.

I have cut some big corners in the above (a text book on plastics and the chemistry of same is hardly called for here) but in a nutshell this is what's happening. Hope it helps. :-)

73 Frank ZS6TMV

[k4kyv]

The first is inherent chemical instability in the material itself, which causes the molecule to break down into smaller fractions over time. Good quality plastics do not exhibit this property to any appreciable degree, but bad ones might.

A good example of this is the plastic used on older air-core plug-in coils, such as the B&W HDVL series.  First, the plastic shrinks and warps, sometimes enough to warp the coil and break the ceramic bar that holds the banana plugs.  Then it begins to crumble.  As it deteriorates, it becomes lossy at rf.  I have had the insulating support strips on those coils to literally burst into flame while the transmitter was operating. If stored in a moist environment like a cellar, the plastic may even become attacked by fungus.

Those old coils used a substance called celluloid acetate.  Later on, they changed the plastic to polystyrene (Victron), which is an excellent rf insulator and doesn't deteriorate when kept out of sunlight, but UV destroys it in no time.  I once built some open wire spreaders out of the stuff, and they turned to powder within a couple of years.

The self-deterioration was particularly bad with the B&W coils.  I have seen others, made by other manufacturers like National and Bud, that didn't deteriorate so badly with time. They may have used another plastic like polystyrene from the outset.

[W1AEX]

I was reminded of these again today when I happened to run into Peter - N2IDU on 75 meters. He uses them spaced 2 feet apart in his open wire feedline. He indicated that they are easy to work with and hold up very well. They're very lightweight hollow tubes that you can slot at the ends, or drill holes to pass your wire feeders through. I'd be inclined to slot the ends, jam the wires into the slots, then fill up the ends with my hot glue gun. They come in 4 inch lengths, have a rigid shape, are made of black non-conductive polyethylene, and are designed to insulate conductors in high voltage fence applications. Peter picked his up at a local Tractor Supply store, but they are also available at Agway outlets and some ACE Hardware stores. You can also order them online direct from the manufacturer at the links below. I figure the price is right for some experimenting this spring!

Available in bags of 25 for $4.70 or boxes of 200 for $17.53.

http://www.fishock.com/store/high-tensile-electric-fence/500-540

http://www.fishock.com/store/high-tensile-electric-fence/500-540t

[W2PFY]

W1AEX

looks like some good stuff for a beverage antenna system.

[ZS6TMV]

The self-deterioration was particularly bad with the B&W coils.

Another example is the viewfinder of my old LeicaFlex SL camera. A thing of beauty... except for one of the plastic parts in the viewfinder which originally was transparent but is now a hazy shade of brown.

And the natural degradation of organic plastics is still a common phenomenon even today. Last year I took a pair of running shoes out of the closet where they had been stored (in the original box) for two years, only to discover that the soles (originally some kind of supple vinyl rubber or a similar compound) had turned into chewing gum: sticky, soft and gooey. Obviously some chemical reaction, perhaps involving a plasticizer, or else a long-term stability problem with the rubbery compound itself, had taken place and turned a formely firm shoe sole into goop.

Chemicals can also be an issue. Beware the plasticizers used in the transparent sleeves used to store documents in, for example. (You know the type: a page-sized transparent plastic envelope, with or without perforation to put it in a binder.) Not only will these plasticisers, which are somewhat volatile, erase the print on thermal paper (cash slips, fax messages etc.) in short order, but they will also attack many plastics, given enough time. Keep your vintage radio parts away from circuit diagrams and such which have been stored in these sleeves, at least when you store them for any appreciable amount of time. (I'm not suggesting that any contact on the work bench etc. is going to destroy anything, of course - we're talking months of storage time here, at least.)

And then there's what happened to my lawn mower. While on vacation, we had a deal with the neighbours' kid to cut the grass every two weeks or so. He tried to save a few bucks by not putting in real two-stroke fuel/oil mix, but he made up his own by putting some engine oil into regular gasoline. When we came back, literally every rubber gasket and washer, and most of the plastic parts, inside the engine had been destroyed by the engine oil, from the priming bulb to the carb. Aargh.

73 Frank ZS6TMV

[The Slab Bacon]

[And then there's what happened to my lawn mower. While on vacation, we had a deal with the neighbours' kid to cut the grass every two weeks or so. He tried to save a few bucks by not putting in real two-stroke fuel/oil mix, but he made up his own by putting some engine oil into regular gasoline. When we came back, literally every rubber gasket and washer, and most of the plastic parts, inside the engine had been destroyed by the engine oil, from the priming bulb to the carb. Aargh.

Now, that is wierd?? I use Lawn Boy 2-stroke mowers, and have for the last 30+ years. I like the fact that 2-stroke oil has additives to lessen the smoking, but I have used SAE#30 motor oil and regular gasoline most of the time. (Or whatever kind of oil that I have an open container of) I have done small engine repairs for most of my life and NEVER seen that problem. I also usually run them with double the oil in the gas (16:1). (maybe that is why my 1967 LB still runs as good as it did when it was new and I beat the Hell out of it with no mercy)

The gasket materials and rubbers/plastics used in them are made to be impervious to gasoline, so motor oil should have no effect on them. I wonder if he put laquer thinner or tolulene or something else wierd in there?? That stuff is another story, they will disolve plastics and screw up rubber!    

[WA1GFZ]

or fuel injector cleaner.
I blew 2 LB's my Dad built. Threw a rod once wide F open and the second rebuild seized the crank when the lower needle bearings got too small and turned about 30 degrees. Dad not pleased.

[Vortex Joe - N3IBX]

or fuel injector cleaner.
I blew 2 LB's my Dad built. Threw a rod once wide F open and the second rebuild seized the crank when the lower needle bearings got too small and turned about 30 degrees. Dad not pleased.

I used to own a LB with the larger engine (4 HP?) that was self propelled. I'd run my oil at 20 to 1 if not a little richer. I figured a fouled plug or two once in a while was worth the extra  money spent to make it last longer.

Remember a hi-performance two stroke oil called "Klotz"? I believe it was a early synthetic based oil with performance additives in it. I really can't say if it ran any better, but it had the characteristic Klotz oil odor from it.  Ditto with the 1963 Vespa Lambretta 125cc scooter I had. The scooter did run a little better. Can't say the same with the Lawn Boy though......

[N0WEK]

When I had my perfect 1961 Merc 50 horse outboard tuned up by the local expert I asked him about the oil mix, which in the original manual called for 20 to 1 of regular 30 wt. He said that the engines haven't really changed, that what changed was the oil. Modern 2 stroke oils are designed for that use, which is why they call for 40 or 50 to 1 mix now. He said go ahead and run at 40 to 1 or if it would make me feel better, a little richer. Everything else I've read on the subject agrees.

[The Slab Bacon]

Well, FWIW, my 67 LB till has the ORIGINAL plug in it!! I have pulled the muffler and cleaned the carbon out of the exhaust ports ONCE!! I usually run it at the high speed setting and dont hesitate to cut wet grass a foot high! It has been an incredible machine and has NEVER been rebuilt!!

I also have a '95 self propelled "commercial series" one as well. It isnt half the mower the '67 is. the older one definately seems to have more BA's than the newer one and it also starts easier. (one pull vs 2 pulls) The only improvement I can see is that it is self propelled and the older one isn't.  The '67 is indestructable!! The only thing I have ever done to it besides an occasional (very occasional) sharpening is to clean the points once, and clean the plug once. Not bad for the 30+ years I have had it!!

Oh, Joe, we used to call KLOTZ "bean oil"!! Used Klotz and Blendzall in 2-stroke dirt bikes back in the good old days...................................

[The Slab Bacon]

When I had my perfect 1961 Merc 50 horse outboard tuned up by the local expert I asked him about the oil mix, which in the original manual called for 20 to 1 of regular 30 wt. He said that the engines haven't really changed, that what changed was the oil. Modern 2 stroke oils are designed for that use, which is why they call for 40 or 50 to 1 mix now. He said go ahead and run at 40 to 1 or if it would make me feel better, a little richer. Everything else I've read on the subject agrees.

IIRC, werent they 24:1?? I thought I remembered that they used a quart to a 6 gallon tankful of 'olene. Outboard tanks were always 6 gallons, IIRC. They could also get away with it because being water cooled they ran much cooler than the air cooled stuff. The later outboards that used those damned surface gap sparkplugs would not tollerate the extra oil without fouling. I hated them and usualy ended up changing them to J4s or J6s. this helped with continued low speed use. (like crabbing)