Hillsborough
Sheffield
S6 2LL
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As expected the 6ft x 1” x 18G (“Wickes Specials”) were the weakest, as we mention in the article on Poles any installer who uses this mast must be called Bertie (as in bodger). I was surprised that the 1” the steel poles weren`t actually that much stronger than the 1” alloy abominations. The 1.25” x 18G pole is worth having over the 1”, but the 16G version is much stronger. We did expect the 1.25” steel pole to be the strongest of the 6ft poles but we didn`t think that it`s superiority over the 1.25” x 16G alloy pole would be so small. Remember that the steel pole will start to weaken as it rusts. The 10 foot x 1.5” pole lasted longer than I thought it would, but it certainly flexes a hell of a lot which is why we only recommend them for aerial up to the size of a Yagi 18.
We don`t actually stock 1.5” poles at 6ft, or 2” x 14G at 10ft, but we do supply 5ft x 1.5” and 8ft x 2.0” x 14G masts, we classify them as satellite poles. We included the tests of this particular length of pole (at the 6ft and 10ft lengths) for the sake of comparison, that and we`d probably be unable to break the shorter 5ft and 8 ft versions ones without bending the T & Ks, or pulling the brickwork apart......
The tests were primarily to establish pole strength, but we realised that they were also testing the 12” T & K brackets we sell, and the “Rawlplug type” wall anchors. Both were very impressive.
The T & Ks obviously flexed a bit under the type of the loadings we were putting on them, but they didn`t bend that far, and never looked anywhere near failing. As for the wall anchors, I`ve got to say that unless your brick is soft or your hole is too big (so you can`t get decent tightening torque on the screws) one has to wonder whether using “Rawlbolt” type fixings is worthwhile, particularly if one remembers the hole drilled in the wall needs to be bigger. You only have to look at the pictures below to see we were putting on so much load that even the strongest poles were failing, yet the (50mm) “Rawlplug” type wall anchors [and the brackets come to that] never showed up any deficiency whatsoever.
So, when it comes to wall anchors how tight is tight ? Well we did a few crude experiments with our M8 x 50mm wall screws and their M10 wall plugs and found that 15 to 20ft/lbs of torque seemed to be about right, and, very approximately, that`s putting full force about 3/4 of the way along a standard (7" long) 13mm spanner. Much tighter than 15 to 20ft/lbs and you`re in danger of twisting the head of the screw or stripping the plug, then it`s a new plug needed. If you don`t have a spare plug and have to complete the job then packing out the hole with sufficient wood so you can put a decent torque on the fixing is preferable to leaving it loose, because it`s doing buggar all if it`s not tight enough ! Stripping the plug is a pain and that wouldn`t happen with a Rawlbolt type fixing, but it`s far preferable to splitting the brick which over tightening one of the latter may well do.
Aerial Pole & Bracket Tests
Obviously as the pole gets longer it gets weaker ! As an example the 6ft x 1.25” x 16G pole failed at 25Kg but the 3ft length needed 62.5Kg to break it.
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We set up a test rig on our back wall and just added weights on the end of the poles till they failed. It was very interesting testing them all to destruction, in fact it was probably the most fun you can have with your clothes on !
Generally, in terms of strength, the masts failed in the order one would expect, see table, but in order to make sense of the results it is important to understand a few points :
A 6ft x 1.25” x 16G pole tested to failure, great fun..... It eventually collapsed at 25Kg loading, that`s 55lbs, on the end of a 6ft pole. And that`s strong !
I must confess to some surprise that the cranked alloy poles weren`t actually any weaker than the straight versions, in fact the 3ft cranks were actually stronger than the three foot straights ! However it should be borne in mind that we could only test the cranked poles in one direction. Testing them with a sideways "twisting" force would just have rotated the pole in its clamps. That said, I suppose one also has to bear in mind a bit of geometry, the distance from the support, to the point at which the force is being exerted, is shorter on a cranked pole.
The above comments don`t apply to the 9ft crank and the 6ft Supercrank poles.
The 9ft x 1.5” crank failed on the bend, and one assumes that was due to the fact it had a 6ft straight pole on the end of it, which is rather more than the 6ft versions have to cope with ! Despite this it took 20 Kg to fail it. That`s behind a 6ft x 1.25” x 16G crank, though it was actually stronger than the 18G variant of that same pole. If using a 9ft crank with a large antenna (e.g. an XB16) I`d chop a foot off it, or more, just to be on the safe side.
The 6ft x 1.5” Supercrank was comfortably stronger than even the 16G version of the 6ft crank. It was apparent that the cranked steel poles were weaker than the straight versions, but not being a metallurgist I wouldn`t know why.
The 3ft x 1.25” x 16G cranked pole was the strongest of all those under test. We were actually about to give up because it was getting dangerous trying to lift that much weight onto the test hook, particularly if it failed and fell on your foot ! Unlike the other poles, which kinked at the top bracket, this pole actually pulled the alloy apart, as in the picture (below right). Note the use of washers on the V bolt(s)......
cranked pole
loaded with
67.5Kg,
and that`s
strong...
The Denouement
There are 20 by the way, that includes cranked poles, plus we tested some twice if the results seemed abnormal.....
The subjects are listed on this page in the following order :
Background to the tests including :
The oldest sample wasn`t actually set up as an experiment, we just needed a lip to which we could attach an inspection light and, since we didn`t want it to rust we cut off a section from a galvanised "T" bracket and screwed that to the wall. We didn`t date it but it must have been done pre 2002, so, since the picture below was taken in March 2012 it`s been out there for 10 years. As you can plainly see, although there is a small amount of rust on the cut surface, it hasn`t spread at all, which is the main thing.
In experiment 3 (back in March 2004) we drilled a hole into a 6x6 galvanised wall bracket and placed it outside on its side so that water would collect in the aforementioned hole. As can be seen from the picture below the hole has rusted, but in the 8 years outside it hasn`t spread at all.
Next, in experiment 2 (Feb 2003), we tried to file off the galvanised surface on a section of galvanised "T". This has been bolted to the outside of our shop since 2003. The picture was taken in March 2012 so its had 9 years to go rusty, and it still hasn`t. Careful inspection of the close up will reveal some slight rust staining near the top edge, but that was caused by a parallel experiment in which we left a painted bracket outside for a few years. Unfortunately we left the latter on top of the galvanised one and that staining actually came off the painted bracket !
Note : we`re not saying the protection on this filed off galvanising is as good as the original finish, but the fact is it still hasn`t rusted, in 9 years......
In the best tradition we`ll give the results in reverse order.
As stated on our Poles & Brackets page I really cannot understand any installer using painted brackets when galvanised are available, it really, really, really is a bodge. Well actually I can understand it. What it means is that the installer is so tight he probably needs a torque wrench to get in his wallet. He saves a quid or two, and the customer, within a year or three, gets a rusty bracket. And if the bracket`s on a light painted wall he has to repaint it every few years ! This has occurred with the install pictured on the right, coffee and cream springs to mind, which is somewhat ironic because the picture was taken at Woolley Edge motorway services (northbound) ! ! !
Basically a galvanised coating can "self heal" and provide a certain amount of protection even where there isn`t much galvanising left, unlike painted finishes where once the corrosion gets under the paint it just spreads and brings off all the protective coating. Incidentally, do not confuse zinc passivation or plating with hot dip galvanising. The former is a far more durable finish than painting but not really in the same league as hot dip galvanising. Pre Galv (where metal sheet is Pre Galvanised before being formed into the component) is also far superior to painted, but is also inferior to hot dip galvanising. It is fair to say that plating and Pre Galv can give a smoother finish than hot dip galvanising because the protection layer is quite a bit thinner, and this may be significant to some people (don`t really know why.....), but their long term rust prevention qualities are some way behind hot dip galvanising.
Anyway, a few years ago we setup a few experiments to monitor how galvanising, or more accurately damaged galvanising, maintains its anti rust properties. I`d be the first to admit that how quickly something rusts does depend on the area where you live, by the sea being the worst environment I`d have thought, but if we put a painted bracket with a damaged coating on our roof it starts showing rust spots within days. Not years, not months, not weeks, days........
Further interesting point, oh yes, there`s more. There is a direct relationship between the corrosion rate of zinc (the protective component in galvanising) and atmospheric levels of sulphur dioxide and levels of the latter have dropped considerably since the 1970s*, thus galvanised products last longer now than they did at one time.
* I`m not an expert in this field but I would think one of the main reasons for this would be the fact coal and oil power stations must now have to be fitted (at great expense I may add) with Flue Gas Desulphurisation equipment to remove said sulphur dioxide from the power stations` combustion gasses.
We are more than willing to give advice to those actually purchasing from us. Could those only seeking information please just find the answer somewhere on this site, or ring an aerial installer local to them, or call the reception advice phone numbers.
To the ridiculous (Pat showing what he thinks)
From the sublime...
It isn`t just about pole diameter, the gauge / thickness of the metal is just as important. As an example a 6 foot x 1.25” x 18G pole failed at only 17.5Kg, but the thicker 16G version didn`t collapse until 25Kg, and that`s a big difference.
What counts is the free / unsupported length of the pole, i.e deducting the length covered by the bracket. This can be significant. For the tests of the 3ft and 6ft poles the T & Ks were 11” apart, but when we put the 10ft poles on we widened them to 20” (to outsides). This is necessary to prevent putting too much strain on the brackets, or the brickwork.... Thus the unsupported length on the 3ft poles was actually only 2ft 1”, on the 6fts it was 5ft 1” and on the 10fts it was 8ft 4in.
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Below is a section of the Zinc Millennium Map (courtesy of the Galvanisers Association) which shows graphically the average annual corrosion rate of zinc [1998 to 2000] around the UK.
The key to the map is shown on the right, though the Galvanisers Association also give an estimate of zinc corrosion down to 10 square Kms.
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