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Post by silverdragon on Apr 7, 2014 8:54:59 GMT
Newton said gravity is a force that attracts. It was many years later that we started to understand WHY gravity attracts..... And I think some people are still investigating that.
I understand the "laws" in place, I just dont understand the mechanics behind the law.
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Post by the light works on Apr 7, 2014 14:02:28 GMT
Newton said gravity is a force that attracts. It was many years later that we started to understand WHY gravity attracts..... And I think some people are still investigating that. I understand the "laws" in place, I just dont understand the mechanics behind the law. gravity attracts because the planet sucks
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Post by chriso on Apr 8, 2014 3:20:32 GMT
I might be able to help on this? First, a basic review of two terms. Work and Power are not the same thing. Not to a physicist anyhow. Work is force applied over a distance. So if I apply a force of 1 netwton over 1 meter, I have done 1 Joule of work (1*1=1) Power is work divided by time. If I did 1 Joule of work in half a second, the average power would of been 2 Watts. (1/(.5)=2). This distinction will be important shortly. Basically, what is going on has to do with how quickly the energy is being applied. When the collision is very high powered, (AKA a lot of work done over little time), the molecules forming the metal container are stretched "too fast" to keep attached to their neighbors. Remember by newtons second law: "objects in motion tend to stay in motion." This collision is that law acting to keep most of the truck at one speed while the sliding load goes right through on another. On the slower deceleration, the same work is done, but over a longer time, meaning the power is less. Though the molecules forming the container are stretched, they are not overstressed and fail. So its an application of newtons second law, and too much power at once. If this is an incomprehensible pile of jargon, please tell me. I would be happy to try to clarify, and like to know how to reduce complex subjects to simpler forms. Its part of my degree*, after all *currently a undergraduate physics major
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Post by silverdragon on Apr 8, 2014 8:15:59 GMT
**CLUNK!**DOH!.....
Thankyou to TLW who tried his hardest, but the simple word "Time" in that sentence fixed it for me... its all about how you slow down. The truck has brakes, they slow down rapid, but do not stop immediately, which is what TLW was trying to say, so the object being braked is different to the object being stopped.
If the object is being braked, the force applied is stretched over time. If it is being stopped, its all at the same instance. Time is the defining factor here. The large object "Restrained" is braked over time, if not restrained, when it hits the bulkhead, its now a collision.
Sometimes however hard you look, you dont see the wood for the tees. If thats because the elephant is stood in front, you have my sympathy....
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Post by chriso on Apr 8, 2014 18:45:28 GMT
Glad I could help! Don't worry, I totally get confusing position and time. I still do so myself everyone now and then. Just the other day I was trying to wrap my head around how waves work (the physics concept, not the things at the beach), and found myself in a similar situation: I was thinking in terms of distance, without considering the time. When I realized time was involved, everything suddenly made sense.
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Post by the light works on Apr 8, 2014 18:56:30 GMT
Glad I could help! Don't worry, I totally get confusing position and time. I still do so myself everyone now and then. Just the other day I was trying to wrap my head around how waves work (the physics concept, not the things at the beach), and found myself in a similar situation: I was thinking in terms of distance, without considering the time. When I realized time was involved, everything suddenly made sense. good thing you weren't thinking of the things at the beach - you'd have to delve into chaos theory. </tangent>
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Post by silverdragon on Apr 9, 2014 7:01:56 GMT
The only way I can work with wave theory is to put a couple of ducks on them.
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Post by the light works on Apr 9, 2014 15:39:55 GMT
I mentioned it a bit earlier, but is poorly secured sheet steel liable to float around in transit? plywood is.
another item that might fit - I have seen people load heavy equipment and trust the tracks to keep it from sliding off the trailer. it would probably depend on some math - but how much grip does a set of steel tracks HAVE on a hardwood trailer deck? I am thinking primarily of sliding off to the side, rather than in a collision.
random thought - is there a point where adding strength of tiedowns is pointless - as it will just mean the trailer will be carried off with the load?
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Post by silverdragon on Apr 10, 2014 7:25:28 GMT
The trailer should remain attached to the load at all times. If the load is going sideways, it should take the trailer with it, that way, recovery is more liable to be just lifting the trailer back on its wheels, and trailers have more tie-down points on them that recovery trucks can get hold of than the load does. Plus the extra weight of the trailer will most often prevent the load from completely tipping over... The complex geometry of the suspension, when you get to lift a wheel off the ground, by that time, a decent driver will have already started his own recovery process to keep it on the road.
Dont know about the USA, but in UK, flat-bed and curtain-side Trailers have a set of hooks along the sides, just under the bed, that dont protrude out from under the bed, for tie down purposes. The more the merrier?.... They are every two foot or so, and I have used every single one on more than one occasion, especially when rope-and-sheeting an awkward load. No, you cant get too many tie-down hooks.
Steel slides on trailer beds... they are slides. Things slide. They are more than often put in place to enable unloading, they have no grip, I hate them. I trip over them, Pallets get stuck on them, roll-cages dont work on them, and to be honest on the rare occasion I have seen them used for what they are supposed to be used for, a pump truck (pallet jack) is just as useful.
Trailer beds should be hardwood. (IMO) For a start its mostly inert, it has grip, its what we are used to, and you know its dirty, so no problems there. Steel decks, fine for roll cages and refrigeration ("Reefers" in U$A) but bad for pallets, unless you have restraining bars and tie-downs inside.
Will sheet steel slide in transit?... YES. Especially if its stacked one sheet on top of another. It will slide Just as easily as anything else, but also once its got its weight behind it, it goes where it wants to go.... usually in a straight line and very fast. The problem is, its unpredictable. If it has rust on the surface, you know it will move, as the rust acts as a lubricant. Dry rust is worse than wet steel. Otherwise, it will stay where it is up until it "breaks" free, and when it breaks free, it goes all the way... Mostly on corners, under heavy braking. I have found driving sheet steel if you adopt a fluid dynamics approach and drive it the same as you would a tanker, you get an easier ride. This is also why sheet steel is chained and not strapped.... Straps will get cut on the edges, work loose, stretch, and break. Chains are what they are, bloody strong, indestructible, and not for moving once they are in place. You hope.
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Post by Cybermortis on Apr 10, 2014 10:46:26 GMT
**CLUNK!**DOH!..... Thankyou to TLW who tried his hardest, but the simple word "Time" in that sentence fixed it for me... its all about how you slow down. The truck has brakes, they slow down rapid, but do not stop immediately, which is what TLW was trying to say, so the object being braked is different to the object being stopped. If the object is being braked, the force applied is stretched over time. If it is being stopped, its all at the same instance. Time is the defining factor here. The large object "Restrained" is braked over time, if not restrained, when it hits the bulkhead, its now a collision. Sometimes however hard you look, you dont see the wood for the tees. If thats because the elephant is stood in front, you have my sympathy.... I usually use the analogy of a bank account and (say) and your electric bill. If you account has (for simplicity) $500 in it every month, and the cost of the electric bill is $2000 then trying to pay your entire electric bill in one go isn't possible without going into the red. However if you pay that $2000 over the course of a year you are only paying $167 per month - less that what is in your account.
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Post by the light works on Apr 10, 2014 14:50:38 GMT
as for taking the trailer with it - I was referring to: if your chains are strong enough to take the trailer with the load, (by a generous safety factor) is there a point where putting on stronger chains is adding nothing but weight?
the rust vs clean polished steel would be a great one for them to test - because it is counterintuitive. (for those who don't deal with such things - if you get two perfectly flat surfaces together, they essentially vacuum seal - and you have to get air between them to get them apart. texture, like rust, breaks that vacuum.
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Post by silverdragon on Apr 11, 2014 7:32:35 GMT
Yes, at that point, you refer to STGO rules, "Oversize", and that is when they call me. Its not just how much chain, its more where and how you attach chain. So saying that, if it is me that gets called, its a case of get every piece of chain you can find at the side of the trailer, then see where you can fit them to provide enough anchorage. To be honest, most of the times, you have talked through the load beforehand and already agreed where chains need to go, as some loads need anchor point built in to actually get transported anyway.
Do I ever put in break points?... Yes. If the load is awkward enough in size that it will get blown over, the same as the towing rigs that are used on the show, I put a length of known breaking strain rope in that will fail rather than take the tumble, however, that now changes the hazard of the load, so in that case, I may need an escort, I need calm weather, and a whole host of other problems. But mostly, if you are driving non hazard non oversize or overweight loads, you cant get enough straps or restraints in place to just be adding weight without it looking wrong. I suppose thats where the experience comes in?... If you are not sure, add another strap.... You have to have the experience to know when to be sure, and when to add the extra strap.
So actually knowing when to stop adding chain is the art form in heavy goods.
More than once, I have built up speed somewhere safe and done a sudden stop just to test if a load will move.
Throwing a ton of chain over from one side to another repeatedly, doesnt matter HOW much you tension that chain, if its a steel pipe, lengthways on the bed, as soon as you hit a hill it will slide either forwards or backwards unless you restrain the ends. Same with sheet steel, you have to throw at least one (strong) chain over the back end to prevent it sliding out backwards on an uphill gradient, especially if its a bumpy road.
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Post by silverdragon on Apr 11, 2014 7:37:06 GMT
I have to give credit for that one. So what is the best way to test that set of ideas. Polished steel, against painted steel, against rusted steel, and all those against steel separated by wooden support dividers that they sometimes put in between the sheets in order to get a fork-lift under the sheets.
The wooden supports crush a little when you tension the steel chains, would that provide extra grip that prevents sliding when compared to no dividers at all?...
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Post by the light works on Apr 11, 2014 14:40:57 GMT
I have to give credit for that one. So what is the best way to test that set of ideas. Polished steel, against painted steel, against rusted steel, and all those against steel separated by wooden support dividers that they sometimes put in between the sheets in order to get a fork-lift under the sheets. The wooden supports crush a little when you tension the steel chains, would that provide extra grip that prevents sliding when compared to no dividers at all?... I would say use the earthquake rig for the test bed - and if you could add a jitterbug (do they use those on tipper trucks in the UK?) to create vibration, that would be better. put a rubber mat down on the shaker table, then lay stacks of 3 sheets of steel in each of the chosen conditions on it. turn on the table and see what steel migrates more. (I am thinking 3-4' square pieces of 1/4" steel; with the idea that that will be the least obnoxious to manipulate on and off the rig, while still providing mass and area for the interaction) I can think of (each in wet and dry condition) polished clean unpolished wire brush finish lightly rusted (patina) heavily rusted (scale) properly painted badly painted.
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Post by silverdragon on Apr 11, 2014 19:48:58 GMT
A whatterbug?... [google].... ah, I see... No. We have trailers with walking floors, we have trailers with pneumatic headboards that push backwards, we have combinations of both, but "Jitterbug" is not happening as far as I know... But then again, I dont drive tipper trucks. Ever. I chose not to, on purpose.
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Post by the light works on Apr 12, 2014 0:52:09 GMT
A whatterbug?... [google].... ah, I see... No. We have trailers with walking floors, we have trailers with pneumatic headboards that push backwards, we have combinations of both, but "Jitterbug" is not happening as far as I know... But then again, I dont drive tipper trucks. Ever. I chose not to, on purpose. it vibrates the truck bed to help sticky stuff fall out. if they show one on youtube it is too covered by other things with the keywords.
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Post by silverdragon on Apr 13, 2014 11:09:47 GMT
I got the idea and tried "Vibrating truck body", and got a result from that. There is a company in UK who can do a conversion.... But I have yet to drive on. As I say, Tipper work is something I avoid.
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Post by the light works on Apr 13, 2014 14:56:37 GMT
I got the idea and tried "Vibrating truck body", and got a result from that. There is a company in UK who can do a conversion.... But I have yet to drive on. As I say, Tipper work is something I avoid. here, there was a time period when everybody who had a tipper truck bought one and used it every time they dumped a load. but then most of them either stopped altogether, or used it very sparingly - because they started having welds cracking. now they are putting them in paving rollers; which helps them compact the asphalt (or substrate), and actually sounds way cool. kind of like a teenager's stereo, but not as rattly.
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Post by silverdragon on Apr 15, 2014 7:30:18 GMT
For compacting tarmac(asphalt) we over here use Vibroplate. Big sheets of metal that do what it suggests.
There have been vibrating rollers about for many years....
For unloading trailers, the walking floor is preferred here, or just tip it skywards and the drive climbs up with a shovel. Its simple, but it works?...
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Post by the light works on Apr 15, 2014 13:26:48 GMT
for our semi trailers with bulk loads, most of them had chain drive "live floors" (basically a conveyor on the bottom of the trailer) but we had the occasional walking floor and the occasional tipper trailer. problem with the tipper trailers is you need 50 feet of vertical clearance to tip them. at our mills, they have a platform that lifts either just the trailer or sometimes the entire semi. that one's at a grain facility - the ones for wood chips and such go much higher.
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