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Extended reach forklift

Extended reach forklift

Extended reach forklift

(OP)
I am hoping someone can tell me I am not going mad.
My firm has recently taken delivery of some flexi/bendi type of forklift trucks. These have a pantograph/scissor type of attachment for double depth racking, which will not extend unless the machine is at 45degree plus angle to ensure there is enough weight behind the front wheels to lift safely (it could topple over if it was at 90 degrees).
My issue is that having felt the truck go light when retrieving a load at full extension 8.4M up, I started to have major doubts. The capacity plate has basic errors on it and wasn’t much help, so I bypassed the management and got some data from the manufacturer:-

Height Retracted Extended Percentage
5.03 1364 1206 88
5.33 1364 1186 86
6.10 1364 1136 83
6.55 1364 1092 80
6.86 1364 1063 77
7.62 1136 989 87
8.38 977 915 93
9.30 841 827 98
9.91 750 750 100
10.80 682 682 100

I can see that the capacity (retracted) up to 6.86M is down to the limit of the hydraulics (1364kg), but I cannot see how the limits when extended improve the higher up you go, and I cannot see how the hell the limits at 9.91 and 10.80 are identical for retracted and extended!
This goes against everything I understand about forklifts; the higher you go the more unstable things get, and the further you move the load centre forward the more unstable it gets. Things just don’t get better the higher up you go, but as I have a beef about these trucks and would like to prove they are crap, perhaps I am blind to something obvious?




RE: Extended reach forklift

matt750,

Can you show us a picture? This sounds like something free-body diagrams were developed for.

--
JHG

RE: Extended reach forklift

Matt750:
We can’t see what you are looking at or dealing with from here. You really do have to show us some sketches and meaningful engineering design info. if you want help. Some copies of parts of the machine’s manual, side view, front view, plan view, significant dimensions, weights, counter weights, C.G’s, cap’ys., etc. etc. Your long understood knowledge that “the higher you go the more unstable things get, and the further you move the load centre forward the more unstable it gets” still basically holds, so the universe hasn’t turned upside down on you. But, the more flexibility (more degrees of freedom, axes of rotation, reach and retraction, etc.) that the machine has, the more different factors might influence its strength or stability. Structural and hydraulic strength will come into play at some point, on various components of the system. From the stability standpoint, if you look at a plan view of the system, you can see overturning components and righting components and their dimensions from some tipping point and calculate the stability, with some factor of safety. And, all of this comes into play on what shows up on your listing. But, without more info. on the system we can’t tell what’s what.

RE: Extended reach forklift

I looked at some videos from Landoll Bendi, an articulated forklift maker. Really interesting adaptation. I don't know what the "percent" column means, but in all cases the load capability decreases as the height goes up.

One thing that affects overturning is how much jerk there is to the drive wheel. At large heights this may be the governing limitation and the extension may be sufficiently small that the vertical load contribution is small compared to the horizontal acceleration contribution, so horizontal extension would not matter as much.

You could try asking the manufacturer what the reason for each of the limits is; from their perspective just providing them is enough to make the user safe.

RE: Extended reach forklift

3DDave:
Thanks for the brain teaser (or kick in the brain), I didn’t see this at first glance. I did notice the anomaly in the retracted cap’y., at that height (7.62M), but didn’t connect the causes. It looks like the mast, as a frame or beam/column/frame starts to control the lifting cap’y. structurally (stresses, deflections or buckling), when the forks are retracted, at about 7M in height. And, as expected, this cap’y. decreases as the height of the column increases. The percent col. is just the ratio btwn. the extended load cap’y. and the retracted load cap’y. at a given height; at 7.62M high, (989/1136) = .87. The cap’y. when extended always decreases with increased height, likely because the scissors (fork extension) causes stress or deflection problems in the mast, or in one of the sections of the mast.

RE: Extended reach forklift

(OP)
The 'percentage' (ratio is a better phrase)column was added by me, to try and give some meaning to the numbers when I eventually try to explain to the management exactly why I am not going to lift to that height/depth without credible information that it is safe. The numbers from the manufacturer just don't add up, yet I know their response will be "the salesman says it's safe, so get on with it". This could quite easily get me fired for job refusal, and it's not going to be easy when so much money has been spent by the management team who had so many working lunches with the salesman to look at the pretty brochures.
I have asked the suppliers for an explanation, just waiting for a response next week. I'll try and "borrow" the handbook for some drawings next week too.

RE: Extended reach forklift

It looks like the capacities decrease with height and the retracted and extended capacities converge with height. The convergence may be because the load cg movement compared to lift height creates a reducing included angle with height. Must the mast be tilted farther back with increasing lift height to where the retract and extend capacity become equal?

Ted

RE: Extended reach forklift

The load table presented in the OP does not make any distinction between bent or straight steering angle. I can only assume that they apply to both and therefore based on worst case for either configuration. The reduction in load rating with height would be due to reduced stability. In the straight configuration the lateral stability of the mast governs because the width between wheels is less that the length of the forklift. When turned 90 degrees the lateral stability increases while stability in the fork direction decreases. But it appears the the worst case is the lateral stability in the straight steering configuration. So this is reported as the load rating.

RE: Extended reach forklift

(OP)
Thanks for all the responses. I got an email from the supplier which said:-

"The capacity is based not only on the load capacity but the structural capacity of the combination of the mast and reach attachment at different elevations. As the elevation increases the variance decreases to where you can see they are identical".

It also looks as though the load I was trying to lift was "more than the 900 or so kg limit (because some other idiot put it up there) so this, plus the difficulty of using the hydraulics gently may have been the cause of the back going light. I will have to try and make sure everyone knows the limits.

Compositpro:- the table given is with the steering at 90deg (retracted position) and the extended figures would be with the wheels at 45 degrees. The deep reach cannot be extended unless it is in this configuration. Because they are used in narrow aisle racking there isn't often the need to operate them "inline" like a normal counterbalance, if that makes sense.

Hydtools:- No the whole mast doesn't tilt, just the fork attachment. I can kind of see what you are saying, and the response from the manufacturer is similar.

Just to round up, the next model down the series has the same "retracted" (90 degree) values (it uses the same mast/hydraulics, and the model I have has more weight at the back and a wider wheel track, so that means it has the higher stability at 45 degrees when extended.
I can see the big picture better now (still not 100%, but enough to answer the question),
thanks for all the input guys!



RE: Extended reach forklift

There are two elements that you have not considered which are the structural integrity of the machine particularly the scissor attachment and the slope of the ground. The 1364kg is undoubtedly the limit for structural integrity and the rest of the numbers deal with tipping the forklift at the front wheel at whatever the slope of the ground is allowed in your manual.

RE: Extended reach forklift

If this unit is as unstable as the OP implies, it sounds as if someone definitely drank the coolaid that the salesman was providing. I dont fully understand the engineering, but since the OP is based in the UK, I offer the following experience for his consideration. A few years ago I was in the market for several low profile telehandlers for use underground. Our previous supplier had ceased production of that part of his manufacturing line. The smallest CAT unit was too big to fit in our tunnels. Somehow JCB came to my attention , and they had what turned out to the almost ideal machine within their agricultural division of all places!!! JCB might not be well known in North America , but being an expat Brit, I knew who they were. I was very sceptical that a farm machine would stand up to the rigors of underground mining. But the sales guy convinced me to generate an immediate PO for four units. They were fabricated in the UK , shipped to my locality in Canada, modified to met some of my unreasonable requests and were taken underground. Proud to say I got some very positive unsolicitated feedback from the operators. If replacement of the OPs units becomes necessary, I strongly recommend contacting JCB to see what they can offer.

RE: Extended reach forklift

Having watched a few videos of those bendi flexi fork lifts they look like a work of art to drive and lift in those sort of confined spaces and for sure, with the main counterbalance at some sort of angle from the lift axis there is a whole lot of things going on to determine the safe load.

For anyone interested I think its this sort of thing https://www.youtube.com/watch?v=Upf-UQAjJBE

Glad you find the real reason was an overload on the pallet you were lifting. Despite the no doubt glib sales talk, load limits for equipment is usually pretty definitive, though they will try to make the best use of it and it will need a perfectly flat floor, level load on the pallet etc.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Extended reach forklift

I just got off the phone with a guy who used a forklift with a 50 foot reach to get A/C units off a roof! I'd never heard of them before. Came to ET and this! Interesting.

Keith Cress
kcress - http://www.flaminsystems.com

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