45KN = 4500kgs?

[Ian Flatters]

So i bought today 2 medium isc pulley blocks for small tree rigging http://www.iscwales.com/pdf/pulleys/aluminium/RP017%20Medium%20prussik.pdf http://www.honeybros.com/gbu0-prodshow/HB91LA.html. So im asking if what i was told is correct that the minimum breaking strength is 45kn which is 4500kgs? Right??

 

Help:confused1:

[Alinicoll]

yes but the working load limit is way lower ie divide that by 10 to be safe so 450kg.

[Ian Flatters]

yes but the working load limit is way lower ie divide that by 10 to be safe so 450kg.

 

Ah yes! SWL is divide by 10. No wonder alarm bells were going off i my head but couldn't think what it was.

 

Plenty good enough for what rigging i had planned for them.

[Bolt]

am I right in thinking, that 450kg is a weight, whereas 45KN is a force (which is in effect weight and movement?

 

Therefore, as soon as you are arresting a falling object you need to condider the weight of the object, and its speed??

 

O Level physics seems a long time ago

[Alinicoll]

They`re fine for small stuff or as a redirect.

[Alinicoll]

am I right in thinking, that 450kg is a weight, whereas 45KN is a force (which is in effect weight and movement?

 

Therefore, as soon as you are arresting a falling object you need to condider the weight of the object, and its speed??

 

O Level physics seems a long time ago

 

Yes thats true. As i understand it 45kn is what a 4500kg static downward load exerts. After that it all gets rather technical.

[Rod]

1 Kn = 1000 Newtons or 225 pounds of force

 

WWL or SWL is worked out by a safety factor of 10 so as already said 450Kg

 

but that is only the maximum load it should be used on it dosn't account for force added when rigging

 

if you are going to 'drop' pieces of wood on to it you need to devide swl by 4

 

this then gives you a maximum weight of wood to work with 112Kgs ish

 

so a beech log of 20 inch diamiter aprrox 2 Ft long (this is if you are say blocking down the stem)

 

if there was no drop i.e the piece was held from a high anchor and there was no slack in the rigging then you could hold 450 Kgs

 

so the same log could be more like 10 Ft

[Ian Flatters]

Also im using 2 blocks to reduce pressure on each block so instead of a single at 45kn the weight pressure from the rope is spread so if my maths are right using half the block (90 degrees insteasd of 180 degrees) would increase this to around 67.2kn per block? I think? If someone could tell me if im right or wrong please

[Bolt]

1 Kn = 1000 Newtons or 225 pounds of force

 

WWL or SWL is worked out by a safety factor of 10 so as already said 450Kg

 

but that is only the maximum load it should be used on it dosn't account for force added when rigging [/color]

 

if you are going to 'drop' pieces of wood on to it you need to devide swl by 4

 

this then gives you a maximum weight of wood to work with 112Kgs ish

 

so a beech log of 20 inch diamiter aprrox 2 Ft long (this is if you are say blocking down the stem)

 

if there was no drop i.e the piece was held from a high anchor and there was no slack in the rigging then you could hold 450 Kgs

 

so the same log could be more like 10 Ft

 

 

as a ball park falling figure, but it depends on how far it has "fallen". The golden rules are to let if free fall as little as poss, ond to smoothly decellerate it using a capstan / etc. What a can of worms

Edited March 11, 2010 by Bolt
looked messy

[Rod]

 

 

depending on how far it has "fallen". What a can of worms

 

it doubles it weight every foot up to 4 foot then it has reached its maximum velocity which is why when blocking down you divide swl by 4

 

 

Also im using 2 blocks to reduce pressure on each block so instead of a single at 45kn the weight pressure from the rope is spread so if my maths are right using half the block (90 degrees insteasd of 180 degrees) would increase this to around 67.2kn per block? I think? If someone could tell me if im right or wrong please

 

 

you cant increase the swl/wll

 

you would be reducing or spreading the load