One for space cat.

[joe-90]

Why is it that a gas fire will quickly warm a room up to a certain comfortable temperature - and then stop? Why doesn't the room just keep getting hotter and hotter?

And how does a washer on a nut and bolt work to stop it loosening?


Just wondering.

 

[bhm1712]

A washer on a nut and bolt does not stop it from working loose. a washer gives more surface area of pressure being applied to the work piece which is being held together to give an even load. A nylock nut or spring washer can help to prevent is from working loose.

The gas fire wont keep heating the room due to the heat output from the gas fire being a set figure For example, if a room required 3 kw of heat per hour to keep it at 21 degrees, a 3kw fire wont heat the room anymore than 21 degrees.

 

[joe-90]

OK but why does a washer allow you to tighten the nut easier and further than without a washer?

And I'm not happy about the fire answer - how does the room know it's reached its maximum? What is the mechanism that makes it stop getting warmer? A pan of water will heat until it boils - even if it's on a much lower light - it just takes longer. Why does the room stop heating?

 

[Space cat]

Why is it that a gas fire will quickly warm a room up to a certain comfortable temperature - and then stop? Why doesn't the room just keep getting hotter and hotter?

The gas fire puts heat energy into the room at an almost constant rate. (It actually drops off very slightly as the room warms up but the effect is minimal.) What changes is the rate at which heat leaks out of the room. This is proportional to the difference between the room temperature and what's outside. So, while the heat input rate is (almost) constant, the rate of loss rises with room temperature until the two are equal. If it helps, imagine trying to fill a bucket which has little holes all the way up the sides. As the water level rises, the leakage rate increases until it is running out as fast as you can put it in.

 

[joe-90]

That's a very clever analogy that is.

 

[bhm1712]

as far as my experience tells me, a washer doesnt allow you to tighten the nut any more than without. You keep tightening with or without a washer and eventually the bolt will shear off or the workpiece will break first.

Washer are purely there to spread the load evenly, so for example if you have a 5.5mm hole with a 5mm nut and bolt without a washer, the pressure will be applied on the very edge of the drilled hole by the back of the nut which can cause distortion or if the material is weak, can pull through.
with a washer the load is spread across say a 10mm area and so it wont pull through or damage the surface as much

In proper applications, a nut and bolt should never ever need to be tightened up as much as is possible, they should be torqued up to a specification which sometimes is not as tight as you think it needs to be!

 

[joe-90]

But doesn't a washer slip and halve the friction?

 

[bhm1712]

http://lmgtfy.com/?q=purpose+of+a+hardware+washer+wiki

 

[wreckedit]

But doesn't a washer slip and halve the friction?

This is very nearly the answer.... The thread if it were stretched out would resemble a ramp and you are trying to force a grooved piece of metal up the ramp. The difference in a dry metal ramp and a lubricated ramp is considerable. So, you can tighten a nut far more with grease, oil or thread locked solution.
The washer helps to reduce the friction of the surfaces of the nut and part, together with other reasons.

 

[geraint]

a washer is there purely to stop damaging the surface that the nut is close to... end of....... it serves no other purpose.

 

[conny]

a washer is there purely to stop damaging the surface that the nut is close to... end of....... it serves no other purpose.

Obviously not an engineer of any description.

 

[PrenticeBoyofDerry]

The answer is simple, A washer is used to clean my smelly socks

 

[libby lou lou]

That's a very clever analogy that is.

You still talking to yourself joe, been a while now?

 

[joe-90]

R u on drugs? I was answering the post above it.

 

[bhm1712]

So, you can tighten a nut far more with grease, oil or thread locked solution.

No you cannot.

You can tighten the nut onto the bolt the same with or without grease, the only difference being that the effort required to tighten to maximum will increase without grease, that being due to the fact that the grease or lube will reduce the friction.