Housing material
Housing material
(OP)
Here another question (I know, I'm asking a lot of questions!). What would be the best spindle housing material. I know that cast iron and malleable cast iron are used a few. Cast iron is a little bit more thermically stable than malleable. Is it a good thing? Personnaly, I would say yes because thermal expension is lowered and the less it moves, the better it is. What's your opinion?





RE: Housing material
RE: Housing material
RE: Housing material
And what about a spindle that run at colder temp. Some of our clients have their machine in a cold environnement (about 0 celcius). The spindle is shutted down for the weekend, stay around 0 celcius. When they turn the motor on, the spindle reach 3600 rpm in less than a few seconds so I wonder if, because the bearing outer ring expands faster than the housing bore (which is in ductile iron), it will shrink the bearing. Furthermore, the spindle is at once loaded before stabilizing its temp. Can those phenomenas be an issue?
RE: Housing material
What size are the bearings?
If the cold housing is thick around the bearing, it will squeeze the life out of the bearing like a boa constrictor
RE: Housing material
If the spindles are cold have a heated oil system, if the spindles get too hot use the oil system to keep them temperature stable. Most precision grinder have temperature controlled systems
The Graphite content of ductile iron reduces the coefficient of friction between the bearing O/d and housing I/d
RE: Housing material
EnglishMuffin, it seems that ductile iron works better than steel so why you'd rather use steel?
RE: Housing material
But there may be some drawbacks not mentioned in the papers, and the housing cost.
RE: Housing material
Greater CTE >could< be helpful in a gradually increasing temperature situation with a very thin housing. The European solution is to warm spindles up slowly. American machine shops expect their spindles to go from 0 to 60 in 5 seconds.
I think the generally greater thermal expansion of brass and bronze would be a dis-advantage on a high speed spindle if the housing is "thick walled." I believe "Thick walls" are a problem for high speed spindles with iron and steel housings. "Thick walled" would have to be defined using a series of FEA analyses and experiments. At a minimum a housing thickness should be 3 or 4 times the bearing outer race thickness. The RAPIDLY warming bearing passes some thermal energy to the housing. The heat conduction will lag behind the temp rise (*), and the housing inner bore, near the bearing will be warmer than the outer sections. For a while at least the warm section is thin compared to the cool section, and thus will have to expand inward, reducing bore diameter, increasing preload and temp generation.
A "high speed" preloaded spindle bearing gets warm rapidly, before the housing temp can rise at all, and can cascade into thermal run-away smoking junk in just a few minutes.
(*)Add large amounts of heat energy by Playing a torch on one end of a 12 inch bar of iron, bronze or even aluminum while holding the other end in your bare hand. It is possible to melt one end before the other end becomes uncomfortably hot
--
Dan Timberlake
RE: Housing material
RE: Housing material
It seems to me, that the brass sleeve takes the advatage of CTE together with better thermal conductivity. When the sleeve has larger axial length it coud provide a non-constraining heat sink for the outer rings.
One of conclusions in the paper could be interesting for JaenMicheling:
it is probably not good idea to make spindle housings of polymer-concrete. :-/