Distortion off BMS

This topic has 13 replies, 9 voices, and was last updated 27 October 2011 at 11:45 by Gary Brooke.

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22 October 2011 at 09:18 #76626
Gary Brooke
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@garybrooke63895
Hi all
Have anew problem.how do you stop long lengths off BMS plate from distortion. A bit off background as to what I was trying to achieve. Had some 1/8 BMS plate left from cutting out main frames so used it for tender frames. All went well with the outside 3 inch wide frames. But when idid the inside frames 11/2 wide by 24 they bent both ways. Cuts where done buy hand with a normal hacksaw. Any thoughts on the cause and is it possible to rectify the bends.
Many thanks
Regards Gary
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22 October 2011 at 09:18 #5714
Gary Brooke
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@garybrooke63895
22 October 2011 at 09:25 #76628
JasonB
Moderator
@jasonb
You will always get stresses in bright due to the rolling when cold, best to use black (hot rolled) in the future.

To rectify try annealing then bending to desired position. Annealing bright before cutting can also help prevent it moving.

J

Edited By JasonB on 22/10/2011 09:26:27
22 October 2011 at 10:01 #76633
Clive Hartland
Participant
@clivehartland94829
I would suggest putting the cutting line a bit closer to the vice jaws! less stress on the metal.

When I was cutting my bits and pieces I was almost cutting along the vice jaws, it makes cleaning up the metal a lot less tiring when filing.

In fact it states this fact in the book of words for making the loco, I am sure the old boys when making the locos did not waste any effort if at all possible.

Clive
22 October 2011 at 10:27 #76635
JasonB
Moderator
@jasonb
Its not so much putting stress on the metal with the cutting action. Its the inbuilt stresses in the metal when it was rolled, as you cut the metal the stresses are released and it bends, same applies for bar & rod – take a lot of one side and it will bend.

J
22 October 2011 at 13:03 #76642
KWIL
Participant
@kwil
If you do not want it to move always anneal it, I have even had hot rolled plate move.
23 October 2011 at 12:06 #76700
Gary Brooke
Participant
@garybrooke63895
Thank you for the advice. Have I got this the right way round, to anneal metal bring to red heat hold there for a time then let cool natural . To harden heat then quench.
Regards Gary
23 October 2011 at 12:46 #76702
Tony Pratt 1
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@tonypratt1
Hi Gary, in simple terms yes that is correct. There is plenty of detailed information on the net if you want to delve further into the subject. Hardening generally is a more involved procedure.

Tony
23 October 2011 at 17:03 #76716
macmarch
Participant
@macmarch
If SWIMBO will allow then if it’s small enough put it the oven with the Sunday roast. Particularly if there is a Yorkshire pud. Leaving it in the oven overnight, to cool slowly with the oven would be better still. Gas mark 7/8 will stress relieve most metals.

If you can then use oversize material machine all over to break the skin.
23 October 2011 at 18:42 #76723
Nicholas Farr
Participant
@nicholasfarr14254
Hi, I agree with Jason to a point, as the term is known as strain hardening.

Recrystallization and Grain Growth

Crystal deformation can have a marked effect upon the mechanical properties of a metal. For instance, when a metal is being rolled in its cold state the crystals of that metal will become greatly elongated in the same direction as the cold working.

The crystalline structure will now be of a fibrous nature and strain hardening of the metal will become evident.

This undesirable structure can be greatly moified by the application of sufficient heat to produce a new growth of equi-axed crystal grains within the cold worked metal.

The temperature at which this takes place is known as the recrystallation temperature and when the metal has cooled down to normal temperature its new structure will be unstrained and the metal will now have regained those properties it had before cold working took place.

It is quite likely that an improvment in the metal’s properties may now be indicated due to a refinment of the crystal grains, provided grain growth has not been allowed to take place.

Grain Growth

The occurance of grain growth, however, can be due to the excessive heating of a metal to a temperature well above its recrystallization point, thus bringing into being a very coarse granular structure similar to that associated with overheated steel.

Grain gowth can also be due to too slow a cooling rate after recrystallization has taken place. It is, therefore, always very important to hold the metal at its recrystallation temperature just long enough to allow the new grain structure to form, and then to control the rate of cooling so that this structure will be one of refined equi-axed crystals.

Enlarged Crystal grains will cause a decrease in the ductility and the tensile strength of a metal; but these properties will be enhanced when normal grain size has once again been restored by recrystallization.

Steel suffers from grain growth at tempertures above 950 degrees C (above transition teperature)

Regards Nick.

Edited By Nicholas Farr on 23/10/2011 18:49:27
23 October 2011 at 22:43 #76743
Chris Trice
Participant
@christrice43267
Brass sections have an annoying habit of distorting if you machine them asymmetrically.

I’m always confused by the difference between annealing and normalising since both involve heating and slow cooling, the latter I thought was for the purposes of stress relieving metal.
23 October 2011 at 23:52 #76748
Nicholas Farr
Participant
@nicholasfarr14254
Hi chris, the annealing process consists of; heating, in the case of steel, to a temperature of 40 degrees C above its upper tranformation temperature, according to carbon content. Holding it at this temperature long enough for the carbon to distribute itself throughout the formed austenite, as a rule the component is held at this determined temperature for 1 hour per 25 mm of thickness. Then allow the component to cool slowly, either in the furnace or in hot ashes or lime.

Normalizing is heating to a temperature of 40 degrees above its upper transformation temperature, according to the composition of the steel, holding at this temperature just long enough to heat the component right through, and allowing it to cool in still air.

Stress relieving consists of heating the steel to a temperature of 550 to 650 degrees C and holding at this temperature long enough for the whole of the coponemt to reach this temperature, then allowing it to cool in still air.

Hope this makes it clearer for you.

Regards Nick.
24 October 2011 at 11:20 #76759
Gray62
Participant
@gray62
Blimey Nick, you’ve just taken me back to my apprentice days in the steelworks when we were given extensive lectures on metalurgy, most of which has long been commited to the far reaches of my memory due to a subsequent career in electronic and computer engineering following the demise of the British Steel Industry.

Thank you for the comprehensive and informative info in your postings.

Time o get the text books out of the loft once again

Graeme
27 October 2011 at 11:45 #76946
Gary Brooke
Participant
@garybrooke63895
Hi all
Once again many thanks for sharing all that information. I think iv’e got it sorted.
Ray l that’s a good idea but as ayorkshire lass will not let anything near her puddings so have had to use the gas barbecue it works. Off to try carry on with our model once again many thanks.
Regards gary
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