hi i'm iris and i'm going to be demonstrating the rockwell hardness tester we use this to test the hardness of metals in the lab there are two variations on the rockwell scale there's b variation and the c variation b variation involves a ball shaped indenter and a hundred kilonewton preload the c variation involves a cone-shaped diamond indenter and 150 kilonewton preload and is for testing harder materials i will be demonstrating the b scale but the c scale is similar here's a piece of brass i put it up here on the platen and i use this hand wheel to raise the platen until it touches the indenter and keep a very close eye on this dial because as soon as they make contact that needle will move there i'm going to continue turning the hand wheel to raise the stage and the dial is going to go around about three times and as you can see the small dial is also moving toward the red dot must stop when it gets to the red dot and the big dial should be about vertical put the zero on the outside scale aligned with the vertical needle now i'm going to apply the load by pushing this handle away from me gently and the large black needle will begin to rotate you'll notice that the small needle also moved now i'm going to unload it by bringing the lever gently towards myself and the dials will move again once the needle settles you can take your reading and since we're on the b variation remember to use the red b scale so we're at 67. now we can unload the specimen by turning the wheel counterclockwise we've heated metals in a furnace when you heat a material the molecules become more active and there's more opportunity for diffusion i'll be demonstrating three different methods of cooling each with a different speed and a different amount of diffusion quench cooling is the fastest and it stops the diffusion next is air cooling i'm going to remove the metal and place it on this heat resistant surface air cooling is a medium speed and diffusion can continue while the part cools more slowly the third kind of cooling is furnace cooling and for this one we simply turn the furnace off and let the part cool with the furnace the insulation of the furnace means that it cools the slowest and that there's the most opportunity for diffusion as it cools this slab is about work hardening metal we're going to be using this roller to do work on this sample of metal and afterwards we're going to be using the hardness tester to test whether the hardness has changed and how much we check our initial thickness record that then we'll put it through the roller check the thickness again put it through the roller check the thickness again and continue doing that until we've reduced the thickness by five percent of its original thickness this knob opens and closes the rollers we want them open just enough to grab the sample then turn this wheel and send it through you want to make sure to put your sample through the smooth side of the rollers not the ridged side 3.45 make sure to alternate the directions that you roll it otherwise it will develop a curvature and become difficult to test in the hardness tester i reached the desired five percent reduction after three rolls next i would test it on the hardness tester and now that i know that it takes three rolls to reduce by five percent i wouldn't have to measure after every roll next time just after every three rolls as you continue passing it through the rollers it gets harder and harder to pass through as i just discovered