Modern Machine-Shop Practice Part 101

| | ference. | | ference. | -------------+--------+-----------+--------+-----------+-------------- | Ins. | | Ins. | | After 1st dip| .50 | .86 | .08 | .14 | " 2nd " | .99 | 1.71 | .08 | .14 | " 3rd " | 1.47 | 2.54 | .26 | .45 | " 4th " | 1.92 | 3.32 | .30 | .52 | " 5th " | 2.30 | 3.97 | .34 | .59 | " 6th " | 2.60 | 4.49 | .40 | .70 |Slight crack | | | | |in expanded | | | | |edge.

" 7th " | 2.94 | 5.25 | .44 | .76 | " 8th " | 3.40 | 5.98 | .50 | .86 | " 9th " | 3.70 | 6.39 | .56 | .96 | " 10th " | 4.40 | 7.60 | .62 | 1.07 | " 11th " | 4.42 | 7.64 | .66 | 1.14 | " 12th " | 4.85 | 8.40 | .70 | 1.22 | " 13th " | 5.24 | 9.02 | .78 | 1.34 | " 14th " | 5.74 | 9.92 | .80 | 1.39 | " 15th " | 6.00 | 10.37 | .86 | 1.49 | " 20th " | 7.90 | 13.65 | 1.24 | 2.14 |After de- | | | | |ducting for a | | | | |crack .06 inch | | | | |wide which | | | | |appeared at | | | | |sixth dip.

"It will be observed that we have here two remarkable phenomena: 1. The reversal of the expansion and contraction as described. 2. The very large amount of contraction on the upper edge compared with what was exhibited in Experiment 5 of entire submersion.

"The table showing Experiment 5 gives a contraction of 2.25 per cent.

after the twentieth cooling, whereas the contraction on the air-cooled edge of Experiment 8 is 13.65 per cent., or six times the contraction of an entirely submerged hoop.

[Ill.u.s.tration: Fig. 1433.--Condition of the hoop after the twentieth cooling.]

"To ascertain whether these unexpected phenomena had any connection with the circular form of the hoop, Experiment 9 was made with a straight bar of iron 3-1/2 inches deep by 1/2 inch thick by 28.4 inches long.

"_Experiment No. 9._--Wrought-iron bar, 3-1/2 inches by 1/2 inch by 28.4 inches long, heated to a dull red, then quenched half its depth in water.

------------------+--------------------+-------------------- | Bottom Edge. | Top Edge.

+--------+-----------+--------+----------- | Expan- |Percentage |Contrac-|Percentage | sion. |on original| tion. |on original | | length. | | length.

------------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 1st cooling | .05 | .18 | .26 | .91 " 2nd " | .10 | .35 | .43 | 1.51 " 3rd " | .10 | .35 | .54 | 1.90 " 4th " | .14 | .49 | .75 | 2.64 " 5th " | .20 | .70 | .92 | 3.24 " 6th " | .30 | 1.05 | 1.25 | 4.40 " 7th " | .34 | 1.20 | 1.50 | 5.28 " 8th " | .38 | 1.34 | 1.56 | 5.53 " 9th " | .39 | 1.37 | 1.66 | 5.84 " 10th " | .40 | 1.40 | 1.76 | 6.19 " 11th " | .41 | 1.43 | 1.84 | 6.48 " 12th " | .44 | 1.55 | 1.96 | 6.90 ------------------+--------+-----------+--------+-----------

"This was cooled half in air and half in water, and the length of the two edges measured accurately after each of twelve coolings. At the end of this experiment the air-cooled edge had contracted 6.9 per cent., while the water-cooled edge had expanded 1.55 per cent. of the original length. The effect on the bar was to make it gradually curve, the water-cooled or extended edge becoming convex, the air-cooled or contracted edge concave.

[Ill.u.s.tration: Fig. 1434.--Experiments with a wrought-iron bar.

Appearance of the piece before heating.]

"Experiment No. 10 was made in order to show the effect of reversing this cooling process. After five coolings, a bar of iron, 28 inches long, 3-1/2 inches deep, and 1/2 inch thick, was curved so that the versed sine of its air-cooled edge was 1-1/2 inches. The coolings were then reversed, what was the air-cooled edge being then immersed in water. After five more coolings the bar was restored to within 1/8 inch of being straight, and the eleventh cooling threw the concavity on the other side of the bar.

[Ill.u.s.tration: Fig. 1435.--Appearance of the bar after the twelfth cooling.]

"_Experiment No. 10._--Wrought-iron flat bar, 28 inches long by 3-1/2 inches by 1/2 inch, heated to dull red, then quenched half its depth in water, up to five heats, then the opposite edge dipped.

-----------+-----------+------------+------------------ | | | Reversed Cooling.

| | +------------------ |Versed sine| | Versed sine |of concave,| | of concave, | _i.e._ | | _i.e._ now |air-cooled | | water-cooled | edge. | | edge.

-----------+-----------+------------+------------------ | Inches. | | Inches.

1st cooling| 5/16 | 6th cooling| 1-3/16 2nd " | 9/16 | 7th " | 7/8 3rd " | 13/16 | 8th " | 3/4 scant.

4th " | 1-3/8 | 9th " | 3/8 full.

5th " | 1-1/2 |10th " | 1/8 | |11th | Brought concavity | | | 1/8 in. on other | | | side.

[Ill.u.s.tration: Fig. 1436.--After the preceding experiment the same bar was reheated and reversed in the water, the eleventh cooling resulting in the above form, the bar bending in the opposite direction from that previously shown.]

"When the author had proceeded thus far, these curious results were shown to several leading scientific men, who expressed interest in the subject, which encouraged the author to extend his experiments under varied conditions with a view of ascertaining the cause for these anomalous effects. These experiments (Nos. 11 to 17) are fully recorded, and the results shown on the diagrams; the actual rings are also on the table before you.

"_Experiment No. 11._--Wrought-iron hoop, turned and bored, 37.1 inches, outside circ.u.mference, by 2.95 inches deep by .44 inch thick, the grain of the iron running the short way of the bar from which the hoop was made, heated to redness, then cooled half its depth in water (see Fig.

1437 at A for final form of hoop after ten heatings and coolings).

-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge.

+--------+-----------+--------+----------- |Contrac-|Percentage | Expan- |Percentage | tion. |on original| sion. |on original | | length. | | length.

-----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 1st cooling| .3 | .83 | .05 | .13 " 2nd " | .64 | 1.72 | .12 | .32 " 3rd " | 1.02 | 2.75 | .22 | .60 " 4th " | 1.38 | 3.72 | .30 | .80 " 5th " | 1.62 | 4.37 | .37 | 1.00 " 10th " | 3.14 | 8.46 | .76 | 2.05 -----------------+--------+-----------+--------+-----------

"_Experiment No. 12._--Wrought-iron hoop, turned and bored, 6 inches diameter (18.85 inches circ.u.mference) outside, by 2 inches deep by .375 inch thick, heated to redness, then cooled, with lower edge barely touching the water (see Fig. 1437 at B for final form of hoop after twenty heatings and coolings).

-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge.

+--------+-----------+--------+----------- |Contrac-|Percentage |Contrac-|Percentage | tion. |of original| tion. |of original |Outside | circ.u.m- |Outside | circ.u.m- |circ.u.m- | ference. |circ.u.m- | ference.

|ference.| |ference.| -----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 5th cooling| .10 | .53 | .16 | .85 " 10th " | .22 | 1.17 | .34 | 1.80 " 15th " | .32 | 1.70 | .48 | 2.54 " 20th " | .48 | 2.54 | .62 | 3.30 -----------------+--------+-----------+--------+-----------

"_Experiment No. 13._--Wrought-iron hoop, turned and bored, 6 inches diameter (18.85 inches circ.u.mference) outside by 2 inches deep by .375 inch thick, heated to redness, then cooled one-fourth its depth in water (see Fig. 1437 at C for final form of hoop after twenty heatings and coolings).

-----------------+--------------------+-------------------------------- | Top Edge. | Bottom Edge.

+--------+-----------+-------------------+----------- |Contrac-|Percentage | |Percentage | tion. |of original| |of original | | circ.u.m- | Extension. | circ.u.m- | | ference. | | ference.

-----------------+--------+-----------+-------------------+----------- | Inches.| | Inches. | After 1st cooling| .06 | .32 | .02 | .10 " 5th " | .28 | 1.50 {|A hair's breadth | | | {|contraction. | " 10th " | .56 | 3.00 { |Returned to origi- | | | { |nal circ.u.mference. | " 15th " | .78 | 4.14 | .02 contraction. | .10 " 20th " | 1.12 | 6.00 | .02 contraction. | .10 -----------------+--------+-----------+-------------------+-----------

"_Experiment No. 14._--Wrought-iron hoop, turned and bored. 6 inches diameter (18.85 inches circ.u.mference) outside by 2 inches deep by .375 inch thick, heated to redness, then cooled one-half its depth in water (see Fig. 1437 at D for final form of hoop after twenty heatings and coolings).

-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge.

+--------+-----------+--------+----------- |Contrac-|Percentage | Expan- |Percentage | tion. |of original| sion. |of original |Outside | circ.u.m- |Outside | circ.u.m- |circ.u.m- | ference. |circ.u.m- | ference.

|ference.| |ference.| -----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 5th cooling| .46 | 2.44 | .06 | .32 " 10th " | .96 | 5.00 | .09 | .48 " 15th " | 1.34 | 7.10 | .18 | .96 " 20th " | 1.80 | 9.10 | .26 | 1.38 -----------------+--------+-----------+--------+-----------

"_Experiment No. 15._--Wrought-iron hoop turned and bored, 6 inches in diameter (18.85 inches circ.u.mference) outside by 2 inches deep by .375 inch thick, heated to redness, then cooled three-fourths its depth in water (see Fig. 1437 at E for final form of hoop after twenty heatings and coolings).

-----------------+--------------------+------------------------------- | Top Edge. | Bottom Edge.

+--------+-----------+-------------------+----------- |Contrac-|Percentage | |Percentage | tion. |of original| |of original | | circ.u.m- | Expansion. | circ.u.m- | | ference. | | ference.

-----------------+--------+-----------+-------------------+----------- | Inches.| | Inches. | After 1st cooling| .05 | .26 | .015 | .08 " 5th " | .30 | 1.60 | .02 | .10 " 10th " | .56 | 3.00 {| A hair's breadth | | | {| contraction. | " 15th " | .74 | 3.92 { | .02 |} .10 | | { | contraction. |} " 20th " | 1.02 | 5.40 {| .03 | } .10 | | {| contraction. | } -----------------+--------+-----------+-------------------+-----------

"_Experiment No. 16._--Cast-copper ring, turned and bored to same dimensions as Nos. 12, 13, 14, and 15, heated to redness, then cooled half its depth in water (see Fig. 1437 at F for final form of hoop after twenty heatings and coolings).

-----------------+--------------------+-------------------- | Top Edge. | Bottom Edge.

+--------+-----------+--------+----------- |Contrac-|Percentage | Expan- |Percentage | tion. |of original| sion. |of original | | circ.u.m- | | circ.u.m- | | ference. | | ference.

-----------------+--------+-----------+--------+----------- | Inches.| | Inches.| After 1st cooling| .01 | .05 | .05 | .26 " 2nd " | .01 | .05 | .08 | .42 " 3rd " | .02 | .10 | .14 | .75 " 4th " | .02 | .10 | .17 | .90 " 5th " |} No change from | .22 | 1.17 " 10th " |} original size | .40 | 2.13 " 15th " |} from 5th to | .56 | 3.00 " 20th " |} 20th cooling. | .70 | 3.70 -----------------+--------------------+--------+-----------

[Ill.u.s.tration: Fig. 1437.]

"It will be unnecessary to occupy much time in a.n.a.lyzing the experiments, as any one who takes a practical interest in the subject will have full information in the diagrams and tables. Professor Stokes drew attention to the fact that, in 1863, similar phenomena had been noticed by Colonel Clark, of the Royal Engineers. His experiments, made at the Royal a.r.s.enal, Woolwich, were published in the 'Proceedings of the Royal Society,' and Professor Stokes had himself attached an explanatory note, the outline of which was as follows:--

"Imagine a cylinder divided into two parts by a horizontal plane at the water-line, and in this state immersed after heating. The under part, being in contact with water, would rapidly cool and contract, while the upper part would cool but slowly. Consequently by the time the under part had pretty well cooled, the upper part would be left jutting out; but when both parts had cooled their diameters would again agree. Now in the actual experiments the independent motion of the two parts is impossible on account of the continuity of the metal; the under part tends to pull in the upper, and the upper to pull out the under. In this contest the cooler metal, being the stronger, prevails, and so the upper part gets pulled in a little above the water-line while still hot. But it has still to contract in cooling, and this it will do to the full extent due to its temperature, except in so far as it may be prevented by its connection with the rest. Hence, on the whole, the effect of this cause is to leave a permanent contraction a little above the water-line, and it is easy to see that the contraction must be so much nearer to the water-line as the thickness of the metal is less, the other dimensions of the hollow cylinder and the nature of the metal being given. When the hollow cylinder is very short, so as to be reduced to a mere hoop, the same cause operates, but there is not room for more than a general inclination of the surface, leaving the hoop bevelled.

"The expansion of the bottom edge was not noticed in Colonel Clark's paper, perhaps owing to the much smaller hoops which he used in experimenting. Accepting Professor Stokes' explanation of the top contraction, it appears that expansion of the bottom may be accounted for by the reacting strain put on the cooled edge when forcing in the top edge, acting in such a way as to prevent the cooled edge coming quite to its natural contraction, and this, when sufficiently great, expresses itself in the form of a slight expansion.

"_Experiment No. 14._--Forged steel hoop, turned and bored, 18.53 inches in circ.u.mference outside by 2.375 inches deep by .27 inch thick, heated to redness, then cooled one-half its depth in water (see Fig. 1437 at G for final form of hoop after three heatings and coolings).

-----------------+--------------------+-------------------+------------- | Top Edge. | Bottom Edge. | +--------+-----------+-------+-----------+ |Contrac-|Percentage | Expan-|Percentage | | tion. |of original| sion. |of original| | | length. | | length. | -----------------+--------+-----------+-------+-----------+------------- | Inches.| |Inches.| | | | | | {|Cracked at | | | | {|water- After 1st cooling| .06 | .32 | -- | -- {|cooled | | | | {|edge one- | | | | {|third depth | | | | {|of ring.

| | | | | " 2nd " | .12 | .64 | -- | -- | | | | | | | | | | {|After allow- | | | | {|ing for " 3rd " | .20 | 1.08 | .05 | .27 {|three small | | | | {|cracks in | | | | {|bottom edge."

The shrinkage of iron and steel by cooling rapidly is sometimes taken advantage of by workmen to refit work, the principles involved in the process being as follows:--

Suppose in Fig. 1438 _a_ _a_ represents a piece of wrought-iron tube that has been heated to a bright red and immersed in cold water _c_ _c_ from the end B to D, _until that end is cold_. The part submerged and cold will be contracted to its normal diameter and have regained its normal strength, while the part above the water, remaining red-hot, will be expanded and weak. There will be, then, a narrow section of the tube, joining the heated and expanded part to the cooled and contracted part, and its form will be conical, as shown at D D. Now, suppose the tube to be slowly lowered in the water, the cold metal below will compress the heated metal immediately above the water-line, the cone section D being carried up into the metal before it has had time to cool; and the tube removed from the water when cold will be as shown in Fig. 1438, from _c_ to D, representing the part first immersed and cooled. To complete the operation the tube must be heated again from the end _c_ to a short distance past D, and then immersed from E nearly to D, and held still until the submerged part is cold, when the tube must be slowly lowered to compress the end _c_ D, making the tube parallel, but smaller in diameter and in bore, while leaving it of its original length, but thickening its wall.

[Ill.u.s.tration: Fig. 1438.]

[Ill.u.s.tration: Fig. 1439.]