By Wm . Y. BUCHANAN A t the presentation of the au th o r’s last
P ap er1 on sand testing, there was very little discussion, the subject m atter being rather diffi
cult to contradict successfully on a first hear
ing. One or two m embers, however, appeared to be not quite in agreem ent with all the ideas for m odifying or improving the existing generally-used A .F.A . m ethods. Others do not appear to grasp quite why these modifications as suggested by the A uthor are required at all.
D uring the past few years various lines of argum ent have been put forw ard, m ainly with the object of eliciting a clear explanation. In this the author appears for the m ost p art to have failed.
H owever, one very good contribution to the discussion, w ritten privately, is worth quoting extensively as it probably furnishes about the best case for the opposition and may represent the views of others who have perhaps not taken as much trouble to express themselves so clearly.
T he author has always held that, w hether or not the A .F.A . test procedure is m aintained exactly a s . at present, though o f considerable im portance, is nevertheless not so im portant as the fact th a t if used in its present form , the interpretation o f the test figures and their appli
cation to foundry practice should be carried out having due regard to the inherent defects in the design of the test-piece and other influences to which the m ethod o f ram m ing is subject at all times. These defects in design and influences affecting the form ation of the A .F.A . test-piece, which tend to perform the function o f the red herring in the well-known adage, have been clearly dem onstrated With extensive experi
mental evidence in the author’s previous Papers on the subject.
A W ritten Criticism
The extracts from the w ritten discussion already referred to are given below in p ara
graph form for convenience of reference in the reply.
Paragraph 1.—“ . . . . In the first place I would like to underline several sentences in
the Paper, such as ‘ Sand testing is am ong the most difficult form s o f m echanical testing to perform with the degree o f precision one associates with the m echanical testing of metals.’
‘ T he subject is not one to be tackled by m ere deduction and argum ent.’
‘ Sand testing is by no means above am biguity.’
‘ The ra te of loading does not seem to have any effect on the com pression strength.’
‘ Since the A .F.A. test piece is most com monly used by those in the committees deal
ing with the m atter, it m ust be accepted as the standard for general use.’
‘ The A.F.A. procedure may be referred to as a test-piece made by a standard ram m ing machine, where the machine only is standard, the degree of ram m ing varying with all con
ditions.’ ”
Paragraph 2.—“ It is very difficult to give a close definition to such terms as ‘ Standard R am m ing ’ and ‘ Degree o f R am m ing,’ and this accounts for much o f the am biguity and misunderstanding. To my mind, it is suffi
cient to regard the A.F.A. ram m ing procedure as a ‘ standard m ethod,’ and to assess the results accordingly. Provided this attitude is adopted I think the A.F.A. procedure is satisfactory, and there is no need for the com plications of the ‘ Index o f R a m m in g ' with its need for the determ ination of the true density of every sand m ixture tested.”
Paragraph 3.— “ I understand that the index of ramm ing is used to calculate the green apparent density to which a sand should be ramm ed so that each test-piece contains the same volume o f dry solid m atter regard
less of moisture content, grain size, dis
tribution bond, and specific gravity. Thus, with a sand of uniform grain-size, each test piece would always contain the same num ber of sand grains no m atter what the moisture content.”
Paragraph 4.— “ I agree that a good m oulder will tend to control the energy of his ram m ing so as to produce the required results (e.g., 125
high perm eability here, high strength there, always understood th a t flowability increased with m oisture content, yet in Fig. 9 you show portions for com pression testing purposes, etc.
T he flowability o f the sand greatly influences the entirely by com pression strength because plasticity is also an im p o rtan t factor, and although these properties are closely connected they m ust be assessed separately and problem s connected with them investigated experimentally.
Fig. 9 o f the last P ap er shows the relation between flowability, com pression strength, and deform ation.
others too high to have any relation to useful m oulding sands, the trend of the tests in these extreme ranges would help to clarify con
clusions in m ore norm al ranges of moisture.
The present A uthor doubts w hether there is any practical significance in this line of re
search, since in no case is a m oulding sand com posed of clay-free m aterial and clean water.
Even the case of loam , which has been brought in, w ith its excessive m oisture content consists of grains o f sand and a thin slurry of clay wash.
Conclusions and research on m oulding sand testing should, however, n o t be based on work done on loam , as the conditions in loam are unusual and no t in the least representative.
H owever, it has been suggested that this line of • w ork, i.e., the effect of w ater additions to clay-free sands, would provide some proof of the intrinsic value of the A .F.A. m ethod of m aking the test-piece, and some very definite conclusions were arrived at. F o r example, that silica and other clay-free sands w ould not ram any harder with increased moisture.
type of sand. W ith three blows of the A .F.A . ram m er, this sand is inclined to be over-ram m ed, and it would not be surprising to find the flow- ability o f the sand m asked in these tests.
Fig. 1 shows a series o f test-pieces m ade by the A.F.A. standard ram m er, using three blows, and repeatedly using one blow to give lighter ramm ing. Since the same sand is used through
o u t the series, the true density is the same throughout, and so the Index o f Ram m ing can be retained constant by keeping the dry apparent-density o r dry weight o f the test-piece constant with increase in m oisture. T he green- strength and perm eability num ber will, of course, follow the trend o f the change in weight of the dry test-piece, so the graphs of the dry weight of the test-piece against m oisture are sufficient for the present purpose.
It will be seen from the dry weight th a t the degree of packing is greatest at 0 per cent, m oisture, and th at from 0 to 6 per cent, the m oisture progressively reduces flowability, when it begins to rise again up to 12 per cent. Here,
¿oad. ^ / / / / / / / / / / / n n n t t / / / / / / / / , / / / / / / ,
/'*nn—*1 s a / v d ; , : J*
/¿UOLQs
&
ki/i
ft
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M O I S T U R E %
Fi g. 1.— Ef f e c t o f Mo i s t u r e o n Ir v i n e Se a Sa n d r a m m e d b y t h e A.F.A. Ra m m e r, s h o w i n g Co n s i d e r a b l e Ch a n g e o f Fl o w a b i l i t y.
This, of course, is in direct contradiction to the underlying idea of the present author’s statem ent that the A .F.A . test-piece is at all times subject to the effect of flowability in the sand being tested, since here is an example of a sand which, though not a legitimate example o f a m oulding sand, yet is good enough for the sake of the argum ent. In D earden’s example he found that, though the A .F.A . test-piece made in the standard way increased rapidly in weight over 2 per cent, moisture, the dry weight of the test-piece rem ained constant; th at this increase was due only to the additional weight of the water. This, in effect, m eans th at he concluded that the sand had a constant flow
ability.
The present A uthor checked this, using Irvine sand for com parison, when it was found that a distinct flowability was present even in this
Fi g. 2 .— Di a g r a m o f Ky l e’s Fi r s t Me t h o d o f Me a s u r i n g Fl o w a b i l i t y o f Sa n d.
then, is distinct evidence of a flowability change, and where the effect of m oisture alone was to be studied there is a com bination o f the flow
ability effect and the true m oisture effect in the A .F.A. test results and conclusions draw n there
from. The effect of m oisture on the other types of sand given in D earden’s P aper have been covered in a previous Paper by the present A uthor, in which the need for separating the true effect o f m oisture from the flowability effect is shown, and there seems little need to repeat it here.
Flowability
Flow ability is the property which enables sand to flow throughout the mass when ram ming energy is applied to the outside of th a t mass. This .property is possessed in a varying degree by all m oulding sands, and m ust be con
sidered in relation to m ould finish and freedom
1 2 7
from voids or loosely packed areas, w hich in turn cause roughness o r even ragged projections o n the casting due to m etal penetration. Very high flowability is found in oil sand, bonded with, say, pure linseed oil and very low flow
ability in certain types of heavily-bonded
“ steel ” sands.
F o r m achine m oulding, using well-finished pattern plates, a sand having good flowability is essential, otherw ise m uch additional hand- m oulding will be required on w hat should o th e r
wise be a finished mould. In addition, low flow
ability will greatly increase the effort required in ram m ing the m ould, w hether by hand, jolting m achine, or jolt-squeeze machine.
T he only Papers dealing w ith the subject of flowability, a p a rt from the A u th o r’s work is th a t o f K yle w hich appeared recently in the A .F.A . publications, and that o f D ietert and F. V altier, also in the A .F.A . publications in 1934. This Paper by Kyle is well w orth study
ing because he has no t merely quoted available data but has set ab o u t the study of the subject independently, and the value o f the P aper to the foundry industry is enhanced by the scarcity o f sim ilar independent research from other sources. W hile the present A u th o r w ould not care to recom m end the m ethods pu t forw ard by Kyle for m easuring flowability in foundry practice, the value o f the w ork in the Paper is no t detracted from on th at account.
In this Paper, the suggestion is m ade, or inferred, that flowability has two distinct phases, first, the flow o f the sand as force is applied during a m oulding operation; and second, the flow of sand due to the weight of m olten m etal in the m ould during casting. This point o f view is rather interesting but its developm ent into any real practical application m ay be quite a different m atter because the principle u nder
lying this idea would m ake it possible to have a set o f conditions where a sand would flow readily under pressure of the metal at a later stage. These preparations are contradictory, because a good flowability during m oulding would hardly disappear later unless ram m ing was reasonably near the lim it and at best the second stage o f flowability is merely the com pletion o f a m oulding operation. On that account the m ethod proposed by D ietert has some theoretical interest because the hardness can be recorded after each successive blow of the ram m er and the degree o f ram m ing carried to any extrem e. W hile this m ethod m ay give d ata o f theoretical interest prim arily, as co n cerning the behaviour o f sand u nder a particular set o f conditions, the present A uth o r has always contended that the D ietert and V altier m ethod was not representative o f foundry practice so far as m oulding is concerned. It would, no doubt, furnish som e inform ation if a particular
m ould were ram m ed to a hardness equivalent to the A .F.A . test-piece m ade by fo u r blows of the ram m er, in w hich case the probable tendency to swelling under m etal pressure would be indi
cated by the reading o f flowability obtained.
K yle describes three m ethods for m easuring flowability: (1) A hardness gradient m ethod of his own design; (2) a hardness differential m ethod som ew hat sim ilar to the present A uth o r’s
Fi g. 3 .— Co m p r e s s i o n Te s t i n g Ma c h i n e s p e c i a l l y m a d e f o r De f o r m a t i o n Te s t s.
m ethod; and (3) sand m ovem ent m ethod as used by D ietert and Valtier. T he third m ethod was used by Kyle to get com parison with the other two m ethods on which he was working.
It should be noted here th a t the present A u th o r’s m ethod was put before the Institute’s Sub-C om m ittee on Sands at least two years before D ietert’s sand m ovem ent m ethod was
published and it m ight usefully have been con specific variables like moisture, the test-pieces can be m ade to the same Index o f Ram m ing.
T he exact degree o f ram m ing o f any m ould or p a rt thereof can thus be reproduced for the determ ination o f flowability if required.
Flardness T op necessary for sands intended for squeezing m achines on the one hand and jolting m achines on the other. The test-piece m ade by com pres
sion as described should cover both.
K yle does n o t consider th a t it is likely that
First Method of Measuring Flowability as Used by Kyle encountering the above-m entioned phenom enon the m ethod was shelved. K yle's test is evidently
T hen the sand was dried to 6 per cent, m oisture and the tests w ere:— 2,390 gm.; 2,452 gm., and 2,515 gm., showing a decided in
crease in weight as the m oisture fu rth e r de
creases. T he size o f the sam ple m akes it diffi
cult to keep the m oisture constant during test
ing. T he figures clearly show th a t the m ethod of filling introduces a very im portant variable, before the ram m ing force is applied fo r the
T a b l e I I .—Author's Sand Tests showing Agreement, in
A nother point in connection w ith K yle’s test, is the necessity for draw ing a graph which m ight be elim inated by m erely using the h ard ness m easurem ents at the top and bottom , which give the sam e inform ation as the graph. In this case, the test would become m uch the same as th a t o f the present A uthor, except for the variation of weight with m oisture as referred to above. T he sam e m ight apply to any variable Duplicate Tests. D ry Sand Sampled on December 26, 1940.
ixture 2£ barrow s black sand (95 per c e n t.); 1 shovel rock sane B entonite (1 .4 per cent.)
(3 per cent.) ; and 10 lbs.
M oisture 8 . 2 per cent. ; 8 . 0 per cent.
Averages.
8 . 1 per cent.
Perm eability .. 9 .8 cms. 31 secs. . . ■•'L9 9 6
9 .8 cms. 31 secs. . . . . J 99 .6
Green strength (compres
sion)
2 1J lbs. 2 0J lbs. 2 0J lbs... 6 . 6 8 lbs. per sq. in.
Dry strength (compression) 440 lbs. 460 lbs... 143.3 lbs. per sq. in.
D eform ation (W.Y.B.
m ethod)
50 51 52 51 50 ... 2 5 .4 thous. or 0.0254 in.
per in.
Flow ability (W.Y.B.
m ethod) B ottom 42 46 48 46
FI owability. K yle’s m ethod. A.F.A. te st piece, 1 blow £ in.
Top 74 75 73 75
B ottom 51 52 51 54
Top 71 73 75 74
Bottom 47 46 52 52
Top 76 76 77 78
Bottom 52 52 53 54
Top 74 76 73 74
Bottom 52 52 52 51
Top 75 77 77 78
Bottom 48 48 50 51
Top 80 79 82 82
Bottom 18 18 19 18
Top 34 39 37 35
Bottom 18 18 17 2 2
Top 37 39 40 41
Bottom 19 21 2 0 19
Top 37 36 34 39
Bottom 9 12 10 14
Top 25 35 34 33
Bottom 9 8 15 12
Top 26 34 31 29
Bottom 9 11 13 2 0
Top 42 33 41 38
61 .3 per cent.
= 70.8
= 64.2
= 71.0 67.3
= 60.9
= 5 0.3 per cent.
= 4 7 .S 54.1
= 35.9 36.7
= 3 4.4
65.9 per cent.
43.2 per cent.
flowability test proper, and this point should be kept in m ind. The error is likely to be accum ulative a t times, and when it is so, it will give an ap p aren t sensitivity to the test-piece w hich m ay prove misleading. T he only way to elim inate this factor, is to use the Index of Ram m ing m ethod of determ ining the weight of sand to be used fo r each test.
affecting flow ability such as clay and the like, the flowability o f the sand would be seriously affected by the w eight o f sand for the test, and this w ould be distinct from the flowability of the sand under pressure during test, although the test-graph obtained w ould be the result of their com bination. T he application o f so heavy a load to the m ovable p a rt of the test would 130
require a large m achine and probably a som e
w hat critical rate of loading.
Second Method for Measuring Flowability used by Kyle flowability expressed by these consecutive tests is variable— the range being from 48 to 68 per cent.
T he effect of the degree o f care w ith which the ram m er is lowered was found to have a considerable influence on the figures, thus:—
T o p 39 43 42 42 1 . , , . co „
Third Method of Measuring Flowability used by Kyle
T he green-strength alone is unsatisfactory, and m ay indeed be definitely misleading, be
ciated with additional patching, which itself will be difficult to accom plish for the same reason.
Author’s Method for Deformation Determination loose pointer, and this applies more particularly to the deform ation test.
(3) W ithout moving the load screw, the com pression plate o f the m achine is then depressed in order to allow the introduction of the 2.000
131 k 2
in. gauge. This operation brings the pointer of the spring balance to a m uch higher reading, and, by rotating the load-screw carrying the m icrom eter, the pointer o f the spring balance is returned to the exact reading of the m axim um strength already noted. T he difference in these m icrom eter readings between the m axim um - com pression reading on the deform ed test-piece an d the spring-balance reading when the 2.000 in. gauge is substituted is the deform ation, ex
cept for the necessary length correction, as the A .F.A . test-piece is, o f course, never exactly 2.000 in. T he prelim inary length m easurem ent furnishes by com parison w ith the 2.000 in.
gauge the correction to add o r subtract.
T he plates o f the m achine m ust a t all times be quite free fro m grains o f sand, as these in
troduce errors in m easurem ent. T he slides of the com pression m otion m ust be quite free, as even a slight friction will readily introduce errors in the m icrom eter readings. T he test- piece should be well form ed, w ith the faces parallel, and have no ragged edges likely to crum ble in handling and so introduce grains o f sand between the test-piece and the com pression plates. H ow ever, w ith these precautions, which, after all, are an every-day necessity in all cases o f m easurem ents of these dim ensions, duplicate tests give very close results.
The A .F.A . test-piece, if m ade by the stan d ard drop-w eight, should be m ade as already indicated, w ith the tube floating on the third blow, an d if the tube has a slight clearance on the ram m er head, a horseshoe-shaped distance- piece, such as described in previous Papers, should be used in order to hold the tube quite vertical during the first and second blows, and thereby ensure th a t the test-piece faces are quite parallel. A distance-piece of ab o u t | in.
thickness seems quite sufficient for the purpose.
Exam ples of duplicate tests on the same sam ple o f sand gave the follow ing deform ation on 2 in.— 55, 54, 56, 54, 53 thousandths when carried ou t after one d ay ’s practice w ith the apparatus.
T able II gives a series of tests as used by the present A uth o r carried ou t on one sam ple of sand w hich was kept in a m ixing drum th ro u g h ou t the testing in order to elim inate drying, an d this procedure is strongly recom m ended.
Preparation o f the Sam ple
T he sand was mixed in a N o. 2 Simpson m ixer, aerated, pu t through a 1 in. m esh riddle, and transferred to the mixing drum fo r testing.
M oisture
T he m oisture percentage was obtained by direct weighing after drying.
M a kin g the Test-piece
T he test-piece is ram m ed by the m ethod
T he test-piece is ram m ed by the m ethod