By Wm . Y. BU C H A N A N .
T he m aterials used in m anufacture of black
ing have been listed at great length elsewhere, including m any form s of carbon m ore or less rare, and, for that reason expensive, but usually the base m aterial is coke breeze and possibly som e additions of fireclay.
W here fireclay is added, it is usually the custom , especially when subsequently mixed by hand, to m ake no further additions except water in the m aking o f blackwash. The author has for a num ber of years used blacking m ade from coke only and added to the resultant black- wash such m aterials as bentonite, Colbond, dex
trin, semi-solid core oil, coal dust o f high volatile content, and even crude oil. The object of the bentonite, C olbond, dextrin and core oil was to prevent the blacking rubbing away readily after drying, although the core oil acts in a m anner different from the clays. The coal dust was used with the same object in view, it being intended that at the drying tem perature the volatile m atter would be driven off and during the process a slight coking or crusting would take place.
Special additions such as alkalis, intended to im prove the suspension of the clays in water, were not used owing to their corrosive action on the mixing tank, but crude oil was tried because o f its action on coke dust, as in the froth flotation process. The application of this crude oil is only possible when an emulsi
fier is used in the mixing process such as is described later in the Paper.
Coke has a specific gravity of about 1.3, i.e., very near to that o f water, is by nature very hard and abrasive tow ards metals even when finely ground, has a low percentage of volatile matter, high fixed carbon, and usually low ash.
Blackwash consists essentially of blacking and water plus additions, varying in concentration from a thin liquid to, in some cases, a heavy mud.
Method of Mixing
Coke dust itself tends to settle in w ater and constant stirring becomes necessary during use.
U p till recently, the usual method which has
been practised w ithout variation for genera
tions consists of a rectangular tank or trough in which the blackwash is mixed and stirred by pushing backw ards and forw ards a wooden rake with a long handle and probably some holes in the blade. The dry m aterials are slowly added and stirred in. T he m oulder always stirs the liquid before removing a bucket
ful for his own imm ediate use. By this means the liquid is always draw n from the top and has a tendency to concentrate as the level drops.
It is, o r was, the usual practice to mix this
F ig . 1.— B a r r e l M i x e r . A, D r i v i n g G e a r ; B, S t i r r e r ; C, B a f f l e s ; D , P a d d l e s .
blackwash in considerable secrecy using various personal tests, such as dipping the hand into the blackwash and observing this as it dried with “ the air of a chef.” M any additions were made, of course, such as clay w ater m ade from com m on red clay, and the preparation of the blackwash m ight occupy a m an’s tim e equiva
lent to about 8 hr. per week for a foundry em ploying 60 corem akers and moulders on dry sand and using two mixed lots o f about 50 gal.
each.
Mechanical Mixing
The au th o r’s experience of this problem covers a num ber of years, and details o f m ethods actually tried out are included in the follow ing notes. T he first type (shown in Fig. 1) consisted o f a b arrel and stirrer. W here an overhead shafting is available for pow er drive, a barrel o r circular ta n k is fitted with a sim ple type o f stirrer and suitable gearing, and preferably a fast and loose pulley. Baffles are fitted to the sides o f th e vessel to assist m ix
ing and prevent the liquid from swirling round bodily, as it thus tends to climb rath e r high
Since the liquid is in this case draw n off from the bottom , and since the heavier liquid comes off first, the blackwash becom es thinner as the level falls. The upkeep on this barrel is n o t excessive, being m ainly due to corrosion, wear, and perhaps the neglect of lubrication o f the gearing and bearings which readily becom e con
tam inated w ith blacking dust.
Wet Grinder Type o f Mixer
T he m achine show n in Fig. 2 first appeared in fo u n d ry advertisem ents ab o u t 1 9 3 3 o r 1 9 3 4 ,
and was p u t on the m a rk e t by the B ritish
“ Rem a ” M anufacturing C om pany, Lim ited.
Fi g. 2 .— Mix in g Ma c h in e d e s i g n e d b y Br i t i s h ‘ Re m a ” Ma n u f a c t u r in g Co m p a n y, Li m i t e d.
a t the outside. A draw-off cock is provided at the bottom o f the barrel or tank.
This type of apparatus, w hich is essentially a stirrer, presents some difficulty in first o btain
ing a solution, as the partly-m oistened m aterials tend to build up heavily on the baffles. W ith constant scraping down, the liquid becomes sm ooth and uniform , and, so long as the m ove
m ent continues, tends to rem ain so, bu t if allowed to settle overnight o r week-end, the m ass becomes solid in the bottom and extremely difficult to start up.
It consisted o f one or two tanks and a system o f piping an d valves fo r d raw ing liquid from the bottom o f the tank or tanks and passing this th rough a wet grinder unit, then delivering it to the to p o f the tank.
The m achine was belt or m o to r driven. It appeared to be very suitable fo r m aterials in which a m ixing and grinding action w as re quired. T he claim s m ade fo r it were th a t it produced 40 gal. of high grade blacking or other facing m aterial in 15 m in., an d there can be little d oubt th a t this o u tp u t w ould be 42
achieved. T he m achine was advertised as being in several sizes, bu t the author has no experi
ence in the operation of these machines.
Emulsifier Type of Mixer
W ith the w et grinder type of m ixer in mind the author had a plant constructed on a similar system, replacing the wet grinder unit with a centrifugal pum p of the “ chokeless ” type, i.e., one constructed to pum p liquids in which an occasional solid piece o f overall size up to 2 in.
entered the pum p and subsequently went through the system. The reason fo r having this m achine constructed was that the materials used were ground and graded and therefore did not require fu rth er grinding.
T he early trials of this m achine fully justified the expectations, so m uch so th a t the m akers m anufactured a num ber of m achines for other foundries, and an illustration of one of these m achines appears in a Paper by R. F. Hudson*
and illustrated diagram m atically in Fig. 3. The tim e fo r filling the tank, adding the dry m aterials, and mixing com pletely was 19 min.
for 50 gal. o f water, plus other materials, m aking in all about 60 gal. o f blackwash.
The action o f this system seems ideal, and by keeping the delivery tube close to the side of the tank and fitting a right angle bend the stream of liquid round the side of the tank sets up a rapid whirlpool effect with a large vortex in the centre. The advantage of this right angle bend which was a later addition to the m achine and the resultant whirlpool was that dry m aterials which norm ally float and do not wet quickly on a quiet surface in this case swirled round once or twice and then shot down the vortex, when it was immediately dispersed in the pum p.
F o r a considerable tim e no mechanical trouble was encountered, and the usual practice was to mix the blackwash in the tank nearest the pum p and deliver to the outer tank for storage and use; a new lot being always ready to follow the one nearly finished. W here black- wash had been unintentioflally allowed to settle in the pum p or occasionally due to severe frost and lack o f shop heating during winter holidays, great difficulty was of course encountered in starting up.
It was usual to put the m achine on mixing at the beginning of the shift, and possibly after the luncheon interval, for a few m inutes and as would be expected, when the mixing process was not in operation for any length o f tim e the small lots drawn from the tap tended to become heavy and consequently the blackwash got pro
gressively thinner. M oulders were instructed to empty their blackwash buckets back into the tank so as to clear out the heavy cake which grows on the bottom , in the interests of
•Proc. T.B Vrl XXX, 1936-37, D .570
econom y, bu t unfortunately they sometimes forgot to remove the hem p swab before doing so, an d this caused the partial dism antling of the tubing to get the system freed again. To guard against this a w ire grid was suspended below the surface level of the liquid, but after a tim e this was discarded as it impeded the m ix
ing process.
W ater was connected to the tanks fo r con
venience, and it was soon observed that with the plug cocks closed w ater leaked quickly from one tank into the other. The w ear was due to the action of the blacking between the sliding surfaces, and when this leakage developed the plug cocks had to be renewed.
T he pum p impeller, although very robust, also wore out and, o f course, the efficiency dropped, off considerably before com plete
re-D
Fi g. 3 .— Em u l s i f i e r Ty p e o f Mix e r. A , 7 0 -g a l. Ta n k; B , 2 -i n. Ch o k e l e s s Pu m p; C , 2 -i n. Tu b e f o r Cir c u l a t io n; D a n d E, Sh u t-o f f Va l v e s; F , Ri g h t-a n g l e Be n d; G , Pa c k in g Gl a n d; a n d
H, Wh i r l p o o l Ac t io n d u r in g Mi x i n g.
newal was necessary. It is possible th a t ex
tremely rapid mixing m ight have been sacri
ficed in the interests of longer life and less repairs, because the pum p seemed to deliver the blackwash under considerable pressure, i.e., m uch m ore than was strictly necessary. The m ost serious trouble from wear, however, arose from the difficulty of keeping the pum p spindle packed tightly. Even w ith frequent renewal o f the packing, the spindle becam e w orn u n evenly into grooves— and the leakage was there
after constant in spite o f frequent packing.
W ater tended to leak away, the m ixture became concentrated and the surrounding floor was always covered with blackwash.
I t m ay be argued th a t the savings in wages for m ixing tim e as com pared with hand mixing w ould allow o f replacem ent parts being bought a t reasonable intervals. On the other hand, special m aterials m ight be used in order to give increased w ear resistance. H ow ever, it seems safe to say th a t in m ost foundries the mixing tim e by hand, even though excessive, would excite less attention than regular appearance of invoices fo r replacements.
On considering this m atter of replacem ents carefully, it becam e obvious th a t the six plug cocks were a source of trouble, which was a m atter o f individual design a n d /o r elim ination w here possible; secondly, th a t the leakage at
age o f w ater from one tank to an o th er causes trouble in mixing.
A plain type o f valve, such as is used for heavy oil (Fig. 5), would be m ore suitable, p ro vided it has a leather o r rubber w asher to ensure a tight joint when closed. If the bore a t the sm allest p a rt o f this valve is kept as large as possible, say a t n o t less than 2 in., there w ould be little tendency fo r it to choke ur> an d less need to clear it by pushing a rod o r wire through from outside, as is required occasion
ally in the case o f the plug cock valve.
T here is an alternative type, intended for corrosive liquids, in w hich a ru b b er tube is in
corporated in the pipe line, an d the valve
FIG.8.
Fi g s. 4 -8 . - Fi g. 4 , De s i g n o f a Co m m o n Pl u g Co c k w i t h a Re s t r i c t e d Bo r e t h r o u g h t h e Pl u g; Fi g. 5, Va l v e s u i t a b l e f o r r u n n in g o f f Bl a c k w a s h; A , Va l v e Se a t i n Ri n g Fo r m; B , Ru b b e r Wa s h e r. Fi g. 6 .— Ci r c u l a t io n b y Co m p r e s s e d Ai r, In j e c t o r Ty p e. Fi g. 7 .—
Cir c u l a t io n b y Co m p r e s s e d Ai r, Si m p l i f i e d Ty p e. Fi g. 8 .— Cu p Vi s c o m e t e r; O , Or i f i c e- T , An n u l a r Tr o u g h.
the pum p spindle would be due to the head of w ater acting, and consequently, if the pum p were raised, this leakage w ould be reduced. If, on the other hand, the pum p were eliminated altogether, the trouble would disappear.
Types o f Control Valve
The plug cock type o f valve (Fig. 4) is the com m onest on the m arket, b u t is n o t suitable fo r blackw ash. T he action of turning off the liquid smears the blackwash into the space be
tween the m achined surfaces, thus wearing a ring clearance through which w ater can bypass round the plug in the closed position. W here tw o tanks are connected to a pum p, this
leak-principle sim ply depends on the pinching o r flattening o f the tube. It m ight, how ever, be assum ed that the ru b b er w ould “ perish ” in tim e, and w ithout an actual trial it is impossible to say w hether the life obtained w ould be any im provem ent on th a t o f the other valves.
Compressed-Air Mixing
D uring repairs and tem porary breakdow n intervals com pressed air was used in mixing, using a com m on 36-gal. w ooden barrel to m ix and contain the blackw ash, into w hich was th ru st an iron pipe connected to the air supply by m eans of a rubber hose and the usual off-on control valve.
44
The mixing, after the prim ary wetting of the time eliminating the undesirable features. The com mon wooden barrel is really too small for obstruction when necessary. This alone would be a welcome im provem ent on the high-speed circulating pum p system which tended to pack the sedim ent harder, and after a week end there was often considerable trouble in restarting.
The experim ent with the injector type of system was followed by a sim pler design, which consisted of a jet of air introduced at the bottom of the vessel o f the same conical design.
The airline was fitted with a small screw valve of suitable design which incorporated rubber valve-facings. This allowed a very low air- consumption, the movem ent of the liquid being just sufficient to prevent continuous settling while the blackwash is being used and at the
irrespective o f price and afraid to m ake any careless interpretation o f instruction regarding weights o f m aterials given to workm en.
Specific gravity is the first obvious m ethod and several form s of hydrom eter, including som e specially m ade, were tried but these were discarded, being found very unsatisfactory since the hydrom eter usually failed to respond to avoidable w here these m aterials themselves have such a low specific gravity. efficient deterrent on carelessness in m easure
m ent o f m aterials used. T he m anipulation o f ce ntration affect the viscosity reading consider
ably. I t was fo u n d th a t w ater gave a reading o f 10.4 seconds an d consequently as the graph appro ach ed this figure large additions o f w ater would m ake less difference. H ow ever, a t n orm al concentrations the viscosity test is very sensitive.
T hough som e foundries use a m u ch heavier
Clacking found by calculation, as in the follow his blacking w ithout frothing?
It was stated also th at most blackings were reasonably good results. Probably this would be considered to be an advantage in the case application, he thought, depended upon indi
vidual practice. of bentonite in suspension was reduced.
If there was an addition of a thin oil to the blacking would it serve the same purpose?
47
W hat w ould happen, w hen using a heavy
Preparation o f Thick Blacking
Mr. H . H a y n e s inquired w hether Mr. pound-foolish. U nfortunately, h e was respon
sible fo r both ends o f the problem ; the castings going ou t as well as the m aterials bought for the facings. T h erefore he could n o t m ake a good show ing in one d ep artm en t an d p u t blam e on som ebody else in another. H e had to shoulder the responsibility in both cases.
T he question o f w hether the sand w ould peel which were no t particularly effective.
A nother point he w ished to m ake was that
he heard o f someone else trying it first. The soda contam ination o f sand was one o f the worst m aterials for reducing refractoriness. H e would like to hear of salt being tried on at least a small scale. Salt m ight contam inate the floor sand for a long time, and then perhaps unexpectedly its refractoriness would be reduced and it would have to be renewed. He was thinking of tests at elevated tem peratures.
M r . H a y n e s said he had tried salt w ater on a casting which cost £300 to make. It was as blue as any casting could ever be expected to be. T he practice had now been introduced throughout the foundry, and salt was a regular constituent of the blacking. T h e core-man could rub his jacket against the side o f a mould and not rub off any blacking. This was the reason why he had m entioned the point con
cerning sea-water acting on the sand in his con
tribution to the discussion of the American Exchange Paper.
Mr. Bu c h a n a n w a s p l e a s e d t o h e a r o f a la r g e
-scale confirm ation of the statement. H is point was th at he was scared of its ultim ate effect on the sand. If there was a reasonable certainty that there would be no deleterious effect, he would certainly try the m ethod, as it was rather novel, but would have to bear in m ind the ulti
m ate effect rather than the effect on any p arti
cular casting. His own practice, however, did not call for m uch im provem ent in cost or results.
M r . H a y n e s said he used an ounce o r H ounces of salt to a q uart of water, and he sug
gested to Mr. Buchanan he should try it in his m ixtures and ascertain how the m ethod worked.
Vote of Thanks
U pon the proposition of M r . H . W i n t e r t o n , seconded by M r . F. A. H a r p e r , a hearty vote of thanks was accorded to Mr. Buchanan for his extremely interesting Paper.
M r . B u c h a n a n responded.
49 E