BCIRA copper cast iron .pdf


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errher

SOz

. [O] +

The acid-caralysis mechanism

5Or

- the hoFbox processj
tor

SOlrH1O+HrSOi,
+

HrSOr

. [O] +

H2SO(

5O2 + HzO

or

H?SOr

H'+

to study the thermal decomposition products of

I

.'_-],.'_-

(ll

tr,,
+r-zc

OH
tl

t

6

acid by oxidation of the sulphur dioxide. The acid initiares
rhe curing ofthe phenolic furan lesin in the same way as in
the acid-catalysed cold-setting binder systems. Suggested
reactions for the curing of SQ,-hardened moulds are shown

'',)->/cH,
|
!l

\-2

Y

cHrOt-r

cH20H
.esrn

Further choins

(c) Acid-caloltsed cure of resin -Crossltnked

Fit. l9 SuSgcstcd rcactions

'fhc reaction involvcs the rr.riar production ofsulphuric

15 )

O l-i

t?-r.c', y'>"
. I ll +
.l

mixture. Currenrly, methylerhylketone peroxide is used.
The sand mixture has a bench life of several hou$, but is
hardened in a marter of seconds, when sulphur dioxide gas
is passed through it.

(see Frg
OH

cured

Furan biaders hardened by sulphur dloxidc gasThis process employs a phenolic furan (PF/FA) resin ;hich
is mixed with sand. A peroxide solution is added to the

OH

-

as

phenolic resins.

HSOi,

(b) D;ssocialion oJ sulphuric acid

cH2oH . H+

rhought to be rhe same

as shown

(protons), it is also involved directly in the curing reactions.
Several complex aromatic compouods containing sulphur
have been found by mass spectrometry, in work at BCIRA

(o) Fonnatioa ol sulphuic ac;d (in sittt)

llzsol .+

is

in Fig. 15, panicularly
whcn inorganic acids are uscd. I{owever, whcn ihc organil
sulphonic acids are uscd there is the possibility thar an
alternative rcaction, shown in Fig, 18, may occur. In rhis
reaction the organic acid would not be acring as a true
catalyst, for although it does supply hydrogeu atoms

from methyl ethyl ketone percxide

in thc curing of

dioxldc-hardcncd phcnolic furan rcrinB.

-

in Fig. 19. The sulphur dioxide gas is consumed in
providing the sulphuric acid catalysr and therefore, if rhe
gassing procedure is carefully controlled, only very limired
air-purging of the hardened core should be required to
remove surplus sulphur dioxide, before the corc is r€moved

sulphut-

resins. As curing procecds, similar reactions occur betwcen

the same type of reactive groups, but the molecules
involved are considerably larger and more complex,
consisting of several interlinkcd phenol, urca and furfuryl
alcohol moleculcs. A typical structure for pan of a cured
PF/FA resin is shown in Fig. t7.
The strong acid catalysts used with cold-setting binders

from the corebox.
Sulphur dioxide rx thc purge air and in air cxtractcd from
around thr corcbox by local vcntilation is easily rcmoved by
the use ofchemical scrubbers, in which rhe aiidic sulphur
dioxide is adsorbed and neurralized by sodium hvdroxide
solution.

can be

Urcthanc bladcr systcmr
Phenolic-isocyaaate cold-s,et lrtoceaa The main
binder materials consist oftwo parts, a phenolic resin and a
diisocyanate (M.D.I. diphenylmethane diisocyanate). A

acids, Frequently

thc phenolic component of the mixturc and the binder
components are mixcd with sand. The amine catalvses the

either strong inorganic acids such as phosphoric acid
nnd :rrlphrrric ncid, or rtrong organic ocidr rrrch lr ltorq.
toluenc sulphonic, benzene sulphonic and xylene sulphonic

in

commercial catalysts supplied to

fou-ndries, combinations of the above acids are used,

tcrti$ry |l|ninc corolyrr, phcrrylpropylpyridinc,

ir

addirion reacrion berwe€n the hydroxyl groups

uddcd to

(-bH) ol

In aikyd_oil/ isocyanats binders th€ crosslinkihg reactions occur between tho unsaturated ethylonic linkages of the linolenic acid component oI the
cil and the isocyanac group. The glyc€ry|-phthalate ester groupings play no part in lhese reactions and 60 are not shown in d€tail.

P

CHt-CH2

-CH:CH

-CH2-CF.|

II

:CH-CHr-CH:CH-(CH2)?-

C-O-gtyceryl

phtholote group

'+

ocN-R

ocN- R-

-NCo

NCO

I

I
CH3-

CH2

-CH:

CH

CH

CH- CH:

N_H

N-H

- tl -CH:CH -

CH

-

(CH2)7

-

C

-O -

glyceryl phtholote group

I

I

R

R

I

NCO

R represents the diphenytmethone
port ol the diisocyonote

HCO

(-NCOI groups can then re6ct with olher linolonic acid chains to form crosslinks b€tw€€n th€ alkyd oil chaiN, snd 30
form an interp€notrating n€twort polymsr.
Thes€ psndent isocyanate

Flg,20 Rc.crlon of .n ellyd oll
May 1983

elth. dlbocy.lat..
153


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