Note: Descriptions are shown in the official language in which they were submitted.
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The abrasive material blastin~ mdchine used in the sand
~lasting process i8 designed to blast particles o~ a~raslv~
against a surface to be cleaned, the impact produced being
e~ective to remove rust and the like from the surface.
As for the abrasive materials~ silica sand and slag are
chiefly used. However9 silica sand and s~ag are brittle and
generally have many cracks in their surfaces~ so that upon
striking the surface to be clec~ned, th~y breaX into fine
pieces, producing a large amount of dust. Therefore, the
blast clec~ning operation~ if carried out in the open air,
would greatl~ i~fluence the nearby housing environment,
forming a cause of enviro~mental pollution. ~here is another
serious problem, nc~mely th~t tha health of the workers who inhale
such dust is endangered.
An object of the present inven-tion is to prevent the
occurrence of environmental pollution du~ to such du~t and to
co~tribute ~o the improvement of wor~cing environme~tal condi-
tions, by coating ~n a~rasive material with a thermosettir.g
resi~ which i~ re~dered in901uble and infusible, whereby the
strength o~ the abrasive material, which may be ~ilica sand
or slag, is increased. ~hus, particulc~rly in the case of
s~lica sand~ which has many cracks~ the resin penetrates even
~o the in~ermost areas o~ the cr~cks, the~eby increasi~g the
impac~ resistance of silica sand.
According to the i~vention5 the presence of the thermosetting
re~in coating ~hat is insoluble and infusible increases the
ef~iciency o~ blast cleaning operatio~ which u~eq an abra~ive
material. Mor~ particularly, when sand blasting abrasive mate-
rial is blown agalnst a surface to be cleaned, said abrasive
material will,
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0~ course, obtain the heat generated by the impact. In this
case, in the present invention, the the~mosetting resin
coating, rendered insoluble and infusible, on the abrasive
material is not melted by the heat of impact; rather it
further sets to thereby improve the blast cleaning efficiency.
The present invention, then, in one aspect, resides
in an.abrasive material for sand blasting., con-
sisting essentially of a.material selected from the group
that consists of silica sand and slag, and a heat-treated
coating thereon Qf a thermosetting resin (other than epoxy
resins), said coating containing a setting catalyst, and
being insoluble and infusible on effect of re-applied heat,
said coated abrasive material being in the form o~ fine,
~ree flowing discrete particles, a:nd said abrasive material
being urther characterized by having a higher degree of
uniformity with respect to particle size, than conventional
abrasive material~ and in that a greater proportion of
the abrasive particles are re-usable than is the case
with conventional abrasive materials; said coating
increasing the strength of the abrasive materialby pene-
trating into.cracks inherent in the abrasive material so
that a substantial proportion o~ the pulveriæed abrasive ::
material can be recovered ater the sand blasting for re-
- use; whereby the heat, generated by.impact when ~he abrasive
material is blow~ against a surface to be.cleaned by the
sand blasting, leaves the insoluble and infusible coating
in this state, and actually continues the setting of that
coating so that sand-blasting efficiency is increased;
and whereby dust formation during the sand blasting is
reduced, thereby increasing environmental protection.
33~2
In another aspect, the present invention resides
in a method of producing abrasive materials for sand blasting,
comprising the steps of: carrying out a first
phase by adding a thermosetting resin, to which a
se~ting catalyst has been added to a material selected from
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the group consisting o~ silica sand and slag; mixing particles
of said abrasive material with said resin while blowing
heated air thereinto so as to independently coat tha
par~icles o~ the resulting-sand-blasting abrasive material
with the resin without causing coalescence of the particles;
and carrying out a s~cond, separate phase by re-heating the
coated abrasive particles to a temperature-of about 300C;
said temperature beiny higher than that employed in the
first phase, while effecting stirring o~ said particles
by means of a heated gas stream or by means o~ a vibration
producing device so as to render the resin coating on
the abrasive material insoluble and inusible whi~e at the
same time leaving the-coated abrasive material in a powdered
condition.
~~ The present invention will now be described in more
detail with reference to the accompanying drawings, in which;
Fig. 1 is a schematic view of an apparatus for produc-
ing sand blasting abrasive materials according to an embodiment of
the invention;
Fig. 2 is a schematic view of the principal portion
of another embodiment of the invention; and
Fig. 3 and 4 are particle size distribution comparison
test graphs showing the data of comparative tests between the pres-
ent invention and the pxior art.
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Re~erring to ~ig. 1~ a material t.an~ 'i containi~ iliea
sand (or ~lag) is adapted ~o supply t~e silica sand (or slag)
to a measuring tank 2 by openi~g an outlet damper 1a disposed
in th~ lower region o~ said material tank 10 After a
predetermined amount o~ s~lica sand (or slag) is measured b~
said measurin~ tank 2, it is dumped~ nto a mixer 3 di~posed below
the measuring ta~k, Also charged- in~o said miæer 3 i8 a setting
catalyst in a fixed prnportion to a thermosetting r sin to be
presen~l~ described, a~d said ~ilica sand and ~etting catalyst
are uniformly mixed for about one mixlute, whereupon a thermo~
set~ing resin i~ a fixed proportion to the silica sand is
charged into the mixer 3 and9 w~ blowing hot air at 80~100~C
from a hot air blower 4 into the mixer, they are mixed for about
five minutes. As a result, the particles of silica ~and have a
thermosetting resin coating of fixed ~hickness ~ormed on their
surfaces and such coatings are dried a:nd set by the action of heat.
The described mixing ~ddin~ resin to the sand or slag) and blowing
heated air thereinto can be.defined as a ~irst phase of the invent-
- ive process.
The amount~ of ~aid thermosetting re in and setti~g catal~st
ma~ be ~uitabl;~ ch ~ gPd accordi ~ to the prope:r~ties of ~h~ ~ilica
sand o:r sla~ used. ~s an èxample, in the.case of No. 4 silica sand
specified in the Japanese Industrial Standards (JI~)j 2 parts
o~ thermos~tting resin and 1 part of set~ing catal~st are used
wi~h respect to 100 parts of ~o. 4 silica sand. As for slag~
proportion~ similar to those described may be used. By the
pro~ess described above 9 the particles of silica sand or slag
are coa~ed with said thermosetting resin independently without
the p~Fticles sticki~g to each other to ~orm a lump or l~nps. In this
3~ case~ since hot air is supplied duri~g the mixing, the thermo-
settin3 resin undergoes a chemical change which renders it
insoluble and infusible to some exte~t. When slag is used,
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howe~er, the resin on the particles of slag become~ viscous
like glue and the viscous condition of the resin lasts longer
than in the case of silica sand~ making it somewhat difficult
to achieve the thermal setting thereof. ~hus, in order to ma~e
the thermal setting complete and also, in the case of silica sand,
to cause the resin, which has penetrated even to the innermost
areas of crack~ peculiar to silica sand, to thermally set
complete~y, the silica sa d or slag mixed a~d resin-coated:.in
the prec~ding process is heat treated again.
10More particularly, the stirred silica sand ~or.slag~
reference hereinafter being made to silica sand) i~ charged
into a hopper 5 and then the treated silica sand flowing out of the bo~tom
o~ said hopper 5 is received on a con~eyor 6 for -transport to a
rotar~ kiln 7. ~his arrangement for receiving the silica
sand from th~ mixe~ 3 and then transporting it b~ the conveyor
6 i~ intended to adaust the rate of supply of silica sand to
the rotar~ kiln 7 according to the capacit~ of the latter. On
the exit side of ~he rotar~ kiln 7, oul;let ports 8 suitably
: spaced apart are formed in the outer peripheral surface of the
rotar~ kiln 7 and hot gas at about 3OOC is blown into the
rotary kiln 7 from the exit of the latter, said hot gas travel-
ing toward the entrance of the rotary kiln and being finall~
expelled into the atmosphere b~ an exhaust fan 9~ As for said
ho~ gas, air heated b~ waste gas resulting ~rom combustion of
kerosene or tha like is used a~d is blown intolthe rotary kiln
7 by a nozzle 10. A:s is. known in the art, the rotar;y kiln 7 ha~
annular rails 11 mounted thereon at a plurality of ~uitable
places and each annular rail 11 is supported by a pair of rollers
12. I~ this way, the rotary kiln 7 i9 rotatably supported on a
support base 13. ~esignated at 14 is a drive~ gear wheel ~ixed
on the outer peripheral surface of the rotary kiln 7 and meshing
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33~
with a drive gear wheel 16 secured to a motor 15, whereb~ the
rota.ry kiln 7 i~ rotated around it~ own axis in o~e direction.
Designated at 17 are support roller~ each abutting against thë iatera
surface o~ the associated annular rail 11. I~hile each support
roller 17 i3 shown located above the associated support rollers 12
for simplicit~ of illustration onl~, actually it is located
betwee~ and above the level of the associated support rolier~
17. ~he suppo~t roller~ 17 serve to preve~ the rotar~ kil~
:~ 7 from inadverte~tly sliding in the direction o~ incli~ation
thereo~. ~he rotary kiln 7 is internally provided with a
plurality o~ stirring vanes 18 extendi~g from the entrance to
th~ middle of the le~gth o~ th0 rotary kiln 7. Accordi~gl~g
with the ro~ary kiln 7 being rotated around its own axis and
w.ith heated air being blown thereinto, if silica sand
transported b~ the conve~or 6 is supplied to the rotary kiln
7 through a chute 199 the silica sand ls repeatedl~ sub~ected
to ~the ac~ion of the stirring vanes 18 scooping it and the~ ~
dropping it with the rota~ion of th~ rotary ~iln 7 around its
own axis and durin~ thi3 action it comes in contact with the
ho~ gas, whereb~ the ~hermosetting resin coatings on the
particles of silica sand undergo a final thermosetting chemical
chanae to be rendered insoluble and infusible. The above-described
repeated heating while stirring can be defined as a second, separate
phase of the invention. The silica sand passing by the stirring
vanes 18 flows inside the rotary kiln while being shaken or vibrated
until it reaches the exit side of the rotary kiln 7 and finally flows
out through the outlat ports 8. In this connection, it is to be noted
that a vibration conveyor 30 shown in Fig. 2 may be used as a heat-
ing and stirring means in place of the rotary kiln 7 shown in
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?ig. 1. More particularl~, the vibration conve~or 30 supported
b~ springs 32 a~d adapted to be vibrated b~ vibra~ion means 33
such as an eccentri.c motor is associated with infrared ray
radiating devices 3~1 locatsd thereabo~e 9 SO that while the
silica ~and supplied to.the conveyor 30 from the conveyor
6 through the chute 19 shown in Fig. ~ is being vibrated a~d
transported b~ the conveyor 30, it is heated b~ the infrared
ray radiating de~iceR 31 so as to render the thermosetting
resin coatings in901uble and ln~usible. Re~erring bac~ to
Fig. 1, the silica ~and particles which have been discharged
~rom the rotary kiln 7 are collected at the lower end of a
buc~et lifter 21 ~ a chute 20. The particles thus collected
are then lifted b~ the bucket li~ter 21 operated b~ a motor
22 and are supplied into 8 hopper 24 disposed in a ~orting
tower 23. Disposed inclined below hopper 2~ is a wire scree~ 25
having the required mesh, and vibrating means 26 is provided
for vibrating the wire screen 25. Desi~nated at 27 are springs
~or supporting the wire screen 25. 0~ the silica sand
particles flowing down the hopper 2~ onto the wire screen 25~'onl~
thos`e having particle sizes below a certain limit are allowed to
pass through the wire screen 25 under the action of the vibrations
imparted thereto while the othe~ having sizes above said limit flow
down o~ said wire screen 25 and are discharged into the outside
of the ~stem. Those passing through the wire screen 25 are then
transported by a conve~or 28 to a product storage tank. Designated
at 29 is an exhaust fan serving to discharge cool air which is
being admitted into the sorting tower 23 ~rom below, whereb~ the
silica sand which was at about 110C when leaving the rotar~
kiln 7 or vibration conve~or 30 is cooled to about 80-50C. ~he
time required for the silica sand to pass through the rotary
kiln 7 or vibration con~e~or 30 is suitabl~ about 1 minute and
332
30 seconds. If the mesh size of the wire screen 25 is changed,
the particle size of silica sand which can be sorted will differ.
Thus, it is convenient to prepare a plurality of wire screens
having different mesh sizes so that they may be selectively
used.
The thermosetting resins available for the present
invention include phenolic resins, urea resins, melamine resins,
polyester resins, and alkyd resins. As an example, such a resin
; is prepared by deriving furfural from pentose which is extracted
from t~e stalks of cone or kaoliang, adding hydrogen to said
furfural to provide furfuryl alcohol, and denaturing the latter
with a phenol.
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Generally, mention may be made of those resins which are
commercially available undex the name of urea-furfur~l
alcohol formaldehyde resins and of phenol furfur~l alcohol
fo~maldehyde resins.
: As for setting catalysts~ it is desirable to use phosphate
typo catalysts such as an aqueous solution of phosphoric acid
(75% concentration) or sulfate t~pe catalysts such as an
aqueous solution of sulfuric acid (~0~ concentration~,
~he effect~ of the abrasive materials prepared according to
.10 the present i~vsntion used for blast cleaning are shown b~low
by way of example in comparison with conventional
abTasi~e materials for blast cleaning"
~1) Result of Comparati~e ~est for Amount of Dust
Abra~ive Matt~rial Used . Amount of Dust
No. 4 silica sand.(JIS, conventional) 361 mg/m~
No. 4 silica sand resin-coated
acco~ding to the invention 22 mg/m3
Slag (conventional) 1~,2 mg/m3
~lag resin-coated according to
20 the in~ention 11,3 mg/m3
~ he above result was obtained by measuring ~he amount of
dust (in mg~ per 1 m~ at a location 11 m do~mstream of the site
for te~t~ ~here an abrasive material was blown against a sur~ace
to be cleaned,
(2) Result of Comparative ~est ~or Depth o~ Indentation~
~o~ 4 silica sand (JI~, con~e~tional) 95
No, 4 silica sand resin-coated
according to the in~ention 104
33~
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~lag (con~en~ional) 100
~lag resin-coated according to
the invention 118 ~
:~he above result wa~ obtai~ed b~ calculating the average
of two blas~ing operatiQns against a surface to be cleaned.
(3) Result of Comparatire ~est for Particle Size Distribu
tion
- Fig. 3 shows the distribution o~ particle sizes o~ ~o~ 4
;:silica sand (JIS, co~ventional) and No. 4 silica sand resi~-
coated according t;o ~he in~ention a~ measured before and after each
ma-terial is blasted once, the particle size ~in mm) bei~g plotted
as~the abscissa and the percentage as the ordinate. According to thIs
graph, it is seen that the distribution of particle si7es o~
No. 4 silica sand resin-coated (the present inventive article)
be~o:re use, as indicated b~ curre I, is such that the paxticle
size range oX ~.1 mm to 0.6 mm covers 93.2~ (13~ ~ 54~ + 26.2~),
demonstrating that the particles are ver~ uniform in size, wherea3
i~ the case of ~o. 4 siliça sand (conven~ional ar~iole) indicated
by curve II, the same pa~ticle size range covers 7~O~ (6~ ~ ~2
~ 36i7~), showiD~ that there is a relatively large amount of varia-
tion i~ particle size. Further, when the particle size distribution
of the material af~er being used once i8 investigated as to pa~ticle
size~ of not les~ than 0.3 mm capable of being re-used, it is see~
that in the case of the present inven~i~e article indicatsd by
curve III, 68.8~ i~ re-usable, whereas in the conYentional a~ticle
indicated b~ cur~re IV, onl;~ 39.~ is re-usable, It i~ also seen
that the amoun~ of dust (pa:F~icle~ o~ not more than 0,2 mm) found
a~ter single bl~sti~æ is 3001% with the present inventive article
and ~a.g wi~h the conventio~a~ article~
_g_
... . ., . , . , , _ , . .. . . . . . . . . .. .. ...... .. ..
33 ~
~ i~. 4 shows tke distribution of particle size~ of slag
(conventional articlej and the same kind of' slag resin-coated
according to the presen~ in~e~io~ as measured before and
after each material is blasted once. The particle size ~in mm)
before said bla~ti~ is indicated by curve I' for the present
inve~tive article an~ by curve II' ~or the conventional article
and the pa~ticle size (in mm) after said blasting is indicated
b~ curves III' for the present in~entive article and by cur~e
IY' ~or the con~entional article. ~he abscissa indicates the
particle size and the ordinate indicates the percenta~e.
Accordi~g to this graph, it is seen that the particle si2es of
not Ies~ tha~ 0.3 mm'after single blasting ~Jhich are capable of
boing re-used cover 73.5% (3~ ~ 9.5% ~- 22.6% ~ 17.1%) with the
present inventive article a~d 60.5% (2.1% ~ 6~ 15.8~ + 18.4~)
with the conventio~al article. It iq also seen that the amount o~
~u~t (par~icles o~ not more than 0.2 mm) found after a sin~le
blas~ing i~ 26~ with the present invention whereas it is 38.
with the conventional article.
~rom the comparative test ~esults described abo~e, it i~ seen
that as ~hown in the item (1) the abras:ive mat~rials resin-coated
according to the invention provide a rate o~ production o~ dust
~hich i much lower than that of the conventional ~rticles
and that particularly in the ca~e o~ silica sand the inventio~
i~ capable of reducing it to about 1~14 of the co~entional
value. This means that the invention preYents environmental
pollutio~ and con~ributes much to the improveme~ of working
en~ironme~tal condition~.
As is clear from the item (2~, the a~rasive materials
resin-coatad according tG the in~ention provide a~ indentation
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depth which i3 no~ ~ery dif~erent ~rom or, rather, greater than
that pro~ided b~ the conventio~al articles, demonstrating
that the invention improves the blast cleaning effect.
: ~uxther, as is clear from the item (~), the abrasive
materials according to the inventio~ retain ~ewer cracks
than the conventional articles, so that a correspondingly
greater proportion of used or blasted material can be
recovered ~or re-use b~ installing an abrasive material recov-
ering device, thus contributing much to the reductio~ o~ cost.
Fkrther,.:the presen~ inventive articles are also superior to
the conventional articleAs i~ respect of reducing the amount
o~ dust.
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