METHOD OF INTERNALLY COATING STEEL DRUMS

METHODE DE REVETEMENT DE LA SURFACE INTERNE DE FUTS EN ACIER

English Abstract

Title of the Invention
METHOD OF INTERNALLY COATING STEEL DRUMS
Abstract of the Disclosure
Drum shells, lids and filling hole covers, prior
to the assembly of these parts to make steel drums, are
pre-treated by spraying with an alkaline solution, iron
phosphate and thereafter with a standard rust inhibitor,
and the interiors of the drum parts are coated by electro-
static spray application with a thermosetting epoxy-based
powder to a critical thickness which eliminates subsequent
cracking and subsequent vulnerability to destructive
substances such as tomato paste and other more corrosive
chemicals. The drum parts are preheated prior to the
application of the powder to accelerate the fusion of the
powder particle coating as well as reduce the associated
material application problems. After application of the
powder to the container interiors, the components are
again subjected to oven temperatures to set and cure the
coating.

Claims

The embodiments of the invention of which an ex-
clusive property or privilege is claimed are defined as
follows:
1. A method for protectively coating the inside
surfaces of a steel drum shell and its related lid and filling
hole cover to render the drum suitable for use as a container
for tomato paste comprising applying a primer coating of
iron phosphate thereto, heating said surfaces to a temperature
of 180 - 220 degrees F, electrostatically spray-coating said
heated surfaces with a therosetting epoxy resin powder
adapted to melt and fuse thereto at said temperature and
building up said fused coating to a thickness of 1.5-3.0 mils,
and heating said surfaces to a temperature of from about 390
degrees F to about 420 degrees F for a period of 5-12 minutes
to set and cure said fused coating.
2. The method of Claim 1, said epoxy resin being
of the diglycidyl ether of bisphenol A type containing a
curing agent selected from the group consisting of aromatic
amines, Lewis acids and acid anhydrides.
3. The method of Claim 1, wherein said resin
powder is spray-coated onto the inside surfaces of the drum
shell in a radial spray pattern which is moved progressively
along the length of the drum shell.
4. The method of Claim 1, wherein said drum shell
is rotated while being spray-coated with said resin powder.
5. The method of Claim 1 wherein said shell
and its related lid and filling hole cover are subjected to
an alkaline wash and water rinse prior to applying said primer
coating of iron phosphate.

6. The method of Claim 1 wherein said shell and
its related lid and cover are spray-rinsed with water after
applying said primer coating of iron phosphate thereto.
7, The method of Claim 1 wherein a rust inhibitor
is applied to said shell, and its related lid and cover
after said primer coating of iron phosphate has been applied.

Description

Related Application
Copending Canadian application Sexial No. 283,326,
filed July 22, 1977 and issued to Canadian Patent No. 1,084,698
on September 2, 1980 entitled "Rotator and Coater System for
Drum Shells" discloses the preferred mechanical system for hand-
lin~ and rotating the drum shells during the application of the
powder coating. As disclosed therein, the drum shells are spun
at about 100 r.p.m. with their axes horizontally disposed while
the powder coating is applied, and the spray applicator head
is moved through the shell and then back through it while the
powder, charged negatively to a voltage of about -90 kv, is
being spray-applied. The present method invention does not,
however, require for its practice drum shell spinning or a~ial
reciprocation of the spray applicator.
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Related Patents and Publications
The subject method employs a Ransburg-type applicating
: s~stem which operates according to the old and well-known
electrostatic principle of applying an elec~rostatic charge to
the powder particles and applying the charged particles to the
grounded shali!lid and ~illi~g hole cover partsO Exemplary
Ran~burg-type application systems are sho~n and d~6cribed in
~ansburg~ et al. 2,463,422, Ransburg, et al. 2,509,448, and
~ansburg 2,567,781, and reference thereto may be had for a
) description o the principles involved and the operational
detail tha~ may be employed.
Summar~ of the Invention
The essential object and advantage of the invention is
to provide a method ox coating the inside surfaces o~ preheated
steel drum parts with an epoxy type of resinous coating ~o that
the coating is i~pervious to attack by highly corrosive
substancss, handling stresses and strains, and other conditions
which tend to break down or rupture such coatings.
Descrip~ion of the Invention
0 The subject method of coating tha drum ~hells, lid~
and covers includes the ollowing steps:
1. Cleaning by abrasion
2. Washing
3. Rinsing
4. Iron phosphate application
5. Rinsing
6. Rust inhibitor application
7~ Preheating

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8. Powder coating application
9. Heati~g to set re5in
First, the drum components are cleaned and abraded by
sho~-blasting with small abrasive grit.to provide anchor patterns
S in the metal or the a~choring o~ the sub~e~uently applied powder.
The drum parts are the~ spray-wa~hed with water o about
160 F. containin~ a sma~l amount o~ alkali, eOg., 1~7% by wei~ht
o~ al~ali.
Next, the drum parts are spray-rinsed i~ water at about
~0 ~ room ~emperature.
The part~ are then sprayed with an iron phosphate
solution of, ~or example, 4.2% by weight of the phosphate in
water, the solution being warm, eOg., 150 F. Thi~ i~ an
important step in the process and it serves the purpo~e o~ pro-
LS viding a primer coating which serves to adhera the epoxy coating
to thQ metal with optimum holdlng powex.
Tha parts are then again spray rinsed with water at
about room temperature.
Next, the par~s are spraye~ wi~h a rust inhibitor
o solution, ~or example, a 0.3/0 by wei~ht 801ution 0~ ~hromia acid
in water, the solution being at about 140 F.
The dr-um parts are then heated u~ti~ th~ir surace
tempexatuxe reache~ about 200 F., the opexative range being from
about 180 to about 220 F.
,5 Immediately after reaching the temperature o~ about
200 F~ or 180 - 220 F., the powder coating i5 ~pxay applied
through a ~onventional Ransburg type o electrostatic ~pray
applicator. At the temperatura o the metal parts, the epoxy
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?ow~er par~icles fuse directl~ to the metal and to ~ach otner
to begin the cross-linki~g process neces~ary to form a pinhole-
fr~e co~ting of 1.5 - 3.0 mil~ in thic~ness. The preferred
thic~;ness is 2.0 - 2.5 mils. For example, under tomato paste
handl`ins conditions a coating thic~ness in excess of 3.0 mil~
leads to rupture or cracking of the coating, particularly on the
s~rfac~ ~f the filling h~le cover, while a coating of less than .
1.5 mils is vulnerable to penetra~ion ~y the food acid o~ the
~omato paste under the stress and strains of drum handling~
~he preerred class of epoxy resin powders for ~se in
the subject process i9 that of the diglycidal etherq of
bisphenol-A resins (DGEsA). Of the~e, those compoun~ed with
aromatic amine, Lewis acid and acid anhydride curing agents are
preferred. The .qelected powder should be ree flowing, having
lr> a particle size range o~ 20 - 150 microns and pre~erably 30 ~ 70 :~
micron~, and have a melting point within ~he range of 180~220 F~
`A fully satisactory epoxy powder coating having such proper~ies :
and characteristics is the 531-7076 gra~e o Du Pont Company~
. powder coatings marketed under the trade mark "FLINTFLEX".
~0 Next, to set and cure the resin, the drum part~ are
heated to a metal surface temperature of about 400 F., i.e.,
from àbout 3~0 F. to about 420 F., or about SLX minute~ e~,
within a range o 5 - 12 minutes.
. Assembled drums, the parts o~ which have been treated
as described above, may safely be used without deterioration of
the dru~s or contents in shipment, or in storage for extended
periods. Such assembled drums are there~ore particularly useful
for the handling and storage of tomato paste, cherries, olives
and other food products which have a gxeat potential '~r
3Q corroding and destroyin~ ~teel container~
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