Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
Back~ n~ of the Invention
This invention relates generally to the cold forming of
ferrous and non ferrous metals such as steel, stainless
steel~ copper, and aluminium and more specificall.y to dry
film lubricant compositions and processes for severe cold
forming operations.
~..
In the cold extrusion, drawing or forming of metal
parts, a current practice is to prepare the parts by applying
a zinc phosphate coating to the parts and then applying a dry
film lubricant or a reactive lubricant to the ~inc phosphate
coating. Dry film lubricants are products containing soap
and borax as their major constituents. Such lubricants are
applied from an aqueous solution at high temperatures
(greater than 140F to boiling) and then dried on the metal
sur~ace. Dry film lubricants generally are used for mild
forming operations.
Reactive stearate lubricants are also applied from
aqueous solution. They consist of solutions of sodium
stearate which are controlled in such a way that they react
with the zinc phosphate coating to form zinc stearate within
the crystal lattice of the coating. This provides a tightly
bonded lubricant system which performs well in many severe
cold extrusion applications.
Both lubricant systems offer the advantage of a dry,
hard film which is not easily physically removed from the
metal surEace. This leads to a cleaner and safer work
environment because oils tend to run off treated parts and
coat the work area. However, there are some severe cold
forming applications where neither system will perform
adequately. At such times the use of an additional lubricant
~such as molybdenum disulfide) or additional processing steps
are required, both of which lead to additional expense.
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We have attempted -to employ additives to a reactive
stearate lubricant which additives included a mica pigment, a
dispersant for the mica, sulfurized oleic acid and a
phosphate ester to provide a severe cold forming lubricant
system. The mica pigment was added to improve the ability of
the lubricant to function adequately in a severe cold forming
process. However, it was found that in a manufacturing
environment, such a lubricant system failed to work
satisfactorily due to the settling of the mica from the
coating bath and the use of such a system was abandoned.
We have now found that certain severe cold forming
applications can be accomplished without need of a pigment
and in some applications the need for a phosphate precoat has
been eliminated.
Brief Summary of the Invention
In accordance with this invention, there i~ provided a
lubricant composition comprising an aqueous, pigment-free
bath containing an alkali metal fatty acid soap such as an
alkali metal stearate, a compound selected Erom the group
consisting of sulfurized fatty acids, chlorinated fatty
acids, phosphate esters of polyoxyethylene based non-ionic
surfactants and mixtures thereof, and a base in an amount to
provide a free fatty acid content between about ~ 1Ø
A process is provided for cold forming metal comprising
applying to the metal surface a dry, pigment-free coating of
:
a~
an alkali metal fatty acid soap and a compound selected from
the group consisting of sulfurized fatty acids, chlorinated
fatty acids, phosphate esters of polyoxyethylene based
non-ionic surfactants and mi.xtures thereof to form a dry,
hard coating and then extruding the metal through a die.
Also provided is a process for cold forming metal
comprising applying to a metal billet a coating of zinc
phosphate, applying to the zinc phosphate a second
pigment-free coating of an alkali metal stearate and a
compound selected from the group consisting of sulfurized
fatty acids, chlorinated fatty acids, phosphate esters of
poloxyethylene based non-ionic surfactants, and mixtures
thereof so as to form a zinc soap with said zinc phosphate
and then extruding said billet through a die.
Also provided is a dry film lubricant system comprising
a zinc phosphate coating reacted with an alkali metal
stearate and a compound selected from the group consisting of
sulfurized fatty acids, chlorinated fatty acids, phosphate
esters of polyoxyethylene based non-ionic surfactants and
mixtures thereof to provide a dry, pigment-free, lubricant
film.
Detailed Description
The lubricant system and process of the invention are
suitable for extreme cold forming operations where reductions
of 35% or more are necessary in forming metal parts. The
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metal parts are dipped in a heated aqueous lubricant bath for
several minutes, removed and dried to provide a hard dry
lubricant film. Optionally, ferrous or aluminum parts are
first provided wi~h a zinc phosphate coating having a coating
weight of approximately 1500 to 3000 mg/ft2 as is
conventional. The parts are next dipped in a reactive
lubricant bath of the invention which contains an alkali
metal stearate, for several minutes. The zinc coating reacts
with the bath and, upon drying, a hard, dry lubricant film is
formed on the part.
The lubricant bath of the invention includes an alkali
metal (Na, K and Li) soap which upon drying will form a hard,
dry lubricant film. Suitable soaps are derived from fatty
acids have 12 to 22 carbons and mixtures thereof. Also
included is an additive compound selected from the group
consisting of sulfurized fatty acids, chlorinated fatty
acids, phosphate esters of poloxyethylene based non-ionic
surfactants and mixtures thereof. The sulfurized and
chlorinated fatty acids are derived from unsaturated fatty
; 20 acids and esters having 12 to 22 carbon atoms in the acid
carbon chain, such as oleic, li.nderic, erucic, linoleic,
linolenic, etc. acids by reacting the unsaturated bonds with
sulfur or chlorine. As us~d herein, the terms chlorinated
and sulfurized fatty acids include esters thereof. Such
materials are available from Keil Chemical Divison, Ferro
Corp. as "sulfur bases" and "chlorinated fatty compounds" and
:
have been traditionally used as additives to fluids for their
e~treme pressure lubricating properties in ~etal working
applications such as cutting oils, water soluble soaps and
drawing compounds but not as lubricant additives for forming
S dry hard films as in our invention. The phosphate esters are
sold as e~treme pressure lubricants and are available under
the trademark Antara~ from GAF Corporation. They comprise a
phosphate radical on a polyethyleneoxy non-ionic surfactant
base. The non-ionic surfactant base consists of a hydrophobe
and polyo~yethylene.
In one aspect of the invention, it is believed that an
important attribute of the additive material is that it has
an acid group which can react with the zinc phosphate to form
a water insoluble zinc soap which is chemically bonded to the
surface of the metal. The combination of these additives and
the stearate provide a dry film with unique lubricating
properties which permits the cold extrusion of certain metal
parts. The forming temperatures are reduced so that the
parts are not heat damaged and the lubricating system avoids
various other operating problems such as sticking in the die.
Because of the added acidity due to the lubricant
additives, the free acidity of the bath must be adjusted to
assure reaction of the ingredients of the bath with the zinc
phosphate coating when a phosphate precoat is used. The
2S adjustment also is used to control the viscosity of the bath.
The "free fatty acid" is adjusted by adding a base such as
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NaOH so as to be within the range of ~ 1.0 with -~ 0.5
preferred. Free fatty acid is determined by placing 100 ml
of 190 proof ethyl alcohol in a 250 ml. Erlenmeyer flask and
adding five drops of phenolphthalein indicator. Sodium
hydroxide (0.lN) is added dropwise until a faint pink color
develops. A 10 ml. portion of the lubricant bath is pipetted
into the alcohol and the alcohol is heated to boiling. While
hot, the alcohol solution is titrated to a pink endpoint with
the 0.lN NaOH and the amount of NaOH used is recorded as the
"free fatty acid points" where 1 ml. = 1.0 point. If the
solution is pink after boiling then it is titrated with 0.lN
sulfuric acid until the pink color is discharged. The amount
of H2SO4 used is the "free alkali points" where 1 ml. = 1.0
alkali point or - 1.0 acid point.
The amount of lubricant additive employed will depend
upon the appl:ication and generally can range from about 1-30
parts by weight per 100 parts of the total combined weight of
fatty acid soap and additive combined. A sufficient amount
~ is used to provide the required lubrication for a given
application. Amounts of add:itive above about 30 parts by
weight make the lubricant coating film soft.
The solution concentration can range from about 2 to 10%
by weight and preferably 4 to 8% by weight "total fatty
solids". Total fatty solids are determined by pipetting a 20
ml sample of the bath into an 18 gram Babcock type test
bottle. A 25 ml. portion of concentrated sulfuric acid is
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then added and the bottle is shaken until the fatty matter
separates. The liquid sample is dilu-ted with 50% aqueous
SO4 until the volume of separated fatty matter can be read
on the graduated neck of the botted directly as percent fatty
solids.
The bath of the invention is formed and maintained by
adding the ingredients with mixing to hot water (~&~ or
above), otherwise the fatty acid portion will separate.
The compositions and process of the invention are
further illustra~ed by, but are not intended to be limited
to, the following examples wherein parts are parts by weight
unless otherwise indicated.
; Examples 1-4
Four different lubricating baths were used to form a
hard, dry film lubricant coa-ting on the surface o~ steel
billets to be formed into hose couplings by cold forward
extrusion. The billets were cylindrical twbes with a length
of about 2~" and a diame-ter of about ~". The billets were
formed into hose couplings by cold forward extrusion where
one end of the billet was reduced to provide a 7" long
section of ]." in diameter with a wall thickness of about 1/8"
extending from about a 1 inch long section of billet o~ the
original dimensions. A zinc phosphate coating was first
formed on the billet and then the billets were dipped for 5
minutes in the reactive lubricant bath, which was at a
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temperature of about 160-170F, removed and allowed to dry. The
bath compositions are given in Table I below:
Table I
~ n Parts by Wei~ht
Ingredient Ex. 1 Ex. 2 Ex. 3 Ex. 4
_
Sodium
Stearate 220 220 160 160
Sulfurized Oleic
Acid* 44 66 16 16
Water 4000 4000 4000 4000
NaOH (50% wt. %) 10 14 5 6
Phosphate Ester
of polyoxyethylene** 0 45
*Base 44, (trade mark of Keil Chemical Division Ferro Corp.);
Sulfur, 14%; Active Sulfur, 5~, Viscosity Q 100F SUS 2400,
210F S~S 200; wt lbs/gal~ 60F 8.4; No. 175.
**Antara LP-700 (trade mark of GAF Corp.); phosphate radical on a
polyethyleneoxy non-ionic surfactant base; Water Soluble liquid;
s. g. 25C 1.20; moisture 0.5% max; pH (10% in H2O) 1.5-2.5;
Acid No. 140~160; phosphorous 5.8% max.
The cold forming operation to produce the couplings
involved a severe (about a 50~) reduction. Previous attempts to
form the part using a standard zinc phosphate coating which had
been reacted with sodium stearate were unsuccessful in forming the
part. A modified dry film of soap and borax was successful in
forming the part without use of phosphate coating but resulted in
excessive heat generation and, due to its hygroscopic nature, many
operating problems. Each of the
-
.
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compositions shown in Table I allawed the parts to be
successfully extruded at lower temperatures (at least 10F)
with the compositions of Example 3 and 4 appearing to give
the best results.
Example 5
The composition of Example 4 was used to coat 400 steel
billets for deep drawing steel grenades. The billets were
cleaned in a caustic solution, rinsed with water, dried,
immersed in the lubricant bath at a temperature of 175-180F
for about 5 minutes and then removed from the bath and dried.
The bath had a total fatty solids content of 7 to 9% and a
free fatty acid content of about 0.5 point. The billets were
subjected to four cold forming operations, with cleaning,
annealing and lubricant application between each forming
operation, to successfully form the grenades. The acceptance
rate was 96.5% which is slightly above the normal rate. The
process previously used a phosphoric acid reactive oil which
was messy to use and corrosive to the skin.
Example 6
The cornposition of Example 4 was used to coat aluminum
billets for forming fire extinguisher bottles by impact
; extrusion. The aluminum billets were first cleaned in an
alkaline solution, rinsed with water, alkaline etched, and
rinsed with water. A number of the billets were coated with
zinc phosphate, rinsed with water and an alkaline solution,
coated with the lubricant composition of Example ~ at a bath
concentration of about 8 percent by weight total fatty solids
at temperatures of about 168-180F and dried. The remaining
billets were coated with lubricant without applying the zinc
phosphate coating. It was noted that a reaction of the
lubricant with the aluminum surface occurred even in the
absence of the zinc phosphate undercoat. Both groups of
billets were successfully impact extruded. Some die pick up
resulted from the phosphate coated parts which could be
remedied by lowering the coating thicknesses by adjusting the
bath concentrations. The process previollsly used to form the
- - bottles incuded a zinc ~ ~r~ undercoat and a soap type
lubricant.
The process and compositions of the invention thus
provide a non-oily, non-hygroscopic, dry, hard lubricant
system which permits the severe cold forming of parts without
die sticking and without damage or discoloration of the parts
due to excessive temperature generation. The lubricant
system is so effective that, as illustrated above, the use of
a phosphate precoating can be eliminated in certain severe
applications which reduces process stops and the possibility
of die pick up of the lubricant.
