Water soluble salt precoats for wire drawing

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] This invention relates to modified water soluble salt precoats for use in the cold drawing of steel wire.

2. Background of the Invention

[0002] Water soluble salt coatings are often applied to steel wire in the form of aqueous solutions prior to drawing. The solution-coated wire is dried and the resulting salt coated wire is then drawn through conventional reducing dies using dry soap lubricants - a process well-known to this art. The water soluble salt coating acts as a lubricant carrier, pulling the dry soap box lubricant into the dies, thus providing lubrication. These dried-­in-place, water soluble salt coatings have proven to be superior to other conventional coatings such as lime or borax coatings because of their improved ability to carry lubricant into the dies. A typical soluble salt composition used for the coating of steel (usually stainless steel) wire contains both sodium sulfate and borax. Such soluble salt compositions provide coatings with excellent crystalline structure, resulting in good soap lubricant pick-up when the coated wire is passed through a soap box, and therefore good drawability. However, such salt coatings are prone to excessive moisture absorption upon exposure to ambient air, particularly when exposed to air having high humidity. Such moisture absorption seriously interferes with, or even prevents, the drawing of the coated wire. On the other hand, soluble salt coatings which provide low moisture absorption provide little or no crystalline structure (i.e. amorphous or glaze type coatings) and are significantly inferior in both lubricant pick-up and drawa­bility. This Hobson's choice problem has not previously been solved.

STATEMENT OF THE INVENTION

[0003] Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients or reaction conditions used herein are to be understood as modified in all instances by the term "about".

[0004] Compositions for coating steel wire have now been discovered which provide uniform coatings with good crystalline structure, soap pick-up, and drawability, while at the same time low moisture absorption even during humid days, i.e. low hygroscopicity.

[0005] The compositions of the invention, which are in the form of dry mixtures prior to dilution with water for use, contain the following components:

A. from 50 to 99.99, preferably from 70 to 89.9% by weight K₂SO₄;

B. from 0 to 49.99, preferably from 10 to 29.9% by weight K₂B₄O₇ and/or KBO₂; and

C. from 0.01 to 5, preferably from 0.1 to 1.0% by weight of an ammonium or potassium soap,

wherein up to 50% by weight, and preferably no more than 10% by weight, of the total potassium ions and ammonium ions pre­sent in A., B. and C. can be replaced with sodium ions. More preferably, substantially none of the potassium and ammonium are replaced with sodium ions, since the more sodium ions present, the greater the hygroscopicity. When sodium ions are present, they can be present in one or more of components A., B. and C., e.g. component C. can be partially or entirely a sodium soap. Also, component A. and/or B. can be a sodium or a potassium salt, or a mixture of such salts, provided the limitation on total quantity of sodium ion is maintained.

[0006] The fact that the above compositions provide good crystalli­nity on steel wire is completely unexpected, since the above compositions without component C. give non-uniform coatings on steel wire which are not useful as such since both soap pick-up and drawability are unsatisfactory. In some unknown manner, the presence of the soap provides an at least partially crystalline uniform coating when the composition in aqueous solution is applied to the steel wire which is then dried or allowed to dry.

[0007] The K₂SO₄ used as component A. can be chemically pure or of a technical grade; the latter being preferred due to cost con­siderations.

[0008] The K₂B₄O₇ used as component B. can also be chemically pure or a technical grade, and is generally available and used herein as the tetrahydrate (K₂B₄O₇·4H₂O). Similarly, the KBO₂, which can be used alone as component B, or in a mixture with K₂B₄O₇ in any proportions, can be chemically pure or a technical grade.

[0009] The ammonium or potassium soap is one or more ammonium and/or potassium salts of a C₁₂-C₂₂ fatty acid or mixture of two or more such C₁₂-C₂₂ fatty acids. The fatty acids are generally saturated and unbranched, with ammonium or potassium stearate being pre­ferred for use herein, although mono- or di-olefinically unsa­turated C₁₂-C₂₂ fatty acids can also be employed, either alone or in mixtures with each other and/or with saturated fatty acids. For example, ammonium and potassium soaps derived from the fatty acid mixtures obtained by the saponification of tallow oil or coconut oil, or a mixture thereof, can advantageously be employed as com­ponent C. Also, ammonium or potassium salts of branched or cycloaliphatic-containing C₁₂-C₂₂ fatty acids can also be employed herein, either alone or in mixtures with unbranched fatty acid salts. Also, ammonium or potassium rosin acids, e.g. abietic acid, can also be employed as component C.

[0010] The wires coated with the coating compositions of the inven­tion are generally steel wires, and usually stainless steel wires. However, other wire substrates can also be coated with the present coating compositions such as mild steel, titanium, vanadium, tungsten, aluminum, copper, nickel, zirconium, etc., and alloys thereof.

[0011] The coatings are applied by contacting the wires with an aqueous solution of the composition of the invention, and allowing the resulting wet coating to dry in place, either with or without the application of heat. The aqueous solutions generally contain from 75 to 400 g/l of the composition in water, preferably from 150 to 250 g/l.

[0012] The wire is contacted with the solution by any convenient technique, either batch or a continuous strand, and allowing the resulting wet-coated wire to air dry before coiling for storage, shipping, or use. The coated wire is then passed through conven­tional cold reduction equipment using a soap box (e.g. containing a conventional dry soap lubricant). The coating on the wire functions as a carrier to carry the dry soap lubricant into the die.

[0013] The steps employed in the treatment of wire according to the invention include the following:

1. Cleaning the wire - cleaning compositions are well-known in the art and do not comprise part of the present invention.

2. Rinsing with water.

3. Pickling - here also, pickling compositions are well-­known and the selection of a pickling composition is not part of the invention.

4. Rinsing with water.

5. Applying the coating composition of the invention as described above.

6. Drying the wire as described above to produce the coated wire of the invention.

The coated wire can then be drawn, also as described above.

[0014] The water used in preparing the aqueous solutions of the invention is preferably distilled or deionized water, but tap water can also be used provided it is not overly hard and has a low dissolved sodium salts content.

[0015] The invention will be illustrated but not limited by the following examples.

EXAMPLES

EXAMPLE 1

[0016] The following aqueous compositions were tested for their morphology and hygroscopicity, when coated on stainless steel panels. Stainless steel panels were coated with each of the following compositions by immersing the panels in the aqueous com­position, removing the panels from the aqueous composition, and allowing them to flash (air) dry.

a) 187.2 g of a mixture of 75 wgt % Na₂SO₄ and 25 wgt % sodium tetraborate·10H₂O per liter of deionized water.
Use temperature 190°F.

b) 187.2 g of a mixture of 75 wgt % K₂SO₄ and 25 wgt % K₂B₄O₇·4H₂O per liter of deionized water.
Use temperature 190°F.

c) to an aqueous solution prepared as in a) was added 5 g/l of sodium stearate.
Use temperature 190° F.

d) to an aqueous solution prepared as in b) was added 5 g/l of ammonium stearate.
Use temperature 190° F.

[0017] The sections of stainless steel panel coated with the above compositions were then tested for hygroscopicity and morphology. The test results are set forth in Table I below. In Table I, RH = relative humidity.

TABLE I

Coating Bath Composition	Hygroscopicity:*		Morpholgy
	90-95% RH/90 min.	Ambient Air/24 hr.
a)	16.5%	107.0%	Crystalline
b)	5.1%	2.7%	Amorphous glaze
c)	16.1%	-	Crystalline/some glaze
d)	7.5%	3.4%	Crystalline/some glaze

* Average percent moisture in the coating. Moisture pick-up measured by weight differential of the uncoated panel and the coated panel before and after air exposure.

[0018] As can be seen from Table I, the composition of the inven­tion, composition d), produced a coating with good crystallinity, and low hygroscopicity.

EXAMPLE 2

[0019] This example shows the effect of relative ratios of sodium and potassium ions on the hygroscopicity of the water soluble salt coatings. In this example, stainless steel panels were coated in accordance with Example 1 using the following compositions, at a concentration of 187.2 g/l in deionized water, set forth in Table II below together with test results. In Table II, M = molarity or gm-moles/liter of solution and RH = relative humidity.

TABLE II

	Coating Bath Composition:				Stearate, M	Hygroscopicity:
	Na,M	K,M	SO₄,M	B₄O₇,M		90-95% RH/24 hrs.
e)	2.23	-	0.99	0.123	-	107.0%
f)	1.98	0.246	0.99	0.123	-	90.2%
g)	0.246	1.98	0.99	0.123	-	10.6%
h)	-	2.23	0.99	0.123	-	2.7%
i)	-	2.23	0.99	0.123	0.016	3.4%

EXAMPLE 3

[0020] This example shows the relative hygroscopicity of lime coatings compared to the coating from a known sodium based salt composition and a low sodium salt composition of the invention. The coatings were produced on samples of the stainless steel wire used in Example 1 according to the procedure of Example 1 from the following aqueous compositions:

j) 187.2 g of a mixture of 75 wgt % Na₂SO₄ and 25 wgt % sodium tetraborate·10H₂O per liter of deionized water.
Use temperature 190° F.

k) 187.2 g of a mixture of 79 wgt % K₂SO₄, 20 wgt % sodium tetra­borate·10H₂O, and 1 mole % of ammonium stearate per liter of deionized water.
Use temperature 190° F.

l) 3% by weight of lime in deionized water.
Use temperature 190° F.

m) 6% by weight of lime in deionized water.
Use temperature 190° F.

[0021] The results are shown in Table III below.

TABLE III

Coating Bath Composition	% moisture pick-up, 80-90% RH, 24 hrs.
j)	28.3%
k)	3.0%
l)	17.6%
m)	18.4%

[0022] As can be seen from Table III above, composition k) in accordance with the invention has significantly reduced hygrosco­picity compared to lime coatings l) and m).

EXAMPLE 4

[0023] Ten different coating bath compositions were evaluated for moisture pick up, morphology, coating uniformity, and crystals per inch on stainless steel panels.

[0024] The stainless steel panels were coated with the coating com­positions and coating baths set forth in Table IV, according to the process given in Example 1, except that the wet-coated panels were dried using a 10 minute bake at 250°F. Moisture pick-up was determined in a chamber which allowed constant temperature and humidity of 80°F and 92% respectively. A Surtronic 3 surface prophylometer was used to determine the number of crystals per inch of coating. Coating characterization and coating appearance were determined by visual observation.

TABLE IV

Coating Bath Ingredients	Coating Bath Composition (g/l)				g/l Stearate	Moisture Pick-Up 120 Min. RH = 92% @ 80 F	Crystals Per Inch	Coating Characterization	Coating Appearance
	Sodium	Potassium	Sulfate	Tetra Borate
A- Sodium Sulfate	54.3	-	113.2	-	-	120%	87	Mixed Glaze/Crystalline	Non-Uniform
B- Sodium Sulfate and Sodium Tetraborate	51.9	-	96.3	19.3	-	98%	126	Crystalline	Uniform
C- Sodium Sulfate and Sodium Stearate Soap (10.0 g/l)	55.0	-	113.2	-	9.3	103%	167	Crystalline	Non-Uniform
D- Potassium Sulfate	-	75.2	92.3	-	-	0%	43	Mixed, Mostly Glaze	Non-Uniform
E- Potassium Sulfate and Sodium Stearate Soap (10.0 g/l)	0.7	75.2	92.3	-	9.3	1%	50	Mixed, Mostly Glaze	Non-Uniform
F- Potassium Sulfate and Sodium Stearate Soap (0.1 g/l)	trace	75.2	92.3	-	0.09	1%	80	Mixed Glaze/Crystalline	Uniform
G- Potassium Sulfate and Ammonium Stearate Soap (0.1 g/l)	-	75.2	92.3	-	0.09	1%	77	Mixed Glaze/Crystalline	Uniform
H- Potassium Sulfate and Potassium Tetraborate	-	72.3	78.6	16.7	-	4%	93	Mixed Glaze/Crystalline	Non-Uniform
I- Potassium Sulfate and Sodium Tetraborate	5.7	63.9	78.6	19.6	-	7%	86	Mixed Glaze/Crystalline	Non-Uniform
J- Potassium Sulfate, Sodium Tetraborate and Sodium Stearate	5.7	63.9	78.6	19.6	0.09	5%	153	Crystalline	Uniform

[0025] In Table IV, coating compositions F, G, and J are com­positions in accordance with the invention, while compositions A, B, C, D, E, H and I are comparison compositions. As can be seen from Table IV, compositions F, G, and J produced uniform coatings while exhibiting low moisture pick up. The only comparison com­position that produced a uniform coating was composition B, which however exhibited an unacceptably high moisture pick up. In fact, compositions A, B and C all exhibited unacceptably high moisture pick up, and hence poor wire drawability properties in humid con­ditions. Coating composition E contains potassium sulfate and sodium stearate soap in accordance with the compositions of the invention, except that the sodium stearate soap is present in too high a quantity, resulting in a non-uniform, mostly glaze coating, having unacceptable wire drawing properties. Coating compositions D, H, and I which are potassium salt compositions in accordance with the invention except that no soap is present therein, all produced unacceptable non-uniform coatings and hence unaccep­tability inconsistent wire drawing characteristics. In comparing coating compositions F, G and J of the invention, composition J containing an alkali metal tetraborate produced the most crystalline coating. Hence, the presence of a tetraborate in the coating compositions of the invention, while optional, is nonetheless highly preferred.

Claims

1. A composition for coating steel wire to facilitate the cold drawing thereof, said composition comprising:
(A) from about 50 to about 99.99 % by weight of a component selected from the group consisting of Na₂SO₄, K₂SO₄, and mixtures thereof;
(B) from about 0 to about 49.99 % by weight of a component selected from the group consisting of Na₂B₄O₇, NaBO₂, K₂B₄O₇, KBO₂ and mixtures of any two or more thereof; and
(C) from about 0.01 to about 5 % by weight of a component selected from the group consisting of potassium soaps, sodium soaps, and ammonium soaps;
wherein the percentages by weight are based on the total weight of components A, B, and C in the composition, and wherein not more than 50 % by weight of the total of sodium plus potassium plus ammonium ions in components A, B, and C of the composition consists of sodium ions.

2. A composition according to claim 1, wherein component C is selected from the group consisting of ammonium stearate, potassium stearate, and sodium stearate.

3. A composition according to claim 1 wherein not more than 10 % by weight of the total of sodium plus potassium plus ammonium ions in the composition consists of sodium ions.

4. A composition according to claim 1, wherein substantially none of the ions in the composition are sodium ions.

5. A composition according to claim 1, wherein component A is present in from about 70 to about 89.9 % by weight.

6. A composition according to claim 1, wherein component B is present in from about 10 to about 29.9 % by weight.

7. A composition according to claim 1, wherein component C is present in from about 0.1 to about 1.0 % by weight.

8. A composition according to claim 1, wherein component B is selected from K₂B₄O₇ and Na₂B₄O₇.

9. A composition according to claim 1, wherein the composition includes water which dissolves components A, B, and C to form an aqueous solution.

10. A composition according to claim 1, wherein the composition contains from about 70 to about 400 grams of the total of components A, B, and C per liter of solution.

11. A composition according to claim 1, wherein the aqueous solution contains from about 150 to about 250 grams of the total of components A, B, and C per liter of solution.

12. A composition according to claim 1 wherein the composition includes water which dissolves components A, B, and C to form an aqueous solution which contains from about 70 to about 400 grams of the total of components A, B, and C per liter of solution.

13. A method for the drawing of steel wire, the improvement comprising coating the wire prior to drawing with a composition comprising:
(A) from about 50 to about 99.99 % by weight of a component selected from the group consisting of K₂SO₄, Na₂SO₄, and mixtures thereof;
(B) from about 0 to about 49.99 % by weight of a component selected from the group consisting of Na₂B₄O₇, NaBO₂, K₂B₄O₇, KBO₂, and mixtures of any two or more thereof; and
(C) from about 0.01 to about 5 % of a component selected from the group consisting of ammonium soaps, potassium soaps, sodium soaps, and mixtures of any two or more thereof;
wherein the percentages by weight are based on the total weight of components A, B, and C in said composition, and wherein not more than 50 % by weight of the total of sodium plus potassium plus ammonium ions in the composition consists of sodium ions.

14. A method according to claim 13, wherein component A is present in from about 70 to about 89.9 % by weight, component B is present in from about 10 to about 29.9 % by weight, and component C is present in from about 0.1 to about 1.0 % by weight.

15. The method of claim 13 or 14 wherein the steel wire is stainless steel.

16. A method according to claim 13 wherein, component C is selected from the group consisting of ammonium stearate, potassium stearate, and sodium stearate.

17. A method according to claim 13 wherein not more than 10 % by weight of the total of sodium plus potassium plus ammonium ions in the composition consists of sodium ions.

18. A method according to claim 13, wherein substantially none of the ions in the composition are sodium ions.

19. A method according to claim 13, wherein component A is present in from about 70 to about 89.9 % by weight.

20. A method according to claim 13, wherein component B is present in from about 10 to about 29.9 % by weight.

21. A method according to claim 13, wherein component C is present in from about 0.1 to about 1.0 % by weight.

22. A method according to claim 13, wherein component B is selected from K₂B₄O₇ and Na₂B₄O₇.

23. A method according to claims 13 to 22, wherein the composition includes water which dissolves components A, B, and C to form an aqueous solution.

24. A method according to claims 13 to 23, wherein the composition contains from about 70 to about 400 grams of the total of components A, B, and C per liter of solution.

25. A method according to claims 13 to 24, wherein the aqueous solution contains from about 150 to about 250 grams of the total of components A, B, and C per liter of solution.

26. A method according to claims 13 to 25, wherein the composition includes water which dissolves components A, B, and C to form an aqueous solution which contains from about 70 to about 400 grams of the total of components A, B, and C per liter of solution.