CA1265392A

CA1265392A - Zinc shot-blasting steel

Info

Publication number: CA1265392A
Application number: CA000520130A
Authority: CA
Inventors: Yoshihiko Sawazaki; Yoshio Nagae; Koji Hetsugi
Original assignee: Nihon Parkerizing Co Ltd
Current assignee: Nihon Parkerizing Co Ltd
Priority date: 1985-10-08
Filing date: 1986-10-08
Publication date: 1990-02-06
Also published as: GB8624168D0; GB2182352A; IT8621921A1; DE3632335A1; GB2182352B; IT8621921A0; FR2588276A1; JPS6283477A; IT1197361B

Abstract

ABSTRACT OF THE DISCLOSURE

A method for improving the corrosion resistance and paint receptivity of a steel surface includes shot blasting the steel surface with particles of zinc or zinc alloy or particles coated with zinc or zinc alloy and then contacting the surface with a nickel containing acidic phosphate liquor.

Description

~ 3g~ P30,09, Background of the Invention This invention concerns a method oE surface treabment for steels in which shot blasting and a phosphate treatment are co~bined.

Conventionally, steel surfaces have been given a phosphate treatment in order to improve the corrosion resistance after painting.
However there is a demand for painting pre-treatment methods for improving the corrosion resistance to a greater extent than is achieved using this method.

For example in the case of large structures such as television towers the construction costs are very high and the structure must be protected from rusting over a long period of time in order to retain its quality over long periods.

As well as the methods involving phosphate treatment, there are also methods in which the steel is zinc plated and then subjected to a phosphate treatment for improving the corrosion resistance of steels. However with these methods the steel must be subjec~ed to an acid washing process in order to activate the surface in sases where there is rust or black scale on the steel prior to the zinc plating process and so a complicated procedure involving acid washing ~ water rinsing ~ plating operations has to be adopted. There are other problems with plating apart from these difficulties, namely (1) a large plating bath is required to deal with large parts and the plant costs are high, (2) the plating bath rnust be controlled and (3) waste water treatment is required for the plating process.

This invention is intended to overccme the aforementioned problems associated with the plant, the cost, and waste water treat-ment.

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53~2 Summary of the Invention The inventors have removed the oxide film oE rust, black scale, etc. from the surface of steel materials and simultaneously formed a zinc or zinc alloy film on the surface as a result of the impact of fine particles of zinc~ zinc alloy or zinc or zinc alloy covered metal by impacting the said particles onto the surface using a shot blasting system as a means of overcoming the aforementioned difficulties. The film of zinc or zinc alloy which is formed on the steel surface has gaps between the zinc aggregates due to the impact of the fine particles~ The invention is achieved by forming a phosphate film by treatment with a phosphate treatment liquor to which nickel ions have been added and filling the gaps between the aforementioned fine particles with phosphate crystals.

Detailed Description of the Invention The fine particIes of zinc, zinc alloy or zinc or zinc alloy covered metal which are used in the invention have a particle size of 0.2 - 1.1 mm. They should have a hardness high enough to remove the oxide film from the surface of the steel material and so particles obtained by coating zinc onto fine iron based particles and then heating the particles to form a zinc film which is alloyed with the iron of the fine iron based p~rticles are best. Such particles are available commercially as Z-Iron Aloyed Shot (hardness Hv >
350-450) which are manufactured by the Sanpo Company. The extent of the film of metallic zinc or zinc alloy which is formed on the surface of the metal material is suitably some 0.1 - 50 g/m2 in view of the economic considerations. The shot time beca~es longer as the extent of the film of metallic zinc or zinc alloy is increased.
Furthermore the amount of shot discharged is increased in cases where the said metal film is to be formed in a short period oE time. In general the projection thickness is 10 - 150 mm.

An acidic phosphate treatment liquor is used for the phosphate treatment liquor, for example the treatment liquor dis-closed in Japanese Patent No. 42-12130 ~1967) can be used. Nickel ion is added to the phosphate treatment liquor and is an essential . .

;3~312 component which suppresses the dissolution of the zinc or zinc alloy film which has been formed on the surface of the steel during the phosphate treatment and it is added at the rate of 0.05 - 10 grams/
liter. If less than 0.05 grams/liter of nickel ion is added the addition does not have a satisfactory effect while the addition of more than 10 grams/liter is economically disadvantageous and the preferred nickel content is 0:1 - 5 grams/liter. The phosphate ion which is included in a normal phosphate treatment liquor is added at the rate of 5 - 100 grAms/liter, the zinc ion is added at the rate of 0.3 - 7 grams/liter, the nitrate ion is added at the rate of 1 - 30 grams/liter, the fluoride ion is added at the rate of O.l - S grams/
liter and the organic acid is added at the rate of 0 - 10 grams/liter.
The nickel ion may be added in any soluble form such as nickel nitrate, nickel carbonate etc.

The phosphate treatment is carried out by dipping or spraying at a temperature within the range of room temperature - 80C
for a period within the range 5 seconds - 10 minutes. The surface on which the zinc or zinc alloy film has been formed can be subjected to an adjusting treatment with an a~ueous solution for surfa~e adjust-ment purposes which contains colloidal titanium in order to speed up the film forming reaction or to help prevent the dissolution of the zinc or zinc alloy during the phosphate treatment. m e known aqueous solutions for surface adjustment purposes which contain colloidal titanium can b~ used, for example an aqueous solution which contains 25 1 - 5ao ppm of titanium ion, 200 - 3000 ppm of phosphate ion, 50 -600 ppm of pyrophosphate ion and which has a pH value of 8.0 - 9.5 can be used for this purpose. The metal which is being treated is next subjec*ed to a phosphate treatment to form a phosphate film on the surface of the said metal and then it is rinsed with water, dried and the paint underooat is established.

Sealing with a conventional aqueous chromic acid or chromium-free solution, a dispersion or solution of resin, an aqueous solution of tannic acid or an aqueous solution of colloidal silica etc. can be carried out after the phosphate treatment in order to improve the corrosion resistance.

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The oxide film on the surface of the metal material is re ved physically by shot blasting fine particles of zinc, zinc alloy, metal which is covered with zinc or metal which is oovered with zinc alloy onto the surface of the metal material and at the same time the aforementioned fine particles become strongly adhered or penetrate into the surface of the metal material and a film of zinc or zinc alloy is formed. This film has gaps since it IS an aggregate formed by the impact of the fine particles and it does not provide the same level of corrosion resistance as a oonventional zinc plating, but a phosphate film is formed by subjecting the surface to a phosphate treatment and the aforementionecl gaps due to the fine particles are filled with phosphate crystals. A film which has good corrosion resistance as a paint undercoating is formed. The nickel ion in the phosphate treatment liquor or the surface adjustment with colloidal titanium suppresses the etching reaction of the phosphate treatment liquor on the zinc or zinc alloy film which has been formed on the steel surface during the phosphate treatment and preven-ts the gaps between the aforementioned fine particles from becoming larger.

Exa~le 1 Rusty SPCC-D steel plates measuring 0.8 x 100 x t50 mm were shot blasted for lO minutes with fine zinc particles of particle size 0.2 - 0.3 mm to remove the rust and at the same time a 15 g~m2 film of metallic zinc was formRd on the surface.

After surface adjustment and phosphate treatment the steel plates were rinsed with water and treated with an aqueous solution which contained trivalent and hexavalent chromium ~"Parcolene~ 62l', 10 grams/liter, supplied by Parker' Chemical Company) and then they were passed through a squeeze roll and dried. The weight of the phosphate film was 1.4 g/m2. The treatment conditions were as follows:

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~26~ 2 Surface Adjustment . . . . _ .. . .
Treatment Liquor A colloidal titanium oontaining liquor ("Parcolene~ Z"~ Parker Chemical Company) Treatment Conditions Spraying, Temperature 50C, Time 5 seconds Phosphate Treatment Treatment Liquor Zn2+ 2.5 g/l, PO34~ 10 g/l, No~ 3 g/l, Ni 2.0 g/l, F 0.2 g/l . _ - _ ., Method of Treatment Spraying, Temperature 70C, _ Time 7 seconds . _ . . . _ The treated steel plates were painted using the bar coating method with an alkyd melamine based paint tregistered trade mark "Amilac No. 1 White", made by the Kansai Paints (Co.)) and after setting for 20 minutes this was baked for 25 minutes in a hot air circulation oven at an atmospheric temperature of 140~C to form a painted sheet with a paint film of thickness 30 + 2 microns and the resulting plates were subsequently subjected to paint film adhesion tests and salt water spray tests with the results shown in Table 1.

Test Methods Paint Film Adhesion Test 1) Checkerboard Erickson Test Cuts were made from the surface of the paint to reach the base ; ~ material in the form of a checkerboard pattern with squares of side 1 mm using an NT cutter and the plate was then pushed out 5 mm with an Erickson tester, stripped wlth cellophane tape and the amount of paint remaining was assessed in terms of number of remaining squares per 100.
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The basis of the assessment was as follows:
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Number of checkerb~ad squares: ~ore than 95 5 points 80 - 95 4 points 60 - 80 3 points 40 - 60 2 points Less than 40 1 point r

2) Impact Test The surface was subjected to an impact using a DuPont type impact tester (Projectile 1/2 inch, weight 500 grams, dropping distance 50 cm~ and then the surface was stripped with cellophane tapc and given the appropriate score.

The basis of the assessment for paint fill adhesion was as follows:

. . ._ _ ___._ , No stripping of the paint film 5 points Area of paint film peeled with respect to the test surface:
LRSS than 5% 4 points 5 - 25~ 3 points 25 - 50~ 2 points More than 50~ 1 point Thus a higher s~ore indicates better paint film adhesion.
Salt Water Spray Tests 1. Painted Plates Cross shaped cuts were made from the surface of the paint on the test sheet to reach the base material using an NT cutter and the plates were then subjected to salt water spray tests in acoordance with JIS-Z-2371 for a period of 120 hours. The painted surfaces were then rinsed with water and dried, stripp~d with cellophane tape and an assessment was made on the basis of the state of peeling of the paint surface.

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~2~53~2 The standards for assessment were as follows:
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Smooth Part Cross Cut Part __ ___ No anomaly No anomaly S points Width of peeling on both sides .. from the cross c~t part:
.. Within I mm4 points Within 2 mm3 points Spcts of peeling Great width of peeling and separation 2 points Surface peeling _ 1 point 2. Unpainted Sheets Salt water spray tests were carried out for 24 hours and an assessment was made on the basis of the area on which white rusting had occurred.

The assessment standards were as follows:
. . _ .. _ . __ __ j Area of white rusting O - 5~ 5 points 5 - 15% 4 points 15 - 35% 3 points 35 - 5Q% 2 points ZOArea of red and white rusting: More than 50~ 1 point . ~

Carried out under the same conditions as in Example I, except that the surface adjustment with colloidal titanium was omitted.

The weight of the phosphate film was 1.9 g/m2. The resul~s obtained were as shown in Table 1.

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Carried out under the same conditions as in Example 1 except that the shot material was changed from fine zinc powder to fine particles of metal covered with zinc-iron alloy (product name:
2-Iron Aloyed Shot, made by Sanpo KoK~)~

The weight of th~ phosphate film was 1.1 g/m2. The results obtained were as shcwn in Table 1.

Reference Exa~ple 1 Steel plates measuring 0.8 x 100 x 150 mm which had been electroplated with zinc at the rate of 15 g/m2 ~ere phosphate treated and painted with alkyd melamine based paint in the same way as in Example 1, the paint films being allowed to set for 20 minutes and then baked and dried at 140C for a period of 25 minutes. The resulting sheets were tested in the same way as in Example 1 and the results obtained were as shown in Table 1.

Reference Example 2 Carried out under the same conditions as in Example 2 except that the nickel ions were omitted from the phosphate treatment liquor. m e results obtained were as shcwn in Table 1.

Reference Example 3 Carried out in the same way as Example 1 except that fine iron particles of particle size 0.2 - 0.3 mm were used in place of the fine zinc particles of particle size 0.2 - 0.3 mm. The results obtained were as shown in Table 1.

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Table 1 . . .
Item Paint Film Adh~ sion Test Salt r~ater S )ray Test Checkerboard I~pactUnpainted Painted S ~ ~ r~ 24 r~rs ~ 120 N ur Ref 2 3 3 4 3 Ref 3 2 _ EfEect of the Invention .
It is possible by means o~ the method of this inven~ion to remove the oxide films such as rust or black scale etc. from the surface of a steel and to provide a zinc plating at the same time : 15without the need for the use of a plating bath, without the need to control any plating bath and without the need for waste water treatment and it is possible to obtain excellent paint undercoating films by treatment with a phosphate treatment liquor to which nickel ions have been added.

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for treating a steel to form a corrosion-resistant paint base coating thereon, comprising forming a film on the surface by shot blasting fine particles of zinc, zinc alloy, zinc covered metal or zinc alloy covered metal onto the surface of the steel and subsequently treating the shot blasted surface by contact-ing the surface with a phosphate treatment liquor which contains nickel ions.

2. The method of Claim 1 wherein the shot-blasted surface is subjected to contact with an aqueous colloidal titanium solution prior to contact with the phosphate liquor.

3. The method of Claim 1 wherein the shot-blasting is conducted under conditions of time and pressure to yield a deposit of from 0.1 to 50 g/m2 zinc.

4. The method of Claim 1 wherein the nickel concentration of the phosphate liquor is from 0.05 to 10 g/1.

5. The method of Claim 1 wherein the shot particles have a particle size of 0.2 to 1.1 mm.