Vinyl coated hot galvanized driven fasteners and method for manufacture thereof

Abstract

Nails are manufactured using a sequence of steps including hot galvanizing of the nails with a zinc/tin/flux composition followed by vinyl coating to provide fasteners which resist corrosion that may result from chemically treated wood and cement infused materials.

Description

BACKGROUND OF THE INVENTION

In a principal aspect the present invention relates to the manufacture of galvanized steel nails used in the construction of chemically treated wood structures and the application of cement fiber siding for buildings. The galvanized steel fasteners are coated with a vinyl material which significantly improves resistance to the corrosive effects of ACQ (Ammoniacal Copper Quatenary) treated lumber, cement fiber lap siding and atmospheric conditions.

Structures made from lumber are often built utilizing chemically treated wood.

The chemically treated wood resists degradation and rotting caused by weather and atmospheric conditions. Heretofore, such chemically treated wood was subjected to treatment with an arsenic based chemical known by the acronym CCA. With the advent of increasingly stringent environmental protection regulations, arsenic based chemicals for wood treatment have been dropped from approval in residential applications. A new chemical known as Ammoniacal Copper Quatenary (ACQ) is now approved as a wood preservative and for treatment of wood to prevent spoliation and rotting. However, ACQ tends to cause degradation and corrosion of fasteners, even those fasteners which are galvanized.

Corrosive effects of fastening materials for building are not limited to ACQ treated lumber. Siding materials, particularly cement fiber lap siding and cedar or redwood siding have well-publicized corrosive properties prompting manufacturers to recommend stainless fasteners or galvanized fasteners with “extra” zinc coating.

As a consequence of the corrosive effects of building materials, a need has developed for an improved fastener and a method for manufacture of such a fastener which resists degradation due to interaction with new preservative chemicals, such as ACQ or interaction with siding products such as cedar, redwood or cement fiber. The present invention relates to such a method and article. The invention relates principally to nails, but may be applied to other components used in the assembly and/or manufacture of lumber products which have corrosive properties. Such fasteners include, without limitation, common nails, box nails, helical (drive screw) nails, smooth nails, roofing nails, siding nails, fence staples, stockade staples, barbed staples, barbless staples and poultry staples.

SUMMARY OF THE INVENTION

Briefly, the present invention comprises a method for manufacture of metal fasteners, nails, or components used in construction especially wherein the construction lumber has been chemically treated or wherein lap siding contains cement. The process comprises the following steps:

First, the fastener or article is galvanized. It is important that a galvanizing process be utilized that:

(a) provides a metallurgically bonded interface between the zinc and the metal substrate,

(b) sufficient zinc is applied to provide corrosion protection; and

(c) the surface of the galvanized article has an appropriate roughness for successfully completing subsequent steps in the process of manufacturing a vinyl coated article.

Second, the article is rinsed by a selected method to prepare the surface for vinyl coating.

Third, the article is dried.

Fourth, the article is coated with a vinyl composition typically by dipping in a tank of vinyl solution.

Fifth, the vinyl coated article is removed from the coating tank and dried.

Sixth, the vinyl is allowed to cure to provide a final coated article or product such as a fastener.

Among the advantages associated with the invention is retardation of degradation of the galvanized coating and thus delay of corrosion and degradation of the underlying metal article or fastener. It is noted that typically the article or fastener will be fabricated from a non-stainless steel alloy.

Thus, it is an object of the invention to provide an improved galvanized article or fastener useful in the assembly of treated wood, cement fiber lap siding and lumber made with acidic woods such as cedar and redwood.

It is a further object of the invention to provide a process for manufacture of vinyl coated, galvanized fasteners that may be driven.

Another object of the invention is to provide a process for manufacture of articles that will resist degradation due to corrosion.

These and other objects, advantages and features of the invention will be set forth in the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWING

In the detailed description which follows, reference will be made to the following figures:

FIG. 1 is a flow diagram illustrating sequential steps in the manufacture of the galvanized articles in the practice of an embodiment of the invention;

FIG. 2 is a microphotograph of a section of a nail made in accord with the process of FIG. 1 at 400×;

FIGS. 3(a), 3(b) and 3(c) comprise a series of microphotographs analogous to FIG. 2 depicting the surface at 400× of a fastener which is not galvanized (FIG. 3(a)), hot dip galvanized (FIG. 3(b)) and electro-galvanized (FIG. 3(c));

FIG. 4 is a bar graph comparing corrosion resistance for various coatings; and

FIG. 5 is another bar graph comparing corrosion resistance for various coatings.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The components which are manufactured and which are processed in accord with the methods of the invention are typically fasteners such as nails and staples (particularly those made from steel and iron based alloys) utilized in the assembly or manufacture of chemically treated lumber, cedar, redwood or cement fiber siding. For example, decks, fences, storage buildings and the like may be manufactured or built from treated lumber. Heretofore, such lumber was treated with arsenic-based compounds. Such compounds inhibited degradation of the lumber due to weathering and the like. Environmental protection regulations now prohibit the use of such arsenic based chemicals or compounds in certain applications and as a result such chemicals have been replaced by alternative chemicals including Ammoniacal Copper Quatenary (ACQ) treated lumber.

The new chemicals, however, tend to corrode steel and iron-based fasteners. Additionally, new developments in home exteriors include cement lap siding which may seriously corrode the fasteners used to secure the siding. Thus there has developed a need for providing fasteners or other construction articles which resist such corrosion. The multiple step process of the invention employs steps including an initial galvanizing step.

It is to be noted that there are multiple types of galvanizing available for fasteners and other items. For example, galvanizing may be effected by a “double hot dipped” method. Such a method employs hot dipping a fastener in molten zinc. In such a process, the fasteners are dipped in and completely immersed into a vat of molten zinc. Double dipping, of course, implies that such immersion occurs twice.

Another method of coating fasteners is to plate such fasteners with a layer of zinc by a process often referred to as peen plating. In such a process cold fasteners are placed in a container of zinc dust along with tiny glass spheres and an activator fluid. As the container rotates, the spheres hammer or peen the zinc dust onto the fasteners. This results in a rather thin layer of zinc deposited on the fastener. The fastener is then typically immersed in a chromate rinse. Of course, chromate processes, such as employed with this method, are also subject to severe environmental regulations and prohibitions.

Another plating method involves electroplating. In such a process, metal fasteners or components are placed into a basket in an electrolyte solution such that a thin film of zinc is deposited by means of electric current from zinc anodes. This is a generally non-economical process. Moreover, the coating may oxidize so that such coated fasteners may be subject to rusting or corrosion rather quickly.

Another process is known as hot galvanizing. In hot galvanizing, also known as a tumble or barrel process, fasteners are coated by a process which combines zinc chips, a flux material and tin with the cold steel fasteners in a barrel or container. The barrel or container is heated in a furnace and the zinc flakes or chips melt and coat the fasteners. This process provides a somewhat uneven, coarse coating although the article is effectively coated with a protective layer of zinc and tin. The flux is typically incorporated in the process to facilitate the coating operation.

In the practice of the invention, it has been found that the hot galvanizing, also known as the tumble or barrel process, is generally considered the most effective manner to initiate the preparation of a superior corrosion resistant fastener or article useful to resist the corrosive effects of the previously noted building materials. Other galvanizing processes may be employed; however, final product properties (adherence of the coating) may be partially compromised. Thus, as a first step as set forth in FIG. 1, the fastener or article is preferably subjected to a hot galvanizing process. The resultant hot galvanized material has a zinc coating weight of 0.8-1.8 oz/ft² and a surface with a degree of porosity or roughness as characterized in Table I and the photo, FIG. 2.

TABLE I
Peak Height	No. of	Ave Peak
Range (in.)	peaks/in	Height (in.)
.001–.009	7–10	0.003

In certain cases, the desire to use hot dipped galvanizing in place of hot galvanizing can be accommodated if an extra step is used to condition the fastener surface to accept the vinyl coating. A dilute acid rinse (15% Hydrochloric acid) has been found to slightly enhance the vinyl coating step in such a circumstance.

Subsequent to the hot galvanizing process, the nail or fastener or article is rinsed or cleaned typically with water though a caustic or acidic rinse may be used. Thereafter, the nail or fastener is dried as it must be substantially free of dust, dirt, oil and contaminants.

Subsequently, the fastener is dipped and coated in a vinyl solution such as the “Waterborne Green Nail Coating” liquid vinyl solution Product Code 160-G-28 marketed by National Coatings, Inc. of Galesburg, Ill. A nail coating solution is available from a variety of manufacturers and is used in the industry to produce “Vinyl Coated” sinkers. Application methods for the vinyl solution include: vertical, horizontal, tumble, centrifuge, belt feed, dip, flow, wipe or rolling.

Typical vinyl compositions and coating parameters are as follows:

TABLE II
                            35% Solids in a
Vinyl Composition:          water-based solution
Application Concentration:  8–12% solids
Solution temperature range: 160–200 Deg. F.
Range of immersion times:   10–15 sec.

Subsequently, as illustrated again in FIG. 1, the vinyl coated item is removed from a dipping tank, dried and cured. Cycle time for curing can vary but a recommended minimum of two minutes at 180° F. to a maximum of five minutes at 325° F. are recommended. The resultant component or item will typically then have a layer of zinc or a zinc and tin alloy in the range of 0.8-1.8 oz/ft² and a vinyl coating approximately 2 mils thick. Coating weight of the vinyl is in the range of 0.05-0.07 oz/ft².

Utilization of such vinyl coated fasteners delays degradation of the galvanized coating and thus precludes corrosion of the underlying or substrate steel or iron based alloy fastener. Following are the results of corrosion tests in two (2) different applications: ACQ Treated Lumber and Cement Lap Siding.

FIG. 4—Treated Lumber Test

The nails were tested in accord with the American Wood-Preservers' Association Standard E12-94. The nails were tested with the ACQ treated lumber. Temperature was held at 120° F. with a relative humidity maintained at 90%. The hot dipped (double dipped) samples are used as the reference base of 1. The increased corrosion resistance number is a factor of the hot dipped number (Example: a 4.33 is 4.33 times more resistant to corrosion than hot dipped).

FIG. 5—Lap Siding Test

Nails were tested following the American Wood-Preservers' Association Standard E12-94 with cement lap siding. Temperature was held at 120° F. with relative humidity maintained at 90%. The double dipped samples are used as the reference base of 1. The increased corrosion resistance number is a factor of the hot dipped number (Example: a 2.0 is 2 times more resistant to corrosion than Double Dipped).C

As FIGS. 4 and 5 illustrate, corrosion protection afforded by the vinyl coating fasteners reduced the corrosion rate by a factor of 2.86 (FIG. 4) when tested in ACQ treated lumber and 2.05 (FIG. 5) in testing with cement lap siding.

It has been found highly desirable to use the hot galvanizing process inasmuch as it provides a rough or partially porous zinc coated surface which is more suited to receive and provide for improved adherence of the vinyl coating. FIGS. 3(a), 3(b) and 3(c) depict the surface character associated with the type or process of zinc coating. The process of FIG. 3(a) is preferred due to the increased surface roughness.

Thus, the nature of the surface of a hot galvanized nail provides an excellent base for the vinyl to bond and also produces a uniform coating. Other types of galvanizing or zinc coating processes were not as useful but can be workable provided there is sufficient zinc deposition as well as enough heat in the zinc coating process to form a metallurgical bond between the metal substrate and the zinc coating. For this reason, electroplating (insufficient zinc) and mechanical galvanizing (no metallurgical bond) techniques are not recommended. Hot dip galvanizing provides the requisite metallurgical bond but the surface is smooth and vinyl adhesion is impaired. Coverage is uneven and the zinc substrate is still exposed in many spots. Poor coverage on the surface of a hot dipped nail can be overcome to some extent by either pretreatment with a dilute (15%) acid or caustic solution or by multiple passes through the coating line (i.e. two or three coats of vinyl solution).

Thus, the invention provides a coated fastener or article which is useful, can be economically manufactured, and which resists corrosion. Multiple other articles may advantageously be treated by the method such as hardware items, hanger straps, screws, bolts and the like.

While there have been set forth specific parameters and steps with respect to the conduct and practice of the invention, it is to be understood that the invention is limited only by the following claims and equivalents thereof.

Claims

1. A method for manufacture of corrosion resistant articles useful in the assembly of chemically treated wood products and corrosive materials comprising, in combination, the steps of:

(a) galvanizing said article by a zinc galvanizing process to provide a zinc base coating of said article;

(b) cleaning said article in a solution;

(c) drying said article;

(d) coating said article with a liquid vinyl composition; and

(e) drying and curing the vinyl coating.

2. The method of claim 1 comprising the step of forming a zinc base coating on said article with a roughness in the range of 7-10 peaks per inch with heights ranging from 0.001-0.009 in and averaging about 0.003 inches prior to coating with said vinyl composition.

3. The method of claim 1 wherein the galvanizing comprises a process selected from the group consisting of hot galvanizing and hot dip galvanizing.

4. The method of claim 1 wherein galvanizing comprises coating the article with said layer of zinc in the range of about 0.8 to 1.8 oz/ft2.

5. The method of claim 2 wherein coating the article with said vinyl composition comprises coating with a layer of vinyl in the range of about 0.5 to 0.7 oz/ft2.

6. The method of claim 1 wherein the step of cleaning the article comprises the step of cleaning in a solution selected from the group consisting of water, a caustic solution and an acidic solution.

7. The method of claim 4 wherein coating the article with said vinyl composition comprises coating with a layer of vinyl in the range of about 0.5 to 0.7 oz/ft2.

8. A method for assembly of a structure wherein at least components of the structure comprise wood treated with ACQ or comprise cement lap siding comprising the steps of:

fastening building components made in accord with the method of claim 1.

9. A method for assembly of a structure wherein at least components of the structure comprise wood treated with ACQ or comprise cement lap siding comprising the steps of:

fastening building components made in accord with the method of claim 2.

10. A method for assembly of a structure wherein at least components of the structure comprise wood treated with ACQ or comprise cement lap siding comprising the steps of:

fastening building components made in accord with the method of claim 5.

11. A method for assembly of a structure wherein at least components of the structure comprise wood treated with ACQ or comprise cement lap siding comprising the steps of:

fastening building components made in accord with the method of claim 6.

12. A method for assembly of a structure wherein at least components of the structure comprise wood treated with ACQ or comprise cement lap siding comprising the steps of:

fastening building components made in accord with the method of claim 7.