U. S. Department of Agriculture, Forest Service
FOREST PRODUCTS LABORATORY
In cooperation with the University of Wisconsin
NEW NAIL TREATING PROCESS INCREASES HOLDING POWER
By J. M. GAHAGAN
Assistant Er. r,.'.
BARREL and BOX and PACKAGES
Digitized by the Internet Archive
NEW 1LIL TRAT.I:, PROCESS I::C.S-S HOLDING P0.
J. M. Gahagan,
assistant t Engineer
Everyone who has used wood may have observed wide differences
in the ease with which nails can be pulled from it. Some of the causes
of difference in nail holding are splitting or mutilation of tie wood
in driving as affected by the nail point, moisture ci, i..--s in thie wood,
and the degree of frictional resistance between the nail surface and the
wood. An understanding of the influence of these factors enzibls one to
account for many of the observed differences in beilavior of nails in
resisting withdrawal from wood and serves as a basis for iLmprovements
which will overcome some of tie more apparent deficiencies.
The holding power of nails centers largely around the
frictional contact of the nail with the wood fibers, hence the improvemLent
of the surface by increasing its frictional resistance offers an excellent
opportunity for enhancing nail-holding power. Such a surface condition
may be obtained by a treatment developed at the Zorest Products Laboratory
for nails and other metal fastenings for wood.
The improved surface is obtained by a chemical treatment
that produces microscopic pitting or etching of the nail surface, thereby
increasing its frictional resistance. To the unaided eye th; pitted
surface of tne F. P. L. nail appears practically the sa.ie as the original
in that there is no apparent roughening. W7hat has &,ctuclly liappeoned,
however, is a breaking up, by means of pits or minute etcihings, of the
smooth surface areas between striations left by tij dies in the process
of drawing wvire in nail manufacture.
A number of tests made on wire nails and staples having this
newly developed type of surface gave decidedly higher values for
resistance to withdrawal than were obtained with similar fastenings
having plain, cement-coated, or grossly roughened surfaces. ,
comparison of the resistance to direct withdrawal of the F. i. L. nail
with that of a plain or a cement-coated nail may be made from Table 1.
Table l.--Average holding power of 7d wire nails driven 1-1/4 inches
and pulled ir.ediately from dry wood of different species
S Side holding : Latio to plain
Species- :Plain:Cement-: F.P.L. Plain : Ceient- : F.P.L.
:nail :coated treated nail : coated : treated
nail : nail : nail : nail
- - - - - - - - - - - - . . . .- : - - -
Lbs. : Lbs. Lbs. Per :Per cent :Per cent
: : cent
Sugar maple......... :374 716 100 : 191
Yellow birch........ 220 -- : 613 100 276
Ponderosa pine...... 75 : 140 216 100 : 187 : 288
Lowland wnite fir...: 72 : 201 : 221 100 : 279 307
No comparison between species can be made from this table since the
specimens do not represent the average quality of each species.
Where specimens were nailed and allowed to season for
several months before testing, the treated nail again gave :iiiier val'ujs
than either plain or cement-coated nails. With staples the treatment
likewise proved effective.
Methods previously advocated for increasing the nai -nloling
power have consisted, in the mLain, of surface coatings or of grossly
roughened surfaces prouucea either by mechanical or chle.ical means.
Surface coatings often have the disadvantage that they may be remove.
in handling, or their effectiveness otherwise lost through disint grationi
with time. nh, grossly roughened surfaces which may be produced in
various ways are, through a slight loss of intimate contact with the
wood fibers, less effective than the microscopic pitting resulting from
the new F. P. L. treatment.
The desired pitted condition of the F. p. L. nail is obtained
as follows: The nails and staples, or the wire from wvicn they are to be
made, are subjected to the action of a 2 per cent solution of ferric
chloride in water in tre presence of mercuric chloride or salts of oti.r
metals, particularly of those falling below iron in tiij electruclemical
series. On removal from the solution, the materials re .llowed to ary
in a wLarm atmosphere after which tiey are exposed at a temperature of
approximately 1000 C., and a relative humidity of about 60 per cent.
The nails, staples, or wire is immediately imoirsed in water in oruer to
fix the adhering iron oxide.
The treatment has not yet been carried out on a large scale,
but its commercial application would appear to present no particular
difficulty. A suitable vat for the initial dippinj is necessary. L
batch of nails, for instance, may be held in a perforated wooden
container, lowered into the ferric chloride solution and allowed to
remain from five to ten seconds, a time sufficiently long to thoroughly
wet the surfaces of the nails. (This step is essentially the same as
the pickling treatment commonly practiced in steel and .-ire mills where
the rod is dipped anad cleaned in an acid solution preparatory uo drawing
into wire.) A dry, hot chamber to receive tne wet nails should be
provided adjacent to the dipping vat. After drying, tlne actual etcning
of the nails is accomplished in a relatively short time by subjecting
them to a hot, humid atmosphere. The hot drying chamber may serve a
dual purpose in this respect if it is provided witn an inlet for live
steam. In this way a moist atmosphere at SO0 C. may be readily obtained.
The object of drying the fastenings before subjecting them to the hot,
humid atmosphere is to minimize scail formation and tc,-reoy secluwr a
finer pitting effect.
After 1-1/2 hours in the S0 per cent relative humLidity chaber
the nails may be removed in the perforated wooden containers .and i".,ersed
in boiling water. During this treatment oxidation of the. iron o.'ide to
the magnetic oxide occurs, giving a black appearance to the nails. Part
of the oxide is loosely held and should be buffed off not only to improve
the appearance of the fastener but also to iore fully expose tae pitted
surface to frictional contact with the wooao The treating solution, biing
of acid character, ;aust necessarily be kept within an acia rang of
PH 3.2 5.0, and observation of this property may re-Idil b3e ruade by the
use of a suitable indicator.
UNIVERSITY OF FLORIDA
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