U.S. patent application number 09/734502 was filed with the patent office on 2002-08-08 for low temperature nitriding and chrome plating process.
Invention is credited to Oglesby, Bob.
Application Number | 20020104588 09/734502 |
Document ID | / |
Family ID | 26866836 |
Filed Date | 2002-08-08 |
United States Patent
Application |
20020104588 |
Kind Code |
A1 |
Oglesby, Bob |
August 8, 2002 |
Low temperature nitriding and chrome plating process
Abstract
A steel part, such as a mechanical centrifuge screen of mild
steel with a nitriding layer on all exposed surfaces of the steel
to form an effectively hardened substrate layer, and electroplating
the nitrided steel part. The surface treatment method provides an
improved wear resistance and effectively provides improved erosion
and corrosion protection of the steel part.
Inventors: |
Oglesby, Bob; (Evansville,
IN) |
Correspondence
Address: |
Gary K. Price, Esq.
Suite 201
111 S.E. Third Street
Evansville
IN
47708
US
|
Family ID: |
26866836 |
Appl. No.: |
09/734502 |
Filed: |
December 11, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60171206 |
Dec 15, 1999 |
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Current U.S.
Class: |
148/220 |
Current CPC
Class: |
C23C 28/00 20130101;
C23C 8/80 20130101 |
Class at
Publication: |
148/220 |
International
Class: |
C23C 008/26 |
Goverment Interests
[0002] Statement as to rights to inventions made under Federally
sponsored research and development
[0003] Not Applicable.
Claims
I claim:
1. A surface treatment method for obtaining improved life of steel
parts, comprising the following steps in the sequence setforth: (a)
Nitriding the steel part on all exposed surfaces; and (b)
Electroplating the nitrided steel part.
2. The method of claim 1, wherein the nitriding is formed by vacuum
ion-nitriding.
3. The method of claim 1, wherein the nitriding is formed by salt
bath nitriding.
4. The method of claim 1, wherein the nitriding is formed by pulsed
ion-nitriding.
5. The method of claim 1, wherein the nitriding is formed by gas
nitriding.
6. The method of claim 1, wherein the electroplating is hard chrome
plating.
7. A surface treatment method for obtaining improved life of steel
parts comprising: (a) applying a nitrided layer about from 0.001 to
0.010 inches thick to the steel part on all exposed surfaces; and
(b) applying a hard chrome plating layer from 0.001 to 0.050 inches
thick to the nitrided steel part.
8. A surface treatment composition comprising: (a) a first layer of
nitriding; and (b) a second layer of hard chrome plating.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] U.S. Provisional Application for Patent 60/171,206, filed
Dec. 15, 1999, with title, "Low Temperature Nitriding and Chrome
Plating Process" which is hereby incorporated by reference.
Applicant claims priority pursuant to 35 U.S.C. Par. 119(e)(i).
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] This invention relates to a surface treatment for obtaining
improved life from mechanical screens as a result of a two-step
process of first nitriding as the first step, then chrome plating
of the nitrided screen as the second step. Each step, individually
is prior art. The combination of the two-steps resulting in an
unexpectedly long screen life.
[0006] 2. Brief Description of the Prior Art
[0007] Prior art processes for improving the life of steel parts,
such as mechanical screens, is to try to improve the hardness by
one of the conventional methods of nitriding of the steel such as
gas nitriding, vacuum ion-nitriding, or carbo-nitriding.
Experiments with these methods have proven not only to not extend
the lifetime of the screens but have actually reduced the lifetime
due to premature corrosive failure from the action of sulfuric acid
on the nitrided parts. Traditional electroplating with hard chrome
has proven to extend the lifetime somewhat by protecting the steel
underneath, but the lack of support from the relatively soft steel
screen eventually leads to surface stress failures which rapidly
degrade to corrosive and abrasive failure. The present invention
process combines these two techniques by nitriding the steel to
form an effectively hardened substrate for the hard chrome plating,
which in turn provides additional erosion and corrosion protection.
This combination duplex coating provides more protection than
either of the individual surface treatments separately, and results
in an unexpectedly long screen life.
[0008] Methods of nitriding is well known to the trade. Chrome
plating is well known to the trade. These are considered competing
processes in the trade.
[0009] Mechanical centrifuge screens of mild steel are common to
the trade. Equipment down time and replacement labor involved with
screen wear and failure is relatively high as compared to the cost
of such screens. It is very desirable to have centrifuge screens
that last longer. A surface treatment which can effectively provide
improved erosion and corrosion protection is an object of the
present process.
[0010] The surface treatment process to having centrifuge screens
last longer is highly applicable to many other steel parts
subjected to material wear. Examples of such medal parts include
tumbler barrels and parts on earth moving equipment such as scoops,
plows, front end loaders, and shovels.
[0011] As will be seen from the subsequent description, the
preferred embodiments of the present invention process overcome the
current life limitations of mechanical steel parts subjected to
wear.
SUMMARY OF THE INVENTION
[0012] The present invention comprises the treatment of steel parts
such as, but not restricted to, mild steel centrifuge screens,
wherein said treatment comprises a first step of conventional prior
art nitriding of the steel to form an effectively hardened
substrate, followed by a second step of conventional chrome plating
of the low temperature nitrided steel part.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Drawings are not required for disclosure of this
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] The present invention comprises the treatment of steel parts
such as, but not restricted to, mild steel centrifuged screens,
wherein said treatment comprises a first step of conventional prior
art nitriding of the steel to form an effectively hardened
substrate layer, the nitriding layer is in the range of 0.001 to 0.
010 inches thick. Methods of nitriding include, vacuum
ion-nitriding, salt bath nitriding, and gas nitriding. Followed by
a second step of electroplating the nitrided steel part by applying
a layer of conventional hard chrome plating. The hard chrome
plating layer is in the range of 0.001 to 0.050 inches thick.
[0015] The present invention process works especially well with
mild steel parts, especially mild steel centrifuge screens.
[0016] This solution to the problem of short life due to high wear
of metal centrifuge screens is also quite applicable to metal parts
subject to wear as a general case.
[0017] The present invention will further be described with
reference to specific tests so that advantageous features of the
invention can well be recognized. The tests were as follows.
[0018] Coal Preparation Plants are required to remove water and
dust particles from coal in order to prepare such coal for
transport. A mild steel centrifuge screen is commonly situated in a
dryer and used in this process of removing water and coal dust from
the coal. A slurry of water and coal are placed into the screen.
The said slurry is caused to spin centrifugally within the screen.
Water and coal particles less than 100 mesh, i.e. coal dust, pass
through the screen holes. The remaining larger coal particles pass
through the dryer for transport. The screen experiences wear based
upon the coal size (mesh), the coal hardness (grind), and the
acidity (ph) of the slurry. In these tests, identical mild steel
centrifuge screens were subjected to wear and durability tests,
using various coal sizes, hardness, and acidity (ph). The tests
consisted of using prior art screens and screens treated with the
present method to the foregoing process. After the tests, the
amount of wear was measured and the results determined as shown
below.
[0019] Test 1
[0020] a.) The subject screens were operated at a throughput rate
of twenty-five (25) tons of coal per hour.
[0021] b.) Coal Size. 28 mesh.times.100 mesh.
[0022] c.) ph: 6.5-7.0
[0023] d. Grind: 40-42
[0024] Results of Test 1
[0025] The screen life of the prior art screen under these
conditions was 365 hours. The screen life of the screen treated
with the present method was 650 hours. The treated screen of the
present invention shows an increase life of 285, hours a 78%
increase.
[0026] Test 2
[0027] a.) The screens were operated at a throughput rate of
twenty-two (22) tons of coal per hour.
[0028] b.) Coal Size. {fraction (1/16)}".times.100 mesh.
[0029] c.) ph: 6.3-6.8
[0030] d.) Grind: 42-44
[0031] Results of Test 2
[0032] The screen life of the prior art screen under these
conditions has 380 hours. The screen life of the screen treated
with the present method was 660 hours. The treated screen of the
present invention shows an increase life of 280 hours, a 74%
increase.
[0033] Test 3
[0034] a.) The screens were operated at a throughput rate of
twenty-one (21) tons of coal per hour.
[0035] b.) Coal Size. 1/8".times.100 mesh.
[0036] c.) ph: 6.4-6.8
[0037] d.) Grind: 44-46
[0038] Results of Test 3
[0039] The screen life of the prior art screen under these
conditions was 320 hours. The scree life of the screen treated with
the present method was 600 hours. The treated screen of the present
invention shows an increase life of 280 hours, an 88% increase.
1TABLE I The results are shown in Table I. Life of Prior Treated
Screen of % of Life Increase Art Screen (hrs) Present Invention
(hrs) of Present Invention Test I 365 650 78% Test II 380 660 74%
Test III 320 600 88%
[0040] From the above tests, it will be noted that the embodiments
of the present invention have remarkably superior wear resistance
and it has been proved that the screens treated with the present
invention method results in an increase screen life of over 70%.
The results of these tests further show that said increase in
screen life is consistent regardless of relevant variables, such
as, coal acidity, size of coal, and hardness of coal.
[0041] Although the description above contains many specificities,
and reference to specific examples, these should not be construed
as limiting the scope of the invention but as merely providing
illustrations of some of the presently preferred embodiments of the
present invention.
[0042] For example, while the invention is discussed in terms of
mild steel centrifuge screens, it is very applicable to mild steel
parts subject to wear as a general case. Beyond that, there are
many other metals, such as stainless steel where this is
applicable.
[0043] Thus the scope of the invention should be determined by the
appended claims in the formal application and their legal
equivalence, rather than by the examples given.
* * * * *