Improvements relating to the Manufacture of Sprocket Wheels.
Year: 1898

page_text: [Communicated from abroad by THE PARISH AND BINGHAM COMPANY, of 1076,
Hamilton Street, Cleveland, Ohio, United States of America.]
Improvements relating to the Manufacture of Sprocket Wheels.
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, do hereby declare the
nature of this invention to be as follows:-
-
My improved method of making bicycle sprocket wheels. and the wheels
thereby produced by cold pressing the metal into proper form offer many advan-
tages over the hot forging process, and the sprockets produced thereby.
By giving a much denser product, the difference being especially increased
at the surface where hardness is most desired.
By giving a clean uniform surface free from scale and imperfections. This
is of considerable importance in the subsequent treatment of the sprocket
before nickeling and causes a considerable saving in the cost of such treatment.
Before the steel can be electro-plated all this scale must be removed and a
chemically clean bright surface prepared. Where the sprocket wheels have
been made by the cold pressing process, this surface is clean, dense and with
few or no imperfections, and hence the cost of preparation for electro-plating
is much less than with those made by the usual process of hot forging.
The process of cold-pressing effects an important and advantageous difference
in the chemical nature of the product made in this way over that made by hot
forging. When steel is heated for hot forging, the surface always burns to a
greater or less degree, depending upon the length of time of heating, upon
the temperature used, and upon the number of times it must be heated for
each step in the process of shaping. This burning at the surface consists in
a chemical union of the iron and carbon of the steel with the oxygen of the
air, whereby the carbon passes off as gaseous oxides and the iron oxide remains
on the surface as scale which must be removed completely by grinding or
pickling before the article can be electro-plated. This burning during hot forg-
ing often takes place to such an extent as to render the product brittle and to
remove a large portion of the carbon of the steel, replacing it by oxide of
iron, or what the practical forger calls taking the life out of the metal. In
consequence of this chemical action many defective sprocket wheels are always
produced by the method of hot forging and often the defect cannot be located
until the wheel is used, thus causing serious loss to the makers of bicycles,
when such wheels must be replaced. In my cold pressing process, the surface
of the metal is not oxidized in the least and thus is not injured in any way.
No scale is formed and no part of the carbon is removed.
In the cold pressing of sprocket wheels there is not only no removal of carbon
from the surface of the metal, but an advantageous chemical change takes
place whereby the surface is made harder. Carbon exists in steel in several
different methods of chemical union. One such combination of carbon causing

page_text: the hardness of the steel to increase, is known as hardening carbon, and gives
to steel the well known effect of quenching or hardening. The cold pressing
of sprocket wheels causes the carbon near the surface of the metal to change
to this hardening condition producing the effect of surface hardening; and at
the same time leaving the interior metal tough.
Cold pressing also increases the rigidity and stiffness of the metal and raises
its elastic limit.
All of these advantageous effects produced in cold-pressing over hot forging
sprocket wheels are intensified in the thinner part or web, because this part,
being small and thin, is more liable to burn through and to become fatally
weak by the re-heating necessary for hot forging, while in cold pressing, this
part has the most of the hardening carbon, and is hence strongest at these
weaker points.
The following description sets forth in detail, one mode of carrying out the
invention; such disclosed mode constituting but one of various ways in which
the principle of the invention may be used.
In carrying out my process a steel sprocket blank of any suitable design is
placed without heating between two compressing dies and the web portion of
the sprocket is compressed to a greatly reduced thickness between the pro-
jecting portions of said dies thereby greatly increasing the hardening carbon
in said web portion.
:
The teeth of the sprocket blank are then punched out in any suitable manner,
and the blank is then placed between the other two dies, having curved.rim
compressing surfaces whereby the teeth are rounded off and the hardening
carbon in the rim and particularly in the wearing surface of the teeth is
increased, but not to so great an extent as in the web portion of the sprocket
blank.
Dated th
0711
1000
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.
[Improvements relating to the Manufacture of Sprocket Wheels,
I, HENRY HARRIS LAKE, of the Firm of Haseltine, Lake & Co., Patent Agents,
45, Southampton Buildings, in the County of Middlesex, do hereby declare the
nature of this invention and in what manner the same is to be performed, to
be particularly described and ascertained in and by the following statement;-
-
My improved method of making bicycle sprocket wheels and the wheels
thereby produced by cold pressing the metal into proper form, offers many
advantages over the hot forging process, and the sprockets thereby produced,
by giving a much denser product, the difference being especially increased at
the surface where hardness is most desired, & also by giving a clean uniform
surface free from scale and imperfections. This latter is of considerable impor-
tance in the subsequent treatment of the sprocket before nickling and causes
a considerable saving in the cost of such treatment. Before the steel can be
electro-plated all this scale must be removed and a chemically clean bright
surface prepared. Where the sprocket wheels have been made by the cold
pressing process, this surface is clean, dense and with few or no imperfections,
and hence the cost of preparation for electro-plating is much less than with
those made by the usual process of hot forging.

page_text: The process of cold-pressing effects an important and advantageous difference
in the chemical nature of the product made in this way over that made by hot
forging. When steel is heated for hot forging, the surface always burns to a
greater or less degree, depending upon the length of time of heating, upon
the temperature used, and upon the number of times it must be heated for
each step in the process of shaping. This burning at the surface consists in
a chemical union of the iron and carbon of the steel with the exygen of the
air, whereby the carbon passes off as gaseous oxides and the iron oxide remains
on the surface as scale which must be removed completely by grinding or
pickling before the article can be electro-plated. This burning during hot forg-
ing often takes place to such an extent as to render the product brittle and to
remove a large portion of the carbon of the steel, replacing it by oxide of
iron, or what the practical forger calls taking the life out of the metal. In
consequence of this chemical action many defective sprocket wheels are always
produced by the method of hot forging and often the defect cannot be located
until the wheel is used, thus causing serious loss to the makers of bicycles,
when such wheels must be replaced. In my cold pressing process, the surface
of the metal is not oxidized in the least and thus is not injured in any way.
No scale is formed and no part of the carbon is removed.
In the cold pressing of sprocket wheels there is not only no removal of carbon
from the surface of the metal, but an advantageous chemical change takes
place whereby the surface is made harder. Carbon exists in steel in several
different methods of chemical union. One such combination of carbon causing
the hardness of the steel to increase, is known as hardening carbon, and gives
to steel the well known effect of quenching or hardening. The cold pressing
of sprocket wheels causes the carbon near the surface of the metal to change
to this hardening condition producing the effect of surface hardening, and at
the same time leaving the interior metal tough.
Cold pressing also increases the rigidity and stiffness of the metal and raises
its elastic limit.
All of these advantageous effects produced in cold-pressing over hot forging
sprocket wheels are intensified in the thinner part or web, because this part,
being small and thin, is more liable to burn through and to become fatally
weak by the reheating necessary for hot forging, while in cold pressing, this
part has the most of the hardening carbon, and is hence strongest at these
weaker points.
In the accompanying drawings I have shown one mode of carrying out the
invention; such disclosed mode constituting but one of various ways in which
the principle of the invention may be used.
3
Figure I is a plan view of a steel sprocket blank before compression;
Figure II is a central sectional view of the web compressing dies;
Figure III is a central sectional view of the sprocket blank after being
operated upon by said dies and after having its teeth punched out, before it is
operated upon by the rim compressing dies;
Figure IV is a central sectional view of the rim compressing dies;
Figure V is a central sectional view through the sprocket blank after it has
been operated upon by the rim compressing dies.
In carrying out my process a steel sprocket blank A, of any suitable design
is placed without heating between two compressing dies B, C, and the web
portion a of the sprocket is compressed to a greatly reduced thickness between
the projecting portions bc of said dies thereby greatly increasing the hardening
carbon in said web portion.
!
The teeth of the sprocket blank are then punched out in any suitable manner,
and the blank is then placed between the other two dies D, E, having curved
rim compressing surfaces d, e, whereby the teeth are rounded off and the har-
dening carbon in the rim and particularly in the wearing surface of the teeth
is increased, but not to so great an extent as in the web portion of the sprocket

page_text: blank, that is to say the web portion of the sprocket is compressed more than
the rim portion, and hence proportionally more of the hardening carbon is found
in the web portion than in the rim portion. This is due entirely to the increased
pressure brought upon the web portion when it is cold flowed, and reduced in
thickness. The peripheral edges of the teeth will be the softest, the opposite
side faces of the teeth will be hardened somewhat, but the web portion of the
sprocket which is subjected to the greatest pressure will have proportionately
more of hardening carbon in its composition than will the rim or teeth of the
sprocket.
;
The finished sprocket blank F is now in its complete form as shown in
Figure V.
Having now particularly described and ascertained the nature of the said
invention, and in what manner the same is to be performed, as communicated
to me by my foreign correspondent, I declare that what I claim is:-
1. A process of forming steel sprocket wheels, consisting in flowing the metal
cold, substantially as set forth.
2. The steps in a process of making steel sprocket wheels, consisting in cold
pressing the rim portion whereby oxidation of the metal is prevented, and cold
pressing the web portion to a greater degree than the rim portion whereby
hardening carbon is increased in said web portion above the amount of hardening
carbon in the rim portion, substantially as set forth.
3. A step in a process of making steel sprocket wheels, consisting in shaping
the metal under cold pressure, whereby surface hardening is produced and the
metal made more dense, substantially as set forth.
4. A steel sprocket wheel, having its teeth surface hardened, the interior
of said teeth being of tough metal and having the carbon in the web portion
mainly in the hardening condition, substantially as set forth.
5. A steel sprocket wheel, having more carbon in the hardening condition
in the surface portion of the teeth than in the interior portion of said teeth,
substantially as set forth.
6. A steel sprocket wheel, having a denser web portion than sprocket portion
and having its teeth and rim denser on the surface than in the interior, sub-
stantially as set forth.
7. A steel sprocket wheel having the opposite side faces of its teeth surface
hardened and having the metal of the peripheral faces of the teeth less hard
than said side faces, substantially as set forth.
101
1
T1 1900
HASELTINE, LAKE & Co.,
45, Southampton Buildings; London, W.C.,
Agents for the Applicant.