A material grinding mill of reversible character having hog-type
hammers formed with chisel edges pivotally mounted on supporting
discs, and further formed with landing areas positioned to contact
the supporting discs so that the chisel edges are prevented from
impacting upon or nicking the discs. The pivoting of the hammers
allows them to rebound when encountering a body of hardened material
so the hammer reverses direction, hence the landing area impacts
on the discs and the discs are protected against being nicked by
the chisel edges of the hammers.
What is claimed is:
1. In a reversible hammer mill the improvement comprising:
a. a rotor assembly having discs each formed with radially projecting
arms angularly spaced apart at distances such that said arms are
substantially symmetrically spaced apart around the circumference
of said rotor discs and expose a portion of said discs between said
b. a drive shaft supporting said rotor assembly;
c. hammer means for connection to each of said arms, each hammer
means having an elongated body formed with a central body pad area
and opposite end portions presenting oppositely facing substantially
flap landing face areas aligned in the direction of traveling during
rotation of said rotor discs, said opposite end portions of said
hammer means being in the same direction of travel thereby presenting
impact edges in the same direction of travel of the rotor assembly;
d. pivot means connecting each of said hammer means to a respective
arm such that each of said landing face areas is positioned to swing
about said pivot pin and impact by one of said flat landing face
areas on an exposed disc while supporting an impact edge spaced
from said exposed portion of each portion.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improved two-way hammer for rotary
mills of reversible character.
2. Description of the Prior Art
In reversible hammer mills having pivoted hammers, the hammers
must be able to pivot or swing in either direction. The response
of the hammers can be rapid where a particularly hard object is
encountered, and the response causes the hammer to swing in a direction
reverse to the direction of rotation of the hammer carrying discs.
When the hammers are formed with sharp edges they are known in the
art as hog-type hammers. It is this type of hammer that has caused
trouble when any hammer is caused to rebound from a hard object.
That rebound causes the sharp edge to notch or nick the supporting
disc. That notch or nick develops ultimate failure of the disc by
The discs are difficult to see, and failure of the mill usually
occurs at an unexpected time, and the damage to the mill or the
cracked rotor discs can be costly.
SUMMARY OF THE INVENTION
A principal object of the invention is to permit the continued
use of hog-type pivoted hammers in reversible hammer mills, while
preventing the occurrence of nicks in the hammer carrying rotors.
The continued availability of hog hammer mills is important and
to allow the continuing use of such mills of the reversible type,
it has been determined that the sharp or chiselled edge of the hammers
must be prevented from impacting on or nicking the supporting disc
when caused to rebound.
Therefore, it is an important object of the invention to provide
hog-type hammers with a landing area adjacent the sharp edges in
position to prevent the sharp edges contacting any part of the discs
on which they are mounted, and to form such a landing area that
will be effective with double ended and reversible hammers.
BRIEF DESCRIPTION OF THE DRAWINGS
The improved two-way double ended hammers are seen in FIG. 1 of
the drawing view which is a vertical section view through the drive
shaft of a reversible mill hammer rotor showing the hammers of this
FIG. 2 is a perspective view of a reversible-type double-ended
DETAILED DESCRIPTION OF THE INVENTION
For purposes of clarity of understanding the environment of the
present invention, there is shown in U.S. Pat. No. 4767066 a reversible
hammer mill having pivotally mounted hammers in a rotor assembly
on the drive shaft.
In FIG. 1 the drive shaft 10 carries discs 11 which have radially
directed arms 12 to receive pivot pins 13 which secure the hog double
ended hammers 14 in pivotal positions at the ends of the arms 12.
It is seen in FIG. 1 that a first disc 11 has three radially directed
arms 12 spaced at 120.degree., and there is a second disc behind
the first disc also with three arms 12 at 120.degree. of spacing,
with the result that the complement of arms assume angular spacing
of 60.degree. such that portions of the discs are exposed. Each
hog-type double-ended hammer has a body 15 formed on opposite sides
of the central body area with projecting portions 16 having substantially
flat faces 17. The outer end portion 18 of the hammer body 15 is
formed to provide sharp knife-like edges 19. The hammer ends 18
define the path of the rotor circle 20.
Each hammer body 15 (see FIG. 2) is formed with two bores 21 so
that either bore 21 may be employed to receive the pivot at pin
13. Thus, the hammers may be used in either position, since each
hammer body 15 has opposite centrally located and outwardly facing
landing areas 16. The landing areas 16 are located so that when
a hammer rebounds in either direction and opposite to the direction
of rotation of the rotor assembly the sharp edges 19 are held away
from the disc 11 to prevent nicking the disc. Thus, the importance
of the respective landing area faces 17 is easily appreciated.
In the field of reversible hammer mills the type of material to
be ground is composed of chunks of material, whether coal, rocks
or other material, which must be impacted by hammers that can be
rotated at speeds necessary to develop the momentum at impact that
breaks up the material. The present double-ended and double edge
hammer bodies are formed of hardened material having weight of the
order of more than one hundred pounds. This weight when travelling
at rotating speeds of 1200 RPM develop an impact force that is sufficient
for normal breaking of the material. However, when the material
is a body of hardened character and mass equal to or greater than
the hammers, the reaction is one where the hammer is forced to rebound
in order to allow the rotor to continue rotation. The rebound reaction
is rapid and the weight of the hammer or hammers can develop a significant
impact. Therefore, the hammer configuration of this invention is
formed with a pad having an area that is large enough to accomplish
the need to keep the hammer edges 19 free of contact with the supporting
The foregoing disclosure is not intended to unnecessarily limit
the scope of the invention or its field of use.