Inclined cutter for surface cleaning head

In apparatus for removing material from the surface of a solid substrate, a rotary cutter cage has a plurality of cutters where each cutter has a plurality of projecting cutter teeth. The improvement comprises an adaptation in mounting of the cutters on the cutter rotary cage to force a lateral movement in the cutters when they impact a solid substrate being treated during rotation of the rotary cutter cage.

FIELD OF THE INVENTION 
This invention relates to surface treatment equipment for removing a layer 
of the surface, and in particular, rotary cutter cages having a plurality 
of cutters for impacting the surface to the treated. 
BACKGROUND OF THE INVENTION 
It is often desirable to remove a layer from a solid substrate such as 
concrete pavement, metal decks, fibreglass decks, and the like, so as to 
prepare the surface for a subsequent finish coating such as painting, 
sealing, or retopping. A hand operated concrete surface treatment 
apparatus is disclosed in U.S. Pat. No. 3,156,231. The rotary cutter cage 
for the apparatus carries a plurality of star-shaped cutter elements. 
During rotation of the cutter cage, the cutter elements impact the 
concrete surface to chip away a layer from the surface. A larger 
self-propelled surface conditioning machine is disclosed in U.S. Pat. No. 
3,266,846. The apparatus includes a rotary cutter cage having several 
cutter elements. The cutter cage is rotated and transported across the 
surface to be treated to remove a layer of material from the surface. U.S. 
Pat. No. 4,275,928 discloses a rotary cutter cage for surface treating 
apparatus where the individual cutters are provided with carbide tipped 
teeth. The individual cutters are mounted on circular bars where each 
cutter element has a cylindrical bore extending therethrough and in a 
direction perpendicular to the plane in which the cutter teeth lie. In 
U.S. Pat. No. 4,040,668 a rotary cutter cage is provided having cutter 
elements with an elongate bore formed therein to provide for a prolonged 
impact of the cutting element on the surface being treated. 
A floor roughing machine is disclosed in U.S. Pat. No. 1,964,746. The 
machine includes a rotary cutter cage having a plurality of cutters 
mounted on the cage. The bore extending through each cutter element is 
considerably larger than the bar on which it is mounted. This provides for 
a loose independent play in each cutter while being held yieldably 
outwardly by centrifugal force developed during rotation of the cutter 
cage. In use, the cutter cage is rotated at speeds of approximately 400 to 
800 rpm. Each cutter member impacts the floor slightly in advance of its 
point of lowest travel and thereafter resumes its outermost position on 
the cage. The bore through each of the cutters is cylindrical and has a 
central axis extending in a direction perpendicular to the plane in which 
the cutter teeth lie. Should a reduced number of cutters be mounted on the 
cutter cage, sufficient space is provided between the cutter disks to 
allow tilting of each disk, so that a disc may slide off a hard spot and 
cut into a softer one. Accordingly, a continued use of the cutters in this 
arrangement tends to round the edges of the bore of each cutter. However, 
the central portion of the bore remains cylindrical with an axis 
perpendicular to the plane in which the cutter teeth lie. 
In the cleaning and grooving of cracks in surfaces, U.S. Pat. No. 2,664,281 
discloses a cutter arrangement which provides for tilting of the 
individual cutter element. The system is particularly adapted for removing 
material from grooves in concrete. The cutter has a central bore 
substantially larger than the bar in which it is mounted. This permits 
freedom of movement in the cutter to move radially and trans-radially as 
well as tipping when a lesser number of spacer washers are used. This 
allows the machine to follow cracks in concrete when gouging them out for 
resealing. 
In principle, all of the surface conditioning machines, as common to the 
above-discussed prior art, rely on the cutter elements impacting the 
surface with the cutter teeth lying in a plane essentially perpendicular 
to the plane of the surface. Thus, the cutter teeth of each cutter element 
on the cutter cage impact the surface straight on, thereby having to 
overcome the resistance of concrete and other surfaces to chipping caused 
by compressive forces. 
SUMMARY OF THE INVENTION 
In accordance with an aspect of this invention, an improvement is provided 
in an apparatus for removing material from the surface of a solid 
substrate. The apparatus comprises a support frame, a rotary cutter cage, 
means for mounting the rotary cutter cage on the frame and means for 
rotating the cutter cage about a central axis. The rotary cutter cage has 
at least one row of a plurality of cutters mounted thereon for impacting a 
solid substrate. The at least one row of cutters is mounted on a bar 
connected to the rotary cage. The bar is spaced from and extends parallel 
to the central axis. Each of the cutters has a plurality of projecting 
cutter teeth and the cutters mounted loosely on the bar. The improvement 
comprises means on each of the cutters for forcing a lateral movement in 
each of the cutter teeth in a direction when the cutters impact a solid 
substrate being treated during rotation of the cutter cage in use of said 
apparatus. 
According to another aspect of the invention a cutter is provided for use 
on a rotary cutter cage of an apparatus for removing material from a 
surface of a solid substrate. The cutter comprises a body portion with a 
bore extending therethrough to receive and be mounted loosely on a bar 
connected to the rotary cutter cage. The body portion carries a plurality 
of outwardly projecting cutter teeth. The cutter has means for effecting a 
lateral movement of the cutter teeth when the cutter is in use on a rotary 
cutter cage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The apparatus 10 of FIG. 1 has a support frame generally designated 12 with 
housing 14 for a rotary cutter cage 16 mounted within and on the frame. A 
motor 18 drives the rotary cutter cage through a belt drive housed within 
belt housing 20. A handle 22 with control switch 24 is mounted to the rear 
of support frame 12. A height adjustment knob 26 is provided conveniently 
at the upper portion of the handle 22 to allow the operator to adjust the 
height of the rotary cutter cage relative to the surface to be treated. 
Not shown in FIG. 1 are hinged wheels at the rear of the support frame 
which operate in conjunction with the front wheels 30 mounted to the 
housing 14. This system allows the operator, by adjusting knob 26, to vary 
the height of the rotary cutter cage relative to the surface to be 
treated, and thereby vary the depth of the layer to be removed from the 
solid substrate. 
Various embodiments are provided for the cutter elements mounted on the 
rotary cutter cage 16 to cause a lateral movement in the cutters of the 
rotary cutter cage when the cutters impact the surface. With reference to 
FIG. 3, the housing 14 has bearing blocks 32 and 34 mounted at each end of 
housing 14. A shaft 36 extends through block 34 to which a drive pulley 38 
is keyed and driven by drive belt 40 housed within belt housing 20. 
Mounted to the other end of shaft 36 is a drive hub 42 having four 
outwardly extending drive pins 44 equally spaced about the hub 42. 
Centrally of the hub 42 is a threaded bore 46 which receives the threaded 
end 48 of a connecting rod 50 of the rotary cutter cage. 
The rotary cutter cage 16 has a central axle 52, which is hollow and 
open-ended at each end 54 and 56. Centrally of the axle 52 is mounted a 
pair of semi-circular segments 58 and 60. At each end of the cutter cage 
16 are end plates 62 and 64. In end plate 62 are blind end holes 68 and in 
plate 64 are apertures 66. Correspondingly in segments 58 and 60 are 
apertures 70. The apertures 66, 68 and 70 are aligned with one another to 
receive the four carrier bars 72 which extend through the aligned 
apertures to be supported by the end plates 62, 64 and the central 
segments 58 and 60. As the bars 72 are passed through the apertures, 
cutter elements 74 and spacer washers 76 are assembled on the bar 72. With 
the bars in place and all cutter elements assembled thereon to provide a 
complete cutter cage 16, the bars 72 are secured in place by way of an end 
plate 78 which is secured to the outside of plate 64 by Allen screw 
fasteners 80. 
The outer side of end plates 62 includes four apertures to receive the 
drive pins 44. Thus the assembled rotary cutter cage is positioned on the 
drive pins 44 and connector bar 50 is passed through bearing 32 and 
threaded into aperture 46 of drive hub 42. This completes the assembly of 
the rotary cutter cage onto the drive system. At the same time, this 
method of assembly for the cutter cage provides for quick removal of the 
cutter cage, should replacement of the cutter elements be required, or the 
installation of another cutter cage having different types of elements is 
desired. This provides for a variety of uses for the surface treating 
apparatus while only requiring different sets of cutter elements. 
In accordance with an embodiment of FIG. 2, a cutter element 74 is in the 
shape of a star having a body portion 82 with outwardly projecting teeth 
84 having hardened cutter tips 86. A cylindrical bore 88 extends through 
the body portion 82 where the cutter tips 86 are symmetrical about the 
central axis 90. The bore 88 is larger than the rotary cutter cage carrier 
bar 72. According to this embodiment, the bar 72 is circular and has a 
diameter less than the diameter of the bore 88. The spacer ring 76 which 
may be a metal O-ring has an internal diameter slightly greater than the 
diameter of the bar 72 where the outer diameter of the ring 76 does not 
exceed the radial extent of the base portion 92 of the cutter teeth. This 
arrangement allows lateral movement of the cutter teeth 86 when the cutter 
element 74 impacts the surface to be treated. The width of the metal 
O-ring in spacing apart adjacent cutters precludes one of the cutters 
interfering with a tilting movement of an adjacent cutter when the cutter 
teeth move laterally. 
With reference to FIG. 5, the difference in diameters between the bore 88 
of each cutter element 74 and the diameter of the carrier bar 72 is shown. 
The rotary cutter cage rotates in the direction of arrow 94 due to the 
centrifugal force of the cutter element 74. The space 96 developed between 
the bore of each element and the bar circumference is located outwardly of 
the corresponding bar. Cutter element 74a is shown as impacting the 
surface 98 of the solid substrate 100. The cutter 74a is demonstrated as 
being raised slightly from its outermost position on the carrier bar 72. 
The depth to which the cutter 74a will cut into the surface 78 of the 
substrate is determined by the positioning of the front wheel 30 and the 
rear wheel 102. The adjustment knob 26 can vary the height of the wheel 
102 by swivelling carrier arm 104 relative to the frame structure 14. As 
the rear wheel 102 is swung upwardly relative to the frame 14 to lower the 
frame towards the surface 98, the respective carrier bar 72 is lowered so 
as to press the cutter element 74a into the surface after it has impacted 
it by an interaction of the carrier bar against the lower portion of the 
bore 88. 
Referring to FIG. 4, the assembled rotary cutter cage 16 is illustrated in 
detail. The connector rod 50, as explained, is threaded into the bore 46 
of the drive hub 42. The inner face 108 of the enlarged head portion 110 
of the connector rod 50 clamps the end plates 62 and 64 between the drive 
hub 42 and the spacer washer 106. The thread direction of threaded bore 46 
is such to ensure tightening of rod end 48 in the bore 46 during operative 
rotation of the cutter cage. A recess 112 is provided in head 110 to 
permit use of an Allen wrench to initially tighten the rod 50. The 
segments 58 and 60 are provided centrally of the rotary cutter cage 16 to 
lend support to the carrier rods 72 to avoid stress cracking in the rods 
during the abuse to which they are subjected in chipping at hard materials 
such as concrete. The rotary cutter cage includes four carrier rods 72 and 
thus provides four rows of cutters across the width of the entire cutter 
cage. The support segments 58 and 60 are offset to ensure that the cutters 
of one row overlap the space between the next row of cutters in the 
central region. As generally shown in FIG. 4, the upper row of cutters 74 
all slant in a first direction, whereas the bottom row of cutters 
impacting the surface slant in an opposite direction. 
With reference to FIGS. 6 and 7, the action is demonstrated in more detail. 
As shown in FIG. 6, the upper edge of the bore 88a is contacting the 
carrier bar 72. Assuming centrifugal force is acting on the individual 
cutters 74, the cutters will tend to slope in the direction shown in FIG. 
6, because the cutter teeth 86 lie in a plane offset laterally of the bore 
contact point 88a. Due to the mass of the concave shaped plate for the 
star-shaped cutter, the cutter tends to pivot about contact point 88a so 
that the individual cutters tilt generally in the direction shown in FIG. 
6. The O-ring spacers 76 may be loose fitting on the bar. This loose fit 
for the spacers may permit a slight tilting in accommodating the overall 
tilting of the adjacent cutters. 
The provision of a concave or dished shape for each of the cutter elements 
74 causes a lateral movement of the cutter teeth 86 during impacting of 
the cutter elements with the surface 98 of the solid substrate. It has 
been found that the best circumferential speeds for operating the cutter 
cage are in the range of 1,800 to 3,000 feet/minute. At these speeds it is 
difficult to properly ascertain what is happening with the cutter teeth 86 
when they impact a surface. However, based on the results of wear patterns 
on the cutter teeth, it is realized that the teeth are moving generally in 
the direction of arrow 114 during impact or at least on initial impact 
with the solid substrate. The bottom portion 72a of the carrier rod is 
contacting the bottom of the bore portion at 88b after the cutter 74a 
impacts a surface in the manner shown in FIG. 5. Due to the cutter teeth 
86 lying in a plane laterally offset of the bore contact area 88b, a 
moment arm is exerted about 88b to tilt the cutter element 74 a in the 
direction opposite to that of FIG. 6 and thus effect a lateral movement in 
a cutter tooth 86 in the direction of arrow 114. As a result, the forces 
imparted by the cutter teeth 86 onto the surface 98 have both a downward 
and horizontal component. 
It is believed to be this lateral sideways movement of the cutter teeth 
which substantially improves the efficiency of this type of cutter element 
compared to those of the prior art. In tests conducted on concrete, the 
effectiveness of the star-shaped cutter teeth having a dish shaped of FIG. 
6, have at least a five-fold and in some instances eight-fold increase in 
effectiveness in removing a concrete surface layer compared to the 
standard star-shaped cutter elements of the prior art patents such as U.S. 
Pat. No. 4,275,928 and U.S. Pat. No. 3,156,231. At these high speeds it is 
difficult to ascertain how the lateral movement in the cutter teeth 
accomplishes this significant improvement. It is theorized, however, that 
the lateral movement of the cutter teeth improve the chipping action due 
to the fact that concrete has resistance to breakage in the compressive 
direction approximately ten times greater than its resistance to breakage 
in the tensile direction. It is believed that the lateral movement of the 
cutter teeth 86 in producing a horizontal component of force take 
advantage of the weaker tensile strength of the concrete compared to its 
compressive strength. The cutter elements in accordance with this 
invention in having a concave or dished shape provide the means for 
effecting lateral movement of the cutter teeth on impacting the surface. 
It is appreciated that the degree of concavity in each cutter element has 
to be within a certain angular range in order to effect this kick-over 
action of the cutters. The angle between cutter tooth faces 86a and 86b 
may range from 90.degree. to 150.degree.. The preferred angle is 
approximately 120.degree.. Once the cutter element leaves the surface 
being treated, centrifugal force in essence resets the cutter to the 
opposite angle, as shown in FIG. 6, to optimize on the extent of cutter 
tooth movement 86 in the direction of arrow 114 of FIG. 7. 
With the remaining cutter elements illustrated in FIGS. 8 through 13, 
various arrangements are provided on the cutters to effect this lateral 
movement in the cutter teeth when impacting the surface being treated. 
With the cutter elements of FIGS. 8, 9 and 10, the cutter element 116 
consists of a body portion 118 having embedded therein carbide tips 120 
symmetrically spaced about the central axis 122 of the cutter element. The 
body portion 118 is scalloped at areas 124 between adjacent carbide tips 
to provide for wear on the carbide tips. A bore 126 extends through the 
body portion 118 of the cutter element 116 as shown in FIG. 9. The bore 
126 consists of a countersunk tapered portion 128 opening to one side 130 
of the cutter element The countersunk portion 128 extends across the major 
portion of the bore leaving a minor portion 132 opening to the other side 
134 of the cutter element. The carbide tipped teeth 120 all lie generally 
in the same plane indicated by dotted line 136. The plane of the cutter 
teeth is laterally offset of the minor cylindrical portion 132. The body 
portion of the cutter element 116 is considerably heavier than the thinner 
plate portion of the cutter element 74. Due to the lateral offset of the 
plane 136 of the cutter teeth relative to the contact area of the cutter 
bore 132 against the bar 72, centrifugal forces acting on the cutter 
elements cause them to tilt generally in the direction indicated in FIG. 
10. As previously explained, at high speed rotations of these cutter 
elements, it is difficult to ascertain exactly what action occurs in the 
cutter teeth. However, it is theorized that on impact the cutter elements 
are tilted further in the direction of arrow 138 on the carrier bar 72 
between the contact point 72a of the carrier bar and 132a of the cutter 
bore. This tilting action is evidenced by wear patterns on the cutter 
teeth where the softer metal in the area 140 is worn off to expose the 
edge of the carbide tips 120. Therefore, in the manner discussed in 
shaping the cutter bore, means is provided for effecting a lateral 
movement in the direction of arrow 138 for the cutter teeth to take 
advantage of the weaker tensile strength of the concrete for purposes of 
removing a layer of concrete from the surface of the solid substrate. 
In FIGS. 11 and 12, another embodiment for the bore configuration of the 
cutter elements for effecting lateral movement of the cutter teeth on 
impact with the surface is illustrated. The cutter element 142 has a 
plurality of cutter teeth 144 about its periphery and all lying in the 
same plane generally indicated by dotted line 146. The cutter teeth 144 
are carried on spikes about the perimeter of the cutter element 142. The 
body portion 148 for the cutter element includes a bore generally 
designated 150 for mounting on the carrier bar 72. The bore 150, formed in 
the body portion 148 of the cutter element, has an axis 152 which is 
tilted relative to the plane 144 within which the cutter teeth 144 lie. 
The bore 150 is oblong as shown in FIG. 12 and has upper and lower bore 
surfaces 154 and 156. In use, the edge portion 158 of the bore face 154 is 
initially in contact with the carrier bar 72 due to the centrifugal 
forces. The cutter element is encouraged to tilt in the direction shown in 
FIG. 11 and on impact tilt further to the position shown in FIG. 11. Once 
the cutter is in contact with the surface, rotation is induced in the 
cutter 142 about the bar 72. Due to the tilted orientation of the bore 
150, the cutter tends to wobble as it rotates about the bar. This wobble 
action enhances the chipping effect of the teeth on the surface as the 
teeth move laterally. In addition, as the cutter rotates, pressure of the 
teeth on the surface is cyclically increased due to the oblong shape of 
the bore 150. This action further enhances the cutter efficiency. 
FIG. 13 illustrates an alternative arrangement for the cutter teeth on a 
cutter element 162. The cutter teeth 164 lie in a plane adjacent a face 
166 of the cutter element which is offset from the minor cylindrical 
portion 168 of the bore 170. The bore 170 also includes a tapered 
countersunk portion 172 which provides an arrangement similar to the bore 
126 of cutter element 116 shown in FIG. 8. As with the action of the 
cutter element demonstrated in FIG. 10, similarly the bore 170 effects a 
lateral movement of the cutter teeth 164 in the direction of arrow 174. 
The cutter teeth 164 are at the end of spike portions similar to those of 
FIG. 11. Therefore, with the embodiments of FIGS. 8, 11 and 13, by way of 
shaping the bore for the cutter elements, the lateral movement in the 
cutter teeth of each cutter element during impact with the surface being 
treated significantly improves the material removal by the chipping action 
of the teeth. 
In order to provide for even wear on the cutters, they are allowed to 
rotate on the carrier bar to avoid the same teeth always impacting the 
surface and wearing the cutter down in one area more than the other. It 
has been found that in treating concrete surfaces, this lateral motion in 
the cutter teeth provides a smoother finish for the treated surface than 
the normal planar types of cutter elements which vertically impact the 
surface being treated. Furthermore, it has been found that the cutter 
elements last considerably longer although they achieve superior results 
concerning the amount of material removed during a comparable timeframe 
for both the prior art types of cutters and the cutters according to this 
invention. It is theorized that by using the cutters according to this 
invention which tend to attack the surface being treated at an angle, 
takes advantage of the weaker tensile strength of the material being 
treated, such as concrete, to provide a superior rate of material removal. 
The cutter elements may include carbide bits embedded therein or may be 
formed of metal which has hardened tips. For example, the star-shaped 
cutters of FIG. 2 may be formed from plate steel with the star-shaped cut 
out and subsequently dished to form the concaved cross section. The 
selected steel may be a high carbon steel such as C-1075 and hardened to a 
Rockwell hardness of up to C60. The concavity in the plate may be formed 
by a progressive die working on the blank plate portion. The shaped cutter 
is then hardened to the desired hardness. The carbide tip cutters may have 
their body portion formed by stamping them from metal or formed by 
investment casting with carbide tips in place in the mold. In forming the 
wall portion in the carbide tip cutters such as in FIG. 8, it is 
preferable to leave the small cylindrical shoulder 132 which has better 
wear characteristics than the arrangement of the conical portion 128 
extending all the way out to the other side 144 of cutter body portion. 
The cutter body portion may be formed from a "Super Impacto"(trademark) 
metal sold by Atlas Steels of Toronto, Canada. In forming the bore, the 
desired angle of the conical portion of the bore or the plane of tilt of 
the cutter teeth relative to the central axis of the carrier bar or collar 
may range from 5.degree. to 75.degree.. Although improved working 
characteristics are achieved when the angle varies from 10.degree. to 
60.degree., and preferably from 15.degree. to 45.degree.. 
The O-ring spacers used with the cutter element 74 of FIG. 2 may be formed 
of spring wire which have an overall external diameter less than the 
height of the body portion of the cutter element to enable the cutters to 
oscillate during use of the cutter elements. 
While preferred embodiments have been described and illustrated herein, a 
person skilled in the art will appreciate that changes and modifications 
may be made thereto without departing from the spirit and scope of this 
invention as defined in the appended claims.