Long life modular link belts suitable for abrasive environments

Improved articulation structure is provided for pivoting links of a modular belt, namely a hinge strip of flexible material such as a thermoplastic elastomer and mating receptacle aperture slots in link ends. The modular links are all alike with flared ends in the slots permitting the hinge strip to flex a limited angle without frictional rubbing with the links. The slots have limited constant widths facing outwardly to prevent movement of the hinge strip in a direction perpendicular to the surface of the belt. Staggered end fingers of the links are half the thickness of a central body portion which provides a smooth top surface without apertures for interdigitation with similar end to end links. This construction is particularly useful for operation in abrasive conditions where wear on conventional pivot pins would significantly reduce belt life.

TECHNICAL FIELD 
This invention relates to modular link belts and more particularly it 
relates to plastic conveyor belts providing long operation life in an 
abrasive environment. 
BACKGROUND ART 
When conveyor belts are required to operate in non-environmentally 
controlled conditions where they are subjected to abrasives, their life 
span is considerably shortened by frictional contact between relatively 
movable parts in the presence of the abrasives. Even in the absence of 
grit and other abrasives, belt wear in the vicinity of relatively movable 
parts is the most significant factor in terminating the useful life span 
of the belt. 
In modular link conveyor belts, modular links are traditionally 
interdigitated at opposite ends and linked together by means of pivot pins 
extending through the interlaced belt end fingers in a pattern forming a 
conveyor surface. The links need to have articulated joints for passing 
over sprockets, for example, conventionally provided by means of the pivot 
pins. 
These pivot pins have provided many problems in construction and operation. 
If they are rigidly mated in tight fitting mating apertures, there is 
little room for thermal expansion for example which can change dimensions 
enough to introduce greater wear, binding or inability to flex when under 
load or impact conditions. If the pivot pins are slidable or loosely 
fitted, they induce significant frictional wear particularly in abrasive 
environments where grit can accumulate in the vicinity of the pivot pin 
bearings. Because of forces acting upon the pivot pins they may be forced 
axially out of position with loading or torsion conditions in the belt. 
This requires countermeasures such as riveted heads on the pivot pins, 
snap catches, and the like. With conventional cylindrical pivot pins, the 
articulation wear when the belt goes around sprockets, etc., generally 
leads to belt failure. If the pins are replaceable, repairs may be made, 
but they are not always easily accessible for removal, since they must be 
retained in place securely during normal belt operation by heads or 
retaining structure so that they will not be moved out of position. The 
expense of pin construction with retention heads and corresponding link 
means specially provided to hold the pivot pins in place is objectionable 
as well as the assembly costs because there are many links connected 
together in a belt. 
A major problem encountered is the accumulation of dirt and grit in the 
vicinity of the pivot pin wear surfaces, casing accelerated abrasive wear 
and early belt failure. 
This frictional pivot pin wear has to some extent been eliminated by the 
provision of a flexible strip forming a so-called "living hinge" replacing 
the conventional pivot pin in J. M. Lapeyre U.S. Pat. No. 4,140,025; Feb. 
20, 1979 entitled Link Chain Having Non-frictional Couplings. Therein, the 
flexible strips replacing pivot pins are secured to the interdigited links 
so that the flexible web forms articulation means at a hinging joint that 
does not frictionally slide over link surfaces or require journalling in a 
bearing surface. 
This prior art belt worked well under light load conditions and for some 
applications. However, for universal adaptability to a range of operation 
conditions, that belt system presented a different set of unsolved 
problems. For example, the material being hinged could be buckled under 
high belt tension loads. The hinging effect also eventually causes 
catastrophic life ending fatigue in the fabric material requiring 
complicated maintenance procedures. Failure is particularly induced under 
heavy belt loads causing tension in the fabric as the joined links pull 
apart from each other, leaving the fabric to bear the belt tension load. 
This reduced the belt load bearing capacity. Furthermore, the accompanying 
belt array presented other operational limitations, such as the inability 
to produce a flat substantially unapertured belt conveyance surface, a 
belt surface that resists torsion caused by load objects, and smooth 
continuous belt edges that can ride upon an adjoining guide rail. 
Accordingly, it is an objective of this invention to provide improved 
conveyor belts and accompanying articulation means resolving the foregoing 
disadvantages of both conventional pivot pin connected link belts and 
those employing substantially frictionless living hinge articulation 
means. 
DISCLOSURE OF THE INVENTION 
There is provided by this invention a long life modular link conveyor belt 
operable in abrasive environments to carry heavy loads on substantially 
flat surfaces that are not easily twisted by torsion forces caused for 
example by unbalanced loading. It has further advantages of low cost 
production with identical universal plastic links coupled together with 
easily manipulated rectangular cross section thermoplastic elastomer 
linking pins, simple replacement of the linking pins when required and 
others that will appear throughout the following description. 
Accordingly flat topped modular plastic links interdigited in a belt 
present a substantially continuous apertureless flat belt edge surface. By 
socketing the links together across the belt width to form in essence a 
single unit, distortions of the belt configuration by torsion forces is 
substantially eliminated. 
A living hinge articulation joint provides all the advantages of long life 
without frictional wear and produces superior performance in abrasive 
environments. The living hinge is employed in a compression mode of 
operation to increase the belt loading capacity and performance under 
tension. The hinge pins are simple strips of substantially rectangular 
cross sectioned flexible plastic material, which is low in cost, easy to 
manufacture and easy to insert and remove. 
The hinge rod is not attached to the links but is rather introduced into 
retaining slits in the interdigited module end fingers without attachment 
or restraint other than that provided by the matrixing slit dimensions. 
The belt loading tension forces compress the hinge rod so that it performs 
well with high belt loads. 
Thus, this invention provides the unexpected combination of superior 
functional belt performance at lower construction and maintenance cost 
than heretofore feasible, as will become more apparent from reference to 
the following description, drawing and claims.

THE PREFERRED EMBODIMENTS 
As may be seen from FIG. 1 the modular links 15, preferably of plastic, are 
coupled together side-by-side 16, 17 and end-to-end 18, 19 by means of 
plastic flexible hinging strips 20, substantially rectangular in cross 
section. The modular links 15 are flat topped to provide a continuous 
substantially flat conveyor belt surface 21 without apertures. Such belts 
have advantages for conveying special products, small items and 
irregularly shaped items. It is seen from FIG. 2 that also the belt edge 
provides a substantially flat continuous surface which is advantageous 
whenever the belt must ride against a guide rail. 
In articulation, the hinge strips, bars, rods or pins 20 are flexed, 
substantially at mid point in the longer rectangular dimension, as 
required in the hinging joints as the belt passes over a sprocket 22, for 
example. Both ends of the links have apertured flared slots 23 with 
substantially half of the slot length providing a rectangular matrix 
receptacle end 24 closely fitting the hinge strip dimensions. The flared 
slot 25 end portion extends from mid-slot at the usual pivot axis 26 
toward the center of the link, and provides a cavity for flexing of the 
strip in its living hinge action in opposite directions over a restricted 
angle or arc which prevents the hinging to exceed the working stresses for 
the particular material being deformed. The hinge bar 20 is thus freely 
movable along the hinging axis for insertion or removal and is retained in 
position axially simply by the friction imposed by the snug fit into the 
rectangular matrix portion 24 of the slot. Such a hinging rod has little 
tendency to move axially under normal belt operations. 
The hinge bar material, typically a thermoplastic elastomer, has a 
stiffness and compressibility for coupling the links together while 
bearing the tension load on the belt. Extrusion of plastic hinge pins 
orients the grain structure of the material in the direction of the pivot 
axis 26. Plastic hinge pins having a narrowed flexing portion are 
susceptible to separating or shredding along the grain (axially) with 
flexure. Orienting the grain along the axis of belt travel requires 
exceptional manufacturing considerations, extrusion being the normal 
method of manufacture. The rectangular shape additionally therefore is 
advantageous since the hinge strips 20, having no narrowed, flexing 
portion susceptible to shredding, may be extruded. Alternatively, the 
hinge strips may be cut from a sheet extruded to give the grain 
orientation shown by the arrows in FIG. 5. 
The side-by-side interdigited link fingers 36, are oriented with the 
rectangular slot ends 24 pointed outwardly from the link, thus causing the 
flared ends in side-by-side links to be alternately directed, as shown in 
phantom view 37 in the end view sketch of FIG. 2. Elasticity in the hinge 
material permits the hinging in the confined flared cavity 25 with the 
link end fingers closely packed side-by-side. In this respect the 
clearance 40 provided by making the slot length longer than the hinge 
length along the belt axis 30 permits a limited degree of extension of the 
hinge strip 20 by elasticity and/or movement toward the flared end under 
belt loading tension. 
The "compression" mode of operation of the hinging material is critical to 
the extension of life and the increased load bearing capacity of the 
living hinge feature. This is feasible by means of the orientation of the 
flared portions 25 of the slots 23 toward the center of the links 15. In 
this respect, consider the reactions encountered on the strip 20 from the 
fingers 35, 36 of the side by side links 15 and 16. The orientation of the 
slot in finger 35 with the rectangular portion to the right leads to the 
reference character 23R to identify that orientation as compared with 23 
wherein the rectangular portion is pointed to the left. Finger 36 has the 
latter slot orientation, as seen better in FIG. 4. 
As the belt is loaded, the (drive) sprocket 22 will exert tension in the 
belt along the drive axis 30. This will tend to move finger 36 to the 
right and finger 35 to the left. In other words the links tend to 
separate. It is desirable under such circumstances for the belt to have 
some play or give for best performance, but the magnitude of play must be 
limited. With the flexible, elastic, compressible material of hinge strip 
20 therefore, the two fingers 35 and 36 may move apart as much as the 
compressibility-elasticity and or movement of the hinge rod permits. 
Consider then that finger 35 may indent the edge 43 and finger 36 may 
indent the edge 44 to bear the load. The snug fit of the hinge strip in 
the rectangular slot portion 24 will prevent buckling, as will the 
clearance 40. An eye view through aligned slots along pivot axes while not 
under going articulation about the sprocket reveals a rectangular 
through-slot roughly twice the length of each rectangular slot portion, 
the view of the complete shared cavities being occluded by neighboring 
link material surrounding the rectangular slot portions. The hinge 
material is thus confined to restrict hinge strip deflection in the 
direction perpendicular to the belt surface 21. 
This edge indentation or compressibility will not cause frictional sliding 
and wear, so that the wear characteristic of the hinge strip material 
depends upon material fatigue, giving the strip long life characteristics. 
There is no tendency to stretch or rupture the hinge strip under load. The 
load bearing capacity of the hinge strip 20 may be increased by increasing 
the effective cross sectional area of the hinge strip 20. 
On the opposite sides of the links 15 are mating socket apertures 48 and 
plugs or pegs 49, which interfit as shown in FIG. 3. Since the hinge strip 
20 is flexible in the direction perpendicular to the belt surface 21, the 
belt would be subjected to torsional forces and deformation of the belt 
surface characteristics, for example when unbalanced loads not equally 
distributed across the belt surface are encountered. It is seen then from 
FIG. 3 that the mating peg and socket structure will give the belt lateral 
stiffness across its width. 
The details of the links 15 and assembly relationship are exhibited in 
FIGS. 4 and 6. The apertured socket female side is seen in FIG. 4 and the 
peg male side is seen in FIG. 6. The flat upper surface 60 is shown. The 
central body portion has approximately twice the lateral thickness of the 
finger porions 35, 36, which are staggered on opposite ends so that the 
links can be closely spaced (FIG. 1) in interdigited relationship. It is 
evident therefore that a single link module 15 is universally used with a 
single hinge pin configuration 20 for the simplest and least costly 
manufacture and assembly. No intricate assembly techniques are involve so 
that the assembly of the belts can be easily mechanized. 
Although the rectangular hinge bar has been shown in a specific embodiment 
of belt link modules forming an apertureless belt surface, one skilled in 
the art can appreciate that similar advantages provided by the hinge bar 
could be realized in many other modular belt configurations using such a 
rectangular hinge bar. 
It is therefore evident that this invention has advanced the state of the 
art and therefore those novel features descriptive of the spirit and 
nature of this invention are set forth with particularity in the following 
claims.