Excavating – Digging edge – Tooth or adaptor
Reexamination Certificate
2001-06-01
2004-05-18
Saether, Flemming (Department: 3679)
Excavating
Digging edge
Tooth or adaptor
C411S512000
Reexamination Certificate
active
06735891
ABSTRACT:
FIELD OF THE INVENTION
The intention of this invention is to make improvements to locking and retention systems for public works, mining and similar machinery which offer interesting new and inventive characteristics with regard to what is known up to the present.
BACKGROUND OF THE INVENTION
Machines for public works, mining and similar projects have the function of removing and loading masses of land and stones. They are fitted with an active edge known as a blade, on which is mounted a number of units designed to penetrate the terrain. These units are usually a series of adapters (these are either welded, bolted or mechanically fixed to the blade) and they have pieces known as points or teeth attached to them, which have the function of penetrating the earth. There are various systems to join the teeth to the adapter, and all of these have a different attachment or locking system. The locking system must ensure that the tooth is perfectly mounted on the nose of the adapter, resisting all forces to which the unit (tooth-locking-adapter) is exposed. The locking system may be formed by a single body (fully integrated) or by various bodies (a pin incorporating retainers or tensors). The pins have different shapes and constitutions. There are pins that are made from metal only, although the most usual ones are those made from a combination of metal and a rubber like material.
The lock elements made up of a combination of metal and a rubber-like material, as opposed to the locking elements made from metal only, are easier to assemble and dismantle, and they offer a better possibility to give tension to the unit and are also good at absorbing moderate forces. But they also have considerable disadvantages that cause breakage and the loss of these elements. These disadvantage are the influence of the temperature on the mechanical characteristics of the rubber like material and the possible deterioration of this due to the absorbing of oils and greases, although the main disadvantage is the high transverse expansion that the rubber-like material undergoes when it is compressed, giving it a tendency to get torn. This implies the imminent loss of the pin.
Until now the locking systems made from a combination of metal and rubber-like material have used compact (or solid) elastomers. A compact (or solid) elastomer is one that is made up of a single phase.
Normally natural rubbers are used. These offer a good level of resistance to traction, abrasion, tearing and fatigue as well as a high resilience. Their limitations include a moderate maximum service temperature (between 70° and 90°) and their sensitivity to oxidation and attack by ozone. As in the case with all non-polar rubbers, they swell appreciably when they come into contact with hydrocarbonate solvents. When they are swollen, their mechanical resistance is considerably reduced and increases their susceptibility to degradation. The property that characterises the rubber is its high elasticity, in other words, its capacity to undergo considerable deformations under relatively weak forces and to recuperate quickly its original shape and dimensions when the deforming force ceases to act upon it, replacing the energy stored during the deformation.
The inconvenience of undergoing a high transverse expansion when it is compressed is common to all compact elastomers that have been used up to now in lock or retention elements.
Because of this high capacity of transverse expansion, the compact elastomer used in pins deteriorates easily as a result of friction or pinching when the pin is being mounted and also when the unit is working. As shown in
FIG. 18
, when a force F
1
is applied to the block of compact elastomer, this responds by compressing itself and showing a transverse expansion (the sheet is made convex). This happens because the compact elastomer maintains constant its volume even though it is subject to forces. If a force F
2
, greater than F
1
, is applied, the transverse expansion increases. If even greater forces (F
3
) are applied continuously, the compact elastomer will continue to expand until it reaches a limit where it ends up breaking. The volume is maintained constant in the four representative states, continually increasing the transverse expansion undergone.
The main problem of the transverse expansion, caused by the maintenance of the same volume on applying a force, causes the compact elastomer to interfere with other bodies (the internal walls of the pinhole, the internal walls of the tooth and the nose of the adapter) and it ends up being subjected to friction, pinching, shearing and folding which inevitably cause it to break. The breakage of the compact elastomer leads to the loss of the tooth. For this reason it is very important for the locking system to be attached strongly and to offer resistance to the forces suffered by the unit.
In
FIG. 11
we can see a unit made up of a tooth, an adapter and a metal-rubber-metal-type laterally introduced “sandwich” pin. In
FIGS. 12
,
12
(BIS) and
13
we can see how the mounting of this pin evolves. In
FIG. 12
the end of the pin is placed in its pinhole and it is then struck with a hammer. The pin penetrates the pinhole compressing the rubber, which joins the metal parts; the end parts made from metal are separated thus forcing the elastomer, which frequently tends to come unstuck and get torn (
FIG. 12
(BIS)). As the pin is introduced the rubber continues to compress, giving rise to a considerable inferior and superior transverse expansion which interferes with the external wall of the tooth and which inevitably causes the rubber to deteriorate (FIG.
13
). Once mounted (FIG.
14
), the rubber remains in a deformed state and it interferes with the internal wall of the nose of the adapter and the internal wall of the tooth. As the unit is subjected to forces, the rubber deteriorates more and more until it breaks.
In order to try to minimise the inconvenience of the transverse expansions that interfere with other bodies, slight modifications have been made to the design of the elastomer elements; but these have not managed to solve the problem.
The modifications carried out to try to minimise transverse expansion are based on the extraction of a part of the elastomer material. Among these modifications we can highlight the perforation of the material and the concave shapes of the sheets.
FIG. 23
shows a retainer/tensor with three needles arranged vertically. In
FIG. 24
the passing needles are arranged laterally in a “sandwich” type pin. In
FIG. 25
the retainer/tensor is pierced vertically and in
FIG. 26
a “sandwich” type pin shows a concave elastomer sheet.
The main problem of the perforated elastomers is that earthen materials known as fines enters the holes. These fines are compacted and prevent the deformation caused by the pressure becoming absorbed by the holes, causing this to be transmitted once again to the ends and it expands transversely, in the same way that a non-perforated elastomer would respond. In addition to this, it also weakens the pin.
The solution of using elastomers with concave shapes does not solve the problem of the transverse expansion either. For large compressions, such as those that take place during the mounting of the pin, the elastomers become deformed and end up interfering with other bodies. In addition, the fact that they are concave means that the pin is weaker, and since it has less elastomer material, its elastic response is lower than that of a pin with a non-concave elastomer.
U.S. Pat. No. 5,731,359 refers to vibration-absorbing elements comprising a foamed thermoplastic polyamide elastomer consisting in a block aimed at holding conduction pipes mainly for the braking system in automobiles, having a carrier, plate with a threaded bolt received on a bore of the vibration-absorbing block, which has a pore size which decreases gradually from the inside towards the outer surface, terminating in a smooth closed surface.
UK patent application 2 150 667 refers to a plastic shock absorber which has a plastic casing holding
Fernandez Martinez Ma del Rosario
I Bertran Nil Vallve
Merino Senovilla Juan Carlos
Moreno Jorge Pallas
Darby & Darby
Metalogenia S.A.
Saether Flemming
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