Patent Application
20150033594
In heavy earth moving equipment or excavators, such as power shovels for mining, it is typical to employ a large dipper or bucket for shoveling the materials from the work site. The dipper is normally provided with teeth on the front to provide a digging action against the surface being worked and further includes a hollow dipper body for collecting the material so removed. On the rear of the dipper, a door is pivotally mounted. A latch mechanism secures the door in its closed position and, when released, allows the door to open. Conventional latch mechanisms typically include a moveable latch lever generally beneath the dipper door. The latch lever is typically coupled to a slidable latch bar that selectively engages a latch keeper. To open the dipper door, the latch lever is moved, which causes the latch bar to slide away from the latch keeper and thereby disengage from the latch keeper. The dipper can be suitably tilted so as to open the dipper door under its own weight plus the weight of any material contained within the dipper body. The door is thereafter closed by swinging the dipper in such a direction so as to cause the dipper door to move by inertia towards its closed position until the latch bar reengages the latch keeper.
In some embodiments, a power shovel dipper door includes a hollow dipper body defining a first end and a second end opposite the first end, a plurality of dipper teeth coupled to the first end, a dipper door pivotally mounted at the second end, and a latch system for releasably securing the dipper door in a closed position. The latch system includes a latch bar and a latch keeper. At least one of the latch bar and latch keeper is movable between a first position and a second position. The latch keeper is engaged by the latch bar when at least one of the latch bar and latch keeper is in the first position. The latch system further includes removable inserts positioned proximate an interface where the latch bar and latch keeper are capable of engaging each other. One or more of the removable inserts includes a tool steel.
In other embodiments, a latch system for a power shovel dipper door includes a latch bar movable between a first position and a second position, a latch keeper that is engaged by the latch bar when the latch bar is in the first position, and removable inserts positioned proximate an interface where the latch bar and latch keeper are capable of engaging each other. One or more of the removable inserts include a tool steel.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
It should be understood that the invention is not limited in its application to the details of construction and the arrangements of the components set forth in the following description or illustrated in the above-described drawings. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
Referring also to
Proximate an interface where the latch bar 110 and the latch keeper 120 are capable of engaging each other, the latch system 100 includes removable inserts 160, 170. In the illustrated embodiment, the inserts 160 and 170 are coupled to the latch bar 110 and the latch keeper 120, respectively. The latch bar insert 160 is received in a recess formed on the latch bar 110. An outer surface of the latch bar insert 160 is flush with an outer surface of the latch bar 110, so that the assembly of the latch bar 110 and the latch bar insert 160 gives a smooth linear appearance. Likewise, the latch keeper insert 170 is received in a recess formed on the latch keeper 120, and an outer surface of the latch keeper insert 170 is flush with an outer surface of the latch keeper 120 so that the assembly of the keeper 120 and the insert 170 gives a smooth linear appearance.
In the illustrated embodiment, the latch bar insert 160 and the latch keeper insert 170 are arranged so as to define a gap 180 therebetween when the dipper door 70 is closed. When the dipper door 70 is swinging toward a closed position, the latch bar insert 160 may contact the latch keeper insert 170 intermittently or occasionally, e.g., via inertia. Through these contacts, the removable inserts 160, 170 may become gradually worn; however, as explained below, the wear life or service life of the removable inserts 160, 170 disclosed herein can be enhanced by using tool steel. Although
For at least the past twenty years, certain carburized steel alloys have been used as the latch keeper insert, with or without a latch bar insert. Where a latch bar insert is used, certain through-hardened steel alloys have been used as a suitable material. The service life of such latch bar and keeper inserts, however, have been typically limited to approximately 10-15 days. Removing and replacing the inserts from the dipper door after the useful service life can be costly and time consuming. First, the dipper door needs to be hauled or hoisted to an open position (e.g., approximately 10° to approximately 20°). This can be accomplished either by temporarily welding a steel support (not shown) between the dipper door 70 and the rest of the dipper 55, or by adjusting the latch lever 130 relative to a corresponding latch lever retainer (not shown) on the door 70 using shims. Once the door is opened, the latch keeper insert can be removed and replaced. In large dippers, the dipper door can weigh on the order of 15-20 metric tons and the latch bar itself can weigh on the order of one metric ton. Removing and replacing the worn latch inserts is therefore be time-consuming and cumbersome. Thus, there has developed a need for removable inserts with a longer service life. Others in the industry, however, have failed to meet this need for at least the past twenty years.
In the illustrated embodiment, to decrease wear on the latch bar 110 and keeper 120, the removable inserts 160, 170 are each made of a tool steel, such as D2 and S7. The nominal composition of the D2 tool steel includes, by weight, approximately 10% to approximately 18% chromium, approximately 1.5% carbon, approximately 1.0% vanadium, approximately 0.7% molybdenum, approximately 0.45% manganese, approximately 0.30% silicon, approximately 0.030% phosphorus, approximately 0.030% sulfur, and the balance iron and incidental elements and impurities. Use of the word “approximately” to describe a particular recited amount or range of amounts is meant to indicate that values near to the recited amount are included in that amount such as, but not limited to, values that could or naturally would be accounted for due to instrument and/or human error in forming measurements. The D2 tool steel can be through-hardened to a Rockwell C-scale hardness of approximately 57 to approximately 59 by placing the steel in a furnace, tempering at a suitable temperature, and subsequently cooling in air.
The nominal composition of the S7 tool steel includes, by weight, approximately 3.25% chromium, approximately 1.40% molybdenum, approximately 0.70% manganese, approximately 0.50% carbon, approximately 0.30% silicon, and the balance iron and incidental elements and impurities. The S7 tool steel can be hardened to a Rockwell C-scale hardness of approximately 54 to approximately 56 by placing the steel in a furnace, tempering at a suitable temperature, and subsequently cooling in air.
Tool steels such as D2 and S7 have been used in the machining world (e.g., for dies and shear blades) for approximately 40-50 years. These steels can attain a high hardness. Generally, the hardness of an alloy is inversely proportional to its toughness. Therefore, the high hardness of the tool steel would indicate that the toughness may be unsuitably low (i.e., brittle) for applications that are exposed to a high impact. The toughness of the tool steel may be further reduced at low temperatures due to a ductile-to-brittle transition, and in light of the fact that a power shovel may be exposed to temperatures lower than approximately −40° C. Therefore, latch inserts for a power shovel dipper door are expected to require high toughness at such low temperatures. For this reason, tool steels were hitherto not used as latch inserts, although they have been used in the machining world.
In the illustrated embodiment, the latch bar insert 160 and the latch keeper insert 170 have different hardnesses, and are of different tool steels. In one particular embodiment, the latch bar insert 160 is made of the D2 tool steel a Rockwell C-scale hardness of approximately 57 to approximately 59, and the latch keeper insert 170 is made of the S7 tool steel with a Rockwell C-scale hardness of approximately 54 to approximately 56. Moreover, a ratio of wear life of the latch bar insert 160 to wear life of the latch keeper insert 170 is approximately two to one. In other embodiments, however, the ratio of the wear life of the latch bar insert 160 to the wear life of the latch keeper insert 170 is different. Moreover, the latch bar insert 160 and the latch keeper insert 170 can be made of tool steels other than D2 or S7, and the latch bar insert 160 and the latch keeper insert 170 may or may not be made of the same tool steel. In yet other embodiments, the latch bar insert 160 and the latch keeper insert 170 have the same hardness.
An illustrative embodiment of the removable inserts is described in greater detail below. Additionally, counterexamples (Examples 1, 2, 3, and 5) were also prepared and tested for comparison. In the examples and counterexamples, removable inserts 160, 170 were applied on a latch system 100 of a dipper door 70 in a power shovel 10. The shovel 10 was used to move material, and the wear on the latch keeper insert 170 was measured as a function of time and material moved. Initially, the latch keeper insert 170 was a generally rectangular box with faces joined at right angles to each other. As the test progressed, however, an edge of the latch keeper insert 170 that contacts the latch bar insert 160 gradually receded and became rounded. The receded length to the latch keeper insert 170 edge was measured vertically and horizontally, as a function of time and material moved.
A latch bar insert was made of a manganese steel bar and a latch keeper insert was made of a carburized steel alloy. Example 1 is a counterexample. The service life of the latch bar and keeper inserts was exhausted after 15 days of moving material. The following Table 1 summarizes the measurements.
A latch bar insert was made of a manganese steel bar and a latch keeper insert was made of a weld overlay. Example 2 is a counterexample. The service life of the latch bar and keeper inserts was exhausted after 13 days of moving material. The following Table 2 summarizes the measurements.
A latch bar insert was made of a stainless steel and a latch keeper insert was made of TOUGHMET®. TOUGHMET is a copper-based alloy with a nominal composition, by weight, of approximately 15% nickel, approximately 8% tin, and the balance copper and incidental elements and impurities. Example 3 is a counterexample. The service life of the latch bar and keeper inserts was exhausted after 3 days of moving material. The following Table 3 summarizes the measurements.
A latch bar insert was made of the D2 tool steel and a latch keeper insert was made of the S7 tool steel. The service life of the latch bar and keeper inserts was exhausted after 54 days of moving material. This represents an approximately fivefold increase in service life of the removable inserts. The following Table 4 summarizes the measurements.
Both the latch bar insert and the latch keeper insert were made of Nano Steel. Example 5 is a counterexample. The service life of the latch bar and keeper inserts was exhausted after 9 days of moving material. To keep the latch system running in place, a welding was required on the latch keeper insert. The following Table 5 summarizes the measurements.
Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.
This application claims the benefit of U.S. Provisional Application No. 61/605,550, filed Mar. 1, 2012, the entire contents of which are hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2013/028136 | 2/28/2013 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61605550 | Mar 2012 | US |
