Patent Application
20120205226
1. Field
The disclosed concept pertains generally to electrical switching apparatus and, more particularly, to circuit breakers. The disclosed concept also pertains to latch assemblies for such circuit breakers.
2. Background Information
Latches are an important part of electrical switching apparatus, such as circuit breakers, and can take the form shown in
In order to optimize performance, the strength and the hardness of the latch plate 6 and the latch shaft 8 are carefully controlled, preferably inexpensively. For example, the latch plate 6 is made of 420 stainless steel and the latch shaft 8 is made of 410 stainless steel. These are copper brazed together and heat treated at the same time. However, the stainless steel will not get hard enough to hold up to life testing and, thus, the tip 12 of the latch plate 6 can deform. Also, a problem with copper brazing certain types of steel, such as 1070 stainless steel, is that the copper braze would melt when such steel is heat treated and, hence, the parts would not stay together in a heat treatment furnace.
Known current practices of rigidly joining the latch plate 6 to the latch shaft 8 include brazing or welding operations. However, for example, cracks in the welds after heat treatment can be an issue with welded parts. These operations present severe limitations on the choice of materials for these components and corresponding heat treatment options. The processes available with acceptable materials limit the component hardness and/or are difficult to control in a repeatable manner in an industrial environment. Hence, there is room for improvement in latch assemblies.
There is also room for improvement in electrical switching apparatus, such as circuit breakers, including a latch assembly.
These needs and others are met by embodiments of the disclosed concept, which provide a latch assembly in which a latch plate and a shaft member of a latch shaft are swaged to retain the latch plate to the shaft member.
In accordance with one aspect of the disclosed concept, a latch assembly comprises: a latch plate having an opening therethrough; and a latch shaft comprising a shaft member and a positioning shoulder disposed on the shaft member, the positioning shoulder having a seating surface thereon, wherein the shaft member passes through the opening of the latch plate, wherein the latch plate engages the positioning shoulder of the shaft member, and wherein the seating surface of the shaft member is swaged to retain the latch plate to the shaft member.
As another aspect of the disclosed concept, an electrical switching apparatus comprises: separable contacts; an operating mechanism structured to open and close the separable contacts; and a latch comprising: a D-shaft, a latch plate having an opening therethrough, the latch plate having a portion structured to engage the D-shaft, and a latch shaft comprising a shaft member and a positioning shoulder disposed on the shaft member, the positioning shoulder having a seating surface thereon, wherein the shaft member passes through the opening of the latch plate, wherein the latch plate engages the positioning shoulder of the shaft member, and wherein the seating surface of the shaft member is swaged to retain the latch plate to the shaft member.
As another aspect of the disclosed concept, a latch comprises: a D-shaft; a latch plate having an opening therethrough, the latch plate having a portion structured to engage the D-shaft; and a latch shaft comprising a shaft member and a positioning shoulder disposed on the shaft member, the positioning shoulder having a seating surface thereon, wherein the shaft member passes through the opening of the latch plate, wherein the latch plate engages the positioning shoulder of the shaft member, and wherein the seating surface of the shaft member is swaged to retain the latch plate to the shaft member.
A full understanding of the disclosed concept can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
As employed herein, the term “number” shall mean one or an integer greater than one (i.e., a plurality).
As employed herein, the statement that two or more parts are “connected” or “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts. Further, as employed herein, the statement that two or more parts are “attached” shall mean that the parts are joined together directly.
As employed herein, the term “swaging” shall mean a process of forging in which the dimensions of an item are altered using a die or dies, a swaging tool or a pressing tool. Swaging is usually a cold working process; however, it is sometimes done as a hot working process. The term “is swaged” as applied to an item (e.g., “an item is swaged”) shall mean that the structure of such item is altered by swaging.
The disclosed concept is described in association with a circuit breaker, although the disclosed concept is applicable to a wide range of electrical switching apparatus.
The latch assembly 34 includes the latch plate 20 having an opening 38 therethrough, and the latch shaft 22 having the shaft member 32 and the positioning shoulder 24 disposed on the shaft member 32. The positioning shoulder 24 has the seating surface 26 thereon. The shaft member 32 and a portion of the seating surface 26 pass through the latch plate opening 38. The latch plate 20 engages the shaft member positioning shoulder 24. The sacrificial section 28 of the shaft member seating surface 26 is swaged to retain the latch plate 20 to the shaft member 32.
The disclosed latch plate 20 is perpendicular to the latch shaft 22. Also, it is desired that the latch edge 40 be hard enough to not deform under Hertzian contact stress (e.g., localized stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads) but not so brittle that it chips when the corresponding circuit breaker 104 (
The latch shaft 22, positioning shoulder 24 and seating surface 26 are a single piece. This can be formed, for example, on a lathe (not shown) in one operation to ensure that the single piece is concentric, has a central longitudinal axis 39, and that the positioning shoulder 24 is perpendicular to the latch shaft longitudinal axis 39.
The disclosed concept employs 1070 or 1095 spring steel for the latch plate 20, in order to get a suitably hard latch edge 40 to prevent deformation, and a 1045 steel latch shaft 22. The two parts are pressed together when the parts are soft and then the latch shaft 22 is swaged to retain the latch plate 20 thereon. When the latch shaft 22 is swaged, the sacrificial section 28 (
Next, the parts are heat treated and plated. All of the formed material of the latch shaft 22 then becomes hardened to Rockwell C (HRC) 35 to HRC 40 for a 1045 steel latch shaft, in order that it will not deform during life testing. The latch plate 20 will then become hardened in the range of HRC 50 to HRC 55 for a 1070 or 1095 spring steel for the latch plate, in order to prevent the latch edge 40 from deforming under Hertzian contact stress. The Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. There are different scales, which are denoted by a single letter, that use different loads or indenters. The result, which is a dimensionless number, is noted by HRX where X (e.g., C for relatively harder steels) is the scale letter.
An example heat treatment process for 1070 spring steel austenitizes (e.g., without limitation, heats the steel to a temperature at which it changes crystal structure from ferrite to austenite; the presence of carbides may occur or be present during a two-phase austenitization) in a match carbon atmosphere (e.g., 0.70%), quenches in water, and tempers the steel to obtain a hardness of HRC 50 to HRC 55. The process cycle can include heating to 1475° F., holding for 3 to 7 minutes at temperature, quenching in water, cleaning the parts to remove quench oil, and tempering at 500 to 700° F. for one hour.
An example plating process for the latch assembly 34 is ASTM B733-04 (2009) Standard Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal.
Referring to
In the example shown and described herein, the circuit breaker housing 105 further includes a pair of opposing side plates (only one side plate 114 is shown), and the status indicating assembly 100 is substantially disposed between the side plates. The opening latch or trip latch 112 includes the latch assembly 34 and the trip D-shaft 102. The latch assembly 34 is pivotally coupled to the side plates 14 (only one side plate 14 is shown) and is structured to pivot, or rock, between the latched position (
The disclosed concept employs a low cost, multipart, purely mechanically joined latch assembly 34. As a result, optimum materials can be employed for the main latch components, which are the latch plate 20 and the latch shaft 22. Hence, a suitably high hardness latch assembly 34 is provided without compromising the hardness during a joining operation as is the case with a prior brazed latch assembly. The joining operation is a swaging operation that locates the latch plate 20 on the latch shaft 22 and locks these main latch components together by only a mechanical force. The cylindrical swaging or pressing tool 30 (
While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.
