AN ELECTROMECHANICAL RELAY AND METHOD OF MANUFACTURING SAME

Abstract: An electromechanical relay, in particular, a moveable contact arm for a relay. The contact arm is manufactured by brazing a pair of contact pieces from both sides to a metal blade. In order to avoid excess brazing material contaminating the contact surfaces, the metal blade is provided with a through-hole over which the contact pieces are centered from both sides. The through-hole serves as a braze reservoir. Thus, excess brazing material flows into the hole which in turn limits braze flow up the contact edges which would result in contamination of the contact surfaces.

Description: AN ELECTROMECHANICAL RELAY AND METHOD OF MANUFACTURING SAME FIELD OF THE INVENTION The present invention relates to an electromechanical switching device, such as, a relay. More particularly, the invention relates to an electromechanical switching device with an electrical contact arm having contact pieces on both sides thereof, which is used, for example, as a moveable contact arm. BACKGROUND OF THE INVENTION In relays and other electromechanical switching devices for switching higher currents, rivet style contacts are commonly used in the making of the electrical contact arms. For example, for a contact configuration having a center contact arm that needs contacts on both sides (e.g. SPDT, Break-Make, Form C) , a rivet contact for this arm has to be preformed, then staked through a hole in the arm and deformed again in order to achieve a matching contact surface on both sides of the contact arm. This known method of making a contact arm requires expensive manufacturing of the contact rivets. Further, the resulting contact arm structure does not pass some harsh application life requirements for particular switching applications. British Patent Specification No. GB-A-l, 158, 119 describes a spring blade assembly, and a method of manufacturing same, having a plurality of superimposed spring blades that are clamped together via connected contact pieces located on either side of the plurality of spring blades. Specifically, the spring blades have aligned apertures formed therethrough, a head contact overlying the apertures on one side of the plurality of spring blades and a backing member overlying the apertures on the other side. The head contact and the backing member are connected to each other by means of soldering or welding. Due to the plurality of superimposed spring blades, the contact pieces have to be connected with good conductivity within the aligned apertures. This requires each contact piece to have a connecting member extending from the head contact and/or backing member into the respective aperture for joining to the other contact piece. As a consequence, the contact pieces have rivet shapes and require expensive manufacturing similar to the rivet contacts described above. It is also known to cut contact pieces from a contact tape and metallurgically join, such as by resistance brazing, the contact pieces to the surfaces of electrical contact arms as desired. No holes need to be formed through the contact arms' surfaces. Such a contact piece typically has a braze alloy backing layer on one side which is used for brazing the contact piece to a planar surface of a contact arm or a blade spring. Contact arms made with brazed contact tape pieces routinely pass harsh application life requirements. However, during the joining/brazing process, excess molten brazing material flows high up the sides of a contact piece and may in some cases flow onto the surface of the contact piece. This is due, in part, to electrodes used in the brazing process which exert a force on the contact pieces to keep them in position and to ensure acceptable electrical contact with the contact arms. This condition can result in contacts welding during operation of the contact arm as well as in shortening the resistance brazing process electrode life. Disadvantageously, the amount or thickness of the braze alloy coating cannot be reduced sufficiently because of limitations in the manufacturing process of the contact tape, i.e., such a braze alloy coating can be achieved only with a specified minimum thickness on the tape. It is thus an object of the present invention to overcome the disadvantages of the existing art. In particular, it is an object of the present invention to provide an electromechanical switch having an electrical contact arm using cheap contact pieces with a simple shape and a planar bottom surface, which contact pieces can be brazed on both sides of a metal blade without excess brazing material affecting the contact surfaces. It is a further object of the invention to provide an electromechanical switch having an electrical contact arm in which a pair of contact pieces are cut from a contact tape having a braze alloy backing. It is still a further object of the present invention to provide an electromechanical switch having an electrical contact arm in which a pair of contact pieces are brazed to respective sides of a metal blade and the contacts are pressed against the metal blade to achieve a predetermined overall thickness between the contact surfaces without a need of removing excess brazing material. SUMMARY OF THE INVENTION The aforementioned problems are obviated by the present invention which provides an electromagnetic switch that includes: a coil assembly having a magnetic core, a coil wound around the core, and a frame that holds the coil and core; a contact assembly having (a) a pair of stationary contact arms arranged opposite one another and with the respective contacts facing one another; and (b) a moveable contact arm arranged between the pair of stationary contact arms and having a metal blade with a through-hole formed therethrough and a pair of contact pieces, each having a planar bottom surface, said contact pieces being brazed with the bottom surface to the metal blade so as to cover the through-hole from both sides and said through-hole being filled at least partially with excess braze material; and means for actuating the moveable contact arm upon energization and de-energization of the coil. The present invention also provides an electrical contact arm, comprising a metal blade having a through-hole formed therethrough, and a pair of contact pieces, each having a planar bottom surface, said contact pieces being joined with the bottom surface to the metal blade so as to cover the through-hole from both sides and said through- hole being filled at least partially with excess joining material . Further, the present invention provides a method of manufacturing an electrical contact arm, comprising the steps of: providing a metal blade having a through-hole formed therein; providing a pair of contact pieces each having a planar bottom surface greater than the through-hole in said blade, each of said bottom surfaces being coated with a layer of joining material; positioning one of said contact pieces on either side of said blade so as to cover said through-hole from either side; joining the contact pieces to the blade by applying heat for melting said layers of joining material while pressing said contact pieces from either side against said blade, the through-hole serving as a reservoir where excess molten joining material flows in; and solidifying the joining material. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference is made to the following description of an exemplary embodiment thereof, and to the accompanying drawings, wherein: FIG 1 is a schematic illustration of the method of the present invention showing contact pieces being cut from a tape and being centered over both sides of a metal blade, the illustration using different scales; FIG 2 is an enlarged sectional view of an electrical contact arm of the present invention with the contact pieces at the beginning of the brazing process; FIG 3 is a sectional view of the contact arm of FIG 2 with the contact pieces after brazing; FIG 4 is an exploded view of a relay of the present invention; and FIG 5 is the moveable contact arm of the relay of FIG 4. DETAILED DESCRIPTION Referring now to FIG 1, there is shown a contact tape 1 which is normally contained on a spool 2. The contact tape l has a specified thickness and width. For manufacturing an electrical contact arm, the tape 1 is cut into single contact pieces 3. A cutting mechanism 4 is shown only schematically and may be any type of known or conventional cutting mechanism. The contact tape 1 is comprised of contact material and is coated on one side with a braze alloy backing. For example, as shown in the drawing, the contact tape 1 and the contact pieces 3 are comprised of three bonded layers: a precious metal mating surface 31, a silver intermediate 32 and a braze alloy backing 33, which layers are shown in the enlarged cross section. In order to manufacture an electrical contact arm with contacts on both sides, which can be used, for example, as a moveable contact arm for a relay, a metal blade 5 is provided with a through-hole 6 at the desired contact position. The metal blade 5 may be made of any material suitable for the desired application, for example, copper alloy. Then, a pair of cut contact pieces 3A, 3B are centered over both sides of the through-hole 6 with the braze backing 33 placed against the blade 5. Each contact piece 3A, 3B is larger in cross-sectional area than the through-hole 6 so that the through-hole 6 is completely covered on both sides of the metal blade 5 and the contact pieces 3A, 3B contact the respective surrounding surfaces of the metal blade 5. As shown in FIG 2 , a pair of electrodes 7 , 8 are brought to the mating surfaces 31 of the contact pieces 3A, 3B. The electrodes 7, 8 exert a force on the contact pieces 3A, 3B to keep the pieces in position and to ensure acceptable electrical contact with the blade 5. A current is then passed through the first electrode 7 , through the blade and contacts assembly 3A, 5 and 3B, to the other electrode 8 for a sufficient amount of time to melt the braze alloy backing 33 on both contact pieces 3A, 3B. The amount of current applied is dependent upon the compositions and other physical characteristics of the various elements. After the current is stopped, the electrodes 7, 8 stay in place for a sufficient amount of time so the braze alloy can solidify. This method results in braze bonding each of the contact pieces 3A, 3B directly to the blade 5 and any excess braze material 34 flowing into the through-hole 6 which serves as a "braze reservoir". Once the braze has solidified, the electrodes 7, 8 are removed, as shown in FIG 3. If desired, the method can also result in bonding the contact pieces 3A, 3B to one another. This can be accomplished by having the excess braze material 34 fill the through-hole 6 completely (as shown in FIG 3) or having the excess braze material 34 from each contact piece sufficiently join with one another in the through-hole 6. As an example, a moveable contact arm for a relay was made using the method of the present invention having the following dimensions: Contact pieces 3A, 3B: length and width 3.5 mm; thickness of precious metal mating surface 31: 0.46mm(minimum) ; thickness of silver intermediate layer 32: 0.12mm(maximum) ; thickness of braze alloy backing 33: 0.02 mm to 0.04 mm; thickness of contact arm blade 5: 0.127 mm; diameter of through-hole 6: 2.39 mm. The braze alloy backing 33 consisted of a common braze alloy composition, for example 15% Ag, 80% Cu and 5% P. FIG 4 shows a relay 40 of the present invention. The relay 40 comprises a base 41, a coil assembly 42 that connects to the base 41, an armature 43, stationary contact members 44, 45 and a moveable contact arm 46 that is actuated by the armature 43 to contact the stationary contacts 44, 45. The moveable contact arm 46 is shown in more detail in FIG 5. The moveable contact arm 46 comprises a metal blade 46a having a through-hole 46b formed therethrough and a pair of contact pieces 46c, 46d that are joined to the metal blade 46a. The through-hole 46b acts as a reservoir to contain any excess joining material used to join the contact pieces 46c, 46d to the blade 46a. The relay 40, and the moveable contact arm 46, may be constructed by the method of the present invention. The embodiments described herein are merely illustrative of the principles of the present invention. Various modifications may be made thereto by persons ordinarily skilled in the art, without departing from the scope or spirit of the invention. For example, the contact tape 1 may be in the form of single strips rather than on a spool 2. Also, the contact pieces 3A, 3B may be cut from the tape 1 in different shapes, for example, in rectangular or circular shapes. Also, the braze alloy backing 33 may consist of any known or conventional brazing material. Further, the braze alloy backing 33 may be melted by another mechanism other than via the use of the electrodes 7, 8 and the application of current therebetween, for example, via the use of a heat chamber. Further, the electrodes 7, 8 may be replaced or supplemented by another mechanism to press and hold the contact pieces 3A, 3B against the metal blade 5. Still further, the contact pieces may also be joined to the blade via any known or conventional metallurgical joining process, other than via brazing, such as, soldering or welding, using a suitable solder or joining material.

Claims: WHAT IS CLAIMED IS: 1. An electromechanical switch, comprising: a coil assembly having a magnetic core, a coil wound around the core, and a frame that holds the coil and core; a contact assembly having (a) a pair of stationary contact arms arranged opposite one another and with the respective contacts facing one another; and (b) a moveable contact arm arranged between the pair of stationary contact arms and having a metal blade with a through-hole formed therethrough and a pair of contact pieces, each having a planar bottom surface, said contact pieces being brazed with the bottom surface to the metal blade so as to cover the through-hole from both sides and said through-hole being filled at least partially with excess braze material; and means for actuating the moveable contact arm upon energization and de-energization of the coil. 2. The switch of claim 1, wherein said metal blade is made from a resilient copper alloy. 3. The switch of claim 1, wherein each of said contact pieces has at least two layers of precious metal. 4. The switch of claim l, wherein each of said contact pieces has a parallelepiped shape. 5. The switch of claim 1, wherein said through-hole has a cross section area of approximately one half to one third of each of the bottom surfaces of said contact pieces. 6. An electrical contact arm, comprising: (a) a metal blade having a through-hole formed therethrough, and (b) a pair of contact pieces, each having a planar bottom surface, said contact- pieces being joined with the bottom surface to the metal blade so as to cover the through-hole from both sides and said through-hole being filled at least partially with excess joining material. 7. The switch of claim 6, wherein said metal blade is made from a resilient copper alloy. 8. The switch of claim 6, wherein each of said contact pieces has at least two layers of precious metal . 9. The switch of claim 6, wherein each of said contact pieces has a parallelepiped shape. 10. The switch of claim 6, wherein said through-hole has a cross section area of approximately one half to one third of each of the bottom surfaces of said contact pieces. 11. A method of manufacturing an electrical contact arm, comprising the steps of: providing a metal blade having a through-hole formed therein; providing a pair of contact pieces each having a planar bottom surface greater than the through-hole in said blade, each of said bottom surfaces being coated with a layer of joining material; positioning one of said contact pieces on either side of said blade so as to cover said through-hole from either side; joining the contact pieces to the blade by applying heat for melting said layers of joining material while pressing said contact pieces from either side against said blade, the through-hole serving as a reservoir where excess molten joining material flows in; and solidifying the joining material. 12. The method of claim 11, wherein the joining material comprises brazing material and the step of joining the contact pieces comprises brazing the contact pieces. 13. The method of claim 12, further comprising the step of cutting said contact pieces from a tape consisting of contact material that is coated on one side with said brazing material. 14. The method of claim 12, wherein the step of brazing comprises resistance heating by applying a pair of electrodes to said contact pieces and passing current therebetween. 15. The method of claim 14, wherein the electrodes are arranged so as to press and hold the contact pieces against said blade until the brazing material has solidified. 16. The method of claim 11, wherein the step of solidifying comprises cooling the contact pieces. 17. The method of claim 12, wherein the step of brazing comprises melting the layers of brazing material until there is sufficient excess molten brazing material in the through-hole to braze the contact pieces to one another. 18. An electrical contact arm manufactured in accordance with the method of claim 11. 19. An electromechanical switch having an electrical contact arm manufactured in accordance with the method of claim 11.

Inventors: WELSH WILLIAM G, WELSH, WILLIAM, G.
Applicants: SIEMENS ELECTROMECH COMPONENTS, SIEMENS ELECTROMECHANICAL COMPONENTS, INC.
Application year: 1997
Main classification: H01H11
IPC codes: H01H11, H01H45, H01H50