Title of Invention

A METHOD OF BRAZED JOINTS OF COMMUTATOR RISER AND ARMATURE COILS OF DC MOTORS AND A SEALING SYSTEM

Abstract

This invention relates to a method of sealing brazed joints of a commutator riser and aramature coils of a DC motor. A method of sealing brazed joints of a commutator riser (9) and aramature coils of a DC motor (1), characterised by the steps of brazing armature conductors (11) to the comutator riser (9); brushing brazed riser joints with insulating varnish; sealing said brazed riser joints and gaps between joints and between face of riser joints and armature overhang with putty (12); curing the applied sealing in an oven; and covering said armature overhang and riser protion with resiglass bandage(S).

Full Text

The present invention relates to a method of sealing brazed joints of commutator riser and armature coils of DC motors and a sealing system. DC motors for use in steel rolling mills and process industries like paper, cement, rubber, etc., are designed keeping in wind the application requirements. Such general purpose DC machines are designed in accordance with recommended dimensions and shaft center height of IEC-72A and IS 8223 and comply with all applicable Indian and International standards. The function of the critical components used in an armature of a DC machine are described below : The armature core is built of low loss cold rolled and coated electrical sheet steel lamination. The armature core is shrunk fitted or keyed onto the shaft. The core is provided with adequate axial holes in stampings for effective ventilation. The slots for insertion of armature coils are skewed for reduced magnetic and operational noise and prevention of swings at slow speed. Armature coils are made from high thermal grade rectangular enameled copper conductors. The coils are placed in open but skewed slot and are held in place by wedges in armature core. The overhang winding portion is held with the help of resiglass tape. The commutator is made of high conductivity hard drawn copper segments of trapezoidal profile. Epoxy class—F spacers having high compressibility to provide dynamic stability at all speeds insulate the commutator segments from each other. Equalizer coils are designed so as to equalize the voltage unbalance in armature. The enameled conductors that are wound to form the equalizer coils are potted with epoxy resin inside a moulded ring, the ends are subsequently brazed to armature conductors. Inset type molded commutator pressing rings are shrunk fitted inside the machined grooves of commutator segments and are used to hold the commutator in position by providing dynamic stability against centrifugal forces. The armature conductors of these motors coming out of the skewed slots of the core that are subjected to high temperatures during operation are grazed to the commutator risers. The brazed joints of commutator; riser and armature coils are subsequently covered with molded armature covering ring. The existing dealing arrangement for preventing the ingress of carbon dust generated due to wear of carbon brushes, relies only on the close fit of the riser covering ring on the commutator surface. However, there is a possibility of seeping of carbon dust in between the commutator surface and it's fitting surface. This ingress of carbon dust will result in localized shorting at riser joints, inter—turn shorting of armature conductors on the overhang and burning of armature covering ring at its face and on the periphery due to localized heating. Such a possibility of carbon dust seeping between the commutator surface and its fitting surface has to be eliminated. The main object of the present invention therefore, is to eliminate the ingress of carbon dust inside a DC motor for preventing localized shorting at joints of commutator riser and armature conductor causing failure by localized heating. This object is achieved by removing the armature riser covering ring and thoroughly sealing the corresponding portion and gap with putty, which totally prevents any ingress of carbon dust. Such a sealing also improves the heat transfer at the joints because of better filling between riser and outer surface of the sealing system. Thus, the present invention provides a method of sealing brazed joints of a commutator riser and armature coils of a DC motor,comprising the steps of brazing armature conductors to the commutator riser,brushing brazed riser joints with insulating varnish, seating said brazed riser joints and gaps between joints and between face of riser joints and armature overhang with putty, curing the applied sealing in an overn and covering said armature overhang and riser portion with resiglass bandage. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS: Fig. 1 shows a cross sectional view of a DC motor armature on which the present invention can be applied. Fig. 2 shows details of armature overhang with covering ring of Fig. 1 . Fig. 3 shows details of armature of DC machine with covering ring of Fig. 1. Fig. 4 shows details of armature of DC machine without covering ring of the present invention. Fig. 5 shows method of modifying the armature by removing covering ring. Fig. 6 shows details of armature of DC machine with commutator riser sealing system (detail of armature overhang without covering ring and sealed risers) Figure 1 clearly shows the armature conductors coming out of the skewed slots of the armature core 6. The armature conductors are brazed to the commutator risers, preferably electrically,to ensure optimum safety against mechanical and thermal overloads. The molded armature covering ring is represented by the reference numeral 2, as shown in Figs. I, 2 and 3. This covering ring 2 has been eliminated in the present invention, as shown in Fig. 4. For eliminating the armature covering ring 2, in accordance with the present invention, the following steps are taken : The brazed riser joints are brushed with insulating varnish, preferably of glass H insulation, for example, FT 2005. After applying the varnish, the brazed riser joints and the gap between riser joints, face of riser joints of armature overhang are covered with an insulating putty. The composition of the putty also can be of class H comprising FT 2005, Mica powder, aerosil powder and chopped glass strands. The putty applied can then be cured in an oven. After brushing with the insulating varnish, the brazed riser joints can be covered by a cap of insulating wrapper 10 (Fig. 5). The cap can be of 0.15 thick glass mica paper. The armature overhang and the riser portion can subsequently be covered with resiglass bandage. The riser face can be brushed with insulating enamel like for example class H ULF—93. The whole assembly can again be cured in an oven. DC motors with the new sealing system of the present invention were comprehensively tested on test bed. Results of better heat transfer and lower temperature rise have been observed. The machines were then subjected to mV drop test on the armature. No cracks were observed on the overhang and the reading of the mV drop test were found to be identical to the tests carried out earlier with motors fitted with molded armature riser covering r ing . WE CLAIM: 1. A method of sealing brazed joints of a commutator riser and armature coils of a DC motor, comprising the steps of : - brazing armature conductors to the commutator riser; - brushing brazed riser joints with insulating varnish; - sealing said brazed riser joints and gaps between joints and between face of riser joints and armature overhang with putty; - curing the applied sealing in an oven; and - coverings said armature overhang and riser portion with resiglass bandage. 2. The method as claimed in claim 1, wherein the armature conductors are brazed to the commutator riser electrically. 3. The method as claimed in claim I or 2, wherein said insulating varnish is of class H like FT 2005. 4. The method as claimed in the preceding claims, wherein said putty comprises FT 2005 mica powder, aerosil powder and chopped glass strands. 5. The method as claimed in claim 1, wherein said brazed riser joints after applying the insulating varnish are covered by a cap of 0.15thick glass mica paper,before applying the putty. 6. The method as claimed in the preceding claims, wherein the riser face is; brushed with insulating enable for example, class H ULF 93. 7. The method as claimed in the preceding claims, wherein after covering said armature overhang and riser portion with resiglass bandage, the assembly is is cured again in an oven. 8. A sealing system for brazed joints of commutator riser and armature coils of DC motors wherein electrically brazed joints of said commutator riser and armature coils are provided with a coating of an insulating varnish and covered by a cap of 0.15 thick glass mica paper, the entire gap between riser joints face and armature overhang is filled with a putty . 9. The sealing system as claimed in claim 8, wherein said putty comprises FT 2005, mica powder, aerosil powder and chopped glass strands. 10. A method of sealing brazed joints of a commutator riser and armature coils of a DC motor, substantially as herein described and i 1 lustrated.

Documents:

804-del-2003-abstract.pdf

804-del-2003-claims.pdf

804-del-2003-correspondence-others.pdf

804-del-2003-correspondence-po.pdf

804-del-2003-description (complete).pdf

804-del-2003-drawings.pdf

804-del-2003-form-1.pdf

804-del-2003-form-19.pdf

804-del-2003-form-2.pdf

804-del-2003-form-3.pdf

804-del-2003-form-4.pdf

804-del-2003-form-5.pdf

804-del-2003-gpa.pdf