Brake shoe back lug attachment

BACKGROUND OF THE INVENTION

This invention relates generally to railroad brake shoes and, more specifically, to the attachment of a lug to a brake shoe.

Conventionally, railroad brake shoes use one of two types of friction material -- cast iron or a composition material. In a composition shoe, such as shown in _USPN 2,948,361, the brake shoe lug is conventionally attached to the brake shoe by clinching lug tangs to the underside of the back plate before the composition friction material is attached to the back plate.

Recently, a new type of brake shoe has been developed to replace the composition shoe. This shoe features a sintered metallic friction material, such as that disclosed in Assignee's copending Application Serial No. 316,652, filed November 2, 1981.

In the manufacture of such shoe, a sintered metallic mix is cold formed with the back plate to produce a cold compact which is then heated and hot pressed. Attempts to produce a shoe which has the lug attached to the back plate before cold forming have proved to be impractical, since no way has been found to prevent collapse of the heated lug during the hot pressing process. Thus, a separate lug has been welded to the back plate after the hot pressed brake shoe has cooled. This method of attachment has been found to be time consuming and expensive. Thus, it is the object of this invention to find a better method of attaching a lug to a sintered metallic brake shoe.

SUMMARY OF THE INVENTION

In one form, this invention comprises providing a pair of spaced slots in a back plate which mate with depressions in the friction material which are formed during cold pressing. The cold compact is then heated to a high temperature and placed in a die containing the cold lug. During the hot pressing step, lug legs are pressed through the back plate slots and into intimate contact with the hot friction material. In another form of the invention, no slots or depressions are formed in the back plate or cold friction material and the cold lug legs are pressed directly through the hot back plate and into the hot friction material during hot pressing.

DESCRIPTION OF THE DRAWINGS

Further objects, features and advantages of this invention will become more readily apparent upon reference to the following detailed description of the invention,-as shown in the acccompanying drawings, in which:

• Fig. 1 is a perspective view of a prior art brake shoe;
• Fig. 2 is a perspective view of a brake shoe having a lug attached according to this invention;
• Fig. 3 is a perspective view of a brake shoe and back plate cold compact, according to one embodiment of this invention;
• Fig. 4 is a perspective view of a die used in forming the cold compact shown in Fig. 3;
• Fig. 5 is a perspective view of a die used to attach a lug to a brake shoe during hot pressing, in accordance with this invention;
• Fig. 6 is a detail view of a lug having its legs inserted through the back plate slots and into the depressions in the friction material prior to hot pressing, according to one embodiment of this invention;
• Fig. 7 is a detail view similar to that of Fig. 6, but shown upon completion of hot pressing;
• Fig. 8 is a detail view of a lug prior to insertion of its legs into the friction material according to another embodiment of this invention; and
• Fig. 9 is a detail view similar to Fig. 8, but shown upon completion of hot pressing.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to Fig. 1, a prior art railroad brake shoe 10 comprises a sintered metallic friction ele- nent 12 mounted on a steel back plate 14. A lug 16 (for attaching the brake shoe to a brake head) has four legs which are attached by welding at 18 to the back plate.

Fig. 2 shows a brake shoe 20 according to this invention which comprises a sintered metallic friction element 22 mounted on a steel back plate 24 and a lug 26. A cold compact according to one embodiment of this invention is shown in Fig. 3. Here the back plate 24 has a pair of spaced slots 28 formed therein which register with depressions 29 in the friction material. To form this cold compact, back plate 24 is mounted in a cold forming die 30, shown in Fig.4, having a curved bottom surface 32 and a pair of protuberances 34 which extend through slots 28. An iron-base, metal powder mix is then placed on top of the back plate 24 and compressed at a pressure of approximately 1240 bar to produce the cold compact of Fig. 3. The protuberances 34 form depressions 29 in the friction material during this operation.

The cold compact of Fig. 3 is next placed in an oven and heated to 870-1100 C. The next processing step uses a hot pressing die 36 which has a curved bottom surface 38 having a depression 40, shown in Fig. 5. A lug 26 is placed in depression 40 and a plug 42 is placed over it so that its top surface-is flush with surface 38. The hot compact is then taken from the oven and placed in the die and the entire assembly is pressed at approximately 1240 bar. Fig. 6 shows the relationship of the lug 26 to the hot compact 22,24 just prior to pressing, with the legs 44, which include a hole 46 and tangs 48, extending into depressions 29. After pressing, the lug 26 is firmly secured in the friction material 22, as shown in Fig. 7. The hole 46 and tangs 48 provide a mechanical interlock between the lug and friction material.

Figs. 8 and 9 show another embodiment of the invention. In this embodiment, the slots 28 are eliminated from the back plate 24 and the protuberances 34 are eliminated from the cold forming die 30 so that the cold compact has no slots or depressions. Fig. 8 illustrates the assembly just prior to hot pressing. It has been found that during hot pressing, the legs 44 of the cold lug 26 will penetrate the steel back plate 24, forming slots 28 therein, and embed themselves into the friction material 22, as shown in Fig. 9. This further simplifies the manufacturing operation.

Thus, this invention provides improved means for inexpensively and securely attaching a lug to a sintered metallic friction material brake shoe.