Stress relieved grinding ball having hard outer shell

• US 6,632,303 B2
• Filed: 01/10/2001
• Issued: 10/14/2003
• Est. Priority Date: 01/10/2000
• Status: Expired due to Term

• Current Assignee: AltaSteel Ltd. (Moly-Cop Chile SA)
• Original Assignee: Stelco, Inc. (Stelco Holdings, Inc.)
• Inventors: Jager, Christian Albert
• Primary Examiner(s): King, Roy
• Assistant Examiner(s): LEROY, DAVID H
• Application Number:
  US09/758,016
• Publication Number:
  US 20020025771A1
• Time in Patent Office: 1,007 Days
• Field of Search: 148/579, 148/575, 148/902, 148/660, 148/622, 148/662, 148/663, 148/906, 148/664
• US Class Current: 148/660
• CPC Class Codes: B24B 31/14 Abrading-bodies specially designed for tumbling apparatus, e.g. abrading-balls
• CPC Class Codes: B24D 18/00 Manufacture of grinding tools or other grinding devices, e.g. wheels, not otherwise provided for

Abstract

A grinding ball having a 55 to 65 Rockwell C hardened outer shell of tempered martensite is adapted for use in a heavy duty grinding environment by stress relieving to stabilize the ball against break-up and/or spalling.

Claims

1. A process for making a grinding ball having a hardened section of tempered martensite wherein said ball has been stress relieved to stabilize said ball against break up and/or spalling, said process comprising:

i) reheating a tempered grinding ball having a hardened section of tempered mantensite to its previous equalization temperature of its earlier tempering process;

ii) holding the grinding ball at the equalization temperature for a period of time sufficient to relieve partially compressive stresses in the tempered martensite section to develop an outer stress relieved martensitic shell and an inner non-stress relieved martensitic section; and

iii) allowing the reheated stress relieved ball to cool.

2. A process of claim 1, wherein said ball has a chemistry of:

3. A process of claim 1 wherein said equalization temperature is in the range of about 100°

C. to 3000°

C.

4. A process of claim 3 wherein said equalization temperature is about 150°

C.

5. A process of claim 1, wherein said ball has a diameter greater than 8 cm where stress relieving of said martensitic section stabilizes said ball against break up as caused by balancing circumferential stresses in a pearlitic core exceeding the tensile strength of the core.

6. A process of claim 5 wherein said reheating step at said equalization temperature for said tempered ball results in minimal hardness reduction in said tempered martensitic shell.

7. A process of claim 1, wherein said ball has a diameter less than 8 cm where stress relieving of said mantensitic section to produce said stress relieved martensitic shell reduces spalling.