Magnetic strips and methods for making the same

• US 5,611,872 A
• Filed: 03/28/1995
• Issued: 03/18/1997
• Est. Priority Date: 08/30/1993
• Status: Expired due to Term

• Current Assignee: The Arnold Engineering Co. (The Kattegat Trust Co. Ltd.)
• Original Assignee: The Arnold Engineering Co. (The Kattegat Trust Co. Ltd.)
• Inventors: Anderson, Richard L., Manning, Neil R.
• Primary Examiner(s): WYSZOMIERSKI, GEORGE P
• Application Number:
  US08/412,165
• Time in Patent Office: 721 Days
• Field of Search: 148/306, 148/307, 420/105, 340/551, 340/572
• US Class Current: 148/306
• CPC Class Codes: C21D 1/18 Hardening C21D1/02 takes precedence; Quenching with or without subsequent tempering quenching devices C21D1/62
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 6/002 containing Cr C21D6/004 takes precedence
• CPC Class Codes: C21D 8/12 during manufacturing of articles with special electromagnetic properties
• CPC Class Codes: C21D 8/1255 with diffusion of elements, e.g. decarburising, nitriding
• CPC Class Codes: C23C 8/22 of ferrous surfaces
• CPC Class Codes: G08B 13/244 Tag manufacturing, e.g. continuous manufacturing processes
• CPC Class Codes: G08B 13/2442 Tag materials and material properties thereof, e.g. magnetic material details
• CPC Class Codes: H01F 1/147 Alloys characterised by their composition treatment thereof for enhancing their electromagnetic properties C21D8/12
• CPC Class Codes: H01F 1/14775 in the form of sheets
• CPC Class Codes: H01F 1/16 in the form of sheets H01F1/147 takes precedence

Abstract

Methods for preparing magnetic strips are provided in which the strips are manufactured to a thickness of less than about 0.003 inches and are made of a ferrous alloy having a carbon content of from about 0.4 to about 1.2 weight percent. The strips are prepared by first manufacturing an alloy having a carbon content below about 0.5 weight percent to the desired thickness and then subjecting the strip to a carburizing step to raise the carbon content in the strip.

Claims

1. A thin magnetic strip that exhibits superior magnetic properties, comprising a ferrous alloy strip having a thickness of between 0.0005 and 0.003 inches, said strip consisting essentially of iron, from about 0.45 to about 0.7 weight percent carbon, from about 2.5 to about 7 weight percent chromium, from about 0.1 to about 2 weight percent molybdenum, and optionally from about 0.05 to about 0.7 weight percent vanadium, from about 0.3 to about 1.2 weight percent manganese, and from about 0.3 to about 1 weight percent silicon, said strip being essentially free of cobalt, said strip having a coercive level of at least about 35 oersteds and a residual induction of at least 7,000 gauss.

2. The thin magnetic strip of claim 1 having a coercive level of at least 40 oersteds.

3. The thin magnetic strip of claim 2 having a residual induction of at least 9000 gauss.

4. The thin magnetic strip of claim 2 having a coercive level of at least about 45 oersteds.

5. The thin magnetic strip of claim 4 having a residual induction of at least 9000 gauss.

6. An electronic article surveillance system utilizing an improved ferrous alloy magnetic component, said component comprising a thin magnetic strip having a thickness of between 0.0005 and 0.003 inches, said strip consisting essentially of iron, from about 0.45 to about 0.7 weight percent carbon, from about 2.5 to about 7 weight percent chromium, from about 0.1 to about 2 weight percent molybdenum, and optionally from about 0.05 to about 0.7 weight percent vanadium, from about 0.3 to about 1.2 weight percent manganese, and from about 0.3 to about 1 weight percent silicon, and being essentially free of cobalt, said strip having a coercive level of at least about 35 oersteds and a residual induction of at least 7,000 gauss.

7. The electronic article surveillance system of claim 6 wherein said strip has a coercive level of at least 40 oersteds.

8. The electronic article surveillance system of claim 7 wherein said strip has a residual induction of at least 9000 gauss.