MXPA06005933A - Tool for coldforming operations with improved performance - Google Patents

Abstract

The present invention relates to cemented carbide for steel tire cord drawing operations. The cemented carbide comprises WC with an ultra fine grain size and>5 but<10 weight-%Co, including grain growth inhibitors (V and/or Cr) and with a specific relation between HV30 and cobalt content.

Description

TOOL FOR CONFIGURATION OPERATIONS IN FRIÓ WITH IMPROVED EFFICIENCY The present invention relates to a method for manufacturing improved cemented carbide tools for shaping or otherwise working materials. The invention has particular application for manufacturing tools for metal work, and specifically tools used in the manufacture of tubular covers and similar articles, such as two-piece beverage cans. A two-piece can is manufactured by a process of wall drawing and embossing. In general, a two-piece can is manufactured by punching metal discs from a metal plate. A metallic "cup" is formed from the disk. The cups formed are pushed through a die forming the body, comprising a plurality of annular rings, generally known as tracing rings, re-drawn and drawn, by a punch that forms the body. The free spaces between the punch forming the body and the plurality of rings become progressively smaller, so that the thickness of the wall of the cup is reduced and the cup is elongated. This process is usually referred to as the sausage operation. It is a particularly demanding operation, which causes high wear on the tools and the operation is sensitive to dimensional changes and lubrication conditions. Due to the tremendous volume of cans for beverages manufactured each year, every slight improvement in the manufacturing process can result in tremendous savings. The tools for imparting a desired configuration, shape or finish to a material, such as dies, punches and the like, must be characterized by extreme hardness, compressive strength and rigidity. This is particularly necessary when forming metals or similar materials. Commercial tools for working materials for mass production must also be resistant to wear, erosion, and chipping or chipping from repeated and continuous stress and abrasion. These tools must also be manufactured from materials that can be designed and machined to lower tolerances than normal and maintain their dimensional stability during a wide range of operating conditions. It is known to manufacture punches, dies, tools for deep drawing and similar tools to work materials from a variety of materials, including metals, cemented carbide and conventional ceramics. These known materials all have certain undesirable limitations. When making tools for forming metal articles, particularly tubular covers such as two-piece beverage cans, the problems of the above known materials become particularly significant.

According to the prior art, a possible way to achieve a better efficiency in the manufacture of cans is the use of ceramic materials, for example alumina or silicon nitride reinforced with filamentary monocrystals as described in U.S. Pat. Nos. 5,095,730 and 5,396,788 respectively, but until now conventional cemented carbide seems to maintain its position as the preferred material. The present invention relates to the recent development of ultra fine grain cemented carbide. For many years there has been a progressive development of cemented carbide with finer grain size. The extension of the grain sizes of the cemented carbide in the ultra fine size range results in a number of positive improvements in relation to the wear processes. Rubbing wear (or grain loss volume) can be reduced by an order of magnitude by little more than reducing the size of the sintered grain by half (in the absence of other wear processes), since grain volume is related to the cube of its diameter. Fracture of the adhesive is another dangerous kind of rubbing wear, in which the separation of welded tool-material work interfaces can strongly induce tensile rupture within the underlying carbide. Ultra-fine hard metals can resist the initiation of such fractures better than thicker ones because of their greater resistance to rupture. Erosion / corrosion of the binder phase is said to be part of the wear mechanism in the wire drawing and deep drawing of beverage cans. In ultra fine cemented carbide, even when the binder content is maintained or even increased compared to conventional cemented carbide, the smaller grain size of the WC results in thinner binder films. Thus the resistance to selective erosion of the soft binder phase by wear particles is reduced. It is reasonable to believe that the thinner binder also gives rise to better oxidation / corrosion properties, since the properties of the binder in the WC interface are different from those of the pure metal. From the above it seems that the main interest in developing thinner sub-micron hard metal, perhaps in the nanometer range, is to raise hardness, maximize wear resistance by rubbing and resistance and at the same time as much as possible keep all other attributes at useful levels. Thus the increased wear resistance of the cemented carbide is achieved by decreasing the grain size of the tungsten carbide to ultra fine and maintaining the binder content so that the hardness is increased.

It is thus an object of the present invention to provide a tool for cold forming and tracing operations, particularly in the manufacture of two-piece cans of aluminum or steel for beverages, by the use of cemented carbide of ultra fine grain which provides a greater efficiency than the tools of the prior art. A particular improvement is achieved in the sausage operation. A combination of grain size and Co binder content that results in the best desired efficiency is represented by 6% by weight of Co with ultra fine WC having a hardness of about 2050 HV, i.e., a higher hardness than the binder grade of 6% by weight of commonly used Co which normally has the hardness of 1775 HV. Examples of the tool and the cemented carbide according to the invention are found in Figure 1 and Figure 2 respectively. Figure 1 shows a sausage die in which A = the cemented carbide die and B = the steel sheath. Figure 2 shows in magnification of 10,000 times the microstructure of an ultra-fine cemented carbide according to the present invention engraved in Murakami. The structure contains WC and Co. binder. Thus, the invention relates to the use of cemented carbide with an ultra fine WC grain size and high hardness which has improved wear resistance in cold forming and tracing operations, particularly in the process of inlaying the manufacture of cans for aluminum and steel beverages. However, the invention has wide applicability for use in manufacturing a variety of other shaped articles, particularly tubular covers, such as dry cell battery covers and aerosol cans. To avoid the well-known difficulties in defining and measuring the grain size of tungsten carbide cemented carbide, and in this case to characterize the "ultra fine cemented carbide", a Hardness / Binder Content ratio is used to characterize the cemented carbide according to the present invention. It makes use of the well-known fact that the hardness of the cemented carbide is dependent on the binder content and the grain size of the tungsten carbide. When the grain size or the binder content decreases, the hardness increases. Thus, the invention relates to a tool for cold forming cemented carbide having a Co content between 5 and 10% by weight, preferably 5.5-8% by weight and more preferably 5.5-7% by weight, with < 1% by weight of grain growth inhibitors V and / or Cr and a hardness with the following ratio between HV30 and Co content in% by weight: HV30 > 2150-52 *% by weight of Co, preferably HV30 > 2200-52 *% by weight of Co, more preferably HV30 > 2250-52 *% by weight of Co, and more preferably the hardness HV30 > 1900. In one embodiment the cemented carbide has 5-8% by weight of Co binder, < 1% by weight of grain growth inhibitors V and / or Cr and a hardness > 1850 to be used as a sausage die in the manufacture of aluminum or steel beverage cans. In another embodiment, the cemented carbide has 5-8% by weight of Co, < 1% by weight of grain growth inhibitors V and / or Cr with a hardness > 1950. In yet another embodiment the cemented carbide has 6-7% by weight of Co and < 1% by weight of grain growth inhibitors V and / or Cr and a hardness of HV 1950-2200. Cemented carbide is manufactured by conventional powder metallurgical techniques, such as grinding, pressing and sintering. The invention also applies to the use of the cemented carbide according to the invention particularly for other cold forming and drawing operations such as the wire laying operation and especially tire wire.

Example 1 Sausage dies for the production of 50 cl steel cans equipped with cemented carbide A and B rings: A. WC - 6% by weight of Co, submicron grain size, Cr3C2 as grain growth inhibitor with an HV30 hardness of 1775, prior art. B. Ultra fine cemented carbide consisting of WC, 6% by weight of Co, and < 1% by weight of V and Cr carbide as grain growth inhibitors, having an HV30 hardness of 2050, invention. The tools were tested with the third ring (the most severely damaged ring) in the production of 50 cl steel cans with the following results. The efficiency factor is related to the level of wear observed on the diameter of the ring after 100,000 cans produced. The rings according to the invention have on average only 74% of wear purchased with the prior art. Table 1 summarizes the average results of 24 rings tested for both samples A and B. Table 1

Claims (10)

1. CLAIMS 1. Ultra fine cemented carbide for deep drawing tools and sausage used for the manufacture of aluminum or steel beverage cans, characterized in that it comprises WC, < 1% by weight of grain growth inhibitors V and / or Cr, and 5-10% by weight of Co, preferably 5.5-8% by weight of Co and with a hardness of Vickers, HV30 > 2150 - 52 *% by weight of Co.
2. 2. Cemented carbide according to claim 1, wherein it has a hardness of Vickers, HV30 > 2200 - 52 *% by weight of Co.
3. 3. Cemented carbide according to claim 1, wherein it has a hardness of Vickers, HV30 > 2250 - 52 *% by weight of Co.
4. 4. Cemented carbide according to any of the preceding claims, wherein HV30 > 1900
5. 5. Use of the cemented carbide according to any of claims 1 -4 for deep drawing and stuffing operations for manufacturing cans for aluminum or steel beverages.
6. 6. Use of the cemented carbide according to any of claims 1-4 for the sausage operation to manufacture aluminum or steel beverage cans.
7. 7. Tool for deep drawing and embossing where it comprises ultra fine cemented carbide comprising WC, < 1% by weight of grain growth inhibitors V and / or Cr, and 5-10% by weight of Co, preferably 5.5-8% by weight of Co and with a hardness of Vickers, HV30 > 2150 - 52 *% by weight of Co.
8. 8. Tool according to claim 7, wherein it has a hardness of Vickers, HV30 > 2200 - 52 *% by weight of Co.
9. 9. Tool according to claim 7, wherein it has a hardness of Vickers, HV30 > 2250 - 52 *% by weight of Co.
10. 10. Tool according to claim 7, wherein it has a hardness of Vickers HV30 > 1900