Lee Wardall reveals the criteria that must be met for steel products to be successfully deployed inbtableting tools
Steel qualities used in the manufacturing of tablet compression tooling can be defined in many ways. However, the key characteristics are generally the cleanliness of the steel, the quality and homogeneity of the microstructure, and the distribution of the carbides within the steel.
There are six main requirements for steels used in the manufacturing of compression tooling. The first is abrasive wear resistance. This is resistance to abrasion and erosion. More carbides and higher hardness improve tools’ wear resistance. Vanadium, molybdenum, chromium andcarbon can also contribute to improved wear resistance. Next on the list is toughness – i.e. good resistance to chipping.
The toughness of the steel can be described as the ability to absorb impact energy without breaking and/or chipping. An increased volume of silicone improves toughness of the steel. Fatigue strength is the ability of the tooling to withstand repeated load cycles without cracking or chipping. A large uneven distributed carbide structure is detrimental and significantly reduces the toughness, fine carbides, evenly dispersed are highly beneficial.
The third requirement is high compressive strength. This is the ability to withstand a constant load without deforming or breaking. Molybdenum contributes to improving the compressive strength of the punches.
Through hardening properties
Good through hardening properties is the next requirement. Temper resistance is the steel’s ability to maintain hardness as the surface temperature becomes elevated while having surface treatments applied or while in use. Molybdenum andtungsten contribute to temper resistance.
High hardness after high temperature tempering and good stability in hardening is also important. Harden ability is the ability of the steel to through harden and form martensite. Correct heat treating is essential. Carbonis also a key element in hardening.
The final requirement is that of corrosion resistance.This is the steel’s ability to resist the corrosive effects of the products it comes into contact with and the environment and conditions they are used and stored in. The chromium contact of the steel has a considerable impact on the steel’s resistance to corrosion.
The ESR process
A key process involved in the production of quality steels is electroslag remelting (ESR). This produces very clean homogenous steel by passing an ingot through reactive molten slag, removing the impurities and producing a refined structure. This process continues until the impurities are removed and a clean homogenous structure is produced. The steels produced are stringently measured and analysed against many standards, including ASTM, DIN, JIS and ISO, to make sure the steels’ cleanliness and quality requirements are met. Adamus HT recognises the importance of the steels’ chemical composition and therefore delivers this information on every tooling shipment in the form of a Certificate of Conformity given independently by the steel supplier.
Standard and speciality steels
Adamus HT uses steel grades that fulfil all the abovementioned requirements and it supplies them only from the world’s leading steel producers. Besides the standard steel grades used by all compression tooling suppliers, the company also offers a series of different speciality steels that can solve the tableting problems with abrasive, sticky and corrosive products as well as products that require higher compression forces than recommended due to the tablet size and dimensions.
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Lee Wardall is with Adamus.
