Choosing the Right Steel Tool

How do you optimise your tablet tooling to achieve the longest possible life out of your tool while minimising issues such as sticking, picking, fracture and/or excessive wear? You design specific tools to address specific problems. In other words, design the tooling for the product being manufactured.

First, you must consider the constraints of the application itself. The formulation and design of the tablet to be produced will impact the type of tooling you choose and may provide insight into potential production pitfalls down the road.

The design of the tool, tool steel used and coating applied are the most important factors in tool optimisation. In this article, we will focus on understanding the basics of tool steel.

How does tool steel impact tool optimisation? Different tool steels are good at addressing different challenges. Is the product abrasive or corrosive? Is it difficult to compress? Is it prone to sticking and picking? Choosing the right tool steel for the challenge at hand is critical to the success of your tablet compression tooling.

CHARACTERISTICS OF TOOL STEEL

Tool steels are evaluated on several characteristics, including toughness, hardness and compressive strength. Each characteristic influences tooling performance differently, depending on the specific application.

  • Hardness is a measure of how well the steel resists wear. How long is the steel going to wear against abrasive properties and deformation? Hardness is rated using the Rockwell C hardness scale, using a hardness tester to see how far a diamond will pierce the steel under a standardised load.
  • Toughness is a measure of how far the steel can be bent without fracturing. How much impact or stress can the steel withstand before breaking? While there is no standard test for toughness, it is most commonly measured by the amount of energy (in foot-pounds or joules) the steel absorbs before it breaks.
  • Compressive strength is the capacity of the steel to withstand a load before fracturing or deforming. How long can the steel resist failure under a compressive load? Using a compression-testing machine, the maximum compressive load a type of steel can bear is tested by placing a test piece between two plates and progressively applying a load until it fails.

In early tool steels used by the tableting industry, toughness was an important characteristic because tablet presses were less accurate and the added flex helped prevent tool damage.

Today, tablet presses are manufactured to extremely tight tolerances so toughness is less important than compressive strength and hardness, which have a greater impact on wear resistance and how long the tooling will last.

However, depending on the application, these characteristics are not always desirable in equal measure. Looking at the graph below, you’ll see the differing characteristics of common tool steels.

Understanding how the varying characteristics of tool steels can impact the performance of your tooling will help you make the right choice to optimize tooling for your application.

What tool steel works best to counteract the challenges of the powder, design or machine qualities? Is a steel that is tough, hard, wear resistant, or powdered metal necessary to provide the best outcome?

TOOL STEEL OPTIONS

Most of our punches come standard with S7 steel, which offers both toughness and compressive strength and is ideal for most general tablet compression applications.

If you are working with a more abrasive powder, consider using a D2 steel that has a higher hardness rating and offers greater wear resistance and compressive strength.

If you are running a product that is corrosive, such as effervescents, salts, magnesium or ascorbic acid, then using a premium stainless steel, such as 440C steel or M340 will help resist corrosion for longer tool life.

For your most challenging applications, those requiring a high compressive strength and significant hardness, a specialised powdered metal such as PM-M4 steel may be the answer.

No matter what your application, gaining a better understanding of how different tool steels can affect the overall performance of a tooling will go a long way in helping you optimize your tablet compression tooling for the longest possible tool life and best product.

Have more questions about how you can optimise your tablet operation? Contact PressTab Tooling info@presstab.com.au 02 8004 9157 credit wilsontool.com/tableting