Stainless Steel Foil & Tool Wrap – How to Use

Toolwrap UK offer two sizes of stainless steel tool wrap from stock. Both sizes contain the same 4.57 square metres of foil but the 20” can be  more economical for smaller components with much less wastage. The tool wrap can be easily cut to size using scissors or snips. Watch this space for videos on how to use our tool wrap successfully, however the below should provide a good overview of how to use our tool wrap effectively.

Why Use Stainless Steel Tool Wrap?

  • 321 Stainless tool wrap is used by toolmakers and component manufacturers and is compatible with heat treatment processes up to 1090 deg C ( 2000 deg F).
  • Enclosing the component in an airtight package using our stainless steel foil mimics the conditions of a vacuum furnace. Ensuring that the package is airtight will prevent the drawing in of excess oxygen. Using stainless steel tool wrap in this way drastically reduces decarburisation, scaling and pitting.
  • This is a great substitution for a vacuum furnace and therefore allows manufacturers to save on the cost of sending out for heat treatment.
  • The same consistency of hardness will be achieved whether the parcel is tightly or loosely wrapped.

How To Use Stainless Steel Foil

  • Cover the top and bottom of the component with the foil and seal the edges with a double crease. Expelling as much excess air from inside of the parcel as possible whilst  being careful to  avoid creating  tears or holes.
  • Usually when employing  tool wrap the aim should be  to enclose a component in an airtight package from the very start  however it may be necessary to create a 5/6mm vent in the package if the component is an awkwardly shaped item where a large amount of air remains inside the wrapped parcel. The package will expand and contract due to the air being trapped inside and this expansion and contraction may result in a tear. Creating a vent will avoid the package tearing during the early part of the heat treatment cycle.
    Some tool makers cite the use of a burning ember inside the envelope so as to eliminate excess oxygen.
  • Once the parcel has reached its maximum temperature the vent should be sealed using tongs for the remainder of the heat treatment cycle.
  • There is an insulation effect when using toolwrap and temperature may need to be increased  to compensate for this effect
  • Double wrapping with stainless tool wrap may be necessary when hardening components with sharp edges; for example tools and dies. However it may be necessary to increase the heating and hardening times further  to compensate for the double wrap. Some trial and error may be necessary to achieve the correct cycle.

Operating Conditions

  • Our tool wrap performs best for air hardening steels. The results for water and oil hardening steel may not be as consistent in achieving full and uniform hardness. High speed tool steels usually require higher temperatures than 1090degC and should be avoided as the foil will have a tendency to fuse to the component at these higher temperatures and may result in the tearing of the parcel and decarburisation. For these high temperatures a nickel based alloy may be preferable which can withstand higher temperatures.
  • Components enclosed in stainless tool wrap can be retained in the parcel during quenching and doing so helps to prevent surface scaling and decarburisation. Unless a rapid quenching is required and the insulation effect of the toolwrap may prevent the required quick hardening.
  • Components hardened using stainless tool wrap usually emerge blued or tan coloured due to the oxidisation of the air trapped inside. This can be easily removed mechanically. To achieve bright components they should be thoroughly cleaned and oil free prior to enclosing in the foil. Take extra care to ensure a completely airtight seal  and then transfer immediately to quenching removing the components from the toolwrap before immersing into the quenching medium .