Hot knives, sometimes known as foam cutters, thermo cutters, hot wire cutters (same concept, but different configuration), or hot rope cutters, are used for a variety of professional and hobbyist applications.
Some examples include architectural modeling, maritime rope cutting, sculptural art, film and theatre stage construction, foam product packaging, advertising sign and display making, insulation shaping, and industrial applications such as cutting electrical boxes, utility hole passes, and plumbing channels.
Some hot knives are created for use on particular materials, but in general, they work well on a variety of materials, including foam, nylon rope, synthetic fabric, wax, rubber, plastic, and more.
The Operating Instructions and Specification Sheet that is included with the PRO-1 Hot Knife provides this warning: “Use proper respiratory protection when working with hazardous materials.”
In order to understand the hazardous attributes of the product you’re using, you should request the Material Safety Data Sheet (MSDS) from the product manufacturer and read it carefully.
Extruded and Expanded Polystyrene Foam are two popular types of foam used for professional and hobbyist processes. Hazards can range from product to product; some foams may even have flame-retardant materials that off-gas particularly dangerous chemicals when heated. Here are two examples of foam MSDS: Atlas EPS Expanded Polystyrene and Dow Chemical’s STYOFOAM™ 1.00 x 24″ Square Edge Extruded Foam Insulation. Some MSDS specifically discuss toxic fumes that can be released in processes like wire cutting and other heat-related operations.
Another popular use of hot knives or hot wire cutters is for rope cutting. Sentry Air has received several inquiries, especially from workers in the maritime industry, regarding fume control solutions for these processes. When rope (e.g. nylon rope) is cut with a hot knife, smoke and fumes are typically released. Customers often complain about the extremely unpleasant odors caused by the melting rope. This is a combination of particulate (in the form of smoke and fume).
Fume & Smoke Control: Consider Local Exhaust Ventilation
We have listed some local exhaust ventilation solutions below that may help reduce particulate and fume exposure to workers:
Filter Media. All of the fume extraction solutions that you see below are equipped with filtration media. Media is selected based on the type and amount of materials being cut by the hot knife. Typically a HEPA filter is used to collect hazardous particulate. This filter is up to 99.97% efficient on capturing particles 0.3 microns and larger. Generally, an Activated Carbon filter is also used to adsorb any volatile organics that may be emitted during the cutting process. Even an impregnated Acid Gas filter may be employed for certain materials. *A Sentry Air Systems Applications Specialist will gladly take a look at your product’s MSDS to ensure filter compatibility and efficiency for your particular application.
Under-the-Table Mounted Configuration. Because many rope-cutting operations are performed on a benchtop or tabletop, we often recommend an under-the-table mounted fume extraction solution. In the configuration pictured below, a Model 300 Fume Extractor [Model # SS-300-MS] is mounted beneath a workbench. There is a 4″ diameter (6″ diameter also available) opening on the work surface to accommodate the inlet of the fume extractor. As the operator cuts the rope above the opening, the negative-pressure fan pulls the smoke away from their respiratory zone and into the filtration system. The Model 300 is capable of air volume up to 350 CFM. Models with greater air volume are also available.
This configuration may also work for small-scale and relatively stationary foam-cutting operations.
|Cutting foam with a hot knife on a downdraft bench [Model # SS-440-DDB]. See Video below, under “Portable Floor Configuration with Flexible Arm”.|
This configuration is well-suited for foam cutting operations. The flexible fume extraction arm can be positioned at a variety of points on large pieces of foam.
|Cutting nylon rope with a hot knife.
Utilizing the Model 300 Portable Fume Extractor for smoke extraction.
The base unit that houses the fan and filtration system can be set atop a shelf while a 4″ diameter opening in the shelf accommodates the flexible arm. This configuration can also be mounted directly to the wall with a Sentry Air mounting kit.