How Hollow Metal Doors Are Made

Since the 1940s, technology has significantly improved the manufacturing process of commercial hollow metal doors. The manufacturing process involves nine steps before a metal door is shipped to a job site for installation. First, the process begins with the raw materials. The standard material for a commercial metal door is galvanized steel.

Galvanized steel is a steel surface that has received a galvanized coating, which has been annealed. Galvannealed steel starts with a galvanized coating, where the steel is dipped in zinc to protect it from rust. After coating, the steel is heated (annealed) to allow the zinc to bond with the surface. The result is a corrosion-resistant matte finish that holds paint well.

Steel shaping for commercial doors involves several key steps:

• Large steel sheets are cut down to the required door size.

• The sheets are bent and formed into the outer shell of the door.

• Reinforcement channels are shaped and added inside the shell for strength.

• Edges are folded or welded to create a seamless, durable frame.

Once the steel shell is shaped and reinforced, it goes through finishing steps. Welded seams are smoothed, and the surface is primed or coated to protect against corrosion. At this stage, the door is also prepared for paint or other finishes to match the building’s desired look.

Key steps in the metal door manufacturing process include:

• Spot welding is used to attach hinges, closers, and lock reinforcements to the inside of the door body.

• After the steel shell is assembled, a core is inserted to make the door more rigid.

• The core can be enhanced with features such as insulation for improved energy efficiency, bullet resistance, or soundproofing.

• Common core types include honeycomb, steel-stiffened, and polystyrene.

• Honeycomb cores were once common, but polystyrene has become the standard due to environmental and performance advantages.

Polystyrene provides a quiet, lightweight fill with excellent insulation properties and is easily used in conjunction with steel stiffeners and other soundproofing materials. Special, rated polystyrene is also commonly used in fire-rated metal doors because of its ability to withstand high temperatures and inhibit flame spread.

Finally, after all the components of the door are assembled, the metal door is then placed through a machine called an edge welder. This automatic welder merges the two edges of the door halves into one finished product. The next step is to move the door into the finishing room. Workers grind and weld edges to smooth them, and sand away imperfections for a finished look. The door is then inspected one last time for quality before being mounted to hangars and entering the painting booth.

Hollow metal doors are typically painted with a baked-on grey water-based primer finish. This low-VOC paint meets lead-free requirements and is ANSI Spec 25010 (the US adoption of ISO/IEC 25010) tested for primers. This primer finish enables customers to paint the door to any desired color after installation easily. After finishing, the door is nearly ready to be shipped to the customer. The last thing done before shipping is to label the door.

Without a proper label, a hollow metal door, even if fire-rated, won't meet fire codes. The fire-rating label provides crucial details to installation crews, building owners, and code inspectors about the door's materials and rating. All fire-rated doors manufactured by CDF are fire rated between 20 minutes to 3 hours and always have proper labels.

Now the hollow metal door is complete! Time to carefully package the door, match it with the order, get it stacked on a pallet, and it's ready to be shipped off.

At CDF Distributors, we deliver strength and style for every opening in your building. From hollow metal doors to fire-rated assemblies, our products meet strict codes while keeping your property secure. Contact our team today to find the perfect fit for your project and get a fast, reliable quote.