Counterweight doors are less common than sectional steel doors or their rolling steel cousins but are still widely used in most of the country. The doors are manually (pushed or pulled) using ropes to guide the door up and down. They come in overhead (like a residential garage door) and vertical lift (straight up the wall) models. Vertical lift counterweight doors come in one and two pieces depending on the height requirements of the door. Newer doors are made the same way except the c-channel and i-beams are made of much lighter aluminum and thinner steel sheeting. The doors have 4 rollers (1 in each corner) that ride up along a j-track. The two piece door would have 8 rollers – 4 for each section. The j-tracks are attached to the wall. Pulleys are mounted at the top of each track. Aircraft cable runs from both bottom roller fixtures through the pulleys and then to a weight canister. The cable is either secured directly to the top of the weight can using u-bolts or run through pulleys attached to the top of the can. The can is made of thin steel shaped into a rectangle and rides up along one side of the door as the door is raised and lowered – thus the name counterweight.
The weight in the can consists of small, flat, round pieces of steel. The weight of the door determines how many of the steel pieces go into the can. Too much and the door will be too easy too open and will come down hard. Too little and the door will be hard to open and will be heavy to close. The can is covered by a weight can cover made of thin galvanized steel or aluminum and is attached to the wall and track. The cover runs from the floor to just above the highest point of travel for the can. Doors must be properly maintained and inspected as they can injure or kill anyone caught under a falling door. Doors that are not adjusted properly can creep down into the opening and be damaged by a forklift or product.
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