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Lockrods are mechanical devices used to secure swing doors on the back end of trailers. They are used for semi-trucks, containers, and small specialty trailers.


History

Patented originally in 1912, the lockrod was first used to secure
railroad Rail transport (also known as train transport) is a means of transport that transfers passengers and goods on wheeled vehicles running on rails, which are incorporated in tracks. In contrast to road transport, where the vehicles run on a pre ...
boxcar doors. Today, sometimes confused with locking bars or bar locks, lockrods have evolved to secure virtually every trailer or container that has a swing door (a door that swings open and closed rather than rolls up). Roll up doors are sometimes used in place of swing doors on trailers that make shorter haul deliveries. Swing doors are most commonly used on
tractor-trailers A semi-trailer truck, also known as a semitruck, (or semi, eighteen-wheeler, big rig, tractor-trailer or, by synecdoche, a semitrailer) is the combination of a tractor unit and one or more semi-trailers to carry freight. A semi-trailer a ...
(dry vans and refrigerated "reefer" vans), intermodal cargo
shipping container A shipping container is a container with strength suitable to withstand shipment, storage, and handling. Shipping containers range from large reusable steel boxes used for intermodal shipments to the ubiquitous corrugated boxes. In the context of ...
s, certain rail cars that carry automobiles, and smaller utility trailers that haul cargo or livestock. Miner Enterprises was the originator of the lockrod and owned patent #1,023,164.


Lockrod use

In 1960, Miner Enterprises acquired White Welding in
Kenosha Kenosha () is a city in the U.S. state of Wisconsin and the seat of Kenosha County. Per the 2020 census, the population was 99,986 which made it the fourth-largest city in Wisconsin. Situated on the southwestern shore of Lake Michigan, Kenosh ...
,
Wisconsin Wisconsin () is a state in the upper Midwestern United States. Wisconsin is the 25th-largest state by total area and the 20th-most populous. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake M ...
and renamed the product line Powerbrace America. Later the name was changed to Powerbrace Corporation, a subsidiary of Miner Enterprises. Powerbrace continues to manufacture lockrods, trailer door hinges, and security lock devices for trailer doors from its Kenosha plant. Trailer doors are secured to the end frame (end wall) of the trailer to make sure the cargo doesn't shift and break down the door, and second, to keep the doors aligned properly by not allowing them to move up and down while in transit ( racking). If racking occurs due to too much play between parts, the parts wear out and eventually will fail to secure the door. The doors and end frame must hold the cargo securely while allowing the doors to swing free and be safely opened and closed with minimal effort. Depending on the size of the trailer, trailer end frame components typically consist of six to ten hinges, two to four lockrods, two trailer doors and the framework itself – all made of metal (usually steel, but sometimes
aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...
).


Lockrod construction

A lockrod assembly consists of top & bottom
cam Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...
s that are welded to the rod/stick of tubing itself, along with a handle assembly. Keepers (usually sold separately), are the part that accepts the cam, and can be welded or bolted onto the end frame of the trailer and remain stationary to the endframe. Mounting hardware attaches the lockrod to the doors (also sold separately). All trailer loading and unloading is done through the end frame of the trailer, which endures the highest forces. The top horizontal member is called a header. The bottom is referred to as the sill. The end frame is the action part of the trailer. The rest of the trailer is made up of the box that sits on the chassis, and includes the floor and running gear (wheels, brakes, lights, etc.). Lockrods come in different lengths and thickness (rod diameter) depending on intended use. Heavy-duty models are one-inch in diameter and are usually made of steel, most often galvanized, but sometimes painted or electropolished for cosmetic reasons. In lighter duty applications, such as smaller utility trailers, a ¾-inch diameter lockrod can be used; these can be made of steel or aluminum. In addition to the rod and handle, the cams and keepers metal matches that of the other lockrod parts. For example, if the lockrod were stainless steel, cams and keepers would be stainless to match. If galvanized lockrods, the cams and keepers would be made of galvanized steel to match. This metal match-up also minimizes
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engi ...
that occurs when two dissimilar metals are in contact with each other. Over the years, manufacturers have designed types of cams/keepers combinations to solve certain door alignment problems.


Types of lockrods


Zero-torque

Powerbrace invented the zero-
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
lockrod concept that became an industry standard. The main benefit of the design is that the cam goes past the center point so that the more pressure that's applied from the inside of the trailer doors (such as when animal weight is shifted against the door) the tighter the cams and keepers engage.


Reach/gather

Refers to the ability of a lockrod cam to "reach" and engage the keeper (gather) while closing the door; this feature helps to overcome resistance from compression seals and warped doors.


Icebreaker

A lockrod model with high door opening leverage, earning its name for its ability to open doors that are frozen shut.


References

* http://www.galvanizeit.org/hot-dip-galvanizing * http://www.evidencesolutions.com/web/Articles-by-DA/how-to-safely-open-trailer-van-doors.html * http://powerbrace.com/
Information on Zero-Torque by Powerbrace Corporation
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