Understanding gear racks

A gear rack is a type of linear actuator that converts the rotational motion of a sprocket into linear motion. It is an essential mechanism in many devices, and a thorough understanding of its terminology is necessary for its design and use in gear rack systems.

Linear actuator

A gear rack acts as a linear actuator, converting rotary motion into linear motion. Imagine a wall-mounted shelf on which several objects, including a square, are placed. When you turn one of the squares, it causes the rack to move linearly, converting rotary motion into linear motion. It's like turning a crank to raise or lower a load on a table - the rotary motion of the crank is transformed into the linear motion of the load.

This simple but effective mechanism has many advantages, making it ideal for a multitude of applications. Let's take a look at these advantages.

Advantages of gear racks

One of the main advantages of gear racks is their high dynamic performance. Here are just a few reasons why gear racks are advantageous :

• They use high-quality servo gears and actuators with backlashes of less than 1 arcminute, enabling them to accelerate loads faster than ballscrews.
• They maintain high speeds while remaining rigid
• They are capable of moving large loads at high speeds with great precision
• They resist external forces

These features make gear racks an ideal choice for applications requiring high dynamic performance and suitable supports.

What's more, unlike linear motors, gear racks offer a number of advantages :

• less expensive, less complex and more economical to produce
• not limited in length, and can therefore handle unlimited travel distances
• low cumulative error over time. This makes them ideal for applications requiring linear motion over long distances, such as rack-and-pinion railroads.

Common applications

Gear racks have many applications in a variety of sectors.
For example, rack railroads use sprockets on locomotives that mesh with a central rack to climb steep inclines. In the pipeline sector, gear racks are used as actuators for handling main valves.

Stairlifts use a rack-and-pinion system, often powered by hydraulic or electrical energy, to move a seat up or down a staircase. Conveyor systems incorporate stationary gear racks for moving the sprocket and transporting objects. Gear racks also contribute to the synchronized movement of several shafts in various industrial machines.

Types of gear rack materials

Gear racks can be made from a variety of materials.

Among these materials, brass, steel and stainless steel are commonly used for their manufacture. For specific applications, plastic gear racks can also be used.

Each material offers its own advantages and disadvantages, so it's essential to choose the right material for your specific application, taking into account its suitability.

Steel

Steel is a preferred material for the construction of gear racks, mainly because of its strength and durability, especially under heavy-duty conditions. Steel gear racks are frequently made from carbon steel for its ability to withstand most environments and maintain dimensional stability. What's more, they can be heat-treated to further enhance their strength.

Carbon steel gives gear racks good relative strength, which means that in a gear, the pinion, often the weakest element, will fail before the rack, increasing the longevity of the assembly.

Technical characteristics of gear racks

It's important to understand the technical characteristics of gear racks so you can choose the one best suited to your application. These specifications include:

• module
• gear circles and angles
• maximum force transmission capacity in a gear rack system, which depends on the torque on the motor-side pinion and its size, as well as the force applied to the rack and the size of the pinion.

By taking these characteristics into account, you can choose the gear rack best suited to your needs.

Module

The module is a unit of measurement that indicates the size of a gear's sprockets. It ensures that tooth geometry is identical to enable consistent tangent speeds between two meshing gears. The tooth height of a sprocket is 2.25 times the module, which is calculated by dividing the tooth height by 2.25. In this context, the key element is the modulus, which guarantees the proper functioning of the gears.

This provides a method for assessing gear tooth geometry. The pitch circle of gears is directly related to the modulus, and is located at specific distances from the root circle and tip circle of the tooth, which are proportional to the height of the tooth, and therefore to the modulus.

Gear circles and angles

Gear circles and angles are important for correct gear operation. The four most important circles on a gearwheel are:

• The addendum circle (top of teeth)
• The dedendum circle (tooth base)
• The base circle (generating the tooth profile)
• The pitch circle (in the middle of the teeth)

The pitch circle is essential in gearing, as the tangential velocities of the gears' pitch circles must be identical for correct operation. The industry generally uses pressure angles of 20 degrees for standard gears, but angles of 14.5 degrees, 25 degrees or 30 degrees can also be used, depending on the specific gear design.

Gear rack installation and maintenance

Correct installation and maintenance of gear racks is essential to their optimal operation and durability. Before installing a gear rack on a sliding gate, it's crucial to choose a rack compatible with the type of gate and the appropriate notches, considering options such as steel for its strength or nylon for quieter operation.

Example of gate installation

Correct installation of a gear rack is essential to avoid unexpected damage to the device. It is important to properly prepare the gate for rack installation, ensuring that the gate is aligned and that its surface is clean and smooth.

The rack is secured by screwing it onto the gate, using screws appropriate to the gate material, and it is imperative that the rack is perfectly horizontal and aligned with the motor sprocket.

Maintenance

Regular maintenance of gear racks is necessary to ensure optimal operation and prolong durability. It is necessary to check the gear rack regularly to ensure that it is not loose or unsoldered, tightening or re-welding if necessary.

The use of silicone lubricant or white lithium grease is recommended for the lubrication of gear rack movement mechanisms, as it offers long-lasting protection and creates a barrier against corrosion.

In summary

In summary, gear racks are essential components of many mechanisms, enabling rotary motion to be converted into linear motion. They offer high dynamic performance and stability, and can handle unlimited travel distances. Gear racks can be made from a variety of materials, such as steel, stainless steel and plastic, and it is essential to choose the right material for your specific application.

It's also important to understand the technical characteristics of gear racks, including module and gear circles and angles, to choose the gear rack best suited to your application. Finally, regular maintenance is necessary to ensure optimal operation and prolong the rack's durability.