Slide Gate Actuator Sizing
KWS Slide Gates are made for a wide variety of applications. Each application has a unique set of design variables which will impact the overall design of the gate. Variables such as the opening size, product density, head height of material on the gate, and even the type of service the unit will be subjected to will have an impact on the construction of the slide gate.
One of the most important, and often overlooked, design elements of a slide gate is the actuator. Correctly sizing the actuator is a key component in the design of a slide gate. There are several different options available for actuating a slide gate including pneumatic cylinders, electric linear and rotary actuators, hydraulic cylinders and manual hand and chain wheels. Regardless of the actuator, calculating the correct opening and closing force is essential for proper operation.
The force required to open and close a slide gate is a function of the size of the gate opening, the type of bulk material in the bin or hopper above the gate, the head height of material on the slide plate and the design of the slide gate. When the slide gate is in the closed position, there is a vertical force pushing down on the slide plate caused by the head load of material above the gate.
The force to open the slide gate must be calculated using the coefficient of static friction between the material and the slide plate and the slide plate to the rollers.
Note: In many cases a slide gate will not be able to close through a static column of material.
In order to determine the opening force required the following variables must first be provided:
- Slide Gate Inlet Length
- Slide Gate Inlet Width
- Slide Plate Thickness
- Bulk Material on Slide Plate
- Bulk Material Density
- Maximum Expected Head Height of Bulk Material above the Slide Gate
Using the variables provided above, the total weight of material on the slide plate can be determined. The maximum calculated height of the material on the slide plate is limited by the hopper design and may be much less than the total height of the hopper. The exact value of this calculated head height is dependent of the angle of repose of the material, density and material flow properties.
Testing of the specific material may be required in order to determine the exact adjusted height to be used for any specific application. Using the formula below the force on the slide plate can be determined.
Wm = H x L x W x D
Eq. 1 – Force on the Slide Plate
Where:
Wm = Weight on the Slide Plate (Lb)
H = Adjusted Height of the Material in the Hopper or under the Conveyor (ft)
L = Length of the Slide Gate Opening (ft)
W = Width of the Slide Plate Opening (ft)
D = Density of the Material in the Hopper (Lb/cuFt)
Using the weight on the slide plate and the coefficient of friction, the force required to open the slide gate can be determined. Testing of the specific material may be required in order to determine the exact coefficient of friction to be used for any specific application. Using the formula below the force to open the slide plate can be determined.
Fs = Wm x μsm
Eq. 2 – Force Required to Open the Slide Gate
Where:
Fs= Force Required to Open the Slide Gate (Lb)
Wm = Force on the Slide Plate (Lb)
μ = Coefficient of Static Friction Between the Material and Slide Plate
Additional friction between the slide plate and the rollers or sliders must also be accounted for. Determining this additional force is dependent on the slide plate thickness and roller or slider design and can be determined through testing of the exact system utilized.
KWS has performed extensive testing to ensure every slide gate is properly sized for the application for which it will be utilized. Each slide gate application is analyzed by the KWS Sales and Engineering staff in order to assure a 100% success rate on every application. Contact a KWS representative today to learn more about the KWS slide gate design.
