Understanding Cam, Brakes, Bearings, and Lubrication
Cam Systems and Brakes
A cam returns to its initial position, and the pads are separated from the face of the drum by the spring action.
Hydraulic Brake Systems
In a hydraulic drive system, stepping on the brake pedal causes the master cylinder piston to push fluid through the pipes. This fluid reaches the pump body and drives the pistons. The piston’s action overcomes the spring resistance, causing friction on the drum pads, which produces braking. When the pedal is released, the spring between the pads retracts, and the fluid recedes.
Pneumatic Brake Systems
In a pneumatic drive system, air from outside is sucked into the compressor through a filter. This air is compressed and sent to a reservoir where it is stored at a given pressure, measured by a manometer. When the pressure exceeds the permitted value, a valve opens to exhaust excess air. To apply the brakes, an admission valve opens, allowing air to pass from the vessel to the cylinder. The air pressure pushes the plunger, which acts on the pads for the drum, causing friction and braking. When the brakes are released, the admission valve closes, stopping the air passage, and the pads return to their initial position.
Bearings
Bearings are mechanical elements whose function is to support and allow rotation of a shaft with the least possible friction. Plain bearings (sliding bearings) remain fixed on the stand and rub against the rotation axis. They are cylindrical pieces with an inside diameter slightly larger than the shaft. The difference between the shaft and the diameter is standardized.
Rolling bearings use rolling elements for contact. They consist of two concentric cylinders, one fixed to the support and one fixed to the axis. There is no slippage between them; instead, the bearing action is produced by interspersed elements on the surface.
- Outer ring: fixed to the support
- Inner ring: hosts the mobile components
- Cage: rotates freely
- Rolling elements: typically balls or pins
Efforts transmitted:
- Axial: Predominant force component along the axis.
- Radial: Supports radial efforts.
- Mixed: Supports both radial and axial efforts; often cone-shaped.
A guided union is a connection between two pieces allowing rectilinear or circular movement relative to each other in one direction, while preventing movement in other directions (e.g., a lathe tool holder).
Lubrication
When parts rub against each other, ridges cause wear, frictional heating, and potential damage to the machinery. To avoid this, lubrication is used to interpose a thin layer of lubricant. The most common lubricants are:
- Mineral oils: Classified according to viscosity, which is the resistance of a fluid to flow through a hole or glide over a surface.
- Grease: An oil that presents in paste form at room temperature.
Lubrication Methods
- External Input: Dropping lubricant onto machine elements.
- Pressure: Lubricant is drawn in and then distributed to the necessary parts of the machine.
- Splash or Drip: A moving piece is submerged in the fluid, driving the oil for impregnation.