The Tube & Pipe Journal - September 2010

THE AXIS OF SAFETY

An overview of bender safeguards

Figure 1

To initiate the bending sequence, the operator must activate two switches simultaneously. This ensures that the operator’s hands are not near the machine at the moment the process starts.

Figure 2

Most equipment manufacturers use a combination of safety devices. A typical combination is a safety mat and electrically interlocked side plates (both in yellow).

OVER the last 40 years or so, most tube benders sold in the U.S. have been equipped with a certain level of safeguarding to prevent operator harm. However, guarding an operator from injury 100 percent of the time is not always easy. After all, a modern tube bender can be considered a collection of synchronized power presses, all intended to form a tube into an infinite number of programmable shapes.

For example, consider a hydraulic clamp and a hydraulic pressure die, which commonly are found on typical CNC tube bending machines. Both devices can be considered power presses, and it’s no secret that a power press can develop enough force to cause an injury. To minimize the hazards, machine tool builders now must install protective systems that go beyond the traditional physical barriers.

THE BASIC BARRIERS CNC tube benders are intended to move automatically after a cycle is initiated. Usually a cycle initiates when an operator presses a set of dual palm

switches that conform to an OSHA standard (see Figure 1).

Some end users demand that the operator maintain contact with both of the palm switches the entire time the machine is moving. Good practice demands an additional device, such as a safety mat (see Figure 2), to ensure operator protection from the bender’s motions.

Physical guards that cover sprockets, chains, belts, and other moving parts also are expected. In addition, emergency-stop switches should be located within easy reach of the operator.

By George Winton, P.E.

ELECTRICALLY
INTERLOCKED DEVICES

A common electrically interlocked guard found on most tube benders involves one or more side plates mounted to a swing (see Figure 2). These side plates are guards that protect an operator from the rotational motion of a swinging bend head as a bend is being formed. This rotating arm is a powerful press that can impart harm to an operator if used without care. This is where the guard plates come into play. If activated, they stop the motion of the bend head. Without this type of guarding, a tube bender usually is considered unsafe to operate.

Moreover, the interlocked switches should be the forced guided type and fail to a safe condition. Thus, a component failure, loose wire, or broken wire breaks a circuit and causes the bend head motion to stop.