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Do your presses meet current safety standards?

August 15, 1999

5 Min Read
Do your presses meet current safety standards?

If your horizontal molding machines were purchased more than a year ago, you should be aware that they may be out of compliance with current safety standards. The revised SPI/ANSI B151.1-1997 safety standard, issued two years ago, has a grace period that runs out next year.

Developed by the Society of the Plastics Industry (SPI) and approved by the American National Standards Institute (ANSI), the standard requires molders to modify existing equipment to comply. The deadline for compliance is July 22, 2000. That means you have less than 12 months to bone up on the latest safety requirements and fix your presses.

Machinery OEMs were given a one-year grace period to comply with the standard, so presses purchased on or after July 22, 1998, should meet the new standards.

To bring your machines up to snuff, start with this article. It was excerpted from an SPI document titled, “Revisions to SPI/ANSI B151.1—Horizontal Injection Molding Machines—Safety Requirement for Manufacture, Care, and Use.” It summarizes some of the changes introduced in the revised SPI/ANSI B151.1-1997 standard, but it does not represent the specific language itself. Call ANSI (see information at the end of this article) to get a copy of the revised standard and consult with your machinery OEM.

All of the following information applies to horizontal injection molding machines only, and applies to new and existing machines.

Interlocks. ANSI B151.1-1997 has sweeping changes since the 1990 revision. To start, the electrical, hydraulic, and mechanical interlock functions on the operator gate have additional safety requirements. The electrical interlock must now be hardwired; the hydraulic interlock must be monitored and can now be actuated by either mechanical or electrical means. The mechanical device (ratchet bar) must now be monitored to verify correct operation each time the operator gate is cycled.

Monitoring is required so that if a failure in either the hydraulic or mechanical interlock safeguard occurs, it will be detected and provide a warning to the operator the next time the operator gate is cycled. Horizontal injection molding machine electrical systems must comply with ANSI/NFPA 79-1994.

Base area guards. Base area guards around the part drop region are required to prevent access under the machine base and into the clamp area. Machine base area openings more than 500 mm (19.5 inches) above the floor now require base area guards. The presence of a conveyor or chute may function as a guard (see ASME/ANSI B20.1-1990).

Barrel and screw position. Certain machine functions are now restricted to further enhance worker safety. To provide additional protection against possible hot plastic spraying into an open mold, screw rotation is permitted with the operator’s gate open only when the nozzle shutoff is in the closed position. During barrel or screw removal, if the injection unit is swiveled out of its normal operating position, screw or plunger motion must be interlocked so that motion is permitted only in manual mode with its forward speed limited to .5 inch/ second.

Pinch points and vents. To protect against possible pinch points between the nozzle and mold sprue, the purge guard interlock must inhibit injection forward carriage motion in addition to inhibiting purging motions. When a machine is being operated in the motion mode of the motion/ no motion option, access to pinch points that may exist if the operator gate opens past the movable platen must be prevented.

The ANSI B151.1 standard no longer refers to the motion/no motion option as a special option. In any mode of operation, closure of a power-operated gate shall not directly initiate a machine cycle. If a vent port is used on the barrel, a cover must be provided over the port to protect personnel from hot plastics and/or vapors that may be expelled.

Large tonnage machines. Large tonnage machines are now defined as those having a distance between tiebars greater than 47 inches. Additional safety measures are required for these large machines. For example, where it is possible to stand between the operator gate (or the rear guard) and the mold area, emergency stop or reverse buttons must be provided inside the operator’s gate and inside the rear guard. In addition to the emergency stop requirement, one of the following additional devices is required:

  • Gate block.

  • Double acknowledgment system.

  • Presence sensing device.

When a working platform is provided in the mold area for operator access during normal production, a presence sensing device shall be provided that prevents or stops hazardous motion in the mold area. When a working platform in the mold area is not provided, either a gate block or a double acknowledgment system shall be provided. Closure of the operator’s gate must require direct and continuous action by the operator.

Exceptions. On existing machines, the following exceptions may apply:

  • Interlock exceptions. Provision for two independent interlocks on the rear guards was not designed into many existing machines. Consequently, this feature cannot be incorporated into these presses without extensive modifications, if at all. So, two independent interlocks are not required by ANSI B151.1-1997 on existing installations. For similar reasons, only machines that have electrically actuated, injection carriage forward motion shall have carriage forward motion inhibited when the purge guard is open, in addition to inhibiting purging motions.

    Guards with secondary equipment. When guards at the parts discharge area require modification to accommodate conveyors or other parts removal devices, additional guarding, presence sensing devices, or interlocked perimeter guards shall be provided by the employer to prevent access to hazards in the mold area and/or to stop hazardous machine motion. However, if the additional guard scheme renders the conveyor or chute unusable, then prominent warning means must be provided by the employer in lieu of such guards.

Ventilation. The employer must also provide a means to ventilate hazardous vapors away from the machine and assure proper press shutdown procedures are followed to protect the workplace environment. As well, the employer is to supply additional safeguarding for automatic mold changes, if necessary.

The SPI/ANSI B151.1-1997 standard was developed by the SPI Machinery Div. and replaces the 1990 standard, which took effect in 1993. The next standard—which SPI has begun work on already—will be issued in 2002 with a 2005 effective date. Contact ANSI for the complete standard; contact the SPI with questions.

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