Three Main Types Of In-Running Nips

Three Main Types Of In-Running Nips

In-running nip points are one of the most common causes of workplace injuries involving machinery. These pinch points occur when the material is pulled into a gradually narrowing opening between two rolls. The force of the moving material can be strong enough to trap and crush body parts, such as fingers, hands, arms, and even hair. Nip point injuries can be extremely serious and even fatal in some cases. Workers who operate or maintain machinery must be aware of the dangers of nip points and take precautions to protect themselves. Some simple safety measures include using guards or shields to block access to nip points and ensuring that loose clothing and long hair are securely tied back before operating machinery.

U.S. Department of Labor, Occupational Safety & Health Administration (OSHA) Dangerous nip points also occur in machinery parts, not in direct contact with the material, such as near pulleys, gears, and spindles—where the linear or rotary motion of the moving equipment occurs through narrowing openings between components. Frequently the machine is running too fast or is too powerful to allow stopping before significant injury occurs.

In-running Nip Points

Anyone who has worked with machinery knows that there are a lot of potential hazards. One of the most common hazards is the in-running nip point, which is caused by rotating parts on the machinery. This can be a very serious hazard, as it can cause amputation or entrapment. In-running nip points can be found anywhere on the machine, but they are most commonly found on belts, pulleys, and gears. The best way to prevent this type of hazard is to ensure that all workers are properly trained on the risks and how to avoid them. Additionally, all workers should wear proper safety gear when working with machinery. There are three main types of in-running nips.

The Three Primary Motions Of Moving Parts

1. Parallel rotating parts

Parts can rotate in opposite directions while their axes are parallel. These parts may be in contact, producing nip point. Stock fed between the rolls may also produce nip points. This danger is common on machines with intermeshing gears, rolling mills, and calenders.

2. Tangentially moving parts

Tangentially moving nip points are also created between rotating and tangentially moving parts. Some examples would be the point of contact between a power transmission belt and its pulley, a chain and a sprocket, and a rack and pinion.

3. Rotating and fixed parts

Nip points can occur between rotating and fixed parts, creating a shearing, crushing, or abrading action. Examples are spoked handwheels or flywheels, screw conveyors, the periphery of an abrasive wheel, and an incorrectly adjusted work rest.

Rotating and fixed parts

Dangerous Practices

When performing safety inspections, I see many cases in which personnel is exposed to dangerous in-running nip points. These situations particularly are prevalent when the material is hand-fed, or personnel is working near the machinery.

It is important for everyone involved in the production process to be aware that there are many, many nip points in most production operations and that these nip points present a high injury risk. It is equally important to be aware that the nip points become even more hazardous when the material or machine is not moving smoothly, such as when feeding problems, erratic speeds, misalignments, breakdowns, and other abnormal conditions are present. Under these circumstances, manual intervention to remedy the problem occurs frequently, and during the urgency and stress of resuming production, dangerous work methods may arise inadvertently.

Manhandling the material, using pry bars or other inappropriate tools, making adjustments on the move that should be done when the machine is stopped, reaching for dropped items, and slipping on cluttered or slippery floors can cause body parts to enter nip points.

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