Machine Design

Fast fillers fail safely

Elmar Industries, Depew, N.Y., is one of the largest manufacturers of automated filling systems in the world.

It produces over 100 different machines which are used to put liquids and particulates into plastic, glass, composite, and metal containers, ranging in volume from 1/2 oz. (15 ml) to 5 gallon (12 liters). Elmar systems employ rotarypiston, bottom-fill, and gravity-and-pocket technology, and come in many sizes from six to 72 filling stations.

One of the challenges for designers of filling systems is handling torque overloads caused by jams. Bottlers typically run fillers at breakneck speeds, up to 600 containers per minute, where torque spikes associated with jams can be catastrophic. To protect drive components, designers usually include shear pins, electronic limit switches, or some type of mechanical stopping device on any axis at risk. Although these solutions generally fulfill the role, they tend to impose more downtime and repair than most bottlers are willing to accept.

Elmar engineers, after considering many options, decided that mechanical torque limiters make the most sense. Their reliable, fail-safe operation provides ample protection; their simple, manual reset mechanism minimizes downtime as well as repair costs. On one of its machines, Elmar uses two such devices — one on the main drive train, another on an elevation stage that adjusts for bottle height.

The primary drive on the filling machine consists of a motor coupled by chain to a feedscrew. Containers lay perpendicular to the screw, nestled between thread faces, and are carried into the filling station at a rate set by the screw pitch and the speed of the motor. To protect the feedscrew mechanism, the drive sprocket mounts directly to a torque limiter. If a misaligned bottle locks up the screw, the drive instantly disengages.

Elmar engineers selected the protection device — a Torq Tender from Zero-Max Inc., Plymouth, Minn. — because of its compact size, face-mount style, speed (up to 200 rpm), and rugged, steel construction.

The mechanical torque limiter works by transferring input power to a central assembly through a rigidly held pawl, which rotates the outer drive housing and driven shaft. When it's overloaded, the torque on the pawl overpowers the springs and the pawl rotates out of its detent. This disconnects the central assembly from the outer drive housing. A simple turn of the device resets the pawl back into its detent and Torq Tender is ready to go.

Another type of Zero-Max torque limiter is used on the height adjuster. The height adjuster consists of a rotating shaft — operating up to 100 rpm — that connects to an elevation stage at one end and a motor (through an H-TLC torque limiter) at the other. Mechanical stops serve as a backup at the high and low point of travel.

Prior to the addition of the torque limiters, the mechanical stops alone were unable to halt the upward travel of the adjusting column. At times, the upward force would overpower the stops, jarring them loose or even free. Downward motion, on the other hand, could develop too much force (if the limit switch failed), bottoming out the column and causing it to jam. The torque limiter solved both problems.

In contrast to Torq Tender, the H-TLC uses a spring-loaded convex pin and detent mechanism, which can be adjusted to react to pre-set overloads. Upon overload, the pin disengages from the detent, shutting down the system. Once the overload is corrected, the HTLC can be quickly reset. Besides its adjustability, the HTLC is corrosion resistant, easy to install, and operates repeatably.

As for longevity, the Zero-Max torque limiters never need service. In the Elmar application, they've been running without incident for over six years, in many cases, around the clock.

For more information on torque limiting devices call Zero-Max Inc. at (800) 533-1731 or visit its website at

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