December 19, 2007

5 Min Read
Shaft Seals Solve Batch Mixer Wear Problem


Food-grade mixer with Inpro/Seal air kit, including airflow detector

Bonsal American Inc. manufactures cementitous building and repair products such as Sakrete dry-mixed concrete, masonry mixes, grouts, and thin-sets. Its production requirements present unique challenges for the equipment used in the manufacture of these varied products because of the abrasive nature of materials such as cement and larger aggregate.


Dry concrete mixer with Inpro/Seal air kit mounted for connection


Inpro/Seal shaft mounting with air kit; commercial SS mixer


Commercial SS mixer with Inpro/Seal air kit mounted

Through the years, Bonsal American acquired a number of horizontal single- and twin-shaft batch mixers from Hayes & Stolz in Fort Worth, TX. A constant maintenance issue was shaft wear and the subsequent replacement cost of shaft assemblies resulting from scoring over time. The mixers were utilizing common packing-gland-style seals that require maintenance personnel to adjust and replace the packing material on a regular basis. Even if the adjustments and maintenance are performed faithfully, product inside the mixer can get into the packing ropes and act like a piece of coarse sandpaper, grinding away at the shaft. Over time, the scoring becomes deep enough into the shaft that the rope can no longer seal and the leaking of product escalates through the seals. Besides being a housekeeping issue, over time a leaking seal will lead to destruction of the outboard bearings, causing downtime and costly repairs. Eventually shaft wear becomes severe enough to warrant an expensive replacement of the shaft and assembly (paddle or ribbon).

Mark Lowry, senior project engineer with Bonsal American, called Hayes & Stolz to discuss possible solutions to the problem. After an extensive investigation of potential solutions, the two companies agreed upon a course of action. Hayes & Stolz presented a solution to this recurrent wear-maintenance-replacement cycle—the Inpro/Seal.

Lowry had a project pending for the White Marsh, MD, plant involving two new twin-shaft mixers. Bonsal American agreed to try the new Inpro/Seal shaft seals on the new installation. Hayes & Stolz got together with the local Inpro/Seal representative and designed a “kit” to incorporate the seals to aid in installation and operation. The kit consisted of regulators and gauges for troubleshooting purposes in the field.

When the time arrived for the mixers to be installed, Hensley was asked to check out the installation to ensure a proper connection was achieved. Once everything was determined to be done properly on the mixers, they were put into operation in the summer of 2002. Since the initial installation, Bonsal American reports that there have been no problems or issues with the mixer seals or with shaft scoring. Lowry and his company’s leap of faith were rewarded with five years—and counting—of maintenance-free service for their efforts. There appear to be no problems on the horizon for what was once a recurring issue.


Articulating Air Mizer PS from Inpro/Seal

Since the initial efforts and success, Hayes & Stolz has formed a unique relationship with Inpro/Seal and utilizes the company’s products on tough applications. Usually these tend to be in abrasive or corrosive applications like Bonsal American’s. However, once the merits of the product are presented, more and more customers purchase these seals even in less abrasive instances because of their maintenance-free qualities.

Additionally, the healthy bond between the supplier and the OEM has allowed Hayes & Stolz to refer long-time customers to Inpro/Seal when service and parts calls are received and the right application appears. As a result of looking out for the customers’ best interests, recurrent problems have turned into happy endings for dozens of old customers.

Hayes & Stolz Industrial Mfg. Company, Ltd., Fort Worth, TX, manufactures material-handling equipment for a wide range of industries. For more information, call 800-725-7272 or visit

Inpro/Seal Co., Rock Island, IL, manufactures a bearing isolator that will provide a high level of permanent bearing protection. Inpro/Seal products are used in a wide variety of rotating equipment applications. For more information call 800-447-0524 or visit

Air Mizer PS Seal

Unlike conventional product seals, the Inpro/Seal Air Mizer PS does not rely on rubbing surfaces or frictional contact to form a seal. Instead, it uses airflow through a tight gap or throttle to create a pressure differential. This pressure performs the sealing function. The Inpro/Seal is unique in that the throttle is allowed to fully articulate to accommodate shaft run-out, deflection, angular misalignment, and axial movement. An air source regulated to a pressure slightly higher than the pressure inside the vessel is required. Some customers integrate a flow detector into their control system to ensure that purge air flows anytime product is present. Because the seal does not rely on contact surfaces, shaft-seal life expectancy is greatly enhanced.

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