"Light as possible" is now the mantra for winding and core-holding components handled by operators and maintenance personnel. As ergonomic programs are implemented, many companies share David Roisum's observation that, "Winders have more man/machine interaction than almost any other manufacturing and converting machinery." (The Mechanics of Winding). As a result, core shafts and chucks and the processes surrounding their use have become early targets for reducing WMSDs (work-related musculoskeletal disorders).

But ergonomic requirements are also tied to production requirements. Core-shaft and chuck components must carry wider roll widths, heavier roll weights and run at higher speeds. And there is little room for increased costs. Lightweight components often have less roll-carrying capacity or speed capabilities, while stronger materials capable of higher roll weights and speeds can be quite expensive. Analysis of key operations at the unwind/ rewind stations clearly indicates the need for engineered ergonomic controls. The challenge is how to do this without compromising the application, while also meeting corporate ergonomic objectives and keeping within budget.

This article provides principles for accurately analyzing the ergonomic risks associated with core shafts and chucks and general roll handling. It also discusses how to develop engineered controls for winding-station activities while understanding the benefits and tradeoffs of materials and features that affect application capabilities and cost targets.

Part One of this series presented general guidelines for identifying caution-zone jobs or activities. Caution-zone jobs are jobs or tasks in which a physical risk may exist. A physical risk is considered a hazard if certain movements or postures that are a regular and foreseeable part of the job occur more than once a day per week and more frequently than one week per year. Table 1 shows some of the primary contributing factors to WMSDs, their characteristics in the workplace and the parts of the body impacted.

Most primary and secondary converting equipment has an unwind or rewind station or both. At the unwind station, the roll is typically delivered from an upstream process, whether on-site primary manufacturing, secondary converting or an outside supplier. The roll is positioned on core shafts or chucks (shafted or shaftless) and the product prepared to run. At the rewind station, similar processes take place, but in a different sequence. Empty cores are positioned on core shafts or chucks (shafted or shaftless) and prepared to receive product. Finished rolls are offloaded and forwarded to the next stage in the process.

Between these two stages in the process, operators lift shafts, chucks or rolls, insert one in the other, operate lifting/handling equipment, align rolls, actuate core shafts or chucks, prepare the product and operate the machine. With cycle times averaging from 10-30 mins, the potential contributing factors for WMSDs are numerous. Work activities where these factors are present are labeled "caution-zone jobs." The identification and analysis of these jobs is where the greatest ergonomic improvement opportunities lie.

For example, a review of the activity at an unwind/rewind station might reveal awkward posture, repeated impact and heavy lifting as physical risk factors for various "caution zone jobs."

Once potential hazards are identified, they should be analyzed to determine the specific physical movement or posture and its frequency during the operator's shift. A hazard exists when the frequency or force exerted is considered excessive. An important first step is to understand "why" a specific activity is performed at the rate it's performed. Often the best ergonomic solution is to eliminate the activity because there is no reason for it. For those activities that are necessary, general guidelines for assessing the level of hazard are available as well as specific tools for assessing heavy lifting and hand/arm vibration hazards.

The next step is to reduce the hazard below the hazard level or to a degree that is technologically and economically feasible. Table 2 shows general guidelines to eliminate ergonomic hazards. These guidelines are applied using engineered or administrative controls. Engineered controls are considered the most effective solutions as they completely reduce the employee's risk of exposure to hazards and do not rely primarily on employee behavior, which is the focus of administrative controls. See Table 3 for examples of each type of control.

As engineered controls go, repositioning work and optimizing workflow can be low-cost ergonomic improvements that yield immediate payback. Other controls such as automated handling are more costly and often impractical for smaller converting operations. For this reason, moderate cost controls, such as providing lighter-weight shafts and chucks, are preferred by many converters.

Reducing the weight of tools that are repeatedly used can prevent WMSDs. But for winding components such as mechanical or pneumatic shafts, it's important to understand several critical factors. In any wind/unwind process, the shaft or chuck is one of the primary load-bearing components. Shaft and chuck designs must factor in roll weights, process speeds, web-transfer processes, handling methods and any other variable that may induce stress during operation. Based on these process criteria, shafts and chucks are de-signed with a relative safety factor to insure they do not fail during operation. Therefore, the first priority, before ergonomic requirements, is to insure that the component specified will withstand the forces applied to it.

Once done, the ergonomic opportunities can be evaluated. For shafts, the biggest opportunity to reduce weight lies in the raw materials used for the body and spindle or journal. Bodies and journals can be manufactured from a variety of materials, each with benefits and tradeoffs.

Numerous properties influence the final ergonomic solution for an application. Tensile strength relates to load-carrying capacity, material density relates to weight, modulus of elasticity relates to stiffness or resistance to bending (deflection) and hardness relates to strength, resistance to impact and overall durability.

Aluminum and carbon fiber are the lightest materials used in shaft design. Aluminum is available in a wide range of bar and tube sizes, while carbon fiber tubes, which are often custom-designed and wound for specific applications, are available in limited sizes. Suppliers have developed engineered aluminum extrusions that result in dramatic weight reduction, without sacrificing strength or increasing cost.

Because a shaft's speed limitation is a function of the deflection of the shaft (controlled by stiffness or modulus of elasticity), carbon fiber shafts (with the stiffness of steel but one-third the weight) are often the optimum solution for such applications. However, converters should expect to pay a premium over a comparable steel shaft. Carbon fiber shafts can also be made more durable with the addition of steel sleeves on the outer diameter with only a moderate weight increase.

Other features such as surface bearings to enable roll loading and on-machine maintenance capabilities provide additional ergonomic benefits. Cost and application impact should be reviewed with respective suppliers.

By balancing application requirements, ergonomic objectives and effective cost controls, converters can successfully navigate the ergo-nomic terrain and match required operational tasks with the capabilities of their most important resource: the people who do the work each day.