Enhancing Material Handling Applications

On the battlefield, maneuverability is crucial to success. In the manufacturing process, moving materials is just as important. Moving product from one production step to the next must be smooth and efficient, other wise bottlenecks can form and create issues down the line. Loss of time, production capacity, increased labor, energy and raw material costs as the expenditure of labor to correct these issues can all arise. If allowed to continue for a prolonged period of time, the higher price to produce erodes earnings and puts the company in a competitive disadvantage. Appropriate and reliable material handling addresses these specific issues and cast nylon plays a key role.

There are several aspects to consider when selecting the right material for the job. A short list of those include the weight to be moved, its size, speed of movement, cost and preferred motion method (sliding, rolling, driving, coasting, etc). The operating environment must also be considered. At what temperature will the moving take place? Will there be any exposure to chemicals or explosive materials? The items being moved must also be considered. For example, a fragile load will need to be handled with more care than a robust one.

The vast range of cast nylon shapes and sizes allows for unique and specific solutions to the varied manufacturing processes. Rollers are a commonly found in shops. Cast nylon tubes are readily available from 1 ½” up to 24" outer diameter. The tubular shape alone, reduces weight and material costs. Wall thickness typically range from 1/4" up to 6". This allows for the right sized roller to be paired with the load that needs to be carried with minimal machine time and material waste. The nature of the casting process also allows these tubes to be produced in various lengths. Nylon tubes are produced from 1' to 10' long which offers flexibility to roller design.

Several characteristics inherent in cast nylon make it useful for a variety of applications. Being corrosion resistant, nylon does not degrade or rust in wet or humid environments. It also holds up well with common wash-down protocols. Elevated acidic or caustic chemicals will degrade nylon under prolonged exposure. FDA compliant formulations of cast nylon are readily available for use in direct food contact. Depending on the application and end user preference, there are 3 common FDA approved nylon colors to choose from, off-white, blue and black. Often, a color that contrasts to the product being produced is preferred for ease of visual inspection.

For roller applications, the Hertzian model for contact stress provides an accurate way to determine the working loads. A roller on a flat, relatively hard surface deforms slightly under load. This deformation does a couple of things. It increases the contact area thereby distributing its weight over a larger area. It also puts strain at the rim of a plastic roller. The amount of load a roller can carry is not only directly proportional to its outer diameter and length, but also its modulus of elasticity. Generally speaking, the higher the tensile modulus of elasticity of a material the more weight the roller can withstand. Compared to other common industrial thermoplastics, unfilled cast nylon's tensile modulus of elasticity is relatively high and allows for increased roller load.

Sometimes, sliding the part from A to B is the solution. These parts are found in the material handling industry as sliding pads, wear pads and guide blocks. While typically simpler in design, the movement is usually slower as it is impeded by friction. The amount of frictional force is determined by the weight of the moving object, multiplied by the coefficient of friction between the moving and stationery object. This coefficient is comprised of a number of features such as finish, and hardness. Typical material values on manufacturing data sheets show a coefficient of friction for a given material on smooth finished steel. The two types of coefficients normally listed are dynamic and static. Dynamic frictional force is measured as an opposing force for an object in motion, sliding on a flat surface. Static frictional force is the force that opposes motion when a force is applied (object remains stationary relative to the surface on which it rests).

For most materials, the static coefficient is higher than the dynamic coefficient of friction. Lubricated grades of cast nylon are commonly produced. These grades reduce both the static and dynamic coefficients of friction which reduces frictional opposing forces. Some lubricants reduce the gap between the static and dynamic coefficients. In high weight, fast moving situations it is important to consider the ability of the sliding pad to disperse frictional heat. This can be done by calculating the Pressure Velocity and comparing this to the manufacturer's specifications. Pressure Velocity is simply calculated by the weight of the load divided by the contact area. This is then multiplied by the surface speed of the weight across the pad.

Getting product through the manufacturing process quickly and safely is complicated. Getting the right piece to the next step, on time is money.