The widely recognized engineering formula, T= K x D x P (to be explained later in this article), was used to provide the chart's values, but it must be understood that every bolted joint is unique and the optimum tightening torque should be determined for each application by careful experimentation. A properly tightened bolt is one that is stretched such that it acts like a very ridged spring pulling mating surfaces together. The rotation of a bolt (torque) at some point causes it to stretch (tension). Several factors affect how much tension occurs when a given amount of tightening torque is applied. The first factor is the bolt's diameter. It takes more force to tighten a 3/4-10 bolt than to tighten a 318-16 bolt because it is larger in diameter. The second factor is the bolt's grade. It takes more force to stretch an SAE Grade 8 bolt than it does to stretch an SAE Grade 5 bolt because of the greater material strength. The third factor is the coefficient of friction, frequently referred to as the "nut factor." The value of this factor indicates that harder, smoother, and/or slicker bolting surfaces, such as threads and bearing surfaces, require less rotational force (torque) to stretch (tension) a bolt than do softer, rougher, and stickier surfaces. The basic formula T = K x D x P stated earlier takes these factors into account and provides users with a starting point for establishing an initial target tightening torque.
Waste pack seals are the most common type of screw conveyor shaft seal because of low cost and simple design and are mounted between a trough end and a flanged bearing by means of common bolts. All KWS waste pack seals are available with neoprene lip seal. Other types of seal cartridges are also available upon request. An opening at the top of the seal housing facilitates the packing of loose fiber material called waste packing. The waste packing forms a seal around the diameter of the shaft. The waste packing can be oiled for specific applications. Waste pack seals can also be used with pedestal trough ends and pillow block bearings.