Mike Sondalini — Thought Leader

(Why threads strip and bolts break) 

When a bolt and nut is tightened to draw the bolt head and nut together it stretches the shank, deforms the threads and loads the object trapped between the bolt head and nut.

The bolt shank acts like a spring being pulled apart and it tries to return to its unloaded condition.

The amount of tension developed in the shank is dependent on the number of turns of the nut.

The size of the torque required to turn the nut has little to do with the tension applied to the bolt shank.

Rather the amount of torque needed to turn the nut reflects the slipperiness of the threads.

Keywords: bolt tension, yield stress, the coefficient of friction.

[Read more…]

This article covers some of the problems that can occur with bucket elevators and provides possible remedies.

Bucket elevators lift bulk materials from one level to another.

They are used on powders, granules, grain, chip shaped products and lumpy materials.

They function well when designed properly for the duty, and used as designed. [Read more…]

A gearbox is used to control the operating speed of industrial equipment.

It converts a high input speed to a lower output speed and so permits one driver element, such as an electric motor, to do numerous duties.

Failure of the gearbox causes the equipment and associated plant to stop.

Proper selection, care, and maintenance of gearboxes is critical to your company’s continued profitability.  [Read more…]

Chemical corrosion occurs at increased rates in agitated conditions.

Typical iso-corrosion curves for alloy metals no longer apply. These curves only show corrosion rates at various chemical concentrations and temperatures in stagnant conditions.

A typical curve is shown below. The curves are available from alloy metal suppliers on request.

When metals are selected for agitated corrosive conditions the curves can only be used in a relative sense.

They help grade the metal selection but they cannot provide absolute corrosion rates. [Read more…]

Vibration in equipment is the result of unbalanced forces.

Out-of-balance is corrected by adding or removing material so that when the equipment is operating the unbalance is controlled to an acceptable level.

Keywords: spring stiffness, damping, center of rotation, center of mass, natural frequency, isolation mount, counterbalance, out-of-phase. [Read more…]

Coatings provide industry with low-cost solutions to difficult chemical corrosion problems.

This article covers the use of rubber, fiberglass, and epoxy linings.

Keywords: rubber lining, resin, composite glass fibers, overlap joints, adhesive, primer, corrosion barrier, repair. [Read more…]

Bridging is the name given to the self- created arch that develops just above the outlet of a bulk material silo or hopper as it empties.

A bridge forms when wall friction holds up the ends of the arch.

To overcome bridging the wall friction must be reduced or prevented from occurring. [Read more…]

Control valves regulate the flow of a liquid or gas by opening or closing internal passages.

They form part of a control loop used to control a process. The control valves respond to instructions from the controller and adjust the internal openings accordingly.

Keywords: sensor, setpoint, trim, actuator, sealing class, tuning, proportional, integral, derivative. [Read more…]

Get mechanical seals working properly.

Mechanical seals are used to keep the bulk contents of rotating equipment such as pumps and compressors from escaping. They do this by sealing the shaft that protrudes from the casing.

They require quality installation and operating conditions for a long life. [Read more…]

Vibration from out-of -balance rotating equipment can be frightening.

The ground shakes, machines jump about, hold down bolts come loose and parts break.

An unbalanced rotating body will produce forces on its bearings and transmit them throughout its structure and into the foundations.

Keywords: rotor, centrifugal forces, balance quality.  [Read more…]

Don’t run centrifugal pumps on the end of the curve. Pumps are designed and selected to operate near their highest efficiency point.

If they operate at the right-hand end of the pump curve the likelihood of cavitation increases.

Keywords: suction pressure, flow velocity, vapor pressure, duty point. [Read more…]