Rotating Shafts Under Bending Stress

Rotating shafts under bending stress. It is common to transmit motion using rotating shafts. The shafts are mounted in bearings and turned by force through a drive arrangement. The shafts usually also carry a load. These loads cause bending and the shaft reacts by producing counter stresses within itself. Provided the reactive stresses are within the shaft’s strength range it will take the load. But if the stresses are greater than what the shaft can take it will bend. Even if the stresses are below the load limit but fluctuate, it is possible that the shaft will break from fatigue. The point of highest stress can be found by looking at the arrangement of the shaft supports and loads and calculating the forces and stresses.
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Orifice Plate Meter Flow Measurement

Orifice plate meter flow measurement. An orifice meter is a circular piece of metal plate placed between flanges in a pipe. In it is a square-edged round hole machined 0.5 to 0.8 pipe diameter in size. Pressure tapping points are placed either side of the plate at specified distances. The orifice causes a flow restriction and produces a pressure drop from one side of the hole to the other. The amount of pressure difference is proportional to the flow of fluid through the hole. The flow is calculated from the pressure difference and flow areas using accurate mathematical formulas. [Read more…]

The 5 Whys Method of Root Cause Analysis

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It’s important when resolving a problem that you address the problem and not a symptom of the problem. Determining the real problem is called finding the root cause. There are special techniques for determining the root cause of a problem. One technique is known as “The 5 Whys.” [Read more…]

Rolling Bearing Vibration Detection

Roller bearing vibration measurement is one of the major condition monitoring tools in regular use. By measuring the velocity, acceleration and frequencies emitted from a rolling bearing it is possible to tell its condition and the likelihood of imminent failure. The technology is well established and well proven but requires a good understanding of equipment vibration characteristics before a user can draw good interpretations from the results.

Keywords: out of balance, vibration analysis, bearing life [Read more…]

Dust Control Concepts

Dust control concepts. Industrial dust is the result of material escaping from the confines of a process or a storage location. The size of the problem depends on the dust’s characteristics and the means of its distribution. The best policy to control dust is to not let it escape from where it ought to belong. There are simple techniques that can be used to manage dust and prevent it from becoming a major health and environmental problem once the mechanism of creation and distribution are under stood. [Read more…]

Non-destructive Testing of Welds

Non-destructive testing of welds. Welding processes and methods can introduce contaminants and metallurgical defects into the weld. If a weld is required to withstand severe loading conditions and stresses it is critical to insure its quality meets minimum standards. Welds can be tested by destructive and non-destructive techniques. Most production is tested by use of non-destructive methods. The most common non-destructive tests to check welds are Visual Inspection, Liquid Penetrant, Magnetic Particle, Eddy Current, Ultrasonic, Acoustic Emission and Radiography. Keywords: NDT, quality control, non-conformance, verification, weld procedure. [Read more…]

Electric Motor Variable Speed Drives Operation

Electric motor variable speed drives operation. Alternating current electric motor speeds can be changed by the use of a frequency converter. This device changes the frequency of the alternating current to the motor. This then changes the rotating speed of the motor’s internal magnetic field. The speed of the rotor responds accordingly and so allows for variable speed control of connected items. When these devices are used there are several issues that need to be addressed to insure successful selection and long-term operation. Keywords: VSD, precise speed control, over- speed, motor controller, frequency inverter. [Read more…]

Work Within The Design Limits

Work within the design limits – Once equipment or a process is allowed to run outside it’s design limits it will fail quickly. The only way to get long-lived, well operating plant and equipment is to keep its individual components working within their service limits throughout their life. Keywords: training manual, procedures, operator manual. [Read more…]

Plant compressed air waste control

Plant compressed air waste control. Every compressed air system will eventually develop leaks from connectors and redundant pipelines. Compressed air is very expensive to make. It is necessary to institute regular inspections for air leaks and fix them immediately.

Keywords: pressure loss, energy loss, air compressor, pressure switch. [Read more…]

Metering & Dosing Pump Operations

Metering and dosing pump operation. Any positive displacement pump can be used as a metering or dosing pump. The purpose of these pumps is to inject a known volume of liquid into a process stream. The primary requirement is that over a given period of time the pump consistently delivers the same amount of liquid. Keyword: gear pump, piston pump, helical rotor pump, diaphragm pump, peristaltic (hose) pump, additive, dosing rate. [Read more…]

Is Your Wet Scrubbing Tower Working?

Is your scrubbing tower working? A wet scrubbing tower is used to clean odors, particles, mists and vapours from a gas stream. The gas is forced through the tower. As it moves from inlet to outlet it is washed and cleaned. The washing is done with suitable chemicals that remove the active components in the gas flow. The gas is cleaned to environmentally acceptable levels and discharged to atmosphere. Keywords: packed tower, packing, fill, mist eliminator. [Read more…]

Flow meters – don’t believe what they tell you

Abstract

Flow meters – don’t believe what they tell you. A flow meter is an instrument that measures the amount of fluid (liquid or gas) that passes through it. The meter in the pipe is the detecting device and increases the count when a specific quantity of fluid passes by. There are several types of flow meters in common use. They include magnetic flow meters, vortex flow meters, mass flow meters, turbine flow meters, rotor blade meters, paddle flow meters, and ultrasonic flow meters. Usual the quoted accuracy on the flow meter specification sheet is for water at 20oC. However when the meter is installed in a process application it is unlikely that the meter will meet the quoted accuracy without site-specific calibration. Keywords: calibration, certified test equipment, flow meter accuracy.

The manufacturer performs laboratory trials of its equipment to insure the flow meter meets their claims for accuracy. Since the manufacturer does not know where their meter will be used they standardise the tests by using water at known conditions. Unless the meter is used in a situation identical to the laboratory conditions the given accuracy is unlikely to be achieved. [Read more…]

Gluing Plastic Pipes so You Can Trust Them

What you will learn from this article.

• Glued plastic pipes must have the joints prepared before gluing.
• Some plastic is joined with glue while others are solvent joined.
• Glued joints do not bond with the plastic but must be ‘hooked’ to it.
• Install thrust brackets if large glued pipes change direction sharply.

Some plastics can be joined with glues or cements. One of the most common of these is PVC. PVC can be either unplasticised (uPVC) or chlorinated (cPVC). Some plastics can be dissolved and chemically bonded together. ABS plastic is such a plastic. [Read more…]

Holiday Detection in Above-ground Tank Bottom Lining Inspection

What you will learn from this article.

• There are two ways to detect holidays in tank linings.
• Explanation of the low voltage ‘wet sponge’ method of testing linings.
• The second method is high voltage spark detection.
• Importance of confirming the presence of sufficient liner thickness.
• The likely trouble spots where linings can thin.

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Set-up Tank Agitator Gearboxes for a Long Life at Low Cost

What you will learn from this article.

• The types of forces developed in a turning agitator.
• Gearbox position and configuration for long-life.
• Bearing arrangements to minimise gearbox loading.
• Simple, strong agitator support arrangements.
• Vapour seals are needed to stop fumes escaping.
• Lots of low maintenance selection and design tips.

Agitated vessels and tanks are common throughout the process and chemical industries. A properly sized agitator with correct proportions to suit the tank will deliver well-mixed product. A correctly sized gearbox with well-chosen bearings and bearing arrangements will need only regular lubrication while giving years of trouble free service. [Read more…]