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Characteristics of Centrifugal Pumps

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Characteristics of Centrifugal Pumps

Pumps are generally grouped into two broad categories—positive displacement pumps and dynamic (centrifugal) pumps. Positive displacement pumps use a mechanical means to vary the size of (or move) the fluid chamber to cause the fluid to flow. On the other hand, centrifugal pumps impart momentum to the fluid by rotating impellers that are immersed in the fluid. The momentum produces an increase in pressure or flow at the pump outlet.

Positive displacement pumps have a constant torque characteristic, whereas centrifugal pumps demonstrate variable torque characteristics. This article will discuss only centrifugal pumps.

A centrifugal pump converts driver energy to kinetic energy in a liquid by accelerating the fluid to the outer rim of an impeller. The amount of energy given to the liquid corresponds to the velocity at the edge or vane tip of the impeller. The faster the impeller revolves or the bigger the impeller, then the higher the velocity of the liquid at the vane tip and the greater the energy imparted to the liquid.

 

Characteristics

Creating a resistance to the flow controls the kinetic energy of a liquid coming out of an impeller. The first resistance is created by the pump volute (casing), which catches the liquid and slows it down. When the liquid slows down in the pump casing, some of the kinetic energy is converted to pressure energy. It is the resistance to the pump’s flow that is read on a pressure gauge attached to the discharge line. A pump does not create pressure, it only creates flow. Pressure is a measurement of the resistance to flow.

Head—Resistance to Flow

In Newtonian (true) fluids (non-viscous liquids, such as water or gasoline), the term head is the measurement of the kinetic energy that a centrifugal pump creates. Imagine a pipe shooting a jet of water straight into the air. The height that the water reaches is the head. Head measures the height of a liquid column, which the pump could create resulting from the kinetic energy the centrifugal pump gives to the liquid. The main reason for using head instead of pressure to measure a centrifugal pump’s energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid changes, but the head will not change. End users can always describe a pump’s performance on any Newtonian fluid, whether it is heavy (sulfuric acid) or light (gasoline), by using head. Head is related to the velocity that the liquid gains when going through the pump.

All the forms of energy involved in a liquid flow system can be expressed in terms of feet of liquid. The total of these heads determines the total system head or the work that a pump must perform in the system. The different types of head—friction, velocity and pressure—are defined in this section.

Gear Pump Operation and Maintenance

1. Introduction

A gear pump uses two meshing, toothed cogs to force water from the inlet of the pump through to the outlet. Figure No. 1 shows a simplified drawing of an external teeth gear pump on the left along with the alternate arrangement of internally pointing teeth.

2. Gear pump Design

Gear pumps use toothed gears turning inside a close tolerance housing to draw-in liquid and then squeezing it out ahead of them. Paddle steamers used the same principle of operation. These pumps are positive displacement pumps and anything drawn into them will be forced out. As a consequence they can generate very high discharge pressures. Materials of construction vary from metals of various types and hardness through to plastics of various types and hardness.

Maintaining the close tolerances between the housing and the cogs is critical to efficient operation. The clearance between the edges of the teeth and the housing and the ends of the cogs and the back and front walls of the housing are very small. Between the teeth and housing it is in the order of 0.1 mm (0.004”) while the clearances between the front and back faces of the gears and the ends of the housing are only 0.025 mm (0.001”). The fine clearances reduce liquid re-circulation back from the high-pressure discharge to the low-pressure suction side and make these pumps one of the most efficient available.

Gear pumps usually have one shaft penetration through the housing for connection to the drive. The gear shafts on the smaller pumps can be supported in journal bearings within the ends of the housing and are lubricated by the product. On larger pumps rolling element bearings mounted in bearing housings are used. To prevent surface to surface contact wear of teeth the product does the lubrication.

3. Gear pump Uses

The design of a gear pump lends itself to use with clean liquids. Insure they draw liquid from well above the bottom of the supply tank in clear liquid space. Both low and high viscosity liquids can be pumped. If food grade products sensitive to shear (i.e. where the churning action of the pump breaks cells and fibres) are to be pumped the size of the pump will need to be increased and the speed reduced.

posted Feb 22 by Wpp08ui

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Types of glass

There are many different types of glass. They differ in terms of their chemical composition, the method used to produce them or their processing behaviour. Generally, they are categorised according to their chemical composition. A differentiation is made between

soda-lime glass, lead glass and borosilicate glass. These three types of glass make up around 95 percent of the cullet glass used in the production process. The remaining 5 percent of glass is special-purpose glass.

Soda-lime glass

Soda-lime glass is the glass produced in by far the largest quantities of all mass produced glass types. As the name indicates, the main constituents in addition to sand are soda and lime. A typical soda-lime glass contains 71 to 75 percent sand (SiO2), 12 to 16 percent sodium bicarbonate (Na2O), 10 to 15 percent lime (CaO) and small quantities of other substances such as dyes. Soda-lime glass is used to make bottles, food jars, simple drinking glasses and sheet glass products. Soda-lime glass is light permeable and has a smooth, fine-pored surface, making it easy to clean. It also expands very quickly under the influence of heat so care should always be taking when putting hot water into a soda-lime glass container.

Crystal glass

Crystal glass looks beautiful when cut as a result of its high refraction index. It has a far higher density than soda-lime glass. In our everyday lives, we use crystal glass to make drinking glasses, vases, bowls, ashtrays and decorative ornaments. Its composition is 54 to 65 percent sand, 13 to 15 percent alkali oxide and several other oxides. Glass containing more than 18 percent lead oxide is also known as lead crystal glass. However, lead oxide is hardly used today in glass production. Crystal glass only accounts for less than 0.5 percent of total tableware glass production in Germany.

Special glass

Special glass is used for special technical and scientific applications. Its composition can vary and it includes numerous chemical elements. Examples of special glass are lenses, glass products used by the electrical and electronics industries and glass ceramics.

How is curved glass made?

Manufacturing curved glass is a time-consuming, highly specialised job. You could almost say it's a ‘pane' to produce.

Workers cut the sheet of glass to size and then clean and polish it, using a UV lamp to check for dust or impurities (any rogue particles would cause the glass to crack or shatter). They construct a steel mould shaped to the curve radius and dimensions of the desired piece. To stop the pane sticking to the mould, the glass is painted with a mixture of detergent and calcium carbonate.

Then, it is placed on the mould and loaded into the kiln. The manufacturers crank up the heat to 700°C, hot enough to loosen the bonds between the silica molecules so that the glass starts to soften and bend to the profile of the mould. Once in shape, the glass is gradually cooled over a period of about two hours.

What It Means to Temper Glass

Tempered glass, or toughened glass, has been heat-treated to make it stronger and safer to prevent injury in case if it ever breaks. In fact, tempered glass is four to five times stronger than annealed, or untreated, glass. In the event of breakage, tempered glass fractures into small, relatively harmless pieces rather than jagged shards.

Most of the glass that you see in commercial and residential spaces has been tempered. Common applications include side and rear windows in vehicles, entrance doors, shower and tub enclosures, racquetball courts, patio furniture, microwave ovens, fireplace doors and grates, and skylights. Tempered glass is also used for interior railings, display cases, office walls, and anywhere else where robust, durable glass is called for.

Steps to Temper Glass:

Glass tempering occurs following the fabrication process via the following steps.

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Working in the mining industry can be a dangerous place if you don’t know what you’re doing. Regular training is essential and understanding the machines you’re working near or operating plays an important role in all aspects of the industry.

Each type of mining equipment comes with its own set of mining activities. The most common types of Mining Equipments and Parts vary depending on whether the work is being carried out above or below ground or mining for gold, metals, coal or crude oil. From drilling machines to excavators, crushing and grinding equipment – the mining industry comes complete with all the right tools. New to the job and want to find out what it all means? Here’s a few of the industry’s most common types of equipment and why they’re important for the job.

Mining Drills

Probably one of the most common pieces of mining equipment, drills are an important part of the underground mining operation. Underground mining is carried out when rocks or minerals are located at a fair distance beneath the ground. But then they need to be brought to the surface. Underground specialized mining equipment such as trucks, loaders, diggers etc. are used to excavate the material and are normally hauled to the surface with skips or lifts for further processing. Drilling is normally required to place explosive charges to liberate the minerals from the overburden material. Underground mining techniques have progressed significantly over the past years, including using remote controlled machinery.

Drills assist in creating holes descending underground. If miners are required to work underground, drills can also be used in ensuring the holes are large enough to serve as a portal for miners to enter. Directional drilling is also a type of mining technology where miners will use the tools and certain methods to drill wells.

 

Overview of Ball Mills

As shown in the adjacent image, a ball mill is a type grinding machine that uses balls to grind and remove material. It consists of a hollow compartment that rotates along a horizontal or vertical axis. It’s called a “ball mill” because it’s literally filled with balls. Materials are added to the ball mill, at which point the balls knock around inside the mill.

How a Ball Mill Works

Ball Mills work by using balls to grind materials. Materials such as iron ore, pain and ceramics are added to the ball mill. Next, the ball mill is activated so that it rotates — either on its vertical or horizontal axis. As the ball bill rotates, the balls bounce around while striking the enclosed material. The force of these strikes helps to grind the material into a finer, less-coarse medium.

For a ball mill to work, critical speed must be achieved. Critical speed refers to the speed at which the enclosed balls begin to rotate along the inner walls of the ball mill. If a ball mill fails to reach critical speed, the balls will remain stationary at the bottom where they have little or no impact on the material.

 

No industry puts its Pumps through the ringer quite like mining. When the price of commodities such as gold spike in the short term, there is no time to lose--companies have to act fast to extract whatever they can as quickly as possible. While this flurry of activity is great for stockholders, it is not ideal for equipment. Many pumps end up falling prey to a myriad of problems that range from corrosion to being crushed by heavier machinery. To protect mine dewatering pumps to the fullest extent, consider these six common threats that pumps may encounter during mining operations.

 

In the mining industry, Hydrocyclones are mineral processing equipment used in slurry pulps to separate coarse and fine particles according to their size and density. The mixture [slurry pulp] is injected into the hydrocyclone in such a way as to create the vortex and, depending upon the relative densities of the two phases, the centrifugal acceleration will cause the dispersed phase to move away from or towards the central core of the vortex.

Coarse particles exit the bottom of the device (underflow) while fine particles are carried by the central air column and exit at the top (overflow). In metal processing applications, the product stream is the overflow (fine particles) and is typically sent to flotation circuits. The product stream is the underflow (coarse particles), as fines are separated from the final product as a means of quality control.

While under certain conditions roping and plugging can occur where the hydrocyclones ceases to classify the particles, the shapes of the discharge are visibly different than normal operating conditions.

The roping condition occurs when the amount of solids in the underflow increases to such a point that its discharge velocity is limited, resulting in the accumulation of coarse solids in the separation chamber. This mass passes through the vortex, causing the inner air core to collapse and the discharge at the apex to take the form of a solid stream (rope) consisting of coarse material with high solids density. Roping conditions reduce recovery rates and efficiency in metals processing and lead to quality losses in copper processing.

 

Industrial Conveyor and Parts have many different designs and uses. Common types are belt, roller, motorized roller and overhead conveyors. We categorize them as floor style (mounted on the floor) or overhead. Use them to move products, create buffers and deliver products in sequence for a production line.

HOW ARE CONVEYORS USED?

Manufacturing engineers include conveyors in their production facilities for many reasons:

Moving products from point A to B (to avoid wasted time walking, or to reduce movements of forklifts, etc)

  • To carry products that are too heavy to for team members to lift

  • To move a product while operators are working on it (or adding to it). Like a final assembly conveyor at an auto plant

  • To avoid injury to workers from repetitive movement. Or to prevent damage to products caused by movement

  • To deliver products to a robot for processing. Or to receive products from a robot that are ready for the next step

 

Polyurethane & rubber Tensioned Screen Mats provide high wear and corrosive resistant screen media for all applications, from scalping to dewatering. Tensioned Screen Mats are available in a wide range of apertures and shore hardnesses.

Tensioned Screen Mats provide superior screening efficiency over conventional screening media, with substantially lower noise levels compared to standard woven wire screens.

The abrasion & impact resistance that Tensioned Screen Mats offer increases the product life span compared to woven wire screens.

 

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Failure analysis of a commercially pure titanium tube in an air conditioner condenser

Joining of titanium and stainless steel is challenging due to the formation of hard, brittle intermetallics. This study focuses on engineering ductile materials for joining transition metals. Friction welding of tube to tube-plate by an external tool, a novel solid state welding process was employed to join titanium tube and stainless steel tube plate. The interlayers engineered were copper, silver and Cu–Zn alloy. The micrographs revealed phase transformations in titanium tube and unaffected stainless steel base. Interface peak microhardness of 458 HV was observed for Ti/Cu–Zn/SS welded sample. The intermetallics formed were characterized by X-ray diffraction and scanning electron microscopy with energy dispersive spectroscopy. A novel shear test procedure was developed to evaluate the maximum shear load. It was found that joints with silver as interlayer withstood the maximum shear load of 56 kN. The shear surfaces were further analyzed and investigated for fracture study.

 

Titanium has today replaced copper alloys as the most favoured tube material for salt water cooled condensers. Main reason is the excellent corrosion resistance of titanium in chloride containing environments. The experience of titanium bar condensers is usually more than satisfactory, even if a few tube leaks have occurred. Possible damage mechanisms by high cycle fatigue, galvanic corrosion, water-droplet erosion and by flow-assisted corrosion are discussed. These perils can be handled by a number of adequate countermeasures analysed in laboratory work and meanwhile proven by plant service.

 

The corrosion resistance of titanium in sea water is extremely excellent, but titanium 、nickel 、zirconium tube are expensive, and the copper alloy tubes resistant in polluted sea water were developed, therefore they were not used practically. In 1970, ammonia attack was found on the copper alloy tubes in the air-cooled portion of condensers, and titanium tubes have been used as the countermeasure. As the result of the use, the galvanic attack on copper alloy tube plates with titanium tubes as cathode and the hydrogen absorption at titanium tube ends owing to excess electrolytic protection was observed, but the corrosion resistance of titanium tubes was perfect. These problems can be controlled by the application of proper electrolytic protection. The condensers with all titanium tubes adopted recently in USA are intended to realize perfectly no-leak condensers as the countermeasure to the corrosion in steam generators of PWR plants. Regarding large condensers of nowadays, three problems are pointed out, namely the vibration of condenser tubes, the method of joining tubes and tube plates, and the tubes of no coolant leak. These three problems in case of titanium tubes were studied, and the problem of the fouling of tubes was also examined. The intervals of supporting plates for titanium tubes should be narrowed. The joining of titanium tubes and titanium tube plates by welding is feasible and promising. The cleaning with sponge balls is effective to control fouling.

 

Titanium is the ninth most abundant element in the earth's crust and the fourth most commonly used structural metal. In nature, it occurs only as a mineral (ore) in combination with oxygen or iron (rutile, TiO2, or ilmenite, FeTiO3).

 

Titanium is a lightweight material whose density is approximately 60 percent of steel's and 50 percent of nickel and copper alloys'. It was recognized in the 1950s as a desirable material for aerospace applications—especially airframe and engine components. In the 1960s and 1970s, titanium was considered for use in vessels and heat exchangers in corrosive chemical process environments. Typical applications included marine, refinery, pulp and paper, chlorine and chlorate production, hydrometallurgy, and various other oxidizing and mildly reducing chemical services.

 

In the 1980s and 1990s, titanium began to be used for many nontraditional applications, including tubulars for geothermal energy extraction and oil and gas production, consumer goods (such as sporting equipment), food processing, biomedical implants, and automotive components.

 

According to the U.S. Geological Survey (USGS), 52 million pounds of titanium were produced in the U.S. in 2000; worldwide, more than 100 million pounds were produced.

 

Titanium sponge is obtained by reacting rutile ore with chlorine and coke, followed by magnesium (Kroll) reduction and then vacuum distillation to remove excess magnesium and magnesium chloride. Titanium sponge is pressed into blocks to make a consumable electrode and then melted in an inert environment under vacuum to produce a titanium ingot.

 

Titanium is well-known for its unique combination of properties, which include low modulus of elasticity, stable and steadfast oxide film (which provides excellent corrosion and erosion resistance), and a high strength-to-density ratio.

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How to Use Different Types of Strapping Material

All interested parties are welcome to join in the ongoing revisions to D3953, Specification for Strapping, Flat Steels and Seals. The standard is under the jurisdiction of Subcommittee D10.25 on Palletizing and Unitizing of Loads, part of ASTM International Committee D10 on Packaging.

 

According to its scope, D3953 covers flat steel strapping and seals intended for use in closing, reinforcing, bundling articles for shipment, unitizing, palletizing and bracing for carloading, truckloading, lifting and lashing. "Most people have dealt with the material covered by D3953 without knowing it," says Anthony Mariano, Independent Metal Strap Co. Inc., and a D10 member.

 

"As one of the first modern materials used for unitizing and bundling, oiled steel strapping is well-known to packaging users, but since the last full review of D3953, there have been many changes in technology, especially in closure methods," says Peter Catlos, chairman of D10.25. These technological changes will be addressed in ongoing revisions.

 

Catlos notes that waxed steel strapping is widely used in the lumber, metals and paper industries. The standard is used to specify strapping products for purchase, in package design and in design of load securement techniques for over-the-road, rail and maritime transport of goods. Section 13 of D3953 includes several test methods for steel strapping.

 

Every person who has ever worked with galvanized steel strapping knows that this can be a potentially dangerous product. When talking to potential customers I hear many stories from people who have been injured by steel banding. Either caused by loose hanging pieces of cut metal strapping or when applying and the steel snapped unexpectedly. 

 

Companies take many safety precautions to protect their employees. Safety glasses, helmets, shoes are part of most workers Personal Protection Equipment (PPE) and still many companies provide their staff with "razor blades" to secure their products. Of course there are always people that deny the risks of steel banding but fact is that people getting cut is very high on the list of job related accidents.

 

Cordstrap already recognized this risk over 50 years ago and invented a safe alternative for steel banding. The latest generation of Cordstrap strapping is a composite strap made of high tenacity polyester yarns embedded in a PP coating. The Cordstrap strapping products are an extremely strong alternative for steel banding. Due to the unique buckle joint Cordstrap's overall system strength will be higher compared with steel banding.

 

Most of all, Cordstrap strapping systems are safe for your products, safe for your employees and safe for your customers. In Australia Cargo Restraint Systems offers a wide range of Cordstrap systems. We always welcome the opportunity to take a closer look at your applications and provide you with a safe solution. Just contact us and it will be our pleasure to assist you.

 

Pallet strapping, or banding is the process of using a metal or plastic strap to unitize, palletize or bundle products together. Strapping is used in a variety of industries from shipping large industrial equipment and lumber to reinforcing cases in e-commerce fulfilment centres. For this reason, there are many grades and types of materials on the market today.

 

Strapping is applied either manually with a hand tool or automatically with a strapping machine. In both cases, a strap or band is feed around the product and pulled taught. A fastening method then secures the ends of the strap around the product and the excess material is removed.

 

Strapping materials are available in many different strengths with specific grades and classifications. It is important to understand these grades and how they can affect your material choice when choosing your packaging. How your product is transported will affect the rating system and materials used. The two associations who grade strapping are the American Association of Railroads and ASTM International. Although ratings can be similar, it is important to understand that the designations are not interchangeable.

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