How to Deisgn and Manufacture Centrifugal Sand Dredging Pumps

A centrifugal sand dredging pump is a device commonly used for sediment transportation and drainage. It is mainly used to extract liquids containing sand, mud or other particulate matter from water bodies, river beds, lakes or ocean bottoms. Its design principle is based on the action of centrifugal force. The rotating impeller generates a high-speed rotating liquid flow, thereby sucking sand, mud and other granular materials into the pump body along with the liquid flow. When the centrifugal sand pump starts running, the driving device drives the rotating impeller to rotate rapidly. Due to the rotation of the impeller, the liquid forms a high-speed rotating liquid flow under the action of the blades, generating strong centrifugal force. Sand, mud and other particulate matter are pumped into the pump body along with the liquid flow, and are discharged through the outlet pipe along with the liquid flow. By continuously repeating this process, the centrifugal sand pump can effectively transport and remove large amounts of sand, mud and other particulate matter to achieve engineering tasks such as desilting, dredging and drainage. This article mainly introduces how to design and make a centrifugal sand pump.

I. How to Design the Centrifugal Sand Dredging Pumps?

Centrifugal sand dredging pumps rely on the action of the rotating impeller to transfer the mechanical energy of the prime mover to the liquid. Due to the action of the centrifugal sand dredging pumps, the velocity energy and pressure energy of the liquid flow from the impeller inlet to the outlet are increased. The liquid discharged by the impeller passes through the extrusion chamber, and most of the velocity energy is converted into pressure energy, and then the liquid is discharged along the discharge pipeline. At this time, a vacuum or low pressure is formed at the inlet of the impeller due to the discharge of the liquid, and the liquid in the suction pool is pressed into the inlet of the impeller under the action of the liquid surface pressure (atmospheric pressure). Thus, the rotating impeller continuously sucks and discharges the liquid.

It is more appropriate to use the centrifugal sand dredging pumps when the flow rate is in the range of 5-20000 square meters per hour and the lift is in the range of 8-2800m, under above performance conditions, the centrifugal sand pump has the advantages of high speed, small size, light weight, high efficiency, large flow, simple structure, stable performance, easy operation and maintenance, etc. Production practice at home and abroad shows that the output value of centrifugal sand dredging pumps is the highest among pump products.

Centrifugal sand dredging pumps have the advantages, but also the disadvantages. The actual use efficiency of the centrifugal water pump is low, and the flow rate changes with the pressure in actual use, the speed requirement is strict, the single-stage lift is low, the pump must be filled with liquid before starting, and the liquid viscosity also has a great impact on the pump performance, it can only be suitable for liquids with an accuracy close to that of water. For a certain flow rate centrifugal sand dredging pumps, there is a corresponding viscosity limit. If the liquid exceeds this viscosity limit, the efficiency of the centrifugal sand dredging pumps will decrease rapidly or even fail to work.

1. What’s the basic parameters of the centrifugal sand dredging pumps?

• Flow of the centrifugal sand dredging pumps

Flow is the medium amount (volume or mass) delivered per unit time.

Flow is divided into volume flow and mass flow.

Volume flow is represented by Q, the unit is m3/h or m3/s. Mass flow is expressed in Qm, the unit is t/h or kg/s.

The relationship between mass flow and volume flow is: Qm =ρQ. ρ is the density of the conveyed slurry (t/m3 or kg/m3), normal temperature clean water ρ= 1 (t/m3).

Flow is the most critical parameter, because the ultimate goal of the user is to deliver the required slurry amount. This parameter is the real transportation value of the system, and its determination method should be based on actual measurement or calculation, and should not be determined by empirical guesswork. The accuracy of this value plays an extremely important role in the centrifugal sand dredging pumps type selection. The provided value should not be too large or too small, and its accuracy should be within the range of plus or minus 10%.

• Head of the centrifugal sand dredging pumps

Head refers to the increase in energy per unit mass of the delivered liquid from the inlet to the outlet of the centrifugal sand dredging pumps (the outlet flange of the centrifugal sand dredging pumps). That is, the effective energy obtained by the centrifugal sand dredging pumps.

The lost head of the pipeline system refers to the energy loss of the pipeline conveying system. This value is an important basis for centrifugal sand dredging pumps selection.

The unit of head is meter (m). It is particularly pointed out that for the conveying of slurry medium, some people have used the slurry head to express. The slurry head is actually the outlet pressure P of the centrifugal sand dredging pumps (unit MPa or kg/cm2), and the relationship between it and the clean water head is: P=0.01ρH ( The unit of P is MPa, and the unit of ρ is t/m3), and the two are different due to the medium density.

The head of the centrifugal sand dredging pumps is theoretically independent of the type, nature and density (or specific gravity) of the fluid being transported, but only related to the state of motion. For the same centrifugal sand dredging pumps to transport different media, such as water, mercury, and various slurry, the generated head is the same, and the discharge height is the same. However, the loss head of the conveying pipeline for transporting different materials is different.

By the way, the head given by the slurry pump samples are all tested under the condition of clean water. Therefore, when calculating the system loss head, it must be converted into the clear water head, so that the model can be selected according to the sample.

• Rotating speed of the centrifugal sand dredging pumps

The speed is the revolutions number per unit time of the centrifugal sand dredging pumps, and the unit is revolutions per minute (r/min).

• NPSH of the centrifugal sand dredging pumps

The flowing liquid produces bubbles, and then the bubbles burst to erode the parts, that is cavitation. Cavitation allowance is the surplus amount that cavitation does not occur under certain conditions. It reflects the suction performance of the centrifugal sand dredging pumps. The unit of NPSH is meters (m).

• Power N of the centrifugal sand dredging pumps

Power is the work done per unit of time, the unit is kilowatts per hour (kW/h). The power of the centrifugal sand dredging pumps refers to the water power of the sand pump, and the calculation formula is as follows.

The calculating formula for the power output from the motor to the centrifugal sand dredging pumps:

In the formula, the unit of density ρ is t/h, the unit of flow Q is m3/h, the unit of lift is m.

ηb: efficiency  of centrifugal sand dredging pumps operating point (%).

I: Motor running current (A).

V: motor working voltage (kV).

cosφ: motor power factor

ηD: the working efficiency of the motor (%).

ηC: transmission efficiency (%)

2. How to confirm the structural form of the centrifugal sand dredging pump?

• Prime mover selection of the centrifugal sand dredging pumps

The centrifugal sand dredging pumps are driven directly by the engine through a coupling, or are driven through a pulley on the engine.

• Structural options of the centrifugal sand dredging pumps

The smaller the volume of the centrifugal sand dredging pumps, the better, as long as they meet the working requirements. The structure can be a double shell structure and a single shell structure.

• Determine the suction caliber of the centrifugal sand dredging pumps

The determination of the centrifugal sand dredging pumps suction diameter mainly depends on the flow rate in the suction pipe. According to domestic and foreign pipeline economic flow rate analysis and relevant standards, the maximum flow rate in the suction pipe is generally not more than 5m/s, usually about 3m/s, and the centrifugal sand dredging pumps suction diameter (D) = discharge diameter (D) at low pressure. From the point of view of improving cavitation performance, the flow rate of the centrifugal sand dredging pumps suction port should be slower, but if the flow rate is slower, the pipe diameter will be larger, which is not economical. Therefore, it is necessary to comprehensively analyze and compare according to the specific situation.

Table 4-1 of《Basics of Centrifugal Sand Dredging Pump Design》P110

An approximate value is chosen based on the calculated diameter, and the flow rate is：

• Preliminary calculation of shaft diameter

Calculate the power of the centrifugal sand dredging pumps shaft according to the formula (2-4) of “Basic Design of Centrifugal Sand Dredging Pump”, check the allowable stress MPa of steel material in the Mechanical Design Manual.

Centrifugal sand dredging pumps shaft calculation

When calculating the shaft diameter, the calculating power Nc is slightly larger than the shaft power. Because the shaft power is the power under the design condition, and the power corresponding to the maximum flow rate when the centrifugal sand dredging pumps is running is greater than the shaft power N.

The calculating power of the centrifugal sand dredging pumps can be calculated according to the formula (4..5) of “Basic Design of Centrifugal Sand Dredging Pumps”.

Nc =1.2N

3. What’s the radial force, axial force and balance of the centrifugal sand dredging pumps’ parts?

• Radial force and balance acting on the impeller of the centrifugal sand dredging pumps

Radial forces acting on the impeller must be taken into account when calculating the shaft and bearings, since the centrifugal sand dredging pumps do not always operate at the design flow, they operates at zero flow when start-up and shutdown.

The radial force of the centrifugal sand dredging pumps can be calculated according to the following empirical formula

P: the radial force acting on the impeller (N)

Qd: design flow

Q: Actual work flow rate

H: centrifugal sand dredging pumps head (m)

B2: the total width of the impeller outlet (including the front and rear cover plates) (m)

D2: the outer diameter of the impeller (m)

ρ: Liquid weight (kg/m’) (the weight of water is 1000 kg/m³)

• Axial force and balance acting on impeller of the centrifugal sand dredging pumps

The single-suction impeller does not have the same symmetry as the double-suction impeller, and there is an axial force due to the unequal pressure acting on both sides of the impeller. The shape of the semi-open impeller is related to the specific speed.Usually the blade inclination is related to the specific speed.

The axial force acting on a semi-open impeller can be approximated by the following empirical formula:

K: Axial force coefficient takes K=0.8

d1: The diameter of the circle whose center is on the inlet edge of the blade and is tangent to the contour of the impeller. The radius at the center of the circle is r1 (meters).

II. How to choose the Material and Casting of Centrifugal Sand Dredging Pumps?

1. Centrifugal sanddredging pumps material

The centrifugal sand dredging pumps are more wear-resistant and lasts longer, the material of the flow parts and the manufacturing process are very important. First of all, centrifugal sand dredging pumps material. At present, centrifugal sand dredging pumps on the market are generally made of cast iron, cast steel, high chrome alloy, rubber and other materials according to different working conditions. Centrifugal sand dredging pumps made of plastic are mainly used in the chemical industry to extract mixtures containing corrosive media, which will not be introduced here. The degree of wear resistance from low to high is cast iron, cast steel, high chromium alloy. Cast iron material is mainly a general term for alloys composed of iron, carbon and silicon. Industrial cast iron generally contains 2.5% to 3.5% carbon. Carbon exists mostly in the form of graphite in cast iron, and sometimes in the form of cementite. In addition to carbon, cast iron also contains 1% to 3% silicon, as well as manganese, phosphorus, sulfur and other elements. Cast iron is also divided into gray cast iron and ductile iron. Gray cast iron has low melting point (1145-1250℃), small shrinkage during solidification, its compressive strength and hardness close to carbon steel, and has good shock absorption. Good wear resistance due to the presence of flake graphite. The casting properties and machining are good. Ductile cast iron is obtained by spheroidizing gray cast iron molten iron, and the precipitated graphite is spherical, referred to as ductile iron. All or most of the carbon exists as free spheroidal graphite, and the fracture is silver-gray. Compared with ordinary gray cast iron, it has higher strength, better toughness and plasticity. Cast steel material is cast steel with carbon as the main alloying element and contains a small amount of other elements. Cast carbon steel can be divided into cast low carbon steel, cast medium carbon steel and cast high carbon steel. The carbon content of cast low carbon steel is less than 0.25%, the carbon content of cast medium carbon steel is between 0.25% and 0.60%, and the carbon content of cast high carbon steel is between 0.6% and 3.0%. The strength and hardness of cast carbon steel increase with the increase of carbon content. Cast carbon steel has several advantages such as lower production cost, higher strength, better toughness and stronger plasticity.

High chromium alloy steel refers to alloy steel with a chromium content of more than 10%. High chromium alloy steel generally has high wear resistance, high compressive strength. After hardening, the surface hardness is high, and has good hardenability, stability and temper softening resistance.

Different materials show different physical properties after casting. In terms of hardness and wear resistance, high-chromium alloy materials are the most wear-resistant, followed by cast steel materials, and cast iron materials are poor. The flow parts material of the centrifugal sand dredging pumps produced by OCEAN PUMP is mainly made of high-chromium alloy material, the chromium content reaches 28%, and the Leeb hardness is about 65. At the same time, trace elements such as manganese and molybdenum are added in the casting process to increase the flexibility of the casting. It also has better toughness while emphasizing the hardness, so that it is not easy to break during use.

2. Centrifugal sanddredging pumps casting process

After the casting material is determined, the next step is the implementation of the casting process. A good casting process can make the material give full play to its characteristics. OCEAN PUMP adopts the lost foam casting process. Lost foam casting (also known as solid mold casting) is to bond and combine paraffin or foam models similar in size and shape to castings into model clusters, brush refractory coatings and dry them, and then embed them in dry quartz sand for vibration modeling. Lost foam casting (also known as solid casting) is to bond and combine paraffin or foam models similar in size and shape to castings into model clusters, brush refractory coatings and dry them, and then embed them in dry quartz sand to vibrate for modeling. It is a new casting method in which casting is formed by pouring under negative pressure to vaporize the model, liquid metal occupies the position of the model, and solidifies and cools to form a casting.

Lost foam casting has the following characteristics.

• Good casting quality and low cost.
• Unlimited material, suitable for all sizes.
• High precision, smooth surface, less cleaning, saving machining.
• The internal defects are greatly reduced, and the casting structure is dense.
• Large-scale, high-volume production is possible.
• Suitable for mass production of the same casting.
• Suitable for manual operation and automatic assembly line production operation control.
• The production status of the production line meets the requirements of environmental protection technical parameters.
• It can greatly improve the working environment and production conditions of the foundry production line, reduce labor intensity and reduce energy consumption.

Introduction to lost foam casting process

1. Lost foam casting process – selection of foam beads

There are three types of foam beads for lost foam casting.

• Expandable polystyrene resin beads (referred to as EPS)
• Expandable methyl methacrylate and styrene copolymer resin beads (referred to as STMMA)
• Expandable polymethyl methacrylate resin beads (EPMMA for short)

Expandable polystyrene resin beads (EPS) are commonly used for casting non-ferrous metals, gray iron and general steel casting.

Bead has the features of translucent beads, pre-foaming ratio 40~60, particle size 0.18~0.80mm (6 sizes).

Generally, the particle size of the original beads selected is less than or equal to 1/9 ~ 1/10 of the minimum wall thickness of the casting.

2. Lost foam casting process – model making

There are two cases.

2.1 Made from foam beads: pre-foaming – curing – foam molding – cooling and ejection.

• Pre-foaming. Before the EPS beads are put into the mold, they must be pre-foamed to expand the beads to a certain size. The pre-foaming process determines the density, dimensional stability and accuracy of the model and is one of the key links. There are three methods for EPS bead pre-foaming: hot water pre-foaming, steam pre-foaming and vacuum pre-foaming. Vacuum pre-foamed beads have high foaming rate, dry beads, and are widely used.

• Curing. The pre-foamed EPS beads are placed in a dry and ventilated silo for a certain period of time, so as to balance the external pressure inside the bead cells, make the beads have elasticity and re-expansion ability, and remove the moisture on the surface of the beads. Curing time is 8~48 hours.

• Foam molding. Fill the pre-foamed and cured EPS beads into the cavity of the metal mold, and heat the beads to expand again, fill the gaps between the beads, and make the beads fuse with each other to form a smooth surface, that is, the model. It must be cooled before the mold is released, so that the model is cooled to below the softening temperature, and the mold can be released after the model is hardened and shaped. After the mold is released, there should be time for the model to dry and dimensionally stabilize. There are two types of equipment: steam cylinder and automatic forming machine.

2.2 Made from foam plastic sheet: foam plastic sheet – resistance wire cutting – bonding – model.

For simple models, the resistance wire cutting device can be used to cut the foam plastic sheet into the required model.

For complex models, first use a resistance wire cutting device to divide the model into several parts, and then glue them to make them a whole model.

3. Lost foam casting process – white mold

Assemble the finished white mold or purchased white mold according to the requirements of the casting, bond with cold glue or hot melt adhesive, repair the gap with lost foam repair paste, paint and dry. In this process, attention should be paid to the white mold density, the use of glue, the use of repair paste, the quality of the coating and whether it is suitable for castings, the temperature and humidity of the drying room and other detailed requirements.

4. Lost Foam Casting Process – Packing

The sand box is placed on the shaking table, the dried lost foam model is placed in the sand box, and the clusters are reasonably formed according to the size of the sand box.

The sand box is shaken, and during the packing process, the sand filling system of the Rongyang lost foam production line is used to fill the whole box with sand. After filling, spread it on top with a clinker cloth and cover with sand.

In this process, note that a layer of sand should be laid on the bottom of the sandbox, and the clusters of the model should be reasonably planned. Generally, small pieces can be placed in 2 layers, and large pieces can be placed in 1 layer. In addition, it is necessary to plan the flow process of molten iron, whether there are gaps for molten iron leakage, pay attention to the inclination of individual castings, and the vibration table needs to be shaken 2-3 times during the whole process.

5. Lost foam casting process – vacuuming

The sand box is transported to the vacuuming or casting area and placed at the pouring riser for pouring.

In the process, pay attention to the pressure during vacuuming. Different castings require different pressures.

6. Lost foam casting process – pouring

The molten iron melted by the electric furnace can be introduced into the pouring riser, the sand box is transported to the sand falling area, the castings are released, and the sand enters the circulation system.

When the solid mold is poured, under the heat of the liquid metal, the EPS model undergoes pyrolysis and gasification, generating a large amount of gas, which is continuously discharged to the outside through the coating sand, forming a certain air pressure in the mold, model and metal gap. The liquid metal continuously occupies the position of the EPS model and moves forward, and the replacement process of the liquid metal and the EPS model occurs. The end result of the replacement is the formation of a casting.

The pouring operation process adopts a method of slow-fast-slow, and maintains continuous pouring to prevent the pouring process from being interrupted. After pouring, the mold vacuum is maintained for 3 to 5 minutes, and then the pump is stopped. The pouring temperature is 30~50℃ higher than that of sand casting.

7. Cooling and cleaning

After cooling, it is the easiest for solid casting to drop sand. It is possible to tilt the sand box to lift the casting out or directly lift the casting out of the sand box. The casting and dry sand are naturally separated. The separated dry sand is treated and reused.

After the centrifugal sand dredging pumps overflow parts are cast, the “four fires” heat treatment is carried out, The supercooled austenite of the casting undergoes martensite or bainite transformation to obtain martensite or bainite structure. Then, it is matched with tempering at different temperatures to greatly improve the rigidity, hardness, wear resistance, fatigue strength and toughness of the casting, so as to meet various processing and use requirements.

• Annealing. Heat the flow parts of centrifugal sand dredging pumps to the appropriate temperature, use different holding times according to the material and size, and then slowly cool (the slowest cooling rate). The purpose is to make the internal structure of the metal reach or close to the equilibrium state, obtain good process and performance, or prepare the structure for further quenching.

• Normalizing. Heating the overflow parts of centrifugal sand dredging pumps to a suitable temperature and cooling them in the air. The effect of normalizing is similar to that of annealing, but the obtained structure is finer, which is often used to improve the cutting performance of materials, and sometimes used as final heat treatment for some parts with low requirements.

• Tempered. In order to reduce the brittleness of the centrifugal sand dredging pumps flow parts, the quenched flow parts are kept at an appropriate temperature higher than room temperature but lower than 710°C for a long time, and then cooled. This process is called tempering.

• Quenching. A heat treatment process for obtaining martensite or bainite structure by cooling in an appropriate way after heating and austenitizing the flow parts of centrifugal sand dredging pumps.

3. Centrifugal sand dredging pumps body strength check

Checking the wall thickness of the vortex chamber:

S: wall thickness of vortex chamber (cm)

[σ]: the allowable stress, the cast iron is 250kg/cm²

Sep: the equivalent wall thickness of the vortex chamber

d. Casting wood mold process

1. Overview

• Mold is the most basic technological equipment in foundry production. Its quality directly affects the shape, scale and accuracy of the centrifugal sand dredging pumps casting.In order to ensure the quality of centrifugal sand dredging pumps castings, reduce consumption, combined with the specific situation of OCEAN PUMP, this standard > standard is formulated.
• The wooden mold must be manufactured according to the requirements of the part drawing, casting drawing or process drawing, and has sufficient strength, rigidity and necessary surface finish and dimensional accuracy.
• On the premise of satisfying the usage performance, the molding materials should be from a wide range of sources, easy to manufacture, and the price should be as low as possible.
• The wooden mold should be easy to use, easy to store and carry.

2. Wood mold material

2.1 Properties of wood

• The texture of the wood should be straight and tidy, the fibers are tough and wear-resistant, the structure is meticulous and compact, and the wood is not easy to deform.
• Soft wood texture, few tree knots, easy to cut.
• Smooth surface after wood processing, easy to demould.
• The wood should be dried naturally or artificially before use, so that the moisture content is less than 10%, and there should be no local presence of high moisture.

2.2 Grading of wood

In order to adapt to the manufacturing requirements of different grades of wood molds (see section 3.1 for the classification of wood molds), the wood is divided into three grades.

Table 1. Timber classification regulations

2.3 Binder

• Requires a strong and durable adhesive bond with sufficient toughness.
• The binder should be widely sourced, inexpensive and easy to formulate.
• Non-toxic, low pollution.

3. Manufacture and process requirements of wooden molds

Classification and application range of wood molds: According to the requirements of batch size, dimensional accuracy and surface finish of castings, wood molds are specified as three grades.

Table 2. Grading regulations for wood molds

The wood molder should first be fully familiar with the part drawings and casting process drawings, and on this basis, determine the grade of the wood mold. Different levels of wood molds should be manufactured according to different levels of process requirements. The process requirements are as follows.

3.1 Manufacturing process requirements for first-class wooden molds.

• Manufactured with first-class glued wood, all rounded corners are made. The material of the working surface of the wood mold shall not be lower than the second grade, and the third grade wood can be used for the unimportant parts.
• Ribs or protruding parts (such as cores, brackets, etc.), which should be made of hardwood or metal, embedded in the wood mold, and fastened with glue or screws.
• The movable block shall be positioned and fastened with dovetail or birch made of hardwood or metal.
• Surfaces, edges, and corners that are particularly susceptible to wear should be covered with gold or plastic plates.
• In addition to glue, the joint part needs to be fastened with wood screws, iron nails or wooden nails.
• The pins are made of metal or plastic, with a metal plate at the knockout.
• The embedded mold release device shall be located at the center of gravity and level with the mold plane. The working surface shall be smooth and painted at least twice after preparation.

3.2 Manufacturing process requirements for secondary-class wood molds

• Made of secondary glued wood. Smaller fillets may not be made, and all filletsoutside and fillets below 3mm (including 3mm) shall be made.
• The ribs or protruding parts, small cores, etc. are not necessarily embedded in the main body. In addition to gluing, they can be fastened with wood screws. The movable block shall be installed with dovetail or birch device.
• The billet is simple to combine, but must be fixed with birch and glue.
• The work surface should be smooth, with a few imperfections permitted to be filled with putty. The wood mold should be painted twice after preparation.
• Other regulations refer to the relevant regulations of the first-class wood mold.

3.3 Manufacturing process requirements for three-level wood molds

• Made of grade 3 wood, fillets below 10mm may not be made, fillets above 10mm and all fillets outside should be made.
• Fasten with wood screws or iron nails, and use bolts and other convenient ways to connect movable
• Ribs, small core heads, etc. can be fastened with wood screws or iron nails.
• The work surface should be smooth, and allow filling of defects with putty.
• After the wood mold is done, it is best to paint it once.

4. Precautions for making wooden molds

• When gluing the boards, first make sure that the joint surfaces are in good contact, then apply glue, and push back and forth until they are all matched, and there should be no gaps or cracks. The wood texture must be staggered.
• When two layers of boards are reinforced with nails or wood screws, the depth of nailing into the lower block shall not be less than two-thirds of the thickness of the lower block(the depth of wood screws nailing into the board shall not be less than one third of the screw length), but not nail through.
• The nails on the same plane should be staggered, the nail caps must be flattened, and nailed into the boardin the direction of the wood grain. The nails should be 10~15mm away from the edge of the board to prevent the board from being broken.
• The structure of the wood mold should have the best strength and stiffness, and the smallest expansion and contraction.
• The location of the positioning pin should have obvious directionality. Metal pins should be used for the positioning pins of large or long wooden molds, and hardwood pins may be used for others.
• The basic size of the casting pattern core head is implemented according to the regulations of JB/T5106. The mud core head that is easy to be installed reversely and dislocated should have their own positioning structures to distinguish them from each other.
• Each part of the wood mold should be colored and marked, see the following table for specific regulations.

Table 3. Wood mold coloring mark

• The finished wood mold must be marked with a center line.Complicated wood molds should be preserved for inspection. The important position of the large and medium pieces should be clearly marked with the center line and the meat line, and they should not be merged with each other, so as to facilitate the modeling.
• When manufacturing the scraper, a sketch of the section should be drawn on the scraper.For large and medium-sized parts and scrapers that have been used for many times, the scraping edge must be inlaid with iron plates.
• The machining allowance of castings not specified in the process shall be implemented in accordance with the provisions of GB/T 11350.The casting shrinkage rate of various alloys is carried out according to the provisions of Table 4.

Table 4. Casting shrinkage of commonly used alloys

The draft angle of the wooden mold not specified in the process is made according to the table below.

• For rounded corners that have not been made, a mark must be drawn and the size of the rounded corners should be indicated.
• The geometry of the wooden mold must comply with the part drawing and process requirements, and the dimensional deviation should comply with the relevant regulations.

4. What’s the assembly process of Centrifugal Sand Dredging Pumps

a. Assembly process rules

1. General requirements in assembly

• Parts of the centrifugal sand dredging pumps must be qualified products and have completed various anti-rust treatments.
• Parts of centrifugal sand dredging pumps should be cleaned during assembly, and no oil, dirt and iron filings are allowed.
• The exposed machined surfaces of carbon steel and cast iron parts should be coated with anti-rust oil or grease.
• After the centrifugal sand dredging pumps are assembled, there must be arrow mark indicating the rotation direction of the centrifugal sand dredging pumps.
• After the centrifugal sand dredging pumps are assembled, they must be marked, and the method shall be implemented according to the standard of Q/SPCN.G.28001《Product Marking and Traceability Control Procedure》.
• After the centrifugal sand dredging pumps performance test is qualified, the water accumulated in the centrifugal sand dredging pumps should be cleaned up.For the parts such as the carbon steel centrifugal sand dredging pumps body flow channel, carbon steel impeller flow channel and outer surface, and carbon steel centrifugal sand dredging pumps shaft should be coated with anti-rust oil or grease. Refer to “Anti-rust Technology of Centrifugal Sand Dredging Pumps Complete Machine”.
• Before the centrifugal sand dredging pumps are packaged, a blind plate of 5mm thick Q235-A material should be installed at the inlet and outlet of the centrifugal sand dredging pumps bodies.If there is a matching flange, it is also installed on the blind plate at the same time.

2. Requirements for assembly and final assembly

• When assembling the flat key and bearing, it is not allowed to hit it directly with a hammer. It should be assembled with a wooden hammer, a copper rod, etc. or special assembly tools.
• When the inner diameter of the bearing is an interference fit such as r6 and s6, it is necessary to perform hot loading, and the temperature is 80-120 °C.
• The joint end of the stud bolt and the parent body should be coated with dry oil, and the length should be consistent and tightened evenly.
• During the assembly process, it is strictly forbidden to scratch the surface of the parts, especially the mating and sealing surfaces, so as not to affect the assembly quality.

3. Assembly of the mechanical seal

• When assembling, each joint surface should be strictly attached, and the friction surface should be coated with industrial vaseline lubricant.

4. Combination

• When the coupling is assembled, lubricating oil should be applied to the inner hole, journal and key, and the force should be uniform during assembly to prevent impact damage to the parts of centrifugal sand dredging pumps.

b. Assembly

1. Cleaning:

Parts of centrifugal sand dredging pumps must be inspected and qualified, the material code should meet the requirements of the drawing, the surface should be cleaned, and the mating surface should be coated with oil. The bearing box of centrifugal sand dredging pumps is cleaned and coated with oil-resistant enamel, and is naturally dried for 24 hours. After passing the inspection, it can be assembled.

2. Assembly of bearings and shaftsof centrifugal sand dredging pumps:

Bearings are heated to 90℃-110℃ in a heating furnace and then installed on the shaft for cooling. First install the bearing gland on the left side of the bearing housing, then put the bearing and shaft assembly into the bearing housing, lean against the left bearing gland, measure the dimensions of the drive end bearing gland and the end face of the bearing outer ring, the CZ pump is at 0.30 -0.70mm, ZA pump at 0-0.42mm clearance. If the ZA pump bearings are used in pairs, install and use a shrink nut to lock the bearings until the outer rings of the two bearings can rotate relatively slightly to obtain a better clearance.

3. Assembly of mouth ring, impeller and centrifugal sand dredging pumps body:

When the mouth ring is assembled with the impeller and the centrifugal sand dredging pumps body, pay attention to make the mouth ring evenly installed in the impeller or pump body to reduce the shape error of the mouth ring as much as possible. After installing the set screw or welding, measure the radial runout of the impeller and the mouth ring and the gap between the two. The measured value should meet the requirements of the general technical conditions for centrifugal sand dredging pumps assembly, and repair the parts that are out of tolerance.

4. Seal installation

• Cartridge mechanical seal installation

When installing the cartridge mechanical seal, first install the seal on the centrifugal sand dredging pumps cover with double-ended studs and nuts. After the centrifugal sand dredging pumps shaft penetrates into the seal shaft sleeve, and the bearing box is connected with the centrifugal sand dredging pumps body, move the stop gasket on the seal away from the shaft sleeve.

In order to reduce the wear of the O-ring during installation, the parts where the O-ring passes can be coated with lubricating oil, but the ethylene-propylene rubber ring should be lubricated with soap or water.

• Packing seal installation

Before the packing seal of centrifugal sand dredging pumps is installed, the length of each circle should be determined according to the outer diameter of the shaft sleeve. After a little flattening, it should be wrapped around the shaft sleeve and pushed into the stuffing box. If there is a water seal ring, it should be installed together as required.

After the packing is finished, press evenly with the packing gland.

5. Install the impeller

• For single-stage centrifugal sand dredging pumps, the impeller should be subjected to static balance test and meet the requirements of technical conditions.After installing the impeller of centrifugal sand dredging pumps on the shaft and tightening the nut, put the entire rotor into the entrifugal sand dredging pumps body and tighten it with the nuts.
• For multi-stage centrifugal sand dredging pumps, in addition to static balance test of impeller, it is also necessary to carry out trial assembly of rotor components, install each impeller and shaft together, make a mark, do dynamic balance test, and the test results should meet the requirements of technical conditions.When installing, push the balance drum, shaft sleeve and all impellers to the right until the first-stage impeller and shaft sleeve are against the shaft shoulder respectively. Measure the clearance between the shaft sleeve and the balance drum to make it ≥ 5. If the clearance is too small, trim the balance drum , so that the gap meets the requirements. Then install the shaft with the first stage impeller on the inlet centrifugal sand dredging pumps casing, install the impeller and the middle section casing with guide vanes on the shaft step by step until the outlet section, fix the centrifugal sand dredging pumps parts with screws, install the balance device, seal and bearing parts, determine the correct middle position of the rotor, and adjust the axial clearance of the tapered bearing to 0.04-0.06mm.

6. Bearing adjustment of horizontal multistage centrifugal sand dredging pumps.

The bearing box of multi-stage centrifugal sand dredging pumps with non-stop positioning shall be aligned and adjusted during installation. Rotate the adjusting bolt to make the bearing box move vertically and horizontally, measure the extreme positions of the bearing box in two directions respectively, take the average value, and finally lock it with the lock nut. Hit the locating pin, then install the seal, bearing, and adjust the rotor axial direction, etc.

7. Coupling installation (centrifugal sand dredging pumps head fixed).

• Membrane coupling installation

Install the coupling at the centrifugal sand dredging pumps end and coupling of the motor end on the corresponding shafts respectively, and use a dial indicator to align the coaxiality of the two shafts (adjust the motor position with a gasket in the vertical direction), so that the radial runout between the two shafts is ≤ 0.1 and the end runout is ≤ 0.05. after meeting the requirements, install the intermediate part. When the rotational speed is greater than 3600 rpm, the radial runout is less than or equal to 0.05, and the end runout is less than or equal to 0.03, if the operating temperature is high (about 130°C or higher), the final correction should be carried out under the high temperature condition when the centrifugal sand dredging pumps are running.

• Claw couplinginstallation

Similar to the membrane coupling, the two flanges of the coupling are respectively installed on the corresponding shafts, and the mutual positions are adjusted with a ruler. If the rotation speed is ≥3600 rpm, it should be aligned according to the alignment method of the membrane coupling.

8. Painted

The painting should be carried out in a clean and dry place, the ambient temperature should not be lower than 5 ℃, and the relative humidity should not be higher than 70%. If the relative humidity is greater than 70%, an appropriate amount of moisture-proof agent should be added to the coating to prevent the coating film from turning white.

Non-steel metal parts, stainless steel parts, chrome-plated, nickel, cadmium, silver, tin and other parts, sliding parts, mating parts, sealing surfaces, rib surfaces, signs and steering signs are not painted.

All non-machined surfaces of centrifugal sand dredging pumps parts other than the above and non-mating surfaces after machining should be painted.

c. Inspection Process of Centrifugal Sand Dredging Pumps

The inspection of the centrifugal sand dredging pumps can be divided into two parts, one is the performance inspection of the centrifugal sand dredging pumps, and the other is the factory inspection of the centrifugal sand dredging pumps. Through inspection to ensure that the centrifugal sand dredging pumps meets both the design and use requirements and the factory standards.

1. Performance tests of centrifugal sand dredging pumps

The performance parameters of the centrifugal sand dredging pumps mainly include flow, head, shaft power, efficiency, speed, necessary NPSH or allowable suction vacuum height, specific revolutions or cavitation specific revolutions, etc. At the beginning of each kind of centrifugal sand dredging pumps design, the requirements of the working conditions are fully considered, and the technical personnel calculate the parameters such as flow, head to match centrifugal sand dredging pumps design according to the requirements, and the trial production can only be carried out after technical verification.The produced centrifugal sand dredging pumps are tested by the national pump product performance test platform to test whether the performance parameters such as flow rate and head meet the requirements. The test standards are as follows.

• GB/T 3216-2016 “Rotary Power Pumps Hydraulic Performance Acceptance Test Levels 1, 2 and 3”.
• API610 11th / ISO 13709-2009 “centrifugal sand dredging pumps for petroleum, petrochemical and natural gas”.
• ANSI/HI 1.6 “American Hydraulic Institute Standard for Sealed/Sealedless Centrifugal Sand Dredging Pumps”.
• GB/T 3214-2007 “determination method of water pump flow rate”.
• GB/T 29529-2013 “Non Evaluation Method for Noise Measurement of Centrifugal Sand Dredging Pumps”.
• GB/T 29531-2013 “Non Evaluation Method for Vibration Measurement of Centrifugal Sand Dredging Pumps”.
• GB/T 1032-2012 “Test Methods for Three-phase Asynchronous Motors”.

The performance of the centrifugal sand dredging pumps is tested by the national pump performance inspection system, usually by the pump industry inspection service center with national quality inspection or provincial inspection and certification, in strict accordance with the centrifugal sand dredging pumps test standards and procedures, and the specific test steps are as follows.

• Install the centrifugal sand dredging pumps in the designated position of the test bench, and connect the motor or gearbox according to the test requirements.
• Select the inlet and outlet pipes according to the diameter of the centrifugal sand dredging pumps.
• Close the outlet valve, open the vacuum pump to extract the air inside the pipeline and centrifugal sand dredging pumps.
• Open the water inlet pipe valve and open the air release valve to check whether there is residual air in the pipes. If there is still air, continue to extract with the vacuum pump, and close the water inlet pipe valve after completion.
• Start the centrifugal sand dredging pumps, check whether the centrifugal sand dredging pumps shaft rotates, whether the steering rotation meets the requirements, and whether the water pump has water leakage, water spray and other sealing problems.
• Close the inlet and outlet valves and check the pressure resistance and sealing performance of the water pump.
• Open the regulating valve to the maximum, divide the flow points within the maximum flow range, and arrange the experimental points.
• After each flow point runs stably, record the data of each instrument.
• After completing the point taking test, close the centrifugal sand dredging pumps and valve according to the steps.

During the test, the temperature of the bearing and other parts should be measured at any time through a thermometer.

• Remove the centrifugal sand dredging pumps and restore the original test platform.Fill in the performance parameter table according to the parameters such as flow, head, shaft power, efficiency, etc. measured by the experiment. If the test speed is inconsistent with the actual required speed, calculate the corresponding parameters according to the reduction formula. After the parameter table is verified to be correct, draw the performance curve of the centrifugal sand dredging pumps. Compare the test performance curve with the design performance curve, analyze the performance difference, and judge whether it meets the design requirements and whether it needs to be changed.

b. Factory inspection of centrifugal sand dredging pumps

When the sales manager submits the delivery application, the quality inspector should follow the steps below to inspect the centrifugal sand dredging pumps.

• The centrifugal sand dredging pumps body, motor (or diesel engine), base and other components shall be subject to surface pretreatment and painting protection as required. The coating shall not be blistered, wrinkled or peeled off, and the color shall be consistent.
• Centrifugal sand dredging pumps nameplates, steering, safety warnings, etc., should be placed in conspicuous positions, clearly marked and complete.

• The centrifugal sand dredging pumps model, accessory model and number of pieces must meet the requirements of the technical agreement.
• The pipe nozzles such as the inlet and outlet of the centrifugal sand dredging pumps should be sealed, the protection and plugs should be intact, and the corresponding flanges, gaskets and seals must also be intact.

• Pressure test: The static pressure test pressure of all pressure-bearing parts is 1.5 times the design pressure, and the pressure holding time is not less than 10 minutes; and the whole centrifugal sand dredging pumps have no leakage.
• The allowable deviation of concentricity inspection, elastic coupling is: radial dislocation ≤ 0.12mm, end face inclination ≤ 0.08mm; end face clearance is controlled within 1 ~ 4mm.

• Connection tightening bolt inspection.

• The crank should be flexible, without blocking, jamming, or abnormal sound.
• Packing as required by the contract or order with the customer.

• Fill out the factory inspection form (attached form)

Centrifugal sand dredging pumps factory inspection report

This report records the performance parameters and factory inspection conclusions of the centrifugal sand dredging pumps, which are in line with national standards and relevant industry standards.

• Main inspection：Zhiguo Zhang
• Audit: Jungang Xing
• Approve: Mi Hengxing Mi

Conclusion

Through the above article content, we have learned how to design and manufacture a centrifugal sand pump. Tai’an Ocean Pump (OCEAN Pump) Co., Ltd. is the leading sand pump machine and sand dredger solutions manufacturer, supplier and exporter in China. We have more than 30 talented sand pump experts and 15,000 square meters factory. More than 4 series 20 kinds of sand pumps, slurry pumps, sand dredgers and related parts had been manufactured to satisfy your pumping requirements. OCEAN Pump is the Certification of New Hi-tech Enterprises by the Government. We provide our customers with a complete set of sand, slurry, gravel pumping solutions and related parts. Our main products include centrifugal portable sand pump, marine sand pump, slurry pump, suction dredge pumps, gravel pump, mud pump, submersible slurry pump, vertical sand pump, simple small sand pump dredger, submersible dredger, mini dredge for sale,  small dredging equipment, small pond dredging equipment, sand suction dredger,  suction dredging equipment, cutter suction dredger , sewage submersible pump, lake dredging equipment, mini dredges for sale, sand dredging machine, river dredging equipment and other parts like discharging sand pipe, floater, rubber hose. They are widely used in mining, metallurgy, coal washing, power plants, sewage water treatment and dredging in such industries as mine, chemical and petroleum. We are looking for pump dealers all over the world.