CA6NM stainless steel pipe not only has good corrosion resistance, weldability, but also has high strength and low temperature toughness . CA6NM belongs to low carbon martensite stainless steel, mainly used for hydropower facilities and mine facilities of the wear parts. Such as turbine blades, turbine, roller screen/feeder. Not only to undergo general corrosion medium, but also to endure the erosion of the sediment, cavitation erosion at runtime. Poor use conditions.
Compare CA6NM and 17-4 ph. CA6NM stainless steel pipe has higher strength, hardness, resistance to cavitation erosion, also keep good toughness and fatigue resistance, underwater and has better weldability
Not only CA6NM stainless steel has good corrosion resistance, weldability, but also has high strength and low temperature toughness .
The casting of CA6NM stainless steel has many advantages in application Its advantages are as follows： 1.High strength and high toughness Rp0.2 > 600 MPa Rm > 800 MPa A > 18% Z > 50% A kv > 100 j. 2 Good low temperature impact properties, fracture toughness and FATT (Brittle transition temperature of -173 ~ -196 ℃). 3 Good welding yao casting and machining performance. 4 Good underwater fatigue resistance and cavitation erosion and wear resistance. 5 High harden ability and good mechanical properties, with heavy section. 6 CA6NM stainless steel castings good engineering nondestructive testing performance.
But CA6NM stainless steel has its prominent shortcomings and engineering practice. Must solve the key technical problems of its shortcomings as follows,
1.The sensitivity of the composition and microstructure deviation. 2.Heat treatment process control and the sensitivity of the mechanical properties change.
3.The phase change process and the complexity of the stress control.
4.It’s easy to have a cold crack defects.
Through the optimization process. We produce CA6NM tube, meeting with ASTM A743 and Astm487, and exported to Quebec, Canada. The microstructure of 100% martensite.
Centrifugal casting process： molten metal is poured into a hollow cylindrical mold spinning about a horizontal or vertical axis at speeds generating more than 100 Gs of centrifugal force. The centrifugal force distributes the molten metal and shapes it into a tubular/cylindrical forms. The high forces involved in this casting method means that the less dense materials including impurities are forced into the center where they can be subsequently removed and gas related defects and shrinkage porosity are reduced thus parts made from centrifugal casting exhibit denser, closer grained structure with improved physical qualities such as tensile strength, yield strength, elongation and uniformity.
1.There is almost no metal consumption at inject system and gating system, so production rate improved much.
2.There is no core when produce hollow castings so greatly improve the metal filling capacity, lower the ratio of wall thickness to length or diameter and simplify the process of sleeve and pipe production.
3.High density, less of defects like pores and slag, high mechanical property.
Easy to manufacture cylinder or sleeve type composite metal castings such as steel back copper sleeve, bimetallic roller, thin wall castings.
1.There are certain limitations in the production of special shaped castings.
2.The inner diameter is not accurate. The surface of inner hole is relatively rough, the quality is poor and the machining allowance is big.
3.It is easy to produce specific gravity segregation. So it is not suitable for easy to segregate like lead bronze, especially not suitable for the casting of the impurity specific gravity greater than the alloy metal liquid.
Metal filter, pouring temperature, casting speed, slag solidification and coating use, casting off mold, gating system and pouring quantitative are all required to identify and solved in centrifugal casting. They directly affect the casting quality and production efficiency.
There are more dregs difficult to remove in some alloy liquid. can placed filters at pouring system to remove scum, such as foam ceramic filter, glass fiber filter.
Centrifugal castings are mostly tube, sleeve or ring type, the filling resistance is small, and the centrifugal force can strengthen the metal filling ability, therefore, centrifugal casting pouring temperature can be relatively lower 5 ~ 10 ° C than gravity pouring temperature.
The casting speed is an important technological factor of the centrifugal casting. The casting speeds while cast forming is vary with different parts and different process.
Low casting speed cause inadequate filling for the vertical casting and like rain phenomenon of liquid metal for horizontal casting. Also it can cause defects like loose textures, slag and uneven inner surface.
Higher casting speed can cause crack, segregation on the parts and expansion box for the sand centrifugal casting. Also it can cause machine vibration, wear, power consumption is too large, etc. So speed selection principle should be on the premise of guarantee the quality of castings, the smallest value is best.
To overcome the defects of subcutaneous shrinkage cavity caused by bi-directional solidification of thick wall centrifugal casting the slagging agent can be poured with liquid metal into mold. The slag covers on the inner surface to prevent heat dissipation. It causes directional solidification from inner to outside to eliminate subcutaneous shrinkage cavity. At the same time, the slagging agent can also be refined metal effect.
Centrifugal casting coating is vital for the quality of the product. It should be different coating according to different materials.
Casting off mold:
In order to improve production efficiency the casting off mold should be as soon as possible on the premise of guarantee quality. Sometimes the castings taken off mold immediately kept into the furnace or a pile of sand in order to prevent the casting crack. As for some castings which is not easy to take off mold but need to slowly cooling to prevent crack it should take away from machine immediately after stop rotation and bury into sand to cooling down slowly until reach to room temperature.
Centrifugal casting pouring system mainly refers to poured cup and pouring groove connected to it, and sometimes also comprises a pouring channel in the mold. we paid attention following principles when designing pouring system.
1. As for castings are long and large diameter the pouring system should make sure the metal liquid can quickly and evenly spread on the inner surface of the mold.
2. As for easy oxidation of pouring liquid metal or using centrifugal sand mold, the pouring groove should balance the metal filling into the mold, as far as possible to reduce metal spatter, reduce the erosion to sand mold.
3. When cast shaped castings, it should be able to make the liquid metal flows into the cavity smoothly for the channel.
At the end of casting the pouring cup and the pouring groove should be no metal and slag. It should be easy to remove if there are any residual metal and slag.
The centrifugal casting is one method of casting. The molten metal is poured into the spinning mould, under the action of centrifugal force it fills and shapes into the tubular/cylindrical forms. The equipment is known as the centrifugal casting machine.
1. Brief introduction
According to the different direction of rotation axis centrifugal casting machine is divided into horizontal, vertical and inclined types. Horizontal centrifugal casting machine used mainly for casting various tubular cast such as gray cast iron, ductile iron pipe and gas pipe, the diameter of a minimum of 75 mm, up to 3000 mm. In addition it can be used for casting large bore copper roller, carbon steel pipe, alloy pipe and steel roll of double layer material with different compositions. The vertical centrifugal casting machine is mainly used for casting various ring castings and smaller non circular castings.
According to the shape, size and production batch the centrifugal casting mould is different. They will be non metal (such as sand, shell or plycast), metal or metal with inner coating layer. Casting speed is an important parameter in centrifugal casting. One is must have the enough centrifugal force to increase the compactness of the casting, the other is the centrifugal force can not be too large so as not to impede the metal contraction. Especially for lead bronze, centrifugal force is too large will produce the segregation between inside and outside of the casting. In general the speed is about dozens to 1500 rpm.
The characteristic of centrifugal casting is that the molten metal is poured into the spinning mould, under the action of centrifugal force it fills and shapes into the tubular/cylindrical forms. The casting has good metal feeding effect, compact structure and good mechanical properties. For hollow castings there is no need of casting head, metal utilization rate can be improved greatly. So for specific shape of the casting the centrifugal casting is a process of material saving, energy saving and high efficiency. But we must pay special attention to safety measures.
The system is consist of centrifugal casting unit, pouring unit, adapter tube unit, core-loading device, pipe mould preheating device, water feeding and spraying device, electrical control system and safety protection cover, etc.
a) Centrifugal casting unit
The unit is the core of the centrifugal casting machine which completes the rotation of pipe mould. Pipe mold speed can be stepless adjustment to meet the process requirements of different diameter. It is consist of main plate base, motor base, adjustable speed motor, the bearing seat, axis, belt transmission and brake, etc.
b) Core-loading device
It completes the coating action of pipe mould. Mainly composed by pneumatic components, paint cans and spraying vehicle.
c) Electrical control system
The pipe mould rotation powered by AC electromagnetic speed motors with stable speed and wide speed adjusting range in order to meet the requirements of different diameters. The electric control system comprises a motor controller, control cabinet, low voltage electrical components, button and indicator lights. It has perfect safety protection measures of interlock, overcurrent and overload.
d) The auxiliary parts
Safety protection cover, water feeding and spraying device, pouring trough and brackets, etc.