Views: 34 Author: Site Editor Publish Time: 2018-07-05 Origin: www.fuchun-casting.com
A pillow block is a pedestal used to provide support for a rotating shaft with the help of compatible bearings & various accessories. Housing material for a pillow block is typically made of cast iron or cast steel.
A pillow block usually refers to a housing with an included anti-friction bearing. A pillow block refers to any mounted bearing wherein the mounted shaft is in a parallel plane to the mounting surface, and perpendicular to the center line of the mounting holes, as contrasted with various types of flange blocks or flange units. A pillow block may contain a bearing with one of several types of rolling elements, including ball, cylindrical roller, spherical roller, tapered roller, or metallic or synthetic bushing.
Bearings used with pillow block housings usually are self- aligning to compensate for angular misalignments. Pillow blocks are available with many different bearing types, including:
Plain bearings are used to constrain, guide, or reduce friction in linear applications. They use a sliding action instead of the rolling action used by ball, roller, and needle bearings. Plain bearings can be constructed of a variety of materials, but are typically bronze, a graphite-metal allow, or plastic. Metal plain pillow block bearings must be lubricated properly to reduce wear and friction. Bronze plain bearings may also be either impregnated with oil or self-lubricating.
Ball bearings have a ball as the rolling element. They are used to provide smooth, low friction motion in rotary applications. Construction consists of an inner and outer ring, balls, and usually a cage or ball separator. Ball pillow block bearings feature an inner and outer ring and balls. They may be equipped with a cage or ball separator.
Roller bearings have a roller as the rolling element. They are used to provide smooth, low friction motion in rotary applications. Construction consists of an inner and outer ring, rollers, and usually a cage or roller separator. There are three principal types of roller bearings used in pillow blocks:
Tapered-roller bearings use conical rollers that run on conical races. They can support both radial and axial loads as well as carry higher loads than ball bearings due to having greater contact area. Tapered-roller bearings contain an inner ring (cone), an outer ring (cup), a cage, and rollers. They have high radial and axial load capacities when used at low to intermediate speed levels. The thrust level of tapered-roller pillow block bearings is about 60% of the radial capacity. They are usually more expensive.
Spherical- roller bearings are self-aligning, double-row, combination radial and thrust bearings. The rolling element in these pillow block bearings has a crowned or spherical shape. Spherical-roller pillow block bearings are superior when dealing with high loads and loads that require tolerance to shock; however, they have limited speed capabilities.
Cylindrical-roller bearings are bearings with high radial capacities and moderate thrust loads. They can be crowned or end-relieved for reduced-stress concentrations. Cylindrical-roller pillow block bearings produce low friction and allow for high-speed.
Needle-roller bearings have a needle roller as the rolling element. They are similar to cylindrical roller bearings but have a smaller diameter-to-length ratio. By controlling the circumferential clearance between rollers, or needles, rolling elements are kept parallel to the shaft axis. Needle roller bearings are designed for radial load applications where a low profile is desired.
Hydrodynamic bearings are fluid film bearings that rely on a film of oil or air to create a clearance between the moving and stationary elements. Hydrodynamic pillow block bearings maintain high stiffness, load capacity, and long bearing life, but are considerably more complex and expensive than standard rolling element pillow block bearings.
Reference:en.wikipedia.org/wiki/Pillow_block_bearing
This is where a batch of steel meets more than one specification or grade. It is a way of allowing melting shops to produce stainless steel more efficiently by restricting the number of different types of steel. The chemical composition and mechanical properties of the steel can meet more than one grade within the same standard or across a number of standards. This also allows stockholders to minimise stock levels.
For example, it is common for 1.4401 and 1.4404 (316 and 316L) to be dual certified - that is the carbon content is less than 0.030%. Steel certified to both European and US standards is also common.
There are many different types of surface finish on stainless steel. Some of these originate from the mill but many are applied later during processing, for example polished, brushed, blasted, etched and coloured finishes.
The importance of surface finish in determining the corrosion resistance of the stainless steel surface cannot be overemphasised. A rough surface finish can effectively lower the corrosion resistance to that of a lower grade of stainless steel.
Various types of stainless steel are used across the whole temperature range from ambient to 1100 deg C. The choice of grade depends on several factors:
In the European standards, a distinction is made between stainless steels and heat-resisting steels. However, this distinction is often blurred and it is useful to consider them as one range of steels.
Increasing amounts of Chromium and silicon impart greater oxidation resistance. Increasing amounts of Nickel impart greater carburisation resistance.
Austenitic stainless steels are extensively used for service down to as low as liquid helium temperature (-269 deg C). This is largely due to the lack of a clearly defined transition from ductile to brittle fracture in impact toughness testing.
Toughness is measured by impacting a small sample with a swinging hammer. The distance which the hammer swings after impact is a measure of the toughness. The shorter the distance, the tougher the steel as the energy of the hammer is absorbed by the sample. Toughness is measured in Joules (J). Minimum values of toughness are specified for different applications. A value of 40 J is regarded as reasonable for most service conditions.
Steels with ferritic or martensitic structures show a sudden change from ductile (safe) to brittle (unsafe) fracture over a small temperature difference. Even the best of these steels show this behaviour at temperatures higher than -100 deg C and in many cases only just below zero.
In contrast austenitic steels only show a gradual fall in the impact toughness value and are still well above 100 J at -196 deg C.
Another factor in affecting the choice of steel at low temperature is the ability to resist transformation from austenite to martensite.
It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1.
It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.
In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.004.
Martensitic, ferritic, duplex and precipitation hardening steels are magnetic.