Product Review and Product Catalogue
Aviceis a mechanical screw apparatus used for holding or clamping a work piece to allow work to be performed on it with tools such as saws, planes, drills,mills, screwdrivers, sandpaper, etc. Vices usually have one fixed jaw and another, parallel, jaw which is moved towards or away from the fixed jaw by the screw.
Vise
Three types of vises
Aviseorvice(seeAmerican and British English spelling differences) is a mechanicalscrewapparatus used for holding or clamping a work piece to allow work to be performed on it with tools such assaws,planes,drills,mills,screwdrivers,sandpaper,etc.Vises usually have one fixed jaw and another, parallel, jaw which is moved towards or away from the fixed jaw by the screw.
Contents
[hide]- 1Types
- 1.1Woodworking vises
- 1.2Engineering vises
- 1.3Others
- 2See also
- 3References
Types
Engineer's bench vise orfitter's vise - image inset shows soft jaws
Woodworker's vise
Without qualification, "vise" usually refers to abench visewith flat, parallel jaws, attached to aworkbench. There are two main types: awoodworking viseandengineer's vise. The woodworker's bench vise main characteristic is its integration into the bench. An engineer's bench vise is usually clamped or bolted onto the top of the bench.[1]
Woodworking vises
Forwoodworking, the jaws are made of wood, plastic or from metal, in the latter case they are usually faced with wood to avoid marring the work piece. The top edges of the jaws are typically brought flush with the bench top by the extension of the wooden face above the top of the iron moveable jaw. This jaw may include a dog hole to hold abench dog. In modern metal woodworkers' vises, a splitnutis often used. The nut in which the screw turns is in two parts so that, by means of a lever, it can be removed from the screw and the moveable jaw can be quickly slid into a suitable position at which point the nut is again closed onto the screw so that the vise may be closed firmly onto the work.Engineering vises
Machine vise - mill
Small machine vise - drill
Formetalworking, the jaws are made of metal which may be hardened steel with a coarse gripping finish. Quick change removablesoft jawsare being used more frequently to accommodate fast change-over on set-ups. They are also kept for use where appropriate, to protect the work from damage.
Metalworking bench vises, known as engineers' or fitters' vises, are bolted onto the top surface of the bench with the face of the fixed jaws just forward of the front edge of the bench. The bench height should be such that the top of the vise jaws is at or just below the elbow height of the user when standing upright. Where several people use the one vise, this is a good guide.
The nut in which the screw turns may be split so that, by means of a lever, it can be removed from the screw and the screw and moveable jaw quickly slid into a suitable position at which point the nut is again closed onto the screw. Many fitters prefer to use the greater precision available from a plain screw vise. The vise may include other features such as a smallanvilon the back of its body.
Vise screws are usually either of anAcme threadform or abuttress thread. Those with a quick-release nut use a buttress thread.
In high production machine work, work must be held in the same location with great accuracy, so CNC machines may perform operations on an array of vises. To assist this, there are several machine-shop specific vises and vise accessories.
Hard and soft machine jaws have a very important difference between other metalworking vise jaws. The jaws are precision ground to a very flat and smooth surface for accuracy. These rely on mechanical pressure for gripping, instead of a rough surface. An unskilled operator has the tendency to over-tighten jaws, leading to part deformation and error in the finished workpiece. The jaws themselves come in a variety of hard and soft jaw profiles, for various work needs. One can purchase machinable soft jaws, and mill the profile of the part into them to speed part set-up and eliminate measurement. This is most commonly done in gang operations, discussed below. For rectangular parts being worked at 45 degree angles, prismatic hard jaws exist with V grooves cut into them to hold the part. Some vises have a hydraulic or pneumatic screw, making setup not only faster, but more accurate as human error is reduced.
For large parts, an array of regular machine vises may be set up to hold a part that is too long for one vise to hold. The vises' fixed jaws are aligned by means of adial indicatorso that there is a common reference plane for the CNC machine.
For multiple parts, several options exist, and all machine vise manufacturers have lines of vises available for high production work.
- The first step is a two clamp vise, where the fixed jaw is in the center of the vise and movable jaws ride on the same screw to the outside.
- The next step up is the modular vise. Modular vises can be arranged and bolted together in a grid, with no space between them. This allows the greatest density of vises on a given work surface. This style vise also comes in a two clamp variety.
- Tower vises are vertical vises used in horizontal machining centers. They have one vise per side, and come in single or dual clamping station varieties. A dual clamping tower vise, for example, will hold eight relatively large parts without the need for a tool change.
- Tombstone fixtures follow the same theory as a tower vise. Tombstones allow four surfaces of vises to be worked on one rotary table pallet. A tombstone is a large, accurate, hardened block of metal that is bolted to the CNC pallet. The surface of the tombstone has holes to accommodate modular vises across all four faces on a pallet that can rotate to expose those faces to the machine spindle.
- New work holding fixtures are becoming available for five-axis machining centers. These specialty vises allow the machine to work on surfaces that would normally be obscured when mounted in a traditional or tombstone vise setup.
[edit]Others
Other kinds of vise include:- hand vises
- machine vises - drill vises (lie flat on adrill pressbed). Vises of the same general form are used also on milling machines and grinding machines.
- compound slide vises are more complex machine vises. They allow speed and precision in the placement of the work.
- cross vises, which can be adjusted usingleadscrewsin the X and Y axes; these are useful if many holes need to be drilled in the same workpiece using adrill press. Comparerouter table.
- off-center vises
- angle vises
- sine vises, which use solving triangles and gauge blocks to set up a highly accurate angle
- rotary vises
- diemakers' vises
- table vises
- pin vises (for holding thin, long cylindrical objects by one end)
- jewellers' vises and by contrast
- leg vises, which are attached to a bench but also supported from the ground so as to be stable under the very heavy use imposed by a blacksmith's work.
Hydraulic cylinder
From Wikipedia, the free encyclopedia
The hydraulic cylinders on thisexcavatorcontrol the machine'slinkages.
AHydraulic cylinder(also called a linearhydraulic motor) is a mechanicalactuatorthat is used to give a linearforcethrough a linear stroke. It has many applications, notably inengineering vehicles.
Contents
[hide]- 1Operation
- 2Parts of a hydraulic cylinder
- 2.1Cylinder barrel
- 2.2Cylinder Bottom or Cap
- 2.3Cylinder Head
- 2.4Piston
- 2.5Piston Rod
- 2.6Rod Gland
- 2.7Other parts
- 3Hydraulic Cylinder Designs
- 3.1Tie Rod Cylinders
- 3.2Welded Body Cylinders
- 4Piston Rod construction
- 4.1Metallic coatings
- 4.2Ceramic coatings
- 4.3Lengths
- 5Special hydraulic cylinders
- 5.1Telescopic cylinder
- 5.2Plunger cylinder
- 5.3Differential cylinder
- 5.4Rephasing cylinder
- 5.5Position sensing "smart" hydraulic cylinder
- 5.5.1A note about popular terminology
- 6References
[edit]Operation
Hydrauliccylinders get their power from pressurizedhydraulic fluid, which is typically oil. The hydraulic cylinder consists of a cylinderbarrel, in which apistonconnected to apiston rodmoves back and forth. The barrel is closed on each end by the cylinder bottom (also called the cap end) and by the cylinder head where the piston rod comes out of the cylinder. The piston has sliding rings and seals. The piston divides the inside of the cylinder in two chambers, the bottom chamber (cap end) and the piston rod side chamber (rod end). The hydraulic pressure acts on the piston to do linearworkand motion.Flanges,trunnions, and/orclevissesare mounted to the cylinder body. The piston rod also has mounting attachments to connect the cylinder to the object or machine component that it is pushing.
A hydraulic cylinder is the actuator or "motor" side of this system. The "generator" side of the hydraulic system is thehydraulic pumpwhich brings in a fixed or regulated flow of oil to the bottom side of the hydraulic cylinder, to move the piston rod upwards. The piston pushes the oil in the other chamber back to the reservoir. If we assume that the oil pressure in the piston rod chamber is approximately zero, the force on the piston rod equals the pressure in the cylinder times the piston area (F=PA).
The piston moves instead downwards if oil is pumped into the piston rod side chamber and the oil from the piston area flows back to the reservoir without pressure. The pressure in the piston rod area chamber is (Pull Force) / (piston area - piston rod area).
[edit]Parts of a hydraulic cylinder
A hydraulic cylinder consists of the following parts:[edit]Cylinder barrel
The cylinder barrel is mostly a seamless thick walled forged pipe that must be machined internally. The cylinder barrel is ground and/or honed internally.[edit]Cylinder Bottom or Cap
In most hydraulic cylinders, the barrel and the bottom portion are welded together. This can damage the inside of the barrel if done poorly. Therefore some cylinder designs have a screwed orflangedconnection from the cylinder end cap to the barrel. (See "Tie Rod Cylinders" below) In this type the barrel can be disassembled and repaired in future.[edit]Cylinder Head
The cylinder head is sometimes connected to the barrel with a sort of a simple lock (for simple cylinders). In general however the connection is screwed or flanged. Flange connections are the best, but also the most expensive. A flange has to be welded to the pipe before machining. The advantage is that the connection is bolted and always simple to remove. For larger cylinder sizes, the disconnection of a screw with a diameter of 300 to 600 mm is a huge problem as well as the alignment during mounting.[edit]Piston
The piston is a short, cylinder-shaped metal component that separates the two sides of the cylinder barrel internally. The piston is usually machined with grooves to fitelastomericor metal seals. These seals are oftenO-rings,U-cupsorcast ironrings. They prevent the pressurized hydraulic oil from passing by the piston to the chamber on the opposite side. This difference in pressure between the two sides of the piston causes the cylinder to extend and retract. Piston seals vary in design and material according to the pressure and temperature requirements that the cylinder will see in service. Generally speaking, elastomeric seals made fromnitrile rubberor other materials are best in lower temperature environments while seals made ofVitonare better for higher temperatures. The best seals for high temperature are cast iron piston rings.[edit]Piston Rod
The piston rod is typically a hard chrome-plated piece of cold-rolled steel which attaches to the piston and extends from the cylinder through the rod-end head. In double rod-end cylinders, the actuator has a rod extending from both sides of the piston and out both ends of the barrel. The piston rod connects the hydraulic actuator to the machine component doing the work. This connection can be in the form of a machine thread or a mounting attachment such as a rod-clevis or rod-eye. These mounting attachments can be threaded or welded to the piston rod or, in some cases, they are a machined part of the rod-end.[edit]Rod Gland
The cylinder head is fitted with seals to prevent the pressurized oil from leaking past the interface between the rod and the head. This area is called the rod gland. It often has another seal called a rod wiper which prevents contaminants from entering the cylinder when the extended rod retracts back into the cylinder. The rod gland also has a rod bearing. This bearing supports the weight of the piston rod and guides it as it passes back and forth through the rod gland. In some cases, especially in small hydraulic cylinders, the rod gland and the rod bearing are made from a single integral machined part.[edit]Other parts
- Cylinder bottom connection
- Seals
- Cushions
[edit]Hydraulic Cylinder Designs
There are primarily two styles of hydraulic cylinder construction used in industry: tie rod style cylinders and welded body style cylinders.[edit]Tie Rod Cylinders
Tie rod style hydraulic cylinders use high strength threaded steel rods to hold the two end caps to the cylinder barrel. This method of construction is most often seen in industrial factory applications. Small bore cylinders usually have 4 tie rods, while large bore cylinders may require as many as 16 or 20 tie rods in order to retain the end caps under the tremendous forces produced. Tie rod style cylinders can be completely disassembled for service and repair.TheNational Fluid Power Association(NFPA) has standardized the dimensions of hydraulic tie rod cylinders. This enables cylinders from different manufacturers to interchange within the same mountings.
[edit]Welded Body Cylinders
Welded body cylinders have no tie rods. The barrel is welded directly to the end caps. The ports are welded to the barrel. The front rod gland is usually threaded into or bolted to the cylinder barrel. This allows the piston rod assembly and the rod seals to be removed for service.A Cut Away of a Welded Body Hydraulic Cylinder showing the internal components
Welded body cylinders have a number of advantages over tie rod style cylinders. Welded cylinders have a narrower body and often a shorter overall length enabling them to fit better into the tight confines of machinery. Welded cylinders do not suffer from failure due to tie rod stretch at high pressures and long strokes. The welded design also lends itself to customization. Special features are easily added to the cylinder body. These may include special ports, custom mounts, valve manifolds, and so on.
The smooth outer body of welded cylinders also enables the design of multi-stage telescopic cylinders.
Welded body hydraulic cylinders dominate the mobile hydraulic equipment market such as construction equipment (excavators, bull dozers, and road graders) and material handling equipment (fork lift trucks, telehandlers, and lift gates). They are also used in heavy industry such as cranes, oil rigs, and large off road vehicles in above ground mining.
[edit]Piston Rod construction
The piston rod of a hydraulic cylinder operates both inside and outside the barrel, and consequently both in and out of the hydraulic fluid and surrounding atmosphere.[edit]Metallic coatings
Smooth and hard surfaces are desirable on the outer diameter of the piston rod and slide rings for proper sealing. Corrosion resistance is also advantageous. Achromiumlayer may often be applied on the outer surfaces of these parts. However, chromium layers may be porous, thereby attracting moisture and eventually causing oxidation. In harsh marine environments, thesteelis often treated with both anickellayer and a chromium layer. Often 40 to 150 micrometer thick layers are applied. Sometimes solidstainless steelrods are used. High quality stainless steel such as AISI 316 may be used for low stress applications. Other stainless steels such as AISI 431 may also be used where there are higher stresses, but lower corrosion concerns.[edit]Ceramic coatings
Due to shortcomings of metallic materials,ceramiccoatings were developed. Initially ceramic protection schemes seemed ideal, but porosity was higher than projected. Recently the corrosion resistant semi ceramicLunac 2+coatings were introduced. These hard coatings are non porous and do not suffer from high brittleness.[edit]Lengths
Piston rods are generally available in lengths which are cut to suit the application. As the common rods have a soft or mild steel core, their ends can be welded or machined for ascrew thread.[edit]Special hydraulic cylinders
[edit]Telescopic cylinder