Guide Lines for Hydraulic Press Selection - By: Naveen Tch

Before discussing about the guide lines for hydraulic press selection, discuss about what is hydraulic press and it’s working principal after that discussing about guide lines.

What is Hydraulic Press

Hydraulic Press Manufacturers is combination of a large and a small cylinder connected by a pipe and filled with a fluid so that the pressure created in the fluid by small force acting on the piston in the small cylinder will result in a large force on the large piston. The operation depends upon Pascal's principle, which states that when a liquid is at rest the addition of a pressure (force per unit area) at one point results in an identical increase in pressure at all points,i.e. uses the hydraulic pressure to compress anything.

Hydraulic Press Exporter has the ability to deliver full pressing force anywhere in the range of stroke. This improves the overall functionality of the hydraulic press.

Machine consisting of a cylinder fitted with a piston that uses liquid under pressure to exert a compressive force upon a stationary anvil or base plate. The liquid is forced into the cylinder by a pump. The hydraulic press is widely used in industry for forming metals and for other tasks where a large force is required. It is manufactured in a wide variety of styles and sizes and in capacities ranging from 1 ton (0.9 metric ton) or less to 10,000 tons (9,000 metric tons) or more.

Guide Lines

Hydraulic presses are available in many types of construction which is also true of mechanical presses. There are many factors to consider when deciding between a hydraulic and mechanical press. These include stroke length, actual force requirements, and the required production rate.

1. Long Stroke Lengths can be an Advantage:
Since the stroke length can be fully adjustable, long stroke lengths provide for ease of setup and flexibility of application. The full stroke may be used to open the press up for
the installation of dies. In production, the stroke length can be set as short as possible to provide for stock feeding and part ejection while maximizing stroking rates.

2. Hydraulic Press Speeds
Most press users are accustomed to describing press speeds in terms of strokes per minute. Speed is easily determined with a mechanical press. It is always part of the machine specifications. The number of strokes per minute made by a hydraulic press is determined by calculating a separate time for each phase of the ram stroke. First, the rapid advance time is calculated. Next the pressing time or work stroke is determined. If a dwell is used that time is also added. Finally the return stroke time is added to determine the total cycle
time. The hydraulic valve reaction delay time is also a factor that should be included for an accurate total time calculation. These factors are calculated in order to determine theoretical production rates when evaluating a new process. In the case of jobs that are in operation, measuring the cycle rate with a stopwatch is sufficient. Most hydraulic presses are not considered high speed machines. In the automatic mode, however, hydraulic presses operate in the 20 to 100 stroke per minute range or higher. These speeds normally are sufficient for hand fed work. The resulting production rate speeds are comparable to that of mechanical OBI and OBS presses used single stroking applications. Here, there is no additional clutch and brake wear to consider in the case of
the hydraulic machine.

3. Force Requirements
When choosing between a mechanical or hydraulic press for an application a number of items should be considered. The force required to do the same job is equal for each type
of press. The same engineering formulas are used.

4. Machine Speed
There is always a possibility that an existing job operated in a mechanical press requires 20 to 30 % more force than the rated machine capacity. The overloading problem may
go unnoticed, although excessive machine wear will result. If the job is placed in a hydraulic press of the same rated capacity, there will not be enough force to do the job. Always make an accurate determination of true operating forces to avoid this problem.
The forming speed and impact at bottom of stroke may produce different results in mechanical presses than their hydraulic counterparts. Each material and operation to form it has a optimal forming rate. For example, drop hammers and some mechanical
presses seem to do a better job on soft jewelry pieces and jobs where coining is required. In some cases, a sharper coined impression may be obtained at a rapid forming rate. In deep drawing, controllable hydraulic press velocity and full force throughout the
stroke may produce different results. Often parts that cannot be formed on a mechanical press with existing tooling can be formed in a hydraulic press that has controllable force
throughout the press stroke and variable blank holder pressure as a function of the ram position in the press stroke.

5. Accessories
Most hydraulic press builders offer many control options and accessories. These include:

1. A distance reversal limit switch which is preset for the depth of ram stroke for automatic return to the top of stroke position.

2. A pressure reversal switch which is set for the highest force delivered before the ram returns automatically to the top of stroke.

3. Automatic or continuous cycling controls which are used in conjunction with automatic feeding equipment.

4. Dwell timers which are adjustable, and are set to open the press after a pre-set dwell period.

5. Ejection cylinders or knockouts which can be actuated at a preset position, time, or pressure.

6. Rotary index tables and other work positioning devices often powered by the press hydraulic system.

7. Hydraulic die cushions which have the advantage of taking up less space than air cushions while offering controllable programmable resistance throughout their
travel.

8. Press Quality
Since the applications for hydraulic presses ranges all the way from simple hand pumped maintenance a press, to machines having very high force capacities, types of construction and desirable features varies accordingly.

Here are just a few design and construction questions that will provide a basis for comparison of one machine with another.
Frame: Compare the weight if possible. Try to determine the character of the frame construction. If a weldment, look at the plate thicknesses, extent of ribbing, and stress relieving.
Cylinder and slide construction: The cylinder size, type of construction used, and availability of service parts are important. Also determine how well the ram travel is guided.
Maximum System Pressure: The pressure at which the press delivers full tonnage is important. The most common range for industrial presses is from 1000 psi (6,894 kPa) to 3000 psi (20,682 kPa). Some machines operate at substantially higher pressures. Higher pressures may accelerate wear. Make sure that replacement parts are readily available.

Horsepower: The duration, length, and speed of the pressing stroke are the major factors that determine the required horsepower.
Speed: Take the time to calculate the speed based on the operations you intend to perform. There are wide variations in hydraulic press speeds.

About the Author

Hydraulic Press Manufacturers and Hydraulic Press Exporter

Article Directory Source: http://www.articlerich.com/profile/Naveen-Tch/188408

Additional Articles From - Home | Business | Material handling