Used Up-Acting Hydraulic Presses for Sale
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About Used Up-Acting Hydraulic Presses
The platen rises into a tool bolted overhead, and the part stays in a nest the operator can load. That upward close is what an up-acting press is for. The cylinder sits under the bed instead of in a crown, which is the opposite of a shop C-frame dropping a slide through a throat. Molding, compression, and a lot of bonded assembly were built around the rising motion. A downward ram will not drop into a fixture that expects the lower half to move. Air-over-oil machines also push upward and can hold for a long time, but a single-acting cylinder is a poor stripper, so ask whether you get real pullback.
Daylight is the open space the mold must occupy before anything moves. Closed height is how near the two members come with the tool installed. Stroke has to include the loading position, not only the thickness of the charge. On a four-post frame the fixture also has to pass between the columns, clamps included. Tonnage is still piston area times pressure, available along the rise rather than at one crank angle. Molding compounds often want a fast close and a much slower press, plus time at pressure. A bump, or breathe, lets gas escape. Heated platens, when the job needs them, bolt to both members and have to be wired for the temperature you actually run.
Guiding matters because an off-center cavity tries to cock the rising platen. Bushings on the posts, and whether that wear is even, tell the story separately from the oil. The upper member has to accept the fixed half of the tool. Return speed is not pressing speed, and it is what sets how fast the operator can unload. A rising platen can trap a hand the same way a falling ram can, so two-hand buttons or a light curtain still have to interrupt the motion. An intermediate plate, common on larger molding frames, changes daylight when it is left in and should be measured both ways.
A used up-acting press should be cycled empty, then asked to hold a force while you watch for drift. Milky oil, a weeping hose, and a noisy pump are the usual repairs. Scored posts are not. Lawton is the builder you will meet most often on this kind of four-post molding frame. Meadoworks takes them from closed press rooms and from consignments. Bring the fixture height and the width between the columns. A clean paint job will not add daylight the posts do not have, and the platens need a truck once they leave the floor.
How to Choose a Used Up-Acting Hydraulic Press
Upward Close Versus a Down-Acting C-Frame
Load the part on the lower platen and let that platen come up when the fixture was built that way. Molding, compression, and a lot of assembly work follow that habit. A down-acting gap machine does the opposite: the slide comes from above and the throat is open for long stock.
If operators need to reach through a C-frame all day, this motion is the wrong one. If the tool is a mold or a nest that sits on the bed, measure the posts before you compare tons. Direction of travel is the decision. Force comes after it. A single-acting upward cylinder that cannot pull back will also struggle to strip.
Posts, Daylight, and Dwell
On a four-post frame the fixture has to live between the columns, not only under the tonnage. Daylight has to swallow the open tool. Closed height has to reach the part. Stroke has to include loading, not only the pressing distance itself.
Ask whether the control can hold at pressure, and whether it can bump to let gas out. Bonding and many molding steps need time, not only force. A machine that only trips to a hard stop will not replace a timer. Then check that the platen stays parallel, because an off-center cavity leaves flash or a crooked assembly. Heated platens are a separate circuit from that timer.
Up-Acting Hydraulic Press Specs to Compare
| Spec | Why it matters |
|---|---|
| Tonnage and direction | Confirm the platen rises. A down-acting machine with similar tons is a different motion and a different tool. |
| Daylight and closed height | The mold or nest has to fit while open and still reach the working position when the platen rises. |
| Column spacing | A four-post frame will not accept a fixture wider than the clear opening, whatever the tonnage. |
| Stroke | Travel has to clear the operator's load position, not only the thickness of the material. |
| Press speed and dwell | Molding and bonded work often need a slow press and time at pressure, not a single trip. |
| Platen size | The tool bolts to the platens. Large tonnage on a small platen still will not fit the mold. |
Tonnage and direction
Confirm the platen rises. A down-acting machine with similar tons is a different motion and a different tool.
Daylight and closed height
The mold or nest has to fit while open and still reach the working position when the platen rises.
Column spacing
A four-post frame will not accept a fixture wider than the clear opening, whatever the tonnage.
Stroke
Travel has to clear the operator's load position, not only the thickness of the material.
Press speed and dwell
Molding and bonded work often need a slow press and time at pressure, not a single trip.
Platen size
The tool bolts to the platens. Large tonnage on a small platen still will not fit the mold.
What to Inspect on a Used Up-Acting Hydraulic Press
Confirm the platen rises
Cycle it empty. If the slide comes down from a crown, you are looking at a down-acting machine.
Measure between the posts
The fixture, the mold, and the clamps have to pass. Tonnage does not widen the opening.
Check bushings and columns
Scored posts or loose bushings let the platen cock. Off-center molding makes that wear obvious.
Hold pressure at the top of the rise
Set a force below the nameplate and watch for drift. Seals and valves announce themselves here.
Look at both platens
Dings, a dish, or a pulled tapped hole change how the tool sits and how the part forms.
Read oil and listen to the pump
Milky oil, a howl, or a wet fitting is a hydraulic repair before the ram can be trusted.
Test the safety circuit
Two-hand buttons or a light curtain should interrupt the rise. A bypassed circuit is not a minor note.
Related Equipment
- Hydraulic Presses
Family overview of gap, straight-side, and up-acting frames
- C-Frame / Gap
Down-acting open throat when you need three-side access
- Straight Side
Guided downward slide when the die must stay parallel
Up-Acting Hydraulic Presses Brands We've Sold
Common Applications
Frequently Asked Questions
Why does an up-acting press push the ram upward?
The cylinder sits below and drives the lower platen up into a fixed upper tool. The part stays in a nest at a height the operator can load, which is why molding and assembly cells use this motion. A down-acting machine drops a slide from the crown instead. If the fixture was built for a rising platen, a conventional C-frame will not be a substitute. Confirm the direction on a dry cycle before you compare tonnage. Also ask whether the cylinder can pull back, because a single-acting rise is weak at stripping.
Is an up-acting press used for molding and assembly?
Often, yes. A mold, a heated platen, or an assembly nest sits on the lower member and the close is upward. Time at pressure matters for a lot of those jobs, so check that the control can hold, not only trip. Some compounds also need a bump so gas can leave. This is still a press, not an injection molding machine. There is no screw and no shot size. If you need to inject resin, you need a different machine. If you need to close a tool and hold it, the rising platen is the right motion.
How do I read daylight on an up-acting press?
Daylight is the open gap the fixture must fit before the platen moves. Closed height is how near the two members come with the tool installed. Stroke is the travel between those positions, and it has to include room to load the part. Stack the mold, the part, and the clamps, then compare. Enough tons with a short opening will not accept the tool. Column spacing is the other limit on a four-post frame. If an intermediate plate can be left in or pinned up, measure daylight both ways.
How is an up-acting press different from a down-acting C-frame?
Direction and access. This platen rises. A C-frame ram comes down through an open throat, which is better for long stock and quick hand work from three sides. The upward frame, especially with four posts, surrounds the tool with columns and favors a fixture that lives on the bed. Both can hold cylinder force through the travel. They are not interchangeable just because the tonnage matches. Pick the motion the tool was built around, then check that the posts actually clear it.
What should I check on the columns of an up-acting press?
Look for scoring, uneven bushing wear, and a platen that rocks when you push it by hand at rest. Off-center molds load one column harder than the others, and the wear will not be symmetrical. Measure the clear opening against your fixture, not against a photo. A bent or deeply scored post is a machine-shop repair, not a hose. Also confirm both platen faces are flat enough for the tool you plan to bolt on. Heat, if the platens are heated, is a separate check of the zones and the wiring.
Can an up-acting press hold force through the rise?
Yes, when the relief valve and the control allow a setpoint before the end of travel. That is the advantage over a crank. Molding and bonded work often add a dwell on top of that force, and sometimes a bump. Confirm both on the actual panel. A machine that only slams to a hard stop will not give you time at pressure. Cycle it, set a force below the nameplate, and see whether the platen stays put. Return speed is a different number from that pressing speed.
