Is a bigger case injection molding machine always safer?

Answer: No. Past 40 percent over demand, vents see excessive pressure and clamp hydraulics waste power.

If the trial shot flashes, is tonnage short?

Answer: Usually. Flash over 0.2 mm at the rim and opposite the gate points to clamp force; one corner only means parallelism.

Can a robot cover a 20 mm stroke shortfall?

Answer: No. Without stroke the part cannot clear the cavity, and no robot reaches the parting line.

How do I estimate power cost?

Answer: Multiply per-part draw by volume. At 3.2 kWh and 50000 parts, a servo machine spends 96000 yuan on power.

Should I buy a used case injection molding machine?

Answer: Yes, after three checks: scored tie bars, parallelism, screw wear. A screw worn past 0.3 mm loses 8 percent shot.

Is 800 Tonnes Enough? Checking a Case Injection Molding Machine

Quick answer: Judge a case injection molding machine by four measurements: clamp force over projected area, tie-bar clearance against mould width, shot size against part weight, and the weight spread over 30 shots. Hit all four and a smaller press will do.

Tonnage has to be back-calculated from projected area
Mould height and opening stroke: does the tool fit
Screw and shot size: what part weight leaves you
Cycle, power and repeatability: one hour of data
What belongs on the acceptance sheet
FAQ

1. Tonnage has to be back-calculated from projected area

An instrument case plant in Changzhou was quoted a case injection molding machine of 800 tonnes. The first trial shot left a 0.4 mm flash line at the lid rim, and three rounds of tool polishing did not close it.

The tool was fine. This body projects 1.05 m by 0.45 m, or 0.47 square metres. At 25 MPa cavity pressure, clamp force must reach 11.75 MN, or 1200 tonnes; with a 1.15 factor, 1400 is the honest answer. An 800 tonne press covers 0.32 square metres. Divide tonnage by projected area and case moulds land at 25 to 30 MPa; below 22 MPa flash opens at the rim.

Projected area	Cavity pressure	Clamp force	Machine	Typical error
0.32 sq m	25 MPa	8.0 MN	800 t	Copying a big case down
0.47 sq m	25 MPa	11.8 MN	1200 t	Trialling on 800 t
0.47 sq m	30 MPa	14.1 MN	1400 t	Shallow-cavity pressure
0.60 sq m	25 MPa	15.0 MN	1500 t	Tonnage without gate area

2. Mould height and opening stroke: does the tool fit

On this 1200 tonne case injection molding machine the tie bars stand 810 mm apart and the mould is 760 mm wide, leaving 25 mm a side.

Case Injection Molding Machine: a closed case seen from the front, translucent body showing the cavity, two black latches beside the handle

The platen range runs 300 to 900 mm against a 620 mm stack, leaving 40 mm of adjustment. Opening stroke gets missed: a 320 mm deep box needs 640 mm plus 80 mm for removal, or 720 mm, against a rated 700. Twenty millimetres short keeps the robot off the parting line, parts come out by hand and the cycle grows 15 seconds. Ejection travel of 180 mm against 60 mm passes, provided pins clear the corners where a 6 mm wall whitens.

Item	Machine	Tool needs	Margin	Verdict
Tie-bar spacing	810 mm	760 mm	25 mm a side	Tight
Mould height	300 to 900 mm	620 mm	40 mm	Pass
Opening stroke	700 mm	720 mm	minus 20 mm	Fail
Ejection stroke	180 mm	60 mm	120 mm	Pass

3. Screw and shot size: what part weight leaves you

Shot size is chosen backwards from part weight. This body weighs 2.4 kg against a 3200 g shot, a 75 percent ratio inside the 60 to 80 percent band. Past 85 percent the screw runs out of stroke and the base picks up a cloud pattern; below 40 percent the melt degrades.

A 75 mm screw at 22 to 1 and 2.4 compression suits polypropylene with 10 percent glass, which needs a bimetallic barrel or the screw scores in three months and shot weight drops 8 percent. The box cools in 95 seconds and plasticises in 18, so 77 seconds of idle screw time allows a 10℃ drop; at 110 seconds the machine is the bottleneck.

4. Cycle, power and repeatability: one hour of data

An hour of running exposes a case injection molding machine faster than any brochure. Log cycle time, part weight, one critical dimension and oil temperature across 30 shots.

Case Injection Molding Machine: a black closed case at an angle on white, black handle along the top, hinges and pale inner layer at left

The baseline is a 210 second cycle, 95 of them cooling. A 2.8 second dry cycle saves 0.8 seconds a shot against 3.6, or 1200 parts a year at 400 shots a day.

Power divides wider. A 55 kW servo machine draws 3.2 kWh per part; a fixed-pump machine of the same tonnage draws 75 kW and 4.4 kWh, or 36000 yuan a year more at 50000 parts. Repeatability shows as a weight spread under 0.3 percent over 30 shots, about 0.05 mm of wall; past 0.8 percent, check the ring. Keep oil at 45℃ plus or minus 2℃, since a 4℃ drift moves dimensions 0.1 mm.

5. What belongs on the acceptance sheet

Four items can be measured on the spot: clamp force within 5 percent of the nameplate, platen parallelism within 0.05 mm over 1 m, dry cycle within 0.3 seconds of the quote, barrel zones within 3℃ of set point. Three are noise: imported servo, German technology, lifetime service.

Item	Pass line	How to measure	If it fails
Clamp force	Within 5 percent	Pressure or strain gauge	Recut area to measured force
Parallelism	0.05 mm over 1 m	Feeler gauge, four corners	Ask for platens to be reground
Dry cycle	Within 0.3 s	Stopwatch, three runs	Convert the gap into output
Barrel zones	Within 3℃	Contact probe, top to bottom	Replace bands or couples

Conclusion

Tonnage, mould space, shot size and repeatability are all measurable; none is a feeling. A case injection molding machine proves itself in the first hour: whether flash appears, whether the weight drifts.

This article discusses only the container (case body) side of specifications and design intent, and does not cover any handling, loading or use of the contents.