Maintenance

Also called the "shot plunger" in the machine manual.

Removing the plunger

Do this when the melting pot or the gooseneck is being replaced:

1. Take out the injection plunger.
2. Ladle all the molten metal out of the melting pot.
3. Remove the gooseneck hold-down bolts and the gooseneck centre pin. (Required on DH-P50, DH-P60 and DH-P80; other models have hold-down bolts only.)
4. Remove the gooseneck yoke. (DH-P50, DH-P60 and DH-P80 only.)
5. Lay two steel tubes, 40–50 mm in diameter and 200 mm long, flat under the furnace. Turn the furnace stand screws to lower the furnace until it rests on the tubes.
6. Lift the gooseneck out, then push the furnace clear with the seat-release cylinder until the melting pot can be hoisted. Remove the melting pot clamps and hoist the pot out.

Note: The injection plunger differs by model. The available drawing is Fig. 2-75, “Plunger Tip and Shot Ring Clearance”. The source files for Fig. 2-76 (980830-1) and Fig. 2-77 (980831) have not been provided.

Preheating and fitting the plunger

Once the melt has reached the set temperature, hang the plunger in the melting pot and let the molten metal heat it for about 10 minutes before fitting it into the gooseneck. Preheating keeps the plunger from seizing inside the gooseneck. See Fig. 2-68, “Gooseneck Replacement Precautions” (source drawing not yet provided).

Why a plunger seizes in the gooseneck sleeve

The plunger has to be replaced or reworked when:

1. The charge is melted too fast, or the melt is hotter than the specified temperature.
2. The plunger is fitted without enough preheating, or is heated up too quickly.
3. Foreign metal has been mixed into the melt.
4. Contamination has built up on the plunger surface or inside the gooseneck sleeve.
5. The plunger fitted is the wrong size.
6. The gooseneck was fitted incorrectly, so the sleeve bore is not concentric with the plunger.
7. The plunger rings fitted are not to specification.

Freeing a plunger seized in the gooseneck sleeve

1. Set the temperature controller to 420 °C, start the machine and hold it with the mold closed.
2. Set injection pressure to 90 kg/cm². Close the injection speed valve, then open it about 1/4 turn. Open the plunger-return speed valve fully.
3. With your left hand, flick the mode selector from manual to full-auto, and immediately press start with your right hand. This produces a return (pull-back) stroke. Repeat several dozen times until the plunger comes free.
4. Once the plunger is free, return every pressure valve and speed valve you changed to its original setting.
5. Take the plunger out and wipe off the metal stuck to it. Mount it in a lathe and polish it with #200 abrasive paper until the scoring is gone. Check the groove depth at the plunger head against Fig. 2-75, “Plunger Tip and Shot Ring Clearance” before refitting it.
6. If the scoring is deep, the gooseneck sleeve bore is scored as well — replace the gooseneck and the plunger together. If the plunger still will not come free after several hundred cycles of step 3, replace the gooseneck, the plunger and the plunger rings.

Oil leaking at the injection cylinder rod

1. Take out the injection plunger.
2. Stop the hydraulic pump and switch off the machine power.
3. Open the pressure bleed valve and confirm the gauge reads zero.
4. Remove the four bolts from the gland ring at the cylinder rod. Turn the gland ring 90° or 180° counter-clockwise so its holes line up with the threaded holes in the cylinder head, then refit the four bolts.
5. Start the machine and run a few injection strokes in single-cycle mode to check for leaks. If it still leaks, repeat steps 1–3.
6. Refit the injection plunger.

Also called the "plunger ring" in the machine manual.

Ring wear and blow-by

Over a long casting run, the reciprocating plunger wears the plunger rings and the gooseneck sleeve. Metal then blows past the injection section of the gooseneck and casting pressure drops. When that happens, the plunger rings or the gooseneck must be replaced.

Rings of the wrong size

Plunger rings that are not to specification are one of the reasons a plunger has to be replaced or reworked.

When the rings must be replaced

If the plunger shows deep scoring when it is removed, the gooseneck sleeve bore is scored as well — replace the gooseneck and the plunger together. If the plunger still cannot be pulled free after several hundred release cycles, replace the gooseneck, the plunger and the plunger rings as a set.

For why a plunger seizes in the gooseneck sleeve and how to free it, see 1. Injection Plunger.

Replacing the melting pot and the gooseneck

For the melting furnace and gooseneck assemblies, see Fig. 2-69, Fig. 2-70, Fig. 2-71, Fig. 2-72, Fig. 2-73, and Fig. 2-74.

1. Take out the injection plunger.
2. Ladle all the molten metal out of the melting pot.
3. Remove the gooseneck hold-down bolts and the gooseneck centre pin. (Required on DH-P50, DH-P60 and DH-P80; other models have hold-down bolts only.)
4. Remove the gooseneck yoke. (DH-P50, DH-P60 and DH-P80 only.)
5. Lay two steel tubes, 40–50 mm in diameter and 200 mm long, flat under the furnace. Turn the furnace stand screws to lower the furnace until it rests on the tubes.
6. Lift the gooseneck out, then push the furnace clear with the seat-release cylinder until the melting pot can be hoisted. Remove the melting pot clamps and hoist the pot out.

Refitting the melting pot and the gooseneck

With the gooseneck removed and the melting pot pulled out, refit or replace them as follows:

1. Set the melting pot back in place and secure it with the clamps.
2. Set the gooseneck back in place and insert the centre pin into its hole. Check that the pot outlet lines up with the centre of the gooseneck throat; move the furnace to adjust if needed.
3. Pull the centre pin back out, raise the gooseneck nozzle end, press the throat packing into place, align the gooseneck and lower it.
4. Line up the gooseneck centre pin hole, drive the pin in and tighten the four hold-down bolts.
5. Fit the packing on top of the gooseneck, put the yoke over it and tighten the yoke bolts.
6. The furnace is now hanging free — adjust the stand screws until they bear on the base plate, then lock them with the nuts.
7. Start the burner, melt the charge and set the melt temperature. Note: the thermocouple probe must sit 150 mm below the metal surface.
8. Once the melt reaches the set temperature, hang the plunger in the melting pot and let the molten metal heat it for about 10 minutes before fitting it into the gooseneck. This keeps the plunger from seizing inside the gooseneck. See Fig. 2-68, “Gooseneck Replacement Precautions” (source drawing not yet provided).

Leakage at the injection section of the gooseneck

Over a long casting run, the reciprocating plunger wears the plunger rings and the gooseneck sleeve. Metal then blows past the injection section of the gooseneck and casting pressure drops. When that happens, the plunger rings or the gooseneck must be replaced.

Reworking the nozzle seat bore of the gooseneck

Over a long casting run, the nozzle repeatedly contacts and separates from the mold, which enlarges the nozzle seat bore in the gooseneck. Metal then leaks at the joint between gooseneck and nozzle, and an oversize nozzle must be fitted.

Long exposure to the flow of molten metal also erodes the injection tube bore, which leaks at the joint between tube and gooseneck. When that happens, rework the tube seat bore in the gooseneck and fit an oversize injection tube.

For why a plunger seizes in the gooseneck sleeve and how to free it, see 1. Injection Plunger.

Replacing the melting pot and the gooseneck

For the melting furnace and gooseneck assemblies, see Fig. 2-69, Fig. 2-70, Fig. 2-71, Fig. 2-72, Fig. 2-73, and Fig. 2-74.

1. Take out the injection plunger.
2. Ladle all the molten metal out of the melting pot.
3. Remove the gooseneck hold-down bolts and the gooseneck centre pin. (Required on DH-P50, DH-P60 and DH-P80; other models have hold-down bolts only.)
4. Remove the gooseneck yoke. (DH-P50, DH-P60 and DH-P80 only.)
5. Lay two steel tubes, 40–50 mm in diameter and 200 mm long, flat under the furnace. Turn the furnace stand screws to lower the furnace until it rests on the tubes.
6. Lift the gooseneck out, then push the furnace clear with the seat-release cylinder until the melting pot can be hoisted. Remove the melting pot clamps and hoist the pot out.

Refitting the melting pot and the gooseneck

With the gooseneck removed and the melting pot pulled out, refit or replace them as follows:

1. Set the melting pot back in place and secure it with the clamps.
2. Set the gooseneck back in place and insert the centre pin into its hole. Check that the pot outlet lines up with the centre of the gooseneck throat; move the furnace to adjust if needed.
3. Pull the centre pin back out, raise the gooseneck nozzle end, press the throat packing into place, align the gooseneck and lower it.
4. Line up the gooseneck centre pin hole, drive the pin in and tighten the four hold-down bolts.
5. Fit the packing on top of the gooseneck, put the yoke over it and tighten the yoke bolts.
6. The furnace is now hanging free — adjust the stand screws until they bear on the base plate, then lock them with the nuts.
7. Start the burner, melt the charge and set the melt temperature. Note: the thermocouple probe must sit 150 mm below the metal surface.
8. Once the melt reaches the set temperature, hang the plunger in the melting pot and let the molten metal heat it for about 10 minutes before fitting it into the gooseneck. This keeps the plunger from seizing inside the gooseneck. See Fig. 2-68, “Gooseneck Replacement Precautions” (source drawing not yet provided).

Removing the injection tube and the nozzle

The nozzle is held on the injection tube (shot sleeve) by a taper fit. To remove it, first heat the assembly so that the zinc inside melts. Tap the nozzle lightly with a hammer, then tighten the nozzle removal nut against the nozzle to force it off the tube.

Fitting the injection tube and the nozzle

Before fitting a new nozzle, clean the tapered faces of both the injection tube and the nozzle. Preheat the tube, fit the nozzle and seat it with a few taps of a mallet.

Leakage at the joint between injection tube and gooseneck

Long exposure to the flow of molten metal erodes the injection tube bore and causes leakage at the joint between tube and gooseneck. When that happens, rework the tube seat bore in the gooseneck and fit an oversize injection tube.

Also called the "shot nozzle" in the machine manual.

When to replace the nozzle

The nozzle is pressed against the mold for long periods, so the contact face gradually dents. Once it no longer seals tightly against the sprue bushing of the mold, molten metal can spray out during injection — replace the nozzle at that point.

The nozzle must also be changed when its bore does not match the bore of the mold sprue bushing.

Standard nozzle dimensions differ by machine model. See Fig. 2-60 (DH-P20–DH-P200) and Fig. 2-61 (DH-P250 / DH-P300). For nozzle and sprue troubleshooting, see Fig. 2-66. For nozzle-to-die dimensions, see Fig. 2-67.

How to replace the nozzle

The nozzle is held on the injection tube by a taper fit. To remove it, first heat the assembly so that the zinc inside melts. Tap the nozzle lightly with a hammer, then tighten the nozzle removal nut against the nozzle to force it off the tube.

Before fitting a new nozzle, clean the tapered faces of both the injection tube and the nozzle. Preheat the tube, fit the nozzle and seat it with a few taps of a mallet.

Changing the nozzle position

Applies to DH-P80 and smaller. See Fig. 2-62, “Shot Port Position Change”.

1. Every machine has two nozzle positions: one at the centre of the front platen (b) and one just below the centre of the front platen (a). Changing between them only requires adjusting the three points where the clamping unit joins the machine base — the nozzle itself stays fixed.
2. Remove the striker block of the seat-release limit switch. See Fig. A.
3. Remove the seat-release tie rod nut and the retaining spring pin. See Fig. B.
4. Loosen the support screw so that the support seat clears the column slide bar by a suitable distance. See Fig. C.
5. Adjust the front platen position with the mold-lifting frame or the crane. See Fig. E.
6. Remove the split pin and the pin from the saddle guide rod, adjust the front platen up or down until the saddle guide rod enters the correct position, then refit the pin and split pin. See Fig. D and F.
7. Hold the rear platen in position with a hydraulic jack (customer-supplied). See Fig. G.
8. Remove the stopper plate and the pulley block shaft, adjust to the correct position with the jack, then reassemble. See Fig. H.
9. Tighten the support screw to secure the support seat, and refit the striker block of the seat-release limit switch in the correct position. See Fig. I and J.

DH-P100, DH-P125 and DH-P150 without seat lift

1. Loosen the spacer block and its hold-down bolts, hoist the gooseneck with the crane, place the spacer block and hold-down in the new position, then lower the gooseneck gently back in and secure it. See Fig. 2-63, “Shot Position Gauge Block”.
2. Adjust the position of the melting furnace, turning the three furnace bolts evenly until it sits correctly. See Fig. 2-64, “Shot Position Change and Pot Clearance”.

Additional note: models with a submerged gooseneck and no seat lift (P130, P160, P190 and similar) use a fixed nozzle position, so no change is needed.

DH-P125 – DH-P500 with hydraulic bed

1. After loosening the seat-lift support rod bolts, the saddle guide rod pin, the seat-release tie rod pin and the seat-lift support rod plate can all be removed. (Turn the support rod bolt counter-clockwise no more than 3–5 turns, just enough to loosen it; otherwise the support drops to the bottom of the machine and cannot be retrieved.)
2. Operate the seat-lift cylinder to raise the assembly slowly and evenly to the required position, then fit the spacer block. See Fig. 2-65, “Hydraulic Machine Shot Position Change”.
3. Put the parts from step 1 back in position and tighten them.

Oil specification

The standard hydraulic oil for this machine is CPC grade 46AW. Do not change to another type of oil. Replace the oil whenever it loses viscosity or the tank is dirty; as a rule, change it once a year.

Where possible, use a water-based fire-resistant hydraulic fluid to reduce the risk of fire. For storage and handling of the oil itself, follow the data sheet from the oil supplier.

Topping up the oil

1. Oil loss is normally caused by leaks. Repair the leak first, then top the oil back up.
2. Use clean equipment for topping up, and add oil of the same grade.
3. Only top up with the machine stopped and the pressure bled off.
4. Clean the filler cap before removing it to add oil.

Draining the oil

Before an oil change, disconnect the lowest fitting in the circuit so that the old oil drains out completely, then work through the following:

1. Switch off the machine power so that the hydraulic pump stops and the machine comes to rest.
2. Open the pressure bleed valve and confirm the gauge reads zero.
3. Open the filler cap, remove the filler screen, put the suction hose of a transfer pump into the tank and pump the oil out.
4. Disconnect the lower fittings of each hydraulic cylinder so that the oil inside drains out.
5. Remove the suction strainer on the pump inlet inside the tank so that the oil in the pump drains out. Clean the strainer and refit it.
6. Clean all sludge out of the tank.

Flushing the hydraulic circuit

1. Once the machine is fully drained, pour about 80 L of circuit flushing oil into the tank. (Ask your hydraulic oil supplier which flushing oil to use.)
2. Remove the injection plunger and open the injection speed valve about 1/8 turn. Set mold open / close and ejection speeds to slow.
3. Start the hydraulic pump and run the machine in continuous full-auto for about two hours.
4. Stop the machine and drain the flushing oil completely, following the procedure above.

Filling with new oil

1. Clean the transfer pump and filling equipment, then pump new oil into the tank until the sight glass shows full.
2. Start the machine and run it in full-auto for about 10 minutes.
3. Stop the hydraulic pump, open the pressure bleed valve, wait for the gauge to read zero, then top the oil back up to the normal level.
4. Refit the filler screen and tighten the filler cap.

Day-to-day oil management

1. Correct level on the sight glass: mid-glass while the pump is running.
2. Never mix in any oil other than the specified grade.
3. If injection speed is erratic or injection is unusually loud after an oil change, loosen the bleed fitting on top of the injection cylinder to release trapped air.
4. Keep the oil below 50 °C. Check the oil temperature regularly, and check the cooling water to the oil cooler.

Hydraulic oil cooler

High-pressure compression and high-speed flow generate friction heat that raises the oil temperature, so a cooler is fitted to bring it back down.

Points to watch:

1. The cooler needs an adequate flow of water at 25 °C or below.
2. Oil temperature is regulated by adjusting the cooling water flow.
3. In cold climates, drain the water out of the cooler when the machine is shut down, so that freezing does not damage it.

The high-pressure hoses on this machine are steel-braid reinforced rubber hose, either bare or with an outer stainless braid. A PVC sleeve may be added depending on the specification and the application. Points to watch:

• Storage: keep dry and out of direct sunlight.
• Temperature: normal working temperature is around 100 °C.
• In use: stay within the rated working pressure, burst pressure and bend radius for the hose specification.
• Service life: under normal use a hose lasts 5 to 8 years. Replace it as soon as it leaks or loses its flexibility — a burst hose is dangerous.

What the strainer does

The strainer sits in the tank on the suction side of the hydraulic pump. It stops dirt in the oil from being drawn into the pump and shortening its life. Clean it on a regular schedule.

The suction strainer filters dirt and debris out of the hydraulic oil before it reaches the pump. It protects pump life and prevents hydraulic faults, so keeping it clean matters.

Cleaning interval

• First clean: after 50 running hours.
• After that: every 500 running hours, or immediately if the hydraulic pump becomes noticeably noisy.

Clean with kerosene or diesel, then blow dry with an air gun.

Removing and cleaning the strainer

1. Stop the hydraulic system and switch off the machine power.
2. Clean around the pump suction flange on the tank, then take out the strainer.
3. Remove the pump suction flange and take out the strainer.
4. If the machine runs water-based hydraulic fluid, wash the strainer in water; if it runs mineral oil, wash it in clean diesel or kerosene. Blow it dry with compressed air before refitting.
5. Replace the strainer if the mesh is damaged anywhere.
6. Watch the O-ring on the flange when removing and refitting the strainer.

Inspection interval

Check the nitrogen pressure in the accumulator every three months.

Checking the nitrogen pressure

Work through the following in order:

1. Stop the hydraulic pump.
2. Open the pressure bleed valve, wait for the gauge to read zero, then close the bleed valve again.
3. Remove the charging port cap on top of the accumulator and fit the charging gauge assembly to the port. (Keep the side handle of the gauge assembly closed.)
4. Turn the handle on the gauge assembly clockwise. Once the charging valve opens, the gauge shows the current nitrogen pressure.

Standard nitrogen pressures:

• Clamping side: 59 kg/cm²
• Injection side: 46 kg/cm²

1. After checking or recharging, turn the handle counter-clockwise, then loosen the side handle to vent the gas trapped in the gauge assembly.
2. Remove the gauge assembly and refit the charging port cap.

Points to watch

1. Charge the accumulator only to the specified nitrogen pressure.
2. Use nitrogen (N₂) only.
3. If the gauge needle falls slowly and steadily to zero after the pressure bleed valve is opened, the bladder inside the accumulator has failed and must be replaced.
4. If the needle does not fall at all after the bleed valve is opened, either the injection speed valve is closed or the hydraulic pump is still running.
5. To check whether the gauge itself has failed, open the pressure bleed valve and see whether the needle returns to zero.
6. Nitrogen pressure should be 65 % of the working pressure. Read the clamping and injection pressure settings in use, and set the accumulator to 65 % of that.
7. Close the pressure bleed valve again once the pressure has been released.

For accumulator inspection and maintenance, bladder replacement and charging instructions, see Appendix 1 and Appendix 2.

Accumulator inspection and maintenance

Gas pressure must be held steady and checked regularly. Check the nitrogen with the PC (pre-charge) kit; as a rule, inspect every part on a regular schedule. The PC kit is used to inflate the bladder after maintenance and during charging. It connects through a dedicated hose to a pure nitrogen cylinder or to an SPN250 nitrogen pump. Use pure nitrogen only — oxygen or any other gas can cause an explosion.

Nitrogen pressure check procedure

Checking the nitrogen pressure is straightforward. The correct procedure is:

1. Release the system pressure to zero, then release the hydraulic pressure inside the accumulator to zero.
2. Remove the protective cap and the gas valve cap.
3. Fit the PC kit and confirm the valves are safe. (A is not tightened, bleed valve B is tightened, C is tightened.)
4. Connect the accumulator gas valve to D.
5. Turn valve A slowly until the gauge pressure rises. If the pressure is correct, continue as follows:
   1. Open valve A.
   2. Open bleed valve B.

If the nitrogen pressure is too high

Turn valve A slowly until the gauge pressure rises, then vent slowly through bleed valve B until the gauge shows the required pressure, and close valve B.

Charging or resetting the pre-charge pressure

If the accumulator has to be charged or the pressure raised (nitrogen pressure too low), proceed as follows:

1. Fit the PC kit as in the nitrogen pressure check procedure.
2. Connect the PC kit to the nitrogen cylinder.
3. Connect the cylinder to valve C of the PC kit with the hose.
4. Open the cylinder valve slowly until the gauge reads slightly above the required pressure, then close it.
5. Loosen valve A to release the pressure inside the PC kit to zero, and open bleed valve B.
6. Remove the hose without turning valve D, and refit the cap on valve C.
7. Close the bleed valve and wait at least five minutes for the accumulator temperature to settle.
8. Turn valve A until the gauge pressure rises; the reading should now be above the target pressure.
9. Trim the pressure down with the bleed valve, then remove the PC kit.
10. Test the gas valve for leaks with soapy water.
11. Refit the gas valve cap and the protective cap.

The accumulator is now ready for use.

Machine lubrication points

For lubrication points on smaller machines, see Fig. 2-58. For larger machines, see Fig. 2-59.

Air filter / regulator

The air filter removes dust and moisture from the air supplied by the compressor and sets the working pressure of the pneumatic circuit. There is a push button on the underside of the unit: press it to drain the water that collects in the bowl.

Kerosene burner

Starting up

1. Check the fuel tank and fill it if the level is low.
2. Open the manual valve in the fuel line.
3. Open the burner air damper to about 1/3.
4. Set the working range of the temperature switch or pressure switch first.
5. Press the burner power switch. The burner purges the furnace with air for about 10 seconds, then ignites as the fuel solenoid valve opens. If the air damper is open too far the flame blows out, so adjust the damper gradually — the smoke density at the stack tells you when it is right.
6. After the burner starts, bleed the air valve on the fuel pump and close it again once no more air comes out.

Once the burner is running, watch for the following

1. Any fuel leaks in the pipework.
2. Whether the burner note stays steady.
3. Smoke density at the stack (how well the air is matched):
   • Normal: almost no smoke
   • Black smoke: not enough air
   • Red flame shooting out of the stack: too much air
   • White smoke: the melting furnace has cracked
4. If the flame goes out during operation, find the cause first. Then press the red reset button on the burner control relay before pressing the power switch to restart.
5. Normal fuel pump pressure is 7–9 kg/cm².

Routine maintenance

1. Drain sludge and water out of the fuel filter bowl regularly, and clear any debris from the bottom of the bowl.
2. Clean the fuel nozzle and the flame eye regularly so that they do not clog with fuel residue.
3. Clean the diffuser disc in front of the nozzle whenever soot or fuel residue builds up on it.
4. Do not tamper with the fuel pump or the burner control relay.
5. Clean the fan blades and the fan housing every six months.

Note: Keep the area below the air intake clear of loose material such as plastic bags or newspaper — anything drawn in can start a fire.

Mold open/close cylinder and seat-release cylinder

If oil leaks at the piston rod, deal with it in this order:

1. With the mold closed, stop the hydraulic pump and switch off the machine power.
2. Open the pressure bleed valve and confirm the gauge reads zero.
3. Remove the four bolts from the gland ring at the cylinder rod. Turn the gland ring 90° or 180° counter-clockwise so its holes line up with the threaded holes in the cylinder head, then refit the four bolts.
4. Start the machine and run mold open / close (or seat advance / retract) a few times in manual to check for leaks. If it still leaks, repeat steps 1–3.

Injection cylinder

If oil leaks at the injection cylinder piston rod, see "Oil leaking at the injection cylinder rod" under 1. Injection Plunger.