Weijin Hot Chamber Die Casting Machine Troubleshooting
Fault Analysis and Trouble-shooting
Once there is an impending fault of die casting machine in its working course,operators should pay high attention to it, observe cool-headedly, judge the position and possible cause of the fault and determine the feasible maintenance method. The operator should note that, they should carry out the work in accordance with “Working Procedure” made by the company; no unprofessional operation is allowed for fear of greater accident. No matter for cold chamber die casting machine or hot chamber die casting machine, all machine faults can be handled as per the following procedures:
Enquire the fault discoverer and learn about the using condition and fault features when the fault occurs. When necessary, reproduce the fault phenomenon on the premise of ensuring equipments and personal safety.
The operational record and maintenance record of equipments shall be referred to.
On the premise of ensuring safety, make preliminary Judgment of fault position through voice-listening, smelling, feeling temperature and vibration and observing the exterior symptom of components, etc.
4.Acknowledgement of Fault Phenomenon
Test with measuring appliance; consult drawing and data; acknowledge the fault phenomenon and analyze reasons for the fault.
5.Determination of Maintenance Plan
Repair the machine and take measures to completely eradicate faults from the source.It is not enough to change components to resume production, source shall be found; sometimes the seemingly irrelevant phenomenon may be the real reason. Reasons for many faults are connected in a chain.
7.Trail Operation of Machine
Ensure that the fault has been removed; resume the production; ensure that the safety equipment is effective.
8.Record and Handover
The above-mentioned procedures are not invariable, especially the order can be changed according to maintenance worker’s degree of familiarity to the machine.
6.2.Fault Analysis and Maintenance Skill
1.Make full use of data and different instructions provided by the machine. Many items can provide plenty of useful information, such as indicator light of PLC (Industrial Computer), different indicator lights for reminding machine state and indicator lights for displaying and operating terminal,ampere meter, pressure gauge and PCB (Printed Circuit Board).
2.Do not be anxious to dismantle and replace before finding the reason; pay attention to finding the fault source. Ask more: Why does it break down? Otherwise the measures taken can only be palliative.
3.Find the hitting-point
Reason searching can be conducted from the first step to the last step or reverse lookup or pitching-in from the middle according to the action process of machine and the transformation process of signal, while the latter one can be more effective.
4.The trial operation of machine is indispensable, which can not only ensure the production but also ensure that the safety protection equipment is effective.
Faults can be commonly divided into the following classifications according to the fault reasons:
The improper adjustment of machine use, such as the improper parameter adjustment of pressure, speed, temperature, distance, position, flow, time, etc. These parameters are set with touch screen, digital dial switch, adjusting screw, adjustable potentiometer, hand wheel, keyboard and other hardware; changing the setting can resume the common faults of die casting machine and eliminate the faults.
If the machine and the requested production technology or peripheral equipment does not match, then another type can be changed to or production technology can be changed; sometimes it also can be achieved through reforming the machine, but which needs the support of professionals.
The machine maintenance is improper or uses the unmatched, easily damaged parts and other components.
The aging of the machine and the damage of components. It mainly occurs at the vice fitting surface of mechanical movement, the motion part of electric parts, the interface component of the circuit board of electronic component and sealing element etc.
The improper processing and assembling of the machine design; the hidden defects can be exposed in use.
6.4Guideline and Analysis of Maintenance Case
Such as: No Mould Locking
Press the mould locking button with manual operation, there is no operation of the hinge of the machine; close the door in place and press the mould locking of both hands with self-motion; there is still no operation of the hinge of the machine.
Please pay more attention to learn the following items:
★Action process of mould locking.
★Hitting-point in the action process of mould locking when checking.
★Checking methods of each step in the action process of mould locking.
★Checking method of each kind of component.
Other faults of different single action also can be checked with this mode.
★Actuating signal process of mould locking and oil valve:
Alternating current power supply of AC 220 V → Stabilized voltage supply (AC 220
V/DC 24 V) →Main control instruction →PLC input →PLC output →amplifier boards →Leading oil valve → Main oil valve→ Oil cylinder
★Flow signal process of mould locking and pressure:
Power supply of AC 220 V → Stabilized voltage supply (AC 220 V/DC 24 V)→Dual ratio amplifier board →Ammeter of pressure flow→ Signal output of PLC pressure flow → Proportional valve of pressure flow→ Overflow valve → Starting pressure
1.Check whether the indicator of mould locking signal output is on
2.When the indicator of mould locking signal output is off:
Check whether the computer input condition meets: check closing door in place with manual operation (or press the mould locking of both hands), mould locking button, sweeper return, thimble back to limit, action of loose core 1 and 2 being in place before mould locking and return in place after mould locking.
3.Check whether there is any signal in the input and output of amplifier board.
4.When the indicator of mould locking signal output is on:Check whether there is any pressure in the pressure gauge of chamber pressure.
5.When there is no pressure in the pressure gauge of chamber pressure:Check the flow setting of mould locking pressure; if the setting is right, then the fault will be handled as the system cannot act as the chamber pressure.
6.When there is some pressure in the pressure gauge of chamber pressure:Check the relay contact between the connection of mould locking valve and the closing door in place. The upper limit and back positioning of periphery sprayer; the back retreating limit of extractor.
7.When there is some pressure in the system and the mould locking is powered on.Check whether the valve element of mould locking valve is blocked. It can be judged through observing the mould locking pipeline.
8.Check whether the hinge is blocked.
9.Check whether the oil cylinder of mould locking is of serious leakage.
6.5.Common Fault and Trouble Shooting of Die Casting Machine
6.5.1.The machine cannot be mould locked or it can stop automatically after the mould locking for a while; it cannot be locked in place or the mould can be opened.
Possible reasons 1: Condition of mould locking is damaged.
(a) The front or back safety door is unclosed.
Fault elimination: Whether the door-closing is pressed in place or check whether the limit switch of safety door is pressed in place? Whether there is any damage occurring to the signal output or limit switch?
(b) No action of the oil valve of mould locking
(i) Check whether there is any signal output or the connection is loose.
(ii) Check the relevant oil valve in oil passage of mould locking, for example,whether the oil valve of mould locking, proportional valve, direction valve and others are blocked, or whether the electromagnet coil is damaged?
(iii) Whether the output pressure and flow (speed) is normal?
(c) The ejector pin does not go back to normal position.
Fault elimination: Whether the adjustment of ejection stroke is oversized and cannot be inducted? Whether there is signal of limit switch or the limit switch is damaged? Whether the relevant oil valve action in oil passage is ineffective or blocked?
(d) The sweeper does not go back to normal position.
Fault elimination: Check whether the limit switch losses efficacy or the air valve action is ineffective or blocked. The sweeper should be girded when the air operated is out of use for fear that the sweeper’s shocking to loose and hanging down which would results in false alarm.
Possible reasons 2: Fault of mould locking with low pressure
(i) Check whether there is any foreign material in mould or the closing is not so well.
(ii) The relevant parameter setting is improper for the mould locking with low pressure, for example: whether the alarm time with low pressure, pressure,position and other parameters are set properly?
Possible reasons 3: The hinge, undercut and steel are seriously damaged and blocked when they are moved to this position.
Fault elimination: Change the seriously worn components.
Possible reasons 4: There is some foreign material, abrasion or garland blocked in the rear section of oil cylinder for mould locking.
Fault elimination: Clean or replace it.
Conclusion: When faults occur, judge the fault position firstly by making use of the alarm and inspection functions of the machine and analyze relevant input and output conditions of the action. Fault reasons can be found and eliminated by inspection of electronic control elements and contacts, control of hydraulic transmission, executive elements and components, component and fitting condition of mechanical parts.
6.5.2.No mould-opening or the mould cannot be opened
Possible reasons 1: Relevant condition of mould opening is damaged.
(a) There is no action of the oil valve for mould opening
(i) Check whether there is signal output of each output point, or whether the connection point gets loose.
(ii) Check whether the relevant oil valve in oil passage of mould opening is blocked,or whether the magnet coil is damaged?
(iii) Whether the corresponding output pressure and flow (speed) of mould opening is right?
(b) The injection does not backward in place.
Fault elimination: Implement fault elimination according to the inspection method that the injection don’t backward in place.
Possible reasons 2: The installed mould is not adjusted as per the operation requirement; the mould locking is too tight and the shutdown time of mould locking is too long.
Possible reasons 3: The mould thickness was not readjusted after the mould temperature rises and expands, which results in that the mould locking force rises and it is difficult to open the mould.
Analysis: If the mould cannot be opened, after ruling out fault reasons caused by the damage of relevant condition for mould opening, we should pay more attention to whether it is caused by improper mould adjustment, too tight mould locking, too long time for mould locking, the temperature of mould and other reasons. As the thickness of mould is different, the mould space of die casting machine adopting hinge mode locking is adjusted by mould adjustment mechanism; adjust the mould space first, then adjust the mould locking force. When the hinge is unbend nearly, the mould folds exactly and the mould locking force is zero at this moment; conducting further mould locking, when the hinge is unbend completely, maximum mould locking force can be generated and locking can be done automatically. The mould will be condensed by hinge effect through the oil cylinder of mould locking, and the draglink (pull rod) will be stretched (both should be within the elastic range) at the same time. If the mould locking is too tight and the mould locking time is too long, the lubricating oil of the hinge will be extruded; under the condition of static pressure
produced by mould locking and dry friction of non-lubricating, the speed and pressure of mould opening will not be strong enough to open the mould. On the other hand,when the mould temperature rises and expands, the deflection of thermal expansion leads to additional increment of mode locking force, thus resulting in the fault of mould opening difficulty.
Fault elimination methods:
(i) Check the faults caused by other reasons except the relevant conditions of mould opening.
(ii) Enlarge the pressure and speed of mould opening; reopen the mould under manual operation after the lubricating.
(iii) Heighten the system pressure within the rated pressure of the system; recover the pressure and each relevant parameter of original system after opening the mould under manual operation.
(iv) As the mould adjustment is conducted under zero load condition, when the above-mentioned two methods are ineffective, the only thing can be done is to loosen the nut of front draglink of the cephalic plate; readjust and reinstall the nut after loosening the mould; adjust the degree of parallelism between the moving and fixed platen. Do not attempt to open the mould forcibly with mould adjustment mechanism under mould locking condition, or it will results in meaningless damage of the mould locking mechanism.
(v) Adjust the mould space and mould locking force as per the mould adjustment procedures strictly; When the trial operation of die-filling is done for a period of time, the mould temperature rises and expands and the mould locking force increases, pay attention to adjust the mould thickness timely to make the mould
locking force return to the original value and avoid the mould opening fault.
(vi) Reduce the downtime of mould locking; remember to open the mould before the downtime; do not shut down when the mould is locked tightly.
Possible reasons 4: The components of toggle link (or bending elbow) mechanism is worn or damaged seriously.
Fault elimination:Replace the seriously worn or damaged components.
Material leakage occurs occasionally; once the material leakage occurs, shut down and inspect the machine immediately; the machine can only continue operating after finding out the reason and being settled. The occurred position and possible reasons for material leakage:
Possible reasons 1: material leakage of the joint position between nozzle and gooseneck
(a) There is some deviation at the center of the water inlet and nozzle of the mould; after working for a period of time, it will result in that the joint position between nozzle and gooseneck loosens for material leakage due to repeated impact.
Fault elimination: Readjust the center. It is suggested that a locating ring should be installed during the mould design which is consistent with the perforation of cephalic platen.
(b) Manufacturing and quality problems. The nozzle and gooseneck does not match, which results in the material leakage.
Fault elimination:Dismantle the nozzle; clean the zinc material on the taper surface of nozzle firstly, then clean the zinc material in the taper hole of gooseneck;grind the two coordinating conical surfaces appropriately and reinstall the nozzle. If there is a top and bottom, the end region of nozzle should be amputated appropriately and regrinding shall be done.
(c) The incorrect nozzle installation results in mismatching of conical surfaces and material leakage.
Fault elimination: The correct installation method is to heat the gooseneck to a certain temperature (above 300℃ approximately), and fit the nozzle into the taper hole tightly. The insufficient heating temperature or the installation under normal temperature will result in that the coordinating conical surface looses and material leakage occurs when working under high temperature.
Possible reasons 2: material leakage at the joint of nozzle and the water inlet of the mould
(a) There is some deviation at the water inlet and nozzle center of the mould, and it is not aligned.
Fault elimination:Readjust the center.
(b) The water inlet and gooseneck of the mould does not match each other; There is some misfit in its water inlet angle and the circular degree and size of the hole.
Fault elimination: Retrofit the water inlet of the mould or replace the nozzle.Manufacture the water inlet of the mould and nozzle as per the standard.
(c) The nozzle buckling force is not enough during the material injection.
Fault elimination: Check and eliminate the oil passage fault of the nozzle buckling;enlarge the nozzle buckling force accordingly.
(d) There is some zinc liquid leakage at the nozzle top when the nozzle leaves.
Fault elimination: Clean the leaking zinc liquid; prolong the delay time of nozzle away or try to improve the cooling condition of water inlet.
Possible reasons 3:material leakage at parting face of the mould
(a) The mould position has not been adjusted well; The mould has not been locked tightly.
Fault elimination: Readjust the mould locking force.
(b) The hinge part is worn seriously, which results in the decline of mould locking force.
Fault elimination: Replace or repair the seriously worn components of hinge part.
(c) The degree of parallelism of mould itself is not so good or the mould is worn seriously after being used for many times.
Fault elimination: Modify the mould.
(d) The degree of parallelism between movable and fixed platen is not adjusted well or there is some deviation after using.
Fault elimination: Readjust the degree of parallelism between movable and fixed platen so as to meet the requirement.
6.5.4The plunger tip is blocked.
Analysis: As the plunger tip and injection sleeve are made under room temperature, the fit clearance is about 0.15 mm and the temperature is about 410℃ when working, the outer diameter of the plunger tip will expand due to heating and thermal expansion, while the swelling trend is small due to the wall thickness of injection sleeve and gooseneck; the working clearance between plunger tip and injection sleeve is only about 0.03～0.06 mm under this hot working condition. If the temperature is too high (above 450℃), it will further reduce the clearance between the plunger tip and injection sleeve, then the clearance fit will change into interference fit and the plunger tip will be blocked. Therefore, the reasons for the blocking of plunger tip are as follows:
Possible reasons 1:The pressure chamber and excessive furnace temperature result in the blocking of the plunger tip.
Prevention method: Control the temperature strictly. There are several aspects of reasons for the out of control of material temperature: thermocouple, temperature controller. Any fault caused by any of the three aspects will lead to the out of control of material temperature, so the material temperature should be judged
according to the surface condition of zinc liquid during the pressure casting; scrabble the scum on the surface of zinc liquid; if the liquid level is clear, of silver color and without hanging iron bar as well as the surface is of eremacausis scorification, it shows that the material temperature is appropriate; if the liquid level is dark red, it shows the oxidation scorification is fast and the furnace temperature is too high; or retest the material temperature with portable thermo-detector, reasons for excessive temperature need to be found from the above-mentioned three reasons and implement fault elimination when the temperature is above 430℃.
Possible reasons 2: There is too much scum on the zinc liquid surface of the crucible; the liquid level is too low.
Fault elimination: Scrabble the scum and add the zinc material in time to guarantee that the liquid level is not lower than 1/3 decimeter of the crucible.
Possible reasons 3: There is some installation error of the machine; the deviation between the axis of injection oil cylinder and the injection sleeve center of gooseneck is excessively large.
Fault elimination: Contact the manufacturer and deal with it.
6.5.5.No material injection
Possible reasons 1: Relevant conditions for material injection are damaged.
(a) The front and rear safety door are unclosed.
Fault elimination: Close the door or check whether the limit switch of safety door is pressed in place. Whether there is signal or damage of the limit switch.
(b) The mould locking process has not been terminated.
Check whether the die locking proximity switch is damaged or without signal.
Possible reasons 2: The limit switch of moving nozzle is not released or damaged.
We're Here to Help
No.20 Huafa Road Ronggui High Tech Industry Park Shunde District Foshan City Guangdong Province