All mold tools are expensive and easily prone to damage and corrosion if they are not maintained properly. In most injection molding shops, the mold storage area often houses a considerable capital investment, often running into millions of pounds.
Before a mold is stored it should be checked for any repairs that are necessary and these should be carried out before the next time the mold is used, A few simple precautions will make sure the mold is in good order for the next time it is required, A basic checklist is as follows:
- The mold should be cleaned and serviced.
- Waterways should be blown out with air.
- The mold should be lubricated.
- Vents should be cleaned.
- All molding surfaces should be sprayed with a mold protective
- All safety switches should be checked for damage and correct function,
- All electrical circuitry should be checked for safety and function- Molds should be stored closed if possible ,if this is not possible, the two mold halves should be protected with a wooden or similar cover to prevent damage.
It is foolish to wait until a machine breaks down before carrying out maintenance. It may also be unwise to do major maintenance work just because a planned maintenance schedule says that the date for doing it has arrived. However, Murphy’s law of cussedness states that a breakdown will always occur at the most inconvenient time- If the breakdown prevents the execution of a large and profitable order，the loss incurred may be much greater than the cost of carrying out planned maintenance.
Some maintenance items should be checked daily: i.e.， hydraulic oil levels，lubrication, leaks on pressure lines, hose connections，plastic mould and electrical wires, including thermocouple leads. Every week the machine should be cleaned down and the oil checked for cleanliness. A little less frequently， thermocouples should be checked by inserting the tip in boiling water and making sure that it indicates 100°C. Timers can occasionally be checked by a stop watch and the screw non-return valve checked for leakage.
Any reports of malfunctioning should be noted and the first convenient opportunity taken to put them right. Among the items that should receive regular, though not necessarily frequent, inspection is tie bars，tie bar bushes，carriage tracks and bushes，toggle link bushes，and lever pins. Hydraulic cylinders should be checked for leakage at the glands. If any undue wear is apparent，time may be saved at a crucial moment by taking the first available opportunity to put matters right. If this procedure is followed，it should not be necessary to carry out the planned maintenance exercise of stripping equipment and replacing worn parts at intervals of six or twelve months. However，a minute inspection of all working parts of the machine at three-montly intervals will generally pay dividends in ensuring steady production.
Nothing is more frustrating than having to wait for parts to be sent from a distant supplier. The agent will often be able to recommend which items are most likely to fail and should be kept in stock. Often money is well spent in this respect as a great deal of time can be saved in waiting for spares. There is a good case for having several machines in the moulding shop from one supplier as this obviates the necessity for carrying too many spares. It is not always good practice，however，to “tool up”，with only one make of machine, particularly in the custom-moulding field. Not all machines have the same versatility and having only one make can be a limitation. However, it is very unwise to go to the other extreme and have a dozen different makes. Perhaps three different makes in a factory of 25 or 30 machines is a good compromise，particularly from the point of view of storing spare parts.
Planned maintenance concerns not only the injection moulding machines. All ancillary equipment, such as mould temperature controllers, granulators, stacking or conveying equipment，is also important. The main factory water-cooling installation should also be cleaned annually and de-scaled if necessary. In this respect, too, occasional descaling of mould coolant channels and cooling channels on the machine oil coolers can bring nothing but benefit.