How to clean properly when maintaining injection molds?
Mold cleaning is a key process in mold maintenance and also a bottleneck restricting mold maintenance. Because the speed of mold manufacturing and development is much faster than the speed of mold cleaning, and the mold needs to be prepared for the next production immediately after rapid cleaning, the time left for mold cleaning is quite limited. Through the investigation of the factory, it was found that the molds arranged in the corridors and workshops in the factory almost occupied the limited operating space of the workshop, just waiting to be cleaned.
Some companies directly reset the mold after the first production without any cleaning treatment and continue to use it for reproduction. If the plastic parts produced are clean, it means that there is no problem with the operation of the mold. Over time, a cultural concept of "temporary firefighting" will be formed within the company. Only when the accumulated residue in the mold affects the quality of the parts or the mold wears, the mold needs to be cleaned, and the cleaning process is just passing by.
Some factories will hire some junior technicians or apprentices in the mold workshop to do some chores of cleaning the mold and template when cleaning and repairing the mold, and then the maintenance technician will separate the mold and template. But in fact, when cleaning molds and templates, the marks will be washed away, making it difficult for maintenance technicians to find and correct mold and part defects.
Admittedly, cleaning molds does not require the talents of a senior mold maker, but it is completely inconsiderate to let a novice who is not familiar with the special functions and defects of the mold or the characteristics of the key sealing area of the mold be responsible for mold cleaning. Because the unreasonable distribution of mold cleaning work will lead to the continuous production of molds with performance defects, and because of the increase of grouting, burrs, corners, premature electroplating or steel displacement, mixed molds, etc., it will also greatly increase the mold budget. Such problems often stem from the maintenance culture of "temporary firefighting", which never monitors or accounts for defects, nor finds the root cause of the problem.
Standardized cleaning procedures
Systematic mold maintenance is based on maintenance requirements and the continuity of maintenance operations. In order to achieve the goal of "cost-effectiveness", it must be noted: Develop a detailed mold cleaning plan. When cleaning different parts of the mold, such as internal cleaning of the press, edge cleaning, general cleaning and cleaning of the main part, different cleaning methods are used.
After the mold has been running for a certain period of time, technicians can determine the procedure and frequency of mold cleaning by visual inspection of electroplating wear, magnetic marks, and the content of residues in the vent and non-vent areas of the mold. Therefore, it is very important to understand the cycle of safe operation of the mold and archive observation reports of residual accumulation and wear in the mold.
Since the mold has a certain operating cycle, all molds should be accompanied by relevant maintenance procedures and maintenance cycle documents. Generally speaking, controlling the internal grease level and the operating conditions of moving parts such as pull teeth, sliders, inner shaft pins and bushings is the key to ensuring stable production. Other factors that affect production include contamination or blockage of water lines and water spray nozzles, leakage of manifolds, rust and corrosion caused by water leakage or condensation, etc. What degree of cleanliness is enough?
Usually after the molding process operation is completed, dirt or residue (with certain chemical composition and physical properties) will be left on the mold. Depending on the type of residue, the requirements for cleaning are also different. Resins such as PVC will produce hydrogen chloride gas, which will corrode various types of mold steel.
Other residues are separated from flame retardants and antioxidants, which will corrode steel. Some pigments and colorants can cause steel to rust, and rust is difficult to remove. Even ordinary sealing water can damage the mold if it is left on an untreated mold surface for too long.
So the mold should be cleaned according to the established production cycle. Each time the mold is removed from the press, the mold's air holes should be opened first, and all the oxidized dirt and rust in the non-critical areas of the mold and template should be removed to prevent it from slowly corroding the steel surface and edges. In many cases, even after cleaning, some uncoated or rusted mold surfaces will soon rust again. So, even if you spend a lot of time brushing unprotected molds, surface rust cannot be completely avoided.
Now many molds have "self-cleaning" vents with a high gloss. Clean and polish the vent to a polish level of SPI#A3, or discharge the residue to the garbage area of the vent by milling or grinding to prevent the residue from adhering to the surface of the roughing mill stand. But if the operator manually polishes the mold with a coarse-grained scrubbing pad, emery cloth, sandpaper, grinding stone or nylon bristle, brass or steel brush, it will cause excessive "cleaning" of the mold.
Generally, when using hard plastic, glass beads, walnut shells, aluminum balls, etc. as abrasives for high-pressure grinding and cleaning of mold surfaces, if these abrasives are used too frequently or improperly, this grinding method will also cause pores on the mold surface, resulting in more mold residues, wear or premature damage or burrs, which is more unfavorable for mold cleaning.
Therefore, by finding cleaning equipment suitable for molds and processing technology, and referring to the cleaning methods and cleaning cycles recorded in the archived files, more than 50% of maintenance time can be saved and mold wear can be effectively reduced.