Maintain Plastic Injection Molds with Ultrasonic Cleaning

Maintain Plastic Injection Molds with Ultrasonic Cleaners

Companies involved in the production of products produced by plastic injection molding are well aware of the costs of dies used to produce their products.  According to this U.S. manufacturer, plastic injection molds can range from $1,000 to $80,000 and more, with an average mold price of $12,000.  These costs provide a substantial incentive to maintain plastic injection molds thereby prolonging service life.

Ultrasonic cleaners provide a way to clean costly injection molding dies and their components in a timely and cost-effective fashion that doesn’t cause wear or require harsh chemicals. In this article we detail how ultrasonic cleaning can address your plastic injection mold cleaning challenges.  It includes a case study describing real-life operations.

Cleaning Challenges for Maintaining Plastic Injection Molds

As noted above, injection molds used to form plastic products can represent sizeable investments and are characterized by complex shapes, precision finishes and vents. 

For example, different molds have different surface tolerances.  Customer-demanded tolerances for a mold surface can be as precise as 0.0002 inch.  That’s why longer injection mold life depends highly on keeping them clean and conducting mold cleaning operations in such a way that extends their life by maintaining surface finish tolerances.

Manually cleaning to maintain plastic injection molds, no matter how carefully applied, cannot access complex shapes, vents, dumps and other mold surface configurations.  Moreover, manual methods such as brushing with solvents run the risk of damaging surfaces, thereby rendering the mold unusable.

These are among the reasons why ultrasonic cleaning is the optimum way to extend injection mold life.

Why Ultrasonic Cleaning Works Best for Plastic Injection Molds

Ultrasonic cleaning uses a process called cavitation – the implosion of billions of microscopic air bubbles – against surfaces immersed in a cleaning solution. 

Bubbles are created by generator-powered transducers bonded to the underside of a stainless-steel tank. When excited the transducers vibrate at ultrasonic frequencies measured in kilohertz (kHz) per second. This causes the tank bottom to act as a membrane creating the bubbles.

The implosions blast loose and carry away contaminants on any surface immersed in the cleaning solution. The process is fast, safe and does not damage products that can be safely immersed in a biodegradable water-based cleaning solution.

While indiscernible to the naked eye the size of these cavitation bubbles varies based on the ultrasonic frequency employed.  Lower frequencies such as 25 kHz create (comparatively) larger vacuum bubbles that implode more vigorously against surfaces and are generally used for removing stubborn contaminants; higher frequencies such as 45 kHz create (comparatively) smaller bubbles that more easily penetrate cracks, crevices and machined holes.

An Ultrasonic Cleaning Cycle for Plastic Injection Molds

The Ultrasonic Cleaner

While ultrasonic cleaners come in several forms and sizes, in this case we describe an industrial ultrasonic cleaner used  by PAM Injection Molding as described in an article published in Plastics Today.

The Elmasonic X-tra ST unit has a 15-gallon tank capacity with internal dimensions approximately 20 x 13 x 14 inches deep. 

Note that tank dimensions should be selected based on the size of parts being cleaned. Many molds are constructed as interchangeable modules that can be configured to make multiple parts and can be disassembled for the cleaning cycle.

Operating features  that make this unit particularly attractive enable users to select either a 25 or 45 kHz ultrasonic frequency based on the extent and tenaciousness of burned on plastic residues.  

For really tough deposits on plastic injection molds operators can activate what is called the “pulse mode” that sends a more powerful blast of cleaning action into the bath. Pulse is also activated to degas fresh ultrasonic cleaning solutions in order to quickly remove cavitation-inhibiting trapped air.

A continuous “sweep mode” provides a slight ± variation in ultrasonic frequency that serves to avoid harmonic distortions resulting in areas of high or no cavitation. Too much intensity can possibly damage highly finished injection mold surfaces.       

In addition to frequency and pulse the control panel allows operators to set cleaning cycle time and cleaning solution temperature. Set and actual parameters are displayed. The unit will start when the set temperature is reached and can operate continuously with auto shut-off at 12 hours or if the solution temperature reaches 90⁰C.

An optional insulated or standard lid helps muffle noise during the cleaning cycle and reduce cleaning solution evaporation.

A Plastic Injection Mold Cleaning Cycle

Biodegradable cleaning solution concentrates are formulated for specific cleaning tasks. An example is Omega Mold Release Agent concentrate with a recommended dilution rate to 10 to 1 with water.   

A mold cleaning cycle is quite straightforward: 

  • After filling the cleaning tank halfway with water the correct amount of concentrate is added then water is added to the fill line.
  • The unit is turned on and the pulse mode activated to mix and degas the solution.
  • Time and temperature parameters are set. A typical cycle is 30 minutes at a temperature of 50 to 60⁰C.
  • Disassembled modules are carefully positioned in the basket, taking care that they are not in contact with each other.
  • Lower the basket into the tank and close the lid. Cleaning starts automatically and will shut off at the end of the timed cycle.

At the end of the cycle parts are removed, rinsed, dried and inspected. If all is satisfactory the molds are put back in service.

Cleaning Solution Maintenance

Contaminants removed during the cleaning cycle accumulate in the solution, which eventually must be drained and replaced. Spent solution should be stored and disposed of following local regulations.  At this time the tank should be cleaned following user manual instructions before being refilled with fresh solution.

Benefits of Ultrasonic Cleaning Plastic Injection Molds

In addition to being easier on the molds and assisting with maintaining plastic injection molds, there are added benefits to using ultrasonic cleaners, such as the Elma X-tra ST, for cleaning plastic injection molds. 

Once a cleaning cycle routine is established, personnel simply load components in the basket, set the cleaning parameters and are free to attend to other tasks. They no longer have to spend time manually cleaning these intricate and costly molds. The ultrasonic equipment can do a job in about 30 minutes average – a task that could take hours if done manually.