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Texturing Methods for Injection Mold Cavity Surfaces

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One part of the injection mold manufacturing process that frequently gets overlooked is texturing.  It’s important to realize that any part made from an injection mold will naturally take on the texture of the mold surface, and this natural texture may not be suitable for a given application.  For this reason, texture is a significant consideration for manufacturers during the production process and it’s essential to establish the right techniques to have the desired finish.

Over time, a system of textures has been established to make them easy to identify and classify.  Knowing this system makes it possible for a manufacturer to accurately communicate what type of texture is necessary for any given part and ensure that the finished product matches the original design.

Another way to ensure that your finished product meets your specifications is to work with a trusted material supplier who has the knowledge and expertise to help manufacturers familiarize themselves with various processes critical to their success.

What is injection molding?

The injection molding process involves making parts through the injection of melted plastic resin into a mold.  Commonly used materials are plastics, thermoplastics and other advanced polymers.  Whichever material is going to be used, it will be fed through and mixed in a heated barrel, then injected into the cavity of the mold, where it will harden into the desired configuration. 

A critical part of the injection mold process is designing the mold itself.  The molds are generally made of metal, usually aluminum, stainless steel or alloyed mold steels, precisely machined to exact dimensional specifications.  The injection molding process is commonly used for the manufacture of various parts and components in a wide range of sizes, from tiny electronic parts to entire automotive panels.

When it comes to the texture, a lot of factors impact the finished surface.  This includes the original design of the mold, materials being injected, dimensions and features of the finished part, mold material and the tonnage of the injection mold press.  The texture plays an important role in the surface finishing and thus impacts on the reliability, performance, and durability of the part.

What is the texturing process?

Mold surfaces can incorporate a wide variety of texturing.  Examples include stripes, wood or leather grains, satin, sand and even images.  Prior to beginning the texturing process, it’s critical that the mold cavity be thoroughly cleaned to ensure there is no oil, grease or other foreign substance that could affect the texture.

Next, sealing needs to be applied to the areas of the cavity surface that will not be exposed to the texturing media.  This will be placed directly on the cavity and consist of adhesive paper, caulk or a corrosion resistant coating.  If a coating is used enough time must be allowed for the coating to dry.  Absorbent cotton can be used to take away any unwanted moisture and provide one last round of cleaning.

At this point, the texturing takes place.  Again, it’s good to remember the fact that any molding process will result in the part being textured.  Chemical etching is the most common form of texturing, and the most popular etchants are ferric chloride (FeCl3) or nitric acid (HNO3).  The etching is usually performed using the flow or dunk method.  The flow method involves allowing the etchant solution to run across and off the mold cavity surface, while the dunk method involves submerging the cavity into a tank of etchant solution.

Laster etching is another popular method.  It uses thermal ablation to impart the texture pattern onto the mold surface without the use of chemicals.

Next, sandblasting takes place. This will eliminate any excess liquid in the cavity and fine-tune the gloss of the texture.  The level of texture can even be controlled based on the coarseness and material of the sand that is used and the pressure with which it is applied.

Finally, it’s important to cleanse the part and add any corrosive resistant coatings that may be required.  This will help preserve the new texture and enhance the durability of the finished product.

It’s important to note a few other factors that can impact the part’s texture and how well it will hold up over time.  First, especially when dealing with steel, the metal’s acid resistance is an important factor.  With further regards to the acid, the ratio of acid within the resin material also matters.  The higher the ratio, the longer the texture will last.  Finally, the pressure of the injection molding also helps determine the part’s durability.

Aluminum can be etched using the same methods as steel but reacts more quickly to the etchants.  The chemical reacting taking place during etching is exothermic, producing heat and raising the etchant temperature; this further increases the corrosive effect of the process.  Solution temperature and exposure timing are critical to a successful aluminum texturing process.

For more information on texturing for injection mold cavity surfaces, the knowledgeable and friendly sales team at Clinton Aluminum is ready to help. Contact us today for assistance with your injection mold needs.

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