Secondary Process Equipment for Profile Extrusion
Just as diverse as profile extrusion, secondary operations during the in line process to achieve special affects or functions are equally diverse. Below are examples of various secondary operations that are performed to enhance or produce functional characteristics of a desired end product.
Surface patterns are Embossed onto the soft plastic to simulate the look of other natural materials, impart a uniform surface texture or to hide small defects in the plastic. A steel engraved embossing roll is positioned in line to force the embossed pattern onto the soft plastic surface. The embossing roll is usually temperature controlled to ensure uniform consistency in the embossing pattern. Because the plastic surface must be soft to accept the embossing, generally the embossing process occurs after the die but before the part is cooled. Some exceptions are to re-heat the surface enough downstream to impart a mild emboss pattern or an embossing tool can be forced into the surface of ridged foam by crushing the material.
Laminating a film onto the surface of a part is commonly used to apply a printed pattern, create a weather resistant surface or to apply other protective layers. The film is often introduced between the die and the first cooling tool. Excellent adhesion is achieved from the heat of a part and where the cooling tool acts to apply the pressure needed to fuse the two surfaces. Lamination can also be affectively achieved downstream utilzing rollers and adhesive applied to the part after it is hard.
Holes, slots or other cut outs are often created in line. An specially designed rotary or sequencing punch is placed in line with the part after the last cooling tank and before the puller. An example of this process is the punching of the nail slots in vinyl siding.
Similar to in-line punching, other fabrication processes can be implemented using special cuts, drills, routers or other tooling for fabrication during the extrusion process.
Post Forming (Belling)
Thermoplastics can be re-heated and then re-shaped. This process is used to transform post formed shapes into extruded parts. An example of this is pipe where the end is heated and then forced over a belling mandrel to form a larger diameter. Another example is the post forming of window profiles to be able to make curved or arched windows.
Co-extrusion – Downstream
Co-extrusion normally occurs at the die, however, it is possible to apply a second material downstream after the rigid part is formed and cooled. The surface of the cooled part must be reheated enough to allow the second material to adequately adhere to the part. This is commonly done when applying flexible barbs onto a rigid window profile.