Secondary Operations

Just as profile extrusion can be as diverse as the need requires, the things that are done to the profile in line with the extrusion process can be as diverse as the need. Various examples of what is commonly done today are outlined below.

Embossing

Embossing a surface pattern onto the soft plastic is done to make the plastic look more like wood, or to impart a uniform surface texture, or to hide small defects in the plastic. In each case, a steel engraved embossing roll is positioned to force the emboss pattern into the soft plastic surface. The embossing roll is usually temperature controlled to ensure consistency. Since the surface of the plastic must be soft to accept the embossing, this is generally done right after the die and before the part is cooled. However, it is possible to re-heat the surface enough downstream to impart a mild emboss pattern. The exception to the need for a heated surface is a rigid foam where the embossing tool can be forced into the surface by crushing the foam.

Laminating

Laminating a film onto the surface of a part is often done to apply a printed pattern such as a wood grain pattern, or to apply a weather resistant surface onto a non-weather resistant substrate, or to apply a protective film. The film is often introduced between the die and the first cooling tooling where excellent adhesion can be achieved with the heat of the part and where the cooling tooling acts to apply the lamination pressure. Lamination can also be done downstream after the part is hard with the use of an adhesive between the film and part, and rollers to apply the film.

Hole Punching

Punching holes, slots, or other cut outs in a part is often done in line. A specially designed rotary or sequencing punch is placed in line with the part, usually after the last cooling tank and before the puller. Probably the best example is the punching of the nail slots in vinyl siding.

In-line fabrication

Just like in-line punching, other fabrication can be achieved if the volume justifies building the necessary fabrication equipment. Special cuts, drilling special holes, routing out shapes, or other fabrication can be done in line.

Post forming (Belling)

Thermoplastics can be re-heated and then re-shaped. This fact is used to post form shapes into extruded parts. The best example is pipe where the end is heated and then forced over a belling mandrel to form a larger diameter to be able to accept the end of a similar pipe without the need for a special fitting. Another example is the post forming of window profiles to be able to make curved or arched windows.

Co-extrusion – downstream

Co-extrusion is normally done 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 be adequately adhered to the part. This is commonly done when applying flexible barbs onto a rigid window profile.