6 PVC Compound Variables

Pellet Colores Tubo Ensayo MIN

The purpose of this article is for our customers and visitors to understand the process involved in choosing the right PVC compound and all the external PVC compound variables that need to be considered.

Even though in our site we've defined what's a PVC compound and how to choose the best for you, we'd like to mention some external factors that you as a manufacturer might have oversighted along your manufacturing process. This aspect have a great impact on the formulation itself.

 

1.- PVC compound variables: machine type and condition

 

We could state that everything starts when making the decision of whether to buy a new machine or a refurbished one. Let's remember that a cheap, and previously used machine, can eventually represent additional hidden costs and might not be the best to manufacture a premium product. On the contrary, there might be certain markets where product quality demands are not so strict and where PVC compound is pretty easy to fuse and process. In this case a second-hand equipment might make sense.

In disregard of your equipment's age, it's always good to regularly give it maintenance in order to control one of the main PVC compound variables.

Among the PVC compound variables there are adaptations that we can apply to our old machines, such as the inclusion of meshes in the head of an extruder, which will allow us to better fuse the PVC compound. However, a worn out equipment will generally bring us greater problems in the process and will generate greater waste. In case of not achieving proper fusion, you can include a more closed mesh or add up to 2 or 3 of these. Just remember, a higher of meshes will increase the internal compression and might damage your equipment.

it is very important that the PVC manufacturer understands and communicates its supplier, the following process variables:

 

PVC Extrusion process variables:

 

  1. Screw length to diameter ratio: a larger machine represents higher PVC melt residence time which promotes fusion.
  2. Screw type: Screw type: there are mixing screws, coveying screws, single or twin screw. These differences will have great impact of how to process plastics.

    Variables del Compuesto de PVC: Tipo de Extrusora
    Depending on your extruder condiiton it may be easier or not to achieve proper fusion.
  3. Screw Compression Ratio: Normally for PVC compounds, screws with a compression ratio of 2:1 and 3:1 are used. This relationship describes the proportion or volume of material that fits in the screw at the beginning of the extruder compared to the end of the screw.
  4. Does the equipment has room for extruder screens? How many are used and what mesh size are they?
  5. Whether or not there is a gas extraction chamber: when the PVC compound is transformed, it releases hydrochloric acid, which in turn serves as a catalyst in its degradation.
  6. The extruder usually has an ammeter to be able to control and monitor the torque exerted during process. This is a great guide not only for the formulator but also as input elements to establish a statistical process control.
  7. Extruder's motor capacity: a machine with a low torque capacity may be suitable for Flexible PVC but not for rigid PVC. It is always important to clarify to the equipment manufacturer what type of PVC your planning to produce.
  8. You need to control and monitor extruder RPM's.
  9. Guarantee that temperatures readings from the pyrometers correspond to reality. You have to know that these differ from the melt temperature as PVC compound has poor heat transfer. The extruder must also have an efficient cooling system that allows to maintain stable temperatures, even after hours or days of work.

Switching to the injection process, in which fusion gets easier due to the compression exerted by the process, it is important for the producer to know the following variables involved:

 

PVC injection process variables:

 

  1. Length and compression related to the screw: this is a similar concept than in the extrusion section but not as critical. Here we normally have a conveying screw that, during back pressure load, gives the necessary friction to the mass.
  2. Injection capacity: It will never be the same to inject rigid compared to flexible PVC. Manufacturers must make sure their equipment is made for both to avoid process stoppage.

    Inyectora de Plástico
    It is important to know all process parameters and capabilities.
  3. Mold cooling: The most important thing is that the inner part of the mold, or the "heart", has a mirror surface finish and good polish without imperfections. This will determine the quality of the injected pieces. Likewise, a stable and homogeneous cooling in the mold will help to avoid adhesions, deformed parts, stuck parts or flow marks in the finished product.

It is very important that the customer knows his equipment and that they communicate all these details to their supplier. At Chemical Compounds we offer technical service and we collect the relevant information for PVC compound tailor-made developments.

 

2.- PVC Compound Variables: Additives added during process

 

Sometimes producers fail to communicate if their PVC compound is mixed with some type of recycled material, filler, lubricant or masterbatch during the process. This information help to accurately design PVC compounds for you. In fact, this is one of the PVC compound variables that can determine success or failure during field tests. So we recommended to be transparent with your technical advisor. Correct communication will result in a faster solution and cost savings.

 

3.- PVC Compound Variables: Customer's product quality and process control

 

Other PVC compound variables involve getting to know process control and internal quality parameters which we could classify as follows:

  1. Raw material control: sometimes customers request a certain pellet size and appearance (brightness or opacity) characteristics that are controlled from the supplier's process.
  2. Process control: customers are often used to certain process conditions and do not want to change them for various reasons, such as keep work as simple as possible. Some examples are: process temperatures, injection speed, extrusion speed or cooling time.
  3. Finished product control: Involves the weight of each piece produced, surface appearance, color, gloss or opacity.

It is of great importance that the transformer identifies these process variables and how they affect their customer.

 

4.- PVC Compound Variables: Finished Product Quality Control

 

This category of PVC compound variables include finished product quality controls that are carried out by the quality team. Giving some examples we have:

  1. Mechanical and physical test - What are elongation and tensile strength requirements?
  2. Fast aging test - Product life cycle
  3. Chemical attack test - Any chemical substance can detriment PVC properties?
  4. Toxicity test - Free from heavy metals
  5. Odor test - How stringent are color match requirements?
  6. Migration test - Does it appears with contact withm any other material?
  7. Hardness test - How flexible or hard does it has to be?
  8. Impact resistance test - Minimum impact resistance to avoid crushing
  9. Transparency test - Is it opaque or transparent?
  10. UV resistance test - Product warranty

These are some examples of avaialble tests that can be performed on a finished product and that your customers might require.

Calidad para controlar las variables del compuesto de PVC

 

5.- PVC Compound Variables: regulation compliance

 

International organizations are increasingly placing restrictions on PVC plastic, forcing producers to find less risky alternatives for the community and the environment. Some of these are the FDA (for its acronym in English, Food and Drug Administration) or REACH (Registration, Evaluation, Authorization and Restriction of Chemicals). These institutions constantly establish regulations of a toxicological nature and force PVC additives and PVC compounds manufacturers to migrate to safer alternatives.

It is important that you are aware of these regulations based on your market and communicate them to your supplier. We would like to mention that at Chemical Compounds we use chemical additives for the PVC industry that are non-toxic, which is why we normally find ourselves working with companies in the medical, food and electrical sectors.

 

6.- PVC Compound Variables: PVC traits that the final user need.

 

Que quiere el cliente sobre las variables del compuesto de PVC
PVC Compound

Many times we find that PVC compound producers do not have the necessary information to accurately develop a formula. We recommended our customers to find out what characteristics their customers value the most. Normally we talk about appearance, some mechanical test, UV resistance and/or the useful life of the product.

In this article it can be concluded that there are so many PVC compound variables that, in order to offer what the customer needs, our technical team needs to be able to access all this very useful information. In addition, it is recommended that the manufacturer identifies and controls all these variables. This in turn, will ensure high-quality products.

If you have any question please ask our technical experts..

Chemical Compounds

 

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