6 variables of the PVC compound

The purpose of this blog is to help our visitors and clients understand the process of selecting a PVC compound and all the variables involved in the purchasing decision.

Although we have already discussed on our website what a PVC compound is and how to choose it, we would like to delve deeper into our experience so that clients can understand the importance of analyzing all the variables of a PVC compound in order to design, produce, and process exactly what is required.

1.- PVC compound variables: type and condition of the machine

We can say that everything begins with deciding whether to acquire a new machine or a pre-owned one. As the saying goes, “what is cheap can be expensive,” and vice versa. Therefore, if a machine is to be used for a premium product line, it is always recommended that the equipment not only be new but also meet the proper specifications for the process and the desired product. Conversely, a relatively older machine may be optimal if the target market has modest requirements and the PVC compound to be processed is considered stable or easy to handle.

We invariably recommend that, to properly control the variables of a PVC compound, regular maintenance be performed on your equipment. It is also important to be aware that older equipment will incur hidden costs for spare parts and higher costs for your PVC compound.

Among the variables of a PVC compound, there are tricks or adaptations that can be applied to older machines, such as installing screens in the head of an extruder, which helps achieve better melting of the PVC compound. However, worn equipment generally leads to greater processing problems and higher scrap. If proper fusion is not achieved, tighter screens or the addition of two or three screens can be considered; exceeding this number could increase internal compression and damage the equipment.

To understand the variables of a PVC compound, it is very important that the PVC processor knows and communicates the following characteristics to their supplier, particularly when using an extrusion process:

Characteristics of the extrusion process: variables of the PVC compound

1. Screw length-to-diameter ratio: A longer machine allows for greater residence time of the PVC, facilitating easier melting.
2. Spindle type: There are mixing screws, conveying screws, conical or convex screws, single and double screws, etc. These will have a great influence on the behavior of the material in your equipment.

   

3. Screw compression ratio: For PVC compounds, screws with a compression ratio of 2:1 to 3:1 are typically used. This ratio describes the proportion or volume of material that fits in the screw at the feed stage of the extruder compared to the end, when the material has been transformed into a molten mass but just before reaching the die head.
4. Whether a screen pack is installed and how many screens are used.
5. Whether a gas extraction chamber is available: during processing, the PVC compound releases hydrogen chloride, which also acts as a catalyst in its degradation.
6. That the team has ammeter This allows for the control and monitoring of the machine's effort or torque. This information is invaluable not only for the formulator but also serves as input for establishing statistical process control.
7. The extruder motor capacity: Equipment with a low-capacity motor may be suitable for flexible PVC but not for rigid PVC. It is always important to clarify with the equipment manufacturer the type of PVC for which the machine will be used.
8. Knowing the revolutions per minute of the equipment and having them appear on the control panel.
9. Ensuring that the temperatures detected by pyrometers accurately reflect reality. It's important to understand that these temperatures differ from the temperature of the mass because... PVC compound It has poor heat transfer. A cooling system is also necessary to maintain stable process temperatures after several hours or days of operation.

Switching to the injection molding process, which is generally more forgiving because the equipment applies higher compression and, as a result, melts PVC more easily, it is important for the processor to understand the variables of the PVC compound involved:

Characteristics of the injection process: PVC compound variables

1. Compression ratio of your spindle and its length: A similar concept to the one explained earlier, although not as critical here. We're usually talking about a conventional transport screw, sufficient to handle the frictional force during the backpressure process.
2. Capacity of your injector: Just like with extruders, injecting rigid PVC is not the same as injecting flexible PVC. Sometimes customers purchase machines that aren't even designed for PVC, which causes many problems and machine downtime.

   

3. Cooling and molding: The most important thing is that the inner part of the mold, or its "core," has a mirror finish and is well polished without imperfections, as this will determine the quality of the injected part. Likewise, stable and homogeneous cooling of the molds will help prevent sticking, deformed parts, stuck parts, and turbulence in the finished product.

It is vital that the client is well acquainted with their equipment and can communicate all these details. This is why at Chemical Compounds, we offer on-site technical service to gather information considered important for the development of their PVC compound.

2.- Variables of the PVC compound: additives added to the process

Sometimes our clients fail to convey whether the PVC compound The material used is mixed with some type of reclaimed material, filler, lubricant, or if masterbatch is added during the process. This is vital information for us who design the formulas for you. In fact, this is one of the variables of the PVC compound These factors can determine success or failure during field testing, so it's recommended to be as transparent as possible with your technical advisor. Clear communication will lead to a faster solution and cost savings.

3.- PVC compound variables: customer process quality controls

Other variables of the PVC compound include understanding the type of internal quality and process controls the client has, which can be classified into three categories:

1. Raw material controls: Sometimes customers request a certain pellet size and appearance (brightness or opacity), characteristics that are controlled from the supplier's process.
2. Process controls: Customers are often accustomed to certain process conditions and are reluctant to change them for various reasons. Some examples include: process temperatures, injection or extrusion speed, and cooling time.
3. Finished product controls: includes weight of manufactured parts, appearance, color, brightness or opacity.

It is of great importance that the transformer identifies these variables in their process and how they affect the rest of their production chain until reaching their customer.

4.- PVC compound variables: finished product quality controls

This category of PVC compound variables includes finished product controls that are typically performed after the product is manufactured. Some examples include:

1. Physical and mechanical tests – What tensile and elongation properties are required?
2. Accelerated aging tests – How much does your material need to withstand?
3. Chemical attack tests – What chemicals is the finished product exposed to?
4. Toxicity tests – Does it have to comply with the RoHS standard?
5. Color tests – How similar should the color be to another piece?
6. Exudation tests – Is there any contact with other material that promotes it?
7. Hardness tests – What is the permissible range for your product to fulfill the function for which it was designed?
8. Impact resistance tests – What is the minimum required impact?
9. Transparency tests – Is it opaque or transparent?
10. UV resistance tests – How long does it promise your customer?

These are just some examples of tests that can be performed on a finished product and that your customers in the market will surely require.

5.- PVC compound variables: regulations to be met

In some markets, and increasingly in international regulations, restrictions are placed on PVC plastic, requiring producers to find safer alternatives for both the community and the environment. You have likely heard of the FDA (Food and Drug Administration) or REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals), institutions that continually establish toxicological regulations and require producers of PVC additives and compounds to choose more consumer-friendly alternatives.

It is important to be aware of these regulations based on your market and to 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; as a result, we frequently work with companies in the medical, food, and electrical sectors.

6.- PVC compound variables: characteristics desired by the user of the finished product

We often find that the transformer of the PVC compound They don't know for sure what characteristics their client needs, and this becomes a communication problem with the manufacturer or formulator. It is recommended to know the PVC compound variables depending on what your customer values; usually, this refers to appearance, some mechanical testing, UV resistance and/or product lifespan.

In this article, it can be concluded that there are so many variables of the PVC compound that, in order to deliver what the client needs, our technical team must have access to all this valuable information. Additionally, it is recommended that the processor identify and carefully control all these variables of the PVC compound to ensure consistent, high-quality products.

If you have any questions or require advice from one of our engineers, Don't hesitate to contact us.

Sincerely. Chemical Compounds