PROBLEM ANALYSIS
AND SOLUTION
We can achieve perfection by solving problems one by one. There is no single solution that will solve all problems.
To solve it, you have to understand it.
Problems in rubber operations can have many different sources. Issues such as formulation, compound preparation, compound storage, production processes, and vulcanization can each be a source of problems in their own right. Therefore, analyses need to be carried out both holistically and at the level of individual details.
The source of the problem may be one or several of these factors. It is necessary for the problems in your operation to be analyzed in detail by expert teams, root cause analyses to be conducted to identify the source of the problems, and engineering studies to be carried out to solve them.
In many operations, the main source of problems has been considered to be the formulation. However, some of the problems believed to be formulation-related can easily be eliminated through improvements to the processes. Conversely, it may also be possible to eliminate problems believed to be process-related through formulation adjustments.
At this point, we support the resolution of problems by identifying their root causes and making improvements based on both formulation and process.
We identify known problems originating from processes or formulations, as well as problems overlooked due to operational blindness, and provide you with support in resolving these problems.
We have categorized some of the most common problems encountered in operations under headings. Detailed explanations are provided below for each heading.
Dispersion Problems,
Scorch / Burning Problems,
Die Head Burning Problems in Extrusion,
Collapse in Complex Cross-Section Profiles on Profile Lines,
Dimensional Imbalance in Multi-Profile Extrusion,
Rubber-Metal Adhesion Problems,
Blooming Problems,
Filtration
Dispersion Problems
One of the most common problems, particularly in white compounds, is dispersion. These problems can be eliminated through the correct selection of raw materials, improvement of formulation design, and implementation of the correct mixing sequence. Similarly, brown & black spots caused by Sulfur or Accelerators can also be eliminated through the use of the correct raw materials and the application of proper mixing techniques. In order to correctly analyze the source of the problem and develop the right solutions, the process, from raw materials to mixing techniques, must be analyzed by experts.
Proper dispersion involves combining all raw materials in a rubber formulation into a uniform and homogeneous mixture.
While rubber chemists often face difficulties in improving overall dispersion quality and batch consistency, they also face challenges in finding ways to reduce compound mixing time and increase Banbury-Internal Mixer output in order to save costs.
The quality of dispersion can vary depending on the equipment and the individual formulation. However, there are general principles that can be applied to achieve an optimum level of dispersion under the most economical mixing conditions.
Dispersion has a direct impact on many physical properties of a rubber compound. Good dispersion ensures consistency of properties within the same batch and consistency of properties between batches. It also creates a smooth surface appearance in finished parts.
Improper dispersion can lead to undesirable physical and mechanical properties, including defects in product appearance, reduced service life, and poor part performance.
Many factors affect dispersion, including rubber formulation, raw material quality, raw material temperature and storage conditions, and the types of raw materials used. The age of the equipment and mixing conditions (mixing time, temperature, pressure, and rotor speed) also play a role in dispersion.
Therefore, it is advantageous for the person preparing the rubber compound to have as much control as possible over the entire mixing process.
Good dispersion is the key to producing rubber compounds that provide optimum part performance. You can contact us to learn more about selecting the right compound for your application.
Compound Scorch Problems
Are you experiencing scorch problems in your compounds from time to time? We solve your scorch problems by examining your formulations, curing systems, rheometer curves, process parameters, and compound storage conditions, and by conducting engineering studies and analyses to determine the most appropriate parameters.
Scorch is one of the problems that tends to occur during the rubber mixing process. Basically, scorch is the premature vulcanization of the compound during processing, which leads to a number of product defects. The factors that cause rubber to scorch during the rubber mixing process are as follows.
1. Compound Quantity
During the final mixing stage, if the amount of compound loaded into the Banbury is too large, it causes the temperature of the rubber to rise too quickly, the discharge temperature to become too high, and may even cause the rubber to scorch. This is particularly evident when mixing high-hardness compounds. Generally, it is recommended that the amount of the final compound loaded into the Banbury should be approximately 0.7 (fill factor). If the mixing process is carried out in an Internal Mixer, the amount of compound accumulated between the rolls should be controlled within a reasonable range. Too little accumulated compound negatively affects dispersion, while too much accumulated compound causes poor heat dissipation, heat buildup, and scorching. Excessive compound accumulation can also lead to problems such as low mixing efficiency.
2. Roll Temperature
Each type of rubber compound has an optimum mixing temperature range. If scorching occurs, the roll temperature of the Internal Mixer may not be appropriate. Adjusting the mixing temperature of the rubber compound is a very important parameter of the mixing process.
Generally, the smaller the rolling distance, the faster the compound heats up, which may cause the compound to scorch. The rolling distance should not be too small, especially for thin and high-hardness rubbers.
3. Addition Time of Accelerators and Sulfur
For most rubbers, it is generally appropriate to add vulcanizing agents during the final stage of mixing. If the vulcanizing agent is added in the Banbury, two-stage mixing is recommended to prevent the rubber compound temperature from being too high when the agent is added, and it is difficult to find a balance between good dispersion and scorch prevention. For single-stage mixing, especially when the compound discharge temperature is high, adding the vulcanizing agents in an Internal Mixer and adding the vulcanizing agents during cooling may be considered. Provided that sufficient and uniform mixing is ensured, reducing the heat history of the vulcanizing agents is the key to preventing scorch.
4. Degree of Dispersion of Sulfur Vulcanizing Agents and Accelerators
If sulfur is not dispersed properly, it will lead to local concentration of vulcanizing agents and accelerators, causing localized scorching of the rubber compound. Therefore, designing a reasonable mixing process, ensuring the dispersion of vulcanizing agents throughout the compound, and strengthening the control of details related to the compound mixing stage can help solve localized curing problems.
During the mixing stage in the Internal Mixer, only part of the compound must never be allowed to circulate. This does not help the dispersion of vulcanizing agents and accelerators; on the contrary, it causes the rubber to scorch.
5. Mixing Time
In general, the mixing time should not be excessively long. All raw materials are evenly dispersed throughout the compound. If the mixing time continues to be extended, the rubber will become “overmixed,” and the molecular chains of the rubber will be affected by mechanical shearing and heat. This not only reduces the physical and mechanical properties of the compound but also causes energy waste and increased costs. Since prolonged mixing increases the temperature of the rolls and the rubber compound, the likelihood of scorching will increase significantly. Therefore, the mixing time should be determined according to the specific situation to ensure the homogeneous dispersion of additives.
6. Storage Time and Conditions of the Final Rubber Compound
The final compound also tends to scorch after being stored for a long period. If a final compound that has been stored for a long time shows a tendency to scorch, you may consider working it on the Internal Mixer before use and adding an appropriate amount of retarder. Storing your compound stocks in a conditioned area will reduce their tendency to scorch.
Die Head Scorch Problems in Extrusion
In extrusion lines, while the planning department requests fast-curing compounds from the mixing department in order to increase production, production reports problems because these compounds scorch in the die head. The main source of the problem is the compound that remains stagnant by hitting barriers at dead points or whose flow slows down significantly, beginning to cure under the effect of pressure and temperature, initially breaking off in small pieces and creating roughness on the surface, and subsequently growing larger and completely damaging the surface. At this point, the most important issue is to correctly design the formulations and extrusion dies together, and, along with a sufficiently fast-curing formulation, to eliminate dead points inside the die or reduce them to the lowest possible level. In this way, it is possible to obtain products that cure quickly but do not scorch in the die head.
Collapse in Complex Cross-Section Profiles on Profile Lines
- Especially in profiles with hollow sections, inward collapse may occur some time after extrusion begins. By the time this problem is detected, a significant amount of product may already have been discarded as scrap. This is a problem that can be addressed through die design, and simply allowing a certain amount of air to enter the die is generally sufficient to solve the problem. For this purpose, the cross-sections of your profiles need to be examined, and engineering studies need to be carried out to design openings that will allow air to enter the die.
Collapse in Complex Cross-Section Profiles on Profile Lines
- From time to time, multiple profiles are extruded simultaneously, especially for simple cross-sections, in order to increase efficiency. However, problems may occur due to high deviations in profile dimensions. In this case, by ensuring the correct design inside the die head and proper flow, it is possible to ensure that each extruded profile remains within the desired dimensional tolerances.
- Our expert teams examine the cross-sections of the profiles you require and carry out the necessary studies to determine the most appropriate die designs and process conditions.
Rubber-Metal Bonding Problems
- From time to time, you may encounter areas on the same product that do not bond at all alongside areas that bond very well. Or, do products from the same autoclave sometimes come out with some products bonded very well while others have no adhesion at all?
- Have bonding-related problems suddenly started occurring even though you previously had no bonding problems in your production?
- We minimize your bonding problems by providing support from metal surface preparation and adhesive selection to the application of the adhesive (Bonding Agent) and formulation design that will provide the best bonding.
- In some of your applications, we can also significantly reduce your labor and adhesive costs by using a single-coat adhesive application.
- Since a bonding problem means that the finished product has to be scrapped, it creates a significant cost. From time to time, even eliminating bonding problems alone can provide substantial savings. In order to eliminate your bonding problems, a comprehensive engineering and root cause analysis needs to be carried out by experts, starting from surface preparation and extending all the way to your formulation.
- Although it is one of the most common causes of finished product scrap, unfortunately, the metal preparation and coating section is one of the areas that receives the least attention in many operations. While some operations apply adhesive using brushes without controlling adhesive thickness, others use spray guns, resulting in high adhesive consumption. There are also often uncontrolled processes in metal preparation.
- With our expert team, by examining your process and product requirements, you can target maximum bonding strength and minimum scrap rates through the most appropriate surface preparation and coating options. You will see that the investment made will pay for itself in a short time through reduced scrap, lower adhesive consumption, and lower labor costs.
Blooming Problems
- One of the most common mistakes made when designing a formulation is not knowing the solubility of sulfur and accelerators in the elastomer. Especially in EPDM, high amounts of accelerators are used to achieve fast curing. However, since some of these accelerators do not have sufficient solubility in the rubber, whitening and blooming may appear on the surface after waiting for a certain period following the vulcanization process. These bloomings are sometimes perceived as insufficient curing, leading to methods such as increasing the curing time or temperature, or adding additional accelerators to the formulation. However, the correct solution is to use accelerators according to their solubility in the rubber. For example, the solubility of TMTD, one of the most commonly used accelerators, in EPDM is only in the range of 0.5–0.7. In order to prevent your blooming problems, detailed studies need to be carried out by experts by analyzing your formulations, rheometer curves, and process parameters to achieve the most appropriate combinations.
Filtration
- Filtration is often an application used, and one that should be used, to achieve clean products with smooth surfaces. At many companies I have consulted for, it was claimed that the compounds would not pass through the filters I used. In fact, one person even brought a filter screen, poured water over it, and claimed, “Even water can barely pass through this; how will the compound pass through?” In the end, we lost the bet that we had entered into over his coffee 🙂
- Based on the flow characteristics and rheological data of your rubber compound, as well as the suitability of your extruder and extruder die head, it is possible to filter your compound through filter screens that are said to be impermeable even to water. The key to this is designing the correct filtration system. Filtration is possible using 80–100 mesh and, in some cases, even 200 mesh filter screens. All the knowledge required for effective filtration will be provided by our expert teams after checking your existing rheological data and the suitability of your equipment.