#TempLogger

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Discover the principles of data acquisition systems (DAQs), their components, and their benefits. Read our blog to gain detailed insights about DAQs.

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Rotational Molding Process Control Past, Present & Future

by Alvin Spence, Centro Incorporated, USA

The effects of various processing conditions are investigated to demonstrate how this method can provide a more precise means by which to control the process. Advancements in this area will provide the molder with a higher quality product, as the cure of the molded part is critical in governing the end product’s mechanical properties.

Traditional Process Control Indicators For polyethylene (PE) materials, molders have historically relied on basic tests and indicators to gauge the quality of the molded part[1]. These indicators have typically been one of the following:

Low temperature impact strength

Bubble content in the wall cross section

Internal surface appearance/color/odor

External surface appearance

While other mechanical tests do exist, low temperature dart impact is by far the most widely used and least expensive test to perform. A correctly processed part will typically yield ductile impact behavior (or acceptable impact strength without failing) depending on the material type, density and melt index. Bubble content is also a common process control indicator, and can greatly influence the mechanical strength of the molded material. High bubble content across the wall thickness of the parts suggests low cure, while little or no bubble content suggests high cure. However, the propensity of bubbles in any material is influenced by other factors such as the material’s melt index and molecular structure[2]. Very high melt flow materials (typically 6 g/10min or greater) will allow bubbles to dissolve relatively quickly, making it more difficult to know if the material is cured properly or over cured. For the most commonly used melt index materials (typically 2 – 6 g/10min) molders like to see some bubbles in the wall of the cross section to know that over cure has not taken place. For natural parts and most colors, the inner surface of the part can provide more process control information. A lumpy or rough surface texture suggests low cure (or a poor quality grind), while a discoloration suggests over cure due to oxidation. When this takes place, the inner surface of the part will exhibit a burnt odor. The external surface of the part may experience poor fill or surface porosity, which could be an indicator of low cure. This could also be due to incorrect resin selection, poor quality grind, or excessive moisture content. The relationships between these traditional process control indicators are summarized in Figure 1.

While in their own way the process control indicators outlined can provide an effective means to gauge the quality of the molded part, they all have the shortcoming of being post-molded control methods.

Current Scientific Process Control Indicators

In the early 1990’s it was discovered that monitoring the internal air temperature of the mold during processing provided a more scientifically precise way to determine the amount of cure experienced by the part during the molding cycle[3]. The first commercial system that was capable of doing this was called the “Rotolog”. It consisted of an insulated electronic system, (used to take temperature measurements) and a radio frequency transmitter. The Rotolog mounts to the arm of the machine and travels with the mold through the oven and cooling chambers, taking temperature measurements (via thermocouples) from inside the mold, transmitting them in real time to a receiver, linked to a PC. Since then, other commercial units such as K-PaqTM, TempLogger, DATAPAC and slip-rings (K-KONTROL) have all been successfully used to gather this data. A typical output for the mold’s internal air temperature can be seen in Figure 2.

From the trace, the following critical points have been identified:

Point A – The beginning of the phase change from solid to liquid, as fine plastic particles begin to melt and adhere to the wall of the mold.

Point B – All of the plastic particles have melted and the polymer is now a high viscosity liquid.

Point C – The mold’s peak internal air temperature (PIAT) experienced during the cycle.

Point D – Phase change from liquid back to solid, as the plastic solidifies.

When considering process control, typically point “C” on the internal air temperature trace has the greatest importance, as this point reflects the highest temperature experienced by the internal surface of the part. In general, the peak internal air temperature (PIAT) has often been directly correlated to the amount of “cure” experienced by the part[4 & 5]. This claim has been substantiated by impact testing parts that have been molded to a range of peak internal air temperatures – see Figure 3. Typically, an optimum  range of cure or “cure window” can be identified for each material with upper and lower cure boundary limits. Knowing what the cure window is for a particular resin, allows the molder some flexibility to adjust the cycle when the need arises, knowing that a good part will still be produced. This is particularly critical when running multiple molds on one arm that may have slight variations in wall thickness, polymer being used or mold size configuration.

In recent years, infrared thermometry (IRT) has been successfully used as a method to provide process control for rotational molding[6]. This system gathers real-time temperature measurements from the external surface of the molds rotating inside the oven and cooling chambers. This data can then be used to control the indexing of the arms to and from the oven and cooler, as well as controlling some of the cooling process parameters. One of the benefits of the IRT system is that it provides a repeatable process when cycle parameters have been established. However, IRT is not capable of providing temperature measurements from inside the mold, which are critical in knowing the thermal cycle experienced by the polymer.

Generally speaking, internal air temperature measurement provides the molder with critical information by which the molding cycle can be controlled. However, the PIAT control parameter has some limitations when considering products made from the same PE material, but molded to different wall thicknesses. For example, would a 1/8” thick part require the same PIAT as a 3/8” part to yield acceptable cure? The answer is probably not, as the 3/8” walled part remains in its molten state for approximately 3 times longer than the 1/8” walled part – see Figure 4. For the thinner walled part to achieve good mechanical properties (i.e. good cure), the material needs a sufficient amount of time to allow bubbles to diffuse from the melt. Bubble removal is a time-temperature relationship. Therefore, the same result can be achieved if the polymer goes to a higher temperature for a shorter period of time or a lower temperature for a longer period of time. For the thicker walled part, the risk of oxidation is much greater due to the extended cycle time. Therefore, it is probably better to process the thicker walled part to a lower PIAT, provided there is enough time available to allow sufficient bubble diffusion to take place to yield acceptable mechanical properties. So, is there a more accurate way to control the process?

The Future for Process Control?

The future of process control could be to utilize some of the methods previously mentioned, but analyze the data they provide in a different way. This process control concept uses the area under the internal air temperature curve, above the melting temperature of the plastic (250°F for polyethylene), as a process control indicator. Figure 5 defines the area under the curve, referred to as the “degree of cure” (DoC), with units of degree-minutes. It is suggested that this measurement  provides a more accurate means to gauge cure than any of the previous methods mentioned, as it can compensate for variations in molding cycle conditions. This method takes into account the time-temperature aspect of processing, potentially a more accurate process control parameter.

The Influence of the Heating Cycle on the DoC

Changes to the oven cycle demonstrate the benefits of measuring DoC. For example, Figure 6 illustrates internal air temperature measurements of the same part molded at three different oven temperatures, using a cast aluminum mold. For these parts, the peak internal air temperature was approximately 420°F for the 700°F oven, 410°F for the 600°F oven and 400°F for the 500°F oven setting. The DoC measurements for these moldings can be seen in Table 1.

From Table 1, the Degree of Cure measurement would suggest that the part molded in a 700°F oven experienced a much lower level of cure than the other two parts, as the material remained in its liquid state for a much shorter period of time.

Correlating DoC to Properties and Appearance

A series of molding trials carried out at Queen’s University Belfast[7] confirmed the relationship between DoC, bubble content and impact properties. During these trials a 3.4 g/10min melt index material was molded with a range of peak internal air temperatures and the ARM impact resistance was measured for each molding. Samples were also cross sectioned and the presence of bubbles was estimated as a percentage of the overall wall thickness. Figures 7, 8 & 9 illustrate DoC, bubble content and impact strength, plotted against PIAT, for a 1/8” wall thickness part.

The results illustrated in Figure 7 indicate that the correlation is similar to what we would expect when using PIAT as a process control indicator, in that a higher degree of cure results in more bubbles being removed from the wall of the part. Similarly, Figures 8 & 9 show as the cure level increases, and the bubbles decrease, the impact strength rises until it reaches a point where the inner wall of the part has oxidized, resulting in brittle failure at a PIAT of 445°F. The data suggests for this particular material, molded with a 1/8” wall thickness, that the maximum allowable DoC lies somewhere between the last two data points on the DoC curve (i.e. between 1,500 and 2,127°F. min).

These experiments were repeated with thicker walled parts (see Figure 10) and found that similar relationships existed. However, the degree of cure value increased for different wall thickness of parts (see Figure 11), therefore making it difficult to have a generic DoC number when trying to use this method as a process control indicator for parts of increasing wall thickness.

While DoC appears to have great potential as a process control tool, more work is needed to prove out the ideas presented in this article with a broad range of materials, process conditions and wall thicknesses.

Conclusions

From this work, the following conclusions are suggested:

Monitoring the peak internal air temperature during the rotational molding cycle can provide a reasonably accurate means by which to judge the cure of the part – provided there are no significant changes in the processing parameters.

Monitoring the Degree of Cure has the potential to provide a higher level process control. This technique has been shown to correlate to traditional methods to gauge cure, such as bubble content in the wall of the part and impact strength.

The DoC value will increase with increasing part wall thickness. While this is not necessarily a limitation, it needs to be taken into consideration when identifying the DoC cure range.

References

Andrzejewski, S. Simple Rules to Follow for Obtaining the Proper Cure for Rotomolded Polyethylene Parts, Rotation, Vol. VI, Issue 3, 1997.

Spence, AG. Analysis of Bubble Formation and Removal in Rotationally Moulded Products, Queen’s University Belfast, Ph.D. Thesis, May 1994.

Crawford, RJ and Nugent, PJ. A New Process Control System for Rotational Moulding, Plastics, Rubber and Composites Processing and Applications, Vol. 17, Issue 1, 1992.

Spence, AG and Crawford, RJ. The Effect of Processing Variables on the Formation and Removal of Bubbles in Rotationally Molded Products, Polymer Engineering and Science, Vol. 36 Issue 7, 1996.

Crawford, RJ and Nugent, PJ. Impact Strength of Rotationally Moulded Polyethylene Articles, Plastics Rubber and Composites Processing and Applications, Vol. 17, Issue 1, 1992.

Nugent, PJ, Little, E and Peev, G. The Use of Non-Contact Temperature Sensing in Extending Process Control for Rotational Molding, Society of Plastics Engineers ANTEC 1997.

Treacy, R. US Rotational Moulding Material Property Differences, MSc. Thesis, Queen’s University Belfast, September 1998.

from an article at RotoWorld® https://rotoworldmag.com/rotational-molding-process-control-past-present-future/ from Blogger http://jamestwalden.blogspot.com/2017/05/rotational-molding-process-control-past.html

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The Importance of DAQ Data Acquisition and Cold Chain Temperature Monitoring Devices

In industries where temperature-sensitive products are involved, such as pharmaceuticals, food, and chemicals, maintaining proper temperature control is crucial. DAQ (Data Acquisition) systems and cold chain temperature monitoring devices are integral tools that help ensure the safe transportation and storage of these goods. By continuously monitoring temperature and other critical parameters, these technologies provide the data needed to prevent spoilage, degradation, and compliance issues.

DAQ Systems and Cold Chain Monitoring

In modern industries, efficient data collection and monitoring are critical for product quality and regulatory compliance.

The cold chain, which ensures the proper temperature control of sensitive goods, is particularly reliant on advanced monitoring systems.

What is DAQ Data Acquisition?

DAQ (Data Acquisition) Systems are used to collect and process real-time data from various sensors like temperature, humidity, and pressure.

These systems help industries monitor operational performance and troubleshoot potential issues efficiently.

The Role of Cold Chain Temperature Monitoring Devices

Cold chain temperature monitoring devices are designed to track the temperature of products throughout their journey, from manufacturing to delivery.

These devices ensure that sensitive goods, such as pharmaceuticals, food, and chemicals, are kept at the proper temperature, preventing spoilage and degradation.

Key Features of Temperature Loggers

Temp Logger are compact devices that continuously record temperature data over extended periods.

They are essential for industries where temperature-sensitive products are handled, such as healthcare and food industries.

Features often include real-time temperature alerts, data storage capabilities, and easy integration with DAQ systems for seamless monitoring.

Integration of DAQ Systems and Temperature Monitoring

By integrating DAQ data acquisition systems with cold chain temperature monitoring devices, businesses can monitor temperature in real-time and gather accurate, actionable data.

This integration allows for improved traceability, early detection of temperature deviations, and enhanced operational efficiency.

Benefits of Using DAQ and Temperature Monitoring Systems

Ensures product quality and safety by preventing temperature violations that could affect sensitive goods.

Improves compliance with industry standards and regulations, particularly for products that require stringent temperature control.

Helps businesses reduce waste, prevent product loss, and maintain customer trust.

Conclusion

The combination of DAQ data acquisition systems and cold chain temperature monitoring devices is crucial for industries dealing with temperature sensitive goods.

These technologies provide enhanced monitoring, data collection, and compliance, leading to better product safety and improved operational performance.

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Temperature loggers are vital tools for monitoring and preserving product quality in cold chain and quality control. They track temperature variations in industries like food, pharmaceuticals, and logistics, preventing spoilage, ensuring compliance with standards, and safeguarding sensitive goods in storage and transit.

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A Guide to Temperature Loggers: Their Role in Cold Chain and Quality Control

Temperature data is essential for maintaining the quality of products in many industries, from food preservation to pharmaceuticals. One of the most crucial tools in this process is the temp logger, a device designed to monitor and record temperature variations in various settings. These devices play a significant role in ensuring that temperature-sensitive goods are stored and transported under the correct conditions, making them an invaluable asset in quality control.

In this article, we'll explore what temperature loggers are, how they work, and their specific applications, particularly in the cold chain industry.

What is a Temperature Logger?

A temperature data logger is a device used to monitor, record, and store temperature data over time. These loggers are equipped with sensors that continuously capture temperature fluctuations at regular intervals, providing deep insights into temperature patterns.

Temperature loggers come in various shapes, sizes, and specifications, depending on their intended application. The data captured by these loggers is crucial for decision-making in industries where maintaining a specific temperature is essential for product integrity and safety.

Applications of a Temperature Logger

Cold Chain Industry

One of the most significant uses of cold chain data loggers is in the pharmaceutical sector, where temperature control is crucial for the efficacy of drugs, vaccines, and other sensitive medical products. These products must be kept within specific temperature ranges to prevent degradation. A cold chain data logger ensures that the temperature is continuously monitored during transport, from storage to delivery, so that the integrity of the products is maintained.

In the food industry, temperature loggers help track the conditions of perishable goods throughout the supply chain, from farm to fork. By using temperature loggers, food companies can prevent spoilage, reduce foodborne illnesses, and ensure products are safe for consumption.

Other Industries

Temperature loggers are also used in industries like chemicals, electronics, and logistics, wherever temperature-sensitive goods require strict monitoring to maintain quality and compliance with regulations.

How Does a Temperature Logger Work?

A temperature logger operates by embedding one or more sensors (such as thermocouples, RTDs, or thermistors) that measure the temperature and convert it into electrical signals. These devices sample the temperature at predetermined intervals and store the data in internal memory for later analysis.

Some advanced models feature built-in communication modules (such as Bluetooth, GSM, or LTE), allowing for real-time data transmission to a central system or PC. In cases where physical access to the device is not feasible, these wireless communication methods provide greater flexibility.

Alerting and Monitoring

Temperature loggers are usually pre-programmed with alert levels. When the temperature exceeds or falls below the preset range, the system triggers an alert, sending notifications via SMS, email, or other methods to designated personnel. This feature helps businesses respond quickly and take corrective actions, ensuring that products remain safe throughout the entire supply chain.

How is Data Retrieved from a Cold Chain Data Logger?

Retrieving data from a cold chain data logger is simple and efficient. Many loggers are designed to function like USB drives, allowing users to plug them into a computer to access the recorded data. Others feature Bluetooth capabilities, enabling seamless connection to PCs or mobile devices for immediate data retrieval. Additionally, some loggers come with GSM or LTE modules, allowing the data to be sent directly to a centralized control system for real-time monitoring and analysis.

Conclusion

Temperature loggers are essential tools in industries that rely on precise temperature control, especially in the pharmaceutical and cold chain sectors. By ensuring that temperature-sensitive goods are kept within safe ranges, temperature data loggers help prevent product damage, maintain quality, and ensure compliance with regulatory standards.

With the increasing demand for safe and efficient supply chains, the use of temperature loggers is expected to grow in the coming years. Companies that invest in cold chain data loggers can significantly improve their supply chain efficiency, enhance product safety, and ultimately drive better decision-making for consistent growth.If you're looking for the best and most reliable temperature loggers, look no further than HuseLive! Contact us today to learn how our solutions can help enhance your safety and efficiency in temperature-sensitive operations.

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Ensuring Cold Chain Integrity with Smart Temperature Monitoring Solutions

In industries like pharmaceuticals, food, and biotechnology, temperature-sensitive products must be stored and transported under precise environmental conditions. Even a slight deviation can lead to product spoilage or compliance violations. That’s where reliable temperature monitoring tools like a temp logger become indispensable.

What is a Temp Logger?

A temp logger is an electronic device used to continuously monitor and record temperature data over time. These devices are crucial in cold chain logistics, where maintaining a specific temperature range during storage and transportation is essential. Temp loggers come in various formats — from compact USB loggers to wireless cloud-based systems — and offer features like real-time alerts, data exports, and long battery life.

Why Data Logger Digital Devices Matter

Modern temperature monitoring has evolved from manual record-keeping to automated solutions. A data logger digital offers unmatched accuracy and reliability, making it the preferred choice for cold chain applications. These digital devices record environmental data at pre-set intervals and provide downloadable reports for audits and compliance.

With advanced models, users can access temperature logs remotely through mobile apps or cloud dashboards, allowing for immediate action in case of temperature excursions. This digitization ensures better efficiency, reduced human error, and greater traceability across the supply chain.

The Role of Cold Chain Temperature Monitoring Devices

Cold chain temperature monitoring devices are designed to ensure that perishable goods remain within required temperature ranges throughout transit. Whether it's vaccines, seafood, or specialty chemicals, these devices help meet stringent regulatory standards such as WHO, FDA, and GxP guidelines.

Integrated with sensors and IoT capabilities, these monitoring systems offer end-to-end visibility of the supply chain. When paired with temp loggers and data logger digital tools, businesses can confidently maintain quality, extend product shelf life, and avoid costly spoilage.

Applications Across Industries

Pharmaceuticals: Ensure vaccine efficacy with real-time temperature data.

Food & Beverage: Monitor meat, dairy, and frozen goods for freshness and safety.

Logistics: Track conditions across multiple storage and transportation points.

Chemical & Research Labs: Maintain optimal environments for sensitive materials.

Conclusion

As global standards for product safety and compliance continue to rise, investing in dependable tools like temp loggers, cold chain temperature monitoring devices, and data logger digital systems has become critical. These technologies not only protect sensitive goods but also build trust, streamline operations, and ensure regulatory compliance — making them essential assets in modern supply chain management.