“Smart” bolts with tension indication make mold installation safer and more efficient | Plastic Technology

In addition to unreliable torque measurement, there is no need to guess whether the mold mounting bolts have been tightened correctly. #closeupontechnology #technologyinaction
The larger the machine, the heavier the mold, and the greater the demolding force when the clamp is opened. All these add up, and for injection molding machines, the safety problem of firmly mounting the mold on the machine platen has always been a problem. Some injection molders solve this problem by adding more bolts or fixtures to fix their molds and arranging for extra bolt tightening inspections, which may be wasteful, and in some cases may even cause mold damage.
The famous injection molding trainer and consultant John Bozzelli (also a long-term contributor to the magazine) said: “I have many customers requesting seminars on how to install molds. Customers are tired of molds falling from the platen, literally dropping Down. Can you imagine cost and safety issues? Obviously, this has become a major issue in our industry and needs attention.”
Gaithersburg, Maryland’s Industrial Indicators (aka Stress Indicators Inc.) (industrialindicators.com) is one company that has caused serious concern about this issue. More than two decades ago, the company developed a “Direct Tension Indication” (DTI) bolt, the indicator of which changes color according to the degree of tension caused by the bolt. In the past 12 years, it has perfected its injection molding technology with the help of some Beta test sites for automobile molding on large presses. Account manager Matthew Hallwig (Matthew Hallwig) said: “The molding market is now growing rapidly.”
According to industry indicators, “There is no clear industry standard for how to properly fix injection molds.” Hallwig pointed out: “We found that molders have incredible variations in bolt types and the types of tools used to tighten them.” According to reports , Some molders have developed complex spreadsheets with notes to calculate the number of bolts required to secure various molds to the platen. Others have difficulty controlling the torque applied by the operator, which becomes more difficult as the bolt size becomes larger and the torque required to tighten the torque doubles.
The wrenches used in some forming machines can be set to apply a certain torque (“torque wrench”) as a standard test for fully tightening bolts. But Industrial Indicators engineers pointed out that torque is a rotational force, not pressure, so it is often mistaken for a joint safety measure. One of the reasons is the unknown and variable friction factor, even if the operator maintains a consistent torque specification, it will change the clamping force of the bolt joint. This phenomenon is more serious when the length of the bolt is too long to be inserted into the bolt hole and reaches the head or bottom of the bolt. The bolts look tight, and if checked with a torque wrench, there will be no warning of any problems, and even if the bolts are not under tension, nothing can be clamped together. According to industry indicators, this is a dangerous deceptive incident, which is easy to ignore unless a tension indicator bolt is used. Moreover, applying too much torque to the quenched bolts may damage the threads of the softer plate steel.
According to industrial indicators, the better answer is its DTI Smartbolt product line, which applies strain gauge technology in a unique way. The front end of each Smartbolt contains a center pin with a chamber containing a pressurized liquid indicator. As the bolt is tightened and stretched, the pressure on the liquid is relieved and the color is changed. According to the pre-selected “design tension” of the bolt, the center of the Smartbolt will appear bright red when loose, and will gradually change from brown to black when fully “tightened”. Customers can choose the design tension in the case of consulting industrial indicators. According to Hallwig, the design tension of SmartBolts used in injection molds is usually set at 35% to 45% (in thousands of pounds) of the fastener’s endurance strength, although this number is sometimes as high as 60%. Hallwig pointed out that a lower design tension can extend bolt life and reduce wear of the pressure plate thread.
Direct Tension Indicator (DTI) SmartBolt can easily and intuitively display tightness or looseness in real time.
DTI SmartBolts can be tightened with conventional tools; they have a one-year warranty; and the indicator is certified to operate between -4 F (-20 C) and 168 F (75 C). SmartBolts comes with a verification sheet that displays the indicator color of the design tension from 0% to 100% (fully tight) at 25% intervals. It is said that the color indicator is accurate within 10% of the design tension. According to reports, if the tightening of the bolt does not exceed its elastic limit (standard load), the indicator cannot be damaged by over-tightening.
SmartBolt sizes range from 5/8 inches to 2 inches in diameter. The cost is only about 10-15% higher than standard bolts, but Hallwig said that this difference can be made up for by increasing safety, thereby reducing the risk of worker injury or damage to expensive molds. SmartBolts can also help users improve operational efficiency by reducing the time required for mold replacement and installing too many bolts, as well as checking the tightness of bolts with a wrench. Another advantage is that it reduces the damage to the pressure plate threads caused by over-tightening the bolts.
Hallwig estimates that about 15 injection molding plants are using DTI SmartBolts to varying degrees, mainly in large-machine car molders. In 2018, an automobile molding machine installed 36 large machines (up to 4,000 tons) on all its presses. On average, the plant needs to change a dozen molds a day. Prior to the installation of SmartBolts, the factory experienced mold slip almost once a week-when the bolts were loose enough to cause the mold to slide down to the platen (although it was still hanging in place), a warning event was issued, and even the mold was completely dropped. Falling situation. According to reports, within six months of installing SmartBolts, the factory’s mold slippage or drop was zero, and the SmartBolts were found to feel “tight” under three different conditions, but reached the lowest point at the bolted connection. A manufacturing manager of the factory told Industrial Indicators, “I have been in this business for 31 years, and the most proud thing in my career is the implementation of SmartBolts.”
The verification diagram of the DTI Smart Bolt shows the gradual change in color from “loose” to “tight”, expressed as a percentage of the maximum design tension.
The situation in the plastics industry seems to favor the introduction of products like SmartBolts. As consultant Bozzelli told Plastics Technology: “During the decades I entered the store, I saw some molds loose-they won’t fall, but they will come close. In recent years, things have gotten worse and worse, it’s me. Problems to check before starting to work on the printing press. Most early processors have some tool background. We work in automobiles or agricultural equipment. Today, there are far fewer processors with any mechanical background or experience. Therefore, simple operations such as tightening bolts cannot be done correctly. No one is trained how to do it. It is assumed that everyone knows how to use bolts, but they don’t. In addition, most shops don’t like to buy tools because they disappear. Torque Wrenches are a bit expensive, so they are usually not bought for workers. If so, they won’t last long in the workshop. Sometimes, workers don’t even know how to use them properly.”
Industrial Indicator is conducting beta testing on a new product line of injection molding machines. Chroma series SmartBolts is one of them, it will display colors in the “loose, tight and over-tight” state. It will also provide digital remote load monitoring and closed-loop tension control. The company’s first batch of new tools will convert the sensed load into a digital value. More importantly, in tightening mode, when the tool feels the correct tension, it will cut off.
Poorly designed profile molds (a mold that does not allow parts to be extruded in the same size between each run) coupled with a lack of understanding of the extrusion process are the causes of waste.

Post time: Oct-15-2020

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