Lead-Free Plastics to Help with X-Ray Shielding

Tags

High gravity compounds, high-density plastics, thermoplastic composite materials, X-ray shielding

Lead has commonly been used in x-ray devices to limit the amount of radiation exposure for patients and operators. This low-cost and high-gravity compound is among the most effective shields, but we also need to remember that its toxicity makes it very difficult and dangerous to handle.

The Need for a Change

Lead poisoning cases came into the spotlight after the Flint fiasco, and the world soon realized that it needed a substitute for lead, as quickly as possible. A number of governments are also moving away from the use of lead. The EU RoHS directive restricts the use of solders made out of lead in electronics. Medical devices are currently exempted from this list, but only because viable alternate solutions are yet to be available in commercial applications.

Investigating Replacements

A number of high gravity compounds such as tungsten and tungsten alloys are currently being researched. High density plastics have truly begun to take over a number of industries and applications, and it is believed that with additional research, they might even have lead’s manufacturability and convenience. LNP Thermocomp HSG PH1100B, a thermoplastic composite material is currently being projected as that alternative. This compound is believed to offer effective X-ray shielding capabilities and it can also be injection melded into complex designs easily.

LNP Thermocomp HSG PH1100B Vs Lead

Researchers conducted several tests to compare the material to lead in an x-ray shield. Results show that at an equivalent thickness, the HSG PH1100B performed the same, or better, than lead at different voltages. A specific gravity of 11, however, causes high viscosity in the HSG PH1100B when compared to other high density materials used in injection melding applications.

Managing the Viscosity

Researchers recommended the following guidelines to help manufacturers process and manufacture the material.

1. Mold simulations could be inconsistent as the HSG material has special formulations. Therefore, it is essential for an experienced engineer to review the designs. Apart from using standard tool-making practices, standard tool steels can also be chosen for glass fibber applications in order to extend the tool life. Designers also need to use basic plastic-design principles considering anisotropic material properties.

2. Pin gates are recommended to be avoided as they can cause material separation during the first-stage injection. Fans and edge gates offer much better alternatives as they produce lower peak pressure, and this can lead to better aesthetics and over all properties. This also causes lesser shear heating, thereby reducing the chances of separation of the resin and the filler.

3. The wall thickness is recommended to be 3 mm at a minimum. Gate design, vent depth and runner lengths also need special attention to boost performance.

Vast advancements improvements in the field of high density materials and thermoplastic composite materials can encourage designers around the world to choose injection melding solutions in all kinds of applications, including x-ray shielding. The HSG material has already shown that it can offer the same benefits of lead, yet avoid the risks and extra machining that is typically involved while using lead.

With the help of these materials, it is entirely possible for manufacturers around the world to come up with new technologies and better equipment. It might be early days in the x-ray shielding department, but the results do look incredibly promising!

Specific-Gravity Thermoplastics Open New Doors

Tags

high density plastic, thermoplastic composite materials

Thermoplastics and High density materials continue another year of growth as recent developments and innovative design changes allow these materials to offer even more benefits in all kinds of environments and applications. Thermoplastics found a place in mainstream business due to their ability to decrease the part count or weight of parts in a particular tool or appliance. Turns out that a new class of heavy plastics and high density compounds are entering the picture, ones that have a specific gravity varying between 1.8 to 10.

A Bit of History

To better understand how this could revolutionize the manufacturing process, let’s take a look at how engineered thermoplastics are made. After a base resin has been chosen, its electrical, mechanical and physical properties are altered and manipulated to achieve desired state. Fillers and replacements such as rubber tougheners (for flexibility), carbon-black fillers (for electrical conductivity) and glass fiber (for strength) are carefully chosen and added to finally create a material that can work wonders in making the manufacturing process faster, smoother and cheaper.

How are High-Specific-Gravity Compounds Created?

High-specific-gravity compounds are created by combining adding mineral or metallic fillers in thermoplastics. Base resins commonly used in this care are crystalline thermoplastics because of their flow properties. Common examples include polyesters, polypropylene, polyurethane and polyamides. Surface chemistry of fillers and particle size distribution is also important to ensure optimal processability..

The Journey from Light to Heavy

High-specific-gravity compounds can be classified into three different weight classes. Lightweight high-specific-gravity compounds have a specific gravity which varies between 1.8 to 4. These heavy plastics are commonly used in medical devices and to replace aluminium, clay or glass. Some of these compounds are used to add strength while others may be used to improve toughness. These compounds can be pigmented from brighter to darker tones.

Middleweight high-specific-gravity compounds have a specific gravity that varies between 4 to 7. These materials are usually designed to become magnetic and they fall in the same class as die-cast zinc. Many safety-restraint components used in automobiles are made using these high density materials and these parts can be colored in darker hues.

Finally, heavyweight high-specific-gravity compounds have a specific gravity that varies between 7 and 10. They offer solutions similar to lead, stainless steel and bronze and are a fantastic lead replacement for shielding x-rays in medical applications. Training rounds are also made using these compounds to minimize the use of lead while allowing the material to withstand muzzle pressure and still manage to disintegrate upon impact. Another application of heavyweight high-specific-gravity compounds can be seen in automobile steering columns.

Why is this Important?

What makes these high gravity compounds so special is that they not only manage to consolidate parts and custom-create properties in order to decrease costs, but also present the ability to dialin specific part weights across the density range, which even manages to touch lead and its alloys. To make matters even more interesting, these engineered thermoplastic composite materials also come with special abilities such as magnetic properties, noise reduction, frangibility, x-ray opacity and x-ray shielding. High-specific-gravity compounds are injection moldable in metal replacement solutions, which also eliminates the need for assembly operations and secondary machining, further reducing costs across the manufacturing channel.