Plastic Gears - Construction, Design and Material Properties of These Industrial Products

Gears are one of several fixed transmission settings in a vehicle used in order to determine power or direction. In industrial product categories, however, the gear is that toothed mechanical part - commonly a wheel or a cylinder - that engages with another toothed part in the transmission of motion from one rotating body to another. In this second definition, there are several materials used in the process. A popular subcategory is known as plastic gears.

Plastic gears are available in a wide array of materials and are constructed in different ways. It may also be designed depending on the industry that makes use of these items. They may be hubless or they may also have pins with or without set screws. They may also be set on a brass insert, a stainless steel hub, aluminum core, Bakelite or nylon. Below are further details about construction, design and materials in the manufacture of these items.

Construction

Plactic gears are produced through two significant processes known as hobbing and shaping. Additionally, though, some molding techniques are also employed in its construction. But then again, these techniques are not relied upon that much because of some disadvantages. Most of the times, molding strategies are not accurate due to mold variations and other inconsistencies. In all these techniques, though, plastic gear fabrication is not as favorable as metal gear processing.

Design - advantages and disadvantages

Despite the disadvantages seen in the manufacture and construction of plastic gears, more industries rely upon these industrial products. Their features have been enhanced through time and they are now designed to meet the requirements of their various applications.

Backing up the different plastic gear designs are some attributes or characteristics in the process. Designing these types of gears is considered a cost effective measure. It is also lightweight, has uniform parts, capable of shock absorption and has low coefficient of friction. Furthermore, it eliminates machining operations.

However, to some extent, the designs have some limitations too. They are relatively less capable of carrying heavy loads and they possess greater instabilities in terms of dimension. They are also affected by chemical products and lubricants.

Properties of different materials used in construction

Plastic gears are produced with different materials including acetal resins and copolymers as well as nylon resins. All of these materials have varied physical and mechanical properties whose strength, dimensional resistance, moisture absorption and fabrication requirements vary from one another. Generally, these materials have the capacity to withstand varied formulations.

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Plastic Slip Sheets - A Good Option For Construction

The construction of the foundation has to be a fairly exact science. If everything is not calculated correctly, many issues can arise. Experts have devised many construction tricks and techniques that are used to avoid potential pitfalls during the building process. One of these involves the usage of plastic slip sheets. Using a slip sheet as reinforcement has been successfully used for many years in construction.

What is a Plastic Slip Sheet?

A slip sheet is a piece of plastic, typically polyethylene. It can be made in varying thickness, but it is often used in a 10ml form. Like the name suggests, the slip sheet is used to reduce friction and prevent movement or slippage. Using plastic slip sheets as reinforcement in foundation building helps to prevent cracking.

The Post-Tension Process

Slab-on-grade foundations are one of the most commonly used types of foundations in the United States. These foundations are quick and inexpensive to build (which is why they are so popular); however, they can be prone to cracking during the curing stage. Concrete can shrink as it dries; this can cause cosmetic damage to future floor finishes like tile, vinyl, wood, and carpeting. The type of soil - called expansive soil - is what ultimately causes the shrinkage and cracks. Expansive soil shrinks and swells as the water content changes.

To avoid the cracks, a process using plastic slip sheets is generally used. This process is called post-tensioning. Post-tensioning compresses the concrete, which helps it to resist shrinking and cracking that can be caused by the difficult soil conditions. In order to post-tension a slab foundation, steel strands are run through the concrete in a squared grid pattern. Each strand of steel is covered in plastic sheathing that protects the steel from corrosion and allows it to move during the stressing operation. The strands have an anchorage on each end. Each strand, along with its sheathing and anchorage, is called a tendon.

During the post-tensioning process, the tendons are usually stressed along one end; however, sometimes they are stressed along both ends. When they are stressed, the steel stretches -- but it is kept in place by the anchorage. This works to compress the concrete, which, in turn, works to keep the concrete from cracking.

How are Plastic Slip Sheets used with Post-Tensioning?

The plastic slip sheets are installed directly below the slab, or between the slab and the bearing surface. They work to allow the tendons to move the slab smoothly across the ground. Without the slip sheets, the tendons would not have a flat, even surface across which to move. The tendons must be able to move easily across the ground in order to correctly stress the steel, as this is the only way in which the concrete will be compacted in order to avoid shrinkage and cracks.

If builders were to neglect to install plastic slip sheets - or if they were to install them incorrectly - the slab would resist moving, which would prevent the post-tensioning process from being successful.

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