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Introduction
This article will present an in-depth discussion on plastic gears.
The article will provide more detail on topics such as:
What are Plastic Gears?
Plastic Gear Design
Materials Used for Plastic Gears
Types of Plastic Gears
Advantages and Disadvantages of Plastic Gears
And much more…
Chapter 1: Plastic Gears Manufacturing
This chapter will discuss what plastic gears are, their manufacturing process, and how they function.
What are Plastic Gears?
A plastic gear is a toothed wheel made up of engineering plastic materials that work with others to alter the relation between the speed of an engine and the speed of the driven parts. The engineering plastic materials used in manufacturing plastic gears can be nylon, which is essentially polyamide resin, and polyacetal.
Methods of Manufacturing Plastic Gears
The manufacture of plastic gears takes the same form as the manufacture of metal gears, the only difference being the material used. Each type of gear is produced to meet the needs of a process or application, which also determines how they will be made. A major difference between manufacturing plastic and metal gears is that plastic material doesn’t have the strength of metal. Temperature variations strongly affect plastic's strength and stiffness, which must be considered when designing plastic gears. Additionally, plastic gears have lower elastic modulus and mesh stiffness, which causes them to deflect under a load.
Regardless of the similarities between metal and plastic gears, plastic gears have additional factors that must be considered during their engineering and design phase.
Plastic Gear Hobbing
Hobbing involves a hob, a round cylinder with teeth cut into the sides. A flat plastic disk is placed next to the hob. As the hob spins, it makes contact with the plastic disc and cuts gear teeth into the side of the disc. Different types of gears can be produced by changing the contact angle of the hob.
Gear hobbing is a fast, continuous process that is economical due to the speed at which gears can be cut and processed. With exceptional accuracy, it produces spur gears, helical gears, splines, worm wheels, and sprockets.
Injection Molding
Injection molding involves the use of a steel mold with the shape and dimensions of the gear. The key to the process is the accuracy of the mold since it determines the final shape of the gear. Molten plastic is forced into the mold under pressure such that the molten plastic reaches every part of the mold cavity. It is an expensive process designed for high-production runs.
Characteristics of Injection Molded Gears
High precision
Good replication
Less expensive
Resistance to abrasion and wear
Rust resistance
Excellent performance
CNC Machining of Plastic Gears
CNC machining is a cutting process capable of producing any type of gear. The process of CNC machining removes layers of plastic material from a plastic disc or rod. Several tools are used in the process, which are programmed using G codes that guide the movement of the tools. It is a time-consuming and more expensive process due to the limited number of gears that can be processed in one run.
The process of CNC machining is ideal for producing precision-shaped gears with exceptionally high tolerances. An additional aspect of CNC machining in the production of gears is broaching, which involves using a broaching tool that cuts out the shape of the teeth. As with all CNC machining, the broaching process can be programmed into the CNC machine.
Characteristics of CNC Machined Plastic Gears
Lower density, reduced weight, and lower inertia
Low maintenance
Can absorb shock and vibrations
Less noise
Low friction coefficient
Self-lubricating and wear-resistant
Long life cycle
Used in food preparation and wet environments
Corrosion-resistant
Differences between Machining and Injection Molding
Speed of Machining
The machining process is faster with lower part volumes. However, if there are high volumes of plastic parts to be manufactured for a longer duration, injection molding is a viable solution, as the manufacturing process can be scaled once the mold is ready. The injection molding process has faster manufacturing capabilities that offset the delay of creating a mold and the upfront cost.
Cost of Production
The cost of the machining process is cheaper when there are only a few hundred parts in production. However, as the volume increases, the cost also increases. In contrast, the price is significantly lower for each part in injection molding. Cost is accrued in the initial stages of injection molding, but once large-volume production of parts begins, this cost distributes with time.
Raw Material Choice
With the machining process, there are many options for raw materials to create parts. The structural strength and durability of the final product are imparted by the core material; therefore, machining is the way to go with harder materials such as high-performance plastics. With injection molding, the types of materials that can be selected are limited. Only softer plastics like thermoplastics and thermoset resins can be worked with because they can be melted and molded without compromising material strength. Injection molding is used to fabricate the most flexible and pliable materials.
High Tolerance
The primary focus of the machining process is on product specifications. Therefore, the machining process delivers products that meet expectations of precision, accuracy, and high tolerances. Only a few variables are involved in the level of control exercised by a computer. But with injection molding, a greater scope and room for defects exist. These defects include flow lines, vacuum voids, warping, and burn marks. This is because injection molding does not consider the tolerances of the part but of the mold.
Design Flexibility
Injection molding offers a high degree of repeatability, but this is only an advantage with fabricating parts of the same design. If the design specifications are changed, creating the new mold requires another high upfront cost. This, in turn, would make the injection molding process cost-inefficient. With machining, the CAD program can be freely tweaked to incorporate any design changes.
Chapter 2: Top Manufacturers of Plastic Gear Making Machines
Many machines are available to produce plastic gears, and they are important in today's society because plastic gears offer advantages such as cost-effectiveness, design flexibility, reduced noise, and corrosion resistance, making them widely used in various industries, including automotive, milling, and mining. Below, we provide a general overview of some well-known manufacturers of machines used for plastic gear production in the United States and Canada.
Arburg - Allrounder Series
Arburg offers a range of injection molding machines that can be utilized for plastic gear production. One of Arburg's popular machines used for plastic gear production is the Arburg Allrounder series. These injection molding machines are known for their versatility, precision, and advanced control systems. They offer features such as high repeatability, efficient energy consumption, and precise temperature control, ensuring the production of high-quality plastic gears. The Allrounder series' popularity is attributed to its ability to meet diverse production requirements, optimize cycle times, and deliver consistent and reliable results in plastic gear manufacturing.
Engel - Victory Series
Engel is a reputable manufacturer of injection molding machines suitable for plastic gear production. One of Engel's popular machines in this field is the Engel Victory series. The Victory series is recognized for its high precision, energy efficiency, and advanced features that make it suitable for producing plastic gears. These machines incorporate servo-electric drives, which offer enhanced control and energy savings, ensuring precise and repeatable molding processes. The Victory series also incorporates multi-component technology, enabling the production of gears with complex designs or multiple materials. These features contribute to the popularity of Engel's Victory series for plastic gear manufacturing applications.
Sumitomo (SHI) Demag - IntElect Multi Series
Sumitomo (SHI) Demag provides injection molding machines suitable for plastic gear production. One of their notable machines in this regard is the Sumitomo (SHI) Demag IntElect Multi series. The IntElect Multi series is specifically designed for multi-component and overmolding applications, making it well-suited for plastic gear manufacturing. These machines are known for their high-speed and high-precision capabilities, enabling the production of precise and intricate plastic gears. The IntElect Multi series incorporates advanced automation features and offers flexibility in material combinations and mold configurations, allowing for efficient and reliable production of plastic gears with complex geometries and multi-material requirements. The combination of high-performance capabilities, advanced automation, and versatility contributes to the popularity of the Sumitomo (SHI) Demag IntElect Multi series for plastic gear manufacturing.
Milacron - Elektron Multi-Shot Series
Milacron offers a range of injection molding machines suitable for plastic gear production. One of their notable machines in this field is the Milacron Elektron Multi-Shot series. The Elektron Multi-Shot series is designed specifically for high-performance multi-shot molding, making it well-suited for plastic gear manufacturing. These machines are recognized for their precision control, fast cycle times, and high repeatability, ensuring the efficient and cost-effective production of plastic gears. The Elektron Multi-Shot series incorporates advanced technologies such as servo-electric drives and precise shot control systems, allowing for the production of complex gear geometries with multiple materials or colors. The combination of precision, speed, and flexibility contributes to the popularity of the Milacron Elektron Multi-Shot series for plastic gear manufacturing applications.
Nissei - NEX Series
Nissei manufactures injection molding machines that can be utilized for plastic gear production. One notable machine from Nissei is the NEX Series. The NEX Series is recognized for its precision, reliability, and advanced technologies, making it suitable for producing high-quality plastic gears. These machines incorporate Nissei's expertise in injection molding and are known for their high repeatability, energy efficiency, and user-friendly operation.
These manufacturers are well-established in the industry and have a track record of delivering quality machines for plastic gear production. However, for specific model numbers, unique features, and the most up-to-date information, it is recommended to contact the manufacturers directly or consult their product catalogs.
Chapter 3: Plastic Gears Design and Materials
About 80% of gears in the US are selected from a catalog. Although this is common practice, the best process is to cooperate with customers’ engineers to design gears to solve specific problems or address design challenges, such as inertia or product contamination. For example, open gearing in the paper, food, or semiconductor processing industries produces significant contaminants.
To engineer the right solution for an application, it is important to consider the various operational parameters, such as torque, RPMs, shock load, backlash requirements, inertia, chemical exposure, and operational temperature. Gear teeth modifications or increased gear width are used to ensure a plastic gear will work in a given application.
Plastic Gears Design Details
Gear Face Width
The face width of a gear tooth is the width of the top of a tooth that is parallel to the axis of the tooth. As the face width of a gear tooth increases, the gear gains greater bending and surface strength.
The face width of a gear has to be smaller than the space where it mates with another gear. Such a condition is referred to as effective face width. The face width should not be confused with the face of a gear tooth, which is the surface of the tooth above the pitch surface. It should be remembered that the face width is the top of a gear tooth that mates with the space between the teeth of another gear.
Gear Module
The size of a gear is expressed as its module. It indicates how big or small a gear is. The module is the ratio of the diameter divided by the number of gear teeth. When choosing a gear, the module and number of teeth determine the gear chosen.
Pressure Angle
The pressure angle of a gear is determined by two tangent lines that intersect the inner circle of the gear and the top arc of a tooth. For many years, the pressure angle was determined to be 14.5°, which was considered the standard. However, modern technology has adjusted and changed that standard. When a gear has a larger pressure angle, the teeth of the gear are larger and stronger.
Gear Tooth Backlash
When the teeth of gears intermesh, there is a space between the teeth that is referred to as the backlash. In designing gears, it is possible to limit the amount of backlash so the teeth mesh together very tightly.
Tooth Temperature
A key factor in using plastic gears is temperature, which influences their performance. The choice of materials used to produce a plastic gear during the design phase addresses the concern regarding temperature. However, it is impossible to calculate the working temperature of a gear properly. Essentially, it is advantageous to monitor gear operation to ensure that the temperature of a gear is not exceeded. Many thermoplastics can operate at temperatures up to 500 °F (260 °C).
Gear Life for Plastic Gears vs. Metal Gears
The root, flank, and wear strength are parameters of considerable importance in estimating gear life. The number of load cycles determines the specific parameters (root pulsating strength and flank strength) for both metal and plastic gears. These parameters for plastic gears strongly depend on temperature and the type of lubrication (oil, grease, or dry running). In contrast, for steel, only one value for the tooth strength calculation is sufficient.
Comparing plastic to steel, it can be seen that Young's Modulus for plastic is about two magnitudes smaller than for steel, e.g., about 2800N/mm2 for POM compared to 206,000 Nmm2 for steel. The permissible bending stress of plastic is also about one magnitude smaller than steel: 25 Nmm2 compared to 250-450 Nmm2 for steel. Since many gears are sized from their strength requirements, the relative deformation of metal gear teeth is lower than that of plastic gears.
However, plastic gears can absorb shock better than metal gears, and most plastic gears have a mechanical stop design to avoid extra wear and tear on the gear teeth and the motor itself. Plastic gears have a longer wear period and a longer life expectancy than many metal gears. Metal gears grind down faster than plastic gears.
Plastic gears do not require backlash adjustment, as with metal gears. Most steel gears require frequent backlash adjustment in order to avoid backlash issues from the shock of operating the gear and motor vibrations. Since plastic gears can absorb these vibrations, the gears can often last for much longer.
Gear Calculation
For gears like PowerCore, the size of the injection-molded gears is limited by the size of the press to about 5” to 6”. In contrast to gears selected from a catalog, gears designed in cooperation with customers’ engineers solve specific problems or address specific design challenges, such as inertia or product contamination with grease. (This is particularly the case with open gearing in paper, food, or semiconductor processing equipment).
To engineer a solution for an application, all the operational parameters, including torque, RPM, shock load, backlash requirements, inertia, chemical exposure (semiconductors), and operating temperature, are considered. Then, alternative solutions, such as tooth modification or increased gear width, can be proposed to ensure the plastic gear will work in a given application.
An integral part of the gear engineering process is calculating gear life. The calculation provides a number of hours for which the gear will last in specified conditions. Conversely, a gear can be designed to last a certain number of hours; for example, medical equipment manufacturers require five years of component life. Over the last 20-plus years, the calculation has proven to be a reliable predictive tool. It allows users to quickly assess if a plastic gear will work in a given application or not, especially when replacing a metal gear.
Sample Gear Calculation
Input Data
z1
21
Number Teeth Pinion
z2
210
NUmber Teeth Gear
n1
1000
RPM Pinion
n2
100
RPM Gear
DP
10
Diametral Pitch
b
1"
Face Width
g
20° degrees
Pressure Angle
t
65°C
Operating Temperature
P
0.75 hp
Transmitted Power
Cs
1.10
Shock Load Factor
Geometry Data Output
dw1
2.10°
Pitch Pinion Diamter
dw2
21.00°
Pitch Diamter Gear
dk1
2.30°
Outside Diameter Pinion
dk2
21.20°
Outside Diameter Gear
Hk1
0.10°
Addendum Pinion
Hk2
0.10°
Addendum Gear
ea
1.74
Contact Ratio
i
10.00
Transmission Ratio
a
11.55
Center Distance
Operational Data Output
V
2.79 m/sec
Pitch Line Velocity
T1
3.9 ft lbs
Torque at Pinion Shaft
T2
39.4 ft lbs
Torque at Gear Shaft
Load and Safety Data Output
Sb2
4.15
Gear Tooth Root Stress Safety
Sg2
2.34
Gear Tooth Flank Pressure Safety
SigmaW2
6.0 N/mm2
Gear Tooth Root Stress
Kw2
0.6 N/mm2
Gear Tooth Flank Pressure
Types of Materials Used in Plastic Gears
One of the benefits of making gears from plastic is the wide assortment of polymers that are available. Included in the many choices are special polymer blends that manufacturers have created to improve the strength and resilience of plastic gears. In most cases, crystalline plastics are used for their strength, durability, and resilience.
Polyacetal Gears
Polyoxymethylene (POM), known as acetal, polyacetal, and polyformaldehyde, is a semicrystalline thermoplastic ideal for producing precision parts that require stiffness, low friction, and dimensional stability. It is produced by the polymerization of formaldehyde and comes in two variations, homopolymer and copolymer, with different properties. There are six different grades of polyacetal, each with different characteristics, with the base characteristics being strength and dimensional stability.
Polyphenylene Sulfide (PPS) Gears
PPS is valued as a high-performance thermoplastic due to its ability to endure high temperatures and have dimensional stability. As with polyacetal, PPS is a rigid, opaque semicrystalline thermoplastic with a melting point of 536 °F (280 °C). It is produced by the reaction between sodium sulfide and dichlorobenzene in a solvent. The key factors that determine the use of PPS to produce gears are its strength, rigidity, and low degradation in high temperatures.
Nylon Gears
Nylon is a polymer known for its toughness and wear resistance. Gears made from nylon are used in applications with increased torque and power, such as conveyors and automated equipment. A major factor in determining the use of nylon gears is the limited amount of noise and vibrations they produce.
Polyamide Gears
Much like nylon, polyamide is chosen for the production of gears due to its ability to withstand high torque at low speeds. Polyamide gears can endure temperatures up to 248°F (120°C). It is an ideal polymer for working with acids, gasses, and saltwater. In certain conditions, polyamide gears are chosen for replacement of metal gears due to their light weight and cost.
Polycarbonate (PC) Gears
Polycarbonate is a transparent thermoplastic with high strength that makes it resistant to impact and fracturing. It is an eco-friendly polymer that is made into gears using a pressure molding process. Like other polymers, PC has exceptional strength with a melting point of 311 °F (155 °C). One of the drawbacks to polycarbonate is its cost, which is higher than the other gear polymers. Manufacturing processes used to produce PC gears include extrusion and injection molding.
Polyurethane Gears
Polyurethane is an ideal gear material due to its many positive properties. It produces little noise and is resistant to chemicals and corrosion with zero backlash. Polyurethane produces a wide assortment of gears, including spur, helical, worm, and pinion gears. The strength of polyurethane guarantees a long service life and low noise compared to other plastics and metals.
The six polymers listed above are only a sampling of the many plastics used to produce plastic gears. The choice of plastic is determined by the application for which they are designed and the necessary strength and service life. The use of plastic gears as replacements for metal gears has rapidly risen as new and more powerful plastics are being developed and produced.
Leading Manufacturers and Suppliers
Chapter 4: Types of Plastic Gears
There are various types of plastic gears, which include:
Plastic Spur Gears
These types of gears are the most used, and they are easy to recognize because of the teeth that protrude from their perimeter. Their teeth and the shaft axis are parallel to each other.
Plastic spur gears do not generate thrust force in the axial direction. They are mounted on parallel axes to transfer movement between two shafts that are also parallel.
Plastic Spur Gear Characteristics
Module: 1-3
Material: MC901
Hardening: None
Tooth Finish: Cut (non-ground)
Grade: JIS N9 equivalent
Plastic Spur Gear Industries
Food
Beverage
Automotive
Forestry
Energy
Unit Handling
Plastic Spur Gear Applications
Small conveyors
Package handling equipment
Farm machinery
Planetary gear sets
Automotives
Plastic Spur Gears With Steel Cores
Their applications are generally the same as plastic spur gears without a steel core.
Plastic Spur Gear with Steel Core Characteristics
Module: 1-2
Material: MC901/SUS303
Hardening: None
Tooth finish: Cut (non-ground)
Grade: JIS N9
Injection Molded Plastic Spur Gears
Injection molded spur gears can be applied in the same industries as other plastic spur gears.
This type of gear has a conical shape with straight or spiral-cut teeth. Plastic bevel gears transfer motion between two intersecting axles, changing the rotation axis. These types of gears are mostly utilized in power tools and automotive applications. The spiral-cut version can be smoother and less noisy than other designs.
Plastic Bevel Gear Characteristics
Module: 1-3
Speed ratio: 1.5-3
Material: MC901
Hardening: None
Tooth Finish: Cut (non-ground)
Grade: JIS 4 equivalent
Lubrication: Not needed
Plastic Bevel Gear Industries
Cement
Food
Beverage
Mining
Energy
Bulk material handling
Plastic Bevel Gear Applications
Medium-to-large conveyors
Mixers
Crushers
Water treatment applications
Plastic Rack or Rack & Pinion Gears
Plastic racks convert rotational motion into linear motion. The teeth are arranged along a straight bar with cylindrical mating gear. One gear axis is fixed. These gears offer short oscillating strokes and are used in steering systems, conveyors, and machinery used for lifting.
Plastic Rack Characteristics
Module: 1-3
Length: 500 or 1000mm
Material: Polyacetal
Hardening: None
Tooth finish: Cut (non-ground)
Grade: KHK R001 5
Molded Flexible Racks
Molded Flexible Rack Characteristics
Module: 0.8-2
Length: 2000mm
Material: Duracon (R)(M25-44)
Hardening: None
Tooth Finish: Injection molded
Grade: KHK R0018
Bendable
Plastic Miter Gears
Plastic Miter Gear Characteristics
Module: 0.5-1.5
Material: Duracon (R)(M90-44)
Hardening: None
Tooth finish: Injection molded
Grade: JIS 6
Low priced
Suitable for light loads
Injection Molded Bevel Gears
Injected Molded Bevel Gear Characteristics
Module: 0.5-1
Speed ratio: 2
Material: Duracon (R)(M90-44)
Hardening: None
Tooth Finish: Injection molded
Grade: JIS 6
Low priced
Suitable for light loads
Plastic Screw Gears
Plastic Screw Gear Characteristics
Module: 1-3
Material: MC901
Hardening: None
Tooth Finish: Cut (non-ground)
Grade: JIS N10 equivalent
Lubrication: Not needed
Plastic Worm Wheels (Worm Gears)
These types of gears transmit power through right angles on shafts that are non-intersecting. Worm gears produce thrust load and are mostly suitable for high shock load applications. However, worm gears offer very low efficiency compared to other gears. Therefore, they are often used in lower horsepower applications.
Plastic Worm Gear Characteristics
Module: 0.5-0.8
Speed ratio: 10-60
Material: Polyacetal
Hardening: None
Tooth Finish: Cut (non-ground)
Grade: KHK W0025
Plastic Worm Gear Industries
Food
Beverage
Automotive
Forest
Energy
Unit handling
Plastic Worm Gear Applications
Small conveyors
Package handling equipment
Farm machinery
Plastic Internal or Planetary Gears
Planetary gears have teeth that are cut around the internal diameter of one gear. One or more spur gears mesh with these center teeth. This, in turn, allows it to run around its internal diameter. Teeth can also be designed so that they are on the outside of the larger gear, so additional gears can run around its outer diameter. These types of gears are commonly used in automotive gearboxes.
Plastic Helical Gears
These types of gears have teeth that are oriented at a certain angle to the shaft, which is a different case in spur gears. This increases the number of teeth in contact during operation to more than one. Plastic helical gears can carry more load than plastic spur gears. Plastic helical gears can share the load between the teeth. This arrangement, in turn, allows plastic helical gears to operate more smoothly and quietly than spur gears. Also, plastic helical gears produce a thrust load during operation, which should be considered during use. Plastic helical gears are mostly used in enclosed gear drives.
Plastic Helical Gear Industries
Cement
Food
Beverage
Mining
Marine
Energy
Forestry
Bulk material handling
Plastic Helical Gears Applications
Medium-to-large conveyors
Mixers
Large pumps
Water treatments
Crushers
Plastic Double Helical Gears
In these types of gears, two helical faces are positioned next to each other with a gap separating them. They are a variation of helical gears. The faces of the gears have identical helix angles opposite to each other. Double helical gears eliminate thrust loads and allow greater tooth overlap and a smoother operation. Double helical gears are also used in enclosed gear drives, just like helical gears.
Plastic Double Helical Gear Industries
Mining
Marine
Heavy-duty industries
Plastic Double Helical Gear Applications
Milling
Steam turbines
Ship propulsion
Plastic Herringbone Gears
These gears are similar to double helical gears, but their helical faces do not have a gap separating them. Compared to double helical gears, herringbone gears are typically smaller. This makes them ideally suited for high shock and vibration applications. However, these types of gears have manufacturing difficulties and high costs, so they are not often used.
Plastic Herringbone Gear Industries
Mining
Marine
Heavy-duty industries
Plastic Herringbone Gear Applications
Milling
Steam turbines
Ship propulsion
Plastic Hypoid Gears
Plastic hypoid gears are similar to spiral bevel gears, but their operating shafts do not intersect as in spiral bevel gears. Instead, in plastic hypoid gears, the bearings support the shafts on either end of the shaft because the arrangement has the pinion set on a different plane than the gear.
Plastic Hypoid Gear Industries
Cement
Food
Beverage
Mining
Energy
Bulk material handling
Plastic Hypoid Gear Applications
Small-to-medium conveyors
Small mixers
Crushers
Water treatment
Bull Plastic Gears
Bull plastic gears are used in combination with pinion gears that provide power to the bull gear. A bull gear can drive multiple pinion gear shafts with speeds being altered by gear changes. In most gear sets, one gear is larger than the other, with the larger gear referred to as the bull gear and the smaller gear or gears referred to as the pinion gears.
Chapter 5: Plastic Gear Advantages and Disadvantages
This chapter will discuss the advantages and disadvantages of plastic gears.
Advantages of Plastic Gears
Larger and Stronger Parts
One major advantage of plastic gears is their ability to handle more load due to their tooth bending and load-sharing properties. Bending stress can try to bend the teeth of the gear and shear the teeth from the bulk material of the gear. These forces cause fatigue and static loading, leading to failures by tooth breakage. Contact stress can cause failure in the surface of the gear teeth and wear. In other words, plastic gear teeth spread the load over more teeth by deflecting more under load. The load-sharing capacity increases the load-bearing capacity of plastic gears.
Lower Cost
Generally, the production of plastic gears is less expensive than that of metal gears. In addition, plastic gears do not require secondary finishing; they typically represent a 50% to 90% saving relative to metal gears.
Molding Design Freedom
Molding plastic offers a greater diversity of efficient gear geometries than metal. Molding is an ideal process for producing shapes such as internal gears, worm gears, and cluster gears, where the cost of metal production can be prohibitive.
Plastic Gear Accuracy
Plastic gears can achieve high levels of precision. This can be done using consistent material quality and accurate molding process control.
Corrosion Resistance
Plastic gears are immune to corrosion, unlike metal gears. They can be used in water meters and chemical plant control because of their relative inertness. They can also be used in other applications where metal gears can corrode or degrade.
Light Weight
Plastic gears are lighter than similarly sized metal gears. The gravities of nylon and acetal are closer to 1.4, while the specific gravity of steel is 7.85.
Good Shock Absorption
Plastic gears can deflect to absorb impact loads more than metal gears. Plastic gears also distribute localized loads that result in misalignment and tooth errors.
Reduced Noise
Plastic gears reduce noise levels because of the plastics’ noise-dampening properties, resulting in quiet gears. This is why plastics are essential for tooth shapes with high precision and flexible materials required for quieter drives.
Inherent Lubrication
Plastic gears have inherent lubricity, making them ideal for printers, toys, and other applications that require low-load and dry gears.
However, more specifically, plastic gears offered by companies like PowerCore have advantages such as:
Metal Core
Allows for a precise and safe attachment to a shaft
Reduces up to 50% thermal expansion of the plastic portion of the gear
Available in stainless steel for corrosive applications and aluminum where low inertia is required
Dissipates heat from plastic gear teeth
Polymer Material
Does not absorb moisture, i.e., the gears retain their precise dimensions in humid or washdown environments
Resistant to chemicals/corrosion
Stress-free, highly crystalline structure
Absorbs shock and vibrations
Noise reduction in gears up to 6 dBa
Can operate in sub-zero temperatures
Gear Sizes and Gear Types
Gear sizes from OD=1/2” to OD=28”
Types include spur, helical, bevel, worm gears and shafts, internal gears, and rack and pinion
Improved transmission efficiency, e.g., 7 to 8% in worm gears, energy savings
When they are under strain, plastic gears can warp. This can be detrimental if the plastic must operate in high temperatures or if the levels of humidity change.
Plastic gears experience greater dimensional instabilities resulting from a larger coefficient of thermal expansion and moisture absorption.
Plastic gears can be negatively affected by certain chemicals.
The initial mold to develop tooth form and dimensions require high costs.
Despite this, the disadvantages of plastic gears are far outweighed by their advantages.
Conclusion
Plastic gears are manufactured from two main methods: the injection molding process and the machining process. The type of manufacturing process depends on the volume of the parts needed to be produced and other factors like the required strength of the parts. As already mentioned, plastic gears offer many advantages over metal gears. Each type of plastic gear has a unique characteristic that makes it suitable for a particular application. Therefore, caution must be taken when selecting plastic gear for a particular application for successful and efficient performance.
Leading Manufacturers and Suppliers
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Plastic overmolding has a long and interesting history, dating back to the early 1900s. The first overmolding process was developed by German chemist Leo Baekeland, who invented Bakelite, the first synthetic plastic. Baekeland used a...
Thermoplastic Molding
Thermoplastic molding is a manufacturing process that works to create fully functional parts by injecting plastic resin into a pre-made mold. Thermoplastic polymers are more widely used than thermosetting...