Summary of application of plastic parts in automobile engines

Time:2021-10-21 15:30:12 / Popularity: / Source:

As we all know, engine operating conditions are complex and harsh, need to adapt to various external environments, so there are generally higher requirements for engine parts. Especially in terms of resin materials related to engines, because of their high requirements for working temperature and pressure, it is necessary to use resin materials with superior performance.
plastic parts in automobile engines 
In automobile engines, thermoplastic engineering plastics are commonly used. Taking engine as an example, following analysis of plastic parts mainly include:
PUR material:
Fuel pipe protection cover, high pressure fuel rail protection cover, high pressure fuel pump protection cover, high pressure fuel pump frame cover. These parts are used to protect components while eliminating abnormal noise. This foamed plastic is used because material can maintain shape after being molded, while texture is softer and cost is lower.·
PA66 (including PA66-GF reinforced material):
Dipstick, intake manifold, cylinder head cover, oil pan harness bracket, chain tensioner arm, engine carbon canister solenoid valve muffler, etc. This material is mainly used for PA66, which has higher fatigue strength and rigidity, its blended modified material has higher wear resistance and better heat resistance.
PA46 (including PA46-GF reinforced material):
It is mainly used for parts of throttle valve. This material has excellent heat and wear resistance, but due to its higher cost, it is generally used less.
Used in oil filter, it has advantages of high strength and wear resistance. Glass fiber reinforced has good durability and good mechanical properties.
It is used for engine water jacket. Because water jacket has been exposed to high temperature and humidity for a long time, PPA is used for this material, which has high tensile strength under high temperature and high humidity, has strong heat resistance and coolant resistance. Therefore, this material is selected.
It is mainly used for some parts of ignition coil, because material has excellent electrical properties and flame retardant ability, at the same time, heat aging temperature is relatively high, which can meet working conditions of ignition coil.
It is mainly used for parts of ignition coils. Main advantages are low water absorption, good flame retardancy, good heat resistance and electrical properties, strong creep resistance under load.

Important properties of plastic

Fluidity of thermoplastics can generally be analyzed from a series of indexes such as molecular weight, melt index, Archimedes spiral flow length, apparent viscosity and flow ratio (process length/plastic wall thickness).
Thermoplastics can be divided into crystalline plastics and amorphous plastics according to whether they crystallize during condensation. So-called crystallization phenomenon is a phenomenon in which molecules move independently from molten state to condensation state, are completely in a disordered state. Molecules stop moving freely, press a slightly fixed position, and have a tendency to make molecular arrangement become a regular model. .
Thermal performance and cooling rate
Different plastic varieties have different thermal properties such as specific heat capacity, thermal conductivity, and heat distortion temperature. Plastics with high specific heat capacity require large amounts of heat to be plasticized, injection molding machines with large plasticizing capabilities should be used. Cooling time of plastic with high heat distortion temperature can be shortened and demoulded early, but it is necessary to prevent cooling deformation after demolding. Plastics with low thermal conductivity have a slow cooling rate, so they must be sufficiently cooled to enhance cooling effect of mold.
Plastics can be roughly divided into two types: moisture absorption, moisture adhesion, and non-absorption or easy adhesion. Moisture content in material must be controlled within allowable range. Under high temperature and high pressure, moisture becomes gas or hydrolysis occurs, which causes resin bubbles, fluidity, appearance and mechanical properties to be poor.
Process parameters
Temperature control
One is to control temperature of barrel. Temperature of plastic is controlled by barrel, so temperature of barrel is related to plasticization quality of plastic. When selecting barrel temperature, main focus is to ensure that plastic is well plasticized and can be injected smoothly without causing local degradation of plastic.
Second is control of nozzle temperature. In order to prevent molten plastic from casting, nozzle temperature should usually be adjusted to be slightly lower than maximum temperature of barrel during operation, but not too low, generally five to ten degrees Celsius lower than maximum temperature of barrel. Third is to control temperature of sol. Sol temperature is actual temperature reached by plasticization of plastic, which can be measured at nozzle or by air jet method.
Pressure control
Injection pressure refers to melt pressure at screw head during injection. Function of injection pressure is to overcome resistance of melt from barrel to cavity, give melt a certain filling speed and compact melt.
Holding pressure refers to pressure that needs to continue to maintain flow of melt in order to compensate for shrinkage of material in mold. Holding pressure has a great influence on quality of molded product. Back pressure refers to pressure that plastic is subjected to during plasticization process. It is pressure that screw needs to generate and surpass before retreating, is also called plasticization pressure. Proper back pressure plays an important role in improving product quality.
Clamping pressure is an important parameter of injection molding machine and clamping force applied to mold. Calculation of clamping force: clamping force is equal to constant of clamping force multiplied by projected area of product.
Time control
Injection molding production cycle, including mold closing, injection, holding pressure, product, cooling, mold opening and product ejection time.
Generally, injection time should not be too long. After cavity is filled, it is equivalent to maintaining pressure under injection pressure. Too long time will increase orientation pressure of product. Generally, filling time of product is 3~10S.
Generally speaking, cooling process is the most time-consuming process in molding cycle. Therefore, reasonable control of cooling time can greatly save production costs. Cooling time range is usually 5 to 120 seconds.

Common injection defects and countermeasures

Lack of material
Lack of material means that mold is not full. It mainly occurs in places far away from gate and thin walls. Main reason is that injection pressure or speed is too low, or holding pressure is insufficient. Improvement method is mainly in terms of equipment: arrange an injection molding machine with a suitable plasticizing capacity, set a suitable plasticizing temperature, shorten injection cycle, etc.:
In terms of molds: avoid excessively long and thin runners, avoid thin walls of molds that are too thin.
Process: Adjust enough feed volume, increase injection pressure, increase injection rate, and increase material temperature.
Voids inside product appear in the form of round or elongated bubbles. Voids often occur in products with relatively thick walls and are in the thickest part. Therefore, holding pressure should be increased, holding time should be increased, mold temperature should be increased, and melt temperature should be lowered.
Flash is also called flash. Most of them occur at points where molds are separated. Main causes are: too low clamping force, gaps in mold, too high molding temperature, too much injection pressure, improper exhaust, etc. Improvement methods include equipment direction (clamping force, mold parallelism, wear condition), mold direction (parting surface accuracy, mold design compatibility), and process direction (decrease injection pressure, reduce feed volume, barrel temperature).
Top white
If demolding force is too high, deformation will occur, which will eventually cause whitening of ejection part, insufficient cooling time, insufficient strength during demolding, and whitening of top. Improvement method: molding process (reduce holding pressure, shorten holding time, advance holding pressure switch, extend cooling time) mold design (select demolding slope according to specifications, and polish mold in demolding direction).

Go To Top