It is not the firs time in Zatec where we found this phenomenom known like Creep, a problem to bear in mind depending on some final applications. Like injection molding company of technical parts in engineering plastics located in Zaragoza(Spain), we help to our customers to chose the adequate raw material based on final requierements. As you can read as follows, we are going to explain you this problem of Creep.
Sometimes, our plastic parts are subjected to constant strain during long time, and therefore, the deformation can increse up to break, even below the resistance of material. Normally, we represent in a graph with deformation or strain based on time, according to tensile tests. A datum to bear in mind is the Young Modulus, very usefull for designers due to we can include this mentioned datum in ecuations of resistance materials or simulations about finite element method by computer to predict the behaviour during lifetime.
The raw material, composition and, obviously, the process of injection molding can influence in their properties, like creep. For example, some materials with glass fiber have a better behaviour for this phenomenom than other unreinforced materials, due to hardness. In fact, the most materials used in Zatec have a lot of content of glass fiber, but this tipe of reinforcement could generate a fragile fracture. By this reason, we must consider some extra additives like impact modifiers or conditioning the humidity in some higroscopyc poliamides, avoiding or minimizing the mentioned fracture, being ductile fracture instead of fragile fracture.
The failure in plastic part could be by excessive deformation and due to formation of cracks. Therefore we will have a non-functional piece. The cracks can appear like an asnwer by applied stress, internal or external overcoming the intermolecular links like hydrogen or Van der Waals forces.
Some typical example is the break around of groves, where the final customer apply a force in screw due to tightening torque in the final assembly. Anyway the break could generates some time after.
Therefore, we can say like final conclusion, the creep is a combination of several factors that we must analyze before in the design phase to avoid the break by Creep.
Somtimes, we have received some quotations where a customer needs a flame retardant plastics, and/or with determinated homologated brand, due to several reasons. Nevertheless It is necessary to take account the type of flame retardant as you can see below, based on depeding on thickness.
An example, one request for quotation where we must us the homologated raw material “x”. But if we inject this thermoplastic we cannot meet the customer’s requirements due to the part had about 1,5 mm of thickness and the mentioned raw material was flame retardant grade V0 based on a test piece of about 3 mm of thickness. By these reasons, we consider necessary to talk about this additive used in several sectors like electronic, electrical or household appliances. We are talking about the flame retardant plastics.
According to UL94 classification (Underwriters Laboratory in EEUU, with their known yellow datasheets) and based on test where the test tube is burned in vertical by flame analyzing up to the fire is self-extinguishing. Therefore the different grades of flame retardant are as follow:
There are other nomenclatures such as 5VA, 5VB with vertical test tube, too. In these cases a burn can produce a hole or not. These cases are not so common than three mentioned nomenclatures before. The lower UL94 classification is for HB grade, where the sample is placed in horizontal. It is known like self-extinguished although this type burn like wood (to understand the simile).
Below you can see a good video from youtube (source:Filoalfa 3D) with different behaviours in final parts (ABS in this case), alhtought obviously there are more flame retardant engineering plastics like Polyamide (PA),Polycarbonate (PC)…
The flame retardant agentes more common to get some grades that we are talking about it are: antimony trioxide, red phosphor (common for dark colors), halogens (fluor, chlorine, bromine, iodine, astatine)… for example. But, sometime these elements can produce harmful smoke for human beings during combustion. By this reason each time is more usual to use flame retardants halogens free, from biological raw materials sustainably manufactured, decreasing the fossil resources besides of carbon emissions to atmosphere.
If you need technical support to chose the adequate enginnering plastic based on your application, we are glad to help you working together from initial design (bearing in mind our injection molding process) up to serial plastic part
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