The technical data presented here refer mainly to the ELESA Standard elements, made of engineering plastics and metal materials.
The main technologies used for the manufacture of plastic products are:
• compression/transfer moulding for Duroplasts
• injection moulding for Technopolymers.
This primary process may be followed by secondary operations such as machining, finishing, assembly, decoration to customize the product (tampoprinting), packaging to guarantee adequate protection during transportation and identification of the product.
DUROPLASTS: Phenolic based (PF) thermosetting plastics that harden during moulding due to irreversible polymerization.
TECHNOPOLYMERS: Thermoplastic polymer materials in which the chemical composition of the molecular chain provides a wide range of mechanical, thermal, and technological properties. The transformation process is based on the melting and subsequent hardening by solidification of the material in the mould. The material itself has a low environmental impact because it can be recycled (reversible solidification).
The main TECHNOPOLYMERS used by ELESA |
||||||
PA |
PA-T |
PP |
POM |
PC |
PBT |
TPE |
Glass-fi bre reinforced polyamide, glass reinforced polyamide, polyamide-based super-polymers |
Special transparent polyamide |
Glass-fi breececec reinforced polypropylene or with mineral fi llers |
Acetal resin |
Special polycarbonate |
Special polyester |
Thermoplastic elastomer |
DUROPLASTS: The use of a mineral filler and natural textile fibres, and optimum selection of the base resin give this material an excellent mechanical strength and a good impact strength.
TECHNOPOLYMERS: The rich selection of basic polymers available and the possibility of combining these with reinforcing fillers or additives, make a wide range of performance levels possible in terms of mechanical strength, impact strength, creep and fatigue.
For an indication of the mechanical strength of components moulded with the plastics listed above, see chapter 4. MECHANICAL PROPERTIES OF PLASTIC PRODUCTS.
The use of thermosetting materials and reinforced thermoplastic polymers with a high thermal resistance, enables ELESA to obtain products with great thermal stability and a limited variation in their mechanical properties at both high and low temperatures.
The recommended operating temperature range for each plastic product in this catalogue is indicated by the “Temperature” symbol, which is shown on the left.
Within this temperature range:
• The material is stable and no significant degradation takes place.
• The user does not normally encounter any problems with the basic function of the product.
The mechanical strength, impact strength, maximum torque and maximum working pressure values indicated in the catalogue were obtained from tests carried out under laboratory conditions (73°F - relative humidity of 50%).
These values may vary over the working temperature range indicated.
Customers are therefore themselves responsible for checking the product’s actual performance in their specific thermal working conditions.
A very general indication as to the working temperature range for the various types of plastics is given in the table below:
| Duroplasts (PF) | from -4°F to 212°/230°F |
| Special, high-resilience polypropylene-based (PP) technopolymers |
from 32°F to 176°/194°F |
| Glass-fi bre reinforced polypropylene-based (PP) technopolymers |
from 32°F to 212°F |
| Polyamide-based (PA) technopolymers | from -4°F to 194°F |
| Glass-fi bre reinforced polyamide-based (PA) technopolymers |
from -22°F to 266°/302°F |
| Glass-fi bre reinforced polyamide-based (PA) technopolymers for high temperatures |
from -22°F to 392°F |
For some types of products with specific functional requirements, narrower operating temperature ranges are recommended.
DUROPLAST: The material and its glossy finish enables the surfaces to be kept in perfect condition, even after prolonged use in the presence of metal machining residues or in abrasive environments like those, for example, of metal machining applications with machine tools.
TECHNOPOLYMER: The surface hardness values are lower than those of Duroplast, but are still within the 60-98 Rockwell range, M scale. Technopolymers are however tougher and have a greater impact strength than Duroplasts.
Some of the tables in Chapter 12 describe the resistance of the plastics used for ELESA products at an ambient temperature of 73°F, in the presence of the various chemical agents they may come into contact with in an industrial environment (acids, bases, solvents, lubricants, fuels, and aqueous solutions).
The tables on page A22, A23 and A26 indicate 3 classes of resistance:
• Good resistance = the product’s functional and aesthetic properties remain unchanged.
• Fair resistance = the functional and/or aesthetic properties are affected to a degree that depends on the type of product and the working conditions. Some limitations in specific applications.
• Poor resistance = product susceptible to chemical aggression. Not recommended for use.
As a general rule, chemical resistance decreases as the working temperature and mechanical stresses to which the product is subjected increase.
Testing of the product’s resistance to chemical agents is essential for use in the presence of high temperatures and high levels of mechanical stress.
In most cases, ELESA plastic standards are used for indoor applications. In any case, due to the
properties of the materials and the measures taken during the design stage, these products may also
be used for outdoor applications, where they are exposed to various atmospheric agents.
• Rapid changes in temperature: within the working temperature range recommended for
each product, rapid changes in temperature do not create problems due to the impact strength
of the materials used.
• The presence of water or moisture may result in processes of hydrolysis and the absorption
of a certain percentage of the water/moisture until a state of equilibrium is reached.
This may
alter some of the material’s mechanical properties.
Examples of materials that absorb water
include polyamides (PA), transparent polyamides (PA-T, and PA-T AR) and duroplasts (PF).
Products made of these materials may undergo slight changes in size due to the absorption
of water, which may affect dimensional tolerances. During the design stage, ELESA normally
takes these possible variations into account in order to minimise their effects and to guarantee
compliance with the technical specifications. The absorption of water results in a significant
increase in impact strength.
The following polymers do not absorb water: polypropylene (PP), thermoplastic elastomers (TPE),
and acetal resin (POM).
Occasional contact with rainwater followed by “drying” does not generally pose any problems
in terms of the strength of the product.
When used in outdoor applications, it is advisable to prevent water accumulating on the product
by installing in such a way that water runs off it quickly.
• Exposure to the sunlight and UV rays in particular. Specific resistance tests have been
carried out using specific equipment for accelerated ageing testing, in accordance with the
ISO 4892-2 standard, and setting the following parameters:
- Radiation power: 550 W/m2
- Internal temperature (Black Standard Temperature, BST): 149°F
- OUTDOOR filter that simulates exposure to the open air, with low shielding against UV rays.
- Relative humidity: 50%.
The relation between the hours of testing and the hours of actual exposure to an outdoor
environment (“Equivalent Hours”) obviously depends on the weather conditions of each
geographic area.
Taking the Average Radiant Exposure per Day (ARED) as a basis for
comparison, the reference values adopted on an international scale include:
- Miami Equivalent Hours = high intensity exposure, typical of countries with a tropical or
equatorial climate (ARED = 9.2 MJ/m2)
- Central Europe Equivalent Hours = mean intensity of exposure, typical of continental climates
(ARED = 2 MJ/m2).
At the end of prolonged tests carried out at the ELESA laboratories, the variation in mechanical
strength was measured tensile/compression breaking, and impact breaking) was measured.
In general, the results show that the mechanical strength of polyamide (PA), polypropylene (PP) and
Duroplast (PF) products is not significantly reduced by exposure to UV rays.
As to the aesthetic appearance of samples exposed to the action of the UV rays, in some cases a
slight variation in the surface appearance of the product was found, on completion of the tests.
For further details on UV ageing tests on specific products, contact the ELESA Technical Department.
The universally recognised classification used to describe the reaction of plastics to flames is obtained from two tests defined by UL (Underwriters Laboratories, USA). These tests are called UL-94 HB and UL-94 V, which define four main types of reaction to flames: HB, V2, V1 and V0 with progressively increasing levels of flame resistance.
UL-94 HB (Horizontal Burning)
The test consists of putting a set of three standardized samples of the plastic (in a horizontal position set at an angle of 45° with respect to their own axis) each one in contact for 30 seconds with a flame applied at their bottom free edge. Two marks are present on the samples at standardized distances from the free end.
A material may be classified HB if, for each of the three samples, the following conditions are applicable:
- the speed of burning between the two marks does not exceed a given standardized value that depends on the thickness of the samples being tested
- the flame is extinguished before the fire reaches the furthest mark from the free edge (that is, from the point of application of the flame).
UL-94 V (Vertical Burning)
The test entails putting a set of five standardised samples of the plastic (in a vertical position) into contact each one twice for 10 seconds with a flame applied at their bottom free edge.
A sheet of cotton wool is placed underneath the samples. The following parameters are measured:
- the time required to extinguish each individual sample each time the flame is applied
- the sum of times required to extinguish the five samples (considering both flame applications specified)
- the post-incandescence time of each individual sample after the second flame application
- whether any material drips from the sample onto the cotton wool set underneath it with a risk of igniting it.
UL Classification of plastics |
||||
UL-94 HB |
For each of the three samples, the speed of combustion between the two marks does not exceed the standardized speed that depends on the thickness of the samples | |||
For each of the three samples, the fl ame is extinguished before it reaches the further mark from the point of application of the fl ame |
||||
UL-94 V |
V2 |
V1 |
V0 |
|
| Time required to extinguish each individual sample after each fl ame application | ≤ 30 s |
≤ 30 s |
≤ 10 s |
|
| Sum of times required to extinguish the fi ve samples (considering both fl ame applications specifi ed) | ≤ 250 s |
≤ 250 s |
≤ 50 s |
|
| Post-incandescence time of each individual sample after the second fl ame application | ≤ 60 s |
≤ 60 s |
≤ 30 s |
|
| Presence of any material dripping from the sample onto the cotton wool beneath it with the risk of igniting it | YES |
NO |
NO |
|
The variables that determine the reaction to the flame include the thickness of the samples and the colouring of the material (in fact, there may be differences between materials with their natural colour and those with an artificial colour and differences depending on the variation in thickness of the sample with the same colour).
Yellow Card: This is a document issued by the Underwriters Laboratories that certifies the reaction of a plastic to flames, following laboratory testing. This constitutes an official recognition of the product’s flame resistance.
The “Yellow Card” indicates the trade name of the product, the manufacturer and related ID number, known as a UL File Number. The flame resistance is certified for specific material thickness and colour.
Some material manufacturers carry out flame resistance tests in independent laboratories, using the same test methods as the Underwriters Laboratories. In such cases, a declaration of conformity but no “Yellow Card” is issued by the manufacturer.
There are groups of ELESA standards with UL-94 V0 classification, identified as AE-V0 by the symbol shown to the left.
Most of the other ELESA products for which no specific indication is given in this regard belong to the UL94-HB category.
ELESA products identified as AE-V0 are made of environment-friendly plastics and are free of PBB (Polybromine Biphenyl), PBDE (Polybrominediphenyl Ether) and in particular of Penta-BDE (Pentabromodiphenyl Ether) and of Octa-BDE (Octabromodiphenyl Ether).
Plastics are generally good electrical insulators. This is particularly useful in certain applications in the electromechanical field, making plastic products preferable to similar metal products.
The extent of a material’s insulating properties is determined by:
• Its surface resistivity
• Its volume resistivity
The table below classifies the materials on the basis of their surface resistivity [Ω].
Typical values for a few of the plastics used by ELESA are:
Material |
Property |
State of material |
Measuring Method |
Value |
PA 30%
Glass-fibre |
Surface resistivity |
Dry |
IEC93, 23°C |
1013Ω |
Conditioned (50% RH equil.) |
1011Ω |
|||
Surface resistivity |
Dry
|
1015Ω cm |
||
Conditioned (50% RH equil.) |
1011Ω cm |
|||
PP 20%
mineral filler |
Surface resistivity |
Conditioned (50% RH equil.) |
ASTM D257 |
1013Ω |
When moulding technopolymers, it is technically easier to make products with a rough matte surface finish, which hides any aesthetic defects such as shrinkage cavities, flow marks, or joining marks caused by non-optimum moulding processes.
However, a rough matte finish makes it more difficult to clean and handle the component after prolonged use. ELESA technopolymer standards have a very fine matte finish so that the product remains easy to clean in time, and is easier to handle for the user. Some groups of technopolymer products have recently been developed with a completely glossy finish, so that they remain clean for a long time.
Over the past few years, the national and international regulatory authorities have laid down a series of regulations for the control of substances that are harmful to man or the environment and for the environment safety management in the industrial field.
The ELESA Technical Department is able to give any kind of assistance also providing any techinical information required on the following International Standards:
• European Directive 2000/53/CE, also known as the ELV (End Life of Vehicles) directive, which is applicable to the automotive. This provides for a gradual reduction in the quantity of heavy metals (Pb, Cd, Hg, and Cr6) present in vehicles.
• European Directive 2002/95/CE, also known as the RoHS, Restriction of Hazardous Substances, directive, which is applicable to the field of electrical and electronic equipment. This provides for a gradual reduction in the quantity of heavy metals (Pb, Cd, Hg, and Cr6) and PBB and PBDE type halogens present in the components used in the electrical and electronic industries.
• European Directive 94/9/CE (known as the ATEX directive), for products used in a potentially explosive atmosphere.
• WEEE Directive (Waste of Electrical and Electronic Equipment).
• European Regulation REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) n.1907/2006 of 18/12/2006 for the use of chemical substances.
Ongoing research and experimentation with new materials that offer increasingly high levels of performance is part of the principle of continuous improvement on which the ELESA Quality System is based. Our partnership with leading plastics manufacturers in the world and the use of mechanical and process simulation programs, also allows us to offer the material that best suits the Client’s specific application.
Many ELESA parts are completely made out of metal. Plastic elements very often contain inserts or functional components made out of metal. The tables in chapter 12 describe the chemical composition and mechanical strength as per the reference standards for the metals used.
Surface treatments for metal inserts and parts: the surface of metal inserts or functional parts is generally treated to ensure maximum protection against environmental agents, in order to maintain the product’s aesthetic and functional qualities.
The protective treatments normally used include:
• Burnishing of steel bushings and hubs
• Zinc-plating of threaded studs (Fe/Zn 8 in compliance with the ISO 2081 standard)
• Matte chromium plating of lever arms and revolving handles shanks.
Metal parts made of brass or stainless steel do not normally require surface treatment.
On request and for sufficient quantity, metal parts can be supplied with protective surface treatments like black/yellow zinc-plating, nickel-plating, Niploy-Kanigen process, chromium plating, anodising and others, heat treatments like nitriding, hardening and case-hardening.
Gaskets: ELESA normally uses gaskets made of synthetic nitrile butadiene rubber (NBR) or acrylonitrile butadiene rubber (BUNA N) for its products, with hardness values ranging from 70 to 90 SHORE A depending on the type of product considered.
The working temperature range for continuous use is -22°F to +248°F. Where a higher chemical and thermal resistance is required, that is, for products in the HCX.INOX, HCX.INOX-BW and HGFT.
HT-PR series, gaskets made of FKM fluorinated rubber are used. For an indication of the chemical resistance values, see the table in chapter 12 on page A24-A25-A26.
The working temperature range is -13°F to +410°F.
On request and for sufficient quantity, flat washers and O-rings made of special materials such as EPDM, silicone rubber, or others may be supplied.
Air filters for filler breather caps (SFC., SFN., SFP., SFV., SFW., SMN. and SMW. series):
• TECH-FOAM type filters: polyester-based polyurethane foam mesh, degree of filtration 40 microns, recommended for temperatures of between -40°F and +212°F for continuous use, and brief peak temperatures of +266°F. This material does not swell in contact with water, petrol, soap, detergents, mineral oils or grease. Some solvents may cause slight swelling of the foam (benzene, ethanol, and chloroform).
• TECH-FIL type filters: made of zinc-plated iron wire (quality as per DIN 17140-D9-W.N.R 10312, zinc-plated as per DIN 1548), degree of filtration 50-60 microns.
The mechanical properties of a moulded plastic component may vary significantly according to its shape and the technological level of the manufacturing process.
For this reason, instead of providing tables containing specific data on the mechanical strength of test pieces of various types of material, ELESA has decided to inform designers of the forces which, in the most significant cases, may cause the component to break. For most products the mechanical strength values indicated in the catalogue are therefore breaking loads.
For some products for which deformation under a load is not negligible and may therefore jeopardise their performance, two load values are provided.
• “maximum working load” below which deformation DOES NOT jeopardise the component’s performance.
• “load at breakage” in accordance with the concepts outlined above.
In these cases, the “maximum working load” will be used as design data to guarantee correct performance while the “load at breakage” will be used for safety tests, applying the relevant coefficients.
Working stress has been taken into account (e.g. the transmission of torque in the case of a handwheel, and the tensile strength of a handle) as well as accidental stress (e.g. an impact with the component), in order to provide designers with a reference for determining suitable safety coefficients, according to the type and importance of the application. All the strength values supplied were obtained from tests carried out at the ELESA Laboratories, under controlled temperature and humidity conditions (73°F - relative humidity of 50%), under specific working conditions, and applying a static load for a necessarily limited period of time.
The designer must therefore take into account an adequate safety coefficient according to the application and specific operating conditions (vibrations, dynamic loads, working temperatures at the limits of the allowed temperature range). In the end, however, the designer is responsible for checking that the product is suitable for its intended purpose.
For some thermoplastics, for which the mechanical properties vary significantly in relation to the percentage of moisture absorbed (see paragraph 1.5), the resistance tests on the element are carried out in compliance with ASTM D570, so that the moisture absorbed is in equilibrium with respect to ambient conditions of 73°F and a RH of 50%.
Compressive strength for levelling elements (working stress):
the levelling element is assembled on its threaded metal stud and placed on special testing equipment. The element is then subjected to compressive stress with repeated and incremental loads until it breaks or undergoes a permanent plastic deformation.
Resistance to transmission of torque (working stress):
Use is made of a electronic dynamometer that applies ncreasing torque values as shown in Figure 1.
Here the dynamometric system is shown in a traditional way to make the comprehension easier.
The mean values of the torque C, obtained in the breaking tests are shown in the tables for the various components and expressed in [ft.lb].
Impact strength (accidental stress):
The special equipment shown in Figure 2 is used. The mean values obtained in the breaking test, shown in the tables for the various models and expressed in [ft.lb], correspond to the breaking work L of the element subjected to repeated impacts, with the falling height of the percussion weight being increased by 0.33 ft each time.
Percussion weight: metal cylinder with a rounded ogival shaped end and weighing 1.5 lb.
Tensile strength of U-shaped handles (working stress):
this test entails fitting the handle to be tested on a dynamometer, and applying two types of stress:
• perpendicular to the mounting screws (F1).
Here the stress on the handle is a combination of pulling and bending
• parallel to the mounting screws (F2).
The load applied by the electronic dynamometer increases gradually in order to obtain a deformation of the tested element within a limit of 0.79 inches/min.
With a view to ensuring the most effective anchoring of the metal inserts to the plastic and the best possible mechanical operation of the element, use is normally made of diamond knurling, of a shape, pitch and depth suited to the stress to be applied. This type of knurling ensures both axial anchoring (that contrasts axial tensile stress) and radial anchoring (to avoid rotation during the transmission of torque) (Fig.3).
For studs, instead of using a common screw available on the market, use is normally made of a specially shaped threaded insert which protrudes a few tenths of inches from the plastic body so as to form a metal face on the screwing plane, thus freeing the plastic of all stress.
Types of assembly that create optimum clamping conditions:
The plastic base on the clamping knob should never rest on the clamping surface. In this way the stud or threaded boss are never subjected to abnormal twisting (“corkscrew” effect) when axial tensile stress is applied. The metal stud (or boss) is therefore only subject to the torque applied to the knob to tighten it.
The plastic base of the clamping knob rests directly on the clamping surface and the stud or threaded boss are therefore also subject to an axial load (“corkscrew” effect), which could jeopardize its anchoring. The values of this force are always higher, with a broad safety margin, than those that may be applied by normal operations performed by hand, but designers who wish to take into account cases of improper use should avoid the situations illustrated in cases 5-6-7.
For knobs in which through holes (FP type) have to be made, the insert is set in such a way that the machining of the hole or the broaching of a keyway only affects the metal part, without the plastic having to be machined in any way.
All threaded studs of the ELESA elements have a chamfered flat end in compliance with ISO 4753 (Fig.4).
THE REFERENCE TOLERANCE SYSTEM IS THE ISO SYSTEM - BASIC HOLE
• Plain holes in the bosses and hubs (see table in chapter 12, page A18).
For the most widely used models, there are various kinds of standardized holes available so the user has a wide selection and is saved the costly task of remachining the hole on assembly. The degree of tolerance is always indicated in the tables of each article, in the hole size column. For cases in which it is more difficult to propose a standardization of the holes that satisfies the broadest range
of assembly needs, either a pre-drilled hole with a simple roughing tolerance (hole with a smaller diameter than that of the shaft on which it is expected to be assembled), or a hub with no hole (not drilled) is used.
• Tapped holes in the bosses and threads of the studs (see table in chapter 12, page A20).
Machining to threads for a normal screwing length - tapped metric holes of built-in metal bosses = tolerance 6H.
- tapped american holes of built-in metal bosses = tolerance 2B.
- metal metric studs or ends of shanks for revolving handles = tolerance 6g.
- metal american studs or ends of shanks for revolving handles = tolerance 2A.
TOLERANCES OF HOLES AND THREADS OBTAINED FROM MOULDED PLASTIC
• Plain holes (for handles with a through hole for assembly in an idle condition on pins).
Despite the considerable difficulties encountered in maintaining the tolerances in a machining process in which numerous factors influence the end result, the size of the diameter of the axial hole is normally respected with a tolerance of C11. The handles may therefore also be assembled on pins made from normal drawn parts. If the pin is obtained by turning from a bar with a greater diameter, a machining process with a tolerance of h11 is recommended, as this gives a suitable free coupling, with the advantage of a quick, simple and inexpensive machining process.
• Inside threads (for handles with no metal bushing to be screwed in and fixed to threaded pins).
They are normally kept undersized so that assembly is slightly forced at ambient temperature.
• Outside threads (for filler breather caps or level indicators with a threaded connector).
In this case, for reasons related to the process technology and the type of plastic, which may absorb small amounts of moisture from the outside environment, the tolerances must be interpreted taking this into account though the tightening of the component assembled is never actually jeopardized in practice.
On all ball knobs or handles of other types, the knurled band indicated as an example in Fig.7 has been ruled out on principle.
This solution is used to hide the burrs that form on the joining line of the mould, thus eliminating the cost of deburring and finishing. From the functional and ergonomical points of view, this solution is not rational, however, in that it causes considerable irritation to the operator’s hands after prolonged use. In addition, apart from this ergonomic consideration, which is, in any case, important, the knurled band accumulates dust and dirt which is almost impossible to remove, with the result that the
handle made in this way always appears “dirty” and is therefore not at all “inviting” to the touch.
The solution of facilitating the elimination of burrs by creating a raised edge along the joining line of the mould (Fig.8) presents the same problems, though to a lesser extent.
Consequently, the following two solutions have been exclusively adopted:
- completely smooth finish: (Fig.9) which entails a higher cost for deburring (to remove the joining line of the mould), subsequent smoothing (to join the surfaces) and polishing (to restore the gloss) but makes the handle comfortable to hold and makes it look always ”clean”;
- finishing with an equatorial groove: (Fig.10) which represents a more economical solution in that it reduces the deburring to simply eliminating the joining line of the mould by turning a small equatorial groove, without having to join the surfaces by lapping and also without any need for polishing.
For elongated handles both for fixed assembly (at the end of levers) and for revolving assembly on shanks, smooth shapes free of grooves and knurls have been adopted exclusively (Fig.11), this benefits the operation of the handles, which is to be used only for gripping a mechanical part that is to be subjected to translating movements. Also in the case of the revolving handles on a shank, knurls, grooves and edges simply irritate the hand of the operator who has to hold it and accumulates dust and dirt.
Various kinds of couplings are used for securing fixed handles to the shaft:
• Handles with brass boss for screwed assembly on a threaded shaft.
• Handles with the nut screw moulded into the plastic for screwed assembly on a threaded shaft.
For executions with threaded holes obtained from the plastic in the mould, the measure of keeping the thread undersized with respect to the specifications laid down in the standards has been taken.
This enables the threads of the nut screw to adapt slightly to the screw, when tightening at ambient temperature, thus creating a coupling with an elastic reaction that gives an effective locking effect.
Even better results may be obtained by hot assembly: the handle is heated to 176÷194°F before being screwed onto the threaded pin. This method of assembly initially facilitates the screwing operation in that the thread of the nut screw is expanded when screwed in and subsequently enables an extremely efficient locking effect to be obtained from shrinkage on cooling, due to the slight roughness of the surface of the thread on the shaft.
The push fit mount handle has the most effective against spontaneous unscrewing in that the elastic coupling is not susceptible to any vibrations or rotary forces exerted by the operator’s hand.
The lock is also such as to ensure that the handle does not come out even when subjected to a normal pulling action along its axis. In relation to this, the results of the research work and tests carried out at the ELESA laboratories are provided and they confirm the technical validity of the coupling.
Assembly instructions: fit the handle onto slight chamfered shaft end and push as far as possible by hand or by means of a small press. Alternatively it is possible to tap the handle with a plastic or wooden mallet until firmly in place. In this case we strongly recommend to use a cloth or other suitable soft material over the product to avoid any surface damage.
Plastic is a poor conductor of heat and has a different thermal expansion coefficient from that of the metal inserts so measures must be taken, while remachining the hole, to stop the hubs and bushings from overheating: in fact, the heat produced is not dissipated and the metal parts expand and create stress inside the body of the plastic which has a damaging effect on the strength of the assembly (Duroplasts).
In addition, for thermoplastics (Technopolymers), temperatures close to their softening point could be reached with the risk of the metal insert coming loose.
It is therefore always necessary to adopt cutting and feed rates that do not produce marked localized heating and to cool intensively when the holes have a large diameter and depth with respect to the size of the bushing.
To conserve maximum gloss of the surfaces, we recommend, once machining has been completed, to avoid leaving the plastic wet for a long time, by removing all residual emulsified water from the surfaces; use oil only, if possible.
The machining processes commonly required for the assembly of handwheels or knobs are:
• Remachining of axial hole in the bosses (blind hole). When remachining the hole of a built-in metal boss, always avoid operating as shown in Fig.12, because both during the drilling operation and during the insertion of the small shaft, an area of the plastic covering may be subjected to stress, with the risk of cracking or detaching the part indicated with cross shading.
The operation shown in Fig.13 is the most rational.
 |
Note that in the ELESA parts, remachining of the axial hole may be performed under the correct
conditions indicated above in that the length of the built-in bushings is always indicated in the
table of each article so, for the depth of the hole, reference should simply be made to the basic
plan. • Remachining of the axial hole in the bosses (case of a through hole). If the drilling operation affects not only the metal boss but also a layer of the covering material, the handwheel must be centred carefully and drilling should be started from the plastic side otherwise, chipping may occur when the tool is removed. • Transversal threading in the boss for grub-screw. To be performed in accordance with the instructions given above. Avoid threading both the metal and the plastic: it is better to drill the hole in the plastic part and thread the metal part only. Drilling or threading operations to be performed entirely in the plastic are exceptional. Bear in mind that the difficulty with which the heat produced locally is dissipated, also through the abrasive action of the plastic on the tool, worsens considerably the latter’s working conditions, resulting a rapid wear of the cutting edges (use hard metal tools). |
The range of ELESA elements is extremely broad and offers designers valid alternatives as regards designs, properties and performance of materials, sizes..., to satisfy the most diverse applicational needs. The customer may however need to ask for changes to the standard part or have it made in different colours to adapt it to special applications. In these cases, the ELESA engineers are at the
customer’s full disposal to satisfy these requests for specially designed parts which, as such and for the modifications they may entail to the mould, must be required in sufficient quantity.
In addition to black, which represents the most commonly used colour for plastic and metal components, a large number of standard elements in this catalogue are available in the following colours:
Warning: the RAL table refers to the colour of paints and are therefore colours with a glossy surface.
All the information about the test values are based on our experience and on laboratory tests conducted under specific standard conditions and in a necessarily limited time interval.
Any values indicated must therefore be taken only as a reference for the designer who will apply adequate safety coefficients to them according to the application of the product. The designer and the purchaser are responsible for checking the suitability of our products for the purpose for which they are to be used under the actual operating conditions.
